In Situ Chemical Reduction (ISCR)

Fundamentals related to selection, design and

distribution of ISCR technologies at contaminated sites

Ravi Srirangam P.E., Ph.D.

PeroxyChem Environmental Solutions

Design and Application of Insitu Treatment Technologies

CT/MA

May 2016

2

BASIC PRINCIPLES OF ISCR

3

The beginning of ISCR for soil and

groundwater applications

“Rediscovery” of McCarty and Vogel Postulated Abiotic Pathways – “oxidation,

reduction, substitution, and dehydrohalogenation reactions occur

abiotically or in microbial systems”

Started with an interest in Abiotic MNA

Butler, E., Hayes, K., 2000. Kinetics of the transformation of halogenated

aliphatic compounds by iron sulfide. Environ. Sci. Technol. 34, 422–429.

Lee, W., Batchelor, B., 2002. Abiotic reductive dechlorination of chlorinated

ethylenes by iron bearing soil minerals. 1. Pyrite and magnetite. Environ. Sci.

Technol. 36, 5147–5154.

Wilson, J. T. (2003). Abiotic reactions may be the most important mechanism in

natural attenuation of chlorinated solvents. Presented at the AFCEE Technology

Transfer Workshop, Brooks AFB, San Antonio, TX.

4

What is ISCR?

• Reduction adds electrons to the contaminant (need an

electron donor)…… Oxidation removes electrons from the

contaminant (need an electron acceptor)

• ISCR involves transfer of electrons to contaminants from

reduced metals (ZVI, ferrous iron) or reduced minerals

(magnetite, pyrite etc.)

• ISCR of CVOCs occurs via both abiotic as well as abiotic

pathways....because both processes occur simultaneously

in the subsurface

5

• Chlorinated Solvents

PCE, TCE, cis-DCE, 1,1-DCE, VC

1,1, 2,2-TeCA, 1,1,1-TCA

CT, CF

• Pesticides

Toxaphene, Chlordane, Dieldrin, Pentachlorophenol

• Energetics

TNT, DNT, RDX, HMX, Perchlorate

• Heavy Metals

Examples of Contaminants Destroyed

Examples of Contaminants That Require Organic Amendment to ZVI for Destruction

• Chlorinated Solvents

1,2-DCA

DCM, CM

Contaminants Treated via ISCR

6

Direct Dechlorination Reactions

Reactions:

Fe0 Fe2+ + 2e-

2H2O 2H+ + 2OH-

2H+ + 2e- H2(g)

R-Cl + H+ + 2e- R-H + Cl-

7

Role of ZVI and DVI (Fe(II)

• Significantly reduced half-lives of CVOCs in the presence of ZVI

• Requires direct contact with ZVI surface

• Reaction is abiotic reductive dehalogenation; minimizes/eliminates DCE/VC

• ZVI provides a long-term source of DVI

to promote indirect chemical reduction

of CVOCs (formation of reactive iron

and iron sulfide minerals)

• β-elimination is the dominant pathway

(~90%); ZVI generates hydrogen so

some biotic reductive reactions are

supported

Typical CVOC Half-lives (Room temperature)

0

1

2

3

PCE TCE cDCE tDCE 11DCE VC CT TCM 111TCA 112TCA

Ha

lf-l

ife

(h

rs))

8

ISCR CONFIGURATION AND CASE STUDIES

9

Common ISCR Implementation Methods

Hydraulic fracturing/injection (120 ft, 37 m)

soil mixing

(40 ft, 12 m)

pneumatic fracturing

(90 ft, 27 m)

Nitrogen

Gas Source

Overburden

Treatment ZoneInjector

Atomized Slurry

in Gas Stream

Packer

Pneumatic

Injection Module

Ferox Injection

Trailer

Direct

injection

(30ft,9m)

continuous trenching

(35 ft, 11 m)

10

Expansion of Granular Iron Grain

Size Range

• 0.25 to 2 mm (-8 to +50 US mesh) for trenched PRBs

• 0.07 to 1.7 mm (-12 to +200 US mesh) for hydraulic fracturing

• Pneumatic/hydraulic injection (microscale, D90 of 140 micron)

