Soil Gas Sensing for Detection and Mapping of Volatile Organics

SOIL GAS SENSING FOR DETECTION AND

MAPPING OF VOLATILE ORGANICS

by Dale A. Devitt, Roy B. Evans, William A. Jury and Thomas H. Starks

Environmental Research Center University of Nevada, Las Vegas

Bart Eklund and Alex Gnolson Radian Corporation

Austin, Texas

J. Jeffrey van Ee, Technical Monitor Advanced Monitoring Systems Division

Environmental Monitoring Systems Laboratory Office of Research and Development

U.S. Environmental Protection Agency Las Vegas, Nevada

Published by

National Ground Water Association 6375 Riverside Drive Dublin, Ohio 43017 PH: (614) 761-1711 FX: (614) 761-3446

CONTENTS

Notice 0 * . 0 . e i i Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . i i i F igu res . . . . . . . . . . . . . . . . . . . . . . . . . . v i Tables . . . . . . . . . . . . . . . . . . . . . . . . . . xi

1 . I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . 1 S o i l gas s e n s i n g f o r d e t e c t i n g and mapping v o l a t i l e o r g a n i c s . . . . . . . . . . . . . . . 1

2 . S i t e S p e c i f i c Parameter C o n s i d e r a t i o n s . . . . . . . 1 9 Chemical and p h y s i c a l p r o p e r t i e s of t h e o r g a n i c compound . . . . . . . . . . . . . . . . 1 9 P r o p e r t i e s of t h e u n s a t u r a t e d zone . . . . . . . 5 9 Hydrogeologic p r o p e r t i e s . . . . . . . . . . . . 7 9 C h a r a c t e r i s t i c s of t h e s p i l l . . . . . . . . . . 8 2 Misce l laneous . . . . . . . . . . . . . . . . . 8 2

3 . Transpor t and Retent ion of Dissolved and Immisc ib le Organic Chemicals i n S o i l and Ground-Water . . . . . . . . . . . . . . . . . . . . 89

Processes governing t r a n s p o r t of o r g a n i c chemica ls through s o i l . . . . . . . . . . . . . 9 2 Movement of hydrocarbon vapor through s o i l . . . . . . . . . . . . . . . . . . . 0 . 1 0 9

4 . Measurement Methodologies . . . . . . . . . . . . . 1 2 5 Sampling methods . . . . . . . . . . . . . . . 1 2 5 Sampling d e s i e n and sampling q u a l i t y a s s u r a n c e t echn iques . . . . . . . . . . . . . . 1 5 7

5 . A n a l y t i c a l Methodologies . . . . . . . . . . . . . . 168 S e l e c t i n g t h e proper methodology . . . . . . . . 1 6 8

6 . S t a t i s t i c a l Treatment of S o i l Organic Vapor Measurements . . . . . . . . . . . . . . . . . 1 9 9

Components of var i ance a n a l y s i s . . . . . . . . 200

c o n t o u r i n g . . . . . . . . . . . . . . . . . . . 2 0 8 7 . Case S t u d i e s . . . . . . . . . . . . . . . . . . . . 2 1 2

Stovep ipe Wells. C a l i f o r n i a . . . . . . . . . . 2 1 3

i n d u s t r i a l s o u r c e s a t P i t tman. Nevada . . . . . 2 3 6 8 . Summary and Conclusions . . . . . . . . . . . . . . 2 5 6

U t i l i z a t i o n of s o i l - v a p o r measurements . . . . . 2 5 6

Chapter 1 . . . . . . . . . . . . . . . . . . . . . . . 17 C h a p t e r 2 . . . . . . . . . . . . . . . . . . . . . . . 85 Chapter 3 . . . . . . . . . . . . . . . . . . . . . . . 1 1 6 Chapter 4 . . . . . . . . . . . . . . . . . . . . . . . 1 6 2 Chapter 5 . . . . . . . . . . . . . . . . . . . . . . . 1 9 4 Chapter 6 . . . . . . . . . . . . . . . . . . . . . . . 2 1 1 Chapter 7 . . . . . . . . . . . . . . . . . . . . . . . 2 5 5

Chapter 3 . . . . . . . . . . . . . . . . . . . . . . . 1 1 9 Subjec t Index . . . . . . . . . . . . . . . . . . . . . . . 2 6 7

I n t e r p o l a t i o n and c o n c e n t r a t i o n

Hydrocarbon plume d e t e c t i o n a t

S t u d y of ground-water contaminat ion from

References

Appendices

V

CHAPTER 1

I N T R O D U C T I O N

SOIL GAS SENSING FOR D E T E C T I N G A N D M A P P I N G V O L A T I L E ORGANICS

I n t e r e s t i n t h e measurement o f c o n c e n t r a t i o n s of v o l a t i l e o r g a n i c c o m p o u n d s I n t h e p o r e - s p a c e g a s e s o f s o i l w a s s t i m u l a t e d b y e n a c t m e n t o f S u p e r f u n d ( t h e C o m p r e h e n s i v e E n v i r o n m e n t a l Response , CompensaEion, and L i a b i l i t y A c t , o r C E R C L A ) and b y t h e November 1984 r e a u t h o r i z a t i o n o f R C R A ( t h e Resource Conserva t ion and Recovery Act of 1 9 7 6 ) w h i c h d i r e c t e d t h e E P A t o p r o m u l g a t e s t a n d a r d s f o r u n d e r g r o u n d s t o r a g e t a n k s t o I n c l u d e p r o v i s i o n s f o r l e a k d e t e c t i o n . The a p p l i c a t i o n s d i s c u s s e d in t h i s r e p o r t a r e p r i n c i p a l l y a p p r o p r i a t e f o r t h e Superfund s i t u a t i o n where c o n t a m i n a t i o n of t h e s u b s u r f a c e h a s o c c u r r e d and m u s t be a s s e s s e d b e f o r e t a k i n g r e m e d i a l a c t i o n : removal and b i o l o g i c a l t r e a t m e n t o f t h e c o n t a m i n a t e d s o i l and g r o u n d water or both. In t h i s c a s e , t h e usua l o b j e c t i v e in measuring o r g a n i c gases i n s o i l i s t o map t h e l a t e r a l e x t e n t o f s o i l and g r o u n d - w a t e r c o n t a m i n a t i o n o r b o t h wh i l e a t t h e same t i m e m i n i m i z i n g t h e number o f c o n v e n t i o n a l m o n i t o r i n g w e l l s w h i c h m u s t be d r i l l e d . Soil g a s c o n c e n t r a t i o n s e r v e s a s a s u r r o g a t e f o r a c t u a l measurements o f t h e c o n c e n t r a t i o n s o f t h e oompounds o f i n t e r e s t i n g r o u n d w a t e r . Maps o f s o i l g a s c o n c e n t r a t i o n s can be used t o s i t e g r o u n d - w a t e r m o n i t o r i n g w e l l s more e f f i c i e n t l y .

V o l a t i l e c o m p o u n d s a r e c o m p o n e n t s i n t h e s o i l a n d g r o u n d - w a t e r c o n t a m i n a t i o n a t many, i f n o t m o s t , S u p e r f u n d s i t e s . F i g u r e 1 . 1 shows t h e r e l a t i o n s h i p between t h e number of v o l a t i l e compounds a n d t h e n u m b e r o f o r g a n i c p r i o r i t y p o l l u t a n t s found i n a s u r v e y of g round-wa te r m o n i t o r i n g d a t a from 1 1 3 S u p e r f u n d s i t e s ( P l u m b , 1 9 8 5 ) . A r e g r e s s i o n l i n e t h r o u g h t h e s e d a t a s h o w s a l i n e a r r e l a t i o n s h i p w i t h g o o d c o r r e l a t i o n between t h e t o t a l number of v o l a t i l e compounds and t h e t o t a l number o f o r g a n i c p r i o r i t y p o l l u t a n t s d e t e c t e d per s i t e . T a b l e 1 . 1 l i s t s t h e 25 compounds m o s t f r e q u e n t l y r e p o r t e d a t S u p e r f u n d s i t e s ; 1 5 o f t h e s e 25 a r e v o l a t i l e o r g a n i c s o l v e n t s . I n a d d i t i o n t o w h a t e v e r t o x i c i t y t h e s e v o l a t i l e s may themselves p o s s e s s , they may se rve as t r a c e r s f o r o t h e r , n o n - v o l a t i l e components provided t h a t t h e i r g a s e s a r r i ve near t h e s u r f a c e in measureable c o n c e n t r a t i o n s .

816 - 84-

a a 82- L s c 0 )I w w 88-

28-

2 2 24-

22-

s 3

g 20- a 9 18- a

2 18-

Q

2 <

0 14-

t5 12-

@ All rurllablo data rveragra

0 On or mow rltor oonaldorod a n outllor and oxuludod l roa avrrrge ( 8 of 101 r l to r erolrsdod)

TOTAL NUMBER OF VOLATILE COMPOUNDS DETECTED PER SITE

Figure 1 . 1 . Relrt ionohip betwceu number of vo la t i l e canpoundr rod organic priority pollutant8 i n ground-wr t er i n the v i c i n i t y of hatrrdour vaste dirporal r i te . (N= 113 r i t co ) (Plumb, 1983).

2

T A B L E 1 . l . 5 Rank Substance of S i t e s

Percent

1 T r l ch lo roe thy lene 2 Lead 3 To luene 4 Benzene 5 6

7 a 9

10

1 1

1 2

1 3 1 4

15 1 6

1 7 18

1 9 20

21

2 2

2 3

2 4

25

P o l y c h l o r i n a t e d b,phenyls

Chloroform

Tet r a c h l o r o e t h y l en@

Arsenic Cadmi um Chr omi um 1 . 1 , l - T r i c h l o r o e t h a n e 21nc a n d compounds E t h y l benzene X y l e n e M e t h y l e n e c h l o r i d e Trans-1,2-Dlchloroethylene Mercury

C o p p e r a n d compounds Cyanides ( s o l u b l e s a l t s ) V i n y l c h l o r i d e 1 , 2 - D i c h l o r o e t h a n e C h l o r oben zene 1 , l - D i c h l o r o e t h a n e Carbon t e t r a c h l o r i d e

Pheno l -

P C B s )

~~

33 30 28 26

2 2

20

1 6 15 15 15 15 1 4

1 4

1 3 1 3

1 2

1 1

1 0

9 8

8 8 8'

8 7

From: The Hazardous Waste C o n s u l t a n t , 1985.

3

Al though t h e p r o c e s s e s govern ing t h e movement o f o r g a n i c s i n t h e s u b s u r f a c e a r e d i scussed i n d e t a i l i n Chapter 2 , a b r i e f d i s c u s s i o n o f t h e p rocess w i l l i l l u s t r a t e t h e l o g i c b e h i n d s o i l o r g a n i c g a s m e a s u r e m e n t . F i g u r e 1 . 2 s h o w s a s u b s u r f a c e c r o s s - s e c t i o n immediately fo l lowing a s u d d e n , high-volume s p i l l of an o r g a n i c f l u i d . The s p i l l e d f l u i d has moved v e r t i c a l l y downward t h r o u g h t h e u n s a t u r a t e d zone t o form a l e n s on t h e water t a b l e ( w h i c h has a 8 p e c i f i c g r a v i t y l e s s t h a n w a t e r ) and h a s l e f t b e h i n d a Column o f soil c o n t a m i n a t e d b y r e s i d u a l product . The o r g a n i c f l u i d l e n s w i l l immediately b e g i n t o move under t h e f o r c e o f g r a v i t y and t o s p r e a d o u t on t h e water t a b l e , Under t h e c o n d i t i o n s s h o w n h e r e , t h e l e n s w i l l c o n t i n u e s p r e a d i n g u n t i l i t e v e n t u a l l y d i s a p p e a r s , f o r a l l p r a c t i c a l purposes . However, most petroleum f u e l s a r e a m i x t u r e o f many compounds w i t h a wide Spectrum of p r o p e r t i e s such a s molecular weight and wa te r s o l u b i l i t y . Some f r a c t i o n of t h e compounds, g e n e r a l l y q u i t e s m a l l , w i l l d i s s o l v e i n ground water and w i l l move downgradient w i t h t h e ground-water g r a d i e n t f l o w . F i g u r e 1 . 3 s h o w s t h e s i t u a t i o n a f t e r t h e s p i l l h a s s t a b i l i z e d d a y s , weeks , or months a f t e r t h e o c c u r a n c e . T h e c o l u m n o f s o i l c o n t a m i n a t e d b y r e s i d u a l p r o d u c t d u r i n g t h e o r i g i n a l s p i l l r emains , The l e n s of o rgan ic f l u i d has sp read downgrad ien t and is much t h i n n e r . The d i s s o l v e d f r a c t i o n of t h e s p i l l e d f l u i d is m i g r a t i n g w i t h t h e g r o u n d - w a t e r f l o w . G a s e s f r o m t h e s p r e a d i n g o r g a n i c f l u l d l e n s have b e g u n t o move upward through the soil column above t h e path o f t h e s p r e a d i n g o r g a n i c p lume. When t h e f l o a t i n g o r g a n i c l e n s h a s d i s a p p e a r e d , t h e v o l a t i l e component d i s s o l v e d i n g r o u n d water w i l l evo lve from t h e g round water i n t o t h e g a s e s o f t he s o i l pore s p a c e s .

I n t h e s i t u a t i o n where t h e r e e x i s t s a f l o a t i n g l e n s o f f r e e o r g a n i c f l u i d , t h e i n i t i a l c o n c e n t r a t i o n o f o r g a n i c g a s e s above t h e l e n s can be e s t ima ted from i t s gas p r e s s u r e . I n t h e s i t u a t i o n where t h e r e e x i s t s a sma l l conce .n t ra t ion o f d i s s o l v e d o r g a n i c v o l a t i l e s i n g r o u n d w a t e r , t h e i n i t i a l c o n c e n t r a t i o n s o f v o l a t i l e o r g a n i c s i n t h e pore s p a c e g a s e s i m m e d i a t e l y a b o v e t h e w a t e r t a b l e can be es t imated from Henry 's Law, a s d i s c u s s e d a t l e n g t h i n C h a p t e r 2 . T a b l e 1 . 2 s h o w s a i r : w a t e r c o n c e n t r a t i o n r a t i o s m e a s u r e d f o r some common i n d u s t r i a l s o l v e n t s a t room temperature (Thompson, 1 9 8 4 ) . F r o m T a b l e 1 . 2 , ;ie w o u l d e x p e c t a g round-wa te r c o n c e n t r a t i o n o f 2 6 p g / L o f T C E tr, y i e l d a p o r e - s p a c e g a s c o n c e n t r a t i o n o f l O p g / L I n t h e u l v a t u r a t e d z o n e immedia t e ly a b o v e t h e w a t e r t a b l e . T h e s e v a l u e s m u s t be r e g a r d e d a s r o u g h a p p r o x i m a t i o n s , b u t t h e y l l l u s t r a t e t h e p o i n t t h a t t h e r e a r e w e l l - u n d e r s t o o d phys ica i l p r i n c i p l e s r e l a t i n g t h e c o n c e n t r a t i o n s o f d i s s o l v e d v o l a t t l e o r g a n i c s i n g round w a t e r t o t h e p o r e space gas c o n c e n t r a t i o n s o f the.se same v o l a t i l e s .

The m i g r a t i o n o f t h e o r g a n i c g a s e s u p w a r d t h r o u g h t h e ~ a d o s e zone is a compl ica ted p r o c e s s , a s d i s c u s s e d i n C h a p t e r

4

Figure 1 .2 , T y p i c a l behavior i n p o r o u s r o i l f o l l o w i n g a sudden, hi8h volume spill (NYDEC, 1984).

Figure 1.3. B e h a v i o r of product a f t e r e p i l l has s t a b i l i z e d (NYDEC, 1984).

TABLE 1.2. AIR/WATER CONCENTRATION RATIOS FOR SOHE COHHON INDUSTBUU, SOLVENTS AT 33OC

Compound A l r : Water Ri t io (ug/i or a m p 6 1 1 or water)

1 , l dichloroethylene (DCE)

1,2 transdlchloroethylene

methyleneohlorlde

1 , 1 , 1 tr lchloroethane (TCA)

t r 1 chloroethylene ( T C E )

carbontetrachlorlde

t e t rachloroet hylene ( P C E )

chloroform

F - 1 13

1:1

1:3

1 r12

1815

1 :26

1 :1

1 :17

1 : 9

4:1 ~~ ~ ~~~ ~~

(Harrln and Thompson, 1 9 8 4 )

7

2, but a s a f i r s t - o r d e r approximation, it can be regarded a s a diffusion process, represented by

aciat = D , C ~ * . C / ~ Y ~ J

where

c - soil gas concentration t - time oo = ditrusion coefficient y - vertical distance a b o v e contaminant ( o r water table)

C o n f i n i n g d i a c u s a i o n t o w c o n e e r v a t i v e w g a s e s ( w h e r e n o chemical or biochemical p r o c e s a e s add t o or s u b t r a c t f r o m t h e p o r e s p a c e g a s e s ) and to a vertical croaa-section in which the s u b s u r i a c e is h o m o g e n e o u s w i t h u n i f o r m p o r o s i t y a n d p e r m e a b i l i t y in the unsaturated zone, it is possible t o outline t h e q u a l i t a t i v e n a t u r e o f t h e e x p e c t e d v e r t i c a l p r o f i l e s of o r g a n i c g a s c o n c e n t r a t i o n s I n s o i l gas. I n t h e r e l a t i v e l y simple situation where the evolution o f t h e o r g a n i c g a s e s f r o m t h e d i s s o l v e d c o m p o n e n t s i n g r o u n d w a t e r h a s r e a c h e d a q u a s i - s t e a d y s t a t e , t h i s e q u a t i o n i n d i c a t e s t h a t s o i l g a a c o n c e n t r a t i o n s linearly decrease from the initial concentration immediately above the water t a b l e predicted by Henry's L a w ( o r T a b l e 1.2) t o z e r o C o n c e n t r a t i o n at the soil surface. Figure 1.4 s h o w s t h i s s i t u a t i o n s c h e m a t i c a l l y . F i g u r e 1 . 5 is a v e r t i c a l profile o f carbon tetrachloride and chloroform above a ground-water contaminant plume in Nevada ( K e r f o o t a n d B a r r o w s , 1 9 8 6 ) . T h e profile exhibits a linear decrease o f Concentration as t h e surface is approached. T h e s e experimental d a t a , s h o w i n g s o i l g a s c o n c e n t r a t i o n s w h i c h i n c r e a s e l i n e a r l y w i t h d e p t h , s u p p o r t t h e p r e d i c t i o n s o f t h e s t e a d y s t a t e m o d e l , T h e s u b s u r f a c e v e r t i c a l c r o s s - s e c t i o n is r a r e l y h o m o g e n e o u s , however; more often, a s u c c e s s i o n o f s t r a t a is e n c o u n t e r e d in w h i c h t h e r e are varying permeabilities, porosities, soil types, and moisture contents. These Varying p r o p e r t i e s i n f l u e n c e t h e u p w a r d m o v e m e n t o f o r g a n i c g a s e s and v a r y i n g v e r t i c a l g a s concentration gradients.

C h e m i c a l and b i o c h e m i c a l processes should a l s o affect t h e vertical gas concentration profiles. F i g u r e 1.6 c o n t r a s t s t h e p r o f i l e s o f P C E and b e n z e n e r e p o r t e d f r o m a s i t e in northern C a l i f o r n i a ( H a r r i n a n d T h o m p s o n , 1 9 8 4 ) . T h e s a m e r a p i d d i s a p p e a r a n c e o f b e n z e n e v a p o r w i t h d i s t a n c e a b o v e the water t a b l e w a s r e p o r t e d in N e v a d a a s s o c i a t e d w i t h t h e v e r t i c a l p r o f i l e of c a r b o n t e t r a c h l o r i d e and c h l o r o f o r m o f Figure 1.5 (Kerfoot and Barrows, 1 9 8 6 ) . A p p a r e n t l y , d i f f e r e n t p r o c e s s e s a f f e c t t h e m o v e m e n t o f h a l o c a r b o n g a s e s s u c h a s tetrachloroethylene, dichloroethane and c h l o r o f o r m t h a n a f f e c t n o n - h a l o g e n a t e d h y d r o c a r b o n s s u c h a s b e n z e n e . S e v e r a l explanations for this d i f f e r i n g b e h a v i o r h a v e b e e n s u g g e s t e d ,

8

8011 Conoontrrtlon m W A T C R TABLE

Figure 1.4. Orqanic gar concentration dirrribution i n t h e vadore gone expected from diffurion.

9

COMPOUND CONCENTRATION

W 0 0 U iL 1 a 3 v) 2

s = 0 0 3

I t 5 e W 0 6

FigUte l a 5 . C h l o r o f o r m a n d c a r b o n t e t r a c h l o r i d e d c t h dirtr ibut ion. Coeff ic ient of de terminat ion ( r 5 . .99) Kerfoot and Barrovr, 1986),

10

i n c l u d i n g b i o l o g i c a l d e g r a d a t i o n , a d s o r p t i o n by o r g a n i c ma t t e r and c l a y s , and water s o l u b i l i t y . Whatever t h e r e a s o n f o r t h e d i f f e r i n g b e h a v i o r o f h y d r o c a r b o n s a n d h a l o e a r b o n s , t h e h a l o c a r b o n s g e n e r a l l y a p p e a r t o behave n c o n s e r v a t i v e l y n a n d a r e , t h e r e f o r e , b e t t e r t r a o e r s f o r 8011-ga8 i n v e s t i g a t i o n s t h a n t h e hydrooarbons ( H a r r i n and Thompson, 1 9 8 4 ) .

The b a s i c a p p r o a o h i n a s o i l - g a s i n v e s t i g a t i o n a t a p a r t i c u l a r s i t e i s now a p p a r e n t . The v e r t i c a l p r o f i l e s o f o r g a n i c g a s e s p resent i n t h e s o i l pore s p a c e s a r e measured and p l o t t e d f o r s e v e r a l l o c a t i o n s a t t h e s i t e . Se lec t ion o f t r a c e r g a s e s f o r t h e s i t e i s a i d e d when p r i o r i n f o r m a t i o n on contaminant c o n u e n t r a t l o n s i n ground water i s a v a i l a b l e . Baaed on t h e v e r t i c a l p r o f i l e s , t h e p a r t i c u l a r o r g a n i c s o i l g a a e s p r e s e n t , a n d t h e s a m p l i n g a n d a n a l y t i c a l m e t h o d o l o g i e s a v a i l a b l e , one o r more t r a c e r g a s e s a r e s e l e C t t 3 d . A sampling d e p t h i s a 1 8 0 s e l e c t e d , b a s e d on t h e m e a s u r e d v e r t i c a l p r o f i l e s , which i s e x p e c t e d t o produce s o i l gas c o n c e n t r a t i o n s wel l a b o v e t h e m i n i m u m c o n o e n t r a t i o n s d e t e c t a b l e w i t h t h e a n a l y t i c a l t e c h n i q u e s a t hand. T h i s is shown 8ChematfCally on F igu re 1 . 4 . When t h i s C o n s t a n t s a m p l i n g d e p t h i s u s e d , s o l 1 g a s s a m p l e s a r e c o l l e c t e d a n d m e a s u r e d a c r o s s t h e s i t e p r e f e r a b l y on a r e g u l a r g r i d p a t t e r n . These v a l u e s a r e t h e n p l o t t e d on a map and a r e c o n t o u r e d e i t h e r b y hand or w l t h a computer a l g o r i t h m . T h e d e s i r e d r e s u l t i s a c o n t o u r p l o t of s o i l g a s c o n c e n t r a t i o n s a t a c o n s t a n t d e p t h a c r o s s t h e s i t e ; t h e i n v e s t i g a t o r hopes t h a t t h i s p l o t 13 r e l a t e d i n a more or l e a s l i n e a r way t o c o n t a m i n a n t c o n c e n t r a t i o n s i n ground water o r i n t h e bu r i ed waste s t r a t u m of i n t e r e s t .

F i e l d measu remen t s o f s o i l g a s have u s u a l l y t aken one of t h r e e b a s i c approaches: ( 1 ) measurement o f e m i s s i o n f l u x e s a t t h e s u r f a c e ; ( 2 ) measurement o f p o r e apace gas c o n c e n t r a t i o n s a t some depth i n gas samples c o l l e c t e d w i t h s u b s u r f a c e p r o b e s or w i t h s h a l l o w , t e m p o r a r y w e l l s ; o r ( 3 ) u s e o f p a s s i v e c o l l e c t i o n d e v i c e s bu r i ed a t r e l a t i v e l y s h a l l o w d e p t h s ( R e i d , 1 9 8 5 ; M a r r l n and Thompson, 1 9 8 4 ; B i s q u e , 1 9 8 4 ; Hanos , 1 3 8 5 ; K e r f o o t and B a r r o w s , 1 9 8 6 ; S p i t t l e r , 1 9 8 5 ) . T h e s e b a o i c m e t h o d s a r e l i s t e d i n T a b l e 1 . 3 . T h e f i r s t two appvoaahes involve c o l l e c t i o n of gas s a m p l e s i n t h e f i e l d f o r s u b s e q u e n t a n a l y s i s ; t h e t h i r d i n v o l v e s a d s o r p t i o n o f t h e gau o n t o a c o l l e c t i o n medium such a s a c t i v a t e d c h a r c o a l : t h e a d s o r b e d g a s is l a t e r p u r g e d from t h e a c t i v a t e d c h a r c o a l and is analyzed i n t h e l a b o r a t o r y . W i t h s u r f a c e c o l l e c t o r s and f l u x chambers and a l s o w i t h d r i v e n probes and temporary Wel ls , gas samples can be c o l l e c t e d w i t h any of t h e t e c h n i q u e s l i s t e d i n T a b l e 1 . 4 . F i g u r e 8 . 2 is a f l o w c h a r t w h i c h d e s c r i b e s t h e p r o c e s s of c o l l e c t i n g a n d a n a l y z i n g a s o i l g a s s a m p l e w i t h d r i v e n p r o b e s a n d t e m p o r a r y w e l l s . C o l l e c t i o n t e c h n i q u e s i n c l u d e d rawing s a m p l e s w i t h a g a s c h r o m a t o g r a p h s y r i n g e d i r e c t l y f r o m t h e s a m p l i n g t r a l n , c o l l e c t l o n of gases by a d s o r p t i o n o n t o a c t i v a t e d

11

G

0 Driven probes

0 Shallow awella a

0 Pe trex tubes

0 Collectors on surface

0 Flux chambers

~~ ~

0 CC syringe

0 Charcoal cartridge

0 Stainless steel cannistera

0 Tedlar or teflon bags

THODS FOR S O 1 Comment

Draeger tubes

Organ i c vapor analyzer

Field GC

tab GC

very crude

over 0 . 5 ppnv

generally Over 1 0 ppbv

can be less than 1 ppbv

12

U 0

I c 3 0

L' 0 a Y 0

t Y U LL

14

Obrorwd \ toncon trat Ion8 \ \ l lnoir Function \ \

Observed PCE concen trrt Ion 8

BEUZENE

w 080

-~ _ _ -

1 1 1 1 d 0 60 160 800 860 loo ?cE

8011 Coneontrrtlon, AOII t

Figure 1.6. Soil-8.0 vertic.1 p r o f i l e at 8 r i t e i n northern California (Marrin and Thompoon, 1984).

13

c h a r c o a l or Tenax from an a i r s t r e a m pumped from t h e probe or w e l l , c o l l e c t i o n i n s t a i n l e s s a t e e l c a n n i s t e r s , and c o l l e c t i o n i n Tedlar o r T e f l o n bags.

T a b l e 1 . 5 l i s t s a n a l y t l C a l methods which have been used i n s o i l g a s i n v e s t i g a t i o n s . T h e s e i n c l u d e : ( 1 ) f i e l d measurements w i t h e i t h e r a p o r t a b l e o r g a n i c gas a n a l y z e r ( O V A ) or w i t h a t r a n s p o r t a b l e g a s c h r o m a t o g r a p h , ( 2 ) l a b o r a t o r y g a s c h r o m a t o g r a p h i c a n a l y s i s o f g a s s a m p l e s ( v i a evacuated f l a s k s or c a n n i s t e r s or t e f l o n or t e d d a r b a g s ) or c h a r c o a l or Tenax c a r t r i d g e s c o l l e c t e d i n f i e l d , o r ( 3 ) l a b o r a t o r y g a s c h r o m a t o g r a p h / m a s s s p e c t r o m e t r y ( G C I M S ) a n a l y s i s o f f i e l d s a m p l e s . These methods a r e d i s c u s s e d i n d e t a i l I n Chapter 4. Another method w h i c h h a s b e e n u s e d i n f i e l d m e a s u r e m e n t s u t i l i z e s c o l o r i m e t r i c d e v i c e s u s u a l l y c a l l e d Draege r t u b e s . T a b l e 1 . 5 a l s o l i s t s t h e u s u a l m i n i m u m d e t e c t a b l e c o n c e n t r a t i o n s a s s o c i a t e d w i t h t h e s e v a r i o u s m e t h o d s i n p r a c t i c e . Draeger t u b e s a r e t h e l e a s t a c c u r a t e a n d , u s u a l l y , t h e l e a s t s e n s i t i v e of t h e methods l i s t e d i n Table 1 . 5 . O V A ' S a r e a l s o r e l a t i v e l y i n s e n s i t i v e and s h o u l d n o t be e x p e c t e d t o p r o d u c e u s a b l e i n f o r m a t i o n w h e r e t h e t o t a l n o n - m e t h a n e h y d r o c a r b o n c o n c e n t r a t i o n s a r e l e s s t h a n 0 . 5 p p m v . T r a n s p o r t a b l e g a s c h r o m a t o g r a p h s h a v e b e e n used i n f i e l d a p p l i c a t i o n s where i n d l v i d u a l g a s s p e c i e s c o n c e n t r a t i o n s were g r e a t e r than 10 p p b v (Barker , 1 9 8 0 ) .

L a b o r a t o r y - b a s e d g a s c h r o m a t o g r a p h y can r e l i a b l y and economically measure i n d i v i d u a l gas s p e c i e s c o n c e n t r a t i o n s down t o 1 p p b v ; a b s o l u t e d e t e c t i o n limits a r e much s m a l l e r b u t such low c o n c e n t r a t i o n s a r e g e n e r a l l y o f l i t t l e i n t e r e s t t o s o i l g a s s u r v e y s . The s e n s i t i v i t y a n d d i s c r i m i n a t i v e a b i l i t i e s o f l a b o r a t o r y - b a s e d G C / M S m e a s u r e m e n t s c a n e x t e n d down t o c o n c e n t r a t i o n s c o n s i d e r a b l y l e s s t h a n 1 p p b v ; however , t h e s u b s t a n t i a l e x p e n s e i s r a r e l y J u s t i f i a b l e i ' n s o i l g a s i n v e s t i ga t i o n s .

The r a n g e o f gas measurement s e n s i t i v i t i e s l i s t e d i n Table 1 . 5 means t h a t s o i l g a s measu remen t s can d e t e c t v e r y s m a l l c o n c e n t r a t i o n s of t r a c e r gases . T h i s s e n s i t i v i t y t o g e t h e r w i t h t h e s p e c i f i c i t y o f t h e g a s a n a l y s e s g i v e s s o i l g a s i n v e s t i g a t i o n s some i m p o r t a n t a d v a n t a g e s o v e r o t h e r i n d i r e c t t o o l s f o r ground-water i n v e s t i g a t i o n s s u c h a s r e s i s t i v i t y and o t h e r e l e c t r i c a l g e o p h y s i c a l t e c h n i q u e s . The e l e c t r i c a l t echniques depend on t h e presence of s u b s t a n t i a l q u a n t i t i e s o f d i s s o l v e d i o n i c s o l i d s i n g r o u n d w a t e r t o c r e a t e d e t e c t a b l e d i f f e r e n c e s i n a q u i f e r c o n d u c t i v i t y be tween t h e c o n t a m i n a n t plume and t h e s u r r o u n d i n g u n a f f e c t e d a r e a s . D e t e c t i o n and mapping contaminant plumes w i t h e l e c t r i c a l methods r e q u i r e s a s i g n i f i c a n t c o n d u c t i v i t y c o n t r a s t between contaminant plume and background a s t h e y a r e o b s e r v e d f r o m t h e s u r f a c e . A r u l e of t h u m b , some t imes q u o t e d , s u g g e s t s t h a t a c o n d u c t i v i t y c o n t r a s t

14

o f 1 . 5 : l or b e t t e r i s u s u a l l y needed w i t h a Nsha l lown a q u i f e r ( w a t e r t a b l e < 30 f e e t ) t o s a t i s f a c t o r i l y map a C o n t a m i n a n t p l u m e w i t h e l e c t r i c a l m e t h o d s . T h i s wou ld r e q u i r e t o t a l d i s s o l v e d s o l i d s c o n c e n t r a t i o n s i n t h e p l u m e t o be a t l e a s t 1 . 5 t i m e s t h e background TDS v a l u e s . F o r deeply bu r i ed a q u i f e r s , t h e n e c e s s a r y c o n t r a s t IS h i g h e r b e c a u s e o f t h e s c r e e n i n g p ~ e s e n c e o f t h e o v e r b u r d e n . Not a l l S u p e r f u n d s i t e s have conduct ive contaminant plumes. Even i n c a s e s where s u c h plumes e x i s t , t h e c o n t a m i n a n t s of i n t e r e s t a r e u s u a l l y o r g a n i c s which add l i t t l e or noth ing t o ground-water c o n d u c t i v i t y . Because of t h e a e l i m i t a t i o n s , e l e c t r i c a l t e c h n i q u e s can be e x p e c t e d t o "underdef ine" contaminant plumes; plume o u t l i n e s i d e n t i f i e d b y e l e c t r i c a l me thods can be e x p e c t e d t o b e l e s s e x t e n s i v e than t h e a c t u a l a r e a of i n t e r e s t . Plume o u t l i n e s d e f i n e d w i t h t h e m o s t s e n s i t i v e s o i l g a s measurement t e c h n i q u e s may t e n d t o " o v e r d e f i n e " g r o u n d - w a t e r c o n t a m i n a n t p l u m e s b e c a u s e t h e o r g a n i c g a s e s r l s i n g from t h e ground-water plume wil l . t e n d t o sp read l a t e r a l l y a s t hey r i s e .

S o i l - g a s measu remen t s have a l s o been sugges t ed a s a means of d e t e c t i n g l e a k s from u n d e r g r o u n d s t o r a g e t a n k s ; i n t h i s a p p l i c a t i o n t h e focus i s on d e t e c t i n g l e a k i n g t a n k s be fo re t h e y become s e r i o u s env i ronmen ta l p r o b l e m s . The & P A hab e s t i m a t e d t h a t t h e t o t a l number o f underground s t o r a g e t a n k s i n t h e U.S. i s i n t h e n e i g h b o r h o o d of 3 , 0 0 0 , 0 0 0 t o 5 , 0 0 0 , 0 0 0 and t h a t a s many a s 1 0 0 , 0 0 0 a r e l e a k i n g t o d a y w h i l e a n o t h e r 3 5 0 , 0 0 0 may l e a k w i t h i n 5 yea r s ( J e y a p a l a n , e t a l . , 1 9 8 6 ; Haza rdous Waste R e p o r t , 1 9 8 4 ; P r e d p a l l , e t a l . , 1984) . Because measurement of v o l a t i l e o r g a n i c vapors i n s o i l p o r e g a s i s p r o b a b l y t h e m o s t s e n s i t i v e known t e c h n i q u e f o r d e t e c t i n g m a t e r i a l l eaked from u n d e r g r o u n d s t o r a g e t a n k s , t h e 1 9 8 4 R C R A a m e n d m e n t s h a v e provoked c o n s i d e r a b l e i n t e r e s t i n such methods. The t e c h n i c a l o b j e c t i v e s of l e a k d e t e c t i o n a r e d i s t i n c t from t h o s e o f s i t e a s s e s s m e n t . . The g o a l i n s i t e a s s e s s m e n t i s t o u s e s o i l - g a s measurements a s a s u r r o g a t e f o r s o i l and g r o u n d - w a t e r s a m p l i n g t o map t h e l a t e r a l e x t e n t o f c o n t a m i n a t i o n . The goa l i n l e a k d e t e c t i o n Is t o provide an a la rm when t a n k l e a k r a t e s exceed a g i v e n v a l u e ( c u r r e n t s u g g e s t e d maximum l e a k r a t e s a r e 0 . 0 5 g a l l o n s / h r ) . To d o t h i s w i t h s o i l - g a s m o n i t o r i n g r e q u i r e s a known r e l a t i o n s h i p be tween l e a k r a t e s o r volumes and a o l l - g a s c o n c e n t r a t i o n s . A s w i l l be d e m o n s t r a t e d , t h i s r e l a t i o n s h i p is h i g h l y a i t e - s p e c i f i c . O t h e r p rob lems a s s o c i a t e d w i t h l e a k d e t e c t i o n b y s o i l g a s m o n i t o r i n g m u s t be s o l v e d t o make t h e technique workable. Among t h e s e problems a r e t h e following:

o New l e a k a g e m u s t be d e t e c t e d i n e n v i r o n m e n t s where s o i l a l r e a d y c o n t a i n s r e s i d u a l v a p o r s f rom p r e v i o u s s p i l l s and l e a k s .

15

o No " a c t i o n l e v e l s " e x i s t t o a i d i n deciding what s o i l gas ooncent ra t ions should t r i g g e r remedial a o t i o n .

o The r e l a t i o n s h i p s between ground-water ooncen t r a t ions of v o l a t i l e o r g a n i c s and t h e r e s u l t i n g s o i l po re g a s o o n o e n t r a t i o n s of tho8e organlo8 a r e very oomplex, r n d p r e d i o t i v e m o d e l s may r e q u i r e more d 8 t 8 a b o u t a p a r t l c u l a r s i t e t h a n a r e l i k e l y t o be a v a i l a b l e ,

o C u r r e n t l y a v a i l a b l e measurement methods w i t h adequate s e n s i t i v i t y m a y b e t o o e x p e n s i v e f o r use a s l e a k d e t e c t o r s .

While t h e problem of d e t e c t i n g l e a k s from underground s t o r a g e tanks r e q u i r e s a d i f f e r e n t technology t h a n does Super fund S i t e a s s e s s m e n t , t h e f o l l o w i n g d i s c u s s i o n s of g a s vapor migra t ion and c u r r e n t measurement technology s h o u l d s e rve a s a background f o r t h e development of leak d e t e c t i o n methods.

16

REFERENCES

1 .

2 .

3.

4.

5 .

6.

7 .

8.

Barker, N i c h o l a s J. and Richard C. Leveson. " A Portable Photoionization GC for Direct Air A n a l y s i s , " A m e r i c a n Laboratory, December 1980.

B i s q u e , R a m o n E. " M i g r a t i o n R a t e s o f Volatile8 from B u r i e d H y d r o c a r b o n S o u r c e s T h r o u g h S o i l M e d i a , " P r o c e e d i n g s o f t h e N W W A I A P I C o n f e r e n c e o n Petroleum Hydrocarbons and O r g a n i c C h e m i c a l s i n G r o u n d W a t e r - P r e v e n t i o n , Detection, and Restoration, National Water Well Association, Houston, Texas, November 5-7, 1984.

H a z a r d o u s W a s t e R e p o r t - - T r e n d s & Analysis. The Next Regulatory Battle: Leaking Underground S t o r a g e Tanks. May 1984.

Kerfoot, H. B. and L. J. Barrows. "Soil-Gas Measurement for D e t e c t i o n of S u b s u r f a c e O r g a n i c C o n t a m i n a t i o n , " r e p o r t , C o n t r a c t 68-03-3245, Environmental Monitoring Systems Laboratory, Las Vegas, Las Vegas, Nevada, February 1986.

Kerfoot, H. B. and Cynthia Hayer. "The Use of Industrial Hygiene S a m p l e r s f o r Soil-Gas Surveying," G r o u n d - W a t e r Monitoring Review, Fall 1986, vol. 6, no. 4.

L a B r e c q u e , D. J., S. L. P i e r e t t a n d A . T. W a l k e r . Lockheed Engineering and Management Services, Inc., and J. w. Hess, Desert Research Institute (EPA Report in Draft), 1984.

Manos, C h a r l e s G., Kenneth R. Williams, W. David Balfour and Shelly J. W i l l i a m s o n . " E f f e c t s o f C l a y M i n e r a l - Organic Matter Complexes on Gaseous Hydrocarbon Emission8 from Soils, "Proceedings of the Second NWWAIAPI Conference on Petroleum Hydrocarbons and Organic Chemfcals i n Ground Water - Prevention, Detection, and Restoration, National Water Well Association, Houston, Texas, November 13-15, 1985.

M a r r i n , D . L. a n d G. H. T h o m p s o n . "Investigation of V o l a t i l e C o n t a m i n a n t s in U n s a t u r a t e d Z o n e A b o v e T C E P o l l u t e d Ground-water," EPA P r o J e c t Report, ProJect CR

17

811018-01-0, R o b e r t S . Kerr E n v i r o n m e n t a l R e s e a r c h Laboratory, Ada, Oklahoma, 1984.

9. New York S t a t e Department of Environmental Conservat ion, D i v i a i o n o f W a t e r , B u r e a u o f W a t e r R e s o u r c e e . wReoommended P r a o t i O O 8 f o r U n d e r g r o u n d S t o r a g e o f Petroleum,w Albany, New York, Hay 1984.

lo. P l u m b , R. H . J r . w D i s p o s a l S i t e M o n i t o r i n g D a t a : O b s e r v a t i o n s and S t r a t e g y I m p l i o a t i ~ n s , ~ Seaond Annua l C a n a d i a n - A m e r i o 8 n C o n f e r e n c e on H y d r o g e o l o g y - G r o u n d w a t e r : A S o l u b l e Dilemma; N a t i o n a l W a t e r W e l l AssooiatiOn, Banff, A lbe r t a , June 25-29, 1985.

1 1 . S p i t t l e r , T, M. and W . S c o t t C l i f f o r d . 'A New Hethod f o r Detection of Organic Vapor8 i n t h e Vadose Zone," N a t i o n a l Water Well Confe rence on C h a r a c t e r i z a t i o n and Monitoring of Organic Vapors i n t h e Vadose Zone, Denver , C o l o r a d o , November 19'85.

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CHAPTER 2

SITE S P E C I F I C PARAMETER CONSIDERATIONS

B e c a u s e o f t h e h e t e r o g e n e o u s n a t u r e of s o i l and p a r e n t m a t e r i a l f o u n d i n t h e v a d o s e z o n e , t h e movement o f o r g a n i c o o m p o u n d s i n b o t h t h e l i q u i d a n d v a p o r p h a s e a r e o f t e n d i f f i o u l t t o p r e d i c t w i t h any d e g r e e o f c e r t a i n t y ( v a r y i n g i n b o t h s p a c e a n d t i m e ) . However , if t h e v a r i a b i l i t y o f s i t e s p e o i f i c p a r a m e t e r s is p r o p e r l y r e c o g n i z e d , c o r r e c t i n t e r p r e t a t i o n s c a n b e m a d e . T h i s c h a p t e r c o v e r s t h e s i g n i f i c a n c e o f t h e p a r a m e t e r s l i s t e d i n T a b l e 2 . 1 , S p e c i a l a t t e n t i o n w i l l be g i v e n t o t h e p a r a m e t e r i n f l u e n c e on soil g a s m o n i t o r i n g a n d on c o n t a m i n a n t p l u m e d e t e c t i o n i n t h e s a t u r a t e d zone.

C H E M I C A L A N D PHYSICAL P R O P E R T I E S OF T H E O R G A N I C C O M P O U N D

( 1 ) Vapor p r e s s u r e : T h e p r e s s u r e o f t h e v a p o r of a l i q u i d conf ined such t h a t t h e v a p o r c o l l e o t s a b o v e i t is r e f e r r e d t o a s t h e vapor p r e s s u r e . T h u s , a t s p i l l s l t e s , o r g a n l c c o m p o u n d s w i t h h i g h v a p o r p r e s s u r e s would be e x p e c t e d t o be p r e s e n t t o some d e g r e e i n t h e v a p o r p h a s e of s o i l p o r e s . H i g h l y v o l a t i l e f u e l s s u c h a s g a s o l i n e a r e known t o e v a p o r a t e r e l a t i v e l y f a s t e v e n i n t h e s u b s o i l , f o r m i n g an e n v e l o p e of h y d r o c a r b o n v a p o r s a round t h e c o r e of t h e s p i l l ( S c h w i l l e , 1 9 7 5 ) . I f a n o r g a n i c compound h a s a n e x c e e d i n g l y low v a p o r p r e s s u r e ( e . g . , p e s t i c i d e s ) , i t would n o t be a good c a n d i d a t e f o r s o i l vapor mon i to r ing . A l i s t of t h e v a p o r p r e s s u r e s of many O r g a n i c compounds can b e f o u n d i n T a b l e 2 . 2 , c o m p i l e d b y Hackay and S h i u ( 1 9 8 1 ) .

( 2 ) Water s o l u b i l i t y : The e x t e n t t o which an o r g a n i c compound ( s o l u t e ) d i s s o l v e s i n a s o l v e n t ( w a t e r ) , is r e f e r r e d t o a s t h e w a t e r s o l u b i l i t y o f t h e compound . O r g a n i c c o m p o u n d s w i t h h i g h w a t e r s o l u b i l i t y would be expec ted t o p a r t i t i o n p r i m a r i l y i n t o t h e l i q u i d w a t e r p h a s e . The r a t e a t w h i c h t h e s e compounds would move through t h e u n s a t u r a t e d zone w o u l d t h e r e f o r e b e c o n t r o l l e d t o a g r e a t e x t e n t b y t h e u n s a t u r a t e d h y d r a u l i c c o n d u c t i v i t y of

19

TABLE 7 . 1 . SITE SPECIFIC P M T E R CW1DE-S

A . Chemical and P h y s i c a l P r o p e r t i e s of t h e Organio Compound.

1 ) Vapor pressure 2 ) Water s o l u b l l i t y 3 ) Henry's law c o n s t a n t 4) Concent ra t ion S ) 7 ) Densi ty

Organic carbon distribution coeff ic leqt (Roc)

8 ) V i 8 C O 8 i t y 8 ) D i e l e c t r i c c o n s t a n t 9 ) B o i l i n g p o i n t

1 0 ) Molecular weight

B. P r o p e r t i e s of t h e U n s a t u r a t e d Zone.

Air f i l l e d p o r o s i t y Volumetric water c o n t e n t Soil organ ic m a t t e r S o i l t e x t u r e Vapor p r e s s u r e of water i n t h e s o i l po res Shape and s i z e of pores Depth of u n s a t u r a t e d zone Retent ion Temperature and t e m p e r a t u r e g r a d i e n t s M i c robl a 1 i n f 1 uence

C . Hydrogeologic P r o p e r t i e s

1 ) Ground water flow ( d i r e c t i o n , v e l o c i t y , g r a d i e n t ) 2 ) Water t a b l e o s c i l l a t i o n s 3 ) L i t h o l o g y o f t h e a q u i f e r

D . C h a r a c t e r i s t i c s of t h e S p i l l

E . Miscellaneous

1 ) R a i n f a l l 2) Background water q u a l i t y 3 ) Barometric p r e s s u r e and w i n d 4 ) P r o x i m i t y t o r i v e r s , l a k e s and p u m p i n g w e l l s .

Data at 25% for g . a o u m l k . r r m Methane 16-01 -102.5 -164 27260

E them 30.7 -1lu.3 - 88.6 3990

PKUp8m 44.11 -189.7 - 42.1 -1

n-0utan 58.13 -138.4 - 0.5 241

labutam 58-13 -159.6 - 11.7 357

2,2-DfWthyl- 72.15 - 16.6 9.5 172 prom-

M a m t 25% tor liquid a l l a n a h, w n-Pmtme 72.15 -129.7 36.1 68.4

Iewmntmm

n-tbxrr

72.15 -159.9

86.17 - %

27.9 n.6

68.95 20.2

24.1

60.4

62.4

61.4

0 . 9

3S.2

w. 5 39.5 40.0 40.4 47.6

47.8 48.0 49. 4

9.5 9.47 9.52

12. s 12.4 u . 2 18.3

67.4

50.6

7l.6

95.9

120

37s

128 125 123 122.2 103.7

140 139 134.7

110 19l 110 147 144 110 m.9

67 .k 2.0

1.1 71 . e 2.4

4. 1

5.2

11.2

5o.e

950%

12%

m-

1=-10

P. kPa * c.lc exptl recam

2-Methyl- 06.17 - psntmns

-153.7 60.3 28.2

3 4 0 t h ~ 1 - 86.17 pntmns

2 ,20i#thyl - 86.17 - 99.9 butane

2,SDfrethyl- 86.17 -128.5 butmm

2-nethyl- 100.21 -18. 3 h b x n

3-nahyl- 100.21 -119 h s x W

2,2DiWthyl- 100.21 -123.8 pntam

2,3Direthyl- 100.21 pbntorr

63.3

49.7

58.0

96.4

90.0

911

79.2

89.8

25.5

42.6

S1.J

6.11

8.ra

8.zl

14

9.18

13.8 175. 13.0 186 15.7 154

12.8 172 11.1 171

18.4 199 21.2 17S U.8 154

19.1 1u 22.5 120

2.9s 209 2.24 273 2.46 251)

2.19 2m 1.17 1Q

2.54 346

2.66 Sl2 4.9) 166

4. 60 11 8

1m-15

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Capomd MI w,* V p o t sol hi1 f t y Huuy'. la con8tnt lb. 2/aml.

P. -1 rocom PrnWUrS %dg

168 * C 8 f c

Heracowne s66.7 56.4 412.2 7.Mx10-12. 0.0017 7. ~ 0 ' ~

"Extrqmlmted valrs fro liquid atate. bCalculmted f ra the srtrmpolated vr~aur prsaaue with a fug.city n t i o correction.

s. SSXlO'l2b

Data at 25% for c y c l a l b m a Cyclopentarm 70.14 - 93.81) 99-26 b2.4

Cyclohexne 04.16 6.55 80.7 12.7

W h y l - 84-16 -142.14 71.8 18.5 cyclqmntam

h) m

Mhyl- 98.19 -126 0 6 100.9 6.18 cyclohexas

1 -cia-2-01- 112.2 - s0.1 129.7 1.93 -thy ICyClO- heXON3

1,4,-tnna- 112.2 - n 119.4 3.02

cyclohexns Dire thy l -

156 160

19.1 18.6

55 19.4 57.5 18.6 66.5 14.1

42 36.7 41.8 M.8

14 16

42.8 JB.0

6.0 S6.1

J.04 88.2

I ,I , 3-Tti- 112.3 - 14.2 104.9 5.5 S o n 159 sthylcyclo- pent-

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2-E thy 1- 156.2 1 iq uid tnphthdene

4.21x10') 8.0 0.0822 3.24~10'~.

0iphe-l 154.21 71 255.9 1.30~10-3 7.48 0.0268 O = O U S 0 .02e .m2 1.0 0.0286 0,0304 7.65 0.0269 7.50 0.0267 7-08 Oo0283 S. !N O.OSS7 3.87 0.0518

s. 80~10-4 s. 92x10'). 7. ssx10-3'

ACUrwQhthens 1S4.21 %.2 W h,

166.2 116

101

277.5

295

3s9

8 , 8 6 ~ 1 0 ' ~

2 . 6 7 ~ 1 0 ' ~

3.86 0.0237 0.0118 0002+0aO2

3.47 3.93 o.mn 0.01~7

0.0265

1.m 0.00775 0.0101 O.ODek-.W2 o.mm 1-98

1.18 0,00903 0.m3m o.w-: ,ma 0.oocUs 0,41365 0.00367 0.00297 0.0w4 0.0041)

1.07 1.29 1.60 1.1s 1.002

ro-sa '0

612'0 602 '0 961 '0 861'0

LOlOO'O ZOlW '0 %TOO-0 ts1OO-0

Zm'=ZlW'O 1100'0 TZTOO'O

10 '0 VTO'O

9cz '0 902 '0 592 '0 092 '0 CK

091

111

KT

2 '912

c 'Lo2

3, h-eenzo- 252.3 175 py rsne

6.67~10'~) 0.0012 0.0038 O.OoQ0

aExtrapolated valuss from liquid state . bCalculated From the artrpolatsd vapor preaaure with a fugacity ratio corCection. CExtrepolatsd from aol id vapor preasure.

Oats For halogenated alkanes and elkecres at 25OC urleas otbnieb Stated. ChloraMthme Hl.5 -97.7 -24.2 570 5S50

4eo(aoa) 7 9 0 0 ( m ~ )

84.9

Trichloro- 119.4 -thane

-%, '

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39.7

61.7

0.95~.05

0.079 ( 1.59

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T&loroeth.rm

133.4 -36.5

1 , 1 , 1 , 2-Tot re- 167.6 -m.t ch1oroeth.m

1 ,1,Z, 2-let re- 167.05 -35 chloroethare

W OI

1,1,2,2,2- m2. J -29 Patachloro- etherm

V iy lch lor ids 62.5 -153.8

1M.S

146.2

162

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1.853 urn 0.283

0.067 H)o 0.018) 1200 0.0455

0.647 (a@)

0.12+02

0.22j04

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f Itormethano 34.03 -1bl. 8 -78.4 3536 1770 l.%(lo.ld ( lo.)

.Extmpoloted v8lwm fra liquid 8t.te. k.lcul8ted fra the sartnpolated vqmr proowre with 8 fujacity ratio aorrectian. %ctr.pohted fnr s o l i d vqmr proaouce. ~C~ICUWCKI using at.oQpheric pre.#ae.

W W

O-DfchlOro- 147.01 -17.0 benzene

.Dichloro- 141.01 -21.7 baWW

53.1

132 1.501

1.sm

10.5 0.1%

173

I74

0. P

0. Yo7

471.7 nm 490 so1

14.2 14s 1s2 92.7

121.2 121 120

0.0902c 8S.1 87.2

0,377 0.302 o.fk-.o) 0.356 0.314 0. Y63 0.354

0.198 0.191 O.lP*.Ol 0.1% 0.190

0.366 0 . W 0. M7

0. Js+.02

0.160 0.2a O.l*. 02

bmtlnrrd) 0.152

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rh

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d

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1; N

41

Iodobenrene 204.01 -31.21 188.3 0.132 180 0.150 229 0.118 340 (300)

p-Oilodobsnrene 529.91 111 285

1,4-8-0- 191.46 68 1% chlorobsnzens

l-Chloro- 162.62 -2.3 258.8 nmphthalecre

* 2-Chloro- 162.62 61 256 mphthslsne h)

1.4 1.86

0.034b 44.88

aExtrqmlsted from liquid state. kdcu la ted f r a the extrapolated vapor pressure with a fugacity ratio correction. CExtrapolated f r a so l id vapor preeeum.

0.t. for pesticiQe cind8m 290.81 112.9 8.39~10~

22.4

11.7

7. J 7.80

0.147

O.lk.02

0. 355

0.0319

fpotw 1 601

r- qg

a

-

s

IO n

n

d

44

w a t e r i n t h e p o r o u s medium. Compounds w i t h h i g h w a t e r s o l u b i l i t y ( f r o m s u r f a c e s p i l l s ) w o u l d o f c o u r s e h a v e s h o r t e r downwar'd t r a v e l t i m e s a s r e f l e c t e d b y c l a s s i c a l breakthrough c u r v e a n a l y s i s . P fannkuoh ( 1 9 8 4 ) p o i n t s o u t t h a t f o r o i l s p i l l s t h e hydrocarbon components w i t h d i f f e r i n g s o l u b i l i t i e s w i l l d i s s o l v e o u t d i f f e r e n t i a l l y and w i l l produce a s i m u l t a n e o u s a g e i n g a n d l e a c h i n g e f f e c t o n t h e s p i l l . S e e t a b l e s b y Hackay and S h i u ( 1 9 8 1 ) f o r a l i s t i n g of t h e s o l u b i l i t i e s of v a r i o u s o r g a n i c compounds.

( 3 ) H e n r y ' s law c o n s t a n t (KH): According t o Mackay and S h i u ( 1 9 8 1 1 , " T h e H e n r y ' s l a w c o n s t a n t i s c o n v e n t i o n a l l y e x p r e s s e d a s a r a t i o o f p a r t i a l p r e s s u r e i n t h e v a p o r t o t h e c o n c e n t r a t i o n i n t h e l i q u i d . " I t is t h u s a c o e f f i c i e n t t h a t r e f l e c t s t h e a i r - w a t e r p a r t i t i o n i n g . Such i n f o r m a t i o n i s h e l p f u l i n u n d e r s t a n d i n g i n what p h a s e an o r g a n i c compound would most l i k e l y be f o u n d . T h u s , a n o r g a n i c compound w i t h a h i g h vapor p r e s s u r e and low water s o l u b i l i t y would be expected t o be f a v o r e d i n t h e v a p o r phase and would t h e r e f o r e be a r e l a t i v e l y good c a n d i d a t e for s o i l vapor m o n i t o r i n g . However, i f t h e d e t e c t i o n o f o r g a n i c s i n g r o u n d wa te r is of p r i m a r y i n t e r e s t , a f a l s e p o s i t i v e m i g h t r e s u l t f r o m t h i s s i t u a t i o n . The r e l a t i o n s h i p be tween s o l u b i l i t y and vapor p r e s s u r e i s p l o t t e d i n F i g u r e 2 . 1 b y M a c k a y a n d S h i u ( 1 9 8 1 ) a n d s h o w s t h a t compounds w i t h i n a h o m o l o g o u s s e r i e s g e n e r a l l y l i e on a 4 5 O d i a g o n a l o f c o n s t a n t H e n r y ' s law c o n s t a n t and t h a t p e s t i c i d e s t y p i c a l l y have v e r y l o w vapor p r e s s u r e s . Mar in and Thompson ( 1 9 8 1 0 have found t h a t a c t u a l f i e l d p a r t i . t i o n c o e f f i c i e n t s a r e l e s s t h a n l a b o r a t o r y c o e f f ' i c i e n t s and t h a t t h e f i e l d d a t a s u g g e s t l a r g e r p a r t i t i o n i n g i n t o t h e l i q u i d ( g r o u n d w a t e r ) p h a s e . They t h e o r i z e t h a t t h i s i s probably t h e r e s u l t of e i t h e r l a t e r a l d i f f u s i o n OF o f e q u i l i b r i u m c o n d i t i o n s t h a t a r e t y p i c a l l y never achieved i n t h e f i e l d between d i f f u s i o n i n s o i l g a s and wa te r .

( 4 ) C o n c e n t r a t i o n : The c o n c e n t r a t i o n r e f e r s t o t h e amount o f o r g a n i c c o m p o u n d p e r u n i t a m o u n t o f s o l v e n t ( a i r l w a t e r ) i n u n i t s s u c h a s g l m 3 , p p b l v . Kreamer ( 1 9 8 2 ) c o n c l u d e d t h a t t h e d i f f u s i o n of a g a s f r o m a r e a s o f h i g h c o n c e n t r a t i o n t o l o w , r e s u l t i n g o n l y f rom t h e e x i s t i n g c o n c e n t r a t i o n g r a d i e n t , was t h e mechanism of g r e a t e s t importance for g a s t r a n s p o r t i n t h e u n s a t u r a t e d z o n e . The c o n c e n t r a t i o n of t h e o r g a n i c compound i n t h e ground

45

4 10

0

a

0 0 a 0

lo8 0

0 .

10

loo

l o s s 10-

H A L O Q t W A T E O H Y D R O C A R D O W 8 P O L Y N U C L E A R A R O M A V I C 8 0 D I E N E 8 C V C L O A L K A W E 8 Y O N O A R O M A T I C 8 P E S T I C I D E 8 A L K A N E 8 $? A L K Y N L 8 oy. *I'

O O

A C K L N E O m v

m .* @

4 0 0 =--%

0

lo-* 1

0 0

lo-@ 0 lo-* 1 0

D

0

& 0

0 0

0 0

0 0

0

lo-? 1 0 ~ ~ 1 0 ~ ~ 100' loo2 loo1 loo lo1 log '

SOLUBILITY. rnol/m'

Figure 2 . 1 .

a

Plot of s o l u b i l i t y vs vapor pressure i l l u s t r a t i n g the tendency for compounds i n a homologoum r e r i e s t o l i e on a 4 5 O d i a g o n a l of constant Henry'r law constant (HacKay and Shiu, 1981).

46

w a t e r w i l l d i c t a t e t o a g r e a t e x t e n t t h e v e r t i c a l c o n c e n t r a t i o n g r a d i e n t o f t h e v a p o r i n t h e u n s a t u r a t e d z o n e , T h u s i f t h e c o n c e n t r a t i o n of t h e o r g a n i c compound i n q u e s t i o n i s low i n t h e g r o u n d w a t e r ( a n d t h e compound i s n o t i n s o l u b l e i n w a t e r ) , t h e n m o s t l i k e l y t h e v a p o r g r a d i e n t w i l l b e d i f f i c u l t t o d e t e c t , a n d e i t h e r a d i f f e r e n t compound s h o u l d b e s e l e c t e d a s a t r a c e r or a more i n t e n s i v e s a m p l i n g g r i d s h o u l d b e imposed t o more a c c u r a t e l y d e l i n e a t e t h e c o n t a m i n a n t plume.

( 5 ) K o c : T h e K O , f o r a n o r g a n i c c o m p o u n d i s a c o e f f i c i e n t t h a t r e l a t e s t h e p a r t i t i o n i n g o f t h e o r g a n i c compound between t h e a d s o r b e d phase and t h e s o i l s o l u t i o n r e l a t i v e t o t h e o r g a n i c c a r b o n f r a c t i o n . T h e K o c r e f l e c t s t h e a f f i n i t y o f an o r g a n i c compound t o a d s o r b o u t o f s o l u t i o n o n t o s o i l o r g a n i c m a t e r i a l . F i g u r e 2 . 2 s h o w s t h e c o r r e l a t i o n b e t w e e n w a t e r s o l u b i l i t y a n d K O , a n d d e m o n s t r a t e s t h a t t h o s e compounds w i t h low w a t e r s o l u b i l i t y o f t e n p o s s e s s h i g h e r K O , v a l u e s ( W i l s o n , e t a l . , 1 9 8 1 ) . A l t h o u g h t h i s v a l u e w i l l r e f l e c t t h e p o t e n t i a l o ? a n o r g a n i c c o m p o u n d t o b e a t t e n u a t e d i n t h e u n s a t u r a t e d z o n e , i t i s of c o u r s e t o t a l l y d e p e n d e n t o n t h e p r e s e n c e o f o r g a n i c m a t e r i a l . O f t e n t h e o r g a n i c c a r b o n c o n t e n t i n t h e u n s a t u r a t e d z o n e w i l l d e c r e a s e w i t h d e p t h ( i n f l u e n c e o f v e g e t a t i o n ) a n d c a n b e a l m o s t e n t i r e l y v o i d i n s u b s u r f a c e c o a r s e m a t e r i a l .

( 6 ) D e n s i t y : T h e d e n s i t y of an o r g a n i c compound r e f e r s t o t h e amount of s u b s t a n c e p e r u n i t voldme ( g / c m 3 ) , [ S c h w i l l e ( 1 9 8 4 ) i n d i c a t e s t h a t n e x t t o s o l u b i l i t y t h e d i f f e r e n c e i n d e n s i t y b e t w e e n c o n t a m i n a n t a n d g r o u n d w a t e r is t h e n e x t m o a t i m p o r t a n t p a r a m e t e r i n d e t e r m i n i n g t h e c o n t a m i n a n t m i g r a t i o n r e l a t i v e t o t h e a q u i f e r . ] Mackay ( 1 9 8 5 ) s t a t e s t h a t d e n s i t y d i f f e r e n c e s of a b o u t 1 p e r c e n t a r e k n o w n t o i n f l u e n c e f l u i d movement s i g n i f i c a n t l y a n d t h a t w i f h few e x c e p t i o n s t h e d e n s i t y d i f f e r e n c e s b e t w e e n o r g a n i c l i q u i d s a n d w a t e r a r e i n e x c e s s o f 1 p e r c e n t and o f t e n 10 p e r c e n t . S u c h h i g h d e n s i t i e s a n d l i m i t e d s o l u b i l i t i e s o f c h l o r i n a t e d h y d r o c a r b o n s ( T a b l e 2 . 3 ) l e d B y e r ( 1 9 8 1 ) t o c o n c l u d e t h a t t h i s was t h e p r i m a r y c a i i s t ! f o r t h e w i d e s p r e a d c h l o r i n a t e d h y d r o c a r b o n c o n t a m i n a t i o n o f u n d e r g r o u n d w a t e r s o u r c e s . Byer ( 1 981 1 a l s o showed how t h e d e n s i t y of an o r g a n i c compound s u c h a s T C E c a n b e u s e d e f f e c t i v e l y t o ‘ . r a p t h e compound i n a recove: .y p r o c e s s ( F i g u r e 2.3).

4 7

0 0

Y

Q 0 d

0 .6

8 . 0

e . 5

0 . 0

A

I I o t Q

0 AI I I II I

1 4

A l , t , 4 - l r l o c h l o r o b o n r o n o B 1 , 4 - D l c h l o r o b o n t o n o C f o t r r o h l o r o o t h r n o 0 C h l o r o b o n x o n o E T o l u o n o F f r l c h l o r o b o n x o n o a O B C P H N l t r o b o n r o n o I 1 , s - D l c h l o r o o t h r n o J C h l o r o f o r m a ~ , 1 - O l e h ~ o r a o t h r n o L b l r ~ 2 - C h l o r o o t h y l ~ o t h o r

Figure 2 . 2 . R e l a t i o n s h i p between the water r o l u b i l i t y of a compound ( r g / l i t c r ) and i t s p a r t i t i o n c o e f f i c i e n t between r o i l organ ic C and r o i l s o l u t i o n ( K o e ) (Wilron, e t a l . , 1981).

48

Hsxrchloroethrrm 1,1,1,2,2-Pmtrchloroethrm Tot r r c h l o r o e t h y l w 1,1,2,2-letrrchlorathrm C u b o n t e t r r c h l o r i b 1,1,1,2-Tetrachlorwth8m Chloroform 1 , 2 , 2 - T r i c h l o r ~ t h y l ~ 1,1,2-Trichlorwth.m 1 , l , l -Tr ichloruetham Hethylem Chlor idb Cir-l,24)ichloroethyleno Tram 1,24 ich loroethy l a m 1 , 2 4 k h 1 0 ~ O d h 8 ~ 1 ,14 ich lo roo thy lam 1 , 1 4 i c h l o r o e t h r m

1Bb.3 u 2 121 2 146 76.7

129 61.7 87

11s.) 74 40.4 6 47 83 37 57

0.005 QI 0.0) QI 0.015 Q

0029 Q

0.08 QI

0.8220 p 0.1100 p

0.4400 QI 2,000 0

0.015 Q

0.4500 p

0.35 QI

0.869 QI 4.00 p 0.55 9,

0.65 Q

2.2091 1.67% 1 6227 1.595s 1.5940 1.5¶69 1 9032 1 4642 1.4397 l .SSp0 1.3266 1.2837 1.2565 1.2351 1.218 1.1757

1 C h l o r i n s t i o n o f e imp le h y d r o c r t b o n r y i e 1 6 8 v r r i e t y of chlorinated hydrocarborn, varying i n p h y r i c r l p r o p e r t i e r i n r regular frohion depending qmn th degree of ch lo r in8 t im. Ueur l l y , 80

t h e c h l o r i n e content o f the hydrocarbon is increraed there i o a progrereive Qcrerae i n peci f ic heat, d i o l e c t r i c constant 8nd r o l u b i l i t y i n water. The r u b r t i t u t i o n o f c h l o r i n e on to t h e h y d r o c a r b o n i m p a r t r an i n c r e 8 e e i n r o l v e n t power, v i r c o e i t y , n o n f l r m m a b i l i t y , chemica l r e a c t i v i t y md dsnsi ty. (Byer, e t rl., 1981)

49

Figure 2.3. Diagram s h o w i n g an economical rnd sa fe way to contain a chlorinated hydrocarbon (TCE) compound rn

The s o - c a l l e d n i t r o g l y c e r i n e t rap c o l l e c t s TCEs from the p l a n t v i a f l o o r d r a i n s . Traps must be c o n c r e t e l i n e d t o p r e v e n t s e e p a g e . I t i s economical t o reprocess TCE when volume u s e d is large (Byer, 1981).

