1

Measurement and Use of Mass Flux and Mass Discharge Cleanup 2013 Melbourne, Australia

Charles Newell, Ph.D., P.E., GSI Environmental Inc.

“Mag 7 Plume”

2 Two Views of the World: Concentration versus Mass Discharge

Site A: Very wide source

Very fast groundwater

Site B: Tiny source

Almost stagnant groundwater

But same maximum groundwater

Concentration…

3 Two Views of the World: Concentration versus Mass Discharge

u  Concentration-based approach may not account for important site characteristics

But same maximum groundwater

Concentration…

Mega Site

Piss-Ant Site

Mass Flux / Mass Discharge Combine flow, size, concentration

5

Mass flux, J Mass per area

per time

Mass discharge, Md

Mass per time ”

Integrate

Definitions

Sir Isaac Newton:

“Method of Fluxions”

“This plume has a mass discharge of 1.5 grams per day.”

6

Five Methods for Mass Discharge

u  Method 1: Transect Method

u  Method 2: Well Capture/Pumping Methods

u  Method 3: Passive Flux Meters

u  Method 4: Using Existing Data (Isocontours)

u  Method 5: Solute Transport Models

Source Strength

Plume Strength

Source

All methods are “ready to go”

7

Method 1: Transect Method

Md = Mass discharge Cn = concentration in polygon n A n = Area of segment n

Step-by-step approach assuming uniform groundwater velocity

1. Draw transect: with polygons (“window panes”) for each well

2. Determine area (W • b = A)

3. Multiply and sum together:

Md = Σ (Cn• An•q)

Nichols and Roth, 2004

CROSS-SECTION W4 W3 W2 W1

< 0.5 ug/L

45 ug/L

74 ug/L

b Polygon

2

Width

Polygon 1

< 0.5 ug/L

Width

8

q = K • i q = Groundwater Darcy velocity i = Hydraulic gradient K = Hydraulic conductivity*

Calculating Mass Discharge: Groundwater Darcy Velocity Term (q)

Variability in groundwater velocity - most applications of the transect method to date have assumed a uniform groundwater. Darcy velocity for the entire transect. However, different values for q may be used for different polygons if sufficient data are available.

Calculation of Darcy Velocity

•  Hydraulic conductivity can be determined by pumping test, slug test, or estimated based on soil type

•  Don’t use porosity – hydraulic calculations for groundwater (such as Theis equation) don’t rely on porosity

Md = Σ (Cn•An•qn)

9 Darcy Velocity (q) or Seepage Velocity (Vs)?

Md = Σ (Cn•An•qn)

Calculation Using Darcy Velocity

Calculation Using Seepage Velocity

Description Darcy velocity is averaged over entire transect area

Seepage velocity is velocity in open pore space

Diagram

Area Used for any Flow Calculation

Use entire transect area: Area = W • H

Use only open porosity area: Area = W • H • n

Flow Calculation

W

H

W

H n=porosity

Flow = K • i • W • H Flow = K • i • W • H • n

K * i =Darcy Velocity (q) K • i = Seepage Velocity (Vs) n

n

Flow = K • i • W • H Flow = K • i • W • H • n n

10

10

Calculate Mass Discharge

by Hand t

N U M B E R 1

Calculator Exercise

11

Building Transects: General Rules

u  Can be permanent or temporary installations u  No special well or sampling points needed u  Can be based on longer single screen wells or

multilevel observations u  Transect must be perpendicular or close to

perpendicular to groundwater flow

Source Strength

Plume Strength

Source

12

Nichols and Roth, 2004

Transect Method: Using High Resolution Data

u  Multi-level sampling means multiple level polygons

u  Sum up all cells to get Mass Discharge (Md) in units of •  Grams per day (g/dy) •  or •  Kilograms per year (kg/yr)

In this case •  Md = 488 g/dy •  or •  Md = 178 kg/yr

w1 w2 w3 w4 w5

b1 b2

b3

b4

b5

b6

Transect GW Flow Direction

Transect

Figure 4-1

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Source: Guilbeault et al., 2005

(a) E

leva

tion

(m)

Ground New Hampshire PCE Site

Water Table

High Resolution Mass Flux Transect

Md: 56 grams per day (Mag 6 Plume)

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Tools for Transect Method: Calculator

Lead author: Shahla Farhat, Ph.D. free at www.gsi-net.com Microsoft Excel-based

15

Key Features of Mass Flux Toolkit •  Streamlines the data input process

•  You pick interpolation method

•  It does the calculations

•  Uncertainty/sensitivity analysis •  Graphical output

•  How to use mass discharge data

•  Overall resource for mass flux

15

16 16

17 Method 2: Well Capture Mass Discharge Calculation

Nichols and Roth, 2004

Md = Mass discharge (grams per day)