• mixed into clean soil backfill following excavation of contaminated soils (0.25 to 2 mm)

• physical mixing of iron and clay into the contaminated zone ( -50 mesh)

• 10 to 70 micron material in conjunction with other biological amendments-Injections

• Nanoscale materials (50-300 nm)

11

Commercial Facility, Mississauga, ON

(February 2008)

• Former dry cleaner • Risk-assessment to address source

and on-site contamination • PRB to prevent off-site migration

• Continuous trencher • Depth of 9 m • 125 m long

12

First ZVI PRB Installation in the Netherlands

• Continuous trencher (CT) was used to

install 120 m long PRB, with 0.3 m

trench width (1.0 m to 5.5 m bgs).

• Two 30 m long HDPE wing sections

were also installed using the CT.

• The PRB consisted of a granular iron

and sand mix with 40% ZVI (v/v).

Start of

trenching

Continuous Backfill of

Iron/sand

Outline of the installed

Iron/sand PRB

Netherlands PRB-February 2007 Results

0

20

40

60

80

Upgradient Downgradient

Co

nc

en

tra

tio

n (

ug

/L)

Transect 1

Transect 2

0

10

20

30

40

Upgradient Downgradient

Co

nc

en

tra

tio

n (

ug

/L)

Transect 1

Transect 2

cDCE

VC

Advantages

• 13 year operating record at oldest commercial facility

• possible benefits due to hydrogen gas, low Eh conditions

(microbial activity)

• at most sites, if 5 to 8 years can pass before rejuvenation or

replacement, then technology is economically attractive

Disadvantages

• Contact -very critical

• Passivation of Iron surfaces

• Increasing implementation costs with Depth

Long Term Performance of Commercial

Systems

15

Engineered ISCR?

Bacterial

inoculation

Simple carbon

donors

ZVI Complex

carbon

donors/ISRM

Engineered

ISCR

16

Engineered Reductants

Engineered ISCR:

• Amendments that combine chemical reductants (especially ZVI) with

materials that stimulate microbial activity (organic carbon in various

forms) are available as commercial products. The products include

EHC® and Daramend®(PeroxyChem), ABC® + (Redox Tech, LLC),

and emulsified zero-valent iron (EZVI) (National Aeronautics and Space

Administration).

• This approach relies on taking advantage of synergies offered by ZVI

and organic carbon to further enhance the ISCR mechanism.

17

EHC® Reagent Composition

EHC is delivered as a dry powder and includes:

Micro-scale zero valent iron powder(standard

~40%)

Controlled-release, food grade, complex

carbon (plant fibers) (standard ~60%)

Major, minor, and micronutrients

Food grade organic binding agent

Sustainable Solution

o By-product ZVI

o Food production by-products

Mechanisms Zone of Influence

Advection and Dispersion

Bacteria

VFAs Nutrients Fe+2 H2

Diffusion between Solid ISCR seams

Direct Chemical Reduction requires contact with ZVI particle

Extended Zone with Biological Reduction and Indirect Iron Effects

H2 Fe+2

Fe+2 H2

H2

VFAs

VFAs

Hypothesized reaction Pathways

Biotic Abiotic PCE

TCE

Cis 1,2-DCE Trans 1,2-DCE

VC

Ethene

Ethane

PCE

TCE

VC

Ethene

Ethane

Chloroacetylene

Acetylene

cis1,2-DCE

Dichloroacetylene

Hydrogenolysis β-elimination

CO2 – CH4 – H2O

CO2 – CH4 – H2O

Hydrogenation

20

DESIGN AND IMPLEMENTATION OF ENGINEERED ISCR

21

Remediation Strategy

Source Area/ Hotspot Treatment

Injection PRB for Plume Control

Plume Treatment

22

1. What should the strategy be based on the site-specific goals?

• Residual source area treatment / Plume treatment / PRB

2. Which product to use, how much, how frequent ?

• Make up of target contaminants

• Desired reduction in concentration of CVOCs?