50

O r g a n i c compounds w i t h s p e c i f i c g r a v i t i e s of less t h a n 1 . O a s s o c i a t e d w i t h s o l u b i l i t i e s o f l e a s t h a n 1 p e r c e n t a r e o f t e n r e f e r r e d t o a s f l o a t e r s , s e e T a b l e 2.4 compi led b y t h e New Y Q r k S t a t e D e p a r t m e n t o f E n v i r o n m e n t a l C o n s e r v a t i o n ( 1 9 8 3 ) . I f t h e f l o a t e r i s a l s o c l a s s i f i e d a s b e i n g h i g h l y v o l a t i l e , t h e compound w o u l d be a good c a n d i d a t e f o r s o i l v a p o r m o n i t o r i n g a s I t w o u l d n o t b e d i l u t e d i n t h e a q u i f e r a n d p o t e n t i a l l y c o u l d e s t a b l i s h a s t e e p e r v a p o r c o n c e n t r a t i o n g r a d i e n t . However , f l o a t e r s would have d i f f i c u l t y moving p a s t s u b s u r f a c e o b s t r u c t i o n s . T h u s , i t wou ld a l s o b e c r i t i c a l t h a t v a p o r c o n c e n t r a t i o n s be c o r r e l a t e d w i t h t h e c o n c e n t r a t i o n o f t h e o r g a n i c f l o a t i n g a t t h e w a t e r t a b l e a n d t h a t a p r o p e r l y s c r e e n e d m o n i t o r i n g w e l l b e u s e d t o a v o i d s a m p l i n g w a t e r d e e p e r i n t h e a q u i f e r .

( 7 ) V i s c o s i t y : T h e v l s c o s i t y o f a l i q u i d o r g a n i c compound i s a m e a s u r e o f t h e d e g r e e t o w h i c h i t w i l l r e s i s t f l o w u n d e r a g i v e n f o r c e m e a s u r e d i n d y n e - s e c o n d s p e r c m 2 . A c c o r d i n g t o S c h w i l l e ( 1 9 8 4 ) , t h e v i s c o s i t y o f t h e o r g a n i c f l u i d ( s u c h a s o i l ) w i l l a f f e c t t h e v e l o c i t y of t h e f l o w p r o c e s s . Mackay ( 1 9 8 5 ) a d d s t h a t i t is t h e c o m b i n a t i o n o f d e n s i t y a n d v i s c o s i t y t h a t w i l l g o v e r n t h e m i g r a t i o n o f an i m m i s c i b l e o r g a n i c l i q u i d i n t h e s u b s u r f a c e . T h u s , i t 1s t h e v i s c o s i t y o f a n i m m i s c i b l e o r g a n i c f l u i d ( s u c h a s o i l ) t h a t w i l l c o n t r o l t h e l e n s t h i c k n e s s o n a w a t e r t a b l e . H o w e v e r , e v e n w i t h h i g h v i s c o s i t y f l u i d s s u c h a s o i l s , H o l z e r ( 1 9 7 6 ) p o i n t s o u t t h a t many m o n t h s a f t e r a s p i l l , i t i s o f t e n t o o l a t e t o d e t e r m i n e w h e t h e r t h e s p i l l w a s . c a u s e d b y a c a t a s t r o p h i c r e l e a s e or a s l o w s t e a d y " d r i p " . F i g u r e 2 . 4 shows t h a t a f t e r 300 d a y s , l i t t l e d i f f e r e n c e i s n o t e d i n t h e t h i c k n e s s o f a s p i l l d e v e l o p e d u n d e r t w o d i f f e r e n t p e r m e a b i l i t y v a l u e s .

(8) D i e l e c t r i c c D n s t a n t : T h e d i e l e c t r i c c o n s t a n t of a m e d i u m i s a p a r a m e t e r t h a t r e l ' a t e s t h e r e l a t i o n s h i p b e t w e e n t w o c h a r g e s a n d t h e d i s t a n c e o f s e p a r a t i o n of t h e two c h a r g e s t o t h e f o r c e of a t t r a c t i o n . I n a c l a y medium t h i s c o n s t a n t r e f l e c t s t h e d e g r e e t o u h i c h t h e c l a y s w i l l e i t h e r s h r i n k o r s w e l l . L i q u i d s w i t h a h i g h d i e l e c t r i c c o n s t a n % ( T a b l e 2 . 5 ) s u c h a s wate r would be e x p e c t e d t o c a u s e t h e c l a y s t o s w e l l . C o n v e r s e l y , t h o s e l i q u l d s w i t h a low d i e l e t r i c c o n s t a n t would c a u s e t h e c l a y s t o s h r i n k a n d , t h e r e f o r e , i n c r e a s e i n p e r m e a b i l i t y a f t e r e x p o s u r e t o c o n c e n t r a t e d o r g a n i c l i q u i d s , T a b l e

51

_I T C OF O W I C EocpaMoS h r m b l e t o Bio- Highly toxic

squntic l i f e 1 i q i i i d Poieomua f lanrneble Corrosive Reactive Vo la t i le Floater b io log ica l dsgraQsble t o

trentmont Acete 1 dehy tk Acetic ac id Acetic enhydrids Acetone cyenohydrin Acetyl braide Acetyl ch lor ide Acrolein Acry l o n i t r i le A l l y l alcohol A l l y l ch lor ide Annoni u hy drox ide Amy1 acetate Anil ine BsnrUlO Benroni t r i l e Banroyl chloride Benryl chloricb Bin ( & l o m e t h y l ) ether Bie (2-chloroieopropy 1)

ether Bie ( 2-chloroethoxy )

asthane 81s (Z-chloroethyl)

ether B i e (Zathylhexy)

phthalste Bmoform

( t r ibro l laethans) Eutyl acetate Butylmine Butyl benryl phthalets Butyric acid

X X

X X

X X

X X

X X

X X

X X

X X

X X

X X

X - X X

X X

X X

X X

X X

X X

X X

b x b X

X X

X X

- - X X

X X

X X

X X

ND

H)

H)

H)

k b n b l e to 010- Highly b x i c

t r e a b m t .quatic l i f e L iquid Poieonous F l n a b l e Corrosive Reactive Volat i le Floater biological dbprdomblm to

- - - - - X - X

Carbon dieulfide - X - Carbon tetrachloride - - - Chlordsns - - - - Chlorobenruna - X - -

- X - - - m Chlorodlbr~aethane - - - Chloraetham X X - - X X X X m 2-Chloroethyl

- - - - - - - - X - - X X -

Chlorowlfonic r i d - - X X - Cmtonldshyde X X X - X

- X

- X X -

1 ,l-Dichloroetharm - X - - 1,2-Dichloroethrrs - X - - 1,l-Dlchloraethyl.m (vinylidone chloride 1 - X - -

1,2-Dichloropropane - X - - 2.2-Dichloropragionie

r i d - - X -

X - X - X - X -

X

X

X

- X

X

X - X

X - X

X

X

X - X

- X

- lksnable to Bio- Highly k i c

I. iq uid Poisomum Flemneble Corroeive Reactive Volat i le f loater biological chgmdoabh to treatment mqustic l ife

Di-ryIcty l phthalate Diaulfoton Dodecy lbnzemau 1 tonic

acid Endr in aldehyds Epichlorohydrin E t h i o n Ethylbsnzau Ethylene dlbnnide E thybnocii.rine Fomic acid Frrrfural tbxrhlorobutadiens Hydrochloric r i d Hydrotlcmric r i d Iwphorocrs Isoprens Ualathion Methylone chloride

0

(dichloroethsns Methyl rsthacrylats ~ ~ ~ i n p h o ~ Nphthenlc acid N i t r i c acid N i t robsnzeca - N-nitrdiaOthyl-inD

PropY 1-i- - N-nlttasodi-Ib

Parathion Phosphorou, oychlorids Phosphorous tr lchlor ide Polychlor i r r t e d

blphenyla (PCBS) Propionic acid

X X - - X X - b -b X X - - X X

X X

X X

X X

X X

X - X - X - X X

X X - -

- - X X

X x X - - - X X

ED ED

StyYrem S u l f u i c acid

X - Sulfur rMPdrloriQ - - 2,4,5-Trichlorophenoxy

retic ac id with mines - X

1,1,2 ,-Tetnchloroeth8ne Tetrachloroethylene ~ ~ t r a e t h y 1

To1 lens 1 ,Z-trant+

l,2,4-Trichlorobenzw l,l,l-Trichloroetham 1,1,2-Trichloroethane Trichloroethylene Triethy lains Vinyl acetate

pyrophosphate

(n Dichloroethy lens VI

X - X - - X

- X

- X

- X

- X

X X

X X

Vinyl chlorids (chloroethylene Ib M) X - - X X X X

x bnotes chemical is i n th i s ntepory. - Denotea c h a i c a l is mt i n t h i s category. NO Denotes (P dots available.

Ofmotes . s a r a d vslrss b a s 3 on chemical grolpa o f d a i l a r type arbetancea.

( N a Yorlc State Dsp.rtrent of Emironnentd Conserwtion, 1983)

10

8

t

k = .0026 cm/s

1 10

I 8 0

I 100

I 8 0 0

Figure 2 .4 . Th ickness of c e n t e r of o i l lens v t r ~ u s t i m e where k valuto ate p e r m e a b i l i t i e r w i t h respect to o i l (Holter, 1976).

56

TABLE 2.5. DIELECTRIC CONSTANTS, DENSITIES AND WATER SOLUBILITIES OF VARIOUS HALOCENATED AND

80 OGENATED SOLVERTS -c Name Deority Water

Conr tant (g/cm3) Solubility

Water Methanol t thanol Ace tone 1-Proprnol 1-but and b-Pentanol Pyridine Phenol Dichloromethrne 1-Broropropane l,l,l-Trichloroethane Ani 1 ine Chlorof o m Bromoform Trichloroethplane Toluene Benzene Carbon tetrachloride Cyclohexene Hexane Tetrachloroethylene

78.5 92.7 24.6 20.7 20.3 17.5 13.5 12.4 9.8 8 09 8.1 7.5 6.9 4.8 4 04 3 .4 2.4 2 . 3 2.2 2.0 1 .9 2.2

1 ,oo 0.79 0.79 0.79 0.80 0.81 0.81

1.05 1.31 1.34 1.34 1.02

2.89 1.48 0.87 0.88 1 a60 0.78 0.65 1.6

0.97

1.48

- Mi sc iblc Hiscibl c Hi 8c ib 1 e Mi bcible Mi rc ible Mi 8c ib 1 e Mi sc ib 1 e Hi ec ible 1.32%

Slightly Soluble Soluble 0.82% 0.102 0.112

S1 igh tly Soluble Slightly Soluble

0.08% 40 q / l

150 mg/l -

(Andereon, et el., 1984)

57

TABLE 2.6 INTRINSIC PERHEABILITY OF SOILS PeaMEATED BY OUIDS

fatriaric Permeability (lO’9cm2) Nonpolar EIOlventr Po 1ar ~0 loeat r

S o i l type Wr tcr It8 tor em Xyleae Ethyl cae foopropy 1 s1i;col aicohoi

Sand 145. 179. 151. 135. 177 . Srndy-clap 1.6 158. 146. 62.8 93 .2 Clay 0.s 10.1 14.0 2.4 6.4

(Andereon, et r l . , 1984)

58

2 . 6 ( A n d e r s o n , e t a l . , 1 9 8 4 ) s h o w s t h e i m p a c t v a r i o u s s o l v e n t s w i l l h a v e o n t h e i n t r i n s i c p e r m e a b i l i t y of v a r i o u s s o i l t y p e s . Such a r e s u l t would oS c o u r s e mean t h a t i n a c l a y s o i l or h o r i z o n t h e c o n c e n t r a t e d o r g a n i c p l u m e w i l l r e a c h t h e ground w a t e r i n a s h o r t e r t r a v e l t i m e a n d t h a t t h e p l u m e w o u l d e x p a n d t o a l a r g e r v o l u m e . I n a d d i t i o n , t h e v a p o r p h a s e moving b a c k t o w a r d t h e s u r f a c e i n t h e same a r e a would n o t b e r e s t r i c t e d t o t h e same d e g r e e .

( 9 ) ' B o i l i n g P o i n t : T h e b o i l i n g p o i n t of a compound is t h e t e m p e r a t u r e a t w h i c h t h e e x t e r n a l p r e s s u r e o f t h e l i q u i d is i n e q u i l i b r i u m w i t h t h e s a t u r a t i o n v a p o r p r e s s u r e o f t h e l i q u i d . T h u s , f o r h i g h e r b o i l i n g p o i n t s t h e r e i s a g e n e r a l a s s o c i a t i o n w i t h l ower vapor p r e s s u r e s . Again , i t i s t h o s e o r g a n i c s w i t h h i g h e r v a p o r p r e s s u r e s and t h u s l ower b o i l i n g p o i n t s t h a t wou ld b e b e t t e r s u i t e d f o r s o i l v a p o r m o n i t o r i n g . A l i s t i n g of t h e b o i l i n g p o i n t s f o r v a r i o u s o r g a n i c compounds is i n c l u d e d i n t a b l e 2 . 2 compi l ed b y Mackay and S h i u ( 1 9 8 1 ) .

( 1 0 ) M o l e c u l a r w e i g h t : T h e m o l e c u l a r w e i g h t o f an o r g a n i c compound i s t h e s u m t o t a l of t h e w e i g h t s of t h e a t o m s t h a t compose i t ( s e e t a b l e 2 . 2 ) . Mackay and S h i u ( 1 9 8 1 ) i n d i c a t e t h a t f o r l i q u i d a l k a n e s t h e r e i s a t endency f o r t h e Henry ' s law c o n s t a n t t o i n c r e a s e w i t h i n c r e a s i n g m o l e c u l a r w e i g h t a s t h e s o l u b i l i t y f a l l s m o r e t h a n t h e v a p o r p r e s s u r e , H i g h m o l e c u l a r w e i g h t h y d r o c a r b o n s ( e s p e c i a l l y a r o m a t i c s ) a r e decomposed th rough b i o d e g r a d a t i o n a t a much s l o w e r r a t e ( A m e r i c a n P e t r o l e u m I n s t i t u t e , 1 9 7 2 ) a n d t h u s would p e r s i s t i n t h e u n s a t u r a t e d and s a t u r a t e d zones l o n g e r .

P R O P E R T I E S OF T H E U N S A T U R A T E D Z O N E

( 1 ) Air f i l l e d p o r o s i t y : The a i r f i l l e d p o r o s i t y o f porous m e d i u m s u c h a s s o i l i s d e f i n e d a s t h e r a t i r ; of t h e v o l u m e of a i r i n t h e s o i l p o r e s t o t h e t o t a l . volume (vo lume o f a i r , w a t e r , and s o i l c o m b i n e d ) . I t is t h u s i n d i c a t i v e o f s o i l a e r a t i o n a n d is i n v e r s e l y r e l a t e d t o t h e d e g r e e of s a t u r a t i o n . The a i r - f i l l e d p o r o s i t y i s a n i m p o r t a n t p a r a m e t e r i n e s t i m a t i n g t h e d i f f u s i o n o f g a s i n s o i l a n d u n c o n s o l i d a t e d m a t e r i a l . T h e d i f f u s i o n c o e f f i c i e n t of o x y g e n is a p p r o x i m a t e l y 1 0 , 0 0 0 t i m e s l o w e r i n w a t e r t h a n i n a i r ( L e t e y , e t a l . , 1 9 6 4 ) . T h u s , s o i l o r g a n i c v a p o r s m i g r a t i n g t o w a r d t h e s o i l s u r f a c e wou ld be r e s t r i c t e d i f t h e w a t e r c o n t e n t

5 9

i n c r e a s e s and t h e a i r - f i l l e d p o r o s i t y d e c r e a s e s . V a p o r s m o v i n g i n t o l o w a i r - f i l l e d p o r o s i t y z o n e s c o u l d p o t e n t i a l l y b e r e s o l u b i l i z e d , Because of t h e r e s t r i c t i o n s i n f l o w a n d t h e p o s s i b l e r e s o l u b i l i t a t i o n , v e r t i c a l s o i l gas p r o f i l e s would be p o o r l y e s t a b l i s h e d . T h i s p a r a m e t e r w o u l d b e e x p e c t e d t o c h a n g e d r a m a t i c a l l y i n t h e u n s a t u r a t e d zone a s i t i s d e p e n d e n t on t h e p o s i t i o n r e l a t i v e t o a w e t t i n g f r o n t ( r a i n f a l l ) a n d o n c h a n g e s i n t e x t u r e ( w a t e r h o l d i n g c a p a c i t y ) .

V o l c r m i . t r i c w a t e r c o n t e n t : The v o l u m e t r i c w a t e r c o n t e n t i s t h e r a t i o o f t h e volume o f w a t e r i n a p o r o u s medium t o t h e t o t a l volume. When t h e w a t e r f i l l s t h e e n t i r e p o r e v o l u m e t h e m e d i u m i s s a t u r a t e d . C o a r s e s o i l s h a v e l o w e r v o l u m e t r i c w a t e r c o n t e n t s a t s a t u r a t i o n t h a n d o m e d i u m t e x t u r e d s o i l s a n d medium t e x t u r e d s o i l s l e s s t h a n c l a y e y s o i l s . Under u n s a t u r a t e d f l o w c o n d i t i o n s , i t i s t h e u n s a t u r a t e d h y d r a u l i c c o n d u c t i v i t y a n d t h e h y d r a u l i c head g r a d i e n t t h a t d i c t a t e t h e c h a n g e i n v o l u m e t r i c w a t e r c o n t e n t w i t h t i m e . As t h e v o l u m e t r i c w a t e r c o n t e n t I n c r e a s e s , t h e a i r f i l l e d p o r o s i t y d e c r e a s e s , and t h e p a t h f o r v a p o r f l o w becomes r e s t r i c t e d . T h u . s , a s t h e p e r c e n t w a t e r i n t h e s o i l p o r e s g o e s u p , t h e p o s s l b l l i t y o f a v e r t i c a l s o i l o r g a n i c v a p o r g r a d i e n t b e i n g e s t a b l i s h e d i s l e s s e n e d and s o i s t h e l i k e l i h o o d of c o r r e l a t i n g s o i l g a s measurements w i t h g r o u n d w a t e r c o n c e n t r a t i o n s . R e i d ( 1 9 8 5 ) h a s l c d i c a t e d l i t t l e s u c c e s s i n s o i l v a p o r n o n i t o r l i , g s t u d i e s when t h e v a d o s e zone c o n t g i n s h i g h c l a y and wa te r c o n t e n t s . Water c o n t e n t i n S u b s u r f a c e l a y e r s h a s a l s o b e e n shown t o be t h e d e c i s i v e f a c t o r i n d e t e r m i n i n g t h e s h a p e o f an o i l b o d y a n d t h e d i s t r i b u t i o n a f t e r p e r c o l a t i o n ( S c w i l l e , 1 9 7 5 ) .

( 3 ) S o i l o r g a n i c m a t t e r : The amount of o r g a n i c m a t t e r i n a s o i l v a r i e s a c c o r d i n g t o t h e v e g e t a t i o n , c l i m a t e , a n d t h e r a t e o f d e c o m p o s i t i o n . A g r i c u l t u r a l s o i l s o f t e n p o s s e s s i n e x c e s s o f 2 p e r c e n t o r g a n i c m a t t e r whereas d e s e r t s o i l s can b e a l m o s t e n t i r e l y v o i d o f o r g a n i c m a t t e r . O r g a n i c m a t e r i a l g e n e r a l l y h a s h i g h s u r f a c e a r e a s a n d exchange p r o p e r t i e s : d e a l f o r a d s o r p t i o n o f o r g a n i c compounds . The K O , v a l u e r e f l e c t s t h e i m p a c t o f t h i s o r g a n i c m a t e r i a l t o a d s o r b o r g a n i c compounds o u t o f s o l u t i o n , C h i o u ( 1 9 8 5 ) s t a t e s t h a t " t h e e x t e n t of u p t a k e of n o n i o n i c o r g a n i c compounds f r o m w a t e r o n a g r e a t v a r i e t y o f s o i l s i s c l o s e l y r e l a t e d t o s o i l o r g a n i c m a t t e r c o n t e n t . I1 C h i o u

60

a l s o i n d i c a t e s t h a t "when s o i l s a r e f u l l y h y d r a t e d , a d s o r p t i o n of t h e o r g a n i c s o l u t e s b y s o i l m i n e r a l s becomes r e l a t i v e l y i n s i g n i f i c a n t compared t o t h e u p t a k e b y p a r t i t i o n i n g i n t o s o i l o r g a n i c m a t t e r , p r e s u m a b l y because water 13 p r e f e r e n t i a l l y adsorbed by m i n e r a l s ."

(4) S o i l t e x t u r e : The t e x t u r e of a s o i l r e f e r s t o t h e p r o p o r t i o n s of v a r i o u s p a r t i c l e s i z e g r o u p s i n a s o i l m a s s . T h e s e p a r t i c l e s i z e g r o u p s a r e t y p i c a l l y c a l l e d s a n d , s i l t , a n d c l a y . F i g u r e 2 . 5 shows t h e t e x t u r a l t r i a n g l e a n d t h e v a r i o u s s o i l t e x t u r a l c l a s s e s . As t h e c l a y c o n t e n t i n c r e a s e s , t h e w a t e r h o l d i n g c a p a c i t y i n c r e a s e s , t h e exchange c a p a c i t y i n c r e a s e s , a n d t h e r a t e o f d i f f u s i o n d e c r e a s e s . T h u s , i f a h i g h c l a y c o n t e n t l a y e r e x i s t s i n t h e s u b s u r f a c e ( t e x t u r a l d i s c o n t i n u i t y ) or i f t h e e n t i r e vadose zone 1s comprised of c l ayey s o i l , i t w i l l a c t a s a r e t a r d i n g l a y e r t o t h e v e r t i c a l f l u x of v o l a t i l e o r g a n i c ca rbons . Swallow and Gschwend ( 1 9 8 3 ) p o i n t o u t t h a t i t 1s t h e r a t e of f l u x t h r o u g h t h e moat r e t a r d i n g l a y e r t h a t w i l l c o n t r o l t h e v e r t i c a l f l u x . F i g u r e 2 . 6 ( A m e r i c a n P e t r o l e m I n s t i t u t e , 1 9 7 2 ) s h o w s t h e p o s s i b l e e f f e c t s of c l a y l a y e r s and l e n s e s on t h e m i g r a t i o n of c o n t a m i n a n t s i n t h e u n s a t u r a t e d zone. Indura t ed l a y e r s such a s p e t r o c a l c i c l a y e r s can a l s o a l t e r t h e f l o w p a t h of c o n t a m i n a n t s b o t h i n t h e l i q u i d and vapor p h a s e s . C o n v e r s e l y , g r a v e l l a y e r s have been shown t o a c t a s a c o n d u i t f o r o r g a n i c vapors t o d i f f u s e l a t e r a l l y f rom more c o n t a m i n a t e d s o i l s (Mar in , e t a l . , 1984) .

( 5 ) V a p o r p r e s s u r e of w a t e r i n t h e s o i l p o r e s : The a q u e o u s vapor p r e s s u r e m e a s u r e d i n s o i l p o r e s i s f o r t h e moat p a r t c o n s i d e r e d t o b e vapor s a t u r a t e d : a s H i l l e l ( 1 9 7 1 ) p o i n t s o u t , a c h a n g e i n m a t r l c s u c t i o n be tween 0 and 1 0 0 b a r s is accompanied b y a v a p o r p r e s s u r e c h a n g e o f o n l y 1 . 6 m i l l i b a r s . T e m p e r a t u r e h a s a much l a r g e r i m p a c t on v a p o r p r e s s u r e a s a l0C change has a l m o s t t h e same e f f e c t a s t h e 1 0 0 - b a r s u c t i o n c h a n g e . S i n c e vapors tend t o move f rom warm t o c o l d a r e a s i n a s o i l , t h e v a p o r s would t h e r e f o r e tend t o move downward d u r i n g t h e day and u p w a r d d u r i n g t h e n i g h t . A t t h e s o i l s u r f a c e and p e r h a p s down e v e n s e v e r a l i n c h e s , t h e vapor p r e s s u r e can drop below s a t u r a t i o n b e c a u s e of h i g h e r g a s m i x i n g and exchange r a t e s . The presence of e l e c t r o l y t e s ( o f t e n c o n c e n t r a t e d n e a r t h e s o i l s u r f a c e v i a e v a p o r a t i o n ) c a n a l s o lower t h e vapor p r e s s u r e . I f t h e vapor p r e s s u r e i n t h e s o i l p o r e s

61

P o r o o n t b y w o l g h t 8 8 n d

Figure 2 . 5 . Textural triangle, rhwing the petcentagar of clay (belov 0.002 a d , r i l t (0.002-0.05 am), and rand (0.05-2.0 mm) i n the baric r o i l textural clasres (American Petroleum I n s t i t u t e , 1 9 7 2 ) ( B i l l e l , 1971).

62

P o r r l b l o M l e r r t l o n o f Product t o Outcrop f o l l o w o d by booond C y o l o Cont rmlnr t lon

Et foot o f C l a y Lona in Soil

Figure 2.6. Posoible migration of product to outcrop folloued by second cycle contamination (American Petroleum Institute, 1972).

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can be r e d u c e d , i t ha8 been shown b y Chiou ( 1 9 8 5 ) t o have a s i g n i f i c a n t e f f e c t on t h e a d 8 0 P p t i o n of o r g a n i c v a p o r s . He s t a t e s t h a t t h e m i n e r a l f r a c t i o n of a d r y or s l i g h t l y hydrated 3011 w i l l be a p o w e r f u l a d s o r b e n t f o r o r g a n i c v a p o r s a t l ower vapor p r e s s u r e 8 and t h a t t h i s may become t h e most i m p o r t a n t p r o c e s s i n t h e u p t a k e o f o r g a n i c compounds b y m i n e r a l r i c h u n s a t u r a t e d s o i l s . F i g u r e 2 . 7 shows t h e impact of r e l a t i v e h u m i d i t y on t h e a d s o r p t i o n of benzene and i n d i c a t e s a l a r g e i n c r e a s e d a d s o r p t i o n a s t h e r e l a t i v e h u m i d i t y drops below 90 p e r c e n t .

T h i s r e l a t 1 ve h u m i d i t y - a d s o r p t i o n phenomena may c a u s e s i g n i f i c a n t r e d u c t i o n s i n t h e amoun t o f o r g a n i c v a p o r measured a t o r near t h e 3011 s u r f a c e . T h u s , deeper s o i l g a s p r o b e s would be a d v i s e d f o r p r e c a u t i o n a r y means ( p r e c l u d i n g t h e use of s u r f a c e gas measuring d e v i c e s ) . P r o b e s l o c a t e d b e n e a t h a dep th of 1 2 i n c h e s i n a l m o s t a l l s i t u a t i o n s would encounter a s a t u r a t e d aqueous v a p o r , t h u s a v o i d i n g t h e i n c r e a s e d a d s o r p t i o n phenomena shown i n Figure 2 . 7 .

( 6 ) Shape and s i z e of p o r e s : Knowledge of t h e s h a p e and s i z e of pores or pore s i z e d i s t r i b u t i o n i n s o i l is i m p o r t a n t i n any u n d e r s t a n d i n g of t h e t o r t u o u s p a t h v a p o r s m u s t t r a v e r s e i n r e a c h i n g t h e s o i l s u r f a c e . F i g u r e 2 . 8 i s a drawing o f t h e p o s s i b l e v a r i a t i o n i n p o r e s i z e an o r g a n i c v a p o r m i g h t e n c o u n t e r . N o t e t h a t some p o r e s a r e t o t a l l y b locked b y i n t e r s t i t i a l w a t e r , and t h e r a t e o f d i f f u s i o n i s thereby reduced b y o r d e r s of magnitude. I t i s . a l s o w o r t h n o t i n g h e r e t h a t t h e t o t a l p o r o s i t y d o e s n o t p r o v i d e any i n d i c a t i o n of t h e pore s i z e d i s t r i b u t i o n . N i e l s o n and Rogers ( 1 9 8 2 ) u s i n g a m a t h e m a t i c a l mode l t o e s t i m a t e r a d o n d i f f u s i o n i n e a r t h e n m a t e r i a l s c a l c u l a t e d t h e d i f f u s i o n c o e f f i c i e n t f o r radon by u s i n g n ine pore s i z e d i s t r i b u t i o n s . F i g u r e 2 . 9 shows t h e impac t v a r i o u s median p o r e s i z e s and w a t e r c o n t e n t s can have on t h e d i f f u s i o n c o e f f i c i e n t . I n t h e d r i e r r a n g e , a d i f f e r e n c e of an o r d e r o f magn i tude i s observed i n t h e d i f f u s i o n c o e f f i c i e n t , and N i e l s o n a n d Rogers a t t r i b u t e d t h i s t o t h e d i f f e r e n c e s i n t he median pore s i z e . Clayey s o i l s t e n d t o have a more u n i f o r m pore s i z e d i s t r i b u t i o n than do coa r se r s o i l s ( H i l l e l , 1 9 7 1 ) whereas t h e c o a r s e s o i l s t e n d t o have l a r g e r mean p a r s s i z e s which w i l l t r a n s f e r f l u i d s f a s t e r under s a t u r a t e d c o n d i t i o n s and v a p o r s f a s t e r under unsa tu ra t ed c o n d i t i o n s . The d i f f u s i o n

64

40

ao

t O

10

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0 0.2 0.4 0.6 0.8 1 .o

RELATIVE VAPOR CONCENTRATION, P / P o

Figure 2 .7 . Benzene u p t a k e by r o i l a $ a f u n c t i o n o f t h e r e l a t i v e vapor c o n c e n t r a t i o n , w h e r e ? i s t h e e q u i l i b r i u m p a r t i a l p r c r r u r e and Po i r t h e raturation vapor p r e r r u r c of t h e compound a t the ryrtem temperature (Chiou, 1985).

6s

OPEN PORE AREA

A IR

Figure 2.8. Crous-aectioual view c%r' * * a i 1 3ore area (Nielroa and Rogerr, 15'82).

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n 0 - a a Y - 4 0 10

t r W

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u r = M I D I A N P O R E R A D I U S

0 0 . 4 0.4 0 . 6 0.8 1 .o M O I 8 T U R E S A T U R A T I O N

Figure 2 .9 . Cornpariaon o f d i f f u a i o n c o e f f i c i e n t ooiature curve8 for varioua median pore a i r s 8 ( l i e l a o n and Rogera, 1982).

67

c o e f f i c i e n t m u s t , t h e r e f o r e , compensate for t h i s t O r t u O U 8 path for vapor f l o w ; t h i s i s a c c o m p l i s h e d b y r e p l a c i n g t h e d i f f u s i o n c o e f f i c i e n t w i t h t h e e f f e c t i v e d i f f u s i o n C o e f f i c i e n t ( s e e chapter 3 ) .

( 7 ) D e p t h o f u n s a t u r a t e d z o n e : D e p t h o f t h e unsa tu ra t ed zone or d e p t h t o t h e w a t e r t a b l e i s a v e r y i m p o r t a n t S i t e parameter i n s o i l o rgan ic vapor monitor ing. S p r e a d i n g o f o r g a n i c c o n t a m i n a n t s i s e n h a n c e d b y a s h a l l o w u n s a t u r a t e d z o n e a s t h e o p p o r t u n i t y t i m e and v o l u m e f o r a d s o r p t i o n a n d r e t e n t i o n 13 d e c r e a s e d . The s h o r t e r t h e v e r t i c a l t r a v e l time 13 i n t h e u n s a t u r a t e d zone, t h e g r e a t e r i s t h e o p p o r t u n i t y f o r m i s c i b l e o r g a n i c s t o be d i s p e r s e d i n t o t h e g r o u n d w a t e r . [ A s t h e u n s a t u r a t e d zone i n c r e a s e s i n s i z e ( v e r t i c a l l y and l a t e r a l l y ) , the p o s s i b i l i t y of t e x t u r a l c h a n g e s and d i s t i n c t h o r i z o n t a l l a y e r s f o r m i n g i s a l s o inc reased . ] [Deeper sampl ing m i g h t be recommended t o a v o i d t h e s e d i s c o n t i n u i t i e s , which w o u l d a l t e r t h e v e r t i c a l vapor g r a d i e n t . 1 Deeper s a m p l i n g c o r r e l a t e s t o i n c r e a s e d c o s t and t o d e c r e a s e d c o n v e n i e n c e , I n t e r m s o f v a p o r m o n i t o r i n g , a d e e p e r u n s a t u r a t e d zone means a g r e a t e r d i s t a n c e o v e r w h i c h a v e r t i c a l v a p o r g r a d i e n t m u s t b e e s t a b l i s h e d . T h u s , b y t h e t ime vapors a r r i v e a t o r near t h e 3011 s u r f a c e f r o m deep wa te r t a b l e s , t h e c o n c e n t r a t i o n may be be low d e t e c t i o n l e v e l s and t h u s p r o v i d e l i t t l e i n f o r m a t i o n o n t h e s p a t i a l e x t e n t of t h e plume. Success fu l vapor c o r r e l a t i o n s u n d e r s u c h c o n d i t i o n s w o u l d r e q u i r e t h e c o n c e n t r a t i o n of t h e o r g a n i c i n t he ground water t o be exceedingly h i g h and t h a t t h e u n s a t u r a t e d zone be comprised p r i m a r i l y of coa r se g r a v e l l y . m a t e r i a 1 .

( 8 ) R e t e n t i o n : D e p e n d i n g on t h e s o l u b i l i t y o f t h e organic compound, t h e t e x t u r e o f t h e soil, and t h e pore s i z e d i s t r i b u t i o n , a c e r t a i n percentage of t h e l i q u i d c o n t a m i n a n t w i l l be r e t a i n e d i n t h e S o i l p o r e s . C o l u m n s t u d i e s b y McKee ( 1 9 7 2 ) showed t h e s p e c i f i c r e t e n t i o n of wa te r t o r ange from 1 0 . 3 7 t o 1 7 . 6 7 p e r c e n t i n t h e s o i l s he i n v e s t i g a t e d whereas t h e s p e c i f i c r e t e n t i a n of g a s o l i n e m e a s u r e d was o n l y 6 . 1 0 p e r c e n t . Other s t u d i e s t h a t he conducted showed t h a t even a f t e r 8 4 4 po re volumes of w a t e r had p a s s e d t h r o u g h a c o l u m n c o n t a m i n a t e d w i t h g a s o l i n e , t he e f f l u e n t s t i l l h a d a g a s o l i n e t a s t e . I n a n o t h e r column McKee passed 3750 pore volumes of a i r and s t i l l c o u l d n o t c o m p l e t e l y v a p o r i z e t h e g a s o l i n e . The e x p l a n a t i o n f o r t h i s comes d i r e c t l y from Figure 2 . 1 0 , where W i l l i a m s and Wilder ( 1 9 7 1 )

68

Figure 2.10. R e l a t i v e p e r m e a b i l i t y graph where h a t e r i s the p e r c e f i t e a t u r a t i o n o f w a t e r and k r i e t h e p e r m e a b i l i t y r a t i o ( r a t i o o f o b s e r v e d permeability a t a g i v e n e a t u r a t i o n r e l a t i v e t o t h e p e r m i a b i l i t y a t 100 percent s a t u r a t i o n ) (Williams and Wilder, 1971) .

69

s t a t e t h a t i n r e g i o n I 1 1 l i t t l e f l o w o f g a s o l i n e w i l l t a k e p l ace . T h i s , they s t a t e , is because:

" T h e s m a l l e r c a p i l l a r i e s a r e f i l l e d w i t h g a s o l i n e o n l y When t h e p r e s s u r e d r o p o v e r c o m e s c a p i l l a r y f o r c e s . T h u s u n t i l t h e pressure drop P a s - P wate r i s g r e a t e r t h a n P c a p i l l a r , if 1s i m p o s s i b l e t o move t h e s n a p p e d o f ? g a s o l i n e b u b b l e s t h r o u g h t h e t h r o a t s (of t h e p o r e ) . As a r e s u l t , t h e g a s o l i n e d o e s n o t f i l l t h e n e c k or p o r e t h r o a t and t h u s becomes e x t r e m e l y d i f f i c u l t t o move. The w a t e r which 1 s used t o f l u s h t h e s a n d w i l l t h e r e f o r e t e n d t o f l o w through u n b l o c k e d a n d c o n t i n u o u s w a t e r f i l l e d c h a n n e l s r a t h e r t h a n t h r o u g h t h e g a s o l i n e - blocked channels ."

A c o n t i n u o u s r e l e a s e of c o n t a m i n a n t o v e r l o n g p e r i o d s o f t i m e , b e c a u s e o f t h i s r e t e n t i o n s o l u b i l i t y f a c t o r , would make i t i n c r e a s i n g l y d i f f i c u l t t o d e s c r i b e t h e e x t e n t and t h e c a u s e of t h e contaminat ion a s pu l se s m i g h t soon over lap .

( 9 ) T e m p e r a t u r e and t e m p e r a t u r e g r a d i e n t s : S o i l t e m p e r a t u r e and t h e g r a d i e n t t h a t is e s t a b l i s h e d w i t h i n t h e u n s a t u r a t e d zone c a n have an impact on t h e s t a t u s o f o r g a n i c c o m p o u n d s . I f g r e a t t e m p e r a t u r e g r a d i e n t s e x i s t ( s u r f a c e l a y c r s ) , thermal d i f f u s i o n w i l l r e a d i l y t a k e p l a c e . H i l l e l ( 1 9 7 1 ) i n d i c a t e s t h a t " t h e e f f e c t of warming t h e s o i l i s t o lower t h e s u c t i o n and r a i s e t h e v a p o r p r e s s u r e of s o i l w a t e r . Hence t h e e f f e c t of a thermal g r a d i e n t is t o induce f low and d i s t i l l a t i o n f r o m warmer t o c o o l e r r e g i o n s . l l T h u s , o r g a n i c vapors mig ra t ing from t h e g r o u n d w a t e r t o t h e s o i l s u r f a c e d u r i n g summer m o n t h s and d u r i n g the daytime w i l l t y p i c a l l y have t o move a g a i n s t a t e m p e r a t u r e g r a d i e n t ( 1 . e . , movement by c o n c e n t r a t i o n g r a d i e n t ) when they e n t e r t h e s u r f a c e h o r i z o n . D u r i n g w i n t e r months when t h e s o i l s u r f a c e may a c t u a l l y f r e e z e , vapors would p o s s i b l y be unable t o escape and w o u l d t h e ' r e f o r e c o n c e n t r a t e o r b e d r i v e n t o move l a t e r a l l y . Organ ic compounds t h a t h a v e b o i l i n g p o i n t s l ower t h a n s o i l t e m p e r a t u r e s w i l l of course be h i g h l y v o l a t i l e , s u c h a s t h e g a s e o u s a l k a n e s p r o p a n e and i s o b u t a n e w h i c h b o i l at-42.1°C and - 1 1 . 7 O C ( s e e t a b l e s b y Mackay and S h i u ) .

S o i l t e m p e r a t u r e can a l s o have a l a r g e impact on m i c r o b i a l g r o w t h . C u l l i m o r e ( 1 9 8 2 ) s t a t e s t h a t

70

lower soil temperatures tend to increase bacterial m i g r a t i o n d o w n t h r o u g h t h e s o i l a n d t h a t P s e u d o m o n a d s w i l l a c t i v e l y d e g r a d e s u b s t r a t e s (substances upon which enzymes act') under aerobic conditions if the ground water temperature is above six to eight degrees oentigrade.

(10) M i c r o b i a l i n f l u e n c e : If conditions are optimum (pH, temperature, aeration, nutrients, detention time), t h e presence of microbial populations in the subsurface can lead to a eignificant biodegradation of organic compounds. The extent of biodegradation would be dependent on the number and s p e c i e s Of m i c r o - o r g a n i s m s r e a c h i n g a c r i t i c a l l e v e l in r e l a t i o n s h i p t o t h e d e g r e e o f d i f f i c u l t y i n breaking down t h e compound in question. Table 2.7 gives a summary of t h e g r o w t h d a t a f o r v a r i o u s micro-organisms on varying substrates in a study b y Jamison et al. (1975). Note that no one organism t h r i v e d o n a l l seven substrates and that no one s u b s t r a t e s u p p o r t e d g r o w t h f o r a l l s i x micro-organism classifications.

A significant lag period is often required for the active microbial population to reach the optimum density. Wilson (1981) showed in his studies that a t h r e e - w e e k l a g p e r i o d w a s r e q u i r e d f o r t h e m i c r o b i a l c o m m u n i t y t o s h i f t i n f a v o r o f nitrobenzene degrading organisms. Table 2.8 shows the fate of organic compounds applied t o a sandy soil i n t h e e x p e r i m e n t b y W i l s o n ( 1 9 8 1 ) . T h e results show that the substituted benzenes degraded t o a m u c h l a r g e r e x t e n t t h a n t h e h a l o g e n a t e d hydrocarbons.

T h e r a t e a n d e x t e n t o f d e g r a d a t i o n 1 s o f t e n c o n t r o l l e d b y o x y g e n ( l i m i t i n g f a c t o r ) a s the decomposition is primarily an oxidative process. Figure 2.11 b y Baehr and Corapcioglu ( 1 9 8 4 ) shows t h e i n f l u e n c e o f d i f f e r e n t l e v e l s o f o x y g e n recharge on biodegradation rates. Raymond (1983) estimated that 3 . 5 pounds of oxygen were required to degrade 1.0 pound o f g a s o l i n e h y d r o c a r b o n s . Thus, the rate at which oxygen will diffuse through a s u b s u r f a c e h o r l z o n w i l l c o n t r o l t h e r a t e of replenishment and thus the rate of decomposition.

I f t h e concentration of the contaminant is too low, i t may be below the m i n i m u m l e v e l r e q u i r e d for maintenance of the micro-organism. However, Bouwer ( 1 3 8 4 ) points out that the simultaneous utilization

7 1

+ Hydrocarh uti l izod by micro-orglnir. - Hydrocarbon not utilized micro-orgnir.

72

6.90 0.25 0.62 0.18 0.81 0.25 0.15 1 .oo 0.16 0.93 0.18

1.04

0.18

0.80 0.13 3.40 0.57 0.90 0.20 0.92 0.16

0.05 0.16

54k 9t 61 f10 54kl 4 94k16 49f 9 50* 7

1 0 1 s Uf16 m 1 3 58i14 aak18

2ti 7

54Ql

NDI ND ND ND

9*11 66kl9 ND ND

ND ND

41f 4 t 31k 9 48t 4 h 1 7 61f 9 3Et 5 1%16 6 f l 2 61k 5 2 & 1 21k13

3 3 9

&15 (34s24) 37f 4 &lo 46kll 39k 3

13i 6 8om 60m

(2% 4)t

a 1.7

91 k15 862 1

73

0.0

8 . 0

8 .8 s g? a.7

5 L 0 CI 0 .0

0 a * @ 8 4 8.4 P

E 8 .8

r" 8.8

8 . 1

f . 0

w

I n t o r m o d l a t o L o w

# 0 . 6 1.0 1.6 0 . 0 8 . 8 8;O

Milligrams of 'Oxygen Per Cubic Centimeter of Soil Recharged Per Year

Figure 2 . 1 1. Biodegradat ion ra te bared on oxygen recharge (Baehr and Corapcioglu, 1984).

74

o f s e v e r a l d i f f e r e n t s u b s t r a t e s i s p o s s i b l e ( secondary u t i l i z a t i o n ) . T a b l e 2 . 9 i n d i c a t e s t h a t s e c o n d a r y u t i l i z a t i o n was p o s s i b l e f o r s e v e r a l non- c h l o r i n a t e d a r o m a t i c h y d r o c a r b o n 8 and c h l o r i n a t e d b e n z e n e s i n a n a e r o b i o b i o f i l m . The h a l o g e n a t e d a l i p h a t i o s w e r e n o t t r a n s f o r m e d u n d e r a e r o b i c c o n d i t i o n s b u t were n e a r l y oompletely oxid ized i n a methanogenic b io f i lm (Tab le 2 . 1 0 ) .

W i t h p e t r o l e u m p r o d u c t s , i t i s t h e s t r a i g h t chain p a r a f f i n i o h y d r o c a r b o n s t h a t a r e most s u s c e p t i b l e t o b i o d e g r a d a t i o n ; t h e branched c h a i n p a r a f f i n s and c y c l o p a r a f t i n s fo l low i n terms of 8 u S C e p t i b i l i t y t o b i o d e g r a d a t i o n . The a r o m a t i c hydrocarbons and the non-hydrocarbon compounds of h i g h m o l e c u l a r weight would be decomposed a t t h e s l o w e s t r a t e (American Petroleum I n s t i t u t e , 1 9 7 2 ) . The f o l l o w i n g example shows t h e d i f f e r e n c e s i n t h e o x i d a t i v e products f o r a s t r a i g h t c h a i n e d p a r a f f i n h y d r o c a r b o n ( h e x a d e c a n e ) a n d a c y c l i c h y d r o c a r b o n ( n - Dodecylbenzene)

+ 1 2 . 5 0 2 4 1 2 ( C H 2 0 ) + 4 C02 + 5 H20 b a c t e r i a l c e l l s

c16 H 3 4 hexadecane

The o x i d a t i v e p r o c e s s w i t h t h e c y c l i c hydrocarbon y i e l d e d o x i d a t i v e p r o d u c t s i n a d d i t i o n t o t h e b a c t e r i a l c e l l s and w a t e r . T a b l e 2 . 1 1 g i v e s t h e pe rcen t b i o d e g r a d a t i o n f o r t h e v a r i o u s components o f g a s o . l i n e i n a s t u d y c o n d u c t e d b y J a m i s o n , e t . a l . ( 1 9 7 5 ) . Note t h a t benzene, t o l u e n e , and x y l e n e were 1 0 0 p e r c e n t d e g r a d e d . T h u s , t h e s e compounds may n o t be good t r a c e r s t o m o n i t o r i n t h e v a p o r phase under c e r t a i n c o n d i t i o n s .

I n t e rms of o r g a n i c vapor mon i to r ing , t h e microbia l i n f l u e n c e may l e a d t o s i t u a t i o n s w h e r e t h e c o n t a m i n a n t i s known t o be i n t h e ground wa te r , b u t i t i s degraded i n t h e a e r o b i c u n s a t u r a t e d zone a t a r a t e f a s t e r t h a n i t w i l l d i f f u s e t o t h e s u r f a c e . An a d d i t i o n a l problem may o c c u r i f g r o u n d w a t e r s a m p l e s a r e t a k e n d i r e c t l y f r o m t h e a e r o b i c zone t h a t e x i s t s a r o u n d w e l l s ; i n s u c h c a s e s t h e m i c r o b i a l p o p u l a t i o n s may be a b l e t o d e g r a d e t h e o rgan ic con taminan t d i s s o l v e d i n t h e ground water ( C u l l i m o r e , 1 9 8 2 ) a n d t h u s g ive a f a l s e conclusion a s t o t h e e x t e n t o f t h e p l u m e . F i n a l l y , t h e

75

TABLE 2.9, AVERAGE UTILIZATION OF SUBSTRATES IN AEROBIC A C m - A F W A C W T f O N

Subs t rat e Influent cona. (I Percentl U 6 / L removal

Primary acetate

Secondary Chlorinated aromatics

chlorobenzene 1,2-dichlorobenzene 1.3-dichlorobenzene 1 ,O-dichlorobenzene 1,2,4-trichlorobenzene

Nonchlorinated aromatics ethylbenzene styrene naphtha1 ene

Halogenated aliphatics chloroform 1.1.1-trlchloroethane tetrachloroethylene

9 0 5 ~ 2 05 9.6f2.4 9.8k1.8

10.8f1.8 9.2f1.6

9 . h 2 7.6f1.5 13.8f3.5

28.5f4.2

9.8k3.7 15 9f3. 3

99.7i0.3

91 f3 97 fl 71 *8 99*1 95f3

99*1

99fl >99

2f20 5227 2f40

'One standard deviation Q f the mean values is given (Bouwer, 1984).

76

T A B L E 2.10. AVERAGE UTILIZATION OF SUBSTRATES IN HETHANOGENIC A C E T A T E - GROWN C W N A F T E R A C C W O W

Substrate Influent conc. * Percent. W L removal

Primary acetate

Secondary Chlorinated aromatics

chl or oben zene 1,2-dlchlorobenzene 1,3-dichlorobenzene 1 4-dichlorobenzene 1,2,4-tr1ch1orobenzene

Nonchlorlnated aromatics ethylbenzene styrene naphthalene

Halogenated aliphatics chloroform carbon tetrachloride 1,2-dlchloroethane 1 1,l -trichloroethane 1,1,2,2-tetrachloroethane tetrachloroethylene bromodlchloromethane dibromochloromethane bromoform lS2-dlbromoethane

100. mglt

22. f5 15*f3 10.f3 10.f3 11.f3

12.0f4 7.9f2

28.8f7

28. f7

22.f3 18.f2 27. fl 15.k4 26. f 3 25. f2 26. f2 27. f2

17.f1

93f2

Oil 5

Of1 5 Of1 5 Oil 5

Of1 5

7t26 8926

-2f29

99f1

- 1 i20 97f3 97f3 76210

>99

>99 >99 >99 >99

*One standard deviation of the mean values 1 s given (Bouwer, 1984).

77

n-8utane dentom n - b a n e n-lbptane n-0ctam O b f ino-Cq Olefino-C5 Olefino-C6 Ioobutoe Cyclopentae C y C l ~ X ~ Uo t hy Icy clopen t am mthy Icy c 1 ohex am 2Uathylkrtene 2Uethy lpent am 34ethy lpentene 2Uethylhsxene 3 4 0 thy lhexam 2UOthylheptM 54othylheptano 4-Methylheptam 2,20i.ethylbut.lle 2,30)Lethylkrtam 2,201.e thy lpentum 2, Mime thy lpentom 5, )-Dime thy l p e n t m 2 ,Mi#thylpentona 2, 5Diwthy lhexmm 2,4Diwthylhexas 2, 30iwthylhexano 3,4-Diaethylhexlne 2,24icrethylhmas 2,20imethylheptae 1,l-Diaethylcyclopentum 1,2 and 1 , 3 D ~ t h y l c y c l ~ o n t a n e 1,s and 1,dDimethylcycl~xona 1,2-Dlwthylcyclohsx.ne 2,2,STrinethylbutone 2,2,4-Trimothyl$entone 2,2,3- Trim thy lpentae 2,s (4- Trim thylpontmm 2,3,S-Trhthylpontae 2,2,5-Trirsthylpontone 1,2,4- Trim thylcyclopentane E thy lpentane E thylcyclopentam E thylcyclohexene Bsnzene E thylbentene T O ~ M 0-X y lene n-Xylem p-Xylem Heavy endo

Om63 Om 55 1mM

Om 54 Om11 1.04 Om 51 Om11 Om 17 O m 12 0.41 0.05 5.29 1.72 1.50 0.74 0.66 0.35 O m 46 0.15 Om 28 Om86 Om42 0.55 0.04 0.48 0.53 0.46 0.54 0.09 0.05 0.09 0.12 0.12 0.02 0.16 0.03 3.47 Om17 1.89 1.97 0.51 0.05 0.08 0.11 0.06 Om 41 1.36 2.22 1.62 3.28 lmO3 8.97

0.57

0. 17 Om 25 O m 78 O m 20 0.10 Om18

Om 16 Om 13 0.05 0.06 0.10 0.04 1.34 0.85 Om 56 0.53 0.37 0.15 0.31 0.08 0.16 Om 37 Om19 0.51 0.02 0.24 0.33 0.22 0.29 Om08 0.04 0.06 0.04 0.10 Troce 0.05 Om02 2.40 Om 10 1.22 1.55 0.35 Trace 0.05 0.04 0.06 0.45 1.61 2.67 2.18 4.29 1.51

11.80

0. m

0.17 Om06 O m 15 Tree T t m Om12 0.14 Om07 0.12 0.04 Trace 0.14 Trace 1. S l Om75 0.47 0.56 0.48 Trace 0.10 Trace 0.09 O m 56 Om15 0.25 T r r e Om 21 Om22 0.20 0.19 Trace Trace Trm Trace Trmx Trace Trce Trace 1.9S Trace

O m 97 1.02 1.02 Troce 0.04 Trace Trace

0 0 0 0 0 0

1.13

0 70 46 49 54 0

16 18 0 0

45 10 75 0 6 7

25 0

58 45 48 25 0 9

11 45 0

20 0

19 04 75 62 25 70 0

26 62 13 54 13 16 25 0 0

51 95

100 100 100 100 loo 100 87

(Jmion, rt o l . , 1975)

78

p r o d u c t s t h a t r e s u l t from t h e o x i d a t i o n process can s o m e t i m e s be more s o l u b l e a n d t o x i c t h a n t h e o r i g i n a l compound.

H Y D R O G E O L O G I C P R O P E R T I E S

( 1 ) Ground-water f l o w ( d i r e c t i o n , v e l o c i t y , g r a d i e n t ) : Once a oontaminant r e a c h e s t h e ground w a t e r , i f i t i s s o l u b l e , i t s f a t e i n t e r m s of d i s p e r s a l w i l l t h e n b e c o n t r o l l e d t o a g r e a t e x t e n t b y t h e d i r e c t i o n and v e l o c i t y of t h e ground-water f l o w . If t h e c o n c e n t r a t i o n of t h e c o n t a m i n a n t i s low and i f t h e s p i l l i s s m a l l , t h e c o n t a m i n a n t is q u i o k l y d i l u t e d by t h e p r o c e s s of m i x i n g and d i f f u s i o n s o t h a t a plume is d i f f i c u l t t o d e l i n e a t e . However, " f o r moat ground water f low r e g i m e s , mass t r a n s f e r is p r e d o m i n a n t l y d i f f u s i o n c o n t r o l l e d and t h e r e f o r e i n d e p e n d e n t of f l o w r a t e s . T h i s is d u e t o t h e g e n e r a l l y low f low v e l o c i t i e s i n n a t u r a l ground w a t e r f l o w f i e l d s " ( P f a n n k u c h , 1 9 8 4 ) . T h u s , knowledge of t h e d i r e c t i o n of flow would most o f t e n b e t h e d e c i d i n g f a c t o r i n t h e i n i t i a l d e c i s i o n t o l o c a t e g a s p r o b e s and m o n i t o r i n g w e l l s . Andrea ( 1 9 8 4 ) p o i n t s o u t t h a t w e l l l o c a t i o n s h a v e s o m e t i m e s b e e n i n a c c u r a t e l y l o c a t e d when t h e d i r e c t i o n of g r o u n d water f low was p r e d i c t e d o n t h e b a s i s o f t h e l o c a t i o n of hydro log ic boundaries and s i t e topography.

Fo r c o n t a m i n a n t s t h a t r e a c h t h e ground wa te r b u t a r e i m m i s c i b l e i n w a t e r ( s u c h a s many p e t r o l e u m p r o d u c t s ) , t h e c o n t a m i n a n t w i l l f o l l o w t h e w a t e r t a b l e g r a d i e n t . I f a s t e e p g r a d i e n t e x i s t s , a g r e a t e r i n t e r f a c e w i l l b e d e v e l o p e d , which w i l l l e a d t o a g r e a t e r o p p o r t u n i t y f o r t h e d i s p e r s a l o f s l o w l y d i s s o l v i n g c o n s t i t u e n t s i n t o t h e ground water .

Water T a b l e O s c i l l a t i o n s : Changes i n t h e depth of t h e water t a b l e can have a l a r g e impact on v e r t i c a l t r a n s p o r t of contaminants . McKee ( 1 9 7 2 ) observed a c o n s i d e r a b l e r i s e i n g a s o l i n e t h a t had f i l t e r e d d o w n t o t h e w a t e r t a b l e a s t h e w a t e r t a b l e rose o v e r a t h r e e y e a r p e r i o d . O s c l l l a t i o n s i n t h e w a t e r t a b l e c o u l d a l l o w hydrocarbons t h a t f l o a t t o move o v e r o r under s u b s u r f a c e o b s t r u c t i o n s t h a t m i g h t o t h e r w i s e p r e v e n t t h e i r f u r t h e r m i g r a t i o n . I n an u n d e r g r o u n d g a s o l i n e t a n k l e a k s t u d y i n Montana, Reichmdth ( 1 9 8 4 ) noted t h a t when t h e water t a b l e was lower d u r i n g t h e w i n t e r , a g r a v e l l a y e r

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was e x p o s e d t h a t pOS8eSSed c o n s i d e r a b l e void space. D u r i n g t h e t i m e of g r a v e l e x p o s u r e , R e i o h s u t h s u g g e s t e d t h a t g a s o l i n e vapors were t r a n s p o r t e d b y h o r i z o n t a l f low. That c o r r e l a t i o n s of s o i l o r g a n i c v a p o r s w i t h g round-wa te r c o n c e n t r a t i o n s c o u l d be i m p a i r e d b y a n o s c i l l a t i n g w a t e r t a b l e is a p o s s i b i l i t y t h a t grows o u t of Marln and Thompson's ( 1 9 8 4 ) s t a t e m e n t t h a t c h a n g e s i n t h e w a t e r t a b l e l e v e l c o n t r i b u t e t o a v e r t i c a l g r a d i e n t t h a t is not i n d i c a t i v e of s t e a d y s t a t e .

( 3 ) L i t h o l o g y of t h e a q u i f e r : Once a c o n t a m i n a n t e n t e r s t h e c o n f i n e s of a n a q u i f e r , i t s f u r t h e r m i g r a t i o n w i l l be d i c t a t e d t o a g r e a t e x t e n t b y t h e p h y s i c a l p r o p e r t i e s of t h e s e d i m e n t s t h a t make u p t h e a q u i f e r ( F i g u r e 2 . 1 2 ) ( A m e r i c a n P e t r o l e u m I n s t i t u t e , 1 9 7 2 ) . B a r r i e r s t o f l o w ( r e t a r d a t i o n of f l o w ) c a n o c c u r i f l a t e r a l c h a n g e s t a k e p l a c e i n e i t h e r t e x t u r e ( u n c o n s o l i d a t e d s e d i m e n t s ) or rock f o r m a t i o n s ( c o n s o l i d a t e d s e d i m e n t s ) . I n s e d i m e n t a r y r o c k s , O s g o o d ( 1 9 7 4 ) s t a t e s t h a t t h e o r i e n t a t i o n o f t h e r o c k a n d t h e p r i m a r y d e p o s i t i o n a l c h a r a c t e r i s t i c s of t h e u n i t a r e a s i m p o r t a n t a s permeabi l i ty and p o r o s i t y i n d i c t a t i n g f l o w . T h e d e p o s i t i o n a l c h a r a c t e r i s t i c s would i n c l u d e s u c h f e a t u r e s a s c e m e n t a t i o n and packing. I n more s t e e p l y d i p p i n g rock u n i t s , O s g O O d ( 1 9 7 4 ) s u g g e s t s t h a t t h e dominant f l o w d i r e c t i o n of t h e h y d r o c a r b o n s would b e p a r a l l e l t o t h e s t r i k e , d o w n s l o p e , a n d t h a t d e v i a t i o n s from t h e s t r i k e d i r e c t i o n wou ld be c o n t r o l l e d b y j o i n t i n g and f r a c t u r i n g . Nan-uniform c h a r a c t e r i s t i c s of t h e a q u i f e r s e d i m e n t s w o u l d , o f c o u r s e , c a u s e n o n - u n i f o r m advancement o f t h e c o n t a m i n a n t p l u m e r e l a t i v e t o t h e ground s u r f a c e a s w a t e r f l o w w o u l d be c h a n n e l e d through zones of lower r e s i s t a n c e . If t h e s e s e d i m e n t s a l s o compr ised a l a r g e p o r t i o n of t h e v a d o s e z o n e , t h e n o r g a n i c v a p o r s w o u l d a l s o fo l low t h e pa th of l e a s t r e s i s t a n c e and would move t h r o u g h t h e f i s s u r e d and f r a c t u r e d rock according t o t h e p a t h s t h a t were d i c t a t e d . L a t e r a l f l o w of v a p o r s c o u l d be t remendous under s u c h c o n d i t i o n s and could t h u s negate a n y hopes f o r c o r r e l a t i n g t h e v a p o r c o n c e n t r a t i o n s w i t h t h e g r o u n d - w a t e r c o n c e n t r a t i o n s . S c h w i l l e ( 1 9 8 4 ) i n d i c a t e s t h a t w i t h f i s s u r e d r o c k s , t h e g a s t r a c e r method would only be u s e f u l i f t h e f i s s u r e d rock were c o v e r e d b y a l a y e r of porous loose rock.

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00 c

Figure 2.12. Hypothetical groundrater syetem (American Petroleum fnmtitutc, 1972).

C H A R A C T E R I S T I C S OF T H E SPILL

G r e a t e r k n o w l e d g e o f t h e h i s t o r y o f t h e s p i l l o a n o f t e n provide t h e i n v e s t i g a t o r w i t h g r e a t e r i n s i g h t a s t o t h e p r o p e r l o o a t i o n f o r s o i l g a s p r o b e s ( f i r s t a p p r o x i m a t i o n ) . Suah o h a r a o t e r i s t i o s a s t h e t o t a l Volume l o s t , t h e l e n g t h of t i m e t h e p r o d u c t was s p i l l e d ( c o n t i n u o u s v s . one-time s p i l l ) , a r e a of t h e s p i l l , and t h e age of t h e s p i l l , oan be v e r y h e l p f u l i n b e t t e r u n d e r s t a n d i n g t h e p o s s i b l e e x t e n t of u n s a t u r a t e d and s a t u r a t e d zone oontaminat ion .

MISCELLANEOUS

( 1 ) R a i n f a l l : D e p e n d i n g on t h e f r e q u e n c y a n d t h e a m o u n t o f r a i n f a l l t h a t o c c u r s , o r g a n i c c o n t a m i n a n t s i n t h e u n s a t u r a t e d z o n e w i l l b e s u s c e p t i b l e t o l e a c h i n g . I n a r e a s o f h i g h r a i n f a l l , o s c i l l a t i o n s i n t h e ground w a t e r may occur which woirld b r i n g c o n t a m i n a n t s c l o s e r t o t h e s o i l s u r f a c e . O b v i o u s l y , any i n p u t of water w i l l l e a d t o d e c r e a s e d a i r - f i l l e d p o r o s i t i e s a n d t o r e d u c e d v a p o r movement. V e r t i c a l c o n c e n t r a t i o n g r a d i e n t s w i l l be a l t e r e d a s v a p o r s r e a c h i n g t h e r a i n f a l l s a t u r a t e d zone w i l l e i t h e r c o n c e n t r a t e , move l a t e r a l l y , or w i l l b e r e s o l u b i l i z e d t o some e x t e n t . Vapor m i g r a t i o n ( u p w a r d , l a t e r a l ) and r e s o l u b i l i z a t i o n can l e a d t o a w i d e r s p r e a d of t h e c o n t a m i n a t i o n a r e a . I f t h e a r e a i n q u e s t i o n i s c o v e r e d w i t h v e g e t a t i o n , t h e n t h e a m o u n t o f l e a c h i n g w i l l be d e p e n d e n t n o t o n l y on t h e amount of r a i n f a l l b u t a l s o on t h e e v a p o t r a n s p i r a t i o n , t h e amount o f w a t e r i n s t o r a g e , and t h e e f f e c t i v e r o o t i n g d e p t h . R a i n f a l l w l l l a l s o d e l a y f i e l d m e a s u r e m e n t s and make i t e x t r e m e l y d i f f i c u l t t o compare s o i l - g a s c o n c e n t r a t i n g b e f o r e and a f t e r a r a i n f a l l e v e n t .

( 2 ) Background wa te r q u a l i t y : The m o r e c o n t a m i n a t e d t h e g r o u n d w a t e r , t h e m o r e d i f f i o u l t i t i s t o d e l i n e a t e t h e s p a t i a l e x t e n t of t h e p a r t i c u l a r c o n t a m i n a n t i n q u e s t i o n . I n some c a s e s , s e v e r a l plumes may e x i s t , t h a t a r e p a r t i a l l y or completely o v e r - l a p p i n g and t h a t r e p r e s e n t d i f f e r e n t s p i l l s o v e r a p e r i o d o f t i m e . G r e a t e r i n s t r u m e n t s e n s i t i v i t y would be r e q u i r e d i n t h o s e c a s e s where t h e b a c k g r o u n d c o n t a i n e d n u m e r o u s o r g a n i c contaminants a t c o n c e n t r a t i o n s t h a t were o r d e r s of m a g n i t u d e h i g h e r t h a n t h e c o n t a m i n a n t b e i n g n i o n i i o r e d ( s e e s e c t i o n o n a n a l y t i c a l methodologies ) .

82

( 3 ) B a r o m e t r i c p r e s s u r e a n d w i n d : E a r l y w o r k b y Bucklngham ( 1 9 0 4 ) showed t h a t changes i n b a r o m e t r i c p r e s s u r e had l i t t l e i n f l u e n c e on s o i l gas t r a n s p o r t i n most c a s e s , w i t h i t s g r e a t e s t i n f l u e n c e on t h e gases i n t h e s o i l pores a t or near t h e s o i l s u r f a c e . I n a s t u d y conducted by Reichmuth ( 1 9 8 4 1 , g a s o l i n e vapor8 d e t e c t e d i n a basement down g r a d i e n t from an unde rg round s t o r a g e t a n k l e a k , w o r s e n e d d u r i n g p e r i o d s of h i g h w i n d and low b a r o m e t r i c p re s su re . He concluded t h a t such c o n d i t i o n s were o p t i m a l f o r maximum e a r t h o u t g a s s i n g . O t h e r f a c t o r s t h a t would m a x i m i z e t h i s g a s e x c h a n g e would b e t h e a b s e n c e of v e g e t a t i o n ( r e s i s t a n c e t o w i n d f low) and t h e p r e s e n c e of c o a r s e p e r m e a b l e s o i l . However, o n e w o u l d h a v e t o c o n c l u d e t h a t i n a l m o s t a l l c a s e s , i f s o i l gas probe8 were l o c a t e d s e v e r a l f e e t b e l o w t h e s o i l s u r f a c e , t h e v e r t i c a l v a p o r c o n c e n t r a t i o n s measured would n o t be i n f l u e n c e d t o any e x t e n t by t h i s s u r f a c e phenomena.