Cwell = concentration in recovery well effluent (grams per liter)

Q = Well pumping rate (liters per day)

Md = Q x Cwell

Measure Q, Cwell from well Contaminant Source Groundwater

Flow Line Dissolved

Contaminant Plume

PumpingWell

Capture Zone

gram liter

liters day

= grams day

x

Figure 4-8

18 Well Capture Mass Discharge Calculation

Calculate mass discharge based on total capture of plume by pumping system

Nichols and Roth, 2004

Md = Mass discharge (grams per day)

Cwell = concentration in recovery well effluent (grams per liter)

Q = Well pumping rate (liters per day)

Md = Q x Cwell

Measure Q, Cwell from well Contaminant Source Groundwater

Flow Line Dissolved

Contaminant Plume

Supply Well

Capture Zone

gram liter

liters day

= grams day

x

Figure 4-8

19

More Sophisticated Version Method 2

u  Integral Pump Tests (IPT) •  Steady state flow conditions, but handles changing

heterogeneous concentrations in plume

Figure 4-9. Estimating Mass Flux Using Integral Pump Test Series Data

Pumping tests with concentration time series measurements

Concentration vs. time during pumping tests (compound specific)

Total contaminant mass flux and average concentration

Transient inversion algorithm (analytical solution)

Groundwater Flow

Contaminated site

Source

of Pollutant

Well 1

Well 2

Well 3

Well 1 Well 2 Well 3 C C C

t1 t2 t1 t2 t1 t2

Isochrones (simplified)

Contaminated plume

Control plane

20 Well Capture Methods Advantages and Limitations

u  Advantages •  Fewer wells •  Better integration of flow and concentration data •  Can use existing pumping system

u  Limitations •  No mass flux data •  Large volumes of water that need disposal/

treatment •  Possible to change plume

characteristics •  Difficult to assure full plume capture

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Method 3 – Passive Flux Meter

u  Permeable sorbent •  Accumulates

contaminant based on flow and concentration

u  Soluble tracers •  Loses tracer based

on groundwater velocity and flux convergence calculations K0 K>>K0

Groundwater Flowlines

t1

t2

t3

Source: Hatfield and Annable

Photo: Dye intercepted in a meter

1. Contaminant adsorbed onto passive flux meter over time to get Concentration

2. Tracer desorbs from passive flux meter over time to get Flow (Q)

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Installation Sampling

Vendor: http://www.enviroflux.com/pfm.htm

Passive Flux Meter

23 Passive Flux Meter Advantages and Limitations

u  Advantages •  “One stop shop” for both flow and concentration •  Easy to install in the field •  No waste generated •  Vendor available to implement this method

u  Limitations •  Some method-specific issues

(lower measurement in pushed wells, slight biodegradation of tracer at one site, competitive sorption under some conditions)

•  Relies on well convergence calculations

24 Method 4 – Use Existing Data (Transect Based on Isocontours)

u  Uses plume map u  Combine with flow data

Two dimensional transect based on isocontour data

1 2 5

10

<0.1 <0.1

1 2 3 4 Transects

Scale (ft) 0 1000

Concentration isopleths (mg/L)

N

Transect 1: Intersection with Contour Lines N-NE S-SW

Concentration (mg/L) for contour lines

Geometric mean concentration (mg/

L) between contour lines

0.1 1 2 5 10 15 10 5 2 1 0.1

0.31 1.4 3.2 7.1 12.2 15 12.2 7.1 3.2 1.4 0.31

Figure 4-12

25 Isocontour Method Advantages and Limitations

u  Advantages •  Does not need special field study. Can use existing,

historical data from existing monitoring system •  Limited additional expense

u  Limitations •  Wide range of opinion about usefulness of this

method •  Can be inaccurate if plume map is built with

only a few wells. For example consider: §  Gas station site with 5 wells throughout entire

plume: not likely to provide high quality mass flux/mass discharge data versus

§  Well characterized site with 40 wells in source zone: likely to provide higher quality data

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Enter flow, concentration data and calibrate model. Below: REMChlor model; 90% of source removed in 2010.