• Estimated mass of CVOCs

• Prevailing geochemistry (DO, ORP)

• Pathways required to treat the suite of CVOCs

• Product longevity

• Product distribution under the site-specific geologic/hydrogeologic

conditions (depth, geology)

• Demand from CEAs

• Site-Specific Design Factor

3. Are other additives required (buffer, bioaugmentation etc.)?

• Potassium bicarbonate / dolomite

• SDC-9 / KB-1

Key Design Questions?

23

1. Can the required product be applied in one event or multiple

events are required?

• Available pore volume v/s injected volume

2. Application Method

• DPT

• Injection Wells

• Fracturing

• Soil Blending

3. ROI and number of injection points?

• ROI increases with permeability-less injection points

• ROI increases with high pressure injections

Key Implementation Questions

24

1. Distribution of Slurries (all engineered ISCR products contain ZVI)

• Top Down / Bottom Up for DPT

• Fracturing (pneumatic/hydraulic)

2. Mixing / Pump Requirements

• Good mixing to eliminate clogging

• Positive displacement pumps/ high flow rate

3. Injection Spacing (horizontal/vertical)

• It is not only about how far you can distribute the reagent

4. Verification of Distribution

• Magnetic separation

• Visual inspection of cores

Key Implementation Questions

25

Methods to Validate ROI

Verification of direct product placement:

Visual observation of fractures in soil cores.

Magnetic separation of ZVI from soil cores.

Monitoring of ground deformation using uplift stakes or tilt meters (usually used during fracturing).

Extended zone of influence:

Groundwater Indicator Parameters (TOC, Fe, geochemical parameters)

26

How Far is Substrate Distributed?

27

Solid ISCR® Design Calculation

Steps 1. Calculate quantity of EHC required

• Hydrogen demand from CEAs and CVOCs in the treatment area

• Multiply the hydrogen demand by specific hydrogen capacity of EHC (94 g

H2/kg of EHC),

• Multiply the theoretical EHC demand by a site-specific design factor (1 to 10)

• If the calculated demand is less than the default value, use the default value

• Recommended default values are:

• 0.15 to 0.25% by wt of soil for plume treatment

• 0.25 to 1.0% by wt. for source area treatment

• 0.50 to 1.5% by wt. for a PRB

2. Assess if the quantity estimated can be injected

• If required EHC slurry volume is less than 15% of the total porosity in the

treatment zone, the quantity can be injected.

• If more than 15%, multiple injection events may be required spaced 6 months

apart.

• If slurry volume is less than 10%, increase the volume by diluting the slurry to

inject at a minimum 10% of the PV.

8 out of 10 times selected

dosage is based on default

values

28

Liquid ISCR Design Calculation Steps

1. Calculate quantity of substrate required

1. Hydrogen demand from CEAs and CVOCs in the treatment area

• Multiply the hydrogen demand by amount of H2 produced per unit quantity of

substrate eg: (0.141 HRC , 0.0145 –Lactate 0.322 -EHC Liquid, 0.359 -soy

bean oil

• Multiply the theoretical demand by a site-specific design factor (1 to 10)

• Calculate the required concentration of TOC in pore water. If the calculated

concentration is less than the default value, use the default value

• Recommended default values are:

• 1,000-5,000 mg/L for plume treatment

• 5000-10,000 mg/L for residual source area treatment

• 10,000-15,000 mg/L for source area and PRB

2. Assess if the quantity estimated can be injected

• If required substrate volume after X dilution is greater than 15% but less than

30% of the total porosity in the treatment zone, the quantity can be injected.

• If it is more than 50%, the dilution factor can be reduced to inject a concentrated

solution or perform multiple applications.

• If it is less than 15%, increase the volume by diluting the solution or increasing

the application rate.

8 out of 10 times selected

dosage is based on default

values

29

SOLID-ISCR CASE STUDIES

30

EHC® Case Study – Source Area /

Grid Injection

• Site: Former Dry Cleaner, OR

• Contaminants: PCE ~ 22,000 ug/L

TCE ~ 1,700 ug/L

DCE ~ 3,100 ug/L

VC ~ 7 ug/L

• Treatment: 10K lbs (4.5 kg) in 5 days

32 injection pts

Target area = 825 ft2 x 20 ft deep

Vertical Interval = 10 to 30 ft bgs

Low permeability lithology

Large seasonality in GW flow

Application rate - 0.6% by wt. to soil

• Material Cost: $1.24/ft3, ~$20,000

31

EHC® Case Study Results -

Indicator Parameters

NW sampling cluster NE sampling cluster

SW sampling cluster SE sampling cluster

0 5

10 15 20 25 30 35 40

0 5 10 15 20 25 30 35 40

Conc.