( 4 ) P r o x i m i t y t o r i v e r s , l a k e s , and p u m p i n g wel l s : The p r e s e n c e of r i v e r s and l a k e s w o u l d mean t h a t c o n t a m i n a n t s r e a c h i n g t h e a q u i f e r w o u l d be i n t e r c e p t e d and d i s p e r s e d even f u r t h e r ( s e e F i g u r e 2 . 1 3 ) . Such i n t e r c e p t i o n of contaminant flow would mean an a l t e r a t i o n i n t h e s u b s u r f a c e b o u n d a r i e s o f t h e c o n t a m i n a n t plume. Ano the r c o n s i d e r a t i o n is t h e p r o x i m i t y o f s o i l - g a s p r o b e s and m o n i t o r i n g w e l l s t o p u m p i n g w e l l s a s s h o w n i n F i g u r e 2 . 1 3 (American Petroleum I n s t i t u t e , 1 9 7 2 ) . A l t e r i n g t h e g round-wa te r t a b l e b y c r e a t i n g a cone of depress ion would cause immiscible o r g a n i c compounds ( f l o a t e r s ) t o move l a t e r a l l y and d e e p e r r e l a t i v e t o t he s o i l s u r f a c e . T h i s c o n d i t i o n w o u l d n o t o n l y a l t e r t h e movement of a p l u m e b u t a l s o t h e d i s t a n c e o v e r which a v e r t i c a l s o i l g a s g r a d i e n t w o u l d have t o be e s t a b l i s h e d .

83

Figure 2.13. Diagram rhowing how o i l on a water table can be trapped i n a cone of d a p r e o o i o n c r e a t e d by drw-doun of I pumping vell (American Petroleum Ins t i tu te , 1972).

84

R E F E R E N C E S

1 . American P e t r o l e u m I n s t i t u t e . The m i g r a t i o n of petroleum p r o d u c t s i n s o i l a n d g r o u n d w a t e r . P u b . No. 4 1 4 9 . Washington, D . C . , 1 9 7 2 .

2. Anderson , D . C . and S. G . Jones. F a t e of o r g a n i c l i q u i d s s p i l l e d on s o i l . N a t i o n a l C o n f e r e n c e on h a z a r d o u s w a s t e and envi ronmenta l ene rgenc le s . Houston, Texas, 1 9 8 4 .

3. A n d r e s , K . G . a n d R . C a n a c e . Use o f t h e e l e c t r i c a l r e s i s t i v i t y t e c h n i q u e t o d e l i n e a t e a h y d r o c a r b o n s p i l l i n t h e c o a s t a l p l a i n d e p o s i t s of New J e r s e y . I n Petroleum H y d r o c a r b o n s a n d O r g a n i c C h e m i c a l s i n Ground W a t e r . Nat iona l Water Well A S S O C . , 1984.

4. B a e h r , A . and M . Y . C o r a p c i o g l u . A p r e d i c t i v e model f o r p o l l u t i o n from g a s o l i n e i n s o i l s and g round w a t e r . I n P e t r o l e u m H y d r o c a r b o n s and O r g a n i c C h e m i c a l s i n Ground Water. Nat iona l Water Well Assoc., 1 9 8 4 .

5 . B o u w e r , E . J . B i o t r a n s f o r m a t i o n o f o r g a n i c m i c r o - p o l l u t a n t s i n t h e s u b s u r f a c e . I n P e t r o l e u m Hydrocarbons and O r g a n i c Chemicals i n Ground Water, Nat iona l Water Well Assoc., 1 9 8 4 .

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McKee, J . E., F. B. Laverty and R . M. H e r t e l . Gaso l ine i n Ground w a t e r . J o u r n a l WPCF, 1 9 7 2 . V o l . 4 4 , No. 2 . p p 293-302 .

New Y o r k S t a t e D e p t . o f E n v i r o n m e n t a l C o n s e r v a t i o n . Technology f o r t h e s t o r a g e of h a z a r d o u s l i q u i d s , a s t a t e of the a r t review. A l b a n y , New Y o r k , 1983 .

N i e l s o n , K . K. a n d V . C . Rogers. A mathematical model f o r radon d i f f u s i o n i n e a r t h e n m a t e r i a l s . U.S. N u c l e a r P e g u l a t o r y C o m m i s s i o n , 1 9 8 2 . N U R E G / C R - 2 7 6 5 .

O a g o o d , J . 0. Hydrocarbon d i s p e r s i o n i n g round w a t e r : s i g n i f i ~ a n c e and c h a r a c t e r i s t i c s . G r o u n d W a t e r , 1 9 7 4 . V o l . 1 2 , N o . 6 . p p 4 2 7 - 4 3 8 .

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2 2 . P f a n n k u c h , H . D e t e r m i n a t i o n o f t h e con taminan t s o u r c e s t r e n g t h from mass exchange p r o c e s s e s a t t h e p e t r o l e u m - g r o u n d w a t e r i n t e r f a c e i n s h a l l o w a q u i f e r s y s t e m s . I n P e t r o l e u m Hydroca rbons and O r g a n i c Chemica ls i n G r o u n d Water, Nat iona l Water Well A s s o a . , 1 9 8 4 .

2 3 . Raymond, R . L . P e r s o n a l communica t ion a s quo ted for A . Baehr i n A p r e d i c t i v e model f o r p o l l u t i o n from g a s o l i n e i n s o i l s and g round w a t e r , 1 9 8 4 . I n Petroleum Hydrocarbons and O r g a n i c C h e m i c a l s i n Ground Water . N a t i o n a l W a t e r Well A S S O C . , 1 9 8 3 .

24. R e i c h m u t h , D . R . S u b s u r f a c e g a s o l i n e m i g r a t i o n p e r p e n d i c u l a r t o g round-wa te r g r a d i e n t s - a c a s e s t u d y . I n P e t r o l e u m Hydroca rbons and Organic Chemicals i n G r o u n d Water, Nat iona l Water Well A S S O C . , 1 9 8 4 .

2 5 . R e i d , G . W . , G . Thompson and C . Oberho l t ze r . S o i l vapor moni tor ing a s a c o s t e f f e c t i v e method o f a s s e s s i n g g r o u n d wat e r d e g r a d a t 1 on from vo l a t 11 e c h l o r i n a t e d hydrocarbons i n a n a l l u v i a l e n v i r o n m e n t . S e c o n d A n n u a l Canad ian /Amer ican C o n f e r e n c e on Hydrogeology - Hazardous Waste i n Ground Water: A S o l u b l e Dilemma. N a t i o n a l Water Well A S S O C . , 1 9 8 5 .

2 6 . S w a l l o w , J . A . and P . M. Oschwend. V o l a t i l i z a t i o n of o r g a n i c compounds from unconfined a q u i f e r s . P r o c . of t h e 3 r d N a t i o n a l S y m p o s i u m o n A q u i f e r Res to ra t ion and Ground Water m o n i t o r i n g . Nat ional Water Well A S S O C . , 1 9 8 3 .

27 . S c h w i l l e , F. G r o u n d - w a t e r p o l l u t i o n b y m i n e r a l o i l p roduc t s . G r o u n d Water P o l l u t i o n Symposium, 1 9 7 1 , A I S H P u b l . No. 1 0 3 , 1975 .

2 8 . S c h w i l l e , F. M i g r a t i o n of o r g a n i c f l u i d s immiscible w i t h water i n t h e u n s a t u r a t e d zone . F r o m B. Yaron, G . Dagan and S. Goldshimd ( e d s . ) P o l l u t a n t s i n Porous Media: The U n s a t u r a t e d Zone between S o i l S u r f a c e and G r o u n d w a t e r . Spr inger -Ver lag , 1 9 8 4 .

2 9 . S c h w i l l e , F . Pe t ro l eum c o n t a m i n a t i o n of the s u b s o i l - a h y d r o l o g i c a l p r o b l e m . I n P . H e p p l e ( e d . ) T h e j o i n t p r o b l e m s o f t h e o i l a n d w a t e r i n d u s t r i e s . P r o c . Sympos ium, T h e I n s t i t u t e o f P e t r o l e u m , B r i g h t o n , January 1 8 - 2 0 , 1 9 6 7 , p p 2 3 - 5 4 .

3 0 . W i l l i a m s , D . E. and D . G . Wilder . Gasoline p o l l u t i o n o f a g r o u n d - w a t e r r e s e r v o i r - a c a s e h i s t o r y , 1 9 7 1 . G r o u n d w a t e r , V o l . 9 , No. 6 . p p 5 0 - 5 4 .

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. 3 1 . W i l s o n , J . T . , C . G . E n f i e l d , W . J . Dunlap, R. L . Cosby, D . A . F o s t e r and L . 8 . B a s k i n . T r a n s p o r t and f a t e o f s e l e c t e d o r g a n i c p o l l u t a n t s i n a sandy s o i l . J . Environ. Q u a l . , 1981 . Vol . 10, No. 4, pp 501-506.

88

C H A P T E R 3

T R A N S P O R T A N D R E T E N T I O N OF D I S S O L V E D A N D I M M I S C I B L E O R G A N I C C H E M I C A L S I N S O I L A N D G R O U N D - W A T E R


A l a r g e v a r i e t y a n d q u a n t i t y o f d i f f e r e n t o r g a n i c c h e m i c a l s , some of w h i c h pose a h e a l t h h a z a r d , a r e a c c i d e n t a l l y or d e l i b e r a t e l y a p p l i e d t o s o i l where t h e y may m i g r a t e t o g round-wa te r . For example , many d i f f e r e n t p e s t i c i d e s , m o s t l y a p p l i e d d u r i n g a g r i c u l t u r a l o p e r a t i o n s , h a v e a p p e a r e d i n t h e g round-wa te r s i n a number of d i f f e r e n t s t a t e s ( P r a t t , e t a l . , 1 9 8 5 ) . I n a d d i t i o n , l a r g e n u m b e r s o f d i s s o l v e d o r g a n i c compounds a r e a c c i d e n t a l l y r e l e a s e d i n t o s o i l f r o m l e a k i n g w a s t e d i s p o s a l s i t e s or s t o r a g e t a n k s . These compounds m i g r a t e downward w i t h f l o w i n g w a t e r a n d c a n e n t e r a n d c o n t a m i n a t e u n d e r g r o u n d w a t e r s u p p l i e s . A s e c o n d l a r g e c l a s s of o r g a n i c l i q u i d s found i n s o i l a r e pe t ro leum p r o d u c t s which a r e r e l e a s e d t o s o i l b y a c c i d e n t a l l e a k s or l a r g e s p i l l s and which may be l a r g e l y i m m i s c i b l e i n w a t e r . T h e s e s p i l l s may o c c u r f r o m u n d e r g r o u n d s t o r a g e t a n k s which have e i t h e r c o r r o d e d , r u p t u r e d , or h a v e f a u l t y c o n n e c t i o n s . S i m i l a r l y , p e t r o l e u m p r o d u c t s m i g h t e n t e r t h e s o i l when a t a n k e r t r u c k r e l e a s e s i t s c o n t e n t s i n a highway a c c i d e n t .

I n a c o m p l e x s o i l , a i r , w a t e r a n d h y d r o c a r b o n s y s t e m , an o r g a n i c c h e m i c a l compound, d e p e n d i n g on i t s p r o p e r t i e s and on t h e s o i l c o n d i t i o n s , may be f o u n d i n a n u m b e r of d i f f e r e n t phases : a s a n i m m i s c i b l e l i q u i d , a s a d i s s o l v e d component o f t h e s o i l - w a t e r s o l u t i o n , o r a s a g a s . I n a d d i t i o n , t h e i m m i s c i b l e l i q u i d may b e f l o w i n g o r i m m o b i l i z e d , a n d t h e d i s s o l v e d c o m p o n e n t s may be moving f r e e l y w i t h i n s o i l s o l u t i o n or may be a b s o r b e d t o s o i l m i n e r a l s u r f a c e s or t o S t a t i o n a r y o r g a n i c m a t t e r i n t h e s o i l . T h i s c h a p t e r w i l l p r o v i d e an overv iew of t h e p r o c e s s e s i m p o r t a n t i n t h e t r a n s p o r t and f a t e o f o r g a n i c c o n t a r n i n a n t s i n s o i l , f o c u s i n g s e p a r a t e l y on ( 1 ) p e t r o l e u m mixtures which a r e t r a n s p o r t e d or r e t a i n e d i n t h e s o i l a s a f l u i d l a r g e l y lmmisc ib l e i n w a t e r and on ( 2 ) s o l u b l e o r g a n i c c o n t a m i n a n t s w h i c h d i s s o l v e r e a d i l y i n w a t e r a n d p r e d o m i n a n t l y move b y c o n v e c t i o n w i t h i n f l o w i n g s o l u t i o n .

Movement of L i q u i d O i l Through S o i l

When a l a r g e q u a n t i t y o f s p i l l e d o i l i s i n t r o d u c e d a t t h e s o i l s u r f a c e , i t w i l l i n f i l t r a t e u n d e r t h e i n f l u e n c e o f g r a v i t y p r i n c i p a l l y a s a n i m m i 8 C i b l e f l u i d e e p a r a t e f r o m w a t e r . The e x a c t p a t h and r a t e of t h e i n f i l t r a t i o n a s wel l a8 t h e e x t e n t o f l a t e r a l m o v e m e n t w i l l d e p e n d i n a c o m p l e x m a n n e r on t h e p e r m e a b i l i t y of t h e s o i l t o wa te r and o i l , on t h e w a t e r a n d o i l c o n t e n t , a n d o n t h e p r e s e n c e o f s t r u c t u r a l v o i d s w h i c h c o n t r i b u t e s u b s t a n t i a l l y t o s p r e a d i n g o f t h e a p i l l . A l t h o u g h a t t e m p t s a r e b e i n g made t o f o r m u l a t e t h e o i l a n d w a t e r t r a n s p o r t problem m a t h e m a t i c a l l y (Baehr and C o r a p c i o g l u , 1 9 8 4 1 , q u a n t i t a t i v e v a l u e s f o r t h e e x a c t wa te r and o i l f l o w p a t h s and f l o w r a t e s i n n a t u r a l s o i l s a r e f o r p r a c t i c a l p u r p o s e s u n p r e d i c t a b l e . N o n e t h e l e s s , e x p e r i m e n t a l o b s e r v a t i o n s , s m a l l c o l u m n e x p e r i m e n t s , a n d m o d e l c a l c u l a t i o n s w h i c h u s e s i m p l i f y i n g a s s u m p t i o n s have produced a g e n e r a l p i c t u r e of t h e oil e n t r y and t r a n s p o r t p r o c e s s w h i c h d e s c r i b e s t h e m a i n f e a t u r e s of a s p i l l e v e n t .

Q a a l i t a t i v e l y , a s o i l e n t e r s t h e v a d o s e zone i t d i s p l a c e s a i r b u t n o t w a t e r f r o m t h e p o r e s p a c e s , a n d i n f l l t r a t e s v e r t i c a l l y u n d e r t h e i n f l u e n c e of g r a v i t y a t a r a t e l i m i t e d b y t h e p e r m e a b i l i t y o f t h e o i l - f i l l e d p o r e s p a c e . A s t h e o i l p a s s e s t h r o u g h a g i v e n r e g i o n o f t h e po rous medium, i t l e a v e s b e h i n d a r e s i d u a l a n d l a r g e l y i m m o b i l i z e d c o n c e n t r a t i o n o f i n s o l u b l e o i l w h i c h v a r i e s b e t w e e n a p p r o x i m a t e l y 5 and 20 p e r c e n t of t h e v o i d s p a c e depending on t h e t y p e o f o i l and t h e c h a r a c t e r i s t i c s o f t h e soil ( D i e t z , 1 9 7 0 ) . T h u s , i f t h e t o t a l q u a n t i t y of o i l s p i l l e d i n t o t h e s o i l i s l e s s t h a n t h e amount r e q u i r e d t o f i l l t h e r e s i d u a l p o r e s p a c e i n t h e vadose z o n e , t h e n t h e body o f t h e s p i l l w i l l n o t r e a c h t h e g r o u n d - w a t e r and w i l l r e m a i n i n a p e n d u l a r v o l u m e p o i s e d above t h e w a t e r t a b l e ( s e e F i g u r e 3 . 1 A ) . I f , h o w e v e r , t h e r e i s a n e x c e s a o f i n s o l u b l e o i l , t h e n p a r t o f t h e f l o w i n g o i l w i l l r e a c h t h e g round-ua te r where m o a t of t h e r ema in ing o i l w i l l s p r e a d i n t o a t h i n f i l m o c c u p y i n g t h e v o l u m e j u s t o v e r t h e s a t u r a t e d - u n s a t u r a t e d zone i n t e r f a c e ( s e e F i g u r e 3.1B).

S t a b i l i z e d O i l S p i l l P r o f i l e

A f t e r t h e t r a n s i e n t i n f i l t r a t i o n p h a s e has c o n c l u d e d , t h e i n s o i c l b l e o i l body w i l l be s p r e a d o v e r a r e l a t i v e l y f i x e d vo lume o f s o i l w h i c h may or may n o t e x t e n d t o g r o u n d - w a t e r . T h o s e c o m p o n e n t s o f t h e o i l body w h i c h a r e s o l u b l e w i l l c o n t i n u a l l y d i s s o l v e i n t o t h e s o i l s o l u t i o n , and s u b s e q u e n t l y may m i g r a t e w i t h f l o w i n g w a t e r . I n a d d i t i o n , v o l a t i l e componen t s o f t h e o i l b o d y exposed t o s o i l a i r i n t e r f a c e s w i l l d v a p c r a t e i n t o t h e soil a i r , a n d s u b s e q u e n t l y may m i g r a t e dpward and i a t e r a l l y b y v a p o r d i f f u s i o n . T h e p r i n c i p l e s used

90

I l l QROUNO 8 U R f A C O

I * I I I

i O I L COYPONEWT8 ; D I 8 8 O L V E D I N W A T E R 8

( A )

Figure 3 , l . Oil r i g r a t i o n pattern (Care No, 1) (Scbwille, 1984) .

QROUNO 8 U R f A C L

U N I A T U R A T E O O I L P H A S E ( O I L B O D Y )

V I 8 U A L LINE O f 8 A T U R A T l O N

- - - - -/- ------- OIL C O U I O N E N T 8 O I 8 8 O L V E D IN W A T € R

W A T E R T A B L E

Piaura 3,1, o i l migration pattern (Care lo. 2 ) (tchwillc, 1984).

91

i n q u a n t i f y i n g t h e s e phenomena a r e d i s c u s s e d i n t h e s e c t i o n d e s c r i b i n g t r a n s p o r t p r o c e s s e s .

Movement of Dissolved Organic Chemicals Through S o i l

U n l i k e o i l p r o d u c t s , many o r g a n i o c o n t a m i n a n t s r e a d i l y d i s s o l v e i n w a t e r and do n o t e x i s t a s s e p a r a t e i m m i s c i b l e l i q u i d s i n s o i l . T h e s e compounds move downward t h r o u g h u n s a t u r a t e d s o i l i n f lowing 8011 s o l u t i o n , where t h e i r movement 13 a t t e n u a t e d t o v a r y i n g d e g r e e s b y a d s o r p t l o n - d e s o r p t i o n r e a c t i o n s w i t h s t a t i o n a r y O r g a n i c m a t t e r a n d s o i l m i n e r a l s u r f a c e s . S i n c e t h e a d s o r p t i o n p r o c e a e e s a r e l a r g e l y r e v e r s i b l e , t hese d i s s o l v e d compounds do not immobi l ize i n s o i l and w i l l move a 8 l o n g a s w a t e r 1s f l o w i n g . T h u s , u n l e s s a p a r t i c u l a r o r g a n i c compound i s c o m p l e t e l y d e g r a d e d b y s o i l m i c r o o r g a n i s m s o r c h e m i c a l r e a c t i o n s , i t w i l l o n l y r e s i d e t empora r i ly i n a vadose zone which r e c e i v e s a n e t a n n u a l i n p u t o f w a t e r a n d w i l l e v e n t u a l l y m i g r a t e t o g r o u n d - w a t e r . A q u a n t i t a t i v e d e s c r i p t i o n o f t h e a d s o r p t i o n and t r a n s p o r t p r o c e s s e s f o r d i s s o l v e d c h e m i c a l s a r e g i v e n i n t h e n e x t s e c t i o n .

P R O C E S S E S G O V E R N I N G TRANSPORT OF O R G A N I C C H E M I C A L S T H R O U G H SOIL

Transpor t of L i q u i d O i l

As a n o i l s p i l l e n t e r s t h e s o i l , i t may sp read l a t e r a l l y a s i t i n f i l t r a t e s downward. The e x t e n t of t h i s l a t e r a l s p r e a d is h i g h l y d e p e n d e n t o f t h e h e t e r o g e n e i t y , p e r m e a b i l i t y and m o i s t u r e s t a t u s o f t h e s o i l - w a t e r p r o f i l e a n d c a n n o t be p r e d i c t e d w i t h any c o n f i d e n c e f o r a n y s o i l c o n d i t i o n s . V i r t u a l l y t h e o n l y q u a n t i t a t i v e i n f o r m a t i o n a b o u t l a t e r a l s p r e a d i n g h a s been o b t a i n e d from s m a l l s c a l e l a b o r a t o r y o i l i n f i l t r a t i o n e x p e r i m e n t s , u s u a l l y i n H e l e - S h a w c e l l s w i t h t r a n s p a r e n t w a l l s ( D i e t z , 1 9 7 0 : S c h w i l l e , 1 9 8 4 ) . I n t h e absence of any q u a n t i t a t i v e i n f o r m a t i o n , s e v e r a l q u a l i t a t i v e comments may b e made a b o u t t h e s h a p e of t h e s p i l l volume r e l a t i v e t o t h e s o i l t e x t u r e of t h e vadose z o n e , For t h e moat p a r t , i n f i l t r a t i o n of o i l i n homogeneous s o i l s of a s i n g l e t e x t u r e w i l l i n t h e a b s e n c e of any l a r g e s t r u c t u r a l V o i d s o r b a r r i e r s t o v e r t i c a l movement be r e l a t i v e l y uni form, and t h e l a t e r a l e x t e n t o f t h e o i l plume w i l l be s m a l l e r i n a c o a r s e t e x t u r e d s o i l ( F i g u r e 3 . 2 A ) t h a n f o r a f i n e - t e x t u r e d s o i l ( F i g u r e 3.28). The s p r e a d i n g of t h e i n f i l t r a t i n g plume w i l l c o n t i n u e w i t h t i m e and w i l l p roduce a cone-shaped vadose zone p r o f i l e u n t i l t h e plume r e a c h e s g r o u n d - w a t e r . I f t h e s o i l i s h e t e r o g e n e o u s o r l a y e r e d , s u b s t a n t i a l l a t e r a l f low can occur a t t h e boundary of a r e g i o n of l ower p e r m e a b i l i t y where t h e o i l w i l l b u i l d u p and f l o w l a t e r a l l y ( F i g u r e 3.2C). I n a d d i t i o n , h l g h l y i r r e g u l a r p lumes of o i l may f l o w t h r o u g h f i s s u r e s and c r a c k s i n bed rock o r v e r y impermeable s o i l and may produce a

92

A - HlQHLY PERMEABLE. HOMOaENOUS SOIL

B - LESS PERMEABLE. HOMOQENOUS SOIL

C - STRATIFIED SOIL W I T H VARYlNa PERMEABILITY

Figure 3.2. Gcner81ired rhrper of rpre8ding COOCI r t i-obile 'arturrtioa (American Petroleum Iartitute, 1972)

93

c o m p l e x l y s h a p e d volume of s p i l l e d m a t e r i a l i n t h e vadose zone ( F i g u r e 3 . 3 ) .

S i n c e s p a t i a l r e s o l u t i o n of t h e hydrooarbon s p i l l volume is g e n e r a l l y t o o imprec ise i n a c t u a l f i e l d s t u d i e s o r c l e a n u p s t o a l l o w a n y g e n e r a l i z a t i o n s t o b e made a b o u t t h e e x t e n t d f s p r e a d i n g , s p e c i f i c i d e a l i z e d S p i l l s h a p e 8 a r e u s u a l l y assumed i n e s t i m a t i n g t h e p o t e n t i a l t o r ground-water contaminat ion . A major assumption made i n c o n s t r u o t i n g t h i s i d e a l i z e d p i o t u r e is t h e c o n c e p t t h a t a f i x e d i m m o b i l i z e d r e s i d u a l o i l volume f r a c t i o n , w h i c h depends o n l y on t h e t y p e o f o i l m a t e r i a l , r e m a i n s i n t h e s o i l a f t e r a s p i l l h a s i n f i l t r a t e d and s t a b i l i z e d . Table 3 . 1 , adapted from in fo rma t ion g i v e n i n D i e t z ( 1 9 7 0 ) , g i v e s p ro to type va lues f o r t h e r e s i d u a l immobilized o i l void f r a c t i o n So ( f r a c t i o n of t o t a l void space ) r e m a i n i n g a f t e r an o i l s p i l l has passed through a volume of s o i l . I n a d d i t i o n , r e s i d u a l v o i d f r a c t i o n s of 0 .05 o r l e s s f o r c o a r 8 e t e x t u r e d s o i l s h a v e b e e n r e p o r t e d b y P fannkuch ( 1 9 8 3 ) and S c h w i l l e ( 1 9 8 4 ) . I t s h o u l d be c a u t i o n e d t h a t t h e s e v a l u e s a r e o n l y rough e s t i m a t e s and t h a t a c t u a l v a l u e s may d i f f e r i n s o i l s of d i f f e r e n t t e x t u r e (Schwl l l e , 1 9 8 4 ) . P a r t of t h e r e a s o n f o r t h e

T A B L E 3 . 1 . R E S I D U A L O I L V O I D F R A C T I O N So ( A D A P T E D FROM 2 . 1 9 7 0 )

~

Type of O i l Residual Void F r a c t i o n

Medium o i l ( d i e s e l , l i g h t f u e l ) 0 . 1 5 L i g h t o i l ( g a s o l i n e ) 0.10

Heavy o i l ( l u b e , heavy, f u e l ) 0.20

l a r g e v a r i a t i o n i n r e p o r t e d v a l u e s f o r t h e r e s i d u a l o i l void f r a c t i o n is t h a t t h e d r a i n a g e of o i l under g r a v i t y f o l l o w i n g w e t t i n g t o a h i g h d e g r e e of s a t u r a t i o n i s a dynamic p r o c e s s which i s very r a p i d d u r i n g t h e e a r l y s t a g e s and which unde rgoes a s l o w b u t c o n t i n u a l decrease w i t h t ime f o r many days a f t e r t h e i n i t i a l r a p i d d r a i n a g e ( F i g u r e 3 . 4 ) . T h u s , t h e r e s i d u a l o i l c o n t e n t i n s o i l a f t e r 5 days may be cons ide rab ly h igher than i t i s a t 1 0 0 d a y s . F o r t h i s r e a s o n , t h e r e s i d u a l o i l v o i d f r a c t i o n , SO, s h o u l d be r e g a r d e d a s a n i n d e x s i m i l a r t o t h e water c o n t e n t “ f i e l d c a p a c i t y w which is v e r y p o o r l y d e f i n e d i n f i n e - t e x t u r e d s o i l s ( H i l l e l , 1 9 7 1 ) . Never the l e s s , t h e r e s i d u a l o i l c o n t e n t i s a use fu l parameter f o r making rough c a l c u l a t i o n s of t h e s p a t i a l volume o c c u p i e d b y a s p i l l . For example, from an e s t i m a t e o f t h e r e s i d u a l v o i d f r a c t i o n p e r c e n t , SO, and t h e t o t a l p o r o s i t y , 0 , one c a l c u l a t e s t h a t a s p i l l of volume, V O , w i l l e v e n t u a l l y occupy a a o i l volume V s where

94

m I n

Figure 3 .3 . I n f i l t r a c i o a o f k e r o s e n e i n t o a p o r o u s m e d i u m t h r o u g h a narrow f i s s u r e a t a r a t e 9 1 1 . 2 5 L/D. Capillary fringe he ight hc is 8 cm. Top: b:binning stage Below: af ter i n f i l t r a t i o n f inished. (Schwi l le , 1984)

95

Figure 3.6. Oil reteat ion capacity 4 8 a fuactioo o f time (Schville, 1975)

96

B Y making 8 p e C l f i O 8 8 8 U m p t i O n 8 a b o u t t h o shag0 O f t h e 011 s p i l l i n t h e vadose zono, t h o a 8 o u n t of o i l r o q u i r e d t o r e a c h t h e ground-water may b e a a l c u l a t o d .

EXAMPLE

A g e a o l i n e t r u o k s p i l l s 1 0 , 0 0 0 g r l l o n s ( 3 7 . 8 5 0 3 ) of g a s o l i n e ( S O -. 1 0 ) on t h o r o i l s u r t r c e . T h o # r r O l i n e i n f i l t r a t e s o v e r a s u r f a c e a r e a of 9 m2. ~ a l c u ~ r t o tire volume of o i l which w i l l r o a c h t h e g r o u n d - w r t o r t a b l e l o c a t e d a t a d e p t h o f 30 m e t e r s a 8 r u a i n g no l a t e r a l movement i n t h e vadose zono. Assume t h a t t h e s o i l p o r o s i t y 6 is 0 . 4 .

S o l u t i o n

The t o t a l vo lume o f r e s i d u a l o i l i n t h o r o i l r f t r r

V S = (37.85 m3)/(0.4)(.10) - 946.25 m 3

s t a b i l i z a t i o n may b e c a l c u l a t e d b y u s i n g Eq. ( 1 ) . Thur

The t o t a l volume V v o c c u p i e d b y t h e o i l i n t h o 30 m t h i c k v a d o s e z o n e , a s s u m i n g n o s p r e a d i n g ( i . e . , a c y l i n d r i c a l plume), is equa l t o

V v - AL ( 2 )

where A i s t h e s u r f a c e s p i l l a r e a (9 m2) and L is t h e depth t o ground-water (30 m). T h u s , i n t h i s case V, .I 2 7 0 m 3 and t h i s volume is f i l l e d b y a q u a n t i t y VV+So - 10 .8 m 3 of o i l , l e a v i n g 27.05 m3 of o i l t o sp read over t he ground-water.

Accumulation Over Ground-Water

When t h e o i l b o d y r e a c h e s g r o u n d - w a t e r , t h o b u l k of t h e m a t e r i a l , which i s l e s s d e n s e t h a n w a t e r , w i l l f l o a t on t h e s u r f a c e o f t h e ground-water i n t e r f a c e and w i l l sp read o u t u n t i l t h e e n t i r e o i l volume occup ies a void volume f r a c t i o n e q u a l t o S o . The t h i c k n e s s , T , o f t h e o i l l e n s which h a s spread over t h e g r o u n d - w a t e r w i l l d e p e n d o n b o t h t h e O i l a n d s o i l p r o p e r t i e s b u t i s g e n e r a l l y roughly equated t o t h e t h i c k n e s s of t h e water c a p i l l a r y zone ( t h e zone above t h e w a t e r t a b l e where t h e w a t e r changes from s a t u r a t i o n t o f i e l d c a p a c i t y ) ( D i e t z , 1 9 7 3 ) . Table 3.2, t a k e n from D i e t z ( 1 9 7 0 1 , g i v e s borne rough e s t i m a t e s for t h e t h i c k n e s 8 of t h e o i l f i l m ad a f u n c t i o n of s o i l t ype . If t h e ground-water ha8 no l a t e r a l v e l o c i t y and t h e s o i l i s h o m o g e n e o u s , t h e l a y e r o f o i l s h o u l d r p r e a d homogeneously over t h e g round-wa te r and form a c i r c u l a r f i l m . If' t h e ground-water has a l a t e r a l v e l o c i t y , the s p i l l should be skewed i n t h e d i r e c t i o n of flow ( F i g u r e 3.5). The a r e a , A G O O f t h e g r o u n d

97

OROUND-WATER CONTAMINATED B Y OOLUBLE COUPONeNTS

QLUlD OIL PLOATtNQ ON WATER TABLE

RESIDUAL 6AtURATlON

Figure 3.5. Subrurfrce redirtribution of a rurfrca rpill (American Petroleum Inrtitutr, 1972)

98

T A B L E 3 . 2 O I L LENS T H I C K N E S S A B O V E G R O U N D - W A T E R

Grain Zone

( m m ) ( c d Extremely coarse-very coa r se . 5 -2 2-9 Very coarse-modera te ly coa r se . 2 - .5 9-22 Moderately coarse-moderately f i n e . 0 5 - . 2 22-28 Moderately f i n e - v e r y f i n e . 015 - .05 28-45

T y p e of Sand Diameter T h 1 ck neb8

w a t e r mound may be r o u g h l y c a l c u l a t e d from t h e volume of o i l , V G , which r e a c h e s t h e ground-water u s i n g equa t ion ( 3 ) .

E s t i m a t e s of t h e f i l m t h i c k n e s s v a r y c o n s i d e r a b l y among d i f f e r e n t r e s e a r c h e r s , i n p a r t b e c a u s e f i l m t h i c k n e s s , l i k e r e s i d u a l o i l s a t u r a t i o n , i s a d y n a m i c q u a n t i t y w h i c h d e c r e a s e s s l o w l y o v e r t ime ( F i g u r e 3 . 6 ) . V a l u e s g i v e n b y S c h w i l l e ( 1 9 6 7 1, l a r g e l y o b t a i n e d from model exper iments , a r e g e n e r a l l y of t h e o r d e r of 1 om o r l e s s . F u r t h e r m o r e , t h e e f f e c t i v e t h i c k n e s s o f t h e o i l l e n s may b e a l t e r e d b y ground-water t a b l e f l u c t u a t i o n s o c c u r r i n g d u r i n g t h e t i m e o f l a t e r a l r e d i s t r i b u t i o n . T h i s v e r t i c a l mot ion can s p r e a d a l a y e r of immobilized o i l over a much g r e a t e r v e r t i c a l t h i c k n e s s t h a n i f t h e r e d i s t r i b u t i o n o c c u r s o v e r a m o t i o n l e s s w a t e r t a b l e .

EXAMPLE ( con t inued from above)

T h e 2 7 . 0 5 m 3 o f o i l w h i c h e n t e r s g r o u n d - w a t e r i s assumed t o form a symmetric c i r c u l a r f i l m o f t h i c k n e s s T .I

0 . 0 1 m. T h u s , u s i n g e q u a t i o n ( 3 ) t h e a r e a of t h e f i l m i s A G .I 6 7 6 2 5 m 2 . I n t h i s c a s e , t h e f i l m w i l l form a c i r c l e of r a d i u s 147 m .

I n p r a c t i c e , t h i s e s t i m a t e of l e n s thickness may be t oo Small i f g round-wa te r l e v e l f l u c t u a t i o n s a r e f r e q u e n t i n t h e a r e a common t o t h e s p i l l boundary. For example, i f t h e e f f e c t i v e t h i c k n e s s of t h e f i l m i s i n c r e a s e d t o 0 . 1 m e t e r , t h e A G i s r e d u c e d t o 6 7 6 3 m 2 and t h e r a d i u s of t h e s p i l l over ground-water reduces t o 4 6 . 5 m.

Transpor t of Dissolved Chemicals T h r o u g h S o i l

T h e m o s t i m p o r t a n t p r o c e s s e s g o v e r n i n g t r a n s p o r t o f d i s s o l v e d o r g a n i c c h e m i c a l s t h r o u g h s o i l a r e m a s s f l o w or c o n v e c t i o n o f c h e m i c a l s w i t h f l o w i n g s o i l a o l u t i o n a n d hydrodynamic d i s p e r s i o n , t h e sp read ing of c h e m i c a l s i n s o i l b y movement a r o u n d s o l i d o b s t a c l e s . Many d i s s o l v e d o r g a n i c

99

z E Y

00 t Y 0 m

5 * P IJ

a0

40

8 0

8 0

10

0 1 I I 1 I I ) 0 60 00 160

Time (days)

I

I 1 I I 1 I I ) 0 60 00 160

Time (days)

Figure 3.6, Relatioa beturoo thickmeor o f o i l layer rod rpr..dial time (Schwille, 1975).

100

c h e m i c a l s do n o t move f r e e l y i n s o l u t i o n b u t a r e a t t e n u a t e d t o v a r y i n g d e g r e e s b y r e v e r s i b l e a d s o r p t i o n t o s t a t i o n a r y s o i l o rganic-mat te r and , t o an e x t e n t , t o c l ay mineral s u r f a c e s .

An i m p o r t a n t i n d e x f o r d e s c r i b i n g a d s o r p t i o n i s t h e d i s t r i b u t i o n c o e f f i c i e n t Kd ( c m 3 g - l ) which i s d e f i n e d a s t h e r a t i o of a d s o r b e d c o n o e n t r a t i o n Ca ( p g g'l s o i l ) t o d i s so lved c o n c e n t r a t i o n C Q ( p g cm-3 s o l u t i o n ) a t equ i l ib r ium, or

ca K d C i (4)

Anothe r i n d e x which is d e f i n e d a s t h e d i s t r i b u t i o n c o e f f i c i e n t p e r u n i t s o i l o r g a n i c o a r b o n f r a c t i o n f o c ( s e e Appendix) i s c a l l e d t h e o r g a n i c c a r b o n d i s t r i b u t i o n c o e f f i c i e n t , K o o (cm3g-11, or

KO, K d / f o c ( 5 )

K O , h a s been shown t o v a r y l e s s between s o i l s t h a n Kd f o r a g i v e n c h e m i c a l ( H a m a k e r a n d Thompson, 1 9 7 2 ) . T h u s , i t r e p r e s e n t s t h e a d s o r p t i o n p o t e n t i a l of a given compound. Large compendia of K O , v a l u e s f o r p e s t i c i d e s and o t h e r o r g a n i c c h e m i c a l s a r e a v a i l a b l e i n d i f f e r e n t r e f e r e n c e s (Kenaga, 1980; Rao and Davidson, 1980; J u r y , e t a l . , 1984).

As a f u r t h e r a t t e m p t t o s t a n d a r d i z e t h e a d s o r p t i o n p o t e n t i a l of a g iven o r g a n i c c h e m i c a l , measurements have been made of t h e a d s o r p t i o n of compounds t o oc t ano l (Lambert , 1968) . The octanol-water p a r t i t i o n c o e f f i c i e n t , K O w , has been measured or c a l c u l a t e d f o r a l a r g e number of organic chemicals (Rao and Davidson, 1980) . Fur thermore , v a r i o u s r e g r e s s i o n c o e f f i c l e n t s have been developed between K O , and K O w , inc luding t h e r e l a t i o n

log KO, - 1 . 0 2 9 l o g KO, - 0.18 ( 6 )

( u s e d b y Rao and Davidson, 1980) f o r 1 3 p e s t i c i d e s ( r 2 - 0 . 9 1 ) . Attempts have a l s o been made t o c a l c u l a t e K O , o r K o w from more b a s i c c h e m i c a l p r o p e r t i e s or from chemical s t r u c t u r e ( B r i g g s , 1 9 6 9 ) . F o r e x a m p l e , K e n a g a ( 1 9 8 0 ) u s e d t h e f o l l o w i n g r e g r e s s i o n w i t h water s o l u b i l i t y , C a ( p g cm-31,

l o g K O , - 3 . 6 4 - 0.55 log C a (7)

t o J b t a i n K O , v a l u e s for a v a r i e t y o f o r g a n i c compounds. He s t a t e d t h a t t h e e q u a t i o n was a c c u r a t e w i t h i n 1 . 2 o r d e r s o f magnitude.

I n t h e Appendix i t i s shown t h a t i n a f lowing s o l u t i o n , t he average e f f e c t i v e v e l o c i t y , V E , of a d i sso lved o r g a n i c chemica l w h i c h undergoes a d s o r p t i o n is:

101

and V w - J,/o is pore water v e l o c i t y

I f a c o n c e n t r a t e d p u l s e o r f r o n t of chemical i s s u d d e n l y app l i ed t o t h e s o i l , not a l l of t h e m o l e c u l e s w i l l move a t t h e same v e l o c i t y V E b e o a u s e of d i s p e r s i o n . However, V E w i l l d e sc r ibe t h e average ve loc i ty of t h e pulse or e q u i v a l e n t l y , t h e ve loc i ty of t h e cen te r of mass of t h e pulse .

EXAMPLE

Three compounds, ch lo r ide ( K o c - O ) , benzene ( K o c = 83 1 and n-octane ( K o c - 6800) a r e introduced i n t o an a q u i f e r of p o r o s i t y 4 - 0 . 5 , water f l u x J w - 1 m d' l , b u l k dens i ty pb = 1.5 ( g cm'3), and o r g a n i c ca rbon f r a c t i o n f o c = . 0 0 5 . C a l c u l a t e t h e ave rage t r a v e l t i m e of these compounds t o a well L - 1000 m downstream.

S O L U T I O N

When E q . ( 5 ) 1s u s e d , t h e Kd v a l u e s of t h e t h r e e compounds (Chloride, benezene, n - o c t a n e ) a r e (Kd = f o c K o c ) 0 , .415, 34 (em3 g-1). From E q . ( 8 1 , t h i s gives v e l o c i t i e s VE of 2.0, 0.89, 0.019 ( m d F 1 ) , r e s p e c t i v e l y . The t r a v e l t i m e , t , t o move a d i s t a n c e , L , t h rough t h e a q u i f e r is s i m p l y t = L / V E , or t - 500, 1124, and 5.26 x lo4 days f o r c h l o r i d e , benezene, and n-octane t o reach the w e l l .

The a v e r a g e t r a v e l t imes do not r ep resen t the e a r l i e s t a r r i v a l t imes o f t h e chemica l p u l s e o r f r o n t , which c o u l d be much s h o r t e r t h a n t h e ave rage t i m e . P r e d i o t i o n of t h e e a r l i e s t t i m e s r e q u i r e s a q u a n t i t a t i v e u n d e r s t a n d i n g or t h e s o i l geometry v a r i a t i o n s which is usua l ly not possible t o o b t a i n i n the f i e l d .

A l s o i m p o r t a n t i n c h a r a c t e r i z i n g d i s s o l v e d c h e m i c a l t r a n s p o r t is t he degradation r a t e of t h e compound which i n t h e a b s e n q e o f d e t a i l e d i n f o r m a t i o n a b o u t s p e c i f i c r e a c t i o q mechanisms is commonly represented b y t h e h a l f - l i f e , TY1 d e f i n e d a s t h e t i m e a t which t h e mas3 of t h e compound d rops t o 5 0 p e r c e n t of i t s i n i t i a l l e v e l w h i l e d e c r e a s i n g e x p o n e n t i a l l y w i t h t i m e . F o r example, i f a compound has a t r ave l time t o an o b s e r v a t i o n we l l equa l t o t w i c e i t s h a l f - l i f e , t h e mass a t a r r i v a l s h o u l d be degraded t o Yh of t h e i n i t i a l mas8 a t the time

102

0

( C

f i 1 9 8 hem

n j e c t i o n . T a b l e 3 . 3 , a d a p t e d c h i e f l y from J u r y , e t a l . 4), g i v e s v a l u e s o f K O , a n d T 1 / 2 f o r v a r i o u s o r g a n i c i c a l s t o g e t h e r w i t h a c a l c u l a t i o n o f t h e t r a v e l t i m e t o

r each 1000 m f o r t h e c o n d i t i o n s g i v e n i n t h e example above . I n c a s e s where t h e documented h a l f - l i f e is c o n s i d e r a b l y smal le r t h a n t h e t r a v e l t i m e , as f o r example w i t h me thy l p a r a t h i o n , i t i s u n l i k e l y t h a t t h e compound w i l l p e r s i s t long enough t o reach t h e well . However, i t should b e s t r e s s e d t h a t t h e g round-wa te r c o n d i t i o n s may d i f f e r c o n s i d e r a b l y from t h e c o n d i t i o n s under which t h e compound h a l f - l i f e was e s t ima ted .

The h a l f - l i f e a n d o r g a n i c c a r b o n p a r t i t i o n c o e f f i c i e n t r e p r e s e n t s o - c a l l e d chemica l benchmark p r U p e r t i e 8 f o r o r g a n i c compounds. These s i n g l e i n d i c e s roughly d e s c r i b e t h e tendency t o degrade and adsorb i n s o l 1 s y s t e m s . They mask much of t h e c o m p l e x i t y of t h e s e p r o c e s s e s a n d , f o r t h a t r e a s o n , should be r e g a r d e d a s lumped p a r a m e t e r s . N e v e r t h e l e s s , t h e v a l u e s o f t h e s e c o e f f i c i e n t s do p r o v i d e v a l u a b l e i n f o r m a t i o n about the p o s s i b l e behavior of t h e compound i n t h e environment . For t h i s r e a s o n , t h e benchmark p r o p e r t i e s a r e u s e f u l t o o l s t o use i n s c r e e n i n g l a r g e numbers of compounds and in p l a c i n g them i n t o s m a l l e r numbers of groups which behave s i m i l a r l y ( J u r y , e t a l . , 1 9 8 4 ) . A f t e r s u c h a s c r e e n i n g p r o c e s s , e x p e r i m e n t a l o b s e r v a t i o n s of s p e c i f i c chemical behavior may be used t o make assessments of t h e expec ted behavior of o t h e r compounds i n t h e same b e h a v i o r g r o u p f o r which no d i r e c t exper imenta l evidence is a v a i l a b l e .

T r a n s i e n t Movement of Dissolved Chemicals

F r o m t h e above i n f o r m a t i o n , i t is p o s s i b l e t o make some gene ra l comments about a s p i l l of chemica l which is c o m p l e t e l y d i s s o l v e d i n w a t e r . The mass v s l o c i t y o f t h e c h e m i c a l , r e t a r d e d b y a d s o r p t i o n compared t o t h e v e l o c i t y of t h e w a t e r , i s r o u g h l y g i v e n b y Eq. (8). The e x t e n t o f l a t e r a l and v e r t i c a l spread i n t h e u n s a t u r a t e d z o n e , a s i n t h e c a s e o f an o i l s p i l l , is v e r y d e p e n d e n t on s p e c i f i c s o i l c o n d i t i o n s and c a n n o t be p r e d i c t e d . i n d e t a i l w i t h any c e r t a i n t y . G e n e r a l s h a p e s s u c h a s t h o s e shown i n F i g u r e s 3 . 1 - 2 f o r o i l s p i l l s r e p r e s e n t p l a u s i b l e p r o f i l e s h a p e s d u r i n g v e r t i c a l i n f i l t r a t i o n .

H o w e v e r , u n l i k e t h e l a r g e l y immiscible o i l volume, t h e c i i ? 7 0 1 v e d chemical mass does not immobilize i n s o i l , and has no s ~ a o l l i z e d p r o f i l e a s l o n g a s w a t e r is f l o w i n g t h r o u g h t h e system. However, i t may move very S lowly downward b e c a u s e o f

103

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.3 . KO, A N D T1/2 VALUES FOR VARIOUS MISCIBLE ORGANIC S, A L O N G WITH AN ESTIMATE OF THE TRAVEL TIME R E Q U I R E D ATE L - 1000 m T H R O U G H G R O U N D - W A T E R USING Eq. 8 WITH w=1md-18 0 - 0 . 5 , Pb 1.5 gem-3, loo = 0 .005

A T R A Z I N E 160 B E N Z E N E 83 B R O H A C I L 72 CARBON T E T R A C H L O R I D E 110 C H L O R I D E 0 DDT 2 . 4 E 5 D I E L D R I N 12000 E P T C 280 E D B 4 4

METHYL P A R A T H I O N 51 00 W O N U R O N 180 N A P R O P A M I D E 300 NAPTHALENE 1300 N I T R O B E N Z E N E 71 N - O C T A N E 6800 P A R A T H I O N 11000 P H E N A N I T R E N E 23000 P H E N O L 27 PHORATE 660 P R O M E T R Y N 61 0 SIMAZINE 140 T C E 150 1 , 1 , 1 - T R I C H L O R O E T H A N E 113 T R I A L L A T E 36 00 T R I F L U R A T I N 7300

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a d s o r p t i o n r e a c t i o n s or may cease t o move e n t i r e l y i f t h e water i n p u t t o t h e s o i l is stopped f o r a prolonged per iod of t i m e and t h e c h e m i c a l is b e l o w t h e f i r s t few m e t e r s where i t migh t a i g r a t e upward w i t h water moving towards a d r y soil s u r f a c e .

O i l Migrat ion After S t a b i l i z a t i o n

When t h e l i q u i d oil phase is s t a b i l i z e d i n t h e s o i l , t h e t m m ! s c i b l e o i l body s h a r e s a l a r g e i n t e r f a c e w i t h t h e s u r r o u n d i n g l i q u i d w a t e r . T h u s , any water p e r c o l a t i n g through .?n c i l s p i l l e i t h e r i n t h e s a t u r a t e d o r u n s a t u r a t e d s o i l - w a t e r

104

z o n e s w i l l p i c k u p d i s s o l v e d components f rom t h e o i l - w a t e r i n t e r f a c e and w i l l c a r r y them downstream a t t h e end o f t h e s p i l l . F r i e d , e t a l . ( 1 9 7 9 ) , a n a l y z i n g e x p e r i m e n t a l r e s u l t s and a p p l y i n g t h e o r e t i c a l c a l c u l a t i o n s , c o n c l u d e d t h a t w a t e r p e r c o l a t i n g t h r o u g h a body of i m m o b i l i z e d s p i l l e d o i l w i l l r e a c h s a t u r a t i o n l e v e l 8 w i t h r e s p e c t t o t h e d i 8 S O l v e d components a f t e r a s h o r t per iod of t ime or e q u i v a l e n t l y a f t e r a s h o r t t r a v e l d i s t a n c e , o f t h e o r d e r o f s e v e r a l t e n s o f c e n t i m e t e r s . T h u s , i n a r eg ion where water i s f lowing , t h e o i l s p i l l a c t s a s a d i s t r i b u t e d s o u r c e o f d i s a o l v e d o r g a n i c c h e m i c a l s a s l o n g a s t h e immiscible m a t e r i a l remains i n p l a c e , Once p r e s e n t a s a d i s s o l v e d component of w a t e r , t h e o r g a n i c compound i s t r a n s p o r t e d b y c o n v e c t i o n and d i s p e r s i o n i n t h e manner desc r ibed i n t h e p rev ious s e c t i o n .

To o b t a i n r o u g h e s t i m a t e s of t h e r e l e a s e of chemical from t h e s t a b i l i z e d s p i l l i n t o g r o u n d - w a t e r , o n e may n e g l e c t h y d r o d y n a m i c d i s p e r s i o n and w r i t e t h e mass f l u x , J,, o f d i s s o l v e d c h e m i c a l a s t h e p r o d u c t of t h e w a t e r f l u x , J,, and t h e s a t u r a t e d c o n c e n t r a t i o n of o r g a n i c C a ( g 01-3)

Js - J w h ( 9 )

T h i s e q u a t i o n t o g e t h e r w i t h knowledge o f g round-wa te r f low r a t e s and o i l component s o l u b i l i t i e s may be used t o r o u g h l y e s t i m a t e t h e f l u x of d i s s o l v e d m a t e r i a l from t h e r e s i d u a l s p i l l i n t o t h e ground-water.

E X A M P L E

For i l l u s t r a t i o n , t h e p r e v i o u s example i s used where a gaso l ine s p i l l sp read i n t o a t h i n 1 cm t h i c k f i l m o v e r t h e g round-wa te r and c o v e r e d a r a d i u s of 1 4 7 m. When F i g u r e 3.7 adapted from Somers ( 1 9 7 4 ) 1s u s e d , t h e s o l u b i l i t y of t h e g a s o l i n e m i x t u r e i s r o u g h l y e s t i m a t e d a s C, = l O ( m g a - 1 ) - 1 0 ( g m - 3 ) . Assume t h a t t h e a q u i f e r h a s a g r o u n d - w a t e r v e l o c i t y of V - 2 ( m d ' l ) and a w a t e r - f i l l e d po ros i ty of + - 0 . 4 . T h u s , t h e ground-water f l u x i s J, - + V - 1 ( m d" 1.

As t h e ground-water f l o w s u n d e r t h e s p i l l , i t w i l l pick u p d i s s o l v e d components u n t i l , a t t h e downstream e d g e , a l a y e r o f f l o w i n g ground-water con ta in ing d i s so lved g a s o l i n e components i s formed ( s e e F i g u r e 3.5). The w i d t h of t h i s z o n e o f c h e m i c a l w i l l depend on t h e e x t e n t o f v e r t i c a l migra t ion b y d i f f u s i o n and d i s p e r s i o n of d i s s o l v e d m a t e r i a l b e l o w t h e s p i l l i n t o t h e ground-water, which may be roughly e s t i m a t e d f r o m known i n f o r m a t i o n a b o u t t r a n s v e r s e d i s p e r s i o n c o e f f i c i e n t s . D i s s o l v e d chemical i n t h i s zone p e r p e n d i c u l a r t o t h e g r o u n d - w a t e r f l o w d i r e c t i o n w i l l d e c r e a s e i n c o n c e n t r a t i o n a t g r e a t e r g round-wa te r d e p t h s

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Figure 3.7. Solubility of h y d r o c a r b o n s i n water (Sorctr, 1974)

106

b e c a u s e o f d i s p e r s i o n . F r i e d , e t a l . ( 1 9 7 9 1 , i n o rder t o p r o d u c e a s i m p l e c o n c e p t u a l m o d e l o f t h e r e l e a s e o f c h e m i c a l f r o m t h e s p i l l , d e f i n e d a n e q u i v a l e n t d i s so lved chemical l a y e r t h i c k n e s s , D , which con ta ined t h e same t o t a l mass of c h e m i c a l a s t h e a c t u a l p r o f i l e b u t which had a l l of t h e chemical a t t h e s a t u r a t e d 8 O l U b i l i t y c o n c e n t r a t i o n ( s e e F i g u r e 3 .8) .

I n a n a l y z i n g t h i s problem b y u s i n g a two-dimens iona l form of t h e d i s s o l v e d chemical t r a n s p o r t e q u a t i o n ( A . 1 4 i n t h e A p p e n d i x ) , F r i e d , e t a l . ( 1 9 7 9 ) , c a l c u l a t e d t h a t t h e e q u i v a l e n t t h i c k n e s s , D , i n ground-water below t h e o i l l e n s c o n t a i n i n g a s a t u r a t e d c o n c e n t r a t i o n o f t h e d i s s o l v e d c h e m i c a l was on t h e o r d e r of 1 m f o r t h e s p i l l g e o m e t r y g i v e n i n t h e p r e v i o u s example . I n t h e example d iscussed a b o v e , t h e g a s o l i n e s p i l l formed a c i r c u l a r p a n c a k e of r a d i u s R i n c o n t a c t w i t h ground-water. T h u s , b y u s i n g t h e i d e a l model of F r i e d , e t a l . ( 1 9 7 9 ) , we c a l c u l a t e t h a t t h e f r o n t o f d i s s o l v e d chemica l f lowing i n t h e ground-water a s i t l e a v e s t h e s p i l l r e g i o n w i l l be a p p r o x i m a t e l y 1 m deep a n d 2 R wide ( p l u s a s m a l l amount of a d d i t i o n a l l a t e r a l w i d t h from d l s p e r s i o n ) , By u s i n g E q . ( 8 1 , we can e s t i m a t e t h e mass f l u x o f d i s s o l v e d c h e m i c a l a s J s = JwCe = 10 ( g m'2d-1). T h e c r o s s - s e c t i o n a l a r e a of flow is A - 2 R D - 2 9 4 m 2 s i n c e R - 1 4 7 m. T h u s , t h e s p i l l d i s c h a r g e s t h e d i s s o l v e d chemical i n t o t h e ground-water a t a r a t e Q = J,A - 2 9 4 0 ( g d ' l ) or Q - 1073 ( k g y r - l ) . S ince t h e t o t a l mass o f t h e s p i l l i n ground-water ( a s s u m i n g a d e n s i t y of 9 0 0 k g m-3) was a b o u t 27.05 m3 x 9 0 0 - 25000 k g , t h i s d i scha rge r a t e would t r a s n s f e r about 1 / 2 3 of t h e s p i l l t o t h e ground- w a t e r i n one y e a r . T h i s w o u l d d i s s o l v e t h e s p i l l i n about 2 3 y e a r s i f t h e e n t i r e s p i l l volume were e q u a l l y s o l u b l e and i f t h e l a t e r a l e x t e n t of t h e s p i l l remained unchanged.

O b v i o u s l y , t h e e x t e n t o f d i s s o l u t i o n i n t o ground-water i s much g r e a t e r when t h e l a y e r o f o i l a t t h e ground-water i n t e r f a c e i s s p r e a d t h i n l y o v e r t h e s u r f a c e t h a n i f t h e immobilized l a y e r is t h i c k e r and has a sma l l e r c o n t a c t a r e a w i t h g r o u n d - w a t e r . I n t h e s e c o n d c a s e from an e a r l i e r example, t h e s p i l l t h i c k n e s s was i n c r e a s e d t o 1 0 cm which d e c r e a s e d t h e s p i l l r a d i u s t o 46.5 m. I f a l l c a l c u l a t i o n s above a r e r e p e a t e d , t h e t h i c k n e s s , D , o f t h e d i s s o l v e d o r g a n i c zone a t t h e e x i t boundary c a l c u l a t e d b y the method o f F r i e d , e t a l . ( 1 9 7 9 1 , d r o p s t o a b o u t 0 . 7 0 m , and t h e d i s s o l v e d c h e m i c a l mass f l u x d e c r e a s e s t o 238 k g l y r . A t t h i s r a t e of d i s s o l u t i o n , i t w o u l d r e q u i r e o v e r 1 0 0 y e a r s t o remove t h e r e s i d u a l s p i l l if' t h e d i s s o l u t i o n process and a r e a e x t e n t r e m a i n e d c o n s t a n t d u r i n g t h e l i f e t i m e of t h e o i l event i n t h e s o i l .

107

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Figure 3.8. Compariron o f actual and i d e a l i t c d c o n c e h t r ~ t i o n depth profi les below a warte r p i l l in ground vater. Tbe equivalent th ickaerr , D, i r def ined ro that the rectangle ha, tbe rame area between the axe0 81 the curve. ( i . e . , the 08me mar8 of chemical) . C i i r the chemical so lubi l i ty in water.

108

O i l D i s s o l u t i o n W i t h i n t h e Vadose Zone

W a t e r p e r c o l a t i n g downward t h r o u g h t h e p o r t i o n o f t h e vadose zone volume contaminated by t h e r e s i d u a l p o r t i o n o f t h e o i l s p i l l w i l l a l s o d i s s o l v e i n t o s o l u t i o n , c r e a t i n g a new source of d i s s o l v e d o i l m a t e r i a l t o c o n t a m i n a t e g r o u n d - w a t e r . The e x t e n t of maas f l o w from t h i s s o u r c e w i l l depend on t h e s p i l l shape , t h e p e r c o l a t i o n r a t e , and t h e e x t e n t of l a t e r a l m i g r a t i o n o f t h e d l a s o l v e d m a t e r i a l . T h i s ma88 flow r a t e i s t o o u n c e r t a i n t o be e s t i m a t e d q u a n t i t a t i v e l y u n l e s s t h e s p i l l s h a p e i s known. A s a r o u g h e s t i m a t e , t h e mass f l u x may be c a l c u l a t e d a s t h e p r o d u c t o f w a t e r ~ e r c o l a t i o n r a t e , s o l u b i l i t y , a n d t h e s p i l l c r o s s - s e c t i o n a l a r ea normal t o f low i n t h e v a d o s e z o n e . I n t h e c a s e o f t h e p r e v i o u s e x a m p l e , assuming 1 ( m y r ' l ) v e r t i c a l d ra inage through t h t s p i l l and A - 9 m 2 a r e a , t h e c a l c u l a t e d mass f l u x i s J w C S A - . 0 9 ( k g y r ' l ) which i s v e r y s m a l l oompared t o t h e r e l e a s e r a t e i n t o t h e g round-wa te r . T h i s i s because t h e i n t e r f a c i a l a r e a between u n d i s s o l v e d o i l and w a t e r i s v e r y much l a r g e r i n t h e l a t t e r c a s e and b e c a u s e t h e d r a i n a g e f l u x i s much s m a l l e r t h a n t h e ground-water f l u x .

S i n k i n g of Heavy I n s o l u b l e Components i n t o Ground-Water

O r g a n i c l i q u i d s which a r e i m m i s c i b l e i n w a t e r and dense r than water cou ld s i n k t h r o u g h t h e s a t u r a t e d ground-water z o n e i f n o t bound i n a r e s i d u a l s t a t e (Anderson and J o n e s , 1 9 8 4 ; Mackay, e t a l . , 1 9 8 5 ) . There has been some l a b o r a t o r y e v i d e n c e o f t h i s p h e n o m e n o n ( S c h w i l l e , 1 9 7 5 ) , a n d i t p r o b a b l y c o n t r i b u t e s t o t h e v e r t i c a l t r a n s p o r t of m a t e r i a l w i t h i n t h e s a t u r a t e d z o n e . T h e s e n a i n k e r a n a s t h e y a r e c a l l e d c o u l d e v e n t u a l l y r e a c h t h e bot tom o f . t h e a q u i f e r i f t h e y a r e n o t immobilized en r o u t e (Mackay, e t a l . , 1 9 8 5 ) .

MOVEMENT OF H Y D R O C A R B O N V A P O R THROUGH S O I L

T h e v o l a t i l e components of t h e o i l m a t e r i a l w i l l r e l e a s e chemical t o t h e vapor phase which w i l l i n t u r n m i g r a t e toward t h e s o i l s u r f a c e b y d i f f u s i o n ( l a t e r a l and v e r t i c a l ) or w i l l sink through t h a s o i l a i r i f t h e p a r t i a l p r e s s u r e of t h e v a p o r is s u f f i c i e n t l y h i g h and i f t h e vapor is denser than a i r . The r a t e of m i g r a t i o n w i l l be a f u n c t i o n o f t h e s o i l r e s i s t a n c e t o v a p o r f l o w , of t h e amount which is r e d i s s o l v e d i n t o t h e l i q u i d p ! 1 ? 3 . , and of t h e amount which i s a d s o r b e d or d e g r a d e d . The m a t h e m a t i c a l d e s c r i p t i o n of t h e t r a n s p o r t p rocess , descr ibed i n d e t a i l i n t h e Appendix, combines a mass b a l a n c e ( E q . A . l ) w i t h t h e f l u x e q u a t i o n f o r vapor movement c a l l e d F i c k ' s Law ( E q . A . 4 ) .

E q u a t i o n ( A . 4 ) d e s c r i b i n g vapor f l u x assumes t h a t vapor is t r a n s p o r t e d o n l y b y d i l f u s i o n , a n d t h i s i s a r e a s o n a b l e

109

a p p r o x i m a t i o n i f t h e a i r phase is s t a g n a n t and if t h e chemical vapor is a d i l u t e component of t h e s o i l a t m o s p h e r e . However, some mass f l o w of v a p o r c o u l d o o o u r , p a r t i o u l a r l y if a l a r g e q u a n t i t y of chemical vapor which is denser t h a n a i r l a e v o l v i n g i n t h e u n s e t u r a t e d z o n e . I n t h i s c a s e , t h e o v e r l y i n g dense vapor could s i n k a8 w e l l a s d i f f u s e t h r o u g h t h e a i r p h a s e and would c o l l e c t a t t h e ground-water i n t e r f a o e ( S c h w i l l e , 1 9 8 4 ) .

Although c h e m i c a l t r a n s p O r t occurs i n t h e vapor phase when mass f l o w o f d f S s O l V 0 d c h e m i c a l compounds 1s n e g l i g i b l e , c h e m i c a l vapor m o l e c u l e s s t i l l l n t e r a o t w i t h t h e l i q u i d and adsorbed phases b y P e d i 8 s O l V i n g when t h e m o l e c u l e s come i n t o c o n t a c t w i t h w a t e r which l a low i n d i s s o l v e d c o n c e n t r a t i o n . The r e l a t i o n s h i p which d e s c r i b e s t h e e q u i l i b r i u m p a r t i t i o n i n g between t h e vapor and l i q u i d c o n c e n t r a t i o n s is c a l l e d H e n r y ' s Law: -

c v K H C L

where K H (cm3 s o l u t i o n / c m ~ a i r ) is t h e d i m e n s i o n l e s s form of Henry's cons t an t ( J u r y , e t a l . , 1 9 8 3 ) . S i n c e H e n r y ' s Law ha8 been shown t o be v a l i d a l l t h e way t o s a t u r a t i o n f o r a number of organ ic chemicals (Spencer and C l i a t h , 1 9 7 0 ) , i t is cotmonly c a l c u l a t e d a s t h e r a t i o l o f s a t u r a t e d vapor d e ? s i t y , C v , t o w a t e r s o l u b i l i t y , C k . V a l u e s o f C c , C g , a n d K H f o r a number of o r g a n i c chemica ls a r e given i n Table 3.4.

The Henry ' s Law c o n s t a n t is a l s o expressed o c c a s i o n a l l y a s a r a t i o of vapor p r e s s u r e t o d i s s o l v e d c o n c e n t r a t i o n , a s , f o r example, i n

p v k H C L

where P ( P a o r J m - 3 ) is vapor p r e s s u r e , and kH has t h e u n i t s The conve r s ion f a c t o r between kH and K H i n E q .

( l o ) , oStained b y u s i n g t h e i d e a l gas law is: of (Pa-m 3 g - l ) .

RT kH = K H ( 1 2 )

where R - 8 .3 ( J mole ' loK' l ) 1s t h e u n i v e r s a l gas c o n s t a n t , T is the abso lu te t empera tu re , and M ( g mole ' l ) is t h e m o l e c u l a r we igh t of t h e compound. An e x t e n s i v e compendium of values of kH for a v a r i e t y of o r g a n i c c h e m i c a l s a r e g i v e n i n Mackay, e t a l . ( 1 F 8 2 ) .

A s s h o w n i n t h e A p p e n d i x , t h e e f f e c t i v e s o i l v a p o r d l f r u s l o n c o e f f i c i e n t for an o r g a n i c c h e m i c a l which is a l s o p r e s e n t i n t h e a d s o r b e d and d i s so lved phases is reduced , o f t e n significantly, compared t o t h e d l f f u 8 i O n c o e f f i c i e n t of a g a s

110

which 1s insoluble. Gas dissolution and bubsequont rdsorption has the effoct of greatly slowing d o w n the transport of t h e c h e m i c a l i n t h e v a p o r p h a s e 8 n d a l s o o f exposing the gas molecules t o degradation prooesses which may only be occurring in solution. However, the Henry's Law partition model Eq. (10) implies that the vapor aonoentration is proportional t o t h e dissolved concentration (and, as shown in the Appendix, to the total concentration). Thus, to the extent that the equilibrium relations a r e valid in soil, the vapor phase concentration may be used t o quantitatively m o n i t o r a v o l a t i l e w a s t e s p i l l . Furthermore, even if t h e relationships are only approximately valid because o f rate-limited nonequilibrium between phases, the vapor phase profile will still give qualitative information useful in deteoting a spill and mapping its spatial extent.