2008 2014 2080

Distance from Source (meters)

Mas

s D

isch

arge

(Kg

per y

ear)

Measurement Method 5 – Computer Models

To get REMChlor: google “REMChlor” and “EPA”

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Five Methods for Mass Discharge

u  Method 1: Transect Method (Sect. 4.1) •  Commonly used. Based on familiar technology

u  Method 2: Well Capture/Pumping Methods (Sect. 4.2) •  Many pump and treat systems doing this now.

u  Method 3: Passive Flux Meters (Sect. 4.3) •  New technology, easy to install, one device for flow and

concentration u  Method 4: Using Existing Data (Isocontours) (Sect. 4.4)

•  Uses existing data. Cost effective, but requires good monitoring network.

u  Method 5: Solute Transport Models (Sect. 4.5) •  Combines flow and concentration data. Helpful to have

experience

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Comparisons of Different Methods

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Comparisons of Different Methods

Summary of contaminant (TCE and DCE) mass discharge rates (g/day) as estimated using PFM and IPT results, and comparison with corresponding estimates based on the Transect Method (TM) (Brooks et al., 2008)

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Comparisons of Different Methods

Summary of contaminant (TCE and DCE) mass discharge rates (g/day) as estimated using PFM and IPT results, and comparison with corresponding estimates based on the Transect Method (TM) (Brooks et al., 2008)

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Comparison of Methods

TM = Transect method PFM = Passive flux meter MIPT = Modified integral pumping test

Method Comparison Based on Two Sites

TM and MIPT

u Relative difference 3% to 46% u (TM – MIPT)/TM

TM and PFM

u Relative difference -21% to 17% u (TM – PFM)/TM

PFM and MIPT

u Relative difference 0% to 35% u (PFM – MIPT)/PFM

Brooks et. al., (2008)

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Where Mass Discharge Has Been Used

61 Case Studies

0

10

20

30

40

1 2 3

1995 19999

2000- 2004

2005- 2009

Specific location (known city or county) Unspecified location within a state, province, or country

Managing  Surface  Water  Quality  with  Mass  Discharge:    Total  Maximum  Daily  Loads  (TMDL)        “The  maximum  amount  of  a  pollutant  that  a  water  body  or  water  segment  can  assimilate  without  exceeding  water  quality  standards.” (1972  CWA)  

u  Copper into River (Alaska): up to 5450 grams per day

u  Dioxin into Houston Ship Channel 0.04 grams per day

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Cwell = Md ÷ QWell Qw = 600 gpm

2 grams day x ÷ x =

106ug g

1 gal 3.79 L

x < 1 ug /L

Cwell = Concentration in extraction well Qwell = Pumping rate for extraction well

Einarson and Mackay, 2001

Using Mass Discharge: Estimating Well Impacts

Use mass discharge of plume to predict constituent of concern concentration in downgradient water supply well

Clean water

Md = 2 grams/day Clean water

Clean water

Source zone

Capture zone

Extraction well

1 600 gpm

day 1440 min

35

Site Prioritization Using Mass Discharge

0.00078 Grams Per day

56,000 Grams

Per day

36

OoM: “Order of Magnitude”

u  Concentration, hydraulic conductivity have a log-normal distribution

Plume Magnitude Classification System Mass Discharge

(grams/day)

Plume Category

< 0.0001 to 0.001 “Mag 1 Plume” 0.001 to 0.01 “Mag 2 Plume”

0.01 to 0.1 “Mag 3 Plume” 0.1 to 1 “Mag 4 Plume” 1 to 10 “Mag 5 Plume”

10 to 100 “Mag 6 Plume” 100 to 1,000 “Mag 7 Plume”

1,000 to 10,000 “Mag 8 Plume” 10,000 to 100,000 “Mag 9 Plume”

>100,000 “Mag 10 Plume” Newell et al., 2011

Distribution by Plume Magnitude – 40 Sites

Sou

rce:

New

ell e

t al.,

201

1

For complete capture and MCL = 5 ug/L: Mass

Discharge (grams/day)

Plume Classification

This Mag Plume Could Impact:

0.001 to 0.01 Mag 2 Plume Domestic well pumping at 600 liters prt day

1 to 10 Mag 5 Plume Municipal well pumping at 400 liters per minute

1,000 to 10,000 Mag 8 Plume Stream with a mixing zone and base flow of 4 cubic meters per second

What Mag Plume Does It Take for Impact?

Newell et al., 2011

Wrap Up

REMChlor

5

Mass Discharge (grams/day)

Plume Category

< 0.0001 to 0.001 “Mag 1 Plume”

0.001 to 0.01 “Mag 2 Plume” 0.01 to 0.1 “Mag 3 Plume”

0.1 to 1 “Mag 4 Plume” 1 to 10 “Mag 5 Plume”

10 to 100 “Mag 6 Plume” 100 to 1,000 “Mag 7 Plume”

1,000 to 10,000 “Mag 8 Plume” 10,000 to 100,000 “Mag 9 Plume”

>100,000 “Mag 10 Plume”

Flux

Discharge