Diffusion Travel Times

For any spill with volatile components, a vapor phase will e v o l v e a b o v e t h e d i s s o l v e d p h a s e a s it m i g r a t e s t h r o u g h ground-water. The maximum vapor Concentration will be given by Eq. (10) where C t is the concentration of dissolved organic material at t h e ground-water interface with the vadose zone. T h i s v a p o r w i l l m o v e u p w a r d t h r o u g h - t h e v a d o s e z o n e b y diffusion (reduced by dissolution and adsorption), b y possible microbial degradation, and by chemical transformations.

A qualitative measure of diffusion for a given chemical, called t h e characteristic d i f f u s i o n t i m e , t ~ , is t h e t i m e required for a n organic chemical with an effective diffuuion coefficient, DE, to diffuse through a distance L ( J u r y , et al., 1983) :

w h e r e D E is given b y Eq. (A.17) of the Appendix. Table 3.5 summarizes values of tD to diffuse L - l m , calculated b y using the procedures in the Appendix,

T h e v a l u e s i n T a b l e 3.5 a r e q u a l i t a t i v e but do allow com pounds t o be grouped into mobile and relatively immobile cat egories of vapor diffusion potential, Thus, for example, ethylene dichloride has a r e l a t i v e l y h i g h s a t u r a t e d v a p o r density (Table 3.4) but only a modest vapor mobility because so much of its total mass partitions into dissolved and adsorbed p h a s e s . C o n v e r s e l y , n - o c t a n e , w i t h e v e n l o w e r v a p o r density,moves much faster because of its low solubility.

Steady-State Diffusion Profiles

F o r t h o s e compounds with reasonably short diffusion times, t h e v a p o r concentration profile w i t h d e p t h s h o u l d r e a c h a

111

TABLE 3.40 SATURATED VAPOR DBNSITY, WATER 8OLUBILITY M D HSHW'S CONSTANT FOB VARIOUS VOLATILE M D 8RfIVOLAFILE ORGAMIC

S8tur8 ted v8p Wa t a r Eenry ' 8

Chemical -08 i t p S o l u b i l i t y Cone t8at Reference*

Benzene Bipheny 1 Carbon Te t r ach lo r ide Chlorobentene Cblor of om Chlotome thane DDT Die ldr in EPTC EDB Ethylene Ethylene Dichlor ide Lindane Methyl Bromide Napthalene Nitrobenzene N-Oc tane Phenol Tr i f l u r a l i n TCE Toluene 1 , 1 , 1-Trichloroe thane Vinyl Chloride

400

7 50 71 960

0 .49

1.2E4 6 . 03-6 1 .OE-4 0.22

4.7E4

1 .OE-3 2 .OE4 1.6 1.8

0.57 2 .OE-3

120

3 20

94

440 150

1.4E3 8.713

1 o8B3 7 05 8 .OE2 4.732 8.OE3

3 .OE-3 1. SE-1 3.732

5 04E3

3 m4E3 1 m3E2 8 oOE3 7 5E2 1 o3E4 3.2El 1.8E3 6 . 6E-1 8 . 2E4 0.3 1 .OE3 5.2E2

9 .OEl 9 e 5132

2200 600

9600 1 SO0 1200 22000

20 6.1 5 09 3 50

3600000 400 1.3

15000 500 1000

1400000 16 67

4400 3000

15000 970000

A A A A A B A A A A C C A A A A A A A C B C A

*A = Jury , e t el., (1984) B =Mackay, et al., (1982) c hOUl88 (1982)

112

TABLE 3.5. TIHE TO DIFFUSE L .I 1 m T H R O U G H A SOIL WITH 4-0.5, a-0.3, Dvair=4300 cm2/d

Benzene Biphenyl Carbon Tetrachloride Chlorobenzene Chloroform Chloromethane DDT Dieldrin EPTC EDB Ethyl ene Ethylene Dlchloride Lindane Methyl Bromide Napthalene Nitrobenzene N-Octane Phenol Tr 1 f 1 urali n Trichloroethylene Toluene l,l,l-Trichloroethane Vinyl Chloride

8.3~101 1 . 4x103 1 .5x102 2 . 9 ~ 1 0 ~ 3 . 9 ~ 1 0 ~ 2.4~105

2.8~102 4.4~101 8 . 5 ~ 1 0 ~ 2 . 9 ~ 1 0 ~ 1.3~103

1.3~103 7 . 1 ~ 1 0 ~ 6.8~103 2 . 7 ~ 1 0 ~ 7.3~103 9 . 8 ~ 1 0 ~ 1 .4x102

4 x 1 0 2

1.1x102

1.2~104

2.2x101

1x102

~- -

2.2x10-1 6 . 6 x 10'2 9.4~10'1 1.5~10'~

2.2 2x10'3 6.7~10'~ 5.9~10'~ 3.5~1 Oo2 3.6~102 4~10'~ 1.3~10'4

5x10'2

1 .4x102 7~10'~ 6.7~10'3 4.4~10'~ 3~10'~ 1.5 9 . 7 ~ 1 0 ~

1.2x10-1

1 a 5

1x10'3

129 51 00 45 292 121 16 2.9~107 4.2~1 O6 1.1~105 500 9.3 343 2 . 4 ~ 1 0 ~ 17 6.2~103 1.7~104 21 9.2~105 2.6~105 77 143 29 10

113

c h a r a c t e r i s t i c f i n a l v a l u e u n d e r certain circumstances (e.g., s t a t i o n a r y s o u r c e o f v a p o r , t i m e i n d e p e n d e n t b i o l o g i c a l a n d c h e m i c a l r e a c t i o n s , r e a s o n a b l y c o n s t a n t m o i s t u r e status over time). A h y p o t h e t i c a l b u t p l a u s i b l e c a s e o f i n t e r e s t t o e x a m i n e is t h e s t e a d y - s t a t e d i s t r i b u t i o n of gas concentration above a source of saturated vapor at the ground-water interface. I t w i l l a l s o b e a s s u m e d t h a t t h e c h e m i c a l u n d e r g o e s a f i r s t order decay process oharaoterlzed by a decay constant v .

For t h i s c a s e , a s s h o w n i n t h e Appendix, the steady-state gas concentration profile a s a function of depth is given by:

where

D v is t h e soil gas diffusion coefficient, and L is the depth t o ground-water. Profiles of concentration f o r v a r i o u s v a l u e s o f Q = q L a r e g i v e n i n F i g u r e 3.9. T h o s e c u r v e s w i t h l a r g e Q represent c o m p o u n d s w h o s e d i f f u s i o n t i m e t h r o u g h t h e s o i l is c o m p a r a b l e t o , or l a r g e r t h a n , t h e half-life of the chemical. Hence, the vapor concentrations drop to low values in the soil.

Vapor Monitoring a s a Detection Method

F r o m t h e p r e c e d i n g d i s c u s s i o n , s e v e r a l c h e m i c a l c h a r a c t e r i s t i c s m a y b e i d e n t i f i e d w h i c h i n d i c a t e w h e t h e r a c o n t a m i n a n t p l u m e w i l l b e a c c o m p a n i e d b y a m e a s u r a b l e v a p o r concentration. First, the chemical must h a v e a n o n - n e g l i g i b l e vapor p r e s s u r e and d e n s i t y a s part of the total concentration. .Thus, compounds with very low values of H e n r y ’ s c o n s t a n t K H or c o m p o u n d s w h i c h a d s o r b Strongly (large Kd) will be unlikely t o have a large vapor density i n soil. S e c o n d , t h e c o m p o u n d m u s t b e s u f f i c i e n t l y m o b i l e in t h e v a p o r p h a s e t o a l l o w v a p o r t o m i g r a t e s i g n i f i c a n t l y b e y o n d t h e s p i l l b o u n d a r i e s . T h e d i f f u s i o n t r a v e l t i m e s , g i v e n in T a b l e 3.5, a r e u s e f u l i n determining whether this criteria will be met. U l t i m a t e l y , t h e s a m e conditions which limit vapor density (small KH, large Koc) will cause large diffusion travel times.

Finally, the compound m u s t b e p e r s i s t e n t e n o u g h t o t r a v e l beyond t h e spill boundaries without degrading into a form which is n o t detectable. D e p e n d i n g o n t h e r e l a t i o n b e t w e e n t h e d i f f u s i o n t r a v e l t i m e and t h e c o m p o u n d half l i f e , t h e v a p o r pror‘ile will d r o p o f f g r a d u a l l y or s h a r p l y b e t w e e n t h e s p i l l and the soil surface, as in Figure 3.9.

114

.2

1 0 .2 .6

- Soil martaco

Vapor concontratlon C/Co

Figure 3.9. Steady r ta te vapor conceatratfon profiler between gtouaduater and the soil surface, for a compound underuoiag f irrt order dewadation. Dheasianleoo parameter Q=qL i s girea eq 15.

R E F E R E N C E S

1 .

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118

A P P E N D I X

MATHEMATICAL T H E O R Y OF DISSOLVED O R G A N I C C H E M I C A L TRANSPORT T H R O U G H S O I L

When a chemica l which 1s presen t a s a d i s s o l v e d c o n s t i t u e n t of s o i l s o l u t i o n is a l s o a d s o r b e d t o s o l i d s o i l m a t e r i a l and has a n o n - n e g l i g i b l e vapor p r e s s u r e , t h e t o t a l c o n c e n t r a t i o n CT ( p g cm-3) of t h e chemical i n u n i t s of mass p e r volume o f s o i l may be w r i t t e n a s

( A . 1 )

Ca ( p g 8'') is t h e mass adsorbed per mass of s o i l C g ( p g om131 is t h e mass d i s so lved per volume of s o l u t i o n C v ( p g c! 3 ) is t h e mass i n vapor per volume o f s o i l a i r

CI (cm3 cm-3) i s s o i l vo lumetr ic water conten t a (cm3 cm-3) is s o i l vo lumet r i c a i r con ten t

pb ( g cm 3 ) i s S o i l d r y b u l k d e n s i t y

Conservat ion o f Mass

The e q u a t i o n which r e p r e s e n t s conserva t ion of mass f o r t h e chemical , c a l l e d a c o n t i n u i t y e q u a t i o n , may be w r i t t e n a s (for one-dimensional f l o w )

( J u r y , e t a l . , 1983)

whare J,a ( v g cm1: d - l ) is t h e f l u x of d i s so lved chemical

and r ( u g cm-3 d ' l ) is a gene ra l r e a c t i o n term r e p r e s e n t i n g t h e n e t r a t e o f t r a n s f o r m a t i o n o f chemical t o another fo rm.

J s v ( p g cm d ' l ) i s t h e f l u x of chemical vapor

F l u x Equat ions

The o n e - d i m e n s i o n a l f l u x o f d i s s o l v e d c h e m i c a l t h r o u g h porous media is cus tomar i ly w r i t t e n

113

3 C L J s l - - D& + JwCL

( A . 3 )

where 3, (om d - l ) is t h e volume of s o l u t i o n and D l ( o m 2 d - l ) is a combined dlffuslon-di8pOrSiOn term r e p r e s e n t i n g t h e s p r e a d i n g o f c h e m i c a l b y m o l e o u l a r o o l l i s i o n s w i t h i n s o l u t i o n and by moving around s o i l s o l i d o b s t a c l e s . I n t h e f i e l d , d i s p e r s i o n is u s u a l l y more impor t an t than d i f f u s i o n .

The o n e - d i m e n s i o n a l f l u x o f chemica l vapor t h r o u g h s o i l , c a l l e d F ick ’ s Law, is u s u a l l y w r i t t e n a s

J~~ = - D ~ a c v / a z ( A . 4 )

where D V (cm2d-l) is t h e S o i l gaseous d i f f u s i o n c o e f f i c i e n t . A commonly used model f o r DV is t he Mi l l i ng ton -Qui rk model

, l O / q a i r DV’ DV

4 2 ( A . 5 )

where D g i r (cm*d’l) 1s t h e g a s e o u s d i f f u s i o n c o e f f i c i e n t of t h e chemical i n f r e e B i t . , and 4 1s s o i l po ros i ty . J u r y , e t a l . ( 1 9 8 3 1 , c o n c l u d e d t h a t t h e v a l u e D a i r = 4 3 0 0 ( c m 2 d - l ) s a t i s f a c t o r i l y d e s c r i b e d i n t e r m e d i a t e m o l e c u l a r w e i g h t compounds.

Phase Re la t ions

I t is common t o u s e s i m p l e e q u i l i b r i u m models t o d e s c r i b e r e l a t i o n s h i p s a m o n g C v , C f i e a n d C , i n a t h r e e p h a s e s o i l - w a t e r - a i r s y s t e m . T h e s i m p l e s t m o d e l t o d e s c r i b e adsorp t ion is the l i n e a r model.

ca - KdCE ( A . 6 )

where Kd ( cm3g- l ) is c a l l e d a d i s t r i b u t i o n c o e f f i c i e n t . T h i s l l n e a r r e l a t i o n s h i p has been s h o w n t o g i v e good a g r e e m e n t w i t h d a t a f o r chemica ls a t d i l u t e Concentrat ions (Kar ickhoff 1981). A t higher c o n c e n t r a t i o n s a nonl inear Freundl ich model

ca = K F c ~ ” ( A . 7 )

where K F a n d N a r e c o n s t a n t s 1 s f r e q u e n t l y b e t t e r t h a n t h e l i n e a r model a t d e s c r i b i n g d a t a (Rao and Davidson, 1 9 8 0 ) .

120

Because Kd is s o i l - s p e c i f i c and b e c a u s e o rgan ic chemica l s p r e d o m i n a n t l y a d s o r b t o s o i l o r g a n i c m a t t e r , a m o d i f i e d d i s t r i b u t i o n c o e f f i c i e n t pe r u n i t o r g a n i c ca rbon f r a c t i o n is a l s o u s e d t o d e s c r i b e t h e chemical a d s o r p t i o n a f f i n i t y

K O C - Kd’fOC ( A . 8 )

w h e r e K O C ( c m 3 g - l ) is a n o r g a n i c c a r b o n d i s t r i b u t i o n c o e f f i c i e n t and f o c is t h e s o i l o r g a n i c ca rbon f r a c t i o n . I n c a s e s where o n l y t h e o r g a n i c m a t t e r con ten t i o n is known, one may c o n v e r t a p p r o x i m a t e l y t o o r g a n i c c a r b o n f r a c t i o n foc b y u s i n g t h e e q u a t i o n

V a l u e s o f K O C v a r y l e s s t h a n Kd be tween 80118 f o r a g i v e n c h e m i c a l ( H a m a k e r and Thompson , 1 9 7 2 ) . T h u s , K O C is a p r e f e r a b l e b e n c h m a r k p r o p e r t y t o u s e t o r e p r e s e n t t h e a d s o r p t i o n p o t e n t i a l of a given compound.

T h e e q u i l i b r i u m r e l a t i o n s h i p be tween C V and C g is c a l l e d Henry’s Law

c V I K H C t ( A . 1 0 )

w h e r e K H ( d i m e n s i o n l e s s ) is c a l l e d H e n r y ’ s c o n s t a n t . S i n c e t h i s l i n e a r r e l a t i o n s h i p commonly p e r s i s t s t o s a t u r a t i o n , K H is u s u a l l y c a l c u l a t e d a s t h e r a t i o of s a t u r a t e d vapor d e n s i t y and water s o l u b i l i t y .

P a r t i t l o n C o e f f i c i e n t s

I t is u s e f u l t o e x p r e s s d i r e c t r e l a t i o n s h i p s between t h e t o t a l c o n c e n t r a t i o n and t h e c o n c e n t r a t i o n i n each p h a s e . T h i s is a c c o m p l i s h e d b y combining t h e c o n c e n t r a t i o n r e l a t i o n ( A . l ) w i t h t h e e q u i l i b r i u m r e l a t i o n s ( A . 6 ) and ( A . l O ) . T h u s , f o r t h e d i s s o l v e d phase

where

121

is called the liquid partition coeffioient (Jury, et al., 1983) . In practice, the third term aKH may be neglected in most casea. In addition, for strongly adsorbed ohemicals (large Kd), only the first term pbKd is nonnegligible. For the vapor phase,

where

is the vapor partition coefficient. For strongly adsorbing chemicals, only the first term pbKd/KH la nonnegligible.

The general transport equations above may be combined b y plugging t h e flux equation expressions ( A . 3 ) - ( A 0 4 ) into t h e continuity equation ( A . 2 ) and b y expressing all concentrations in terms o f the total concentration CT w h e n t h e p a r t i t i o n c o e f f i c i e n t d e f i n i t i o n s ( A . 1 2 ) and ( A . 1 4 ) are used. This results in the equation (assuming Uniform soil properties)

( A . 1 5 ) where

( A . 1 6 )

is the effective chemical convective velocity, and

is t h e e f f e c t i v e d i f f u s i o n - d i s p e r s i o n c o e f f i c i e n t . F o r volatile organic chemicals which have a high vapor density, the second term in e.g. A . 1 7 dominates the first if the soil air c o n t e n t i s h i g h a n d i f t h e w a t e r c a r r y i n g t h e d l s s o l v e d chemical is not moving rapidly through the soil. Thus, in this case,

( A . 1 8 )

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C o n v e r s e l y , i f t h e c h e m i o a l h a s 8 low vapor d e n s i t y o r i f t h e a i r p h a s e is n e g l i g i b l e ( f . e . , ground w a t e r f l o w ) , t h e n t h e f i r s t term dominate8 t h e second term and

Degradation Rates

T h e c o m b i n e d p r o c e s s e s o f b i o l o g i c a l a n d o h e m i c a l deg rada t ion of organio ahemica ls a r e extremely complex , and can depend on a v a r i e t y o f f a c t o r s s u c h a s i e m p e r a t u r e , o r g a n i c ma t t e r c o n t e n t , water c o n t e n t , and microbia l ' popu la t ion d e n s i t y . T h u s , t h e s p e c i f i c f o r m o f t h e r e a c t i o n t e r m r is o f t e n d i f f i c u l t t o i d e n t i f y i n a g i v e n s i t u a t i o n . F o r t h i s r e a a o n , s i m p l e i d e a l i z e d f o r m s a r e o f t e n used t o g i v e a p p r o x i m a t e e s t i m a t e s . The most common form 1s t h e f i r s t order d e g r a d a t i o n model

where p ( d ' l ) is a f i r s t o r d e r d e g r a d a t i o n r a t e c o e f f i c i e n t . I t is r e l a t e d t o t h e e f f e c t i v e h a l f l i f e T i 1 2 ( d ) o f t h e compound by t h e equa t ion

Steady S t a t e P r o f i l e s

If t h e compound is p r e s e n t a t s a t u r a t i o n l e v e l i n ground water and d i f f u s e s upward w h i l e unde rgo ing f i r s t o r d e r d e c a y , t h e p r o f i l e w i l l e v e n t u a l l y r e a c h a s t e a d y s t a t e va lue whose shape is descr ibed by t h e s t e a d y s t a t e f o r m of Eq. ( A . 1 5 ) w i t h V E = 0 and r - ~ C T , o r

( A . 2 2 )

w i t h C(L) - CO and C ( 0 ) - 0. The s o l u t i o n t o t h i s e q u a t i o n may be w r i t t e n a s

s i n h ( a 2 ) '(') co s i n h ( q L )

123

( A . 2 4 )

C H A P T E R 4

MEASUREMENT M E T H O D O L O G I E S

The f o l l o w i n g s e c t i o n s d i s c u s s s a m p l i n g and a n a l y t i c a l m e t h o d o l o g i e s f o r m o n i t o r i n g v o l a t i l e o r g a n i c s i n t h e s u b s u r f a c e . The s e c t i o n s a r e : Sampl ing Methods, Sampl ing Design, Q u a l i t y Assurance, and A n a l y t i c a l Methods.

SAMPLING METHODS

T h i s s e c t i o n p r e s e n t s v a r i o u s sampling methodologies u s e d t o monitor s u b s u r f a c e c o n t a m i n a t i o n . These methods i n c l u d e : h e a d s p a c e m e a s u r e m e n t s , g r o u n d p r o b e s , f l u x c h a m b e r m e a s u r e m e n t s , and s a m p l i n g w i t h s o r b e n t s ( u s u a l l y p a s s i v e sampl ing) .

The t e c h n i q u e s i d e n t i f i e d a r e capable of provid ing a yes or no answer t o whether s u b s u r f a c e hydrocarbon c o n t a m i n a t i o n i s p r e s e n t , H o w e v e r , t h e t e c h n i q u e s do n o t a l l p r o v i d e a n e q u i v a l e n t m e a s u r e m e n t . The g r o u n d p r o b e and h e a d s p a c e measurement t e c h n i q u e s measu re a s o i l g a s c o n c e n t r a t i o n , t h e f l u x chamber t e c h n i q u e m e a s u r e s a n e m i s s i o n r a t e , a n d t h e p a s s i v e sampl ing technique measures some func t ion of an average s o i l g a s c o n c e n t r a t i o n . The t e c h n i q u e ( s ) s e l e c t e d f o r a p a r t i c u l a r a p p l i c a t i o n w i l l be dependent on t h e o b j e c t i v e s of t h a t s t u d y .

A l l t h e t e c h n i q u e s can be d iv ided i n t o two s t e p s , sample c o l l e c t i o n and a n a l y s i s . A n a l y t i c a l i n s t r u m e n t a t i o n f o r h y d r o c a r b o n a n a l y s i s i s c o m m e r c l a l l y a v a i l a b l e b u t i s r e l a t i v e l y complex and e x p e n s i v e . The s a m p l e c o l l e c t i o n equ ipmen t d i s c u s s e d i s n o t g e n e r a l l y commerc ia l ly a v a i l a b l e , b u t is usua l ly s imple t o c o n s t r u c t and o p e r a t e , however some of t h e equipment descr ibed i s p r o t e c t e d b y p a t e n t ,

V a r i o u s t e c h n i q u e s h a v e b e e n s u c c e s s f u l l y u s e d f o r ground-water contaminat ion i n v e s t i g a t i o n s a t a v a r i e t y of s i t e s . H o w e v e r , t h e t e c h n i q u e s d i s c u s s e d be low a r e n o t s t a n d a r d methods and have n o t yet been adequa te ly eva lua ted . T h e r e f o r e , b e s t r e s u l t s w i l l be o b t a i n e d when t h e t echniques a r e used b y e x p e r i e n c e d i n v e s t i g a t o r s who a r e f a m i l i a r w i t h t h e me thods used a n d t h e l o c a l geo logy and h y d r o l o g y . A l l t h e t echn iques a r e dependent on t h e movement of v o l a t i l i z e d o rgan ic s p e c i e s u p

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t h r o u g h t h e o v e r l y i n g s o i l . Any l i m i t a t i o n s of t h i s t r a n s p o r t w i l l l i m i t t h e u t i l i t y of t hese t e c h n i q u e s . The s u i t a b i l i t y of e a c h t e c h n i q u e f o r v a r i o u s t y p e s o f s i t e o o n d l t i o n s is d i s c u s s e d and compared i n t h i s s e c t i o n .

Headspace Measurements

T h i s s e c t i o n d i s c u s s e s t h e d e t e r m i n a t i o n of hydroca rbon c o n c e n t r a t i o n s b y a n a l y z i n g t h e h e a d s p a c e g a s f r o m s a m p l e s c o l l e c t e d i n a d r y w e l l or from s o i l c o r e s .

Headspace Measurements i n D r y Wells-- Sampl ing t h e headspace i n e x i s t i n g s u b s u r f a c e s t r u c t u r e s

is a ' s i m p l e t e c h n i q u e t h a t c a n y i e l d v a l u a b l e p r e l i m i n a r y i n f o r m a t i o n . The t e c h n i q u e i n v o l v e s c o l l e c t i n g g r a b s a m p l e s or u s i n g a p o r t a b l e h y d r o c a r b o n a n a l y z e r t o measure t h e headspace c o n c e n t r a t i o n i n m o n i t a r i n g w e l l s , s t o r m s e w e r s , u t i l i t y v a u l t s , or o t h e r s u b s u r f a c e s t r u c t u r e s . The r e s u l t s o b t a i n e d p rov ide i n f o r m a t i o n r e g a r d i n g t h e c o m p o s i t i o n and e x t e n t o f a n y c o n t a m i n a n t p l u m e and a s s i s t i n d e v e l o p i n g an o p t i m a l s a m p l i n g s t r a t egy for s ubsequent i nves t 1 g a t i ve work .

R e c o m m e n d e d u s e - - I t i s r e c o m m e n d e d t h a t h e a d s p a c e measurements be made a t e x i s t i n g s u b s u r f a c e s t r u c t u r e s a 3 t h e f i r s t p h a s e of any s u b s u r f a c e c o n t a m i n a t i o n i n v e s t i g a t i o n . T h e t e c h n i q u e is q u i c k , s i m p l e , and e c o n o m i c a l . F u r t h e r m o r e , i t c a n s a v e s u b s t a n t i a l amoun t s o f t i m e a n d money b y p r o v i d i n g i n p u t d a t a f o r s e l e c t i o n of an a p p r o p r i a t e s ampl ing s t r a t e g y .

T e c h n i q u e a p p l i c a t i o n s - - H e a d a p a c e ---- s a m p l i n g 13 t y p i c a l l y employed a s p a r t of' any R e m e d i a l I n v e s t i g a t i o n / F e a 3 i b i l i t y S t u d y ( R I F S ) . One example i s g i v e n below.

A t a n k e r t r u c k s p i l l c a u s e d 5 , 5 0 0 g a l l o n s of J e t f u e l t o c o n t a m i n a t e an a r e a of h i g h g r o u n d - w a t e r . A p r e l i m i n a r y s t u d y i n s t a l l e d g r o u n d - w a t e r m o n i t o r i n g wel ls a l o n g two p e r p e n d i c u l a r lines. A s u b s e q u e n t s t u d y was under t a k e n t o d e v e l o p s a m p l i n g m e t h o d s a n d t o d e f i n e t h e c o n t a m i n a n t p l u m e ( R a d i a n C o r p o r a t i o n , 1 9 8 4 ) . T h e f i r s t s t a g e o f s a m p l i n g i n v o l v e d r e m o v i n g t h e w e l l c a p s and c o l l e c t i n g headspace samples i n g a s s y r i n g e s f o r o n - s i t e g a s c h r o m a t o g r a p h / f l a m e i o n i z a t i o n d e t e c t o r ( C C I F I D ) a n a l y s i s . A d d i t i o n a l measurements were made b y u s i n g a p o r t a b l e toLa l hydroca rbon a n a l y z e r . The r e s u l t s o f t h e h e a d s p a c e a n a l y s e s i n d i c a t e d t h a t t h e plume had i n c r e a ? e d i n a r e a s i n c e t h e i n i t i a l s t u d y . T h e r e f o r e , t h e g r i d d e d s a r n p l i n a a rc !a w a s expdnded a c c o r d i n g l y , p r i o r t o an i n t e n s i v e , f o 1 1 ow- u p i n v e s 1; 1 g a t i on .

I , i m i t , t l o n s - . ' ! 'he l i m i t a t i o n s a s s o c i a t e d w i t h t h i s ------- ---. s a n 1 ~ 1 i n g t e c h n i q u e i n c l u d e :

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o i n t e r f e r e n c e s ( e . g . , methane i n s e w e r s ) ;

o s u b s u r f a c e s t r u c t u r e s or w e l l s a r e n o t always p re sen t a t i n v e s t i g a t i o n s i t e s (or not o p t i m a l l y l o c a t e d ) ;

o v o l a t i l e h y d r o c a r b o n s p e c i e s c a n d i f f u s e o u t o f unsealed s u b s u r f a c e s t r u c t u r e s ; and

o n e g a t i v e t e s t r e s u l t s a r e i n c o n c l u s i v e , i . e . , t h e a b s e n c e o f h y d r o c a r b o n s i n t h e h e a d s p a c e o f a s u b s u r f a c e s t r u c t u r e d o e s n o t g u a r a n t e e t h a t hydrocarbons a r e no t p re sen t i n t h e su r round ing s o i l .

Headspace Measurements of S o i l Cores-- The headspace gas or e x t r a c t e d S o l i d s of a s o i l c o r e can

be a n a l y z e d t o de te rmine hydrocarbon c o n c e n t r a t i o n s . To o b t a i n a sample, a technique known a s g r a b s a m p l i n g can be u s e d . An w u n d i s t u r b e d w s o i l c o r e is c o l l e c t e d b y u s i n g a n auger or by d r i v i n g a t ube i n t o t h e g r o u n d and is t h e n s e a l e d i n a sample c o n t a i n e r . Using t h i s t e c h n i q u e , l i q u i d a s w e l l a s g a s e o u s h y d r o c a r b o n c o n t a m i n a t i o n c a n be d e t e c t e d d i r e c t l y . Two a p p r o a c h e s can be t a k e n . F i r s t , t h e sample c o n t a i n e r can be ha l f f i l l e d w i t h s o i l . Hydroca rbons can t h e n v o l a t i l i z e i n t o t h e v a c a n t headspace. Care should be taken t o e n s u r e headspace and s o i l w i t h o u t p r o v i d i n g any h e a d s p a c e . S o i l g a s is t h e n e x t r a c t e d d i r e c t l y from s o i l pores .

Recommended use--This method of measuring hydrocarbons is recommended when t h e s a m p l i n g c rew h a s a m o d e s t l e v e l o f t e c h n i c a l e x p e r t i s e or when s o p h i s t i c a t e d sampling equipment is e i t h e r not a v a i l a b l e or n o t c o s t - e f f e c t i v e . The method w o r k s b e s t when s a m p l i n g s a n d y s o i l s c o n t a i n i n g l i t t l e o r g a n i c ma t t e r .

The t e c h n i q u e of grab-sampling of s o i l c o r e s is t y p i c a l l y bo th s i m p l e and q u i c k t o p e r f o r m . M i n i m a l l y , t h e method r e q u i r e s o n l y one p e r s o n , one hand a u g e r , and sample s t o r a g e c o n t a i n e r s . A n a l y s e s c a n be performed o f f s i t e a t a l a t e r d a t e .

Techn ique a p p l i c a t i o n s - - C r a b s a m p l i n g of s o i l co res can be accomplished u s i n g a v a r i e t y of equipment a s i l l u s t r a t e d b y t h e r e c e n t r e v i e w f rom t h e U.S. E P A ( 1 9 8 4 ) . The r e v i e w is s ~ m n a r i z e d i n Table 4 . 1 . A number of r e s e a r c h e r s have a p p l i e d t h i s t e c h n i q u e t o d e t e c t i n g hydrocarbon S o i l gases a t va r ious s u b s u r f a c e l e v e l s . I n mos t c a s e s , s h a l l o w s o i l g a s s e s were c o l l e c t e d t o a s s e s s v e r y d e e p s o u r c e s o f v a p o r s , Var i e ty is evident i n sampling d e p t h , c o l l e c t i o n e q u i p m e n t , s t o r a g e , and a n a l y t i c a l methods.

127

t 3 r @

a

a

1 Y P .

I)

t c i . a . c)

126

t f I Y

L

0 . w

i

i c c .

For e x a m p l e , H o r v i t z ( 1 9 5 4 ) r e p o r t e d u s i n g a hand a u g e r o r d r i l l i n g equipment t o s e a r c h f o r o i l a n d g a s . S a m p l e s w e r e c o l l e c t e d a t 8 t o 12 f o o t d e p t h 8 a n d b r o u g h t t o t h e s u r f a c e . The s a m p l e s w e r e s t o r e d i n g l a s s j a r s or c a n s , a n d w e r e l a t e r a n a l y z e d b y u s i n g a vacuum a n a l y t i c a l - c o m b u s t i o n t e c h n i q u e . I n a n o t h e r s t u d y , H o r v i t z (1954) u s e d a p i s t o n - t y p e c o r i n g d e v i c e t o c o l l e c t s h a l l o w s o i l s amples d u r i n g o f f s h o r e o i l and g a s p r o s p e c t i n g a c t i v i t i e s . F o r t h i s s t u d y , s a m p l e s w e r e s t o r e d i n p l a s t i c b a g s ( w i t h a r e p o r t e d s h e l f - l i f e o f s e v e r a l m o n t h s ) , a n d t h e n e x t r a c t e d s a m p l e s w e r e a n a l y z e d b y u s i n g g a s c h r o m a t o g r a p h y (GC). H o r v i t z n o t e d t h a t o n s h o r e samples need t o b e c o l l e c t e d a t a d e p t h g r e a t e r t h a n 6 f e e t t o e n s u r e a q u a l i t y s a m p l e w h e r e a s s h a i l o w e r d e p t h s w e r e s u f f i c i e n t f o r o f f s h o r e sample c o l l e c t i o n .

D e v i n e and S e a r s (1977) c o l l e c t e d and a n a l y z e d o v e r 1,000 c o r e s i n a s e a r c h f o r o i l a n d g a s d e p o s i t s i n A u s t r a l i a . S a m p l e s w e r e c o l l e c t e d b y m e c h a n i c a l l y d r i l l i n g t o a 9 t o 10 - foo t dep th and t h e n b y i n s e r t i n g a c o r i n g d e v i c e . S a m p l e s w e r e s t o r e d i n h e a t - s e a l e d p o l y e t h y l e n e b a g s . S a m p l e p r e p a r a t i o n f o r a n a l y s i s b y G C i n c l u d e d a c i d l e a c h i n g a n d c r y o g e n i c a l l y t r a p p i n g t h e h y d r o c a r b o n s .

S m i t h and E l l i s (1963) a 1 3 0 c o l l e c t e d s o i l c o r e s ( 0 - 4 0 f o o t d e p t h ) i n c a n s s o l d e r e d t o s e a l i n t h e s a m p l e . For C C a n a l y s i s , t h e headspace g a s was removed from t h e c a n s th rough a h o l e i n t h e t o p b y u s i n g a g l a s s s y r i n g e . T h e y c o n d u c t e d s t u d i e s c o n c e r n i n g t h e e f f e c t o f r e f r i g e r a t e d v e r s u s n o n - r e f r i g e r a t e d s a m p l e s t o r a g e . T h e i r r e s u l t s i n d i c a t e d t h a t h y d r o c a r b o n c o n c e n t r a t l o n s d e c r e a s e d i n s a m p l e 3 s t o r e d a t 68-95OF v e r s u s r e f r i g e r a t e d s a m p l e s s t o r e d a t 3 2 O F o r p a s t e u r i z e d samples ( exposed t o 185OF f o r s h o r t p e r i o d s ) . T h e y a l s o c a n c l u d e d t h a t t h e o r g a n i c c o n t e n t i n s o i l s a m p l e s may i n t e r f e r e w i t h h y d r o c a r b o n d e t e c t i o n f r o m u n d e r l y i n g o i l and g a s d e p o s i t s . However, H o r v i t z (1972) r e f u t e d t h i s c o n c l u s i o n when he r e p o r t e d t h a t g r a s s and r o o t s c o n t r i b u t e n e g l i g i b l e amounts of s a t u r a t e d h y d r o c a r b o n s t o t h e soil a t m o s p h e r e . I n a d d i t i o n , H o r v i t z d i s a g r e e d w i t h t h e n e e d f o r s a m p l e r e f r i g e r a t i o n b y s t a t i n g t h a t m i n i m a l h e a d s p a c e a b o v e t h e sample was t h e key t o a l o n g s h e l f - l i f e .

I n o t h e r o i l a n d g a s e x p l o r a t i o n e f f o r t s , P o g o r s k i and Q u i r t ( 1 9 8 1 ) c o l l e c t e d soil samples a t a 2 f o o t d e p t h b y u s i n g h a n d o r power a u g e r s . I n s t e a d o f u s i n g p l a s t i c b a g s f o r s t o r a g e , t h e y u s e d s p e c i a l l y d e s i g n e d a l u m i n u m c a n s . T h e s a m p l e s w e r e s e a l e d i n t h e a i r - t i g h t c a n s and l a t e r w e r e a n a l y z e d b y G C . S i m i l a r m e t h o d o l o g i e s h a v e b e e n u s e d b y s e v e r a l o i l a n d g a s e x p l o r a t i o n companies ( E k l u n d , 1985).

L i m i t a t i o n s - - T h e p r i m a r y l i m i t a t i o n of t h i s t e c h n i q u e 1 3 t h a t i t fs b e t t e r s u i t e d f o r m e a s u r i n g adso rbed o r g a n i c s r a t h e r

129

t h a n f r e e o r g a n i c s i n t h e i n t e r s t i t i a l p o r e s p a c e s . Hanisch and McDevitt ( 1 9 8 4 ) r e p o r t e d t h a t any h e a d s p a c e p r e s e n t i n t h e s a m p l e c o n t a i n e r w i l l l e a d t o d e s o r p t i o n of o r g a n i c s from t h e s o i l p a r t i c l e s . U n l e s s t h e s o i l t y p e , h e a d s p a c e v o l u m e , t e m p e r a t u r e , sample h a n d l i n g t e c h n i q u e s , and s t o r a g e time are h e l d c o n s t a n t , r e l a t i v e c o n o e n t r a t l o n l e v e l s b e t w e e n s o i l samples a r e not comparable.

Ano the r l i m i t a t i o n t o t h i s technique is t h e p o s s i b l e l o s s of v o l a t i l e h y d r o c a r b o n s w h e n t h e s ample f a removed f rom t h e g r o u n d or t r a n s f e r r e d f o r a n a l y s i s . Sample e x p o s u r e t o t h e atmosphere h a s been s u c c e s s f u l l y a v o i d e d b y c a p p i n g t h e s a i l c o r e t u b e s . Bednas and R u s s e l l ( 1 9 6 7 ) c a p p e d t u b e s w i t h s e a l i n g wax and r e p o r t e d a s h e l f - l i f e of a t l e a s t 1 2 months . T h e i r work involved d e t e c t i n g n a t u r a l gas l e a k s b y t r e n c h i n g t o t h e d e s i r e d sampling depth and b y d r i v i n g t u b e s ( 2 6 i n x 2 i n ) i n t o t h e t r e n c h w a l l s . A c a r r i e r g a s was used t o f l u s h s o i l gas from t h e samples t o a G C a n a l y z e r . Han i sch and McDev i t t ( 1 9 8 4 ) r e p o r t e d a t e c h n i q u e u s e d a t s e v e r a l h a z a r d o u s w a s t e s i t e s . The c o r e sample r used ( s e e F i g u r e 4 . 1 ) c o n s i s t s of a b r a s s c o r e s l e e v e w h i c h i s p r e s s e d i n t o t h e s o i l t o a s u f f i c i e n t d e p t h t o f i l l t h e s a m p l e r b u t n o t s o d e e p a s t o compress t h e sample. The method works b e s t for c l a y s and s i l t s of medium mois ture conten t . A f t e r e x c e s s s o i l is removed, t h e s l e e v e i s s e a l e d w i t h a T e f l o n - l i n e d c a p . The s a m p l e s a r e s t o r e d a t room tempera ture . Headspace ( i . e . , p o r e s p a c e ) g a s c o l l e c t e d b y a sy r inge through a p o r t a r e analyzed b y G C .

I n a d d i t i o n t o loss of v o l a t i l e hydrocarbons, d e g r a d a t i o n of o r g a n i c compounds may a l s o o c c u r b e c a u s e o f t i m e d e l a y between c o l l e c t i o n and a n a l y s i s . T h i s c o l l e c t i o n method i s no t a p p r o p r i a t e f o r rocky s o i l s n o r i s i t w e l l s u i t e d for l o o s e s a n d y s o i l s t h a t may n o t b e a d e q u a t e l y h e l d i n t h e t u b e sampler . Sample r e t a i n i n g r i n g s can be used w i t h some s a m p l e r s t o r e t a i n coa r se samples.

Driven Probes

For t h e d r i v e n g r o u n d - p r o b e t e c h n i q u e , a d r i v e t i p i s a t t a c h e d t o a ground probe which i s then forced i n t o t h e ground. T h i s m i n i m i z e s d i s t u r b a n c e o f t h e s a m p l i n g e n v i r o n m e n t . Openings i n t h e tube near t h e l e a d i n g edge a l l o w s o i l g a s e s t o e n t e r t h e t u b e . Sample g a s i s e x t r a c t e d from a p o r t a t t h e u p p e r end of t he tube u s i n g a g a s - t i g h t s y r i n g e . A n a l y s i s is performed b y u s i n g G C .

An i m p r o v e m e n t t o t h e g r o u n d - p r o b e t e c h n i q u e i s t o min imize t h e i n t e r n a l volume of t h e s a m p l e r . T h i s means a : . ~ T . 3 : ? l a ~ - sample volume is n e c e s s a r y t o purge t h e sys tem, and, c o n s e q u e n t l y , a more r e p r e s e n t a t i v e s a m p l e i s o b t a i n e d .

130

TEfCOW R I N O

T E f L O N C A P L I W I R W A I H E R

Figure 4.1. S o i l core rrrple oleeor (Ernioch and McDeritt, 1984)

131

A p p l i c a t i o n s o f s m a l l - v o l u m e , d r i v e n g r o u n d p r o b e s a r e presented i n a l a t e r s e c t i o n .

Recommended Use-- The ground p r o b e t e c h n i q u e has been s u c c e s s f u l l y used a t

a v a r i e t y of s a m p l e s i t e s . For g r o u n d - w a t e r c o n t a m i n a t i o n i n v e s t i g a t i o n s , s m a l l - v o l u m e , d r i v e a b l e g r o u n d p r o b e s a r e p r e f e r r e d , a 1 though l a r g e r - v o l u m e p r o b e s have b e e n u s e d w i t h good r e s u l t s . The g r o u n d - p r o b e t e c h n i q u e i s w e l l - s u i t e d f o r ground-water i n v e s t i g a t i o n s e x c e p t i n t h e p r e s e n c e of wet o r c l a y e y s o i l s or n e a r s u r f a c e r o c k s t r a t a . I n a d d i t i o n , t h i s t echn lque has been a c c u r a t e l y used t o map p lumes . I n g e n e r a l , t h e g round-p robe t e c h n i q u e is r e l a t i v e l y S e n s i t i v e and can be used t o measure s u b s u r f a c e g a s c o n c e n t r a t i o n s w h i l e a v o i d i n g s u r f a c e i n t e r f e r e n c e s . D r i v e n ground p r o b e s a l s o o f f e r t h e user t h e a b i l i t y t o sample below impermeable s o i l and t o mod i fy t h e sampling depth t o i n c r e a s e s e n s i t i v i t y ,

Technique App l i ca t ions - - A p p l i c a t i o n s r e p o r t e d i n t h e l i t e r a t u r e f o r b o t h

large-volume ground p robes and smal l -volume g r o u n d p r o b e s a r e p r e s e n t e d i n t h i s s e c t i o n . The i n t e r n a l volume of t h e ground p r o b e s i g n f f l c a n t l y a f f e c t s t h e measurement p r o c e s s and t h e u t i l i t y of t h e r e s u l t i n g d a t a . The s m a l l i n t e r n a l volume g round p r o b e s can be used t o a t t e m p t t o m e a s u r e t h e " t r u e n s o i l - g a s c o n c e n t r a t i o n . The s m a l l volume p e r m i t s t h e a i r i n s i d e t h e probe t o be purged and a s m a l l ( e . g . , 1 m L ) sample t o be c o l l e c t e d w i t h o u t s u b s t a n t i a l l y a l t e r i n g t h e e q u i l i b r i u m of t h e s o i l - g a s c o n c e n t r a t i o n . A l t e r n a t i v e l y , t h e u s e o f l a r g e i n t e r n a l vo lume g r o u n d - p r o b e t y p i c a l l y i n v o l v e s s a m p l i n g s e v e r a ; l i t e r s of soil g a s . T h i s s ampl ing may n o t p e r m i t a " r e p r e S e n t a t i v e " s o i l - g a s s a m p l e t o be c o l l e c t e d u n d e r most c o n d i t i o n s b u t a l l ows f o r t h e soil gas t o be c o n c e n t r a t e d p r i o r t o . a n a l y s i s or m u l t i p l e a l l q u o t s t o be e x t r a c t e d , The l a r g e - v o l u m e g r o u n d p r o b e s a r e t y p i c a l l y u s e d f o r i n v e s t i g a t i o n s t h a t s e e k t o d e t e r m i n e r e l a t i v e s o i l g a s c o n c e n t r a t i o n s or t h a t a r e c o n c e r n e d w i t h w h e t h e r o r n o t contaminat ion a f f e c t s a given a r e a .

Large-Volume Ground Probes-- Ground p r o b e s h a v e b e e n w i d e l y u s e d . F o r e x a m p l e ,

Russe l l a n d Appleyard (1915) used a 2 f o o t long p r o b e (shown i n F i g u r e 4 . 2 ) which was hammered i n t o t h e soil t o t h e d e s i r e d d e p t h , a n d then t h e i n n e r r o d was pushed down a n o t h e r 1 / 4 i n . N e g l i e and F a v r e t t o ( 1 9 6 2 ) used a s i m i l a r d e s i g n ( s e e F igu re 4 . 3 ) a n d procedure excep t t h a t t h e o u t e r tube was r a i s e d 0 . 7 t o 1 . 0 f o o t a f t e r p l a c e m e n t t o p r o v i d e a pathway f o r s o i l gas t o e n t e r t h e s a m p l e . T h e y d e t e c t e d maximum h y d r o c a r b o n c o i t c e n t r a t l c n s i n t h e s o i l g a s immediately a f t e r i n s e r t i n g t h e p r o b e . : lowever , N e g l i e and F a v r e t t o c o n c l u d e d t h a t g r a b s a m p l i n g o f s o i l c o r e s p r o v i d e d b e t t e r r e s u l t s t h a n t h e i r

132

Figure 4.2. Ground-probe d r r i g n w e d by Rurre11 and Appleyard (1915).

133

Pipre 4.3. Crouod-probe derign ured by Neg1i8 aod ?avretto (1962)

134

t e c h n i q u e . T a c k e t t ( 1 9 6 8 ) u s e d a p r o b e w i t h a s l i g h t l y d i f f e r e n t d e s i g n t o a v o i d p l u g g i n g t h e s a m p l i n g p o r t d u r i n g i n s e r t i o n . A s l o t was c u t i n t h e s i d e n e a r t h e t i p t o a l low s o i l gas t o be pul led i n t o t h e probe ( s e e F igure 4 . 4 ) . DeCamargo ( 1 9 7 4 ) m o d i f i e d T a c k e t t ' s d e s i g n s o t h a t s a m p l e s c o u l d be c o l l e c t e d i n g l a s s ampules which could t h e n be s e a l e d and s t o r e d f o r l a t e r a n a l y s i s .

O t h e r r e s e a r c h e r s have used d r i v e n probes w i t h p e r f o r a t e d e n d s t o m e a s u r e l a n d f i l l g a s e s ( T h o r b u r n , e t a l . , 1 9 7 9 ; C o l e n u t t , e t a l . , 1 9 8 0 ) , carbon d i o x i d e and oxygen ( L o v e l l , e t a l . , 1 9 8 0 ) and t o d e t e c t hydrocarbon s p i l l s ( S p i t t l e r , e t a l . , 1 9 8 5 ) . For example , Thorburn , e t a l . ( 1 L i 9 ) , sampled l a n d f i l l gases b y u s i n g a probe i n w h i c h a po in t ed rod was p l a c e d i n s i d e t h e t u b e d u r i n g p r o b e i n s e r t i o n and was t h e n removed b e f o r e sampling ( s e e F igure 4 . 5 ) .

T r a c e r R e s e a r c h C o r p o r a t i o n ( T R C ) h a s u s e d h o l l o w , p e r f o r a t e d m e t a l p r o b e s f o r a number of S i t 8 i n v e s t i g a t i o n s w i t h p o t e n t i a l l y c o n t a m i n a t e d g r o u n d - w a t e r ( L a p a l l a , e t a l . , 1 9 8 4 ; Marr in , e t a l . , 1 9 8 4 ) . For d e p t h s o f l e s s t h a n 1 0 f e e t , p r o b e s a r e d r i v e n t o t h e d e s i r e d sampl ing d e p t h s , For depths g r e a t e r t han 10 f e e t , t h e p r o b e 1s d r i v e n ahead o f t h e bot tom o f a h o l l o w stem auger t h a t has been advanced t o j u s t above t h e d e s i r e d dep th . S o i l gas is pumped from t h e s a m p l i n g l o c a t i o n a t a r a t e of 0 . 5 t o 0 . 8 g a l l m i n f o r s e v e r a l m i n u t e s . Then a s y r i n g e i s u s e d t o c o l l e c t s a m p l e s f o r G C a n a l y s i s . O t h e r s ( L o v e l l , e t a l . , 1 9 8 0 ; Walther , e t a l . , 1 9 8 3 ) have r e p o r t e d use of t h i s method.

T r a c e r R e s e a r c h C o r p o r a t i o n ( L a p a l l a , e t a l . , 1 9 8 4 , Marr in , e t a l . , 1 9 8 4 ) has documented sampling r e s u l t s f rom o v e r 1 2 s i t e s w i t h v a r y i n g s i t e c o n d i t i o n s such a s g round-wa te r depth of 10 t o 1 2 5 f e e t , v a r y i n g c l a y and m o i s t u r e 1 . eve l s i n t h e s o i l , and d i f f e r e n t o r g a n i c con taminan t s p r e s e n t . Tracer C o r p o r a t i o n f o u n d t h a t t h i s t e c h n i q u e d e t e c t e d o r g a n i c compounds i n a l m o s t a l l s i t u a t i o n s , even above one s i t e w i t h a 30 f o o t c a l i c h e l a y e r o v e r l y i n g t h e g round-wa te r t a b l e . The t e c h n i q u e c o u l d be u s e d t o map known p l u m e s a c c u r a t e l y ; however, i t i s n o t s u i t a b l e f o r w e t , c l a y e y s o i l s or where an u n c o n t a m i n a t e d a q u i f e r o v e r l i e s one t h a t is p o l l u t e d , Sampling r e s u l t s f r o m t h e s o i l g a s a n d t h e p o l l u t e d g r o u n d - w a t e r c o r r e l a t e d w e l l even w i t h r e p e a t s a m p l e s on s u c c e s s i v e days , T R C ( L a p a l l a , e t a l . , 1 9 8 4 ; Marrin, e t a l . , 1 9 8 4 ) h a s r e p o r t e d t h a t g a s o l i n e v a p o r s i n s o i l a c t d i f f e r e n t l y than c h l o r i n a t e d o r g a n i c v a p o r s . Mar r in ( 1 9 8 5 ) r e p o r t s t h a t t h e T R C g r o u n d p r o b e s can be used t o map g a s o l i n e plumes a t s i t e s where t h e water t a b l e i s r e l a t i v e l y sha l low or where probes can be d r i v e n b e l o w t h e o x i d a t i o n zone i n s o i l s . Petroleum hydrocarbons a r e o f t e n a b s e n t f r o m t h e s h a l l o w s o i l g a s o v e r l y i n g g a s o l i n e - p o l l u t e d g r o u n d - w a t e r ; t h i s i s b e l i e v e d t o b e d u e t o

135

U E P T U M

IPE UNION

Figure 4.4. Crouod-probe design wed by Tackkett (1968).

136

BAMPLINQ OF Q A 8 E 8 F R O M LANDFILL

--+I DIAMETER 0.2 IN.

SAMPLINQ TUBE

(ALUMINUM)

S T E E L R O D

-r 2 IN.

I

8 .7 FT.

Figure 4 . 5 . G r o u n d - p r o b e d e s i g n u s e d by Thorburn, e t a l . (1979) .

137

S i o d e g r 3 c l a t d o n O F t h e g a s o l i n e v a p o r s l m t h e n e a r - s u r f a c e s o i l l a y e r s .

S e v e r a l r e s e a r c h e r s h a v e u s e d n o v e l g r ~ u n d - , p r o b e v a r i a t i o n s . F o r e x a m p l e , J o n e s a n d D r o z d ( 1 9 8 3 ) s e a r c h e d f o r o i i a n d g a s d e p o s i t s b y a u g e r i n g a h o l e t o a 1 3 f o o t d e p t h , i n s e r t i n g a n i n f l a t a b l e r u b b e r p a c k e r ( p r o b e ) t o i s o l a t e t h e b o t t o m o f t h e h o l e , a n d t h e n p u m p i n g s o i l gas t o a p o r t a b l e G C f o r a n a l y s i s . T h e y a l s o s a m p l e d a t s h a l l o w e r d e p t h s ( 1 t o 2 f e e t ) a n d d e t e c t e d more h i g h m o l e c u l a r w e i g h t c o m p o u n d s . T h e y r e p o r t e d t h a t t h e d e e p e r s a m p l i n g d e p t h s p r o v i d e d more r e l i a b l e r e s u l t s ( S c h m i d t , 1 9 8 5 ) . O t h e r r e s e a r c h e r s h a v e u s e d s i m i l a r t e c h n i q u e s . F o r e x a m p l e , L o v e l l , e t a l . ( 1 9 8 0 1 , u s e d t h e e q u i p m e n t s h o w n i n F i g u r e 4 . 6 . S w a l l o w ' s ( E k l u n d , 1 9 8 5 ) t e c h n ' i q u e was s i m i l a r e x c e p t t h a t t h e v o i d v o l u m e o f t h e s a m p l e r was m u c h l a r g e r . As s e e n i n F i g u r e 4 . 7 , t h e s ample r was a p l u g g e d c o r e h o l e . S p i t t l e r a n d C l i f f o r d ( 1 9 8 5 ) u s e d a m e t h o d s i m i l a r t o S w a l l o w ' s . A h o l e was a u g e r e d t o a d e p t h of 1 2 - 1 8 i n . T h e h o l e was c a p p e d , a n d a p r o b e c o n s t r u c t e d o f p l u m b i n g f i t t i n g s was i n s e r t e d i n t o t h e h o l e . A p p r o x i m a t e l y 0 . 0 0 3 5 f t 3 / m i n of soil g a s was r e m o v e d f o r 4 . 6 m i n u t e s u n t i l t h e s o i l - g a s c o n c e n t r a t i o n became c o n s t a n t . A n a l y s i s was p e r f o r m e d i n t h e f i e l d b y u s i n g a p o r t a b l e C C .

P o g o r s k i a n d Q u i r t ( 1 9 8 1 ) m a n u a l l y c o l l e c t e d h e l i u m g a s s a m p l e s b y u s i n g a n a p p a r a t u s d e s c r i b e d a s a l o w - d e a d - v o l u m e , n o n c l o g g i n g s t e e l p r o b e . T h e a p p a r a t u s i s a t y p e o f a u g e r w h i c h a l l o w s s a m p l e g a s e s t o b e p u m p e d f r o m t h e b o t t o m . V a n B a v e l ( 1 9 6 5 ) h a s d e s c r i b e d s a m p l i n g s o i l g a s e s b y i n s e r t i n g t h e n e e d l e o f t h e s a m p l i n g s y r i n g e t o t h e d e s i r e d d e p t h . T h o u g h e x c e e d i n g l y s i m p l e , t h i s t e c h n i q u e h a s o b v i o u s l i m i t a t i o n s .

S m a l l - V o l u m e G r o u n d P r o b e s - - . As m e n t i o n e d p r e v i o u s l y , s m a l l - v o l u m e p r o b e s a r e

b e l i e v e d t o be a d v a n t a g e o u s I n o b t a i n i n g a more r e p r e s e n t a t i v e s a m p l e . U s e of t h i s t y p e of p r o b e h a s b e e n r e p o r t e d b y s e v e r a l r e s e a r c h e r s . V a r i a t i o n s i n d e s i g n s a r e s h o w n i n F i g u r e s 4 . 8 ( u s e d b y S w a l l o w a n d G a c h w e n d , 1 9 8 3 ) a n d 4 . 9 ( u s e d b y W a l t h e r , e t a l . , 1 9 8 3 ) . T h e l a t t e r w a s u s e d t o o b t a i n m e a s u r a b l e b e n z e n e c o n c e n t r a t i o n s a c r o s s a t r a n s e c t l i n e t h a t c o r r e s p o n d e d t o a p l u m e o f known a r e a . L a B r e c q u e , e t a l . ( 1 9 8 4 1 , m o d i f i e d W a l t h e r ' s d e s i g n a n d u s e d i t f o r t h e s a m p l i n g o f a g a s o l i n e s p i l l a t D e a t h V a l l e y N a t , i o n a l M o n u m e n t ( s e e F i g u r e s 4 . 1 0 , 4 . 1 1 , a n d 4 . 1 2 ) . T h e s a m p l i n g m a n i f o l d s h o w n i n F i g u r e 4 . 1 2 was s h o w n t o g i v e c a r r y o v e r b e t w e e n s a m p l e s . S a m p l e e n t r y h o l e s w e r e c o v e r e d w i t h 8 x 1 0 - 4 i n . s i n t e r e d s t a i n l e s s s t e e l d i s k s t o a v o i d b l o c k a g e . T h e y c o n c l u d e d t h a t t h e g r o u n d p r o b e t e c h n i q u e p r o v i d e d b e t t e r r e s u l t s t h a n g e o p h y s i c a l m e t h o d s u s e d t o d e f i n e t h e d i m e n s i o n s o f t h e p l u m e b u t t h e g r o u n d p r o b e s w e r e p r o n e t o f a l s e p o s i t i v e r e a d i n g s . A s i m i l a r d e s i g n was l ~ v e d b y K e r f o o t , e t a a l . ( 1 9 8 6 ) , t o i n v e s t i g a t e a s i t e

138

Equipment for determination of mercury and r a d o n i n s o i l a i r a e u s e d a t Cachinal, 1J. Chile. (1) 100 mm dia. 3-4 m deep auger drill h o l e ( 2 ) loose soil ( 3 ) rubber packer (4) 25 tam die. Dural propa (5) packer preeeure line ( 6 ) PTFE 5 mm dio. line ( 7 ) duat filter (8 ) line to radon monitor (9) radon monitor (10) line to mercury spectrometer ( 1 1 ) mercury spectrometer (12) l i n e to pump ( 1 3 ) 1 1. pump ( 1 4 ) outlet.

Figure 4 . 6 . Ground-probe des ign of Lovell, et el. (1983).

139

VACUUM

F i g u r e 4.7. Ground-probe d e s i g n used by Swallow and Gschwend, 1983,

140

a W A Y V A L V E

T E N A X Q C T R A P

F l T f l N Q

- P O U N D I N G P L A T E Ill- - P I P E

- - T U B I N Q - C O U P L I N Q

Figure 4.8. Ground-probe derign ured by Swallow and C8chvand' (1983).

141

d i l

I -IRON PIPE-II . . . - . - - - - -

S A M P L I N G P I P E

D R A E Q E R O A S D E T E C T I O N T U B E

A N D 0 - R I N Q S T I P 3 I I R O N S A M P L E R I I

- Configuration for hamering rampler into roil

b-Placement of rampling pipe w i t h Draeger tube into the rampler

Figure 4 . 9 . Crouod-probe d e r i g n used by Waltbcr, e t a1. (1983).

142

PROVE TIP PROSE W A F T

A A'

CROSS-SECTION A- A'

Figure 4.10. Ground-probe design ured by L a b r e c q u e , e t r l . (1984).

143

Figure 4.11. Gr o u n d - p r o b e d r i v e r 8nd e x t r a c t o r ueed by L8Brecque, et a l . 1984).

144

Figure 4 .12 . Sampling mani fo ld and pump ured k b t a c q u e , a t a1 . (1984).

145

c o n t a m i n a t e d w i t h h a l o g e n a t e d o r g a n i c compounds. They found t h a t t h e s o i l gas c o n c e n t r a t i o n v a r i e d s i g n i f i c a n t l y ( r e l a t i v e s t a n d a r d d e v i a t i o n - 42 p e r c e n t ) f o r adgacent l o c a t i o n s (1088 than 7 f e e t a p a r t ) . T h i s sampling v a r i a b i l i t y was n o t c o n s t a n t and g r e a t l y e x c e e d e d t h e a n a l y t i c a l v a r i a b i l i t y . A l a t e r survey a t t h e same s i t e showed a much s m a l l e r v a r i a b i l i t y of 1 2 1 r s d (Kerfoot and Hayer, 1 9 8 6 ) .

Radian C o r p o r a t i o n ( 1 9 8 4 ) h a s d e s i g n e d and used s e v e r a l d i f f e r e n t small-volume, d r i v e a b l e ground p r o b e s . Sampl ing was c o n d u c t e d a t t h e s a m e s i t e i n D e a t h V a l l e y s t u d i e d b y LaBrecque , e t a l . The s a m p l i n g m e t h o d u s e d b y t h e R a d i a n C o r p o r a t i o n i n v o l v e d i n s e r t i n g g round p r o b e s ( t h e d e s i g n 1s i l l u s t r a t e d i n F igu re 4 . 1 3 ) t o a d e p t h of 3 f e e t , r a i s i n g t h e o u t e r t u b e 2 i n , , and a l l o w i n g t h e p r o b e t o s i t f o r 2 hours . s a m p l e s w e r e c o l l e c t e d u s i n g s y r i n g e s a n d e v a c u a t e d s t a i n l e s s - s t e e l c a n i s t e r s . The c a n i s t e r s were f i t t e d w i t h flow r e g u l a t o r s t o p r o v i d e a c o n s t a n t s a m p l e f l o w o f 3 . 5 x 1 0 - 4 f t / m i n o v e r t h e 4 - h r . s ampl ing p e r i o d , [The s t u d y showed t h a t t h e plume had advanced compared t o e a r l i e r s t u d i e s b y t h e U.S. G e o l o g i c a l Survey and t h a t O n l y t h e l i g h t e r mo lecu la r weight compounds i n t h e gaso l ine were p r e s e n t a t 1 ppbv-carbons l e v e l or g r e a t e r a t t h e n e a r s u r f a c e l e v e l . ] T h e ground probes u s e d i n t h i s s t u d y were a d e q u a t e t o d e f i n e t h e g e n e r a l a r e a o f c o n t a m i n a t i o n ; however , an i n s u f f i c i e n t number were a v a i l a b l e f o r d e m a r c a t i n g t h e a c t u a l p l u m e d i m e n s i o n s ( R a d i a n Corpora t ion , 1 9 8 4 ) .

I n a n o t h e r i n v e s t i g a t i o n , Crow, e t a l . ( 1 9 8 5 1 , used 32 s m a l l - v o l u m e , d r i v e n g r o u n d p r o b e s t o d e t e r m i n e t h e e f f e c t i v e n e s s o f s o i l - v e n t i n g t e c h n i q u e s . A p i l o t h o l e was d r i l l e d w i t h i n 2 f e e t o f t h e f i n a l d e p t h b y u s i n g a 4 i n . ho l low-s t em a u g e r . The ground p r o b e s ( s e e F i g u r e 4.14) were i n s e r t e d and d r iven t o 1 6 t o 22 f e e t below t h e ground s u r f a c e and t h e n were s e a l e d i n p lace b y u s i n g cement g r o u t . For t h i s p a r t i c u l a r s i t e , C r o w i n d i c a t e d t h a t s a m p l i n g a t s h a l l o w e r d e p t h s would n o t have provided a c c e p t a b l e d a t a . Compressed a i r was used t o c l e a r any b locked s a m p l e e n t r y h o l e s . The g round p r o b e s s a t i n p l a c e f o r 24 h o u r s b e f o r e d a i l y s a m p l i n g was b e g u n . R e p r o d u c i b l e r e s u l t s were o b t a i n e d from a n a l y s i s o f r e p e a t s a m p l e s from a s i n g l e p r o b e and samples from d u p l i c a t e probes.

L i m i t a t i o n s - - T h e m a j o r l i m i t a t i o n s i n u s i n g s o i l g a s p r o b e s a r e t h a t they a r e b e s t s u i t e d f o r shal low s a m p l i n g ; t h e y a r e n o t w e l l s u i t e d f o r r o c k y or w e t , c l a y e y s o i l s ; a n d o b t a i n i n g a r e p r e s e n t a t i v e sample is d i f f i c u l t . Other p rob lems i n c l u d e : t h e method is l abo r i n t e n s i v e , sample p a r t s may become occluded d u r i n g p r o b e i n s e r t i o n , and ambien t a i r can i n some c a s e s m i g r a t e d o w n t h e o u t s i d e o f t h e p r o b e s h a f t a n d d i l u t e t h e sample.

146

- 1 1 2 I N C H T e f L O N T U B E

\

/ T E f L O N C L U a

4 INCH 8 P A C E

Figure 4.13. Ground-probe deriga used by Radiaa Corporation (1984)

147

4.14.

I

L 8 E P T U M 7

I II I Pl' P I P E

c

Ground-probe d e s i g n wed by Crow, e t a l . (1985).

148

Sur face F l u x Chambers

The s u r f a c e f l u x chamber t echn ique involves t h e use of an e n c l o s u r e d e v i c e t o sample g a s e o u s e m i s s i o n s f rom a known a u r f a c e a r e a . Sweep a i r f l o w 8 t h r o u g h t h e chamber. The e x i t g a s l a a n a l y z e d o n - s i t e o r c o l l e o t e d f o r l a t e r a n a l y s i s . Knowledge of t h e f low r a t e of a i r t h r o u g h t h e chamber and of t h e c o n c e n t r a t i o n of t h e e x i t gas e n a b l e s t h e e m i s s i o n r a t e t o be c a l c u l a t e d .

Recommended Use-- The s u r f a c e f l u x chamber i s p a r t i c u l a r l y a p p l i c a b l e t o

m e a s u r i n g p o p u l a t i o n e x p o s u r e s s i n c e g a s e o u s e m i s s i o n s a r e b e i n g m e a s u r e d a t t h e s u r f a c e l e v e l . However , s u r f a c e hydrocarbon l e v e l s a r e g e n e r a l l y lower t h a n s u b s u r f a c e l e v e l s ; t h e r e f o r e , t h e use fu lness of t h e f l u x chamber method is l i m i t e d where t h e s o i l - g a s c o n c e n t r a t i o n i s low. B e s t r e s u l t s a r e o b t a i n e d when s o p h i s t i c a t e d s a m p l i n g techniques ( e .g . , s t a i n - l e s s s t e e l e v a c u a t e d c a n i s t e r s ) a n d / o r s e n s i t i v e d e t e c t i o n s y s t e m s ( e . g . , G C ) a r e u s e d . The t e c h n i q u e m i n i m i z e s d i s t u r b a n c e of t he s o i l or of any a s s o c i a t e d emission p r o c e s s e s . S a m p l i n g i s q u i c k ( n o r m a l l y r e q u i r e s 1 1 2 h r pe r s a m p l i n g p o i n t ) , r e q u i r e s s imple e q u i p m e n t , and is s u i t e d t o most s o i l t y p e s . Rad ian C o r p o r a t i o n ( S c h m i d t , e t a l . , 1 9 8 3 ) r e p o r t e d 8 8 . 5 p e r c e n t t o 1 2 4 p e r c e n t r e c o v e r i e s when a 3 6 - c o m p o n e n t o r g a n i c s t a n d a r d was used and uas in t roduced i n t o the sampling s y s t e m . I n a d d i t i o n , a r a n g e of 2 . 3 x 1 0 - 1 1 t o 1 . 1 x 1 0 - 4 l b / t t 2 / m i n was d e t e r m i n e d ( R a d i a n C o r p o r a t i o n , 1 9 8 4 ; Schmidt , e t a l . , 1 9 8 2 ) . The Radian Corpora t ion ( B a l f o u r , e t a l . , 1 9 8 5 ) a l s o r e p o r t e d a c c u r a c i e s o f b e t t e r t h a n k 1 0 p e r c e n t a n d a n a l y t i c a l v a r i a b i l i t i e s w i t h i n f20 p e r c e n t de t e rmined b y an independent a u d i t .

Techn 1 que A p p l i c a t1 0113'- I n 1 9 8 3 , E k l u n d and Schmidt ( 1 9 8 3 ) performed a review on

the development of t h e f l u x chamber s a m p l i n g t e c h n i q u e . T h i s r e v i e w r e v e a l e d o n l y t h r e e g r o u p s o f r e s e a r c h e r s u s i n g t h i s method for measuring hydrocarbon emiss ion r a t e s . However, t h i s method h a s l o n g been used t o measure f l u x e s of non-hydrocarbon gases , S e k u l i c a n d Delaney ( 1 9 8 0 ) sugges t ed the a p p l i c a t i o n of t h i s m e t h o d f o r m e a s u r i n g h y d r o c a r b o n e m i s s i o n s f r o m a w a s t e w a t e r t r e a t m e n t l a g o o n . T h e i r d e v i c e c o n s i s t e d o f a f l o a t i n g t r u c k inner tube w i t h t r a n s l u c e n t p l a s t i c cover ing one end . Sweep a i r was u s e d t o f o r c e a s a m p l e t o a p o r t a b l e o r g a n i c v a p o r a n a l y z e r ( O V A ) e q u i p p e d w i t h a F I D . Ano the r r e s e a r c h e r , Zimmerman ( 1 9 7 7 1 , used a 2 . 4 - f o o t d i a m e t e r f l u x chamber w i t h a c o l l a p s i b l e top t o measure biogenic hydrocarbon e m i s s i o n s . A n a l y s i s took p l a c e w i t h i n 2 4 h o u r s u s i n g t h r e e s e p a r a t e G C s t o examine a b road r a n g e of hydrocarbon s p e c i e s . T h e f l u x chamber u s e d b y S c h m i d t ( 1 9 8 3 1 , c o n s i s t e d o f a s t a i n l e s s s t e e l / a c r y l i c c h a m b e r ( s e e F i g u r e 4 . 1 5 ) w i t h

149

S A M P L E COLLECTION A M 0 A W A L Y O I O \

FLOW CONTR OL

C A R

Figure 4.15. S u r f a c e f l u x chaaber and peripheral equipment (Ekluad, et alas 1984).

i m p e l l e r , u l t r a - h i g h p u r i t y s w e e p a i r a n d r o t a m e t e r f o r measuring f l o w i n t o t h e c h a m b e r , and a s a m p l i n g m a n i f o l d f o r m o n i t o r i n g a n d c o l l e c t i o n o t t h e s p e c i e ( s ) o f i n t e r e s t . P o r t a b l e F I D - a n d p h o t o i o n i z a t i o n d e t e c t o r ( P I D ) b a s e d a n a l y z e r s were used t o o o n t i n u o u s l y monitor total hydrocarbon concentrations in the chamber outlet gas s t r e a m , S a m p l e s w e r e a l s o c o l l e o t e d f o r s u b s e q u e n t GC analysis once a steady-state emission rate was obtained. A i r and s o i l / l i q u i d t e m p e r a t u r e s w e r e m e a s u r e d by using a thermocouple. The system pressure was monitored by using a magnahelic pressure gauge. T h i s t e c h n i q u e h a s b e e n a p p l i e d t o determine the area of contamination at two J e t fuel (JP-4) spill s i t e s ( R a d i a n C o r p o r a t i o n , 1 9 8 4 ; R a d i a n Corporation-T, 1984).

L i m i t a t i o n s - - T h e s u r f a c e f l u x c h a m b e r t e c h n i q u e has s e v e r a l l i m i t a t i o n s w h i c h s h o u l d b e c o n s i d e r e d p r i o r t o s e l e c t i o n . T h e s w e e p a i r d i l u t e s t h e g a s s a m p l e w h i c h decreases t h e sensitivity of the method. This t e c h n i q u e is not s u i t e d f o r s i t e s w i t h c a l i c h e or other semi-impermeable soils or when the soil sampled is s a t u r a t e d w i t h w a t e r w h i c h blocks g a s t r a n s p o r t p a t h w a y s . I n a d d i t i o n , t h e m e t h o d h a s a n i n h e r e n t e f f e c t o n t h e e m i s s i o n r a t e being m e a s u r e d . T h e s e e f f e c t s h a v e b e e n i n v e s t i g a t e d (Koerner, et al., 1984; Zohdy, et al., 1974), a n d m o d i f i e d c h a m b e r s h a v e b e e n d e v e l o p e d [ H a t h i s , et al. (198O)J to minimize these effects. Finally, It s h o u l d b e n o t e d that g a s c o n c e n t r a t i o n s at t h e s u r f a c e a r e normally lower than at subsurface locations.

Sorbent Samplers

S o r b e n t samplers can be used to collect soil gases during a given time period. The sampling time is a d j u s t e d t o provide a s u f f i c i e n t q u a n t i t y o f t r a p p e d g a s f o r a n a l y s i s . T h i s technique p r o v i d e s a n i n t e g r a t e d s a m p l e that c o m p e n s a t e s for any short-term fluctuations in soil gas concentration.

Recommended Use-- S o r b e n t s a m p l e r s a r e well-suited for a l m o s t any site.

The sorbent sampler technique is beat suited for c a s e s when t h e soil g a s h y d r o c a r b o n concentration is expected t o be very low. T h e sampling duration can b e v a r i e d to e n s u r e t h a t s u f f i c i e n t m a t e r i a l is collected for analytical detection. This technique is useful for determining whether contamination is p r e s e n t , but o t h e r t e c h n i q u e s a r e m o r e a p p r o p r i a t e f o r o b t a i n i n g more specific information.

Technique AppliCatiOn8-- A w i d e v a r i e t y o f s a m p l e gas extraction and accumulation

procedures h a v e b e e n reported. I n general, t h e y i n v o l v e t h e a d d i t i o n o f a s o r b e n t s a m p l e r to s a m p l i n g t e c h n i q u e s such as ground probes, collection cana, or flux chambers.

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S e v e r a l r e s e a r c h e r s h a v e u s e d p a s s i v e s a m p l e r s i n c o n j u n c t i o n w i t h g r o u n d p r o b e s t o d e t e c t t h e p r e s e n c e o f h y d r o c a r b o n s . For example , Boys ( 1 9 6 7 ) pumped sample gas from a ground probe f o r 30 s e c t o 1 0 m i n and r e c o r d e d t h e volume. H e t h e n used h i s p a t e n t e d method o f u s i n g a r e f r i g e r a t e d G C column f o r a n a l y z i n g t h e s o i l g a s e s . I n o t h e r w o r k , t h e e x h a u s t g a s f r o m g r o u n d p r o b e s h a s b e e n t r a p p e d b y u s i n g a c t i v a t e d c h a r c o a l ( C o l e n u t t , e t a l . , 1980) , Tenax (Swa l low, e t a l . , 1 9 8 3 1 , a n d D r a e g e r t u b e s ( W a l t h e r , e t a l . , 1 9 8 3 ) . Colenut t and Davies (1980) c i t e o t h e r r e s e a r c h e r s u s i n g s i l i c a g e l , g r a p h i t i z e d carbon b l a c k , and porous polymers.

O the r r e s e a r e h e r s have used c o l l e c t . i c n cans or some s o r t of enc losure t o o b t a i n gas s a m p l e s . For e x a m p l e , P e a r s o n , e t a l . (19651 , pumped g a s f rom an e n c l o s u r e t h r o u g h a s e r i e s of c h i l l e d lmpingers c o n t a i n i n g absorbing s o l u t i o n t o measu re t h e radon-222 f l u x f rom s o i l . D u r i n g t h e i r i n v e s t i g a t i o n , t h e y e x p e r i e n c e d a l a r g e v a r i a b i l i t y i n t h e i r r e s u l t s which t h e y a t t r i b u t e d t o s o i l d i s t u r b a n c e from t h e edge of t h e e n c l o s u r e . T h e r e a f t e r , c a u l k was used t o S e a l t h e e n c l o s u r e w i t h t h e s a m p l i n g s u r f a c e . K r i s t i a n s s o n and Malmquis t ( 1 9 8 2 ) a l s o measured radon b y u s i n g d e t e c t o r s i n i n v e r t e d c u p s p l a c e d i n s h a l l o w h o l e s a n d r e f i l l e d w i t h s o i l . R y d e n , e t a l . ( 1 9 7 8 ) , m e a s u r e d t h e n i t r o u s o x i d e f l u x f r o m s o i l s b y c o n t i n u o u s l y p u m p i n g g a s from an enc losu re and b y t r a p p i n g t h e sample i n m o l e c u l a r s i e v e s . K a r i m i ( 1 9 8 3 ) u s e d e n c l o s u r e d e v i c e s t o s a m p l e a t h a z a r d o u s w a s t e s i t e s , The p r o c e d u r e i n v o l v e d p u m p i n g g a s o u t o f t h e e n c l o s u r e , t r a p p i n g hydroca rbons i n a column of a c t i v a t e d c h a r c o a l , and ana lyz ing samples by G C and G C I M S . Fluxes were measured f o r t e n s e l e c t e d o r g a n i c compounds and r a n g e d from 4.3 x l o a 1 ' t o 1 . 2 x 1 0 - 9 l b / f t * - s e c .

McCar thy ( 1 9 7 2 ) c o l l e c t e d mercury e m i s s i o n s b y u s i n g e n c l o s u r e s on t h e g round s u r f a c e ( f o r 2 - h r p e r i o d s ) w i t h a n amalgamation on a s i l v e r s c r e e n p l a c e d i n s i d e t h e e n c l o s u r e . As repor ted b y Kanemasu, e t a l . ( 1 9 7 4 1 , some i n v e s t i g a t o r s have used h y d r o x i d e s o l u t i o n s i n i nve r t ed cans t o measure t h e carbon dioxide f l u x . These i n v e s t i g a t o r s r e p o r t e d t h a t t h i s s t a t i c c o l l e c t i o n method y i e l d s f l u x e s 20 percent lower than a dynamic ( f l u x chamber) method.

Rouse ( 1 9 8 4 ) u s e d a s l i g h t l y d i f f e r e n t p r o c e d u r e t o p a s s i v e l y measure s o i l s u r f a c e gases . G l a s s v i a l s f i l l e d w i t h a n a b s o r b i n g s o l u t i o n w e r e b u r i e d 6 l n c h e s deep i n b a c k f i l l e d holes and l e f t i n t h e f i e l d f o r 1 month. Rouse found t h a t t h e d e p t h a t w h i c h t h e v i a l was p l a c e d ( a few i n c h e s t o a few y . i r C s ) d i d n o t a f f e c t t h e r e s u l t s . I n a d d i t i o n , he c o n c l u d e d t h a t t h i s p r o c e d u r e p r o d u c e d s i m i l a r r e s u l t s t o t h e g r a b

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Figure 4.16. Curie-point v i m accumulator device (Voorhecs, 1980).

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0.88 g a l g r r o l l n o a t P O t t d o p t h 1 I 8 # , 0 0 0 B u l l d u g 8 n d d o o r #

I t h r o u g h O r n d

I I

b u i l d u p a n d deo' ry t h r o u g h wot o l r y

T o t 8 1 lor o o u n t r r o m r l n 1 0 X

1 8 a 4 6 0 b r o k o r o u n d m o n I t o r d t o r 10 d r y a I P O 0 t . l . C . / d r y

D A Y 8 E L A P S E D

Figure 4.17. Bu i ld -up and r t t e n u a t i o n o f v o l r t i ~ c r from ( r r o l i n e t h r o u g h 8 rand column and t h t o u l h u a d i r t u r b e d wet c l a y r o i l 8 8 a e r r u r e d by Curie-point wire ramplat (Birqur, 1984)

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s a m p l i n g s o i l c o r e t e c h n i q u e a n d t o a n a m b i e n t a i r s n i f f e r survey.

A p a s s i v e sampling technique using activated charcoal was d e v e l o p e d by P e t r e x C o r p o r a t i o n r n d h a s a p a t e n t p e n d i n g . R e p o r t e d a d v a n t a g e s o f t h i s d e v i c e inolude: ( 1 ) the s a m p l e r s are simple and rugeed, (2) sampling and analyais a r e r e l a t i v e l y i n e x p e n s i v e , ( 3 ) l i g h t h y d r o c a r b o n s c a n b e detected, and (4) the technique appears to be r e l a t i v e l y u n a f f e c t e d by w e a t h e r and s i t e conditions. Bisque (1984) describes the sample device a s a t h i n f e r r o m a g n e t i c ( C u r i e - p o i n t ) w i r e c o a t e d w i t h a c t i v a t e d c h a r c o a l . T h e p r o c e d u r e i n v o l v e s placement o f the wire i n a g l a s s t u b e w h i c h is b u r i e d 6-12 in. b e l o w t h e s u r f a c e a n d l e f t f o r s e v e r a l w e e k s . W h e n t h e s a m p l e is retrieved, the wire is placed i n a v a c u u m c h a m b e r , is h e a t e d , and t h e d e s o r b e d hydrocarbons are analyzed by Curie-point mass spectrometry. Although this method is limited b y f r o z e n g r o u n d and s a t u r a t e d soils, meteorological and hydrological conditions have a minimal effect.

A p p l i c a t i o n s o f t h e technique have been widely reported. V o o r h e e s ( 1 9 8 4 ) , d e s c r i b e d t h e u s e o f P ~ t r e x t u b e s t o i n v e s t i g a t e ground-water w h i c h w a s 44-feet b e l o w the surface and contaminated w i t h t e t r a c h l o r o e t h y l e n e ( T C E ) at t h e R o c k y M o u n t a i n Arsenal. Twenty-five Petrex samplers (one is shown in Figure 4.16) were placed a l o n g t w o t r a v e r s e lines. T h e p l u m e b o u n d a r i e s a n d a g r e e d w e l l w i t h t h e r e s u l t s o b t a i n e d f r o m monitoring wells. Chloroform was the o n l y m a d o r c o m p o n e n t not detected i n t h e ground-water by the trapping device. Voorhees ( 1 9 8 4 ) d e s c r i b e d a n o t h e r s t u d y c o n d u c t e d at R o c k y M o u n t a i n A r s e n a l t o d e t e c t v a r i o u s h y d r a z i n e s a n d t h e i r o x i d a t i o n products. None of these species could be positively i d e n t i f i e d b e c a u s e o f h i g h b a c k g r o u n d c o n c e n t r a t i o n s of n a t u r a l l y occurring petroleum deposits in the area.

B i s q u e ( 1 9 8 4 ) p r e s e n t e d the results of a quality control study. Approximately one quart each o f g a s o l i n e , d i e s e l f u e l , and c r u d e o i l w e r e i n t r o d u c e d at 10-foot d e p t h I n soil media that varied from tight clay containing 10 percent f r e e w a t e r t o d r y c o l l u v i a l m a t e r i a l . I n all c a s e s , t r a c e e m i s s i o n s w e r e d e t e c t a b l e at t h e s u r f a c e w i t h i n hours. F i g u r e 4.17 s h o w s c o n c e n t r a t i o n v e r s u s t i m e d a t a f o r e a c h s o i l t y p e . C o n t a m i n a t i o n could s t i l l b e d e t e c t e d a f t e r 60 d a y s . T h e o b s e r v e d d i f f u s i o n p a t t e r n from the point source contamination is shown in Figure 4.18.

Limitations--The Petrex tube sampling technique and other passive techniques require a long sampling time and d i s t u r b t h e sampling s i t e , I n addition, high background concentrations may interfere with obtaining accurate measurements. T h e e f f i c i e n c y sf t h i s c o l l e c t i o n m e t h o d c a n n o t b e d e t e r m i n e d since, unlike

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the surface flux chamber technique, the sample enters the tube by passive diffusion, and the volume of gas s a m p l e d is not 1nea8Ured .

S a m p l e c o l l e c t i o n by pumping soil gas from collection cans or ground p r o b e s a180 has limitations. T h e pumping may disturb the equilibrium between the soil gas and the gas sorbed on soil partloles. It may cause dilution and/or contamination of the sample by ambient air.

Kerfoot and Mayer ( 1 9 8 6 ) give the following limitations for passive charcoal soil-gas samplers with analysis by thermal d e s c r i p t i o n : it is not quantitative, there may be thermal decomposition o f tightly sorbed and less volatile compounds, and chemical decomposition of the samples is promoted.

SAMPLING DESIGN AND SAMPLING QUALITY ASSURANCE TECHNIQUES

T h i s s e c t i o n d i s c u s s e s t h e a p p r o a c h n e c e s s a r y t o make optimal use o f t h e a v a i l a b l e r e s o u r c e s a n d t o e n s u r e adequate data quality when making soil-gas measurements.

Sampling Strategy

T h e s a m p l i n g strategy should be devised t o o b t a i n all necessary and required information with a minimal expenditure o f t i m e a n d r e s o u r c e s . P r i o r t o d e v e l o p i n g a s a m p l i n g strategy, any available information pertaining to the following items should be collected and evaluated: type of contaminant p r e s e n t ; a m o u n t o f c o n t a m i n a n t p r e s e n t ; l e n g t h o f t i m e contaminant has been present; direction and r a t e of flow of ground-water; depth to ground-water; geological soil properties of the site; number, type, and location of existent subsurface structures ( e . ~ . , wells and sewers); existent s a m p l i n g and a n a l y t i c a l r e s u l t s ; a n d a n y a n e c d o t a l e v i d e n c e of contaminat 1 on.

The above information, along with the objectives of the test program, should be used to tailor a sampling strategy to t h e s p e c i f i c c i r c u m s t a n c e s e n c o u n t e r e d . A n e x a m p l e c o n t a m i n a t i o n p r o b l e m 1s d i s c u s s e d b e l o w a n d s e r v e s t o i l l u s t r a t e t h e p r o c e s s o f developing a sampling strategy. Examples of specific sampling strategies may be found in the r e f e r e n c e s t o t h e individual sampling methods discussed in Section 1II.A.

A t a h y p o t h e t i c a l s i t e , a n u n d e r g r o u n d storage tank containing industrial/organic wastes is suspected o f leaking based upon inventory control records and tank-tightness tests. Little information is available regarding t h e s i t e , a n d no existing observation wells are present. Furthermore, nearby

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w e l l s ( a p p r o x i m a t e l y 1 m i l e d i s t a n t ) i n e v e r y d i r e c t i o n provide community d r i n k i n g w a t e r , and t h e p r e s s i s a w a r e o f t h e s i t u a t i o n . T h e o b J e c t i v e i s t o d e t e r m i n e t h e e x t e n t of any contaminant plume.

The f i r s t s t e p a f t e r background i n f o r m a t i o n c o l l e c t i o n and e v a l u a t i o n is t o e s t a b l i s h a g r i d system over t h e a i t e w i t h t h e s u s p e c t e d s o u r c e a t t h e c e n t e r . The number of p o i n t s t h a t s h o u l d be sampled i s v e r y s i t e a n d p r o J e c t s p e c i f i c . The n u m b e r w i l l depend on t h e r e s o u r c e s a v a i l a b l e , t h e p r o J e c t o b j e c t i v e s , and t h e l e v e l o f r i s k t h a t i s a c c e p t a b l e . I n g e n e r a l , i t is much more r e s o u r c e - i n t e n s i v e t o prove t h a t an a r e a i s not contaminated t h a n t o r o u g h l y d e l i n e a t e t h e e x t e n t of a c o n t a m i n a n t plume. I n o u r example, a g r i d of 10 rows of 10 sampling p o i n t s e a c h w i t h p o i n t s and rows s e p a r a t e d b y 50 f e e t m i g h t be u s e d . Once a l l t h e d e s i g n c o n s i d e r a t i o n s d i s c u s s e d b e l o w h a d b e e n m e t , m e a s u r e m e n t s m a d e a t a p p r o x i m a t e l y a dozen s e l e c t e d sampl ing p o i n t s c l r cumscr ib ing t h e p o i n t s o u r c e w o u l d i n d i c a t e t h e d i r e c t i o n o f a n y c o n t a m i n a n t plume. A more r e f i n e d secondary phase of sampling c o u l d t h e n be p l a n n e d . A t r a n s e c t of e q u i - s p a c e d s a m p l i n g p o i n t s i n t h e d i r e c t i o n o f t h e p l u m e would i n d i o a t e t h e l o c a t i o n of t h e p l u m e f r o n t . Once t h i s h a s been d e t e r m i n e d , s e v e r a l l i n e s of e q u i - s p a c e d s a m p l i n g p o i n t s pe rpend icu la r t o t h e t r a n s e c t l i n e w i l l i n d i c a t e t h e l a t e r a l e x t e n t o f t h e plume.

The n e x t c o n s i d e r a t i o n i s t o s e l e c t a s a m p l i n g method. The s e l e c t i o n w i l l depend upon t h e c o n t a m i n a n t s p e c i e s , t h e s i t e c h a r a c t e r i s t i c s , t h e e x p e r t i s e a v a i l a b l e , and any time and budge t c o n s t r a i n t s . I n t h e e x a m p l e c a s e , a s a m p l i n g a n d a n a l y t i c a l system such a s ground probes and o n - s i t e a n a l y s i s of t h e gas samples m i g h t be s e l e c t e d t o p r o v i d e r a p i d f e e d b a c k t o s i t e 1 nv8.s t 1 gat or s .

A t h i r d c o n s i d e r a t i o n i s what s p e c i e s t o moni tor . T h i s is, of cour se , dependent on t h e sampling method s e l e c t e d . T h e c h o i c e ( t r a c e r g a s ) s h o u l d b e a compound t h a t is d e t e c t a b l e a t low c o n c e n t r a t i o n s , has low molecular weight so t h a t i t w i l l be p r e s e n t n e a r t h e p l u m e f r o n t , b u t n o t s o l i g h t t h a t i t is r a p i d l y l o s t t o t h e a t m o s p h e r e . The t r a c e r g a s s h o u l d b e r e l a t i v e l y i n e r t and i n s o l u b l e i n water so t h a t a t t e n u a t i o n is n o t a p r o b l e m . F i n a l l y , t h e t r a c e r compound m u s t be r e a d i l y a t t r i b u t a b l e t o t h e c o n t a m i n a n t plume and not t o background s o u r c e s o r a n a l y t i c a l i n t e r f e r e n c e s . I n o u r e x a m p l e , a compound w o u l d be s e l e c t e d t h a t was t y p i c a l l y p r e s e n t i n t h e s t o r a g e tanks . Good c a n d i d a t e s m i g h t be a c h l o r i n a t e d s o l v e n t such a s T C E , benzene, or t o t a l hydrocarbons.

A f o u r t h c o n s i d e r a t i o n i s t h e s e l e c t i o n of a s a m p l i n g horizon or d e p t h . So i l -gas measurements a r e t y p i c a l l y made a t

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d e p t h s f rom 0 t o 1 0 f e e t u n l e s s e x i s t i n g w e l l s a r e p r e s e n t . S a m p l i n g a t d e p t h s be low 1 0 f e e t n e g a t e s t h e a d v a n t a g e s i n t e rms o f t i m e a n d e f f o r t o f u s i n g s o i l - g a s m e a s u r e m e n t s r e l a t i v e t o o t h e r o p t i o n s . C e r t a i n s a m p l i n g m e t h o d s s u c h a s s u r f a c e f l u x chambers o r C u r i e - p o i n t wire samplers c a n b e u s e d a t o r n e a r t h e s u r f a o e . O the r methods, s u c h a s g r o u n d p r o b e s , c a n b e u s e d a t v a r i a b l e d e p t h s . When u s i n g g r o u n d p r o b e s , i t is r e c o m m e n d e d t h a t s e v e r a l v e r t i c a l p r o f i l e s b e per formed a t s a m p l i n g p o i n t s known t o be c o n t a m i n a t e d . T h i s i n f o r m a t i o n c a n t h e n b e u s e d t o s e l e c t a s a m p l i n g d e p t h t h a t y i e l d s c o n c l u s i v e r e s u l t s f o r s u b s e q u e n t s a m p l i n g p o i n t s . I n o u r e x a m p l e , g r o u n d probes w o u l d b e d r i v e n t o 6 t o 1 0 f e e t u n t i l c o n t a m i n a t i o n i s f i r s t e n c o u n t e r e d . O n c e a o o n t a m i n a t e d p o i n t i s f o u n d , a d d i t i o n a l g r o u n d p r o b e s c o u l d b e d r i v a n n e a r b y . S a m p l e s c o l l e c t e d a t o n e - f o o t d e p t h i n t e r v a l s w o u l d t h e n show what a s u i t a b l e s a m p l i n g d e p t h w o u l d b e . I t i s u s e f u l , d u r i n g s u b s e q u e n t s a m p l i n g , t o p e r i o d i c a l l y perform v e r t i c a l p r o f i l e s r a t h e r t h a n a l w a y s t o s a m p l e a t a f i x e d d e p t h . T h e v e r t i c a l p r o f i l e s w i l l i n d i c a t e w h e t h e r t h e t y p i c a l s a m p l i n g d e p t h s h o u l d b e m o d i f i e d ; deeper t o i m p r o v e s e n s i t i v i t y , or s h a l l o w e r t o i m p r o v e p r o d u c t i v i t y .

A f i n a l c o n s i d e r a t i o n i s t h e l e n g t h o f t i m e 8 p e n t s a m p l i n g a t a n y g i v e n p o i n t . T h i s i s d e p e n d e n t o n t h e s a m p l i n g m e t h o d s e l e c t e d a n d o n t h e s e n s i t i v i t y d e s i r e d . Methods t h a t r e q u i r e a probe/sampler t o b e p l a c e d i n t h e g r o u n d may r e s u l t i n a d i s t u r b a n c e o f t h e e q u i l i b r i u m a m o n g f r e e p r o d u c t , a d s o r b e d p r o d u c t , a n d g a s i n t h e s o i l - p o r e s p a c e s . T h e t ime r e q u i r e d t o a l low t h i s e q u i l i b r i u m t o b e r e e s t a b l i s h e d p r i o r t o i n i t i a t i n g s a m p l i n g c a n b e a s m u c h a s o n e d a y . A l s o , f o r m e t h o d s s u c h a s a c c u m u l a t o r d e v i c e s , t h e s a m p l i n g d u r a t i o n c a n b e e x t e n d e d t o lower t h e d e t e c t i o n l i m i t o f t h e m e t h o d . T h e f i n a l c h o i c e o f s a m p l i n g d u r a t i o n m u s t b e b a a e d u p o n e x p e r i e n c e , p r e l i m i n a r y r e s u l t s , a n d s i t e a n d p r o j e c t s p e c i f i c f a c t o r s , I n o u r e x a m p l e , s i n c e a b s o l u t e c o n c e n t r a t i o n s a r e n o t r e q u i r e d , t h e g r o u n d p r o b e s c o u l d b e d r i v e n t o t h e d e s i r e d d e p t h , a l l o w e d t o e q u i l i b r a t e f o r a s l i t t l e a s o n e h o u r , a n d t h e n t h e s amples c o u l d b e c o l l e c t e d .

Q u a l i t y A s s u r a n c e

T h i s s e c t i o n a d d r e s s e s s a m p l i n g q u a l i t y c o n t r o l . A n a l y t i c a l q u a l i t y c o n t r o l is d i s c u s s e d i n t h e n e x t c h a p t e r . Q u a l i t y c o n t r o l m u s t b e a n i n t e g r a l p a r t of a n y s a m p l i n g p l a n a n d is n e c e s s a r y so t h a t t h e r e s u l t s o b t a i n e d f o r t h e p r o j e c t a r e m e a n i n g f u l , 1 . 0 . . t h e d a t a a r e o f a k n o w n q u a l i t y . T h e e x a c t q u a l i t y c o n t r o l c h e c k s r e q u i r e d f o r a n y p r o j e c t w i l l b e d e p e n d e n t o n t h e s a m p l i n g a n d a n a l y t i c a l methods s e l e c t e d . T h e f o l l o w i n g l i s t of q u a l i t y c o n t r o l c o n s i d e r a t i o n s is a p p l i c a b l e t o most s o i l - g a s m e a s u r e m e n t programs:

159

o d e t a i l e d s a m p i i n g p r o c e d u r e s a n d s c h e d u l e s c l e a r l y written and consistently followed;

o samples labeled with all pertinent information:

o d a t a c o l l e c t e d on appropriate data sheets and reviewed daily;

o s a m p l e l o g s , c h a i n - o f - o u s t o d y forms, a n d o t h e r paperwork kept up-to-date and reviewed daily.

o sampling blanks collected at least daily;

o repeat measurements at a control point;

o background measurements made at least daily;

o a m i n i m u m o f 10 p e r c e n t o f s a m p l e s c o l l e c t e d i n duplicate; and

o a m i n i m u m o f 10 p e r c e n t o f s a m p l e s a n a l y z e d i n duplicate.

T h e v a l u e o f k e e p i n g g o o d r e c o r d s a n d o f u s i n g a consistent t e c h n i q u e 13 o b v i o u s . S a m p l i n g b l a n k s a r e useful f o r d e t e c t i n g c o n t a m i n a t i o n w i t h i n t h e s a m p l i n g s y s t e m that w o u l d not b e d e t e c t a b l e from a n a l y t i c a l blanks. B a c k g r o u n d m e a s u r e m e n t s a l l o w c o m p a r i s o n t o m e a s u r e m e n t s i n t h e contamination zone t o ensure observed c o n t a m i n a t i o n is n o t due to problems with the sampling method or implementation.

D u p l i c a t e and repeat sampling permit statistical analyses t o d e t e r m i n e t h e v a r i a b i l i t y a s s o c i a t e d w i t h t h e s a m p l i n g procedure. For s i t e s w h e r e t h e t e m p o r a l V a r i a b i l i t y exceeds the spatial variability, r e p e a t s a m p l i n g m a y b e r e p l a c e d w i t h side-by-side d u p l i c a t e s a m p l i n g . Side-by-side aamples should be expected t o s h o w g r e a t e r variability t h a n r e p e a t s a m p l i n g s i n c e n o t w o d i s c r e t e s a m p l i n g l o c a t i o n s a r e p e r f e c t l y identical. With the sampling methods that require t h e s a m p l i n g l o c a t i o n t o be disturbed, e.g., ground probes, the side-by-side sampling locations must b e s u f f i c i e n t l y s e p a r a t e d so t h a t t h e p l a c e m e n t and s a m p l i n g at o n e p r o b e d o e s n o t e f f e c t the soil gas concentration at t h e a d j a c e n t probe. T h i s d i s t a n c e will v a r y d e p e n d i n g o n t h e s o i l c h a r a c t e r i s t i c s , b u t s h o u l d be assumed to be at least 3 feet.

W h e n e m p l o y i n g s a m p l i n g methods that permit the reuse of sampling components for multiple sampling p o i n t s , c a r e m u s t be t a k e n to avoid c r o s s - c o n t a m i n a t i o n of samples. T h i s can best b e p r e v e n t e d b y c l e a n i n g s a m p l i n g c o m p o n e n t s b e f o r e e a c h

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sampling point and b y performing sampling blank and background measurement8 a f t e r any meaaurements showing h i g h l e v e l s of c o n t a m i n a t i o n . S h o u l d t h e b l a n k / b a c k g r o u n d d a t a s h o w a significant oontamination problem, the 8ampling components need to be thoroughly cleaned and retested, or replaced.

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Xlmmerrnan, P. P r o c e d u r e s f o r C o n d u c t i n g H y d r o c a r b o n Emission Inventories of Biogenic S o u r c e s and S o m e R e s u l t s o f R e c e n t I n v e s t i g a t i o n s . P r e s e n t e d at t h e 1 9 7 7 EPA

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E m i s s i o n I n v e n t o r y / P a c t o r Workshop, R a l e i g h , N o r t h Carol ina, September 13-15, 1977.

50. Zohdy, A . A . R., G . P . Eaton and D . R . Mabey. Application of S u r f a c e Geophys los t o Ground-Water I n v e s t i g a t i o n s . Techniques o f Water Resources I n v e s t i g a t i o n s . U . S . Geo- l o g i c a l Survey, B K . 2 , Chap. D1, 1974, p . 116.

167

C H A P T E R 5

ANALYTICAL M E T H O D O L O G I E S

S E L E C T I N G T H E P R O P E R METHODOLOGY

The method chosen t o ana lyze 8011 gas 18 dependant on t h e p o l l u t a n t being monitored, the c o n c e n t r a t i o n of t h e p o l l u t a n t , t h e m a t r i x accompanying t h e p o l l u t a n t , and t h e i n f o r m a t i o n expected t o be obta ined from t h e a n a l y t i c a l r e s u l t s . Expec ted c o n c e n t r a t i o n s f o r o r g a n i c s p e c i e s i n s o i l g a s can vary from t h e p p t ( t r i l l i o n ) volume l e v e l ( w e l l below most a n a l y t i c a l d e t e c t i o n l imi t s ) i n background measurements t o h i g h p e r c e n t b y volume l e v e l s i n a measurement made d i r e c t l y o v e r a h i g h l y v o l a t i l e l i q u i d l e n s such a s g a s o l i n e . The concen t r a t ion l e v e l a c t u a l l y measured w i l l depend on t h e sampling method and o n t h e amount of d i l u t i o n o r c o n c e n t r a t i o n which o c c u r s d u r i n g t h e sample c o l l e c t i o n . F l u x chamber me thods d i l u t e t h e s o i l g a s w h i l e a c c u m u l a t o r d e v i c e m e t h o d s c o n c e n t r a t e t h e s o i l g a s components. The a n a l y t i c a l s e n s i t i v i t y of t h e method c h o s e n f o r s o i l g a s a n a l y s i s m u s t be c o n a i s t a n t w i t h t h e s a m p l i n g method, t h e s o i l t y p e , p o l l u t a n t q u a n t i t y a n d v o l a t i l i t y , g round-wa te r plume dep th , and t h e d a t a r equ i r emen t s , Measuring emission r a t e s a t t h e s u r f a c e w i t h a c c e p t a b l y low v a r i a n c e or mapping t h e f r i n g e of a plume a t t h e s u r f a c e where t h e plume is of low v o l a t i l i t y , 13 a t a g r e a t d e p t h , or where t h e 8011 h a s a h i g h a d s o r p t i v i t y o r low p e r m e a b i l i t y , would r e q u i r e a v e r y s e n s i t i v e a n a l y t i c a l technique. The same t e c h n i q u e would need t o be g r e a t l y m o d i f i e d t o a n a l y z e a s ample o v e r a g a s o l i n e plume i n sandy s o i l .

I n some c a s e s , t h e p o l l u t a n t s p e c i e s which r e q u i r e s m o n i t o r i n g is not t h e major component i n t h e s o i l g a s , and t h e d e t e r m i n a t i o n o f t h a t s p e c i e s is c o m p l i c a t e d b y t h e s a m p l e mat r ix . A very s e n s i t i v e t e c h n i q u e may n o t be a p p r o p r i a t e if i t r e s p o n d s t o t h e components i n t h e m a t r i x a s w e l l a s t h e s p e c i e s of i n t e r e s t . I n s u c h c a s e s , s e l e c t i v i t y 1 3 r e q u i r e d a n d can be o b t a i n e d b y i s o l a t i n g t h e d e s i r e d s p e c i e s d u r i n g c o l l e c t i o n , s e p a r a t i n g t h e d e s i r e d s p e c i e s f r o m t h e s a m p l e ~ a t r i c e s d u r i n g t h e a n a l y s i s ( l , e . , c h r o m a t o g r a p h y ) , or d e t e c t i n g o n l y t h e compound of i n t e r e s t ( s e l e c t i v e d e t e c t i o n ) . S p e c i f i c exam-ples of such cases a r e c o n c e n t r a t i n g hydrocarbons G I I a porous p o l y m e r a b s o r b e n t w h i l e e x c l u d i n g t h e h i g h l y v c l a t l l e h y d r o c a r b o n s , permanent g a s e s , and water ; u s i n g h i g h r e s a l u t i o n c a p i l l a r y c o l u m n s t o s e p a r a t e benzene f r o m o t h e r

168

h y d r o c a r b o n s i n g a s o l i n e ; and d e t e c t i n g t r a c e l e v e l s of t o x i c halogenated compounds i n s o i l gas by u s i n g a n e l e c t r o n c a p t u r e d e t e c t o r o r a H a l l E l e c t r o l y t i c Conduc t iv i ty Detec tor ( H E C D ) .

I n a d d i t i o n t o s e n s i t i v i t y and s e l e c t i v i t y , s e v e r a l o t h e r c o n s i d e r a t i o n s a r e r e q u i r e d t o d e t e r m i n e t h e d e g r e e o f a n a l y t i c a l s O p h i 8 t i c a t l O n t h a t 1s n e e d e d f o r a s p e c i f i c measurement. T h e q u e s t i o n s t h a t need t o be a s k e d a r e l i s t e d below.

( 1 ) I s d e t a i l e d s p e c i a t i o n r e q u i r e d o r w i l l a t o t a l o r g a n i c v a l u e provide t h e d a t a r e q u i r e d ?

Sometimes a t o t a l o r g a n i c va lue 1s a l l t h a t is needed t o monitor t h e movement of a g round-wa te r plume o r t o d e t e r m i n e t h e e m i s s i o n r a t e s f r o m s u r f a c e o r d o w n h o l e e m i s s i o n experiments . D e t a i l e d s p e c i a t i o n is r e q u i r e d i f t h e m i g r a t i o n and f l u x r a t e s o f i n d i v i d u a l components a r e d e s i r e d . Often a few d e t a i l e d s p e c i a t i o n ana lyses can be used a s a p r o f i l e , and i n d i v i d u a l r e s u l t s c a n be e x t r a p o l a t e d from t o t a l o r g a n i c va lues .

( 2 ) I s t h e a n a l y t i c a l t e c h n i q u e t o be used t o determine t h e r e l a t i v e c o n c e n t r , a t i o n o r w i l l a b s o l u t e c o n c e n t r a t i o n va lues be r e q u i r e d ?

R e a l - t i m e p o r t a b l e a n a l y z e r s ( e . g . , F I D s and P I D s ) a r e very c o s t e f f e c t i v e and e a s y t o use f o r o b t a i n i n g r e l a t i v e l e v e l s o f o r g a n i c compounds of s i m i l a r composi t ions . T h i s can be e x t r e m e l y u s e f u l i n s c r e e n i n g t h e s a m p l i n g p o i n t s b e f o r e d e c i d i n g on more r e s o u r c e i n t e n s i v e remote a n a l y s i s or before p l o t t i n g t h e r e l a t i v e concen t r a t ion a c r o s s a homogeneous plume. I f t h e s a m p l e components i n t h e plume v a r y w i t h d i s t a n c e o r depth, t h e p o r t a b l e ana lyze r can f a i l t o g i v e c o r r e c t r e l a t i v e values a s w i l l be shown l a t e r .

( 3 ) I f t h e s a m p l e s c o l l e c t e d a r e t o be a n a l y z e d i n t h e l a b , w i l l t h e sample r e q u i r e t h a t t h e l a b be on s i t e o r c a n i t be i n a c e n t r a l i z e d l a b o r a t o r y remote from t h e sampling s i t e ?

T h i s q u e s t i o n i s dependen t on two f a c t o r s : t h e s t a b i l i t y of the components of i n t e r e s t and t h e a n a l y t i c a l s o p h i s t i c a t i o n r e q u i r e d t o do t h e a n a l y s i s . I f t h e s a m p l e ' s s h e l f l i f e i s l e s s t h a n 24 h o u r s , t h e n a n a l y s i s m u s t be p e r f o r m e d i n t h e f i e l d . I f t h e a n a l y s i s i s s o c o m p l i c a t e d t h a t 1 0 g i S t i C S o r cos t p r o h i b i t i t a use l n t h e f i e l d , t h e n t h e s a m p l e w i l l have t o b e s e n t t o t h e l a b . When a sample c a n n o t be s t o r e d f o r t r a n s p o r t t o t h e l a b o r t h e a n a l y s i s i s t o o compl i ca t ed t o t a k e t o t h e f i e l d , a n o t h e r method f o r a n a l y s i s o r sampling mus t be itsed.

169

Portable VOC Analyzers

The use o f portable V O C analyzers for fugitive emission screening, source i d e n t i f i c a t i o n , and i n d u s t r i a l h y g i e n e monitoring has proven t o be very valuable, and they have also been used t o analyze V O C S in sail gas. Of the commercially a v a i l a b l e p o r t a b l e analyzers, soveral types a r e useful f o r soil- gas measurements. T h e s e a r e the nondispersive infrared detectors, flame ionization detector (FID) analyzers, and the photoionization detector (PID) analyzers. The manufacturer's descriptions of selected portable analyzers are given in Table 5.1 . These portable analyzers generally p r o v i d e r e a l - t i m e measurements without performing separations; however, some have chromatographic capabilities a s a n option. T h e advantages of portable analyzers include:

o The analyzers are easy to transport in the field.

o The operation of the analyzer requires minimum operator skill.

o T h e e l i m i n a t l o n o f t h e s a m p l e c o l l e c t i o n s t e p s minimizes the u n c e r t a i n t i e s and e x p e n s e o f s a m p l e collection, storage, and transport.

o D a t a a r e p r o v i d e d i m m e d i a t e l y w h i c h e n a b l e t h e investigators to make timely discussions in the field.

The disadvantages of the portable analyzer include:

o T h e l i m i t e d s e n s i t i v i t y b e c a u s e o f t h e l a c k of a concentration step.

o T h e l i m i t e d s e l e c t i v i t y and i n t e r f e r e n c e problems because of the lack of a separation step.

o T h e l i m i t e d a c c u r a c y b e c a u s e o f t h e i n a b i l i t y t o calibrate adequately for the mixtures found i n s o i l vapors.

T h e various analyzers o n the market (Anastas, et al., 1980) have their unique advantages, disadvantages, and areas f o r u s e a s m o n i t o r s o f s o i l g a s for VOCs. T h e following section will discuss the t y p e s of analyzers best suited f o r soil gas analysis.

FID analyzers-- The FID is the most widely used detector for the analysis

of V O C s b y gas chromatography. It is also o n e o f t h e m o s t widely used f o r portable analyzers. The Century Organic Vapor

170

TABLE 5.1. DESCRIPTION OF SELECTED PORTABLE ANALYZERS

Comary S y o t a l i r a

I4 1bm

e.=

0.3 #m&

.cnc 0 bra

8.2 Ur

n .-

0.273 U h nc 4 h

9 lbo

n .- 5 l k

81.508

- n 4 b n

10 lk

811 .m

A n a l y z e r ( O V A ) is a n e x a m p l e o f a n F I D instrument. T h e F I D responds t o organic compounds with a sensitivity of < 1 ppmv f o r methane b u t d o e s not r e s p o n d t o i n o r g a n i c c o m p o n e n t s in air. T h e C e n t u r y O V A c a n be o p e r a t e d c o n t i n u o u s l y w i t h a s a m p l e probe c o l l e c t i n g a sample at approximately 1 t o 2 L/min or as a GC with a n isothermal (ambient or ice bath) column a n d w i t h g a s s a m p l i n g v a l v e s . T h e total range can be scaled t o 3 ranges or as a single scale from 1 t o 10,000 l p m v a n d h i g h e r by u s i n g a d i l u t i o n p r o b e . T h e O V A is p o w e r e d by a b a t t e r y p a c k a n d contains a hydrogen tank w h i c h s u p p l i e s t h e f u e l f o r t h e FID. The FID oxidant is ambient air.

A n a d v a n t a g e of t h e OVA 1 s i t s r e s p o n s e t o a wide range o f o r g a n i c c o m p o u n d s w i t h sub-ppmv s e n s i t i v i t y . I t is a l s o easy .to u s e , has a wide range, and has optional chromatographic capabilities. T h e g r e a t e s t d i s a d v a n t a g e of t h e O V A is i t s v a r i a b l e r e s p o n s e t o d i f f e r e n t o r g a n i c compounds. S e v e r a l studies h a v e b e e n m a d e t o d e t e r m i n e r e s p o n s e f a c t o r s f o r organic S p e c i e 3 ( B r o w n , et al., 1980; Dubose and Harris, 1981: Dubose , et al., 1981; W i l l e y , et el., 1976). T h e r e s p o n s e factors w e r e f o u n d t o vary f r o m 0.2 t o more t h a n 100. T a b l e 5.2 s h o w s h o w t h e v a r y i n g r e s p o n s e f a c t c r s a f f e c t t h e c o n c e n t r a t i o n r e p o r t e d b y t h e OVA. T h e large 1.ange in values reported in Table 5.2 also indicates the OVA response is h i g h l y variable. T h e e q u a l carbon response typical of the FID is not found f o r t h e O V A w h e n used i n t h e n o n - c h r o m a t o g r a p h i c mode. H o w e v e r , h y d r o c a r b o n s d i s p l a y l e s s v a r i a t i o n t h a n o r g a n i c compounds containing heteroatoms such a s o x y g e n or n i t r o g e n a s shown in T a b l e 5.2. Using an OVA for gasoline detection would result in smaller errors due to calibration than other p o r t a b l e a n a l y z e r s . T h e OVA h a s b e e n used e x t e n s i v e l y f o r g a s o l i n e detection.

T h i s p r o b l e m of c a l i b r a t i n g t h e OVA can be minimized by using t h e G C o p t i o n and b y c a l i b r a t i n g f o r e a c h i n d i v i d u a l compound. H o w e v e r , environmental samples contain such a large number of components that a d e q u a t e c h r o m a t o g r a p h i c s e p a r a t i o n c a n n o t be o b t a i n e d with t h e a m b i e n t t e m p e r a t u r e OVA c o l u m n . A n o t h e r d i s a d v a n t a g e o f t h e O V A is t h e h i g h s a m p l e f l o w r e q u i r e d ( 1 t o 2 L/min). F o r s o i l - g a s m e a s u r e m e n t s s u c h as soil-core or ground-probe m e a s u r e m e n t s , r e m o v i n g s o i l g a s at this r a t e w o u l d b e d i f f i c u l t w i t h o u t d i s t u r b i n g the SOil/gaS e q u i l i b r i u m or d r a w i n g i n a i r f r o m a b o v e t h e s o i l . T h e s e n s i t i v i t y of flux chamber measurements will be limited b y the OVA since t h e diluting sweep gas flow rate needs to be e q u a l t o or greater tnan the OVA sample flow rate.

D e s p i t e t h e problem m e n t i o n e d a b o v e , t h e OVA h a s b e e n u s e d s u c c e s s f u l l y a s a s c r e e n i n g t o o l f o r g r o u n d - p r o b e m e a s u r e m e n t s , t o c o r r e l a t e o t h e r m e a s u r e m e n t t e c h n i q u e s ( G l a c u m , e t a l . , 1 9 8 3 ) , to d e t e r m i n e w h e n s t e a d y - s t a t e

172

Actual Colacentration ( p p r ) Required t o Came

10,000 p p r fo r t rumen t Rerpoore+ ?rrily/Compouad OVA

Alkrner /Ethane a-Butme n-Bexrac

Alkenes /Ethylene 1 -But ene I-Buena

Aromatic r/Benaene Toluene o-Xylene

Alcobo l8 /~ than01 1 -Pro pan01 1 -But 8no 1

kidr/Pormic Acid Acetic & i d Butyric Acid

6,500 (4,400 t o 15,800)

4,100 (3,800 t o 4,500) 5,000 (4,600 t o 5,500)

4,700 (3,900 t o 5,800)

7,100 (6,300 t o 8,200)

4,900 (3,900 t o 6,600) 5,600 (5,100 t o 6,200)

2,900 (2,800 t o 3,100) 3,900 (3,600 t o 4,300) 4,300 (2,800 t o 8,500)

43,900 (36,100 t o 56,000 9,300 (7,700 t o 11,600)

14,400 (8,900 t o 23,400)

142,000 (106,000 t o 198,000) 16,400 (11,100 t o 26,500) 6,000 (3,800 t o 31,400)

53,800 (18,700 t o 264,000) 7,800 (6,200 t o 10,200)

78,900 (50,100 t o 138,000)

*Both inrtnmentr were calibrated t o metbrne a t 8,000 p p r (Dubose, e t a1 ,, 1981)

173

c o n d i t i o n s h a v e b e e n r e a c h e d i n f l u x chamber e x p e r i m e n t s (Radian C o r p o r a t i o n , 1 9 8 4 1 , and t o a d J u s t t h e s w e e p - a i r f l o w r a t e t o a c h i e v e t h e d e s i r e d c o n c e n t r a t i o n range i n f l u x chamber exper iments . When u s i n g t h e O V A for t h e s e purposes , one s h o u l d remember t h a t changes i n c o n c e n t r a t i o n r ead ings could be due t o a change i n t h e o rgan ic Composition i n s t e a d of a Change i n t h e a c t u a l c o n c e n t r a t i o n . Likewise , a s t a b l e c o n c e n t r a t i o n r ead ing may b e d u e t o a change i n t h e t o t a l o r g a n i c c o n c e n t r a t i o n complemented w i t h a change i n c o m p o s l t i a n . However, i n c a s e s where t h e composition of t h e ground-water plume is homogeneous, t h e O V A s h o u l d p r o v i d e a c o n v e n i e n t s c r e e n i n g t o o l of t h e r e l a t i v e t o t a l o rgan ic c o n c e n t r a t i o n .

P I D ana lyzers - - -The P I D h a s become p o p u l a r a s a d e t e c t o r f o r p o r t a b l e

a n a l y z e r s because of i t s h i g h s e n s i t i v i t y t o c e r t a i n compounds, i t s e a s e o f o p e r a t i o n , and b e c a u s e no f u e l g a s o r f l a m e is r e q u i r e d .

T h e P I D i o n i z e s compounds whose i o n i z a t i o n p o t e n t i a l s a r e c l o s e t o or lower than t h e energy of t h e lamp u s e d . D i f f e r e n t e n e r g y lamps a r e a v a i l a b l e f o r a n a l y z i n g d i f f e r e n t compounds a l lowing f o r some s e l e c t i v i t y . W i t h t h e 1 0 . 2 eV lamp, a l k a n e s h a v e l i t t l e o r n o r e s p o n s e w h i l e a l k e n e s , a r o m a t i c s , o r g a n o s u l f u r compounds , and c a r b o n y l compounds h a v e h i g h r e s p o n s e s . A l c o h o l s , h a l o g e n a t e d a l k a n e s , and most i n o r g a n i c g a s e s have no r e s p o n s e . W i t h a 1 1 .7 eV l a m p , a l l o f t h e s e l e c t i v i t y f o r o r g a n i c compounds except methane is l o s t . The r e p o r t e d s e n s i t i v i t i e s f o r benzene a r e 0 . 1 ppmv i n a i r and have a r a n g e u p t o 2 0 0 0 ppmv f o r b e n z e n e . Another f e a t u r e of t h e P I D 1 s t h a t i t i s e s s e n t i a l l y a n o n - d e s t r u c t i v e d e t e c t o r which a l l o w s s a m p l e s t o be c o l l e c t e d a f t e r p a s s i n g t h r o u g h t h e d e t e c t o r .

The t h r e e m a j o r p o r t a b l e a n a l y z e r s a v a i l a b l e a r e t h e Photovac l O A l O p o r t a b l e G C , t h e H N U p h o t o i o n i z e r , and t h e A I D Model 5 8 0 P I D system. The Photovac is designed a s a GC b u t can be opera ted i n a cont inuous mode w i t h t h e a d d i t i o n of a p u m p . S a m p l e s a r e i n j e c t e d i n t o t h e column and a r e s e p a r a t e d b y u s i n g a dry a i r c a r r i e r g a s . Packed columns u p t o s i x m e t e r s i n l e n g t h and c a p i l l a r y columns can be used i n t h e p o r t a b l e G C . S e n s i t i v i t i e s down t o 0 . 1 p p b v for hydrogen s u l f i d e a r e q u o t e d b y t h e m a n u f a c t u r e r . Photovac a l s o now markets a p o r t a b l e P I D i n s t r u m e n t c a l l e d " T I P " f o r g a s a n a l y s i s which is d e s i g n e d t o be u s e d a s a cont inuous a n a l y z e r .

T n e HNU p h o t o i o n i z e r is a c o n t i n u o u s a n a l y z e r w i t h t h e l a m p c o n t a i n e d i n t h e sample p r o b e . The s m a l l p r o b e volume . i i ~ o w s t h e d e t e c t o r t o r e s p o n d i n a s l i t t l e a s 3 seconds a n d r e q u l r e s o n l y a s m a l l sample s i z e . The sample f l o w r a t e is 3 p p r o x i m a t e l y 0 . 5 L l r n i n . T h r e e l a m p s ( 9 . 5 eV, 1 0 . 2 eV, 1 1 . 7

174

eV) a r e a v a i l a b l e . The A I D 580 is s i m i l a r t o t h e H N U except t h e lamp is @nClOsed i n t h e u n i t and is no t i n t h e probe . The sample f low r a t e is approx ima te ly 0 . 5 t / m i n , a n d t h e e x i t is p lumbed fo r easy c o l l e c t i o n of samples f o r l abora to ry ana lys i s .

The a d V 8 n t a g e s o f t h e P I D a n a l y z e r s a r e t h e g r e a t e r s e n s l t l v l t y f o r many compounds compared t o t h e F I D , t h e s e l e c t i v i t y f o r c e r t a i n c l a s s e s o f c o m p o u n d s , t h e nondes t ruc t ive n a t u r e of t h e P I D , and t h e a b s e n c e of f u e l g a s . The d i s a d v a n t a g e s a r e t h e h i g h l y v a r i a b l e response f a c t o r s f o r each compound, matr ix e f f e c t s such a s quenching of t h e r e s p o n s e because of oxygen (Freeman, 19801, and t h e low response or lack of a r e s p o n s e f o r some compounds s u c h a s t h e flUOrOCarbOn8. The Photovac used w i t h a column c o u l d minimize some of t h e s e problems.

The u s e f u l n e s s of t h e P I D ana lyze r s is i n screening s o i l vapors con ta in ing non-methene hydroca rbons i n t h e p re sence of h i g h l e v e l s of methane o r when a m b i e n t l e v e l s o f methane i n t e r f e r e w i t h monitoring low l e v e l s of nonmethane p o l l u t a n t s . They can be u s e d t o s c r e e n f o r compounds b y c l a s s such a s aromatics and organosulfur or f o r i nd iv idua l components such a s v i n y l c h l o r i d e . A s w i t h the F I D ana lyze r s , t he values obtained f o r t h e P I D s h o u l d n o t be c o n s i d e r e d a b s o l u t e . When t h e r e sponse is used a s a r e l a t i v e v a l u e , t he organic composition and m a t r i x m u s t be homogeneous ove r t h e a r e a o r t i m e b e i n g compared.

Other analyzers- Two o t h e r t y p e s of p o r t a b l e a n a l y z e r s have been used t o

d e t e c t t r a c e l e v e l s of V O C s i n a i r . The l o n g - p a t h - l e n g t h I R a n a l y z e r s have s e n s i t i v i t i e s i n t h e low ppmv. The H I R A N - I A gaa analyzer has a v a r i a b l e path l eng th c e l l ( range 0 . 7 5 m t o 20 m ) s o t h a t a r a n g e f rom l e s s t h a n 1 ppmv t o lQ,OOO ppmv can be ana lyzed . The wavelength Is a l s o v a r i a b l e and a l l o w s f o r m o n l - t o r i n g a l m o s t any o r g a n i c component. A m i c r o p r o c e s s o r model can be used t o monitor up t o 1 1 components. The a n a l y z e r is c o n c e n t r a t i o n - d e p e n d e n t and h a s a sample f low r a t e of 30 l l m i n .

The a d v a n t a g e of t h e M I R A N - I A p o r t a b l e a n a l y z e r is t h e a b i l i t y t o monitor many of the r e a c t i v e o r g a n i c compounds such a s p h o s g e n e , e t h y l e n e o x i d e , and f o r m a l d e h y d e s which a r e d i f f i c u l t t o sample and t o analyze w i t h o t h e r t e c h n i q u e s . The d i s a d v a n t a g e of t h e H I R A N - I A i s t h e l a r g e c e l l volume w h i c h is required for ppmv measurements. A l a r g e volume of s o i l gas i s needed t o o b t a i n t h a t k i n d of s e n s i t i v i t y . Such a volume is seldom a v a i l a b l e except w i t h d i l u t e d f l u x chamber measurements. T o t a l o r g a n i c v a l u e s a r e r e l a t i v e a t b e s t , w h i l e i n d i v i d u a l compounds can be s e l e c t i v e l y mon i to red and q u a n t i t a t e d a t t h e c h o s e n w a v e l e n g t h . The M I R A N - I A p o r t a b l e model weighs 32

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p o u n d s w h i c h i s 8 u b S t a n t l a l l y more t h a n t h e P I D a n d F I D a n a l y z e r s . I n a d d i t i o n , t h e s t a b i l i t y and t h e r u g g e d n e s s of t h e o p t i c a l ana lyze r s would be expeoted t o be l e s s t h a n t h e PID or P I D a n a l y z e r s .

Ano the r oommonly used p o r t a b l e ana lyze r is t h e Baoharach TLV S n i f f e r . I t i s a h o t - w i r e d e t e c t o r which meabureb v a p o r s which can be c a t a l y t i o a l l y oombusted. I t has a r ange of 2 p p a v t o 1 0 , 0 0 0 ppmv and a nominal sample flow r a t e of 2 L / m i n . L i k e t h e F I D , t h e T L V S n i f f e r r e s p o n d s s i m i l a r l y t o a l l o r g a n i c compounds and h a s v a r i a b l e r e s p o n s e f a c t o r s (Brown, e t a l . , 1 9 8 0 ; D u b o s e , e t a l . , 1 9 8 1 ) . A s a r e s u l t , i t h a s t h e same advant.ages, d i sadvan tages , and uses as t h e F I D a n a l y z e r l i s t e d above.

Conclusions-- T h e p o r t a b l e a n a l y z e r s designed f o r ambient -a i r a n a l y s i s

have l i m i t e d uses as a n a l y z e r s of s o i l gases . T h e i r a d v a n t a g e s a r e t h e e l i m i n a t i o n o f sample c o l l e c t i o n and t r a n s p o r t i o n , and theimmediate a v a i l a b i l i t y of resul ts . The ma jo r d i s a d v a n t a g e s a r e v a r i a b l e r e s p o n s e t o d i f f e r e n t c l a s s e s of compounds and l a r g e sample volume r e q u i r e m e n t s . Having a d c t e c t i o n l i m i t of 1 ppmv can l i m i t u s e i n some c a s e s . The uses f o r p o r t a b l e a n a l y z e r s i n c l u d e s c r e e n i n g w e l l s and g r o u n d p r o b e s t o d e t e r m i n e i f more a c c u r a t e and expens ive sampling e f f o r t s a r e n e e d e d a n d t o o p t i m i z e f l u x c h a m b e r c o n d i t i o n s b e f o r e c o l l e c t i n g a sample fo r d e t a i l e d a n a l y s i s .

Remote a n a l y s i s - - I n a l m o s t a l l c a s e s , t o a c c u r a t e l y de t e rmine t h e amount

o r composition of o r g a n i c compounds i n s o i l g a s , a s a m p l e has t o be c o l l e c t e d and t a k e n t o a l abora to ry where c o n d i t i o n s a r e s t a b l e enough t o suppor t t h e l e v e l of s o p h i s t i c a t i o n r e q u i r e d t o a n a l y z e t h e s a m p l e . The l a b o r a t o r y could be a mobile f i e l d l a b on t h e s i t e or a modern a n a l y t i c a l l a b on t h e o t h e r s i d e o f t h e c o u n t r y . W i t h e i t h e r s i t u a t i o n , a r e p r e s e n t a t i v e sample m u s t be c o l l e c t e d , and i t s i n t e g r i t y m u s t be m a i n t a i n e d u n t i l i t can be a n a l y z e d . The s a m p l i n g method m u s t be co rnpa tab le w i t h t h e a n a l y t i c a l m e t h o d . I f t h e a n a l y s i s i s n o t v e r y s e n s i t i v e , a l a r g e s a m p l e m u s t be c o l l e c t e d . I f t h e sample m u s t be s e n t a c r o s s t h e c o u n t r y , t h e c o n t a i n e r m u s t be i n e r t and r u g g e d . The f o l l o w i n g s e c t i o n s w i l l d i s c u s s f i r s t t h e sample c o l l e c t i o n and s t o r a g e methods and t h e n t h e a n a l y t i c a l m e t h o d s w h i c h a r e u s e d or c o u l d b e u s e d f o r s o i l - g a s measurement.

Sample c o l l e c t i o n - -

i n t o two c l a s s e s : Sample c o l l e c t i o n methods of V O C s i n g a s e s a r e d i v i d e d

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o A d s o r b e n t methods where t h e g a s i s passed th rough a s o l i d a d s o r b e n t which r emoves t h e V O C s f r o m t h e inorganic gas matr ix .

o Whole a i r methods where the e n t i r e sample is placed i n a con ta ine r and is t ranspor ted t o t h e l a b ;

A d s o r b e n t methods--The a d s o r b e n t method i s a t t r a c t i v e because i t concen t r a t e s t h e components of i n t e r e s t and removes many of t h e components known t o add t o the i n s t a b i l i t y of t h e sample and which i n t e r f e r e w i t h t h e s a m p l e a n a l y s i s . The a d s o r b e n t c o n t a i n e r s a r e g e n e r a l l y s m a l l and can be e a s i l y t r a n s p o r t e d t o and from t h e f i e l d . The l i m i t a t i o n s o f t h e a d s o r b e n t m e t h o d s a r e i r r e v e r s i b l e a d s o r p t i o n , i ncomple t e a d s o r p t i o n ( b r e a k t h r o u g h ) , a n d a r t i f a c t f o r m a t i o n . I r r e v e r s i b l e a d s o r p t i o n occurs when adsorbed components cannot be comple t e ly d e s o r b e d . I d e a l l y f o r t h e a n a l y s i s of V O C s , a d s o r b e n t s s h o u l d b e t h e r m a l l y d e s o r b e d s i n c e s o l v e n t d 8 s O r p t i O n i n c r e a s e s a r t i f a c t s , d i l u t e s t h e sample components, and i n t e r f e r e s w i t h t h e a n a l y s i s . Incomple t e a d s o r p t i o n i s charac te r ized a s a breakthrough and r e s u l t s i n t h e l o s s of t h e more v o l a t i l e s ample components. A r t i f a c t formation can occur d u r i n g thermal deso rp t ion o r from r e a c t i o n w i t h t h e a d s o r b e n t m a t e r i a l and t h e sample . A l l t h r e e of t h e s e poss ib l e problems m u s t be f u l l y i n v e s t i g a t e d d u r i n g t h e s a m p l i n g m e t h o d v a l i d a t i o n , and a s t r i c t q u a l i t y c o n t r o l plan m u s t be followed t o insure the method is performing w i t h i n acceptab le limits

The a d s o r b e n t ma te r i a l s most o f t e n used f o r sampling V O C s a r e a c t i v a t e d c h a r c o a l and p o r o u s p o l y m e r s s u c h a s T e n a x . Other a d s o r b e n t s which have been used a r e molecu la r d i e v e s , s i l i c a g e l , and a c t i v a t e d a lumina . Charcoa l h a s been u s e d e x t e n s i v e l y . i n i n d u s t r i a l h y s i e n e a p p l i c a t i o n f o r monitoring V O C s , and N I O S H h a s p u b l i s h e d a s t a n d a r d method f o r c h a r c o a l ( W h i t e , e t a l . , 1 9 7 0 ; N I O S H , 1 9 7 4 ) . C h a r c o a l has a h i g h adso rben t e f f i c i e n c y f o r a l l o r g a n i c compounds b u t r e q u i r e s s o l v e n t d e s o r p t i o n . Desorption e f f i c i e n c i e s can vary w i t h t h e l o t of the manufacturer ( S a a l w a e c h t e r , e t a l . , 1 9 7 7 ) . Carbon d i s u l f i d e i s u s e d a s t h e s o l v e n t and i n t e r f e r e s w i t h t h e determination of components more v o l a t i l e than n-butane. S i n c e t h e s o l v e n t c a n n o t be c o n c e n t r a t e d w i t h o u t v o l a t i l e l o s s , t he s e n s i t i v i t y of t h e method is l i m i t e d . The use of c h a r c o a l a s an a d s o r b e n t f o r s o i l - g a s c o l l e c t i o n has been r e p o r t e d b y C o l e n u t t and Davies (1980) and K a r i m i ( 1 9 8 3 ) . A p a t e n t e d m e t h o d u s i n g a C u r i e - p o i n t wire coated w i t h a c t i v a t e d charcoa l i s used b y P e t r e x C o r p o r a t i o n ( B i s q u e , 1 9 8 3 ) . I n s t e a d of p a s s i n g t h e sample through an adsorbent bed, Petrex allows t h e sample t o d i f f u s e i n t o t he coated wire ove r 3 t o 15 d a y s , The wire i s then a n a l y z e d b y C u r i e - p o i n t mass spec t romet ry . The technique is very s e n s i t i v e and does n o t a f f e c t t h e g a s / s o i l

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equilibrium. Absolute quantitation determined b y using this technique is difficult, and long sampling times are required to obtain high sensitivities.

T h e p o r o u s p o l y m e r a d s o r b e n t Tenax-GC has been used extensively in ambient air measurements . Several good reports have charaoterlzed the breakthrough volumes for a large number of compounds, t h e a f f e c t O f m o i s t u r e a n d s a m p l e f l o w , of desorption efficiency, and of artifact formation (Brown and Purnell, 1979; Krost, 1982). Tenax has been found effective f o r m o s t o r g a n i c c O m p O U n d 8 e x o e p t f o r h y d r o c a r b o n s a n d halocarbons that are more volatile than n-hexane, l o w molecular w e i g h t a l c o h o l s , a m i n e s , a n d a l d e h y d e s . C o m p o u n d s c a n effectively be thermally desorbed to obtain sub ppbv detection limits. Varying amounts of artifaots have been reported for Tenax; some of them are believed t o be due t o o x i d a t i o n of Tenax and t o improper cleaning of the adsorbent. Because of the artifact peaks and the inability to trap the less volatile compounds, Tenax cannot be used to obtain total VOC values, but it would be an ideal method t o monitor individual components when it is shown that they are not affected by these problems. Tenax-GC has been used to analyze soil gas from ground probes. Swal low and Gschwend (1983) monitored benzene, toluene, and trichloroethylene in ambient air and at two depths in the soil a b o v e the ground water. They reported values a s low as 0.2 ng/L with a precision of &lS percent.

Whole air methods-- Whole air methods of analysis of VOCs in soil gas have been used extensively. T h e method could be divided into two subcategories. One involves removing the soil gas from the soil and transporting it to the lab, and the other involves transporting the soil with the gas. For collection of soil g a s , three different containers can be used:

o plastic bags made of Tedlar or Teflon,

o passivated stainless-steel canisters and syringes, and

o glass syringes.

When evaluating which container to use, several factors should be considered:

o Sample hold time and stability over the hold time

o Sample handling and shipping and the durability of the container .

o S a m p l e c o n t a i n e r c l e a n i n g p r o c e d u r e s a n d m e m o r y effects.

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T h e use of plastic bag8 for air samples is inexpensive and oonvenient. However, several studies havo been made using Tedlar and Teflon bags (Seila, et al., 1976; Lonneman, et al., 1 9 8 1 ) and have found that oontamination wa8 signifloant i f t h e bag8 were exposed to light. Other problems found with plastic bags are permeation o f o O m p o u n d 8 i n t o a n d out o f t h e b a g 8 during storage and sample leakage enoountered during handling and transportation. Plastio b a g s a r e not r e c o m m e n d e d f o r soil-gas analysis unless the s t o r a g e times are less than 4-8 hours and the conoentratlons are high.

S t a i n l e s s - s t e e l c a n i s t e r s with a pa881Vated interior surface have been used for a wide variety of V O C measurements i n c l u d i n g s o i l - g a s m o n i t o r i n g . T h e c a n i s t e r s h a v e b e e n described by Harsch ( 1 9 8 0 ) . and hydrocarbon, halocarbons, and carbonyl COmpOUnd8 have been found to be stable for as long as three weeks (Oliver, et al., 1 9 8 5 1 Westberg, et al., 1 9 8 2 ) . T h e c a n i s t e r c a n be p r e s s u r i z e d t o hold more than 2 0 L of sample and oan be shipped easily without any sample loss. T h e o a n i s t e r s c a n e a s i l y b e o l e a n e d s i n c e t h e y w i t h s t a n d temperatures up to 15OOC and c a n b e e v a c u a t e d t o very l o w p r e s s u r e s . B e o a u s e n o l i g h t o a n enter the canisters, t h e possibility of photoohemical r e a o t l o n s is minimized. T h e passivation prooess used to produce oanisters has been applied t o the production of stainles s - s t e e l s y r i n g e s ( S c i e n t i f i c Instrument Specialist, Inc., MOSCOW, Idaho). These syringes would have the same advantages as the canisters plus the added value of easy sample C O l l ~ C t i O n . A 8Oil-gas sample could be drawn slowly when the syringe is used with the disruption of t h e soil-gas equilibrium being minimized. Slowly drawing a small sample when a canister 1s u s e d r e q u i r e s vacuum f l o w regulation. Sample dilution is required to obtain s a m p l e s smaller than canister volume (generally greater than 0.5 L).

T h e r e a r e two m e t h o d s f o r c o l l e c t i n g a s a m p l e in canisters. One involves using a pump to fill the canister. T h i s technique requires a cl e a n , inert p u m p and enough sample to purge the canister before filling it. The other method is t o first evacuate the canister and then to bring the canister to atmO8pheriC pressure with sample. The first technique would n o t be oompatible with most s o i l gas techniques except flux chamber methods. The second method has been found to work for b o t h g r o u n d p r o b e a n d f l u x c h a m b e r m e t h o d s ( R a d i a n Corporation-S, 1984; Crow, et el., 1 9 8 5 ; Radian Corporation-T, 1 9 8 4 ) . B y using a vacuum flow r€#gUlatOr, the rate of sampling c a n b e c o n t r o l l e d to m i n i m i z e b o t h s o i l / g a s e q u i l i b r i u m disturbances and migration of atmospheric gas into the sampler. Detection limits of 1 p p b v have been obtained b y u s i n g t h e canister method.

L79

C l a s s c o n t a i n e r s s u c h a s s y r i n g e s ( R a d i a n C o r p o r a t i o n , 1 9 8 4 ; T h o r b u r n , e t e l . , 1 9 7 9 ; M a r r i n , e t a l . , 1 9 8 4 ; R a d i a n C o r p o r a t i o n - S , 1 9 8 4 ; Crow, e t a l . , 1985; Radian Corporation-T, 1984; Wood, e t a l . , 1 9 8 0 ; Dowdell, e t a l . , 1 9 7 2 ) and e v a c u a t e d f l a s k s (Thorburn , e t a l . , 1 9 7 9 ) have been Used t o o o l l e c t 8011- g a s s a m p l e s . G l a s s h a s b e e n f o u n d t o b e i n e r t a n d n o n c o n t a m i n a t i n g f o r m o s t o r g a n i c compounds . Most g l a a s s y r i n g e s and f l a s k s r e q u i r e a T e f l o n v a l v e o r s e a l t o be g a s - t i g h t . H o w e v e r , t h e T e f l o n c a n b e a s o u r c e o f contaminat ion . C r o u n d - g l a s s j o i n t 8 have been u s e d ; however , t h e y a r e n o t comple te ly g a s - t i g h t , and samples cannot be s t o r e d f o r any l e n g t h of t i m e . B e c a u s e o f t h e f r a g i l e n a t u r e of g l a s s , i t c a n n o t b e s h i p p e d very e a s i l y and is used mostly f o r o n - s i t e ana lyses . S ince g l a s s can t r a n s m i t l i g h t , i t h a s been s u g g e s t e d t h a t s a m p l e s o o u l d be a f f e o t e d b y p h o t o c h e m i c a l r e a c t i o n s and should be kept O u t of d i r e c t s u n l i g h t .

A n o t h e r method f o r s a m p l i n g s o i l g a s e s i s t o p u m p t h e s o i l gas d i r e c t l y i n t o a sample loop f o r i n j e c t i o n i n t o t h e GC (Weeks, e t a l . , 1 9 8 2 ) . T h i s r e q u i r e s a l a r g e volume of s o i l g a s f r o m a vaouum p u m p . T h i s would d i s r u p t t h e s o i l / g a s e q u i l i b r i u m and c a n p u l l i n a t m o s p h e r i c gas a r o i n d t h e ground probe.

The c o l l e c t i o n of s o i l c o r e s i s d e s c r i b e d i n c h a p t e r 4 (Head-space Measurement) and is an a l t e r n a t i v e t o o o l l e c t i o n of s o i l gas a l o n e . The s o i l c o r e s a r e s e a l e d and a r e s e n t t o a l a b o r a t o r y where s o i l g a s can be removed and a n a l y z e d . The a d v a n t a g e s o f t h i s t e c h n i q u e a r e t h a t t h e s o i l i t s e l f can a l s o b e a n a l y z e d b y o t h e r p h y s i c a l or c h e m i c a l m e t h o d s , t h e t e c h n i q u e r e q u i r e s r e l a t i v e l y l i t t l e e x p e r t i s e or equipment, t h e samples a p p e a r t o h a v e a l o n g s h e l f l i f e , a n d a more a c c u r a t e s o i l g a s measurement can be ob ta ined under l a b o r a t o r y cond i t ions than i n t h e f i e l d . The d i s a d v a n t a g e of t h i s method. is l o s s o f v o l a t i l e s d u r i n g t h e c o r i n g of t h e sample and t r a n s p o r t . I n some c a s e s , o b t a i n i n g a r e p r e s e n t a t i v e sample m a y b e d i f f i c u l t . T h e s a m p l e c a n a l s o be a f f e c t e d b y b i o l o g i c a l a c t i v i t y i n s o i l .

Sample Analysis-- A n a l y s i s o f s o i l - g a s samples i s p e r f o r m e d i n e i t h e r an

o n - s i t e m o b i l e l a b o r a t o r y o r a r e m o t e l a b o r a t o r y . T h e i n s t r u m e n t a t i o n of t h e m o b i l e l a b o r a t o r y i s l i m i t e d t o equipment which i s e a s i l y s e t u p , r u g g e d , a n d r e q u i r e s a m i n i m u m a m o u n t o f power and s u p p o r t equipment. Methods which r e q u i r e s u b a m b i e n t t e m p e r a t u r e p r o g r a m m i n g , c r y o g e n i c c o n c e n t r a t i o n , and d e t e c t o r s w i t h vacuum systems such a s mass spec t rometers a r e g e n e r a l l y excluded from m o b i l e l a b o r a t o r i e s . T h e o r e t i c a l l y , a n y i n s t r u m e n t d i s c u s s e d h e r e oan be made mobile, b u t exper ience has shown t h a t i t i s only c o s t e f f e c t i v e

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t o u s e a n i n s t r u m e n t s p e c i f i c a l l y d e s i g n e d f o r t h e m o b i l e l a b o r a t o r y .

M o b i l e l a b o r a t o r y i n s t r u m e n t s - - T h e s i m p l e s t m o b i l e l a b o r a t o r y i n s t r u m e n t s a r e t h e p o r t a b l e a n a l y z e r s which have c h r o m a t o g r a p h i c o p t i o n s . T h i s i n c l u d e s t h e Photovac w i t h a PID and t h e C e n t u r y O V A w i t h a PID, These have s i m p l e i n J e c t i o n s y s t e m s , e i t h e r a g a s s a m p l i n g v a l v e ( O V A ) o r a s y r i n g e i n J e c t i o n p o r t (Pho tovao) , The Photovac ha8 an i n t e r n a l column s p a c e which c a n h o l d a 1 1 8 " column u p t o 6 m e t e r s l o n g o r a 25 meter c a p i l l a r y column. There is no tempera ture c o n t r o l for t h e column. The O V A has a n e x t e r n a l column which could be of any s i z e and la a t ambient tempera ture . These i n 8 t r u m e n t s a r e easy . t o t r a n s p o r t and use and, i n t h e case of t h e Photovac, can be v e r y s e n s i t i v e w i t h p p b v d e t e c t i o n l i m i t s . T h e a d d e d a d v a n t a g e of t h e o h r o m a t o g r a p h i c c a p a b i l i t i e s l a t h a t i n d i v i d u a l Compound8 may b e mon i to red and q u a n t i t a t e d w i t h a c c u r a t e r e s p o n s e f a c t o r s . Because of t h e complex n a t u r e of moat environmental samples i n c l u d i n g 8011 gas , t h e u n c o n t r o l l e d t e m p e r a t u r e of t h e column i n t h e s e p o r t a b l e a n a l y z e r s does not a l low t h e h i g h r e s o l u t i o n s e p a r a t i o n needed t o i d e n t i f y and t o q u a n t i t a t e f o r moa t o o m p o n e n t s a c c u r a t e l y . R e p r o d u c i b l e r e t e n t i o n t imes a r e d i f f i c u l t t o a c h i e v e i n t h e f i e l d b e c a u s e of t e m p e r a t u r e f l u c t u a t i o n s , and s e p a r a t i o n of components w i t h a wide range of v o l a t i l i t l e s is d i f f i c u l t w i t h o u t t e m p e r a t u r e p r o g r a m m i n g . T h e s e a n a l y z e r s can b e u s e f u l i f t h e s a m p l e c o n t a i n s l a r g e amounts of easy t o s e p a r a t e con taminan t s s u c h a s t h o s e found i n a c h e m i c a l s p i l l o r i f only a v o l a t i l i t y range l a needed such as t o t a l C 2 - C 4 compounds. G a s o l i n e s a m p l e s a r e o f t e n c h a r a c t e r i z e d b y compar ing t h e f u n c t i o n of t h e t o t a l o rgan ic compounds i n v o l a t i l i t y range.

A s t e p above t h e p o r t a b l e G C s a r e t h e f i e l d G C s . These a r e s m a l l , s t u r d y G C s t h a t c o n t a i n temperature . c o n t r o l l e d ovens and a v a r i e t y o f i n j e c t o r s and d e t e c t o r s . Some of t h e modules which have been used f o r s o i l g a s a r e t h e V a r i a n Mobel 6 0 0 0 ( H a r r i n , e t a l . , 1 9 8 4 1 , S h i m a d z u Model G C - M i n i 2 ( R a d i a n C o r p o r a t i o n , 1 9 8 4 ; R a d i a n C o r p o r a t i o n - S , 1 9 8 4 ; R a d i a n C o r p o r a t i o n - T , 19841 , C a r l e A G C (Wood, e t a l . , 19801, and t h e HNU GC 301 ( R a d i a n C o r p o r a t i o n - S , 1 9 8 4 ) . T a b l e 5 . 3 c o n t a i n s t h e d e s c r i p t i o n s g i v e n b y t h e m a n u f a c t u r e r s o f s e l e c t e d p o r t a b l e G C s . T h i s l i s t l a not exhaus t ive and does n o t mean t o e x c l u d e o t h e r G C s w h i c h c o u l d J u s t a s e a s i l y be used i n t h e f i e l d . The components of t h e G C s s u c h a s 1 n J e c t i o n p o r t s and d e t e c t o r s can u s u a l l y be s e l e c t e d . I n some c a s e s , t empera tu re programming i s a v a i l a b l e . Because t h e s e G C s a r e s m a l l e r t h a n s t a n d a r d models , t h e number of columns and t h e i r l e n g t h s can be l i m i t e d . The b e s t r e s u l t s a r e o b t a i n e d w i t h a n i n s t r u m e n t h a v i n g a h e a t e d g a s s a m p l i n g v a l v e f o r i n j e c t i o n of t h e g a s samples. The d e t e c t o r s moat commonly found a r e t h e F I D , P I D , and t h e E C D . The H N U G C 301 i s unique i n t h a t i t has both an

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ax4

OlCOI

F I D and a P I D w h i c h c a n b e o p e r a t e d e i t h e r s e p a r a t e l y o r i n s e r i e s . The P I D can be added t o o t h e r i n s t r u m e n t s i f t h e r e is room. T h e ECD is ext remely s e n s i t i v e and is s e l e c t i v e f o r moat halogenated compounds w i t h d e t e c t i o n limits of 1 . 0 p p b v w i t h n o c o n c e n t r a t i o n of t h e sample ( M a r r i n , e t a l . , 1 9 8 4 ) . I n one s t u d y , both a c ryogen ic oonoen t ra t ion s t e p and an E C D were used t o a n a l y z e t r l o h l o r o f l u o r o m e t h a n e a n d d i ch lo rod i f luo romethane below the 100 p p t v ( p a r t s pe r t r i l l i o n ) l e v e l (Weeks, e t a l . , 1 9 8 2 ) .

The c h r o m a t o g r a p h y oolumns chosen f o r f i e l d a n a l y s i s depend on t h e t y p e s of C O m p O U n d s and on t h e i r v o l a t i l i t y . A n o n p o l a r m e t h y l s i l i c o n l i q u i d p h a s e , & ~ c h a s SE-30, has been used e x t e n s i v e l y f o r h y d r o c a r b o n s and h a l o c a r b o n s . Columns packed i n s t a i n l e s s s t e e l have been used more e x t e n s i v e l y f o r f i e l d use t h a n t h o s e paoked i n g l a s s and c a p i l l a r y c o l u m n s . The p a c k e d c o l u m n s h a v e a h i g h e r o a p a c i t y t h a n c a p i l l a r y columns, and l a r g e volumes of s a m p l e s can be i n j e c t e d w i t h o u t t h e need f o r c r y o g e n i c c o n c e n t r a t i o n s t e p s . The lower c a r r i e r gaa- f low r a t e s of o a p l l l a r y columns would r e q u i r e a l m o s t a m i n u t e t o i n j e c t a 1 m L s a m p l e and would c r e a t e v e r y broad peaks w h i l e a packed column a t a t y p i c a l c a r r i e r f l o w r a t e o f 30 m L / m i n would t a k e 2 seconds t o i n j e c t 1 mL, S t a i n l e s s s t e e l i s chosen over g l a s s b e c a u s e i t is e a s i e r t o i n s t a l l and does not break d u r i n g t r a n s p o r t or use.

The c h r o m a t o g r a p h i c d a t a can be acqu i r ed i n t h e f i e l d on s t r i p o h a r t r e c o r d e r s , on i n t e g r a t o r s , or on a p o r t a b l e computer. Most of t h e p o r t a b l e G C s can be supp l i ed w i t h sma l l s t r i p c h a r t r e c o r d e r s . Small i n t e g r a t o r s such a s t h e HP 3390 c a n be u s e f u l t o s t o r e c a l i b r a t i o n in fo rma t ion and t o i n t e g r a t e peak a r e a s or h e i g h t s . A p o r t a b l e compute r w i t h c h r o m a t o g r a p h i c s o f t w a r e becomes v e r y u s e f u l when t h e raw da ta needs t o be s t o r e d , when more than one d e t e c t o r i s b e i n g u s e d , and w h e n t h e d a t a f rom d i f f e r e n t a n a l y s e s or d e t e c t o r s needs t o be compared.

O f f - s i t e l a b o r a t o r y i n s t r u m e n t s - - W h e n p o s i t i v e identification i s n e e d e d , when very low d e t e c t i o n l imits a r e r e q u i r e d , when d i f f i c u l t s a m p l e m a t r i c e s a r e e n c o u n t e r e d , or when e n v i r o n m e n t a l c o n d i t i o n s p r o h i b i t an o n - s i t e a n a l y s i s , 3011 gas samples w i l l have t o be s e n t t o an o f f - s i t e l a b o r a t o r y . T h e o f f - s i t e l a b may have t h e i n s t r u m e n t a t i o n d i s c u s s e d a b o v e , b u t g e n e r a l l y a h i g h e r a a p h i s t i c a t i o n o f i n s t r u m e n t a t i o n is used.

I f l o w d e t e c t i o n l imi t s a r e r e q u i r e d , t h e samples can be c o l l e c t e d on a s o l i d adso rben t or i n a s t a i n l e s s - s t e e l c a n i s t e r and s e n t t o a l a b w h e r e t h e s a m p l e c a n be c r y o g e n i c a l l y c o n c e n t r a t e d . The o r g a n i c components of a l a r g e r volume o f s o i l g a s c a n be t r a p p e d a t c r y o g e n i c t e m p e r a t u r e s b y u s i n g l i q u i d oxygen, l i q u i d a rgon , or d r y i c e l a c e t o n e b a t h s . To t r a p

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l a r g e v o l u m e s of s a m p l e , water n e e d s t o b e removed f rom t h e s a m p l e . P e r m a p u r e d r i e r s , p o t a s s i u m o a r b o n a t e ( K 2 C O 3 ) ( C o l e n u t t , e t a l . , 1 9 8 0 1 , a n d m a g n e s i u m d i c h l o r a t e [Hg(ClO4)2] ( S c h m i d t , 1 9 8 3 ) h a v e been u s e d t o r e m o v e water from a i r s a m p l e s . R e c o v e r i e s o f h a l o g e n a t e d h y d r o c a r b o n s a r e g o o d w h e n these d r y i n g m e t h o d s a r e u s e d , b u t tor p o l a r c o m p o u n d s s u c h at3 a l c o h o l s a n d a l d e h y d e s , v a r i a b l e r e c o v e r i e s h a v e b e e n f o u n d . For i n j e c t i o n of v o l u m e s smaller t h a n a p p r o x i m a t e l y 2 5 0 m L , no d r y i n g m e t h o d is r e q u i r e d . T h e s a m p l e is t r a p p e d o n g l a s s b e a d s or g l a s s wool p a c k e d i n 1 1 8 i n . s t a i n l e s s - s t e e l t u b i n g . T h e f r o z e n s a m p l e s a r e t h e r m a l l y d e s o r b e d b y u s i n g h e a t c a r t r i d g e s a n d b o i l i n g water a n d a r e i n j e c t e d o n t o a c o l u m n b y s w i t c h i n g a g a s - s a m p l i n g v a l v e .

A d s o r b e n t s a m p l e s a r e i n d e c t e d b y p l a c i n g t h e c a r t r i d g e s i n t o a b l o c k h e a t e r a n d t h e r m a l l y d e s o r b i n g a t a h i g h t e m p e r a t u r e i n t o a f l o w of a n i n e r t g a s s u c h as h e l i u m . S i n c e m o s t a d s o r b e n t s d a n o t h a v e a n a f f i n i t y f o r w a t e r , n o d r y i n g m e t h o d is r e q u i r e d . For h i g h - r e s o l u t i o n a n a l y s i s of a d s o r b e n t s a m p l e s , a s e c o n d c o n c e n t r a t i o n s t e p is n e e d e d t o k e e p t h e d e s o r b e d e f f l u e n t f r o m “ b r o a d e n i n g ” b e f o r e i t r e a c h e s t h e c o l u m n , A c r y o g e n i c t r a p or a s m a l l e r s e c o n d a r y a d s o r b e n t i s g e n e r a l l y u s e d t o f o c u s t h e sample b e f o r e a n a l y s i s .

T h e c h r o m a t o g r a p h i c s e p a r a t i o n a v a i l a b l e i n t h e l a b o r a t o r y c a n b e s u p e r i o r t o t h a t i n t h e f i e l d . T h e use o f s u b a m b i e n t t e m p e r a t u r e p r o g r a m m i n g a n d c a p i l l a r y c o l u m n s a l l o w s most v o l a t i l e compounds t o b e s e p a r a t e d . T h e c h r o m a t o g r a p h i c c o n d i t i o n a n d c o l u m n s u s e d h a v e b e e n d e s c r i b e d i n s e v e r a l p a p e r s ( K r o s t , e t a l . , 1 9 8 2 ; W e s t b e r g , e t a l . , 1 9 8 2 ; J e l t e s , e t a l . , 1 9 7 7 ; C o x , e t al., 1982; W e s t b e r g , e t a l . , 1 9 8 4 ) . I n most a n a l y s e s , a n o n - p o l a r m e t h y l - s i l i c o n , f u s e d - s i l i c a c a p i l l a r y c o i u m n h a s S e e n u s e d . T h e s e c o l u m n s c a n s e p a r a t e u p t o 300 d i f f e r e n t c o m p o u n d s . T h e o v e n t e m p e . r a t u r e i s u s u a l l y p r o g r a o r n e d f r o m s u b a m b i e n t t e m p e r a t u r e s t o o v e r 100°C t o s e p a r a t e t h e f u i l r a n g e of V O C f o u n d i n e n v i r o n m e n t a l s a m p l e s .

‘The d a t e c t i o n m e t h o d s u s e d f o r a n a l y s i s o f s o i l - g a s saz? :es i n c l u d e :

o F l a m e i o n i z a t i o n d e t e c t o r ( F I D ) f o r t h e f u l l r a n g e of o r g a n i c c o m p o u n d s ;

o P h o t o i o n i z a t i o n d e t e c t o r ( P I D ) f o r t h e a r o m a t i c h y d r o c a r b o n s a n d s u l f u r s p e c i e s ;

o E l e c t r o n c a p t u r e d e t e c t i o n ( E C D ) f o r s e l e c t i v e d e t e c t i o n o f h a l o a e n a t e d h y d r o c a r b o n s ;

c Z 3 l i Z i ? c t r a l y t i c C c n d u c t i v i t y d e t e c t o r ( H E C D ) f o r t h e s a e o i f i c d e t e c t i o n o f h a l o g e n a t e d s p e c i e s , n i t r o g e n

1 6 4

e l e m e n t s c o n t a i n i n g o r g a n i c s , or s u l f u r c o n t a i n i n g species; and

o T h e f l a m e p h o t o m e t r i c d e t e c t o r ( F P D ) f o r s u l f u r and phosphorus compounds.

G o o d r e v i e w s h a v e b e e n W r i t t e n d e s c r i b i n g t h e m e r i t s and limitations of these detectors (Farwell, et al., 1 9 8 1 ; H i l l , et al., 1 9 8 2 ; S e v i c k , 1976). I n a d d i t i o n t o t h e s e s t a n d a r d GC d e t e c t o r s , s e v e r a l o t h e r c o n f i g u r a t i o n s h a v e b e e n u s e d s p e c i f i c a l l y f o r s o i l gas. T h e s e include the combinations of t h e FID-PID-HECD described by Earp and C o x ( 1 9 8 2 ) a n d used f o r soil-gas m e a s u r e m e n t s by the Radian Corooration (1984, S-1984, T - 1 9 8 4 ) . T h e c o m b i n a t i o n o f t h e F I D a n d P I D p r o v i d e s q u a l i t a t i v e i n f o r m a t i o n t o a i d i n t h e i d e n t i f i c a t i o n o f h y d r o c a r b o n s w h i l e t h e H E C D c a n s e l e c t i v e l y d e t e c t a n d q u a n t i t a t e h a l o g e n a t e d h y d r o c a r b o n s . T h e m u l t i p l e d e t e c t o r m e t h o d c o m b i n e d w i t h h i g h r e s o l u t i o n c h r o m a t o g r a p h y i s a p o w e r f u l t o o l p r o v i d i n g a c c u r a t e q u a n t i t a t i o n f o r a l l h y d r o c a r b o n and h a l o g e n a t e d s p e c i e s w i t h a h i g h d e g r e e o f c o n f i d e n c e i n t h e c o m p o u n d i d e n t i f i c a t i o n . U n i d e n t i f i e d c o m p o u n d s c a n b e e a s i l y c l a s s i f i e d a s a n a l k a n e , a l k e n e , a r o m a t i c , or h a l o g e n a t e d hydrocarbon from the responses of the detector .

A n e w t e c h n i q u e which has been applied t o the analysis of h a z a r d o u s w a s t e is G C w i t h F o u r i e r t r a n s f o r m i n f r a r e d s p e c t r o m e t r y ( G C / F T I R ) ( S h a r e r , et al., 1984). T h e FTIR can quickly, with good s e n s i t i v i t y , s c a n t h e i n f r a r e d s p e c t r u m of a n e l u t i n g peak w h i c h c a n t h e n be quantitated b y using an FID or other CC detector. T h e i n f r a r e d s p e c t r u m , a f t e r s o m e data m a n i p u l a t i o n , c a n be c o m p a r e d t o a s p e c t r a l l i b r a r y t o make i d e n t i f i c a t i o n s . A s i m i l a r t e c h n i q u e w h i c h h a s b e e n u s e d e x t e n s i v e l y in e n v i r o n q e n t a l a n a l y s i s is GC mass spectrometry (GCIHS). A mass spectrometer is used to obtain a m a s s s p e c t r u m of t h e e l u t i n g G C p e a k s . A m a s s s p e c t r u m c a n sometimes make p o s i t i o n i d e n t i f i c a t i o n s a? u n k n o w n c o m p o u n d s , a n d , i n t h e s i n g l e ion m o d e , it is e x t r e m e l y . s e n s i t i v e a n d selective for the compound of interest, A good review of the GC/HS t e c h n i q u e h a s been published (tenNoever, et al., 1979). The cost of these two techniques, compared to the possible benefits, h a s b e e n the m a i n f a c t o r t h a t h a s l i m i t e d t h e i r u s e i n s o i l - g a s measurements.

C o n c l u s i o n - - M o d e r n a n a l y t i c a l l a b o r a t o r y m e t h o d s have o e e n d e v e l o p e d t o t h e point w h e r e V O C s i n s o i l g a s c a n b e s e p a r a t e d and q u a n t i t a t e d in the sub-ppbv concentration range, and identification can be made with a high level of confidence. T h e r e s e a r c h e r ' s j o b is t o d e t e r m i n e w h a t l e v e l o f saphistication is necessary. T h e use of portable a n a l y z e r s and field C C s t o s c r e e n t h e s a m p l e c a n o f t e n p r o v i d e the a'nswers

185

needed t o make t h i s d e c i s i o n . A r e a s where b e t t e r methods a r e needed i n c l u d e t h e c o l l e c t i o n and d e t e r m i n a t i o n of o x y g e n a t e d c o m p o u n d s , o f s u l f u r compounds, and of n i t r o g e n c o n t a i n i n g compounds. D e t e r m i n a t i o n s of t h e s e compounds a r e d i f f i c u l t b e c a u s e of t h e i r p o l a r n a t u r e compared t o t h e non-polar n a t u r e of t h e h y d r o c a r b o n s and h a l o g e n a t e d h y d r o c a r b o n s . D r a s t i c m e a s u r e s a r e g e n e r a l l y r e q u i r e d t o o b t a i n a r ea8Onab ly low d e t e c t i o n l i m i t f o r t h e s e c o m p o u n d s s u c h a s t h e f i e l d c o l l e c t i o n of s u l f u r s p e c i e s t h a t makes use of t h e d e a c t i v a t e d c ryogenic t r a p s descr ibed b y Farwel l ( 1 9 7 9 ) .

- Q u a l i t y Assu rance /Qua l i ty Cont ro l ( Q A I Q C )

'For an a n a l y t i c a l p r o c e d u r e t o have any v a l u e , a Q A / Q C program m u s t be d e s i g n e d s o t h a t t h e q u a l i t y of t h e d a t a i s d e f i n e d ( 1 . e . . c o n f i d e n c e limits) and so t h a t a s su rance e x i s t s t h a t t h e method i s per forming a t t h a t l e v e l . Most a n a l y t i c a l me thod Q A / Q C p l a n s c o n t a i n a c a l i b r a t i o n s t e p , a l i n e a r i t y check, a Q C s t a n d a r d a n a l y s i s , a b l a n k a n a l y s i s , a d u p l i c a t e a n a l y s i s , and a n a u d i t s a m p l e o r i n t e r l a b o r a t o r y s a m p l e a n a l y s i s . A t y p i c a l c a l i b r a t i o n and q u a l i t y c o n t r o l s c h e d u l e f o r v a r i o u s a n a l y t i c a l s y s t e m s i s g i v e n i n T- rb le 5 . 4 . The Q A / Q C p lan should address t h e s a m p l i n g method, t h e a n a l y t i c a l m e t h o d , and t h e d a t a r e d u c t i o n and r e p o r t i n g s t e p s . T h e a c c e p t a n c e c r i t e r i a c h o s e n a r e l i m i t e d b y t h e a v a i l a b l e a n a l y t i c a l and sampling t echn iques performance, b u t they should be s e t b y t h e d a t a r e q u i r e m e n t s needed t o make t h e n e c e s s a r y d e c i s i o n s . These r e q u i r e m e n t s s h o u l d be d e t e r m i n e d f o r each p r o j e c t d u r i n g t h e i n i t i a l Data Q u a l i t y O b J e c t i v e p l a n n i n g phase of t h e p r o j e c t before any d a t a i s acqu i r ed .

Method C a l i b r a t i o n - - C a l i b r a t i o n methods vary depending on t h e ins t rument used

and t h e l e v e l of c o n f i d e n c e r e q u i r e d . The p o r t a b l e o r g a n i c a n a l y z e r s h a v e s i n g l e c a l i b r a t i o n c a p a b i l i t i e s which l i m i t t h e i r u s e when a c c u r a t e v a l u e s a r e n e e d e d . Most a n a l y z e r m e t h o d s u s e a s i n g l e c o m p o n e n t s t a n d a r d a t s e v e r a l c o n c e n t r a t i o n s s u c h a s methane or hexane f o r F I D and benzene f o r P I D a n a l y z e r s . Since none of t h e ana lyze r response f a c t o r s a r e u n i v e r s a l f o r V O C s , c a l i b r a t i o n p r o c e d u r e s u s i n g a s i n g l e component d o n o t p r o v i d e a c c u r a t e v a l u e s f o r t h e e n t i r e range of V O C compounds. The v a l u e s o b t a i n e d w i l l a l s o v a r y g r e a t l y Ln k e e p i n g w i t h t h e compound t h a t i s used t o c a l i b r a t e t h e a n a l y z e r .

C a l i b r a t i n g G C s c a n be more s p e c i f i c , and t h e a c t u a l m e t h o d or s t anda rd used depends on t h e d e t e c t o r . For f i e l d G C s w i t h F I D s , a s i n g l e c o m p o n e n t s t a n d a r d such a s propane or n e x a n e can be u s e d t o c a l i b r a t e t h e i n s t r u m e n t . I f t h e V O C s c a n b e s e p a r a t e d i n t o carbon number c l a s s , c o n c e n t r a t i o n can be c a l c u l a t e d b y assuming an e q u a l c a r b o n r e s p o n s e f o r t h e F I D .

186

TABLE 5.4. SUMMARY OF SUGGESTED CALIBRATION AND QUALITY CONTROL REQUIREMENTS FOR ANALYTICAL S Y S T m S

l u c e ~ t a w a Critarla

4) Drift c b c k

4) D r i f t c k c k

?ortabla CU ?ID 1) l u l t i p i m t calibrat iom Cbroutqrapb (wro plea t b r r mp-

rcala cacntratloam)

2) &re/apam callbratiom

Dally, prior I . tbao t o tastily

b i l y . prior Dmara t o t8atimg

Corralation cedf G i r t s . 9 9 5

brralmtiom c w f f i c l n t s. 995

TABLE 5,4.(continued) TW or of Typm of

I n a t ruwot Dm t ec t or Cml ib rmt ion/QC Tma t

?ort.LIm Caa ? I D 4) DrIft c b u k

(Contioumd) ChroNto~r8ph

c OD W

PI0 1) I k l t l p I o t cmllbrmtloo (mmro plum thrmm mp- mcale coumotrmt l o a m )

2) &ro/mpms cmlibrmtloa

Daily. m t kmscom conelmmion or tma t i y

At .tart of Bmommaa or prow- t 0 l m . n

Daily. prior Bmasemm t o tmstiq

Lceptmoco Crlterim Corrr tiw &t lom

comff lc i r t

off-lit. C.. Cbtautqrapb

D air or

....

TABLE 5.4. (continued)

Off-Slte k. tID S) Duplicate .O.ly.O. Chroutolrapb (Coat imud)

TABLE 5.4.(continued)

c \F, c

O t h e r w i s e , t h e c o n c e n t r a t i o n v a l u e s are reported in the units of volume r a t i o s of c a r b o n (1.0.) ppmv-C). For e x a m p l e , o n e ppmv of hexane would be reported as 6 ppmv-C.

O n l y t w o p r i m a r y g a s s t a n d a r d a r e a v a i l a b l e f o r GC calibration, and they are the NBS propane and benzene standards. T h e p r o p a n e s t a n d a r d is a v a i l a b l e in concentrations of i ppm, 3 p p m , 10 p p m , 50 p p m , 1 0 0 p p m , a n d 5 0 0 p p m . A l l o t h e r s t a n d a r d s c a n b e c e r t i f i e d b y u s i n g the NBS propane standard. These standards have been found to be very stable e v e n at t h e 1 p p m level.

T h e P I D d e t e c t o r is m u c h more d i f f i c u l t t o c a l i b r a t e because the response factors vary more t h a n t h o s e o b s e r v e d f o r the F I D f o r each compound. To accurately quantitate samples, a r e s p o n s e f a c t o r f o r e a c h c o m p o n e n t o f i n t e r e s t w o u l d b e required. I n m o s t c a s e s , a single compound such as benzene is used to calibrate the response. If a k n o w n m i x t u r e o f o r g a n i c compounds is b e i n g monitored, such as that found in a gasoline spill, the mixture can be used to calibrate t h e i n s t r u m e n t and t o p r o v i d e a n u m b e r q u a n t i t a t i n g t h e tota; a m o u n t o f t h a t mixture in a given sample. This Works w e l l if t.le c o m p o s i t i o n a t t h e s i t e is h o m o g e n e o u s a n d i f t h e r e a r e n o o t h e r significant sources of t h e c o m p o u n d s i n t h e m i x t u r e . Dr. T o m Spittler o f the U.S. €PA Region 1 calibrates a PID f o r gasoline b y a n a l y z i n g t h e h e a d s p a c e a b o v e k n o w n a m o u n t s o f g a s o l i n e d i s s o l v e d i n w a t e r ( C l a r k , et al., 1 9 8 3 ) . W o r k i n g l e v e l standards a r e p r e p a r e d a c c o r d i n g t o t h e p r o c e d u r e s i n E P A M e t h o d 6 2 4 ( U S E P A , 1982). T h e d i l u t e ( e . g . , 40 p p b ) gasoline-in-water standards are stored u n d e r l i q u i d m e r c u r y i n serum vials. When needed, air is introduced into the vial, and a headspace s a m p l e i s c o l l e c t e d . T h i s c a n a l s o b e used as a q u a l i t a t i v e c h e c k f o r m a t c h i n g r e t e n t i o n t i m e s a n d f o r fingerprinting the sample with the source.

O n c e t h e i n s t r u m e n t 1 s c a l i b r a t e d , a q u a l i t y c o n t r o l standard should b e analyzed which comes c l o s e t o a p p r o x i m a t i n g t h e e x p e c t e d c o n c e n t r a t i o n and m a t r i x o f t h e s a m p l e s . T h i s sample is a c h e c k t o s e e if t h e c a l i b r a t i o n w i l l a c c u r a t e l y provide a c o n c e n t r a t i o n value for t h e components of interest. For the F I D , a mixture of c o m p o n e n t s is a n a l y z e d by u s i n g t h e single c o m p o n e n t r e s p o n s e factor t o s e e if it c a n accurately Identify and q u a n t i t a t e t h e c o m p o n e n t s w i t h i n a s e t l i m i t . T h i s Q C s t a n d a r d a n a l y s i s p r o v i d e s a good i n d i c a t i o n o f t h e day-to-day variability of the instrument.

D u p l i c a t e a n a l y s e s and samples are required t o determine the variability o f t h e s a m p l i n g a n d a n a l y t i c a l t e c h n i q u e . N z s t e d d u p l i c a t e s a m p l e s , w h e r e s a m p l e s a r e c o l l e c t e d i n d u p ~ . i c a t e n n d a n a l y z e d i n d u p l i c a t e , p r o v i d e a m e a n s t o statistically d e t e r m i n e t o t a l v a r i a n c e o f t h e method and the

192

a m o u n t o f v a r i a n c e w h i c h r e s u l t s from bo th t h e a n a l y t i c a l method and t h e sampling method.

B l a n k a n a l y s e s a r e r e q u i r e d t o d e t e r m i n e t h e l e v e l of con tamina t ion which r e s u l t 8 f rom t h e sampl ing and a n a l y t i c a l me thods . F i e l d b l a n k s a r e g e n e r a t e d b y p a s s i n g a gas from a c l e a n source through t h e s a m p l i n g a p p a r a t u s and c o l l e c t i n g i t b y t h e method b e i n g u s e d . T h i s s a m p l e is s e n t t o t h e l a b and is ana lyzed a s i f i t were a r e a l sample. Contaminat ion b e c a u s e of t h e a n a l y t i c a l system is determined b y i n j e c t i n g a volume of c l e a n a i r o r n i t r o g e n i n t o t h e i n s t r u m e n t . B l a n k s s h o u l d be r u n p e r i o d i c a l l y and a n a l y t i c a l s y s t e m blanks r u n between t h e a n a l y s i s of h igh - l eve l samples and low-let21 samples.

To d e t e r m i n e t h e a b s o l u t e a c c u r a c y a n d l a b - t o - l a b v a r i a b i l i t y , a u d i t s a m p l e a n a l y s e s and i n t e r l a b o r a t o r y c o m p a r i s o n s t u d i e s a r e r e q u i r e d . Performance a u d i t samples a r e unknown samples p r o v i d e d b y one l a b and s u b m i t t e d t o a n o t h b r l a b t o be a n a l y z e d s i m u l t a n e o u s l y w i t h t h e s o i l - g a s samples . I n t e r l a b o r a t o r y c o m p a r i s o n s c o n s i s t ‘of c o l l e c t i n g a l a r g e s a m p l e , d i v i d i n g t h a t l a r g e s a m p l e i n t o s m a l l e r s a m p l e s , sending them t o s e v e r a l l a b s f o r a n a l y s i s , and compar ing t h e r e s u l t s . A u d i t s a m p l e s have n o t been deve loped s p e c i f i c a l l y for s o i l - g a s measurements; however, t h e E P A h a s e s t a b l i s h e d an e x t e n s i v e r e p o s i t o r y of o r g a n i c g a s e o u s compounds a t a wide r a n g e of c o n c e n t r a t i o n s t o be u s e d a s a u d i t m a t e r i a l s f o r e m i s s i o n s a n a l y s i s ( J a y a n t y , e t a l . , 1 9 8 3 ) . T h e r e a r e no publ i shed r e s u l t s f o r i n t e r l a b o r a t o r y compar ison f o r s o i l - g a s a n a l y s i s ; h o w e v e r , many o f t h e s a m e t e c h n i q u e s h a v e been compared f o r t h e a n a l y s i s of a m b i e n t a i r ( B a l f o u r , e t a l . , 1 9 8 4 ) . The r e s u l t s of t h i s s t u d y o f f i v e l a b o r a t o r i e s u s i n g t h e same m e t h o d ( G C I F I D ) w i t h d i f f e r i n g a n a l y t i c a l p r o c e d u r e s showed a c o e f f i c i e n t of v a r i a n c e of 1 1 percent i n t h e v a l u e of t o t a l nonmethane hydrocarbons.

Concl u s 1 ons-- The l e v e l o f Q A / Q C e f f o r t r e q u i r e d depends on t h e d a t a

accuracy and p r e c i s i o n r e q u i r e m e n t s . I n any c a s e , t h e Q A / Q C p r o g r a m s h o u l d e s t a b l i s h t h e l i m i t s of b o t h t h e s a m p l e c o l l e c t i o n and a n a l y s i s me thods and s h o u l d e n s u r e t h a t t h e y c o n t i n u e t o pe r fo rm w i t h i n t h e s e limits. Accurate c a l i b r a t i o n methods f o r p o r t a b l e a n a l y z e r s have n o t been d e v e l o p e d , and c a l i b r a t i o n of a l a r g e number of compounds f o r P I D , E C D , and MS i s d i f f i c u l t . There i s a need f o r s t a n d a r d r e f e r e n c e m a t e r i a l f o r V O C s i n s o i l a s w e l l a s a c c u r a t e Q C s t a n d a r d s and i n t e r l a b o r a t o r y comparison s t u d i e s .

193

R E F E R E N C E S

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2 .

3 .

4 .

5 .

6 .

7 .

8 .

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B a l f o u r , U . D . , R . G . W e t h e r o l d a n d 0. L . L e w i s . E v a l u a t i o n o f Air E m l s s l o n s f r o m H a z a r d o u s W a s t e T r e a t m e n t , S t o r a g e , and Di8pO8al F a c i l i t i e s . E P A - I E R L 68-02-3171, Task Number 6 3 , 1 9 8 4 .

B i s q u e , R. E. M i g r a t i o n R a t e 8 of V o l a t i l e s from Burled Hydrocarbon Source8 t h r o u g h S o i l Media. P r o c e e d i n g s of P e t r o l e u m Hydrocarbons and O r g a n i c Chemica ls i n Ground Water, Houston, Texas, November 5 - 7 , 1 9 8 4 , p p . 267-271.

B i s q u e , R. E. New G e o c h e m l c a l T e c h n i q r e Used i n t h e Denver Basin. Western O i l Repor t e r , p p . 23-26, June 1983.

Brown, G . E., 0. A , D u B o s e , W . R . P h i l l i p s a n d G . E. H a r r i s . Response F a c t o r s of VOC Analyzers C a l i b r a t e d w i t h Methane f o r Se lec t ed Organic Chemicals. E P A 600 /2 -81 -002 , NTIS P B 8 1 - 1 3 6 1 9 4 , 1 9 8 0 , U . S . E n v i r o n m e n t a l P r o t e c t i o n Agency, Research T r i a n g l e Pa rk , N C . 491 p p .

Brown, R . H . and C . J . P u r n e l l . C o l l e c t i o n and Ana,lysis of Trace Organic Vapor P o l l u t a n t s i n Ambient Atmospheres , T h e Pe r fo rmance of a Tenax-GC Adsorben t Tube. J . Chromatogr. 1 7 8 , p p . 79-90 , 1979.

C l a r k , A . E . , H . L a t a i l l e a n d E. L . Taylor . The Use of a P o r t a b l e F I D Gas Chromatograph f o r R a p i d S c r e e n i n g of Samples f o r P u r g e a b l e O r g a n i c Compounds i n t h e F i e l d and i n t h e Lab. Presented a t t h e N o r t h e a s t R e g i o n a l S e c t i o n M e e t i n g o f t h e A s s o c i a t i o n o f A n a l y t i c a l C h e m i s t s , Bennington, V T , June 28-29 , 1 9 8 3 .

C o l e n u t t , B . A . and D . N. D a v i e s . The Sampl ing and Gas Chromatographic A n a l y d i s of O r g a n i c Vapours i n L a n d f i l l S i t e s . I n t e r n a t i o n a l J o u r n a l of Environmental A n a l y t i c a l Chemistry, Vo l , 7 , p p . 2 2 3 - 2 2 9 , 1980 .

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9.

10.

1 1 .

12.

13.

14.

15.

16.

17.

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K r o s t , K . J., E. D . P e l l f z z a r i , S . G. Walburn and S. A . Hubbard. C o l l e c t i o n and A n a l y s i s of Haza rdous O r g a n i c Emissions. Anal. Chem. 54, p p . 810-817, 1982.

Lonneman, W . A . , J. J. B u f a l i n i , R. L o Kuntz and S. A . Heeks. Contamination from F l u o r o c a r b o n F i l m s . E n v i r o n . S c i . Technol. 15 , p p . 99-103, 1981.

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H a r r i n , D . L . and G. M . Thompson. Remote D e t e c t i o n of V o l a t i l e Organic Contaminants i n Ground Water Via S h a l l o w Soil Gas Sa,mpling. Proceedings of Petroleum Hydrocarbons and O r g a n i c Chemica l s i n Ground W a t e r , Hous ton , T e x a s , November 5-7, p p . 172-187, 1984.

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C H A P T E R 6

S T A T I S T I C A L TREATMENT OF S O I L O R G A N I C V A P O R MEASUREMENTS


S o i l o r g a n i c vapor (SOV) measurement is usua l ly performed i n an e x p l o r a t i o n phase of an i n v e s t i g a t i o n . The s t a t i s t i c i a n h a s two d u t i e s a t t h e s t a r t of such an i n v e s t i g a t i o n . They a r e (1) t o de te rmine a method f o r t ak ing t h e measurements i n s u c h a way a s t o meet r e q u i r e m e n t s f o r d a t a p r e c i s i o n i n a r e a l i s t i c and c o s t e f f e c t i v e manner , and ( 1 1 ) t o h e l p d e t e r m i n e t h e l o c a t i o n s f o r t h e i n i t i a l exp lo ra to ry survey i n accordance w i t h p r i o r knowledge about t h e s i t e and t h e o b d e c t i v e s and budge t of t h e p r o j e c t . The d e t e r m i n a t i o n o ? t h e p r e c i s i o n o f t h e measurements and t h e s i z e of t h e c o n t r i b u t i o n s of v a r i o u s s o u r c e s of e r r o r i s t h e s t a r t i n g p o i n t i n t h e planning of a l l good sample su rveys . The measurements m u s t r e p r e s e n t t h e SOV c o n c e n t r a t i o n s i n t h e s o i l a t t h e s i t e s where t h e samples a r e t a k e n . The measurements w i l l be w o r t h l e s s i f t h e y m e r e l y r e p r e s e n t t h e e r r o r s g e n e r a t e d i n o b t a i n i n g , h a n d l i n g , and ana lyz ing t h e samples . One s h o u l d n o t w a i t t i l l t h e end of a s u r v e y t o de te rmine t h e p r e c i s i o n of t h e measurements, f o r t hen i t may be too l a t e t o save t h e s t u d y f rom bad d a t a . O b v i o u s l y i t i s i m p o s s i b l e t o c o m p l e t e l y e l i m i n a t e e r r o r s . However, b y use of proper s t a t i s t i c a l t e c h n i q u e s , i t i s p o s s i b l e t o measu re t h e e f f e c t s of t h e va r ious sou rces of e r r o r on t h e p r e c i s i o n of t h e measurements and, I f necessa ry , t o f i n d t h e most economica l means f o r r e d u c i n g t h e e f f e c t s so a s t o a t t a i n a des i r ed l e v e l of p r e c i s i o n .

The p r o p e r methods f o r choice of l o c a t i o n s f o r t h e t a k i n g of measurements i s unique t o each s i t e b e c a u s e of t h e c h a n g e s i n o b j e c t i v e s , budgets , and p r i o r knowledge between s i t e s . The d e c i s i o n concerning l o c a t i o n of s a m p l e p o i n t s m u s t be made i n c o n c e r t w i t h t h e o t h e r p r i n c i p a l p a r t i c i p a n t s i n t h e s t u d y and , because of t h e e x p l o r a t o r y n a t u r e of t h e S O V i n v e s t i g a t i o n s , m a y i n l a r g e p a r t be s u b j e c t i v e . Some words o f a d v i c e on p o s s i b l e s a m p l i n g p a t t e r n s have b e e n g i v e n i n a p r e c e d i n g c h a p t e r .

199

T e c h n i q u e s f o r a s s e s s i n g m e a s u r e m e n t p r e c i s i o n and c o n t r i b u t i o n s of v a r i o u s sOUrce3 Of e r r o r t o t o t a l e r r o r a r e d i s c u s s e d i n t h i s c h a p t e r a l o n g w i t h 8ome comments on t h e use o f t h e f i n a l s u r v e y d a t a i n i n t e r p o l a t i o n a n d c o n t o u r i n g procedures .

COMPONENTS OF V A R I A N C E A N A L Y S I S

The c e n t r a l s t a t i 8 t i C a l procedure involved i n t h e process of measuring and i m p r o v i n g precision i s c a l l e d components of v a r i a n c e a n a l y s i s , T h i s procedure i s based on a model f o r t h e measur.ements t h a t i n c l u d e s an equat ion of t h e form,

where Y i i s a measurement o f t h e c o n c e n t r a t i o n of an o rgan ic v a p o r i n s a m p l e i , u i i s t h e e x p e c t e d v a l u e of s u c h a measurement ( 1 . e . , t h e ave rage of a h y p o t h e t i c a l popu la t ion of r epea ted measurements on samples taken a t t h e same l o c a t i o n and u s i n g t h e s a m e t e c h n i q u e ) , and c i j i s t h e e r r o r i n t h e measurement coming from source j ( 3 - 1 , . . . , k ) . The measurements a r e s a i d t o be p r e c i s e i f t h e s u m of t h e e ' s on t h e r ight-hand- s i d e o f t h e e q u a t i o n 1 s n e a r z e r o w i t h h i g h p r o b a b i l i t y . H e n c e , t o o b t a i n p r e c i s e m e a s u r e m e n t s , o n e w a n t s t h e c o n t r i b u t i o n s e i j from each of t h e v a r i o u s s o u r c e s of e r r o r t o be small w i t h h i g h p r o b a b i l i t y ,

T o d e v e l o p t h e a b o v e m o d e l e q u a t i o n , o n e m u s t be s u f f i c i e n t l y f a m i l i a r w i t h t h e sample a c q u i s i t i o n , h a n d l i n g , and a n a l y s i s p r o c e s s t o s e a r c h o u t and l i s t a l l t h e major sources of e r r o r . S i n c e t h e s i z e of e r r o r s vary from sample t o sample and c a u s e v a r i a t i o n i n measu remen t s , i t i s common t o r e f e r t o s o u r c e s of e r r o r a s s o u r c e s of e r r o r v a r i a t i o n o r s o u r c e s of v a r i a t i o n . For example , a n a l y t i c a l errors c a u s e v a r i a t i o n between a n a l y s e s of subsamples of a s a m p l e of s o i l g a s . I f one c o n s i d e r s s o i l o rgan ic vapor measurements taken b y drawing s o i l g a s i n t o a s o i l p r o b e , w i t h d r a w i n g g a s from t h e p r o b e w i t h a s y r i n g e and f i n a l l y i n s e r t i n g t h e g a s from t h e s y r i n g e i n t o a gas chromatograph f o r measurement of a chemica l c o n c e n t r a t i o n , t h e n t h e v a r i a t i o n i n g a s c h r o m a t o g r a p h measurements of gas from s e v e r a l s y r i n g e s t a k e n f rom t h e same p r o b e a f t e r a s i n g l e p u r g e and r e l a x a t i o n of vacuum w o u l d r ep resen t t h e v a r i a t i o n c a u s e d b y such t h i n g s a s a i r l e a k a g e i n t o t h e s y r i n g e s a n d a n a l y t i c a l e r r o r s i n t h e g a s chromatography. I f s e v e r a l s y r i n g e s of g a s a r e wi thd rawn from each o f s e v e r a l c l o s e l y s p a c e d p robes a t a sampling l o c a t i o n , the v a r i a t i o n of t h e average measurements f o r t h e p r o b e s w o u l d g i v e i n f o r m a t i o n c o n c e r n i n g combined v a r i a t i o n caused by sho r t range s p a t i a l d i f f e r e n c e s i n c o n c e n t r a t i o n s o f t h e SOV being measu red , b y d i f f e r e n c e s i n i n s e r t i o n of p robes , b y d i f f e r e n c e s

200

i n t h e v a c u u m a c h i e v e d i n t h e p u r g i n g o f t h e p r o b e s , a n d perhaps by leakage of surface air into t h e probes. It is W i s e t o d e t e r m i n e t h e s i z e s o f t h e c o n t r i b u t i o n s o f t h e v a r i o u s sources of error variation t o the total variability o f t h e d a t a prior t o t h e i n v e s t i g a t i o n o f t h e spatial distribution of the S O V . Knowledge of the contribution of the sources o f v a r i a t i o n a l l o w s t h e i n v e s t i g a t o r t o d e t e r m i n e h o w best t o a l l o c a t e resourcea t o o b t a i n preciae estimates of SOV concentrations (or p e r h a p s t o d e t e r m i n e that the study will not be able to obtain d e s i r e d l e v e l s o f p r e c i s i o n a n d t h e r e f o r e s h o u l d n o t b e c o m p l e t e d ) . F o r e x a m p l e , i f t h e r e is a l a r g e i r r e g u l a r variation b e t w e e n m e a s u r e m e n t s at t h e s a m e s a m p l i n g l o c a t i o n t a k e n at s u b s t a n t i a l l y different times (say a week apart), the investigator will have t o d e t e r m i n e w h e t h e r t h i s v a r i a t i o n is d u e t o d i f f e r e n c e s i n m e a s u r e m e n t p r o c e d u r e s or is d u e t o changes in environmental conditions such a s ambient t e m p e r a t u r e a n d a t m o s p h e r i c p r e s s u r e . I f t h e c a u s e is c h a n g e i n measurement prouedures, t h i s v a r i a t i o n m i g h t b e s u b s t a n t i a l l y r e d u c e d by a d d i t i o n a l t r a i n i n g and practice. I f the cause of the large variation over time is due t o e n v i r o n m e n t a l f a c t o r s , i t may b e n e c e s s a r y t o establish one or more control sites and to measure at t h e control sites whenever measurements a r e t a k e n at o t h e r s i t e s . T h i s w o u l d p r o v i d e the information needed t o make measurements taken at different times comparable.

As 'is i m p l i e d b y i t 3 n a m e , t h e c o m p o n e n t s o f v a r i a n c e technique uses variance ( t h e s e c o n d m o m e n t a b o u t t h e m e a n ) a s t h e m e a s u r e o f t h e v a r i a t i o n c a u s e d b y e r r o r s . I f t h e probability distribution of the errors is n o r m a l ( G a u s s i a n ) a s is a s s u m e d i n variance components analysis (the error terms a r e assumed t o b e i n d e p e n d e n t r a n d o m v a r i a b l e s w i t h E ~ J h a v i n g n o r m a l d i s t r i b u t i o n with m e a n z e r o and unknown variance ( r g 2 ) ,

t h e s h a p e a n d s p r e a d o f t h e d i s t r i b u t i o n i s c o m p l e t e l y d e t e r m i n e d b y t h e variance. U n d e r t h e assumption of a ,normal d i s t r i b u t i o n f o r Y i , t h e p r e c i s i o n o f t h e m e a s u r e m e n t i s measured b y i t s v a r i a n c e ; the smaller the variance, the better the precision. H o w e v e r , f o r most o t h e r t y p e s o f p r o b a b i l i t y d i s t r i b u t i o n s , v a r i a n c e d o e s not c o m p l e t e l y characterize the spread of t h e d i s t r i b u t i o n . I n a d d i t i o n , f o r m a n y n o n n o r m a l d i s t r i b u t i o n s , t h e s p r e a d o f t h e d i s t r i b u t i o n changes as the mean, pi, changes. It is i m p o s s i b l e t o e s t i m a t e v a r i a n c e s o f the E ~ J i f t h e variances are not constant (i.e., if they change w i t h the magnitudes of the measured concentrations). H e n c e , if variances c h a n g e as the mean changes, it is vital that the data be transformed in such a way as t o stabilize variances r e l a t i v e to the m e a n , Typically, if one can stabilize the variance with a t r a n s f o r m a t i o n , t h a t t r a n s f o r m a t i o n a l s o m a k e s t h e d i s t r i b u t i o n m o r e s y m m e t r i c (see Section 4F of Hoaglin et al., 1 9 8 3 1 , and t h e r e b y a better a p p r o x i m a t i o n t o t h e normal. A frequently u s e d v a r i a n c e - s t a b i l i z i n g t r a n s f o r m a t i o n for data

20 1

- 6

- 4

-8

- 2

- 1

0

- 1 1 2 4

- 4 - 6 4 Skowod Donelty Corvo

-3

- 2

- 1

0

- 2 - 1 0 1 2 0 4

Figure 6 .1 . Denrity curve8 for aom81 8ad rkcwed dirtributioa.

202

f r o m d i s t r i b u t i o n s t h a t a r e s k e w e d t o t h e r i g h t i s t h e l o g a r i t h m i c t r a n s f a r m a t i o n of t h e measurement 2 i n t o Y w i t h

Y-log(Z + m )

where m 1s a nonnegat ive c o n s t a n t such a s t h e minimum d e t e c t i o n l i m i t , 1 , o r , i t a l l t h e m e a s u r e m e n t s a r e c o n s i d e r a b l y l a r g e r t h a n 1 , t h e m i n i m u m measurement m i n u s 1 . Another commonly employed t r a n s f o r m a t i o n f o r d a t a t h a t a r e skewed t o t h e r i g h t 13 t h e s q u a r e - r o o t t r a n s f o r m a t i o n (1.0. . X - 4 2 ) which does not reduce l a r g e va lues r e l a t i v e t o t h e s m a l l e r o b s e r v a t i o n s q u i t e a s much a s d o e s t h e l o g a r i t h m i c t r a n s f o r m a t i o n . For d i s . c u s s i o n s o f m e t h o d s f o r d e t e r m i n i f i g when a n d how t o t r a n s f o r m d a t a s e e H o a g l i n , e t a l . (19831, and Sche f fe (1959, S e c t i o n 1 0 . 7 ) .

The p l a n n i n g o f a n e x p e r i m e n t t o o b t a i n d a t a f o r t h e e s t i m a t i o n of va r i ance components is very much dependent on t h e n a t u r e a n d c o s t s of t h e v a r i o u s o p e r a t i o n s i n v o l v e d i n t h e t a k i n g of S O V measurements. A r e v i e w and b i b l i o g r a p h y of t h e l i t e r a t u r e f o r t h e d e s i g n and a n a l y s i s o f experiments planned f o r v a r i a n c e component e s t i m a t i o n is g i v e n b y Anderson ( 1 9 7 5 ) . A d e t a i l e d d i s c u s s i o n o f t h e t h e o r y of v a r i a n c e components e s t i m a t i o n i s g i v e n i n S c h e f f e ( 1 9 5 9 , C h a p t e r s 7 a n d 8). C o m p u t e r p r o g r a m s a r e a v a i l a b l e f o r components of v a r i a n c e a n a l y s i s i n most mainframe s t a t i s t i c a l sof tware packages ( e . g . , P R O C V A R C O M P i n t h e SAS package - s e e Ray, 1982, p . 2 2 3 ) .

A s a n e x a m p l e o f t h e u s e o f t h e r e s u l t s o f v a r i a n c e components a n a l y s i s , s u p p o s e one can t a k e k s y r i n g e s o f g a s f r o m e a c h o f m p r o b e s l o c a t e d on t h e nodes of a s m a l l g r i d c e n t e r e d o n a s a m p l i n g l o c a t i o n . I f t h e m o d e l f o r t h e measurement of t h e gas from s y r i n g e 1 taken a t probe h 13

where is t h e e x p e c t e d v a l u e of Y h i , ~h is t h e e r r o r which r e s u l t s f rom measur ing a t p r o b e h , c h i i s t h e e r r o r w h i c h r e s u l t s f rom sampling probe h w i t h s y r i n g e i , then t h e v a r i a n c e o f t h e mean o f t h e k m m e a s u r e m e n t s g i v e s a m e a s u r e d c o n c e n t r a t i o n f o r t h i s sampling l o c a t i o n t h a t has v a r i a n c e

I f t h e v a r i a n c e components a n a l y s i s has es t imated v ( C h ) t o be 1 0 and v ( C h i ) t o be 20, t h e n t h e e s t i m a t e d p r e c i s i o n of F i s given i n terms of t he va r i ance (10/rn + 2 0 / ( m k ) ) . The numbers k a n d rn may b e a d j u s t e d w i t h i n t h e l i m i t s o f c o s t s a n d f e a s i b i l i t y t o r e d u c e t h e v a r i a n c e t o a d e s i r e d l e v e l and t h e r e b y t o i n c r e a s e t h e p r e c i s i o n of t h e measured c o n c e n t r a t i o n o b t a i n e d f r o m each s a m p l i n g l o c a t i o n . For m - 1 and k - 4 , V ( l )

203

i s e s t i m a t e d t o b e I5 which i s a l m o b t a i n e d for m-2 and k-1. I f t h e c o s t of a p r o b e i s r b o u t t h e 8ame a 8 t h e c o s t of t h e a n a l y s i s of a s a m p l e , t h e second o p t i o n would be p r e f e r a b l e t o o b t a i n a d e s i r e d v a r i a n c e O f 15 . The s e e o n d o p t i o n m i g h t be e s s e n t i a l i f i t is no t f e a s i b l e t o t a k e k a8 l a r g e a s 4.

Variance Components Ana lys i s Example

I n t h i s s e c t i o n , d a t a from t h e Case S t u d y 2 . 0 , h e r e a f t e r c a l l e d t h e P i t tman Case S t u d y , o f t h e c h a p t e r on e a s e s t u d i e s t h a t f o l l o w s , w i l l be u s e d t o i l l u s t r a t e some o f t h e p o i n t s t h a t were made concern ing var iance components a n a l y s i s t h a t was made a b o v e . T h e s t u d y was r u n t o t e s t a n SOV s a m p l i n g p r o c e d u r e b y compar ing i t s r e s u l t 8 w i t h d a t a o b t a i n e d f r o m n e a r b y w e l l s . The S O V d a t a c o n s i s t o f g a s chromatograph measurements of c h l o r o f o r m c o n c e n t r a t i o n 8 ( i n p p b v ) i n g a s o b t a i n e d i n 2 5 0 ~1 s y r i n g e s from probes . Although no s p e c i a l experiment was performed t o measure v a r i a n c e components , t h i s s t u d y d o e s p rov ide d a t a from which some v a r i a n c e components may be e s t ima ted .

The f i r s t s t e p i n a v a r i a n c e eomponents a n a l y s i s of t h i s da t a is a s e a r c h f o r an a p p r o p r i a t e t r a n s f o r m of t h e d a t a t o move i t toward no rma l d i s t r i b u t i o n c h a r a c t e r i s t i c s . Table 6 .1 i s o b t a i n e d from t h e d a t a i n T a b l e 6 . 2 o f t h e P i t t m a n C a s e S t u d y b y o r d e r i n g t h e 2 3 s e t s of r e p l i c a t e a n a l y s e s according t o t h e s i z e of t h e i r sample means. I n T a b l e 6 . 1 , t h e s t a n d a r d d e v i a t i o n s o f l o g t r a n s f o r q a t i o n s a n d o f s q u a r e - r o o t t r a n s f o r m a t i o n s of t h e sample d a t a a r e g i v e n a l o n g w i t h t h e s t a n d a r d d e v i a t i o n s f o r t h e raw d a t a provided i n Table 6 . 2 . If one looks a t t h e s t a n d a r d d e v i a t i o n s of t h e raw d a t a f o r t h e s m a l l e s t 8 means and f o r t h e l a r g e s t 8 means , i t i s o b v i o u s t h a t t he sample s t a n d a r d d e v i a t i o n s a r e i n c r e a s i n g a l o n g w i t h t h e m e a n s . I f o n e d o e s t h e same t h i n g f o r t h e s t a n d a r d d e v i a t i o n s of t h e l o g - t r a n s f o r m e d d a t a , one f i n d s t h a t t h e s t a n d a r d d e v i a t i o n s a r e g e t t i n g s m a l l e r a s t h e sample mean i n c r e a s e s which i m p l i e s t h a t t h e t r a n s f o r m a t i o n h a s o v e r compensa ted f o r t h e skewed d i s t r i b u t i o n . F i n a l l y , when o n e checks t h e f i r s t and l a s t 8 s t anda rd d e v i a t i o n s f o r t h e square ' r o o t t r a n s f o r m e d d a t a , one f i n d s no e v i d e n c e of t r e n d of t h e sample s t a n d a r d d e v i a t i o n s w i t h t h e s a m p l e means. Hence, i n t h i s c a s e , t h e s q u a r e - r o o t t r a n s f o r m a t i o n seems a reaaonable choice ,

T h e a n a l y t i c a l (be tween s y r i n g e s ) e r r o r v a r i a n c e f o r t h e square-root t ransformed chloroform measurements of t h e P i t tman Case S t u d y may now be e s t i m a t e d w i t h t h e p o o l e d e s t ima to r of t h e v a r i a n c e ,

204

where s x i 2 i s t h e s a m p l e v a r i a n c e c a l c u l a t e d from t h e n i s q u a r e - r o o t t r a n s f o r m e d m e a s u r e m e n t s t a k e n a t l o c a t i o n 1 ( i - l , . . . ,231. From t h e squa re - roo t t r a n s f o r m a t i o n s of t h e d a t a i n T a b l e 6 . 2 , one f i n d s sp2 -0 .0836 and s p - 0 . 2 9 ( b a s e d on 4 3 degrees of f reedom).

I n t h e c a s e s t u d y , measurements were taken a f t e r each of a s e r i e s of purges of t h e same p r o b e . These meaaurementa a l l o w e s t i m a t i o n o f " b e t w e e n - p u r g e W v a r i a n c e . Two s y r i n g e s u e r e loaded w i t h g a s a f t e r e a c h o f f o u r p u r g e s of t h e p r o b e . The r e s u l t s of t h e ana lyses of t h e gas i n t h e s y r i n g e s a r e g iven i n Table 6 . 2 . The usua l model f o r t h e a n a l y s i s of t h e t r a n s f o r m e d measurements i s

X i J - !J + P i + E i J

where !J i s t h e mean, p i i s a random v a r i a b l e r e p r e s e n t i n g t h e d e v i a t i o n a s s o c i a t e d w i t h fo l lowing purge i and i s d i s t r i b u t e d N ( 0 , u p 2 ) , i s t h e random v a r i a b l e r e p r e s e n t i n g e f f e c t o f s y r i n g e ( a n a l y t i c a l e r r o r ) J t a k e n a f t e r p u r g e 1 a n d i s d i s t r i b u t e d N ( 0 , a a 2 ) , and t h e random v a r i a b l e s a r e independent o f o n e a n o t h e r . ( T h e r e i s s o m e d o u b t c o n c e r n i n g t h e i n d e p e n d e n c e and i d e n t i c a l d i s t r i b u t i o n of t h e s e measurements i n t h a t vacuums a c h i e v e d d e c l i n e d from p u r g e t o s u c c e e d i n g p u r g e , Pe rhaps i t i s impoaaible t o o b t a i n a t r u e between purge var iance e s t i m a t e b e c a u s e of t h i s p r o b l e m . ) The a n a l y s i s of v a r i a n c e o f t h e t r a n s f o r m e d purge d a t a gave a mean s q u a r e f o r a n a l y t i c a l e r r o r of 0 . 1 3 baaed on 4 d e g r e e s o f f r e e d o m . T h i s e s t i m a t e o f u a 2 i s r e m a r k a b l y c l o s e , c o n s i d e r i n g t h e s m a l l number o f d e g r e e s of f r e e d o m , t o t h e v a l u e 0 . 0 8 3 6 o b t a i n e d e a r l i e r . The between p u r g e s mean s q u a r e i s 0 . 3 3 , baaed on 3 d e g r e e s of f r e e d o m , S i n c e t h e e x p e c t e d v a l u e o f t h i s mean s q u a r e unde r t h e above model 1s Ua2+2up2, t h e e s t i m a t e of t h e between purges component of var iance would be

S p 2 - ( 0 . 3 3 - 0 . 1 3 ) / 2 - 0 . 1 0 ,

o r , when t h e more p r e c i s e e s t i m a t e of 6a2 found e a r l i e r is used

S p 2 - ( 0 . 33-0.08)/2-0.12.

T h e p r o b l e m w i t h vacuum and t h e s m a l l number o f d e g r e e s o f f reedom a v a i l a b l e f o r b e t w e e n - p u r g e s - c o m p o n e n t e s t i m a t i o n s h o u l d make one s u s p i c l o u s of t h e accuracy of e i t h e r e s t i m a t e ,

The e x t r e m e v a r i a b i l i t y o f t h e e s t i m a t o r 3 2 of a v a r i a n c e 0 2 based o n s m a l l numbers of d e g r e e s o f f r e e d o m i s s e l d o m a d e q u a t e l y a p p r e c i a t e d . Table 6.3 i n d i c a t e s how t h e l e n g t h of confidence i n t e r v a l s f o r 0 2 based o n e s t i m a t e s 3 2 v a r i e s w i t h

" 2 .

205

T A B L E 6.1. S A M P L E S T A N D A R D D E V I A T I O N S F O R RAW A N D T R A N S F O R M E D C H L O R O F O R M M E A S U R E NTS O R D E R E D BY

( 2 - C h l o r o i o r ~ m e a s u r e m e n t , Y Sample Sample SZ S Y SX

Rank Mean s i z e

5 6

10 10.5 12.3

25 27 27

0 0 0 3 0.49 0 . 5 9 2 0.19 0.31

0.3 0.06 0.09 0.5 0.04 0.06

2 0.09 0.22 0.17 0.46 5

2 0.07 0.20

9 27 3 5 0.20 0.53 10 28 3 5 0.18 0.45 11 30 3 1 0.03 0.09 12 32.1 2 0.2 0.01 0.02 13 45.6 3 0.2 0.01 0.02 14 55 3 2 0.03 0.12 15 72.9 3 0.1 0.00 0.01

1 6 17 18 19 20 21 22 23

112 115 161 171 26 6 326 37 6 51 1

12 0.11 0 . 5 5 6 0.05 0.28 6 0.03 0.22 0 0 0 6 0.02 0.17

10 0.03 0.29 6 0.02 0.15

17 0.03 0.37

( K e r f o o t , 19851

T A B L E 6 . 2 . C H L O R O F O R M C O N C E N T R A T I O N S ( p p b v ) M E A S U R E D O N G A S E S D R A W N A F T W H O F A S E R U S OF P U R G E S OF T H E S A M E P R O B E

Syr inge 1 S y r i n g e 2

1 10.7(3.271 ) * 1 6 - 4 ( 4 * 0 5 0 ) Purge 2 6 .6 (2.569 1 8 . 5 ( 2 . 9 1 5 )

3 1 0 . 5 ( 3 . 2 4 0 ) 9.8(3.130 1 4 10 .0 (3 .162) 6 .7 (2 .588)

( K e r f o o t , 1 9 8 5 )

d e g r e e s o f f r e e d o m . The t a b l e 1 s b a s e d on an a s s u m p t i o n o f normally d i s t r i b u t e d data w h e r e a s r e a l ( a n d e v e n t r a n s f o r m e d ) d a t a a r e n o n n o r m a l , and u s u a l l y t h e v a r i a b i l i t y o f t h e e s t i m a t o r s2 is even greater than t h a t i n d i c a t e d b y t h e t a b l e .

206

A l s o n o t e t h e r a p i d l y d i m i n i s h i n g r a t e o f d e c r e a s e i n c o n f i d e n c e i n t e r v a l l e n g t h s o n c e t h e n u m b e r o f d e g r e e s o f f r e e d o m e x c e e d s 20. T h i s m a k e s 20 d e g r e e s o f f r e e d o m a r e a s o n a b l e g o a l i n p l a n n i n g a n e x p e r i m e n t t o e s t i m a t e a var 1 ance .

TABLE 6.3. C O N F I D E N C E INTERVALS FOR u* BASED N O N s2 AS A F U N C T I O N OF DEGREES OF FREEDOM (D.F.) A N D

U M I N G A N O R M A L D I S T R I B U T I O N FOR D A T A

D.F . 95s C O N F I D E N C E I N T E R V A L

2 0.27a2S02S39 .21s2 3 0.32a2S02S1 3.8932

10 0.49s2S0253.08s2 20 0 .58s2S02S2. 0 8 3 2 30 0.64,2S02S1 .78s2

I t i s i m p o r t a n t t o e s t i m a t e t h e be tween-probe v a r i a t i o n of t h e m e a s u r e m e n t s t o d e t e r m i n e how w e l l a n i n d i v i d u a l m e a s u r e m e n t c h a r a c t e r i z e s t h e c o n c e n t r a t i o n o f t h e o r g a n i c vapor i n t h e immedia t e v i c i n i t y of t h e s a m p l i n g p o i n t . I n t h e P i t t m a n s t u d y , s e v e r a l p r o b e s were p l a c e d a t l o c a t i o n s o n l y a few f e e t a p a r t n e a r w e l l No. 627 ( s e e F i g u r e 7.26 o f t h e c a s e s t u d y ) . The r e s u l t s f r o m t h e t h r e e l o c a t i o n s (E23; E23, S3; and E20, S3) a r e e m p l o y e d t o o b t a i n a n e s t i m a t e o f s p a t i a l v a r i a t i o n . The model employed i s :

X i J -u+ A i + P i j + ‘ i j

w h e r e X i i s a r andom v a r i a b l e w i t h a N ( 0 , o ~ ~ ) d i s t r i b u t i o n r e p r e s e n t i n g t h e e f f e c t of l o c a t i o n 1 , p i 3 is a random v a r i a b l e w i t h a N ( 0 , 0 p 2 ) d i s t r i b u t i o n r e p r e s e n t i n g t h e random e f f e c t of p u r g e j w i t h i n l o c a t i o n 1 , and t h e C ~ J i s d e f i n e d a s i n t h e p r e v i o u s m o d e l . T h e r a n d o m v a r i a b l e s a r e a s s u m e d t o b e i n d e p e n d e n t , T h e mean s q u a r e f o r e r r o r i n t h e a n a l y s i s o f v a r i a n c e o f t h e s q u a r e - r o o t t r a n s f o r m e d d a t a i s 0.182 and is an e s t i m a t e o f ( a p 2 + u a 2 ) b a s e d on 6 d e g r e e s of f r e e d o m . T h i s e s t i m a t e a g r e e s s u r p r i s i n g l y w e l l w i t h t h e p r e v i o u s e s t i m a t e s for t h e s u m o f t h e two v a r i a n c e s . The mean s q u a r e f o r b e t w e e n l o c a t i o n s i s 2 1 . 0 3 6 a n d r e p r e s e n t s a n e s t i m a t e o f ( a 2 + ~ a 2 ) + 3 ~ ~ 2 . Hence t h e e s t i m a t e of a~~ i s (21.036-.182)/3 - 6 . 6 5 . T h i s e s t i m a t e i s b a s e d on o n l y t w o d e g r e e s of freedom and is e x t r e m e l y u n r e l i a b l e . I n a d d i t i o n , t h e i n v e s t i g a t o r s i n t h e P i t t m a n s t u d y b e l i e v e t h a t t h e v a r i a t i o n o b s e r v e d i n t h e d a t a from t h e t h r e e p r o b e s was p r i m a r i l y due t o t h e t i m e d e l a y s

20 7

i n g e t t i n g t h e s a m p l e s a n a l y z e d r a t h e r t h a n b e i n g d u e t o shor t - range s p a t i a l v a r i a t i o n i n chloroform c o n c e n t r a t i o n s . If t h e e s t i m a t e h a d been a more r e l i a b l e e s t i m a t e of s h o r t - r a n g e s p a t i a l v a r i a t i o n , i t w o u l d i n d i c a t e t h a t t o i m p r o v e t h e e s t i m a t e d c o n c e n t r a t i o n a t a s ample p o i n t s l g n i f i o a n t l y , one m u s t average measurements over t h e r&sults from s e v e r a l c l o s e l y spaced ( b u t n o n - i n t e r f e r i n g ) probe8 a t t h a t l o o a t i o n . Based on t h e var iance components model g i v e n above , t h e v a r i a n c e of t h e a v e r a g e of t h e measurements on 8 s y r i n g e s from eaoh of m p u r g e s from each of n c l o s e l y s p a o e d p r o b e s a t a sample l o c a t i o n is given by t h e formula,

When v a r i a n c e between probe8 1s t h e major source of v a r i a t i o n , a s i t is i n t h i s c a se , t h e o n l y way t o s u b s t a n t i a l l y r e d u c e t h e v a r i a n c e o f t h e mean X is t o i n c r e a s e t h e n u m b e r , n , of probes, When v a r i a n c e be tween p u r g e s is t h e major s o u r c e of v a r i a t i o n , one may i n c r e a s e m o r n , and t h e c h o i c e c o u l d b e made on t h e b a s i s o t c o s t s . S i m i l a r l y , when a n a l y t i c a l e r r o r i s t h e major s o u r c e , one c o u l d c h o o s e on t h e baq i s of c o s t t o i nc rease rn, n , or 8 , i n o r d e r t o dec rease t h e va r i ance of X .

Once a g a i n i t s h o u l d b e p o i n t e d o u t t h a t t h e a b o v e d i s c u s s i o n of t h e c o m p o n e n t s o f v a r i a n c e a n a l y s i s o f t h e P i t t m a n d a t a i s a n i l l u s t r a t i o n o f p r o c e d u r e . I n a c t u a l p r a c t i c e , one should no te t h a t t h e measurements of s a m p l e 8 from d i f f e r e n t p u r g e s of t h e same probe a r e n e i t h e r independent nor i d e n t i c a l l y d i s t r i b u t e d . T h e r e f o r e , one s h o u l d use o n l y t h e sample from a f t e r t h e f i r s t purge i n measuring c o n c e n t r a t i o n s . T h i s e f f e c t i v e l y removes " b e t w e e n p u r g e s " a s a n e s t i m a b l e v a r i a n c e component. For e a c h p o s s i b l e va r i ance component, i t i s necessary t o c o n s i d e r w h e t h e r t h e a s s u m p t i o n s of v a r i a n c e components a n a l y s i s a r e r e a s o n a b l e . I n a d d i t i o n , a s was done above, i t i s necessary t o d e c i d e or t o i n v e s t i g a t e f u r t h e r t h e c a u s e s of l a r g e v a r i a n c e c o m p o n e n t s ( i , e . , was t h e l a r g e between probe var iance due t o s h o r t - r a n g e s p a t i a l v a r i a t i o n o r d i f f e r e n c e s i n t i m e s t h e g a s w a i t e d i n s y r i n g e s b e f o r e a n a l y s i s ) .

I N T E R P O L A T I O N A N D C O N C E N T R A T I O N C O N T O U R I N G

O n e o f t h e p r i n c i p a l r e a s o n s f o r t ak ing SOV measurements is t o e s t ima te t h e l o c a t i o n of a p o l l u t a n t plume. Ano the r r e a s o n may be t o i n d i c a t e a p o s s i b l e s o u r c e f o r a p o l l u t a n t plume. Data ana lyses used t o f u r t h e r t h e s e o b j e c t i v e s u s u a l l y i n v o l v e i n t e r p o l a t i o n b e t w e e n s a m p l e p o i n t s and t h e d r a w i n g o f concen t r a t ion c o n t o u r s ( i s o p l e t h s ) . B e f o r e d i s c u s s i n g t h e s e a n a l y s e s , i t i s i m p o r t a n t t o p o i n t o u t a few t h i n g s about t h e d a t a . SOV measurements a r e measurements of c o n c e n t r a t i o n s of

c e r t a i n g a s e o u s c h e m i c a l compounds nea r t h e s u r f a c e . They do not n e c e s s a r i l y r e p r e s e n t t h e c o n c e n t r a t i o n s ( o r some monotone t r a n s f o r m a t i o n o f t h o s e c o n c e n t r a t i o n s ) of t h e compounds d i r e c t l y below t h e s a m p l e p o i n t s a t t h e l e v e l . o f t h e p l u m e . A p o s i t i v e SOV measurement a t a s a m p l i n g l o c a t i o n may b e a f a l s e p o s i t i v e ( 1 . e . ) t h e plume d o e s n o t e x t e n d b e l o w t h e s a m p l i n g p o i n t ) i n t h a t t h e p o s i t i v e measurement may be d u e t o l a t e r a l movement i n t h e e a r t h o f t h e g a s from t h e p!ume a r o u n d a l e n s o f i m p e r m e a b l e Clay o r rock, or i t may b e c a u s e d b y e r r o r s i n t h e s a m p l i n g and a n a l y s i s . A a n o n e - d e t e c t e d w m e a s u r e m e n t may b e a f a l s e n e g a t i v e ( 1 . 8 . . plume i s below samp.1ing p o i n t ) c a u s e d b y an Impermeab le l a y e r between plume and s a m p l i n g d e v i c e , by b i o d e g r a d a t i o n of t h e compound, b y slow t r a n s p o r t r a t e , or by s a m p l i n g and measurement e r r o r . T h u s a v e r y i r r e g u l a r s p a t i a l p a t t e r n of SOV measurements may be due t o one or more o f s e v e r a l c a u s e s . Even a f a i r l y r e g u l a r s p a t i a l p a t t e r n of SOV measuremen t s may n o t be i n d i c a t i v e of t h e a c t u a l l o c a t i o n of t h e p o l l u t a n t plume because of l a t e r a l d r i f t o f t h e v a p o r . Under t h e very b e s t of c i rcumstances , t h e S O V m e a s u r e m e n t s r e p r e s e n t some m o n o t o n e t r a n s f o r m a t i o n d i s t o r t e d b y measurement errors o f t h e c o n c e n t r a t i o n s of t h e compounds below t h e sampling p o i n t s a t t h e l e v e l of t h e plume.

T h e r e a r e many methods of i n t e r p o l a t i o n a v a i l a b l e t o t h e i n v e s t i g a t o r such a s l i n e a r , i n v e r s e squared d i s t a n c e , s p l i n e s , and k r i g i n g . Most s u c h m e t h o d s , s u c h a s t h e f i r s t t h r e e men t ioned a b o v e , a r e d e t e r m i n i s t i c ( 1 . e . ) do n o t r e l y on a p r o b a b i l i t y mode l ) w h i l e some, u s u a l l y denoted a s k r i g i n g , do depend on p r o b a b i l i t y m o d e l s , T y p i c a l l y t h e v a r i o u s common i n t e r p o l a t i o n p r o c e d u r e s g i v e s i m i l a r r e s u l t s concern ing t h e g e n e r a l p a t t e r n o f S O V c o n c e n t r a t i o n s . T h e a d v a n t a g e o f k r i g i n g ( b a s i c a l l y a r e g r e s s i o n procedure t h a t uses in fo rma t ion about t h e s p a t i a l c o r r e l a t i o n of o b s e r v a t i o n s ) i s t h a t i t a l s o p r o v i d e s an e s t i m a t e d s t a n d a r d e r r o r for each i n t e r p o l a t i o n . However, t h a t e s t ima ted s t a n d a r d e r r o r i s h i g h l y d e p e n d e n t on t h e p r o b a b i l i t y model (commonly r e f e r r e d t o a s t h e s p a t i a l s t r u c t u r e model i n g e o s t a t i s t i c s ) . The p r o b a b i l i t y model m u s t be e s t i m a t e d anew f o r e a c h SOV s t u d y because o f t h e u n i q u e c h a r a c t e r i s t i c s of d i f f e r e n t s i t e s . Good e s t i m a t i o n o f a model r e q u i r e s more and b e t t e r d a t a t h a n a r e usua l ly ob ta ined i n an S O Y s t u d y . F o r t h i s r e a s o n , i t seems b e t t e r t o u se a s i m p l e s p l i n e or i n v e r s e - s q u a r e i n t e r p o l a t i o n p r o c e d u r e , and i f an i n d i c a t i o n of t h e amount of e r r o r t h a t may b e i n v o l v e d i n t h e i n t e r p o l a t i o n 1s d e s i r e d , c r o s s - v a l i d a t i o n t e c h n i q u e s ( s e e Efron , 1 9 8 2 , Chapter 7) may be employed.

F i n a l l y , c a r e m u s t be t a k e n i n t h e u s e o f c o m p u t e r i n t e r p o l a t i o n and c o n t o u r i n g p a c k a g e s s o a s n o t t o o b t a i n m i s l e a d i n g c o n t o u r s . A t y p i c a l s i t u a t i o n i n w h i c h mis leading c o n t o u r s occur i s one i n which an o b s e r v a t i o n 1s s e v e r a l o r d e r s o f m a g n i t u d e l a r g e r t h a n t h o s e o b t a i n e d a t neighboring p o i n t s

209

( s e e Figure 6 . 2 1 , In t h i s oabo t h e r e w i l l urually be several oontour l i n e 8 o i r o l i n g t h e p o i n t w i t h the l a r g e o b s e r v a t i o n ; the l o o a t i o n 8 O f t h e s e oontours r e f l e o t almost nothing other than the ldiosynorasier of t h e oontouring paokage. I t would b e b e t t e r t o remove the80 o i r c l i n g oontours r n d merely t l a g the large bbservation.

1 3 10 9 1 1

15

1 2

10

11

1 4

16

Figure 6 . 2 , Misleading contours,

210

R E F E R E N C E S

1 . A n d e r a o n , R. L . D e s i g n s a n d E s t i m a t o r s f o r V a r i a n c e C o m p o n e n t s . I n A S u r v e y o f S t a t i s t i c a l D e s i g n a n d L i n e a r M o d e l a , J . N . S r l v a s t a v a , e d . N o r t h - H o l l a n d P u b l i s h i n g C o . , New York, N Y , 1975 . p . 1 - 2 9 .

2. E f r o n , 8 . T h e J a c k k n i f e , t h e B o o t s t r a p a n d O t h e r R e s a m p l i n g P l a n s . S o c i e t y f o r I n d u s t r i a 1 a n d A p p l i e d M a t h e m a t i c s , P h i l a d e l p h i a , P A , 1 9 8 2 . 92 p p .

3. H o a g l l n , D . C . , F. M o a t e l l e r a n d J . W , T u k e y . U n d e r s t a n d i n g R o b u s t a n d E x p l o r a t o r y D a t a A n a l y s i s . J o h n W i l e y & Sons, New Y o r k , N Y , 1 9 8 3 . 447 p p .

4. S c h e f f e , H. T h e A n a l y s i s of Variance. John WileY b S o n s , New York, N Y , 1959 . 477 p p .

21 1

C H A P T E R 7

CASE STUDIES

I N T R 0 DUCT I ON

V o l a t i l e c o m p o u n d s a r e c o m p o n e n t s i n g r o u n d - w a t e r con tamina t ion a t many, i f n o t mos t , Super fund s i t e s . S o i l v a p o r c o n c e n t r a t i o n s e r v e s a s a s u r r o g a t e f o r a c t u a l measurements of t h e c o n c e n t r a t i o n s of t h e compounds of i n t e r e s t i n g round-water . The u s u a l o b j e c t i v e i n measu r ing o r g a n i c v a p o r s i n s o i l i s t o map t h e l a t e r a l e x t e n t of s o i l and g r o u n d - w a t e r c o n t a m i n a t i o n or b o t h w h i l e a t t h e s a m e t i m e m i n i m i z i n g t h e n u m b e r of c o n v e n t i o n a l m o n i t o r i n g w e l l s wh ich m u s t b e d r i l l e d . Maps of s o i l v a p o r c o n c e n t r a t i o n s c a n be u s e d t o s i t e g r o u n d - w a t e r mon i to r ing w e l l s more e f f i c i e n t l y .

The b a s i c a p p r o a c h i n a s o i l - g a s i n v e s t i g a t i o n a t a p a r t i c u l a r s i t e i s s i m p l e i n concep t . The v e r t i c a l p r o f i l e s of o r g a n i c v a p o r s p resent i n t h e s o i l pore spaces a r e measured and p l o t t e d f o r s e v e r a l l o c a t i o n s a t t h e s i t e . S e l e o t i o n of t r a c e r g a s e s f o r t h e s i t e 1 s a i d e d when p r i o r i n f o r m a t i o n o n contaminant c o n c e n t r a t i o n s i n ground-water i s a v a i l a b l e . Based o n t h e v e r t i c a l p r o f i l e s , t h e p a r t i c u l a r o r g a n i c s o i l g a s e s p r e s e n t , a n d t h e s a m p l i n g a n d a n a l y t i c a l m e t h o d o l o g i e s a v a i l a b l e , o n e o r m o r e t r a c e r g a s e s a r e s e l e c t e d . A sampl ing d e p t h i s a l s o s e l e c t e d , b a s e d o n t h e m e a s u r e d v e r t i c a l p r o f i l e s , wh ich i s e x p e c t e d t o produce s o i l g a s c o n c e n t r a t i o n s w e l l a b o v e t h e m i n i m u m c o n c e n t r a t i o n s d e t e c t a b l e w i t h t h e a n a l y t i c a l t e c h n i q u e s a t hand . By u s i n g t h i s c o n s t a n t s ampl ing d e p t h , s o i l gas samples a r e c o l l e c t e d and m e a s u r e d a c r o s s t h e s i t e p r e f e r a b l y on a r e g u l a r g r i d p a t t e r n . T h e s e v a l u e s a r e then p l o t t e d on a map and a r e con toured e i t h e r b y h a n d or w i t h a computer a l g o r i t h m . The d e s i r e d r e s u l t is a c o n t o u r p l o t of s o i l - g a s c o n c e n t r a t i o n s a t a c o n s t a n t d e p t h a c r o s s t h e s i t e ; t h e i n v e s t i g a t o r h o p e s t h a t t h i s p l o t is r e l a t e d i n a more or l e s s l i n e a r way t o c o n t a m i n a n t c o n c e n t r a t i o n s i n g r o u n d - w a t e r or i n t h e b u r i e d w a s t e s t r a t u m of i n t e r e s t .

T w o c a s e s t u d i e s a r e p r e s e n t e d a s f l l u s t r a t i o n s of t h i s b a s i c a p p r o a c h , W h i l e n e i t h e r c a s e i s a S u p e r f u n d s i t e , t h e t e c h n i q u e s u s e d a r e v e r y s i m i l a r t o i n v e s t i g a t i o n s which m i g h t h e c a r r i e d o u t a s p a r t o f a S u p e r f u n d R e m e d i a l I n v e s t i g a t i o n F e a s i S i l i t y S t u d y . T h e f i r s t c a s e s t u d y i l l u s t r a t e s t h e use of s c i l - g a s m e a s u r e m e n t s a s a means of d e l i n e a t i n g a p l u m e o f i : a s ~ i i n s f rom a l e a k i n g u n d e r g r o u n d s t o r a g e t a n k a t a r u r a l

212

s e r v i c e s t a t i o n . I n t h e s e c o n d c a s e s t u d y , s o i l - g a s measurements a r e used t o examine t h e e x t e n t of g r o u n d - w a t e r o o n t a m i n a t i o n o r i g i n a t i n g f r o m s u r f a c e i m p o u n d m e n t s a n d underground s t o r a g e t a n k s a t a l a r g e i n d u s t r i a l p l a n t .

H Y D R O C A R B O N PLUHE D E T E C T I O N AT S T O V E P I P E WELLS, C A L I F O R N I A

Gasol ine Plume His tory

I n Hay 1979 t h e o d o r o f g a s o l i n e was d e t e c t e d i n an unused w e l l n e a r a Chevron s e r v i c e s t a t i o n a d j a c e n t t o t h e S t o v e p i p e Wel l s H o t e l i n Dea th V a l l e y Nat ional Monument. The l o c a t i o n of S tovepipe Wells (La Brecque, e t a l . , 1984) i s s h o w n on F i g u r e 7.1; F i g u r e 7.2 shows t h e l o c a t i o n of t h e s e r v i c e s t a t i o n and h o t e l complex. A s a m p l e c o l l e c t e d f rom t h e w e l l showed t h a t a l a y e r of g a s o l i n e had accumula t ed on t h e water t a b l e , Se rv ioe s t a t i o n r e c o r d s i n d i c a t e d t h a t be tween O c t o b e r 7, 1978, and September 4, 1979, a s much a s 19,000 g a l l o n s of unleaded g a s o l i n e were lost. No r e c o r d s were a v a i l a b l e p r i o r t o O c t o b e r 7, 1978, b u t t h e r e was e v i d e n c e t h a t t h e b u r i e d s t o r a g e t a n k was a l r e a d y l e a k i n g a t t h a t t i m e . T h e t o t a l p r o d u c t l o s t was p r o b a b l y c o n s i d e r a b l y i n e x c e s s of 20,000 g a l l o n s . The N a t i o n a l Pa rk S e r v i c e r e q u e s t e d t h a t t h e USCS a s s e s s t h e sp read ing and t h e hydro log ic e f f e c t s of t h e g a s o l i n e l e a k on t h e ground-water sys t em,

The USGS d r i l l e d s e v e r a l Wel l3 i n May, 1980; F i g u r e 7.2 s u m m a r i z e s t h e USCS r e s u l t s . I n 1980 w e l l K 3 c o n t a i n e d s e d i m e n t s s a t u r a t e d w i t h g a s o l i n e , b u t wel l J6 c o n t a i n e d n o d e t e c t a b l e gaso l ine . By f a l l 1983, a s t r o n g g a s o l i n e o d o r was d e t e c t e d i n well 56, i n d i c a t i n g t h a t t h e gaso l ine had cont inued t o migra te eastward. There was cons ide rab le q u e s t i o n . a s t o t h e e x a c t d i r e c t i o n o f t h e f l o w of g a s o l i n e , i t s w i d t h , and i t s a r e a l e x t e n t .

Hydrogeologic S e t t i n g

The S t o v e p i p e W e l l s s t u d y a r e a i s l o c a t e d on n o r t h - d i p p i n g a l l u v i a l - f a n sed imen t s . Cround-water 13 t h e o n l y l o c a l s o u r c e o f w a t e r a v a i l a b l e t o t h e S t o v e p i p e W e l l s H o t e l and a s s o c i a t e d f a c i l i t i e s . T h e l o c a l a q u i f e r c o n s i s t s o f u n c o n s o l i d a t e d , g r a v e l l y , sandy s i l t having a t r a n s m i s a i v i t y of about 315 m 2 / d , Depth t o w a t e r r a n g e s from abou t 2 5 f e e t j u s t n o r t h o f t h e h o t e l t o a b o u t 145 f e e t a t a s u p p l y wel l up t h e a l l u v i a l west of t h e h o t e l . D i r e c t i o n of g round-wa te r f l o w i n t h e v i c i n i t y o f t h e h o t e l is t o t h e e a s t ; t h e r e g i o n a l water t a b l e appears t o have d e c l i n e d s l i g h t l y between 1977 and 1978.

Ground-water q u a l i t y i n t h e v i c i n i t y of t h e h o t e l va r i ed from 5 2 5 0 m g / l t o 8790 m g / l t o t a l d i s s o l v e d s o l i d s ( T D S ) i n J u n e 1980. TDS c o n s i s t s p r i m a r i l y o f sodium, c h l o r i d e , and s u l f a t e , w i t h h i g h c o n c e n t r a t i o n s of b o r o n a n d i r o n .

21 3

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S o i l Gas Measurements

C o n c e n t r a t i o n s o f o r g a n i c v a p o r s i n s o i l a t a d e p t h of a p p r o x i m a t e l y 5 f e e t were mapped w i t h a s y s t e m w h i c h i n v o l v e d d r i v e n s t e e l p r o b e s , a s p e c i a l s a n r p l i n g m a n i f o l d , g a s s a m p l e c o l l e c t i o n w i t h a s y r i n g e , and f i e l d a n a l y s i s v i a a f i e l d gas c h r o m a t o g r a p h w i t h a p h o t o i o n i z a t l o n d e t e c t o r . The p r o b e , shown i n F i g u r e 7 . 3 , was a b o u t 98 i n c h e s i n l e n g t h w i t h a n o u t s i d e d i a m e t e r o f 314 - inch and an i n s i d e d i ame te r of 1 / 4 - i n c h ; t h e s h a f t was c o n s t r u c t e d o f 4 1 3 0 c a r b o n s t e e l . T h e p r o b e t i p was a c y l i n d e r o f 3 1 6 s t a i n l e s s s t e e l , 0.87 i nches l o n g , ' w i t h a n o s e t a p e r e d a t 30 d e g r e e s . S i x p o r t s w e r e s p a c e d r a d i a l l y a r o u n d t h e c i r c u m f e r e n c e o f t h e c y l i n d e r . F r i t s - porous s t a i n l e s s s t e e l d i s c s m e a s u r i n g 3-mm d i a m e t e r b y 3-mm t h i c k - were p r e s s e d i n t o t h e p o r t s t o s e r v e a s s c r e e n s . Pore s i z e was 2 0 m i c r o n s , c h o s e n t o a l l o w s o i l v a p o r p a s s a g e w h i l e e x c l u d i n g m o a t s o i l p a r t i c l e s . A l e n g t h o f 3 m m O D T e f l o n t u b i n g was c o n n e c t e d t o t h e p o r t s i n t h e p r o b e t i p ; t h e p r o b e was c o m p l e t e d b y t h r e a d i n g t h e 3 m m T e f l o n t u b e t h r o u g h t h e p r o b e s h a f t . [ N O T E : T e f l o n i s n o l o n g e r r e c o m m e n d e d f o r s o i l - g a s s a m p l i n g b e c a u s e some h y d r o c a r b o n s t e n d t o a d s o r b o r d i f f u s e i n t o t h e m a t e r i a l . T h e L G A S p r o b e u s e d i n t h e f o l l o w i n g P i t t m a n , Nevada, c a s e s t u d y u s e d s t a i n l e s s s t e e l . ]

M o d i f i e d f e n c e - p o s t d r i v e r s were u s e d bo th t o i n s e r t and t o remove t h e p r o b e f rom t h e g r o u n d . The d r i v e r was a 2 . 5 - i n c h O D c y l i n d e r w i t h a 1 . 5 - i n c h I D . The d r i v e r a n d e x t r a c t o r a r e shown i n F i g u r e 7.8. I n s e r t i o n of t h e p r o b e was d i f f i c u l t a t S t o v e p i p e W e l l s b e c a u s e m u c h o f t h e s i t e was covered b y c o b b l e - and b o u l d e r - b e a r i n g s a n d s and g r a v e l s . To r e d u c e t h e wea r and t e a r on t h e s a m p l i n g p r o b e , a 1 . 2 5 - i n c h s t e e l r o d was f i r s t d r i v e n through most o f t h e s a m p l i n g d e p t h , t h e n removed s o t h a t t h e p r o b e c o u l d b e d r i v e n t o t h e d e s i r e d dep th . A f t e r e x t r a c t i o n , t h e s o i l p r o b e c o n e was removed f o r c l e a n i n g . A c l e a n cone was then r e i n s t a l l e d and used t o sample t h e n e x t l o c a t i o n .

A t a c h o s e n s a m p l i n g l o c a t i o n , t h e probe was d r i v e n i n t o t h e g r o u n d t o t h e d e s i r e d s a m p l i n g d e p t h ( a b o u t 5 f e e t a t S t o v e p i p e W e l l s ) , t h e f e n c e p o s t d r i v e r and s t e e l d r i v e c a p were r e m o v e d , a n d t h e f r e e end o f t h e 3-mm T e f l o n t u b e w a s a t t a c h e d t o t h e s a m p l e p o r t o f t h e g a s s a m p l e c o l l e c t i o n m a n i f o l d a s shown i n F i g u r e 7 . 5 . T h e m a n i f o l d was a 3 - w a y T - c o n n e c t o r which connec ted t h e sample p o r t t o a Mininert v a l v e a n d a s h u t - o f f v a l v e wh ich i n t u r n was c o n n e c t e d t o a M i n e S a f e t y A p p l i a n c e s ( M S A ) S a r n p l a i r m a n u a l p u m p . To o b t a i n a sample , t h e s h u t - o f f v a l v e was opened and a 75-ml volume of g a s

p u r g e d f r o m t h e p r o b e w i t h t h e p u m p . A gas chromatograph s y r i n g e was t h e n used t o e x t r a c t a s a m p l e f o r a n a l y s i s t h r o u g h t h e M i n i n e r t v a l v e ; s y r i n g e s w e r e t a g g e d and i m m e d i a t e l y ;,n;Llyzed.

216

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Figure 7 . S a SOV 8ampling m8aifold.

219

A n a l y s i s was p e r f o r m e d w i t h a P h o t o v a o Model l O A l O P o r t a b l e P h o t o i o n i z a t i o n Gas Chromatograph d e s i g n e d t o a n a l y z e v o l a t i l e h y d r o c a r b o n 8 i n c l u d i n g a l k a n e s above e t h a n e , and c y c l i c compounds s u c h a8 b e n z e n e , t o l u e n e , x y l e n e , and o t h e r a r o m a t i c s . T h e d e t e c t o r of t h i 8 p a r t i c u l a r G C was a vacuum u l t r a v i o l e t p h o t o i o n i z a t i o n s y s t e m w h i o h i o n i z e s h y d r o o a r b o n s w i t h b o n d i n g e n e r g i e s o f 1 0 . 2 eV o r l e s s . D i f f e r e n t h y d r o c a r b o n s a r e d e t e c t e d w i t h d i f f e r e n t e f f i c i e n c i e s ( d i f f e r e n t r e s p o n s e per atom of c a r b o n ) i n t h i s d e v i c e ; t h e s o i l vapor d a t a below a r e g i v e n i n t e r m s of t h e e q u i v a l e n t c o n c e n t r a t i o n of benzene.

B a c k g r o u n d c o n c e n t r a t i o n s o f t o t a l n o n - m e t h a n e hydrocarbons and f i v e i n d i v i d u a l h y d r o c a r b o n s i n a m b i e n t a i r were measured a t l o o a t i o n s 2-km e a s t and 2-km west of t h e s t u d y a r ea : t h e observed va lues a r e l i s t e d i n T a b l e 7 . 1 . F i g u r e 7 . 6 shows t h e t o t a l non-methane hydroca rbon ( N M H C ) c o n c e n t r a t i o n s i n s o i l gas a s ppmv-benzene e q u i v a l e n t s t h r o u g h o u t t h e s i t e . The h a t c h e d a r e a o u t l i n e s t h e l o c a t i o n of t h e g a s o l i n e plume d e t e r m i n e d from d r i l l i n g . From T a b l e 7 . 1 , b c c k g r o u n d N H H C c o n c e n t r a t i o n s were o n t h e o r d e r of 1 . 0 t o 1 . 5 ppmv (benzene e q u i v a l e n t ) . A s s u m i n g t h a t a N M H C s o i l - g a s c o n c e n t r a t i o n of t w i c e background d e f i n e s t h e l imi t s of t h e contaminant plume, t he 3 . 0 - p p m v NMHC a o i l - g a s contour a g r e e s r e a s o n a b l y w e l l w i t h t h e l imi t s of t h e g round-wa te r plume es t ima ted from d r i l l i n g . However, t h e N M H C s o i l - g a s plume a p p e a r s t o l i e n o r t h of t h e p l u m e o u t l i n e e s t i m a t e d f r o m d r i l l i n g , a n d s o i l g a s c o n c e n t r a t i o n s i n t h e v i c i n i t y of wel l SP6 a r e lower t h a n t h o s e b o t h upgradlen t a n d downgradient of well SP6 .

F i g u r e s 7 . 7 t h r o u g h 7 . 1 1 s h o w p l o t s of t h e f i v e o r g a n i c vapor components measured: e t h a n e / p r o p a n e , b u t a n e , p e n t a n e , b e n z e n e , a n d i s o o c t a n e . T h e l i g h t e s t c o m p o n e n t s , e thane /propane , do n o t c o r r e l a t e w e l l w i t h t h e g a s o l i n e plume. Ambi e n t a i r background c o n c e n t r a t i o n s of t h e s e component8 were i n t h e range of 0 . 6 t o 1 . 4 ppmv (benzene e q u i v a l e n t s ) , and t h e e t h a n e l p r o p a n e v a l u e s shown o n F i g u r e 7 . 7 a r e i n t h e r ange of 0 . 1 t o 1 . 8 ppmv; t h e s e comparat ively h i g h background v a l u e s may e x p l a i n t h e b e h a v i o r o f t h e s e compounds. Pentane and benzene ( F i g u r e s 7 . 9 and 7 . 1 0 ) were measured a t c o n c e n t r a t i o n s above ambient a i r background va lues a t only a few l o c a t i o n s and were a l s o p o o r l y c o r r e l a t e d w i t h g r o u n d - w a t e r c o n c e n t r a t i o n s . Butane and l s o o c t a n e ( F i g u r e s 7 . 8 and 7 . 1 1 , r e s p e c t i v e l y ) were measured i n concen t r a t ions s i g n l f i c a n t l y above b a c k g r o u n d , a n d y i e l d e d smooth c o n t o u r p l o t s which agreed w e l l w i t h t h e plume o u t 1 lnes es t lmat ed from g r o u n d - w a t e r sampl i n g . Ver t i c a l Cross-Sect i o n s

A v e r t i c a l c r o s s - s e c t i o n o f r e l a t i v e o r g a n i c vapor concen t r a t ions was e s t a b l i s h e d b y d r i l l i n g a n o r t h - s o u t h l i n e

220

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o f f i r e w e l l s a c r o s s t h e ground-water p lume . Four o t h e r wel ls were d r i l l e d f o r o t h e r purposes . Wells were d r i l l e d b y u s i n g a hol low-stem auger t o minlmlze d i s t u r b a n c e of subsu r faoe o r g a n i c vapor concen t r a t ion8 , Samples were c o l l e c t e d b y d r i v i n g a 2 - i nch I D s p l i t - s p o o n s a m p l e r , l i n e d w i t h f o u r S h e l b y tube8 each 4.5 inches long. HOad8paCe g n a l y s i s was u s e d t o e v a l u a t e t h e samples c o l l e c t e d . T h i s t echnique c o n s i s t e d of p l a c i n g a s o i l sample i n an a i r t i g h t c o n t a i n e r , t h a n Sampl ing t h e h e a d s p a c e g a s e s i n t h e c o n t a i n e r a f t e r an e g u i l i b r i u m was reached between sample and h e a d s p a c e , The c o n o e n t r a t i o n s t h u s measu red a r e r e l a t i v e ; t h e v a l u e s o b t a i n e d a r e not t h e a c t u a l o r g a n i c vapor concen t r a t ions i n t h e s o i l b u t s h o u l d b e a l i n e a r f u n c t i o n of t h e a c t u a l c o n c e n t r a t i o n s . Samples were t r a n s f e r r e d from t h e She lby t u b e s d i r e c t l y i n t o o n e - p i n t mason j a r s r i t t e d w i t h M i n l n e r t v a l v e s . Samples were allowed t o s t a n d f o r a t l e a s t 3 hours a t 2 4 O C p r i o r t o a n a l y s i s by gas chromatograph.

F i g u r e 7 . 1 2 is a q u a l i t a t i v e summary o f w e l l - d r i l l i n g r e s u l t s a c r o s s t h e S t o v e p i p e W e l l s s t u d y s i t e . F i g u r e 7 . 1 3 s h o w s v e r t i c a l p r o f i l e s o f e t h a n e l p r o p a n e , b u t a n e , b e n z e n e , pentane, and i s o o c t a n e observed i n headspace s a m p l e s from w e l l S P 5 w h i c h i s c o n s i d e r e d t o b e a b a c k d r o u n d w e l l . Concentrat ions of t h e s e components r ema in r e l a t i v e l y c o n s t a n t a t a l l d e p t h s b o t h above and below t h e w a t e r t a b l e . F i g u r e s 7 . 1 4 t h r o u g h 7 . 1 8 show v e r t i c a l c r o s s - s e c t i o n s of h e a d s p a c e c o n c e n t r a t i o n s of e thane lp ropane , bu tane , benzene, pen tane , and i sooc tane observed i n s a m p l e s f rom w e l l s 3 6 5 1 , S P 4 , S P 1 , S P 3 , and SP2. T h i s f i v e - w e l l t r a n s e c t l i e s p e r p e n d i c u l a r t o t h e a x i s of the plume n e a r i t s l e a d i n g edge ; a t t h i s l o c a t i o n no f r e e p roduc t was o b s e r v e d s t a n d i n g o n t h e w a t e r t a b l e w h i l e o n l y g a s o l i n e c o m p o n e n t s d i s s o l v e d i n g r o u n d - w a t e r w e r e o b s e r v e d . A l o n g t h e c r o s s - s e c t i o n , c o n t a m i n a t i o n appears t o extend downward i n t o t h e water t a b l e f o r s e v e r a l f e e t . I n t h e v a d o s e z o n e , e t h a n e l p r o p a n e a n d b u t a n e o c c u r i n g r e a t e s t concent ra t ion j u s t above t h e water t a b l e , a s expected.

C o n c l u s i o n s

The s u r v e y o f o r g a n i c v a p o r s i n s o i l s c o n f i r m e d t h e p o s i t i o n of t h e c o n t a m i n a n t plume d e l i n e a t e d b y g round-wa te r s a m p l i n g , B u t a n e , i s o o c t a n e , and t o t a l o r g a n i c v a p o r s were c o r r e l a t e d s t r o n g l y w i t h g r o u n d - w a t e r c o n c e n t r a t i o n s ; plume l i m i t s d e t e r m i n e d from t h e s e SOi l -gaS components agreed wel l w i t h w e l l - s a m p l i n g r e s u l t s b o t h i n plume l o c a t i o n and e x t e n t . E t h a n e l p r o p a n e had weaker c o r r e l a t i o n s probably because t h e i r a m b i e n t a i r background c o n c e n t r a t i o n s were of t h e same o r d e r of magnitude a s t he s o i l - g a s c o n c e n t r a t i o n s .

228

Figure 7.12. S u m m a r y of drilling rerultr, Augurt 1906, Stovepipe Wellr, California.

Figure 7 . t 3 . Level8 of volrtile orgraico in u e l l SPS 18 fuoctioo of d e p t h , Augurt 5 , 1 9 8 4 , Stovepipe Wallo, Califoroir.

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231

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Figure 7.18. Crorr-rectioa o f ethaae/propane levelr ( p p ) a c r o r r the c o a t a m i n r a t plume, A u ~ u r t 1984, Stovepipe Wellr, California.

235

STUDY OF G R O U N D - W A T E R C O N T A M I N A T I O N FROM I N D U S T R I A L S O U R C E S AT P I T T M A N , N E V A D A

The P i t t m a n , Nevada , s i t e i s a p o r t i o n of t h e e a s t - w e s t r ight-of-way of a m a j o r m u n i c i p a l s u p p l y a q u e d u c t c a l l e d t h e P i t t m a n L a t e r a l . The s t u d y s i t e (Wal the r , e t a l . , 1 9 8 3 ) ( s e e F i g u r e 7 . 1 9 ) l i e s i n u n d e v e l o p e d d e s e r t a b o u t 1 1 m i l e s s o u t h e a s t of Las Vegas and downgradient of a chemical r e f i n i n g and processing complex. The complex was o r i g i n a l l y c o n s t r u c t e d d u r i n g World War I 1 t o r e f i n e manganese o r e ; o the r a c t i v i t i e s which have been performed t h e r e i n c l u d e t i t a n i u m r e f i n f n g and t h e p r o d u c t i o n o f i n t e r m e d i a t e c o m p o n e n t s o f p e s t i c i d e s . Ground-water contaminat ion a t t h e s i t e p r o b a b l y began s h o r t l y a f t e r t h e c o n s t r u c t i o n o f t h e complex; from the mid-1940's t o t h e l a t e 1 9 7 0 ' s , unknown q u a n t i t i e s of l i q u i d and s o l i d w a s t e s were r o u t i n e l y d i s p o s e d of i n l e a c h p i t s and i n un l ined ponds on p r o p e r t y b e l o n g i n g t o t h e c o m p l e x . A m a j o r l e a k was d e t e c t e d i n 1 9 7 6 i n an unde rg round s t o r a g e t a n k on p r o p e r t y l e a s e d b y one o f t h e c o m p a n i e s o p e r a t i n g i n t h e c o m p l e x . Approx ima te ly 3 0 , 0 0 0 g a l l o n s of benzene a r e t h o u g h t t o have been r e l e a s e d i n t h a t i n c i d e n t .

D e p t h t o g r o u n d - w a t e r v a r i e s s i g n f f i c a n t l y o v e r t h e l e n g t h of t h e c o n t a m i n a n t p lume, f rom 5 5 t o 6 0 f e e t a t t h e s o u t h e r n r e g i o n s o f t h e plume t o 1 0 t o 1 2 f e e t i n t h e P i t tman a r e a . Figure 7 . 2 0 shows a n i d e a l i z e d c r o s s - s e c t i o n a l o n g t h e a x i s of t h e plume from t h e sou rce t o i t s d i scha rge i n La8 Vegaa Wash. A hydrau l i c g r a d i e n t of 0 . 0 1 2 has been r e p o r t e d f o r t h e a r e a w i t h a l i n e a r g r o u n d - w a t e r f l o w v e l o c i t y e s t i m a t e d i n e x c e s s o f 1 0 0 0 f e e t l y e a r . The s u r f i c i a l g e o l o g y h a s b e e n c h a r a c t e r i z e d a s u n c o n s o l i d a t e d sand and g r a v e l a l luvium 30 t o 1 0 0 f e e t t h i c k . Below t h e s e l a y e r s t h e h y d r o l o g i c bo t tom is composed o f a c o m p a r a t i v e l y impermeable mudstone i n t e r s p e r s e d w i t h t h i n l a y e r s of s a n d and g r a v e l . Bands of low p e r m e a b i l i t y c a l i c h e a r e f o u n d t h r o u g h o u t t h e r e g i o n . P a l e o - c h a n n e l s ( b u r i e d d e p o s i t s o f s a n d and g r a v e l ) a n d s u r f a c e d r a i n a g e c h a n n e l s have been s u g g e s t e d a s c o n d u i t s which may a c c e l e r a t e contaminant movement.

U n c o n f i n e d g r o u n d - w a t e r o c c u r s i n t h e P i t t m a n L a t e r a l a r e a a t depths of 6 t o 1 2 f e e t i n c a l c i f i e d b u t u n c o n s o l i d a t e d a l l u v i u m . Since t h e e a r l y 1 9 7 0 ' s , a s e r i e s of m o n i t o r i n g w e l l s h a v e been i n s t a l l e d b y t h e company r e s p o n s i b l e f o r t h e b e n z e n e l e a k a n d b y t h e U .S . Bureau o f Reclamation. Figure 7 . 2 1 shows c o n c e n t r a t i o n s o f t o t a l d i s s o l v e d s o l i d s i n g r o u n d - w a t e r measured i n m o n i t o r i n g w e l l s i n t h e a r e a downgradien t of t h e i n d u s t r i a l complex. F r o m h y d r o l o g i c s t u d i e s b y t h e company r e s p o n s i b l e f o r t h e benzene s p i l l , a plume o f o rgan ic s o l v e n t s a n d p e s t i c i d e s w a s i d e n t i f i e d ; F i g u r e 7 . 2 2 s h o w s i s o c o n c e n t r a t i o n l i n e s o f benzene i n ground-water. The a r e a l e x i e n t o f t h e s o l v e n t plume i s a b o u t 0 . 6 s q u a r e m i l e s and u n d e r l i e s r e s i d e n t i a l a n d commerc ia l p o r t i o n s o f P i t t m a n .

2 36

N E V A D A

,SITE

N

t Figure 7.19. General location map.

237

S o u t h

B M I COMPLEX

h) W W

P I T T Y A N 0 4 s

T A l L l N a POW08 : a Y . w 0

A

1 7 0 0 - V

0 0 .. r

MUDDY C R E E K FORMATION c

c 0

- 1000-

- U -

18000 11. 14000 W 2 0 0 0 0 0 0 0 10000

Figure 7.20. Eydrogeo1ogic cro8r-rcctim with the loc8tioua of rampling borehole8 8loag tha coat8min8nt p l u w .

. T o t a l D laeo lvod

Figure 7 .21 . Crouad-water q u a l i t y bared on to t81 d i r r o l v e d rol idr (U.S. Bureau of Reclamation, 1983).

239

0

I I

N A p p r o x l m r t e . 60.10

. 6

m i l e 8

?+re 7 .22 . Irocontour projec t ion of benzene concentration8 ( p p ) i n ground-water (from data 1982-February 1983).

240

B e n z e n e c o n c e n t r a t i o n s i n g r o u n d - w a t e r h a v e b e e n r e p o r t e d t o r a n g e f rom i n e x c e s s o f 5 0 0 , 0 0 0 m g / l n e a r t h e s o u r c e t o 5 - 1 0 m g / l i n t h e v i c i n i t y o f t h e P i t t m a n l a t e r a l . These c o n t a m i n a n t p l u m e s move d o w n g r a d i e n t t h r o u g h t h e u n c o n f i n e d a q u i f e r f r o m t h e i n d u s t r i a l c o m p l e x t h r o u g h t h e s t u d y a r e a t o d i s c h a r g e u l t i m a t e l y i n Las V e g a s Wash, t h e major s u r f a c e a n d s u b s u r f a c e d r a i n a g e p a t h f o r t h e L a s V e g a s V a l l e y . F i g u r e 7 . 2 3 is a c r o s s - s e c t i o n a l o n g t h e P i t t m a n L a t e r a l ( p e r p e n d i c u l a r t o t h e p l u m e ) o f t h e v a d o s e z o n e , t h e u n c o n f i n e d a q u i f e r , a n d t h e u n d e r l y i n g c l a y f o r m a t i o n w h i c h f o r m s a b a r r i e r t o d o w n w a r d m o v e m e n t f r o m t h e u n c o n f i n e d a q u i f e r . F i g u r e 7 . 2 4 shows t h e s t u d y a r e a a n d t h e l o c a t i o n s of m o n i t o r i n g w e l l s , t h e d r i l l i n g l o g s f o r t h e s e l o c a t i o n s p r o v i d e d t h e i n f o r m a t i o n u s e d t o p r e p a r e F i g u r e 7 . 2 3 . T h e g r o u n d - w a t e r c o n t a i n s a v a r i e t y o f o r g a n i c a n d i n o r g a n i c c o n t a m i n a n t s . H o w e v e r , t h e v o l a t i l e o r g a n i c compounds o f i n t e r e s t t o t h i s s t u d y a r e c h l o r o f o r m i n t h e c o n t a m i n a n t p l u m e o n t h e e a s t e r n s i d e o f t h e s i t e a n d b e n z e n e a n d c h l o r o b e n z e n e i n t h e p l u m e o n t h e w e s t e r n s i d e . T a b l e s 7 . 2 a n d 7 . 3 l i s t t h e m o n i t o r i n g w e l l s wh ich were s a m p l e d t o g e t h e r w i t h t h e i r r e s p e c t i v e c o n c e n t r a t i o n s of c h l o r o f o r m , b e n z e n e , a n d c h l o r o b e n z e n e , a s w e l l a s t h e d a t e s of s a m p l i n g . F i g u r e 7 . 2 5 is a p l o t o f t h e g r o u n d - w a t e r c o n c e n t r a t i o n s o f t h e s e t h r e e c o m p o u n d s a s a f u n c t i o n o f d i s t a n c e a l o n g t h e P i t t m a n L a t e r a l , p e r p e n d i c u l a r t o t h e p l u m e . F i g u r e 7 . 2 5 s h o w s t h a t t h e r e a r e two d i s t i n c t p l u m e s : o n e p l u m e o n t h e e a s t e r n e n d of t h e s t u d y a r e a e x h i b i t i n g s i g n i f i c a n t c o n c e n t r a t i o n s o f c h l o r o f o r m , a n d a n o t h e r t o t h e w e s t e x h i b i t i n g l a r g e c o n c e n t r a t i o n s o f b e n z e n e a n d c h l o r o b e n z e n e .

A s a t e s t o f t h e s o i l - g a s s a m p l i n g s y s t e m d e s c r i b e d i n t h e S t o v e p i p e W e l l s c a s e s t u d y ( F i g u r e s 7 . 3 - 7 . 5 1 , s o i l - g a s s a m p l i n g was c o n d u c t e d a l o n g t h e P i t t m a n L a t e r a l t o d e v e l o p p r o f i l e s o f v o l a t i l e o r g a n i c c o n c e n t r a t i o n s ( K e r f o o t a n d B a r r o w s , 1 9 8 5 ) . F i g u r e s 7 . 2 6 a n d 7 . 2 7 show t h e s a m p l i n g p l a n f o r a s e r i e s of s a m p l e s c o l l e c t e d a t a 4 - f o o t d e p t h . F i g u r e 7 . 2 6 s h o w s t h e s a m p l i n g p l a n u s e d o v e r t h e c h l o r o f o r m p l u m e w h i l e F i g u r e 7 . 2 7 s h o w s t h e s a m p l i n g p l a n u s e d o v e r t h e b e n z e n e / c h l o r o b e n z e n e p l u m e .

F o r c h l o r o f o r m a n a l y s i s , t h e A I D g a s c h r o m a t o g r a p h w i t h e l e c t r o n - c a p t u r e d e t e c t o r ( A I D G C I E C D ) was s e l e c t e d ; t h i s i n s t r u m e n t h a s r e l a t i v e l y h i g h s e n s i t i v i t y t o c h l o r o f o r m . T h e c h r o m a t o g r a p h c o l u m n was a s t a i n l e s s s t e e l t u b e , 1 / 8 - i n c h i n I D a n d 6 f e e t i n l e n g t h p a c k e d w i t h 1 0 p e r c e n t D C - 2 0 0 o n 8 0 / 1 0 0 - m e s h C h r o m o s o r b H P . T h e d e t e c t o r a n d i n j e c t i o n p o r t c p e r a t e d a t 37OC; t h e c o l u m n , a t 43OC. T h e c a r r i e r g a s was a p p r o x i m a t e l y 20 cm3/min of 5 p e r c e n t m e t h a n e i n a r g o n ( P - 5 ) . T h e c h l o r o f o r m d e t e c t i o n l i m i t f o r t h e A I D G C / E C D was 5 p p b v , S a m p l e s e t s f r o m e a c h p r o b e l o c a t i o n a n d d e p t h p o i n t c o n s i s t e d o f t w o o r t h r e e H a m i l t o n S e r i e s 1 0 0 G a s t i g h t s y r i n g e s . T h e s e w e r e 2 5 0 u l c a p a c i t y e x c e p t f o r t h e v e r t i c a l p r o f i l e s t u d y

24 1

Figure 7.23. Eydroiaoloiic crooo roction of the tranoect.

24 2

Figure 7.24. Locatioaa of monitoring well. aloag the P i t t u n Lateral ( U n S C O , 1984).

i - 100

r o t o r .

TABLE 7.2. CONCENTRATIONS OF CHLOROFORl IN GROUND WATER W L E S COLLECTED FROM WELLS ALONG THE P I T " LATERAL (micrograaPe/liter)

WELL NUMBER

DATE 61 7 619 62 1 623 62 5 627 629 631 6 33

3/83 d < 10 28 500 430 181 11 a0 d

11/84 b b 850

4/85 B b 0 570 1000 175

h) 8/85 b * b 541 732 b * &

d = not detected 8 = not aampled

$;... ...

Q

I ...

I Q n

ae

m

8

YY

??

n

II

80

24 5

800 .

600

000

0 .

0 2

DISTANCE ALONO PITTYAN LATERAL (100' . o f f o o t )

<e 8011- O r . Conaontrrtlon (ppbv)

'*b around 0 Wrtor Conaontrrtlon (Ygll)

Figure 7 .25 . Ground-water concaotra t ioar of chloroform, benzene and chlorobeazcoc.

246

631

0.

N I Figure 7.26.

663

0

(j 0

N t

0

629 627 625 623 621

k 2 0 0 f t . 4

Probo location$ i n the area of the c b l o r o f o d tetracbloride.

849

0 d 0 84s

0

fJ 0

641

0

Figure 7,27, Probe locr t ionr i n the a r e a of the bearena/ chlorobenrene contaminant plume.

24 7

TABLE 7.4 OBSERVED CBLOBOFORn CONCENTBATIONS OVER THE CHLOROFOWl

Date, N o . of Well, Location

7-17-85:

623 S 20 623 N 20 623 W 20 623 E .20

7-18-85:

625 ENE 20 625 W S W 20 625 NNW 20 625 SSE 20

7-22-85 :

627 N 20 627 W 20 627 S 20 627 E 20, S 3 627 E 23, S 3 627 E 23, 627 E 20

7-23-05:

625 SSE 25 627 E 20, N 3 631 E 20 623 E 40 623 E 42

621 W 20

1-24-05:

629 W 20 629 E 20 629 N 20 629 S 20

hloroforn Sy ringe No. 1

24.9 12.7

119 8

378 . 2 272.3 330 .9 -

73.0 32 45.4 54

166 119 -

49 2 171

5 32.2 32.7

11

12.4 33.1 22.3 30.9

Ioncen t x lyringe No. 2 v

26.2 11.8

108 4

381 0 1 264 7 313.6 -

72 e 7 23 45.8 54

161 119 -

516 171

5 31.9 24.5

10

8.5 23.8 25.3 31.2 -

ion (ppbv) Syringe no. 3

28.9 12.3

bad rample 117

369 . 9 261 . 2 332.4 -

72.9 30 45 04 57

155 99 -

5 24 t ana l y rec

5 lot analyzec

22.1

11

9.6 25.5 26.6 29.3

L!lLuLW

mean [SD/RSD]

27 [ 2/7% J 12.3 [O. 5/4%1 115 [a/% I 6 [ 3/50% I

376 [6/2% I 266 [ 6/2%] 326 [ 10/3% I bad p o i n t

72.9 [ O . 1 / O X ] 28 5/18% I 45.6[0.2/0%] 55[2/4% I 161 [6/4%] 1 12 [ 12 / 11x1 bad point

511[17/3%] 171 [O/O%] 5 [O/O% I 32.1 [0.2/1%] 27 [ 5/19% I

10.5 [ O . 3/3%]

10 [ 2/20%] 27[5/19%1 25 [2/8%] 30 [ 1/3% I

-2.2.

Coumentr

impling grid rotated 22' t o ivoid ear 1 ier >robe loca t ionr

I f t . x 3 f t . rquare

to replace >ad point8

two pointr :heck s p a t i a l

grad i en t

24 8

n c z :

P

Y

2

t c c t W 0 t 0 0

Iy t a

s s s 0 2

oooo=

6000.

4000

8000.

1000-

1000-

0 - a

Dl8TANCL ALONQ PITTUAN LATERAL (100'a o f f o o t )

-8- Chloroform (uo/l)

-8- boatono ( u o l l )

-8- Chlorobonxono (ug/i)

Figure 7.28. Chloroform concentration# at &-foot depth a# a func tioa of diatance acroaa plume .

249

w h e r e 1 0 0 0 u l s y r i n g e s were u s e d b e c a u s e o f low s o i l - g a s c o n c e n t r a t i o n s .

T a b l e 7.4 l i s t s t h e o o n c e n t r a t i o n s of c h l o r o f o r m found i n s o i l g a s o v e r t h e e a s t e r n p l u m e : F i g u r e 7.28 c o m p a r e s t h e a v e r a g e s o f t h e c h l o r o f o r m 8011-gas c o n c e n t r a t i o n s measured i n t h e v i c i n i t y o f e a c h m o n i t o r i n g w e l l w i t h a v a i l a b l e g r o u n d - w a t e r m e a s u r e m e n t s f r o m T a b l e 7.2. F i g u r e 7.28 i n d i c a t e s good q u a l i t a t i v e ag reemen t b e t w e e n t h e s h a p e s o f t h e s o i l - g a s and g r o u n d - w a t e r p r o f i l e s d e s p i t e t h e f a c t t h a t t h e ground-water s amples were t a k e n a t t imes u p t o s e v e r a l m o n t h s e a r l i e r t h a n t h e s o i l - g a s m e a s u r e m e n t s . F i g u r e 7 . 2 9 is a s c a t t e r p l o t of s o i l - g a s c h l o r o f o r m c o n c e n t r a t i o n s v e r s u s g r o u n d - w a t e r c h l o r o f o r m c o n c e n t r a t i o n s ( f r o m T a b l e s 7.2 a n d 7.4, r e s p e c t i v e l y ) . T h e c o r r e l a t i o n c o e f f i c i e n t f o r t h i s s c a t t e r p l o t is 0.848.

A v e r t i c a l p r o f i l e o f s o i l - g a s c o n c e n t r a t i o n s o f ch lo ro fo rm and ca rbon t e t r a c h l o r i d e was o b t a i n e d n e a r Wsll 623 i n t h e e a s t e r n p l u m e ; T a b l e 7 . 5 l i s t s t h e d a t a o b t a i n e d from s u c c e s s i v e samples a t 1 - f o o t i n t e r v a l s t o a d e p t h o f 6 f e e t a t a l o c a t i o n where t h e w a t e r t a b l e d e p t h was 12.5 f e e t . F i g u r e 7 . 1 2 is a p l o t of t h e v e r t i c a l p r o f i l e s o f c h l o r o f o r m a n d c a r b o n t e t r a c h l o r i d e a t t h i s l o c a t i o n . Both g a s e s e x h i b i t e s s e n t i a l l y l i n e a r i n c r e a s e s i n c o n c e n t r a t i o n w i t h d e p t h : s t r a i g h t l i n e s f i t b y l e a s t - s q u a r e s f i t b o t h g a s e s , w i t h a c o r r e l a t i o n c o e f f i c i e n t g r e a t e r t h a n 0 .99 .

A n a l y s i s o f s o i l - g a s s a m p l e s t a k e n o v e r t h e - w e s t e r n b e n z e n e / c h l o r o b e n z e n e p lume was p e r f o r m e d w i t h two d i f f e r e n t i n s t r u m e n t s : ( 1 ) a P h o t o v a c G C w i t h p h o t o i o n i z a t i o n d e t e c t o r ( P h o t o v a c C C / P I D ) , and ( 2 ) an A I D G C w i t h p h o t o i o n i z a t i o n d e t e c t o r ( A I D C C I P I D ) . T h e P h o t o v a c G C I P I D had a 5 p e r c e n t S E - 3 0 , 1 / 8 - i n c h T e f l o n co lumn and u l t r a p u r e a i r was u s e d a s a c a r r i e r g a s . T h e t e m p e r a t u r e - c o n t r o l l e d A I D G C / P I D u s e d a 6 - f o o t , 1 -8- inch I D s t a i n l e s s s t e e l column w i t h 3 p e r c e n t SE-30 o n 8 0 / 1 0 0 mesh C h r o m o s o r b H P . T h e i n J e c t o r p o r t a n d d e t e c t o r o p e r a t e d a t 89OC and t h e co lumn a t 82OC. U l t r a p u r e n i t r o g e n was u s e d a s t h e c a r r i e r g a s . T h e P h o t o v a c G C / P I D b e n z e n e d e t e c t i o n l imi t was 1 p p b v , a n d t h e A I D G C / P I D c h l o r o b e n z e n e d e t e c t i o n l imit was 3 p p b v .

C o n c e n t r a t i o n s of benzene and d i c h l o r o b e n z e n e i n s o i l - g a s s a m p l e s t a k e n o v e r t h e w e s t e r n plume were a l l l e s s t h a n 1 0 p p b v and were n o t d e t e c t e d a t a l l i n many samples . These low c o n c e n t r a t i o n s a r e u n e x p l a i n e d a l t h o u g h t h e i n v e s t i g a t o r s s p a c u l a t e d t h a t b i o d e g r a d a t i o n m i g h t be r e s p o n s i b l e .

T h e s e t w o c a s e s t u d i e s i l l u s t r a t e t h e u s e o f s o i l - g a s n~t:.:.urements as a means of d e l i n e a t i n g ground-water c o n t a m i n a n t

250

4 0 0

8 0 0

P O 0

100

0

O R O U N D - W A T E R C H L O R O F O R M C O N C E N T R A T I O N

( U O I L )

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p l u m e s . I n t h e f i r s t s t u d y , v a p o r s f r o m l e a k e d g a s o l i n e ( d i s s o l v e d i n g r o u n d - w a t e r and p O 8 S i b l y l y i n g on t o p of t h e w a t e r t a b l e ) moved upward t h r o u g h a p p r o x i m a t e l y 40 f e e t of a l l u v i a l o v e r b u r d e n ( l a r g e l y s a n d s a n d g r a v e l s ) i n c o n c e n t r a t i o n s l a r g e enough to, be measurable a t d e p t h s of about 5 f e e t . By sampl ing s o i l gas o v e r t h e e n t i r e s t u d y a r e a w i t h s t e e l p r o b e s d r i v e n t o 5 f e e t and b y a n a l y z i n g t h e samples i n t h e f i e l d w i t h a t r a n s p o r t a b l e g a s c h r o m a t o g r a p h , t h e l a t e r a l e x t e n t o f t h e plume could be mapped. Not e v e r y vapor component a p p e a r e d t o be a good t r a c e r of g r o u n d - w a t e r c o n t a m i n a t i o n : t o t a l non-methane hydroca rbons , bu tane , and i s o o c t a n e appeared t o o u t l i n e a p l u m e w h i c h was n o t i n c o n s i s t e n t w i t h t h a t e s t i m a t e d f r o m g round-wa te r s a m p l i n g . C o n t o u r s drawn w i t h e thane lp ropane and benzene d i d n o t r e s e m b l e t h e ground-water plume. Benzene c o n c e n t r a t i o n s near t h e s u r f a c e were s o low a s t o be n e a r l y u n m e a s u r a b l e d e s p i t e s u b s t a n t i a l q u a n t i t i e s i n g r o u n d - w a t e r ; t h i s i m p l i e s t h a t some phenomenon d e p l e t e s benzene from t h e o r g a n i c vapors a t some p o i n t i n t h e m i g r a t i o n pa th . The cho ice of t r a c e r i s t h e r e f o r e q u i t e impor tan t .

I n t h e s e c o n d s t u d y , s o i l - g a s c o n c e n t r a t i o n s of chloroform d e f i n e d a plume o f c h l o r o f o r m i n t h e ground-water d o w n g r a d i e n t of a l a r g e i n d u s t r i a l p l u m e . Here t h e depth t o w a t e r was a b o u t 20 f e e t i n d e s e r t a l l u v i u m . G r o u n d - w a t e r c o n c e n t r a t i o n s of benzene of 2 - 5 m g / l c a u s e d n o measu rab le s o i l - g a s c o n c e n t r a t i o n s of benzene. A g a i n , b e n z e n e a p p e a r s t o be o f l i t t l e u s e a s a t r a c e r . P e r h a p s t h e m o s t i m p o r t a n t r e s u l t of t h e second s t u d y i s t h e l i n e a r r e l a t i o n s h i p between d e p t h a n d s o i l - g a s c o n c e n t r a t i o n s o f c h l o r o f o r m a n d carbon t e t r a c h l o r i d e i n Figure 7.30. T h i s b e h a v i o r is e x a c t l y w h a t would b e e x p e c t e d i f s i m p l e d i f f u s i o n p rocesses were t h e p r i m a r y mechanism governing t h e v e r t i c a l m i g r a t i o n of the gases . F i g u r e 7.30 l e n d s hope t h a t i t may be p o s s i b l e t o d e r i v e a q u a n t i t a t i v e r e l a t i o n s h i p between o r g a n i c c o n c e n t r a t i o n s i n ground-water and t h o s e i n Soil g a s , a t l e a s t i n some l o c a t i o n s .

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254

REFERENCES

1 . B u e c k e r , D . n T e a h n l c a l Summary of S o i l and I n S i t u Gas S a m p l i n g S t u d y , B a s i a M a n a g e m e n t , I n c . , H e n d e r s o n , Nevada . " E c o l o g y a n d E n v i r o n m e n t , I n c . , E P A D r a f t Report , June , 1984 .

2 . K e r f o o t , H. B . and L . J . Barrows. "Soil-Gas Measurement f o r D e t e c t i o n of S u b s u r f a c e O r g a n i c C o n t a m i n a t i o n . " L o a k h e e d E n g i n e e r i n g and Management S e r v i c e s Company, I n o . , EPA D r a f t Repor t , 1985 .

3. L a B r e c q u e , D . J . , P i e r e t t , S. L . a n d A . T . B a k e r . " H y d r o c a r b o n P lume D e t e c t i o n a t S t o v e p i p e W e l l s , C a l i f o r n i a . L o a k h e e d E n g i n e e r 1 n g a n d Management S e r v i a e s , I n c . , a n d J . W . H e s s , D e s e r t R e s e a r c h I n s t i t u t e , EPA Draf t Repor t , 1 9 8 4 .

4 . W a l t h e r , E. G . , D . LaBrecque and D . D . Weber. " S t u d y of S u b s u r f a c e C o n t a m i n a t i o n w i t h G e o p h y s i c a l Moni t o r i n g Methods a t H e n d e r s o n , Nevada." Lockheed Engineer ing and Management S e r v i c e s Company, I n c . , and R . B. Evans and J. J . van E e , E M S L - L V , E P A , P r o c e e d i n g s of t h e N a t i o n a l Conference on Management of U n c o n t r o l l e d Haza rdous Waste S i t e s , Washington, D . C . , 1 9 8 3 .

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CHAPTER 8

S U M M A R Y A N D C O N C L U S I O N S

UT I L I 2 AT I O N OF S O I L - V A P O R ME AS UREHENTS

S o i l - v a p o r measurement is a u s e f u l t o o l i n s u b s u r f a c e i n v e s t i g a t i o n s . I t 8 most popular use l a i n mapping t h e e x t e n t of ground-water and u n s a t u r a t e d zone contaminat ion r e l a t e d t o s u r f a c e s p i l l s , l e a k s f r o m s t o r a g e t a n k s , and l e a c h a t e s a n d l e a k a g e from waste d i s p o s a l s i t e s . The technique has p o t e n t i a l a p p l i c a t i o n i n most Superfund s i t e i n v e s t i g a t i o n s b e c a u s e many of t h e most f r e q u e n t l y observed contaminants a t Superfund s i t e s a r e v o l a t i l e o r g a n i c s . V o l a t i l e o r g a n i c s a r e s u c h a common componen t of g r o u n d - w a t e r c o n t a m i n a t i o n from S u p e r f u n d and i n t e r i m s t a t u s R C R A f a c i l i t i e s t h a t V O C a n a l y s i s h a s b e e n s u g g e s t e d a s a d e t e c t i o n i n d i c a t o r parameter f o ? i n t e r i m s t a t u s R C R A monitor ing.

Transport P r o c e s s e s

Organ ic l i q u i d s s p i l l e d or a p p l i e d on t h e s u r f a c e w i l l tend t o migrate downward through t h e vadose zone and w i l l l e a v e a c o n e of m a t e r i a l c o n t a m i n a t e d b y r e s i d u a l amounts of t h e o rgan ic . Many p r o p e r t i e s of b o t h t h e o r g a n i c l i q u i d and t h e s u b s u r f a c e w i l l i n f l u e n c e t h e downward migra t ion of t h e o r g a n i c a n d i t s subsequent behav io r , as d i s c u s s e d i n C h a p t e r s 2 and 3 . Once a l o w - d e n s i t y o r g a n i c l i q u i d has reached . t he water t a b l e , i t w i l l b e g i n t o c r e a t e a "mound" and t o s p r e a d . B e h a v i o r of e a c h o r g a n i c c o n t a m i n a n t w i l l be governed b y i t s i n d i v i d u a l c h a r a c t e r i s t i c s such a s d e n s i t y , water s o l u b i l i t y , and t e n d e n c y t o a d s o r b o n t o c l a y s and o r g a n i c c o n s t i t u e n t s of s o i l s . The l o w - d e n s i t y f l u i d s w i l l f l o a t o n t h e w a t e r t a b l e and c o n t i n u e t o s p r e a d ; some f r a c t i o n of t h e va r ious o r g a n i c components w i l l d i s s o l v e i n g round-wa te r and move w i t h g r o u n d - w a t e r f low a s governed b y D a r c y ' s Law. Organic l i q u i d s which a r e immiscible i n water a n d denser t han water could s i n k t h r o u g h t h e s a t u r a t e d g r o u n d - w a t e r zone i f n o t b o u n d t o s o i l as r e s i d u a l s .

The v o l a t i l e components of t h e contaminant w i l l r e l e a s e chemica l t o t h e v a p o r p h a s e , which w i l l t h e n e i t h e r m i g r a t e toward t h e soil s u r f a c e b y d i f f u s i o n or s i n k through t h e s o i l a i i * i f t h e p a r t i a l p r e s s u r e of t h e vapor is h i g h and t h e vapor fs d e n s e r t h a n a i r . T h e r a t e of m i g r a t i o n w i l l be a f u n c t i o n of t h e soil r e s i s t a n c e t o vapor f l o w , o f t h e amount which is

256

r e d i s s o l v e d i n t o t h e l i q u i d p h a s e , and of t h e amount which i s adsorbed or degraded. I n most i f n o t a l l c a s e s , t h e r a t e s of vapor m i g r a t i o n w i l l be much f a s t e r t han r a t e s of ground-water movement. For a s i t u a t i o n where t h e d i s s o l v e d components have m i g r a t e d d o w n g r a d i e n t o f t h e o r i g i n a l s p i l l l o c a t i o n , i n i t i a l s o i l v a p o r c o n c e n t r a t i o n s o f t h e o r g a n i c c o n t a m i n a n t i m m e d i a t e l y above t h e water t a b l e can be p r e d i c t e d from Henry 's Law, a s d i s c u s s e d i n Chapters 1 and 3. Chapter 1 d i s c u s s e s t h e s i m p l e s i t u a t i o n where t h e o r g a n i c vapor i s n c o n s e r v a t i v e w and i s n o t d e g r a d e d or a b s o r b e d , where t h e vadose ( u n s a t u r a t e d ) zone i s homogeneous i n composi t ion, and where t h e r a t e of vapor l o s s f r o m t h e s u r f a c e i s s m a l l c o m p a r e d t o t h e a q u e o u s c o n c e n t r a t i o n . An e x a m p l e m i g h t be a c h l o r i n a t e d o r g a n i c s o l v e n t i n a homogeneous sand. I n t h i s c a s e t h e o r y p r e d i c t s a l i n e a r d e c r e a s e f r o m t h e i n i t i a l H e n r y ' s Law v a p o r c o n c e n t r a t i o n j u s t a b o v e t h e w a t e r t a b l e t o n e a r z e r o c o n c e n t r a t i o n a t t h e s u r f a c e . A s d i s c u s s e d i n Chapter 1 , f i e l d d a t a e x i s t which confirm t h i s b e h a v i o r i n c e r t a i n s i t u a t i o n s . C h a p t e r 3 p r e s e n t s a s o l u t i o n of t h e s l i g h t l y more complicated s i t u a t i o n w h e r e t h e o r g a n i c v a p o r u n d e r g o e s f i r s t - o r d e r d e g r a d a t i o n or a d s o r p t i o n . These two i d e a l i z e d s i t u a t i o n s a r e p r o b a b l y uncommon i n n a t u r e s i n c e t h e s u b s u r f a c e v e r t i c a l c r o s s - s e c t i o n i s r a r e l y homogeneous. I n g e n e r a l , t h e l e a s t permeable l aye r of t h e v e r t i c a l s e c t i o n w i l l c o n t r o l t h e r a t e o f v e r t i c a l m i g r a t i o n . T h e v e r t i c a l p r o f i l e s o f g a s p e r m e a b i l i t y , m o i s t u r e c o n t e n t , a n d s o i l p r o p e r t i e s w i l l u s u a l l y b e h a r d t o e s t i m a t e a t a p a r t i c u l a r s i t e ; t h u s , d e t e r m i n a t i o n o f t h e r e l a t i o n s h i p be tween t h e v a p o r s o u r c e ( r e s i d u a l a m o u n t s i n s o i l a n d c o n c e n t r a t i o n s d i s s o l v e d i n g round-water ) and t h e r e s u l t i n g vapor c o n c e n t r a t i o n p r o f i l e s w i l l g e n e r a l l y not be p o s s i b l e .

The f a c t t h a t a mathematical expres s ion cannot u s u a l l y be w r i t t e n t o r e l a t e s o l l - g a s c o n c e n t r a t i o n s t o g r o u n d - w a t e r c o n c e n t r a t i o n s o f v o l a t i l e o r g a n i c s d o e s n o t o b v i a t e t h e u s e f u l n e s s of s o i l - g a s surveys . De tec t ion of v o l a t i l e o r g a n i c s i n s o i l v a p o r s i n d i c a t e s t h a t t h e r e i s c l e a r l y a source of t h e o r g a n i c s somewhere i n t h e s u b s u r f a c e , and i n c r e a s i n g s o i l - g a s c o n c e n t r a t i o n s w i l l u s u a l l y i n d i c a t e i n c r e a s i n g amounts of a s u b s t a n c e . M a p p i n g o f s o l l - g a s c o n c e n t r a t i o n s m e a s u r e d a t un i fo rm d e p t h , can b e u s e f u l i n d e f i n i n g t h e l a t e r a l ex ten t o f s u b s u r f ace contaminat ion .

S o i l - G a s Surveys

F i g u r e 8 . 1 i s a f l o w c h a r t o f t h e p l a n n i n g a n d execu t ion o f a s o i l - g a s s u r v e y . P r e l i m i n a r y s a m p l i n g is performed t o d e t e r m i n e v e r t i c a l p r o f i l e s o f s u b s u r f a c e o r g a n i c v a p o r c o n c e n t r a t i o n s a t s e v e r a l l o c a t i o n s w i t h i n t h e s i t e t o be s u r v e y e d . A t r a c e r gas m u s t be c h o s e n ; s e l e c t i o n o f t r a c e r g a s e s f o r t h e s u r v e y 1 s a i d e d w h e n p r i o r i n f o r m a t i o n i s

25 7

I Preliminary sampling: vertical profiles I

Selection of tracer gases

Sampling on a grid at uniform depth'

1 Sample analysis I

I Data analysis I

Figure 8.1. Flowchart of roil-gar rurvcyr.

258

a v a i l a b l e a b o u t t h e t y p e s and c o n c e n t r a t i o n s o f v o l a t i l e o r g a n i c s f o u n d i n g r o u n d - w a t e r . H a l o g e n a t e d o r g a n i c s a r e g e n e r a l l y p r e f e r r e d a s t r a c e r s b e c a u s e t h e y t e n d t o be n ~ ~ n s e r ~ a t i ~ e w and r e s i s t a n t t o d e g r a d a t i o n ; measu remen t s of t o t a l h y d r o c a r b o n c o n c e n t r a t i o n s may a l s o g i v e good r e s u l t s . Based on t h e p r e l i m i n a r y v e r t i c a l p r o f i l e s , a s a m p l i n g d e p t h is chosen which a p p e a r s l i k e l y t o provide gas c o n c e n t r a t i o n s l a r g e e n o u g h t o b e r e a d i l y q u a n t i f i e d b y a v a i l a b l e a n a l y t i c a l t e c h n i q u e a . S o i l - g a s s a m p l e s a r e t h e n c o l l e c t e d o v e r t h e s u r v e y a r e a on a p r e d e t e r m i n e d g r i d a t t h e u n i f o r m s a m p l i n g d e p t h . The s a m p l e a a r e analyzed o n s i t e o r a r e t r a n s p o r t e d t o a l a b o r a t o r y f o r a n a l y s i s . Data a n a l y s i s c o n s i s t s of p l o t t i n g t h e . v a l u e s o n a map o f t h e s u r v e y a r e a a n d d r a w i n g i s o c o n c e n t r a t i o n l i n e s e i t h e r b y h a n d o r w i t h a c o m p u t e r a l g o r i t h m . T h e f i n a l o b j e c t i v e of t h e s o i l - g a s su rvey w i l l be t h e s i t i n g o f m o n i t o r i n g w e l l s t o o b t a i n r e p r e s e n t a t i v e m e a s u r e m e n t s o f g r o u n d - w a t e r c o n c e n t r a t i o n s o f t h e c o n t a m i n a n t s or t o o b t a i n c o r e s a m p l e s t o d e t e r m i n e t h e c o n c e n t r a t i o n s of t h e contaminants i n t h e S o i l s .

Sampling Devices

F i g u r e 8 . 2 is a s c h e m a t i c o f t h e s a m p l i n g and a n a l y s i s process . S o i l vapor samples a r e o b t a i n e d w i t h any of s e v e r a l methods . The a v a i l a b l e methods inc lude headspace measurements, g r o u n d probes, f l u x chamber measurements, and p a s s i v e s a m p l i n g . While any of t h e s e t e c h n i q u e s may be used t o d e t e c t subsu r face hydrocarbon con tamina t ion , they a r e not e q u i v a l e n t . The g r o u n d probe and h e a d s p a c e measurement techniques measure a 30 f l -gas c o n c e n t r a t i o n , t h e f l u x chamber t e c h n i q u e m e a s u r e s an e m i s s i o n r a t e , and t h e p a s s i v e sampling technique measures some f u n c t i o n of an a v e r a g e s o i l - g a s c o n c e n t r a t i o n . The t e c h n i q u e c h o s e n u i l l d e p e n d o n s t u d y o b j e c t i v e s , on t h e m a g n i t u d e o f s o i l hydroca rbon v a p o r c o n c e n t r a t i o n s , and o n t h e s e n s i t i v i t y o f a v a i l a b l e a n a l y t i c a l i n s t r u m e n t a t i o n . The f l u x chamber is g e n e r a l l y a p p r o p r i a t e for a p p l i c a t i o n s where a measure of human e x p o s u r e 13 t o be d e t e r m i n e d and where s o i l - g a s c o n c e n t r a t i o n s a r e r e l a t i v e l y l a r g e b e c a u s e t h e i n t r o d u c t i o n o f s w e e p a i r e f f e c t i v e r y d i l u t e s t h e o r g a n i c vapor C o n c e n t r a t i o n s . The p a s s i v e s a m p l i n g t e c h n i q u e s s e r v e t o i n t e g r a t e s o i l - g a s c o n c e n t r a t i o n s o v e r some p e r i o d o f t i m e a n d c o u l d be o f use where d e t e c t i o n of v e r y low c o n c e n t r a t i o n s is n e c e s s a r y , G r o u n d p r o b e s a r e p r o b a b l y t h e m o s t w i d e l y u s e d t e c h n i q u e because of speed and c o s t , Headapace measurements can be used i n p r e l i m i n a r y s u r v e y s t o m o n i t o r c o n c e n t r a t i o n s i n monitor ing w e l l s , s t o r m s e w e r s , u t i l i t y v a u l t s , o r o t h e r s u b s u r f a c e s t r u c t u r e s , a n d a s a f i r s t s t e p i n p l a n n i n g more e x t e n s i v e i n v e s t i g a t i o n s . The t e c h n i q u e can a l s o be u s e d t o m e a s u r e h e a d s p a c e c o n c e n t r a t i o n s o f o r g a n i c v a p o r s i n c o n t a i n e r s h o l d i n g soil c o r e s a m p l e s : t h i s a p p r o a c h h a s b e e n u s e d t o

2 5 9

SAMPLING QEVICE

SAMPLE COLLECTION I

I SAMPLE ANALYSIS I

Figure 8.2. Flatchart of 80iI-ga8 mearurementr.

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p r o v i d e v e r t i c a l p r o f i l e s o f r e l a t i v e o r g a n i c v a p o r c o n c e n t r a t i o n s . Sample C o l l e c t i o n

A c c u r a t e d e t e r m i n a t i o n o f t h e c o n c e n t r a t i o n and composi t ion of o r g a n i c compounds i n s o i l g a s u s u a l l y r e q u i r e s t h e c o l l e c t i o n o f s a m p l e s w h i c h a r e subsequen t ly analyzed i n a l a b o r a t o r y where c o n d i t i o n s a r e s u f f i c i e n t l y s t a b l e t o p e r m i t G C a n a l y s i s . A n a l y s i s may t a k e p l a c e i n a m o b i l e f i e l d l a b o r a t o r y or i n a s o p h i s t i c a t e d modern a n a l y t i c a l l a b o r a t o r y a t c o n s i d e r a b l e d i s t a n c e f rom t h e s i t e . I n e i t h e r c a s e , a r e p r e s e n t a t i v e s a m p l e m u s t be c o l l e c t e ? , and i t s i n t e g r i t y m u s t be m a i n t a i n e d u n t i l i t can be a n a l y z e d . The s a m p l i n g t e c h n i q u e m u s t be c o m p a t i b l e w i t h t h e a n a l y t i c a l m e t h o d . R e l a t i v e l y i n s e n s i t i v e a n a l y t i c a l methods r e q u i r e l a r g e samples. Long s a m p l e t r a n s p o r t d i s t a n c e s r e q u i r e r u g g e d s a m p l e c o n t a i n e r s . Sample c o l l e c t l o n methods f o r V O C s i n gases can be d i v i d e d i n t o two c l a s s e s :

o a d s o r b e n t methods where t h e g a s 1 3 passed t h r o u g h a s o l i d a d s o r b e n t w h i c h r e m o v e s t h e V O C s f r o m t h e i n o r g a n i c gas m a t r i x ; and

o w h o l e - a i r m e t h o d s i n w h i c h t h e e n t i r e s a m p l e i s p l a c e d i n a c o n t a i n e r a n d t r a n s p o r t e d t o t h e l abor a t o r y .

A d s o r b e n t m a t e r i a l s m o s t o f t e n u s e d f o r V O C s a r e a c t i v a t e d c h a r c o a l and p o r o u s po lymers s u c h a s Tenax. O the r a d s o r b e n t s which have been used a r e m o l e c u l a r s i e v e s , s i l i c a g e l , and a c t i v a t e d alumina. T h e adsorbent method i s a t t r a c t i v e b e c a u s e i t c o n c e n t r a t e s t h e gas components of i n t e r e s t and removes many of t h e components known t o add t o t h e i n s t a b i l i t y of t h e s a m p l e and t o i n t e r f e r e w i t h t h e sample a n a l y s i s . The adsorbents a r e small and can be e a s i l y t r a n s p o r t e d t o and f r o m t h e f i e l d . The l i m i t a t i o n o f t h e a d s o r b e n t m e t h o d s a r e p o s s i b l e i r r e v e r s i b l e a d s o r p t i o n , i n c o m p l e t e a d s o r p t i o n , and a r t i f a c t f o r m a t i o n . I r r e v e r s i b l e a d s o r p t i o n o c c u r s when adsorbed components cannot be comple te ly d e s o r b e d . I n c o m p l e t e a d s o r p t i o n 13 a130 c a l l e d breakthrough and r e s u l t s i n t h e l o s s of t h e more v o l a t i l e sample components. A r t i f a c t f o r m a t i o n can o c c u r d u r i n g t h e r m a l d e s o r p t i o n o r from r e a c t i o n o f t h e sample w i t h t h e a d s o r b e n t m a t e r i a l . A l l t h r e e of t h e s e p o s s i b l e p r o b l e m s m u s t be f u l l y i n v e s t i g a t e d d u r i n g s ample method Val 1 dat 1 o n .

C o l l e c t i o n o f w h o l e - a i r s a m p l e s i s p r o b a b l y t h e m o s t widely used technique i n s o i l - g a s i n v e s t i g a t i o n s . I n s e l e c t i n g an a p p r o p r i a t e c o n t a i n e r , t h e i n v e s t i g a t o r s h o u l d c o n s i d e r t h e l e n g t h of t ime which t h e samples m u s t b e h e l d i n t h e c o n t a i n e r ,

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t h e need for r u g g e d n e s s i f t h e s a m p l e s a r e t o be sh ipped l o n g d i s t a n c e s , and t h e a b i l i t y t o c l e a n t h e o o n t a i n e r b e t w e e n s a m p l e s . T h r e e d i f f e r e n t Classes of conta iner ' s have been used i n such i n v e s t i g a t i o n s :

o p l a s t i c bags made of Tedlar o r Te f lon ;

o p a s s i v a t e d s t a i n l e s s - s t e e l c a n n i s t e r s and s y r i n g e s ; and

o g l a s s s y r i n g e s .

T e d l a r and T e f l o n bags a r e c o n v e n i e n t and i n e x p e n s i v e . However, p h o t o c h e m i c a l r e a c t i o n s can d e g r a d e s a m p l e s i f t h e bags a r e exposed t o l i g h t ; sample leakage du r ing t r a n s p o r t can occur ; and g a s s p e c i e s can pe rmea te i n t o t h e bags and o u t of t h e bags d u r i n g t r a n s p o r t and s t o r a g e . Consequent ly , p l a s t i c bags a r e n o t recommended for s o i l - g a s s u r v e y s u n l e s s s t o r a g e t imes a r e s h o r t , and concen t r a t ions a r e h i g h .

P a s s i v a t e d s t a i n l e s s - a t e e l c a n n i s t e r s a r e s t u r d y and impervious t o l i g h t , and t h e y can be c l e a n e d e a s i l y , Samples can be h e l d for p e r i o d s u p t o s e v e r a l days i n p rope r ly prepared c a n n i s t e r s . S t a i n l e s s - s t e e l s y r i n g e s a r e o n t h e marke t which s h o u l d have t h e same a d v a n t a g e s a s t h e c a n n i s t e r s . However, s u c h d e v i c e s a r e e x p e n s i v e and r e p r e s e n t a c o n s i d e r a b l e investment .

C l a s s c o n t a i n e r s such aa s y r i n g e s have a l s o been used t o c o l l e c t gas samples. However, g l a s s c o n t a i n e r s u s u a l l y r e q u i r e T e f l o n v a l v e s and s e a l s which can be a sou rce of contaminat ion. Because g l a s s t r a n s m i t s l i g h t , t h e y s h o u l d be k e p t o u t of d i r e c t s u n l i g h t t o avoid photochemical r e a c t i o n s i n t h e aamplee, Because of t h e i r f r a g i l i t y , such v e s s e l s a r e m o s t a p p r o p r i a t e f o r o n - s i t e u s e . G l a s s s y r i n g e s a r e t h e moat popular dev ices f o r c o l l e c t i o n of s o i l - g a s samples when o n - s i t e a n a l y s i s i s planned . Sample Analys is

A n a l y t i c a l methods t y p i c a l l y u s e d i n s o i l - g a s s u r v e y s tnalude p o r t a b l e V O C a n a l y z e r s , f i e l d g a s c h r o m a t o g r a p h s , and l a b o r a t o r y - b a s e d G C s . The method chosen t o a n a l y z e s o i l - g a s s a m p l e s d e p e n d s o n t h e p o l l u t a n t b e i n g m o n i t o r e d , t h e ~ o n c e ~ i t ~ r a t i o n s of r e s p e c t i v e p o l l u t a n t s p e c i e s , and t h e i n f o r m a t i o n t o be o b t a i n e d f r o m t h e a n a l y t i c a l r e s u l t s . S x p e c t e d c o n c e n t r a t i o n s f o r o r g a n i c s p e c i e s i n s o i l g a s can r ange from t h e p p t v l e v e l (be low m o s t a n a l y t i c a l d e t e c t i o n ' I a n l t , ~ ) i n t l a c k g r o u n d m e a s u r e m e n t s t o s e v e r a l pe r c e n t b y vo:~.iae i n measurements made d i r e c t l y o v e r a l i q u i d l e n s of a r t p h l y v o l a t i l e o r g a n i c f l u i d s u c h a s g a s o l i n e . The

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c o n c e n t r a t i o n l e v e l a c t u a l l y m e a s u r e d w i l l d e p e n d on t h e sampling method u s e d and on t h e degree of d i l u t i o n ( a s i n f l u x chambers) o r c o n c e n t r a t i o n (€18 i n charcoa l or Tenax adso rp t ion d e v i c e s ) . More s e n s i t i v e m e t h o d s may b e n e e d e d a t p l u m e f r i n g e s t h a n a t l o c a t i o n 8 n e a r t h e s o u r c e . Some o f t h e c o n s i d e r a t i o n s invo lved i n s e l e c t i n g t h e a p p r o p r i a t e a n a l y t i c a l t echnique(8) a r e

o t h e need f o r d e t a i l e d chemical s p e c i a t i o n ;

o t h e n e e d f o r r e l a t i v e values or a b s o l u t e

o t h e need f o r o n - s i t e ana lyses ; c o n c e n t r a t i ons ;

o t h e methods of sample c o l l e c t i o n

P o r t a b l e V O C a n a l y z e r s can be use fu l a t s i t e s where t o t a l hydroca rbon c o n c e n t r a t i o n s a r e g r e a t e r t h a n 1 p p m v . Such c o n c e n t r a t i o n s a r e n o t uncommon a t l e a k i n g g a s o l i n e s t o r a g e tanks and g a s o l i n e s p i l l s i t e s . P o r t a b l e V O C a n a l y z e r s can be p a r t i c u l a r l y c o n v e n i e n t when used i n c o n j u n c t i o n w i t h dr iven g r o u n d p r o b e s t o s a m p l e d i r e c t l y f r o m t h e p r o b e s . T h e a d v a n t a g e s of p o r t a b l e V O C a n a l y z e r s a r e t h e e l i m i n a t i o n o f sample c o l l e c t i o n and t r a n s p o r t ; t h e i r major d i s a d v a n t a g e s a r e c a l i b r a t i o n p r o b l e m s , t h e need f o r l a r g e s a m p l e volumes, and lack of s e n s i t i v i t y .

G a s chromatography i s used where c o n c e n t r a t i o n s l e s s than 1 ppmv m u s t be measured o r where chemical s p e c i a t i o n i s needed. D e t e c t i o n m e t h o d s u s e d f o r G C a n a l y s i s of s o i l - g a s samples 1 ncl ude :

o f l a m e i o n i z a t i o n d e t e c t o r ( F I D ) f o r v o l a t i l e hydrocarbons ;

o p h o t o i o n i z a t l o n d e t e c t o r ( P I D ) f o r a r o m a t i c hydrocarbons and s u l f u r spec ie s :

o e l e c t r o n c a p t u r e d e t e c t o r ( E C D ) f o r h a l o g e n a t e d hydrocarbons ;

o H a l l e l e c t r o c o n d u c t l v i t y d e t e c t o r ( H E C D ) f o r d e t e c t i o n of ha logenated s p e c i e s , n i t r o g e n - c o n t a i n i n g o r g a n i c s , or s u l f u r - c o n t a i n i n g s p e c i e s ;

o f l a m e p h o t o m e t r i c d e t e c t o r ( F P D ) f o r s u l f u r and phosphorous compounds.

F i e l d g a s c h r o m a t o g r a p h s a r e used where s a m p l e s can be c o l l e c t e d and ana lyzed on s i t e . The s imples t f i e l d i n s t r u m e n t s a r e p o r t a b l e VOC a n a l y z e r s w i t h chromatographic o p t i o n s s u c h a s

2G3

t h e Pho tovac e q u i p p e d w i t h a P I D a n d t h e Century O V A e q u i p p e d w i t h a F I D . The u s e f u l d e t e o t i o n l imits f o r s u c h f n s t r u m e n t s a r e u s u a l l y o n t h e o r d e r o f 1 p p m v . A s t e p a b o v e t h e " p o r t a b l e " G C s a r e t h e n i l e l d m G C s r s m a l l , s t u r d y G C s w i t h t e m p e r a t u r e - c o n t r o l l e d o v e n s and a v a r i e t y of 1 n J e o t o r s and d e t e c t o r s . B e s t r e s u l t s a r e o b t a i n e d w i t h i n s t rumen t s w i t h h e a t e d - g a s sa 'mpling v a l v e s f o r i n j e c t i o n of t h e gas samples. The d e t e c t o r s most commonly found a r e t h e F I D , P I D , and t h e E C D . T h e E C D i s q u i t e s e n s i t i v e , w i t h d e t e c t i o n l i m i t s f o r halogenated compounds i n t h e ppbv range .

S o i l - g a s s a m p l e s w i l l need t o be s e n t t o an o f f - s i t e l a b o r a t o r y when p o s i t i v e ohemioa l s p e c i e s i d e n t i f i c a t i o n i s r e q u i r e d , when v e r y low d e t e a t i o n l imits a r e r e q u i r e d , when d i f f i ' c u l t s a m p l e m a t r i c e s a r e e n c o u n t e r e d , o r w h e n e n v i r o n m e n t a l c o n d i t i o n e p r o h i b i t o n - s i t e a n a l y s i s. Combinations of d e t e c t o r t y p e s i n m u l t i - d e t e c t o r s y s t e m s a r e u s e f u l f o r s p e c i f i c t y p e s of a n a l y s e s . Mass spec t rog raphs can be used where p o s i t i v e i d e n t i f i c a t i o n of c h e m i c a l s p e c i e s i s o t h e r w i s e d i f f i c u l t . Modern a n a l y t i c a l l a b o r a t o r y method8 a r e r e a d i l y a v a i l a b l e w i t h t h e c a p a b i l i t y t o s e p a r a t e a n d q u a n t i t a t e V O C s i n s o i l gas a t concen t r a t ions l e s s than 1 p p b v a n d t o i d e n t i f y g a s s p e c i e s w i t h h i g h c o n f i d e n c e . T h e i n v e s t i g a t o r ' s t a s k is t o o h o o s e a l e v e l of s o p h i s t i c a t i o n which accomplishes t h e survey o b J e c t i v e s a t a r easonab le c o s t .

Q u a l i t y Assurance and Q u a l i t y Cont ro l

The d e s i r e d product of most s o i l - g a s surveys i s a contour map o f s o i l - g a s c o n c e n t r a t i o n s , i n e i t h e r t w o o r t h r e e d i m e n s i o n s . The i n v e s t i g a t o r u s u a l l y i n t e n d s t o u s e t h e contoured s o i l - g a s measurements a s a s u r r o g a t e f o r o t h e r more e x p e n s i v e measurements s u c h a s ground-water or s o i l r e s i d u a l c o n c e n t r a t i o n e . The i m p o r t a n t f a c t o r s a r e t h e l o c a t i o n a n d s h a p e o f t h e c o n t o u r s and t h e i r r e l a t i v e magnitudes, not t h e i r a b s o l u t e concen t r a t ions . However, i nd iv idua l measurements m u s t b e comparab le t o one ano the r i n o rde r t o draw t h e con tour s . To i n s u r e c o m p a r a b i l i t y , a s o i l - g a s s u r v e y , l i k e any o t h e r e n v i r o n m e n t a l m e a s u r e m e n t s p r o g r a m , n e e d s a q u a l i t y a s s u r a n c e / q u a l i t y c o n t r o l p r o g r a m , E P A p o l i c y r e q u i r e s a w r i t t e n Q A / Q C p l a n f o r any environmental measurements program. T h e Q A / Q C p l a n s h o u l d a d d r e s s t h e s a m p l i n g m e t h o d , t h e a n a l y t i c a l method, and t h e d a t a r educ t ion and r e p o r t i n g s t e p s . D i s c u s s i o n o f a n a l y t i c a l Q A / Q C s h o u l d i n c l u d e m e t h o d c a l i b r a t i o n a n d p r i m a r y a n d f i e l d s t a n d a r d s . D u p l i c a t e ana lyses and samples a r e necessa ry t o determine t h e v a r i a b i l i t y of t h e s a m p l i n g and a n a l y t i c a l t echniques . Blank ana lyses a r e r equ i r ed t o determine t h e l e v e l of c o n t a m i n a t i o n a t t r i b u t a b l e t o t h e s a m p l i n g m e t h o d a n d t o t h e a n a l y t i c a l method. To d e t e r m i n e t h e a b s o l u t e a c c u r a c y and l a b - t o - l a b v a r i a b i l i t y ,

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a u d i t s a m p l e a n a l y s i s and i n t e r l a b o r a t o r y compar ison s t u d i e s a r e r e q u i r e d .

Data Analys is

A n o t h e r u s e f u l s t e p i n a s s u r i n g t h a t measurements a r e oomparable is a oomponents of va r i ance a n a l y s i s , a s t a t i s t i c a l p r o c e d u r e w h i c h d e v e l o p s a m o d e l t o a d s e s s t h e e r r o r i n r e p o r t e d c o n c e n t r a t i o n s a t t r i b u t a b l e t o e a c h s t e p i n t h e sampling and a n a l y s i s procesd.

D a t a a n a l y s i s f o r s o i l - g a s s u r v e y s u s u a l l y i n v o l v e s i n t e r p o l a t i o n b e t w e e n s a m p l e p o i n t s a n d t h e d r a w i n g o f c o n t o u r s . B e c a u s e s o l l - g a s m e a s u r e m e n t s r e p r e s e n t c o n c e n t r a t i o n s of c e r t a i n gas s p e c i e s nea r t h e s u r f a c e , t h e y d o n o t n e c e s s a r i l y r e p r e s e n t t h e c o n c e n t r a t i o n s of t h e compounds i n an under ly ing a r e a of s o i l c o n t a m i n a t i o n or of g round-wa te r plume ( o r a c o n s i s t e n t or wmonotonen t r a n s f o r m a t i o n of t hose c o n c e n t r a t i o n s ) . U n d e r t h e b e s t of c o n d i t i o n s , s o i l - g a s measurements r e p r e s e n t a monotone t r a n s f o r m a t i o n d i s t o r t e d by measurement e r r o r s o f t h e c o n c e n t r a t i o n s of t h e compounds i n s o i l or ground-water below t h e poin t of measurement.

Many m e t h o d s o f i n t e r p o l a t i o n be tween d a t a p o i n t s a r e a v a i l a b l e t o t h e i n v e s t i g a t o r , such a s l i n e a r , i n v e r s e s q u a r e d d i s t a n c e , s p l i n e s , a n d k r i g l n g . Mos t s u c h m e t h o d s a r e d e t e r m i n i s t l c and do n o t r e l y o n a p r o b a b i l i t y model w h i l e k r i g i n g d o e s n e e d s u c h a m o d e l . T h e v a r i o u s common i n t e r p o l a t i o n methods t y p i o a l l y g ive s i m i l a r r e s u l t s c o n c e r n i n g t h e g e n e r a l p a t t e r n of S O i l - g a S c o n t o u r s (wh ich i s the f i n a l o b j e c t i v e of a s u r v e y ) . K r i g i n g has t h e a d v a n t a g e t h a t i t p r o v i d e s an e s t i m a t e d s t a n d a r d e r r o r f o r e a c h i n t e r p o l a t i o n . However, t h e e s t i m a t e d s t a n d a r d e r r o r i n k r i g i n g i s h i g h l y d e p e n d e n t on t h e p r o b a b i l i t y model which m u s t be deve loped aga in f o r e a c h new s u r v e y b e c a u s e e a c h s i t e i s u n i q u e . Good e s t i m a t i o n _ of a model r e q u i r e s more and b e t t e r d a t a than a r e u s u a l l y a v a i l a b l e from a S O i l - g a S survey . For t h i s r e a s o n , u se o f a s i m p l e s p l i n e or inverse-square i n t e r p o l a t i o n procedure i s probably more e f f i c i e n t . I f an e s t i m a t e of t h e i n t e r p o l a t i o n e r r o r i s d e s i r e d , p r o c e d u r e s o t h e r t h a n k r i g i n g c a n be employed.

Ca re m u s t be used i n employing computer i n t e r p o l a t i o n and contour ing p a c k a g e s . Such packages a r e i l l - e q u i p p e d t o d e a l w i t h s i t u a t i o n s where a d j a c e n t d a t a p o i n t s d i f f e r by s e v e r a l o r d e r s of magnitude. Such s i t u a t i o n s a r e n o t uncommon i n s o i l g a s d a t a b u t do not n e c e s s a r i l y r e p r e s e n t cor responding changes i n t h e v a r i a b l e s of u l t i m a t e c o n c e r n ( s o i l o r g r o u n d - w a t e r c o n c e n t r a t i o n s ) . Because such l a r g e i s o l a t e d va lues a r e l i k e l y t o r e p r e s e n t anomalies a s enhanced g a s - f l o w p a t h s , i t w o u l d be

265

b e t t e r t o s i m p l y f l a g t h e s e v a l u e s r a t h e r t h a n t o i n c o r p o r a t e them i n t o t h e i n t e r p o l a t i o n p rocess .

Case S t u d i e s

T h e two c a s e s t u d i e s presented h e r e i l l u s t r a t e t h e uae of s o i l - g a s measurements a8 a means of d e l i n e a t i n g g r o u n d - w a t e r c o n t a m i n a n t plume8. I n t h e f i r s t s t u d y , v a p o r s f rom l e a k e d g a s o l i n e ( d i s s o l v e d i n g round-wa te r and p o s s i b l y l y i n g on t o p of t h e w a t e r t a b l e ) moved upward t h r o u g h approximately 40 f e e t of a l l u v i a l o v e r b u r d e n ( l a r g e l y s a n d s a n d g r a v e l s ) i n c o n c e n t r a t i o n s l a r g e enough t o be measured a t depths of about 5 f e e t . By s a m p l i n g soil g a s o v e r t h e e n t i r e s t u d y a r e a w i t h s t e e l p robe8 and b y a n a l y z i n g t h e samples i n t h e f i e l d w i t h a t r a n s p o r t a b l e gas c h r o m a t o g r a p h , t h e l a t e r a l e x t e n t of t h e plume c o u l d be mapped. Not e v e r y vapor component appeared t o be a good t r a c e r of ground-water c o n t a m i n a t i o n . T h e c h o i c e of t r a c e r i s t h e r e f o r e q u i t e important .

I n t h e s e c o n d s t u d y , s o i l - g a s c o n c e n t r a t i o n s o f c h l o r o f o r m d e f i n e d a p lume o f c h l o r o f o r m i n g r o u n d - w a t e r which was d o w n g r a d i e n t of a l a r g e i n d u s t r i a l p l u m e . The most i m p o r t a n t r e s u l t of t h e s e c o n d c a s e s t u d y l a p r o b a b l y t h e o b s e r v e d l i n e v r e l a t i o n s h i p . b e t w e e n d e p t h a n d s o i l - g a s c o n c e n t r a t i o n s of c h l o r o f o r m and c a r b o n t e t r a c h l o r i d e w h i c h w o u l d be e x p e c t e d i f s i m p l e d i f f u s i o n p r o c e s s e s were t h e primary mechaniam governing t h e v e r t i c a l migra t ion of t h e gases . T h i s c a s e s t u d y l e n d s hope t h a t i t may be p o s s i b l e t o d e r i v e a q u a n t i t a t i v e r e l a t i o n s h i p be tween o r g a n i c c o n c e n t r a t i o n s i n g r o u n d - w a t e r and t h o s e i n s o i l g a s , a t l e a s t f o r some gas s p e c i e s and a t some l o c a t i o n s .

B o t h c a s e s t u d i e s i n v o l v e d t h e use o f o t h e r methods t o s u p p o r t t h e d a t a t h a t were ob ta ined from t h e s o i l - g a s me thods . Geophys ic s and hydrogeologlc in fo rma t ion from e x i s t i n g w e l l s i n t h e v i c i n i t y of t h e s o i l - g a s su rveys were u s e f u l i n t h e d e s i g n o f t h e s u r v e y and t h e i n t e r p r e t a t i o n of t h e r e s u l t s . Like any s t e p i n a g r o u n d - w a t e r s t u d y s o i l - g a s m e a s u r e m e n t s b y t h e m s e l v e s a r e a u s e f u l b u t n o t e x c l u s i v e means f o r d e f i n i n g t h e e x t e n t of ground-water contaminat ion from o rgan ic s .

26 6

FIGURES

Number

1 . 1

1 . 2

1 * 3

1.4

1 . 5

1 . 6

2 . 1

2 . 2

2 . 3

2.4

2 . 5

2.6

Rela t ionsh ip between number of v o l a t i l e compounds and o rgan ic p r i o r i t y P o l l u t a n t s i n ground-water i n t he v i c i n i t y o f hazardous waste d i s p 0 8 a l s i t e s ( N - 1 1 3 8 i t e s ) e e 0 . . Typical behavior i n porous s o i l fo l lowing a d u d d e n , h i g h volume e p i l l . . . . . . . . . . . . . . . . . Behavior of product a f t e r s p i l l has s t a b i l i z e d . . . Organic gas c o n c e n t r a t i o n d i s t r i b u t i o n in t h e vadose zone expectted from d i f f u s i o n . . . . . . . . . Chloroform and carbon t e t r a c h l o r f d e depth d i s t r i b u t i o n . . . . . . . . . . . . . . . . . . . . Soil-gas v e r t i c a l p r o f i l e a t a s i t e i n n o r t h e r n C a l i f o r n i a . . . . . . . . . . . . . . . . . . . . . P l o t of l o g s o l u b i l i t y v s l o g vapor p r e s s u r e i l l u s t r a t i n g t h e tendency f o r compounds i n a homologous s e r i e s t o l i e on a 4 5 O d iagona l of constant Henry's law c o n s t a n t . . . . . . . . . . . .

Page

2

5

6

9

10

1 3

46

R e l a t i o n s h i p between t h e water s o l u b i l i t y o f a compound ( m g / l i t e r ) and i t s p a r t i t i o n c o e f f i c i e n t between s o i l organic C and soil s o l u t i o n ( K O , ) . . . . . . . . . . 48 Diagram s h o w i n g an economical and s a f e way t o c o n t a i n

Thickness of c e n t e r of o i l l e n s veraus time where k

ch lo r ina t ed hydrocarbons (TCE) compounds . . . . . . values a r e p e r m e a b i l i t i e s . . . . . . . . . . . . . . Textural t r i a n g l e , showlng t h e percentages o f c l a y , s i l t , and sand i n t h e b a s i c s o i l t e x t u r a l c l a s s e s . . . . . . . . . . . . . . . . . . Poss ib le mig ra t ion o f product t o o u t c r o p followed by second c y c l e contaminat ion . . . . . . .

5 0

56

6 2

6 3

vi

2 . 7 Benzene uptake by 8011 a8 a f u n c t i o n o f t h e r e l a t i v e vapor concen t r a t ion . . . . . . . . . . . . 65

2 . 8 C r o s s - s e c t i o n a l view o f s o i l pore a r e a . . . . . . . 66

2 . 9 Comparlson of d i f f u s i o n o o e f f i c i e n t moisture curves f o r va r iou r median pore 8 i z e 8 . . . . . . . . 67

2 . 1 0 R e l a t i v e p e r m e a b i l i t y graph where Swater is t h e pe rcen t s a t u r a t i o n . . . . . . . . . . . . . . . . . 6 9

2 . 1 1 Biodegrada t ion r a t e based on oxygen r echa rge . . . 74

2 . 1 2 Hypothe t i ca l ground-water system . . . . . . . . . . 81

2 . 1 3 Diagram Showing how o i l on a water t a b l e can be t r a p p e d i n a oone of d e p r e s s i o n c r e a t e d by drawdown of a pumping w e l l . . . . . . . . . . . . . 84

3.1 O i l m i g r a t i o n p a t t e r n ( A . B ) . . . . . . . . . . . . . 91

3 . 2 Genera l ized shapes of s p r e a d i n g cones a t immobile s a t u r a t i o n ( A . B . C ) . . . . . . . . . . . . 93

3 . 3 I n f i l t r a t i o n o f kerosene i n t o a porous medium . . 9 5

3.4 O i l r e t e n t i o n c a p a c i t y as a f u n c t i o n of t ime . . . . 9 6

3 . 5 Subsur face r e d i s t r i b u t i o n of a s u r f a c e s p i l l . . . . 9 8

3.6 R e l a t i o n between t h i c k n e s s of o i l l a y e r and s p r e a d i n g t ime . . . . . . . . . . . . . . . . . . . 1 0 0

3 . 7 . S o l u b i l i t y of hydrocarbons i n water . . . . . . . . . 106

3 .8 Comparison of a c t u a l and i d e a l i z e d c o n c e n t r a t i o n depth p r o f i l e s below a waste s p i l l i n ground water . . . . . . . . . . . . . . . 108

3 . 9 Steady s t a t e vapor c o n c e n t r a t i o n p r o f i l e s between groundwater and t h e s o i l s u r f a c e . f o r a compound undergoing f i r s t o r d e r deg rada t ion . . . . . . . . . 1 1 5

4 . 1 S o i l c o r e sample s l e e v e . . . . . . . . . . . . . . . 1 3 1

4.2 Ground-probe des ign used by Russe l l and and Appleyard . . . . . . . . . . . . . . . . . . . 133

4 . 3 Ground-probe des ign used b y Negl ia and F a v r e t t o . . . . . . . . . . . . . . . . . . . . . 1 3 4

v i i

4 . 4

4 . 5

4 . 6

4 . 7

4 . 8

4 . 9

4 . 1 0

4 . 1 1

4 . 1 2

4 . 1 3

4 . 1 4

4 . 1 5

4 . 1 6

4 . 1 7

4 . 1 8

6 . 1

6.2

7 . 1

7 . 2

7 . 3

G r o u n d - p r o b e d e s i g n u s e d by T a c k k e t t . . e . m . . 136

G r o u n d - p r o b e d e s i g n u s e d b y T h o r n b u r n , e t a1 . 137

G r o u n d - p r o b e d e s i g n of L o v e l l , e t a1 . . . . . . 139

G r o u n d - p r o b e d e s i g n u s e d by Swallow a n d Oschwend 1 4 0

G r o u n d - p r o b e d e s i g n u s e d by Swallow a n d Gsahwend . . 141

G r o u n d - p r o b e d e s i g n u s e d by Wal ther , e t a 1 . e 1 4 2

G r o u n d - p r o b e d e s i g n u s e d b y L a B r e c q u e , e t a 1 . . . 1 4 3

G r o u n d - p r o b e d r i v e r a n d e x t r a c t o r u s e d by L a B r e c q u e , e t a 1 . . . . . . . . . . . 1 4 4

S a m p l i n g m a n i f o l d a n d pump u s e d b y L a B r e c q u e , e t a 1 . . . . . . . . . 1 4 5

G r o u n d - p r o b e d e s i g n u s e d by Radian C o r p o r a t i o n . . 1 4 7

G r o u n d - p r o b e d e s i g n u s e d by Crow, e t a l . . . . . 1 4 8

S u r f a c e - f l u x chamber a n d p e r i p h e r a l e q u i p m e n t . . . . . . . . . . . . . . 1 5 0

C u r i e - p o i n t wire accumulator d e v i c e . . . . . 1 5 3

B u i l d - u p a n d a t t e n u a t i o n of v o l a t i l e s from g a s o l i n e t h r o u g h a s a n d c o l u m n a n d t h r o u g h u n d i s t u r b e d wet c l a y s o i l . . . . . . . . . . . 1 5 4

H y p o t h e t i c a l d i f f u s i o n p a t t e r n a n d m e a s u r e d s u r f a c e f l u x a n o m a l y . . . . . . . . . . . . . 1 5 5

D e n s i t y c u r v e s f o r n o r m a l a n d s k e w e d d i s t r i b u t i o n . . . . . . . . . . . . . . 2 0 2

M e a n i n g l e s s COntOUPS . . . . . . . . . . 2 1 0

L o c a t i o n o f s t u d y a r e a . . . . . . . . . . . 214

C o m p a r i s o n o f t h e a s s u m e d l o c a t i o n of g a s o l i n e p l u m e from USGS we l l s a t t h e b e g i n n i n g of f i e l d w o r k (May 1 9 8 0 ) w i t h t h e p l u m e e x t e n t s h o w n b y s u b s e q u e n t L o c k e e d w e l l s . . . e . . . . . . . 2 1 5

Diagram o f Lockheed-EMSCO SOV probe t i p a n d s h a f t . . . . . . . . a ~ ~ ~ ~ . e . . . . . 2 1 7

v i i i

7 . 4 SOV probe d r i v e r and e x t r a c t o r . . . . . . . . . . 218

7 . 5 SOV sampling man i fo ld . . . . . . . . . . . . . . . . 219

7 . 6 Hap of t o t a l o r g a n i c vapor i n ppm a s benzene from SOV sampl ing , Augus t 1984, Stovepipe Wells, C a l i f o r n i a . . . . . . . . . . . . 222

7 . 7 Hap of e t h a n e l p r o p a n e from SOV sampling, August 1984 , S t o v e p i p e Wells, C a l i f o r n i a . . . . . . 223

7 . 8 Map of bu tane from SOV sampling, A u g u s t 1 9 8 4 , Stovepipe Wells, C a l i f o r n i a . . . . . . . . . . . . . 224

7 . 9 Map of pentane from SOV sampling, A u g u s t 1 9 8 4 , Stovepipe Wells, C a l i f o r n i a . . . . . . . . . . . 225

7 . 1 0

7 .11

7 . 1 2

7 . 1 3

7 . 1 4

7 . 1 5

7 . 1 6

7 . 1 7

7 . 1 8

Hap of benzene from S O V sampling, A u g u s t 1 9 8 4 , Stovepipe Wells, C a l i f o r n i a . . . . . . . . . . 226

Hap of i s o o c t a n e from SOV sampling, A u g u s t 1984 , Stovepipe Wells, C a l i f o r n i a . . . . . . 227

Summary of d r i l l i n g r e s u l t s , A u g u s t 1 9 8 4 , Stovepipe Wells, C a l i f o r n i a . . . . . . . . . . . . . 229

Levels of v o l a t i l e o r g a n i c s i n wel l SP5 a s a f u n c t i o n of d e p t h , A u g u s t 5 , 1984 , Stovepipe Wel ls , C a l i f o r n i a . . . . . . . . . . . . 230

Cross - sec t ion of i s o o c t a n e l e v e l s ( p p m ) a c r o s s t h e contaminant plume, A u g u s t 1984, Stovepipe Wel ls , C a l i f o r n i a . . . . . . . . . . . . . . . . . 231

Cross - sec t ion of benzene l e v e l s ( p p m ) a c r o s s t h e contaminant plume, A u g u s t 1984, Stovepipe Wells , C a l i f o r n i a . . . . . . . . . . . . . . . . 2 3 2

Cross - sec t ion of pen tane l e v e l s ( p p m ) a c r o s s t h e Contaminant plume, A u g u s t 1984 , Stovepipe Wells, C a l i f o r n i a . . . . . . . . . . . . . . . . 2 3 3

Cross - sec t ion of bu tane l e v e l s ( p p m ) a c r o s s t h e contaminant plume, A u g u s t 1984 , Stovepipe Wells, C a l i f o r n i a . . . . . . . . . . . . . . . . . 2 3 4

Cross - sec t ion of e t h a n e l p r o p a n e l e v e l s ( p p m ) a c r o s a t h e Contaminant plume, A u g u s t 1984 , S t o v e p i p e Wells, C a l i f o r n i a . . . . . . . . . . . . . . . . 2 3 5

ix

7 . 1 9 General l o c a t i o n map . . . . . . . . . . . . . . . 237 7 . 2 0 Hydrogeologio c r o s s - s e c t i o n w i t h t h e l o c a t i o n s

of s a m p l i n g boreholes a long t h e contaminant p l u m e . . . . . . . . . . . . . . . . . . . . . . . 238

7 . 2 1 Ground-water q u a l i t y based on t o t a l d i s s o l v e d S o l i d s e . . . 239

7 . 2 2 f s o c o n t o u r p r o J e c t i o n of benzene c o n c e n t r a t i o n s ( p p m ) i n ground-water. . . . . . . . . . . . . . . 2 4 0

7 . 2 3 Hydrogeologic c r o s s s e c t i o n of t h e t r a n s e c t . . . . . 242

7 . 2 4 Locat ions of monitor ing w e l l s a long t h e Pi t tman L a t e r a l . . . . . . . . . . . . . . . . . . . . . 243

7 . 2 5 Ground-water c o n c e n t r a t i o n s of ch loroform, benzene, and chlorobenzene . . . . . . . . . . . . . 246

7 . 2 6 Probe l o c a t i o n s i n t h e a r e a o f t h e ch loroform/carbon t e t r a c h l o r i d e . . . . . . . . . . . 2 4 7

7 . 2 7 Probe l o c a t i o n s i n t h e a r e a o f t h e benzene/ chlorobenzene contaminant plume. . . . . . . . . . . 247

7 . 2 8 Chloroform c o n c e n t r a t i o n s a t 4 - f O O t dep th a s a f u n c t i o n of d i s t a n c e a c r o s s plume. . . . . . . . . . 2 4 9

7 . 2 9 Soi l -gas chloroform c o n c e n t r a t i o n s a t 4-foot depth a s a f u n c t i o n o f ground-water chloroform c o n c e n t r a t i o n . . . . . . . . . . . . . . . . . . . 251

7 . 3 0 Chloroform and carbon t e t r a c h l o r i d e dep th d i s t r i b u t i o n . C o e f f i c i e n t of d e t e r m i n a t i o n . . . . . 254

8 . 1 Flowchart of s o i l - g a s s u r v e y s . . . . . . . . . . . . 2 5 8

8 . 2 Flowchart of s o i l - g a s measurements . . . . . . . . 260

X

TABLES

Number Page

1 . 1 Most f r e q u e n t l y r e p o r t e d s u b s t a n c e s a t 546 N P L s i t e s . . . . . . . . . . . . . . . . . . . . . 3

1 . 2 Air lwater c o n c e n t r a t i o n r a t i o s f o r some common i n d u s t r i a l s o l v e n t 8 a t 23oC. . . . . . . . . . . . 7

1 . 3 S o i l gas mon i to r ing . . . . . . . . . . . . . . . . . 1 2

1 . 4 S o i l gas mon i to r ing . . . . . . . . . . . . . . . . 1 2

1 . 5 Analy t i ca l methods f o r s o i l gas sampling . . . . . 1 2

2 . 1 Site s p e c i f i c parameter c o n s i d e r a t i o n s . . . . . . 2 0

2 . 2 Phys ica l and chemica l p r o p e r t i e s of va r ious o r g a n i c compounds. . . . . . . . . . . . . . . . 21

2 . 3 Chlo r ina t ed hydrocarbons . . . . . . . . . . 49

2 . 4 L i q u i d group c l a s s i f i c a t i o n of v a r i o u s o r g a n i c compounds. . . . . . . . . . . . . . . . . . . . . . 5 2

2 . 5 D i e l e c t r i c c o n s t a n t s , d e n s i t i e s and water s o l u b i l i t i e s of v a r i o u s ha logenated and nonhalogenated s o l v e n t b . . . . . . . . . . . . . 57

2 . 6 I n t r i n s i c p e r m e a b i l i t y of s o i l s permeated by water and o r g a n i c l i q u i d s . . . . . . . . . . . . 5 8

2 . 7 Summary o f organism growth i n v a r i o u s s u b s t r a t e s . . . . . . . . . . . . . . . . . . . . . 7 2

2 . 8 F a t e o f o r g a n i c Compounds a p p l i e d t o a sandy s o i l . . . . . . . . . . . . . . . . . . . . . . . . 73

2 . 9 Average u t i l i z a t i o n of s u b s t r a t e s i n a e r o b i c acetate-grown b i o f i l m column a f t e r a c c l i m a t i o n . . . 7 6

2 . 1 0 Average u t i l i z a t i o n of s u b s t r a t e s i n methanogentic ace t a t e -g rown b i o f i l m column a f t e r a c c l i m a t i o n . . . . . . . . . . . . . . . . . . 7 7

X I

2 . 1 1 Biodegrada t ion of t h e components of g a s o l i n e . . 7 8

3 . 1

3 . 2

3 . 3

3 . 4

3.5

4 . 1

5 . 1

5 . 2

5.3

5.4

6 . 1

6.2

6 . 3

7 . 1

7 . 2

Residual o i l v o i d f r a c t i o n , So . . . . . . . . . . . 94

O i l l e n s t h i c k n e s s above g r o u n d - w a t e r . . . . . 9 9

KO, and T1/2 values for V a r i O u 8 m l a o i b l e o r g a n i c chemicals a long w i t h an e s t i m a t e of t h e t r a v e l time r e q u i r e d t o m i g r a t e L - 1000 m through ground water u s i n g eq. 8 w i t h J w = l m d ' l , (0 . 0 . 5 , pb . 1 . 5 gcm-3, f o c - 0.005 . . . . . . . . 104

S a t u r a t e d vapor d e n s i t y , Water s o l u b i l i t y and Henry's cons t an t K H f o r VariOUS v o l a t i l e and s e m i v o l a t i l e o rgan ic chemica ls . . . . . . . . . . . 1 1 2

Time t o d i f f u s e L = 1 m th rough a s o i l w i t h (0-0.5, amO.3, Dvair-4300 cm2d' f o c - .005 u s i n g eg 6 and ( A 1 7 1 . . . . . . . . . . . . . . . . 1 1 3

C r i t e r i a f o r s e l e c t i n g s o i l sampl ing equipment , . 1 2 8

D e s c r i p t i o n of s e l e c t e d p o r t a b l e a n a l y z e r s . . . . . 171

Ins t rument response t o s e l e c t e d o r g a n i c compounds. . . . . . . . . . . . . . . . . . . . . . 173

D e s c r i p t i o n o f s e l e c t e d p o r t a b l e gas chromatographs . . . . . . . . . . . . . . . . . . . 1 8 2

Summary o f suggested c a l i b r a t i o n and q u a l i t y c o n t r o l requirements f o r a n a l y t i c a l sys tems. . . , 187

Sample s t anda rd d e v i a t i o n s f o r raw and t ransformed chloroform measurements o rde red b y s i z e o f sample mean . . . . . . . . . . . . . . . 2 0 6

C h l o r o f o r m c o n c e n t r a t i o n s ( p p b v ) measured on g a s e s drawn a f t e r each o f a s e r i e s of purges o f t h e same p r o b e . . . . . . . . . . . . . . . . . . 2 0 6

Confidence i n t e r v a l s f o r u 2 based non s 2 a s a f u n c t i o n o f degrees of freedom and assuming a n o r m a l d i s t r i b u t i o n for d a t a . . . . . . . . . . . . 2 0 7

Background c o n c e n t r a t i o n s a s ppmv benzene. . . . . . 221

Concen t r a t ions o f chloroform i n ground water samp!t.s , ' o l l e c t c d f rom w e l l s a l o n g t h e Pi t tman l a t e r i l l ( m i c r o g r a m s l l i t e r ) . . . . . . . . . . . . . 244

7 . 3 Concentrations o f benzene and chlorobenzene

7 . 4 Observed ohloroform aoncentratlons over

i n ground-water sample8 co l lected from Well8 along t h e Pl t tman l a t e r a l (mlcrogrrms/llter) . . . 245

t h e ahloroform contaminant plume . . . . . . . . 248

7 . 5 Chloroform and carbon tetrachloride concentration8 l n s o i l gas as funotlona o t depth. . . . . . . . 252

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SUBJECT INDEX

Index Terms Links

A

Activated aluminum 177 261

Activated charcoal 11 152 156 177

Adsorption 11 60 61 64 68

92 101 103 104 111

120 121 177

Aerobic 71 75 76

Aerobic biofilm 75

AID gas chromatograph 241

Air filled porosity 59 60

Aqueous vapor pressure 61

B

Bacharach TLV sniffer 176

Barometric pressure 20 83 85

Benzene 3 8 13 64 71

75 102 138 158 168

174 178 186 192 221

246

Biodegradation 52 59 71 74 75

78 250

Boiling point 20 59 70

C

Canisters 14 146 178 183

Capillary zone 97

Carbon tetrachloride 7 8 10 104 112

113 250 252

Characteristic diffusion

time 111

Charcoal cartridge 14

Index Terms Links


Chlorinated hydrocarbons 47 49 50 75

Chloroform 8 10 156 204 242

245 246 248 250 252

Clay lens 61

Components of variance

Analysis 200

Concentration 20 45 47 82 120

121 208 209 212 228

Conservation of mass 119

Continuity equation 119 122

Contour plot 11 220

Contouring 200 208 209 210 265

Core sampler 130

Criteria for selecting soil

sampling equipment 128

Cryogenic concentration 180 183

Curie point mass spectrometry 156 177

Curie point wire samples 153 154 155 159 177

D

Decay constant 114

Density 20 47 51 114

Density curves 202

Depositional characteristics 80

Dielectric constant 20 49 51 57

Diffusion 8 9 11 45 59

61 64 70 79 105

109 114 120 122 157

Diffusion coefficient 8 59 64 68 110

111 114 120 122

Diffusion travel times 111 114

Dispersion 105 107 120 122

Distribution coefficient kd 101 120 121

Draeger tubes 12 14 152

Driver probes 11 130

Index Terms Links


E

Effective chemical

convective velocity 122

Effective diffusion-

dispersion coefficient 68 112

Effective half life 123

Effective velocity ve 101

Electron capture detection 184

Emission fluxes 11

Emission rate 125

Equivalent thickness 107

F

Fick's law 109 120

FID 149 151 169 170 172

175 176 181 185 186

192

Field GC 12

First order degradation rate

coefficient 123

Flame photometric detector 185

Floaters 51 83

Flux chamber 11 125 149 150 151

152 157 159 168 172

174 175 176 179 183

184 259

Fourier transform

infraredspectrometry 185

Freundlich model 120

G

Gas standard 187

Gaseous diffusion

coefficient 120

GC gas chromatograph 11 14 129 216 220

GC/FID 126

Index Terms Links


GCMS 14 152 185

Geophysical techniques 14

Grab sampling 126 127 132 152

Graphitized carbon black 152

Gravity 4 90 94

Ground probes 125 130 132 133 134

136 137 138 139 140

141 142 146 147 148

151 152 157 150 159

160 172 178

179 180

Ground water flow 4 20 79 105 123

157 213 236 256

H

Half life T ½ 102

Hall electronconductivity detector 169 184 263

Headspace concentrations 126 228

Headspace measurements 125 126 127

Heavy insoluble components 109

Hele-shaw cells 92

Henry's law 4 8 110 111

114

Henry's law constant 20 21 45 46 59

110 111 112 114 121

Hydrodynamic dispersion 99 105

Hydrologic boundaries 79

I

Interstitial water 64

Inverse square interpolation 209 265

K

Kriging 209 265

Index Terms Links


L

Lens thickness 51 99

Lithology 20 80

Long path length IR gas analyzer 175

M

Mass flow 99 109 110

Microbial growth 70

Millington-Quirk model 120

MIRAN IA gas analyzer 175

Molecular sieves 152 177

Molecular weight 4 20 59

Monitoring well 51 79 83

126 156 212 236 241

250 259

Multiple detector 185

O

Organic carbon distribution

coefficient, KOC 20 47 101 121 122

Organic carbon fraction 47 101 102 121

Organic material 47 60

Organic priority pollutants 1 2

Organic vapor analyzer 12 149 170

Oxidative process 71 75

Oxygen 59 71 135 172 174

P

Partition coefficients 45 48 121 122

Passive samplers 152

Passive sampling 125

Performance audit 193

Pesticides 19 45 89 101

Petrex tubes 152 156

Petro calcic layers 61

Index Terms Links


pH 71

PID 151 169 170 174 175

176 181 183 184 185

186 192 193

Pittman, Nevada 216 236 237 238

Plastic bags 129 178 179

Pore space 1 4 8 11 15

90 130

Pore volumes 60 68

Pore water velocity 102

Porous polymers 152 168 177 178

Portable total hydrocarbon

analyzer 126

Portable VOC Analyzers 170

Primary standard

Probability distribution 201

Probes 11 64 79 82 83

135 138 146 159 172

Pseudomonads 71

Q

Quality assurance 125 157 159

Quality assurance

quality control 186 264

R

Rainfall 20 60 82

Residual void fraction 94

Resistivity 14

Retention 20 68 70 96

S

Sample matrix 168 264

Secondary utilization 75

Silica gel 152 177

Site topography 79

Index Terms Links


Soil aeration 59

Soil gas concentration 1 8 11 15 16

82 125 132 138 146

149 151

Soil organic matter 20 60 61 89 121

Soil texture 20 61 92

Spatial pattern 209

Speciation 169

Spline procedure 209

Stainless steel canisters 14 146 178 179 183

Storage tanks 1 15 16 83 89

Stovepipe Wells, California 213 214 216 222 223

224 225 226 227 229

231 232 233 234 235

Superfund sites 1 15 16 212 256

Syringes 11 129 130 135 138

146 178 179 180 181

200 203 204 205 208

216

T

TDS 15

Tedlar bags 14 178 179

Teflon 14 130 178 179 180

Teflon bags 17 178 179

Temperature 20 59 61 70 71

123 151 179 180 181

183 194

Tenax 14 152 177 178

Thermal desorption 105

Toluene 75 178

Transverse dispersion

coefficient 105

Travel times 59 68 102 103 104

Index Terms Links


U

Unsaturated zone 4 8 19 20 45

47 59 60 61 68

70 75 82 90 91

103 110

V

Vadose zone 4 9 19 60 61

80 90 92 94 97

109 111

Vapor density 110 111 114 121 122

123

Vapor flux 109

Vapor pressure 19 20 45 46 59

61 64 70 110 114

119

Variance stabilizing

transformation 201

Velocity 51 79 97 103 105

122 136 236

Viscosity 20 51 122

Volumetric water content 20 60 102 119

W

Water holding capacity 60

Water solubility 4 11 19 20 45

47 48 101 112 121

Water table oscillations 20 79

Wetting front 60

Whole air methods 177 178

Wind 83

Soil Gas Sensing for Detection and Mapping of Volatile Organics

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Transcript of Soil Gas Sensing for Detection and Mapping of Volatile Organics