(mg/L

)

Time post EHC injection (months)

Sulfate

0

5

10

15

20

25

0 5 10 15 20 25 30 35 40

Conc.

(mg/L

)

Time post EHC injection (months)

Methane

0

1

2

3

4

5

6

0 5 10 15 20 25 30 35 40

Conc.

(mg/L

)

Time post EHC injection (months)

Dissolved Oxygen

-300 -250 -200 -150 -100 -50

0 50

100 150

0 5 10 15 20 25 30 35 40

OR

P (

mV

)

Time post EHC injection (months)

ORP

32

EHC®

Case Study Results

PCE

TCE

c-DCE

VC

0

2,000

4,000

6,000

8,000

1 5 8 12 14 18 22 24 31 34

Conc.

(ug/L

)

Time post injections (months)

SE sampling cluster

0

2,000

4,000

6,000

8,000

10,000

12,000

1 5 8 12 14 18 22 24 31 34

Conc.

(ug/L

)

Time post injections (months)

SW sampling cluster

0

5,000

10,000

15,000

20,000

25,000

30,000

-18 0 1 5 8 12 14 18 22 24 31 34

Conc.

(ug/L

)

Time post injections (months)

NW sampling cluster

0

1,000

2,000

3,000

4,000

5,000

6,000

-18 0 1 5 8 12 14 18 22 24 31 34

Conc.

(ug/L

)

Time post injections (months)

NE sampling cluster

33

Upstate NY Case Study

ISCR pilot and Full scale Injections

• Manufacturing site with DCE stall historically

• An ISCR (EHC) pilot test was previously

conducted in the CVOC source area in Feb

2011.

• Full scale injections were designed as

multiple events spread over 2 years both in

the source area and downgradient (PRB) to

prevent offsite plume migration

Design parameters:

• The injections were conducted around

monitoring wells MW-11, MW-17 and MW-07

in Sep 2011 and Apr 2013

• Bioaugmentation was done using SDC-09 at

the end of each injection event

34

EHC®

Case Study Results

35

EHC®

Case Study Results

36

• Site: Confidential Site, KS

• Contaminant: Carbon Tetrachloride

2600 ft / 800 m plume

• Treatment: 48K lbs (21.7kgs) EHC PRB

• Application PRB installed down-gradient of

Strategy: source area

Installed line of injection points

10 ft / 3 m apart

PRB extends width of plume =

270 ft / 90 m long

Installed in 12 days using direct

inject

ISCR PRB- Plume Treatment

Courtesy of Malcolm Pirnie (Arcadis)

discharges into

small creek

37

44<1

<1

120067

25<1 <1

19

1575

16

72<1

5.825

<1

EHC Treatment Zone

Monitoring well andCT concentration (ug/L)

N

Property Line

0 300 600

SCALE IN FEET

May 2010

60<1

<1

57062

31<1 <1

21

1635

21

120<1

1334

<1

EHC Treatment Zone

Monitoring well andCT concentration (ug/L)

N

Property Line

0 300 600

SCALE IN FEET

October 2009

70<1

<1

1400130

29<1 <1

21

2117

62

260<1

1589

<1

EHC Treatment Zone

Monitoring well andCT concentration (ug/L)

N

Property Line

0 300 600

SCALE IN FEET

April 2009

150<1

<1

620170

49<1 <1

37

1254

110

490<1

28170

<1

EHC Treatment Zone

Monitoring well andCT concentration (ug/L)

N

Property Line

0 300 600

SCALE IN FEET

October 2008

82<1

<1

1400300

57<1 <1

13

1946

380

650<1

25280

<1

EHC Treatment Zone

Monitoring well andCT concentration (ug/L)

N

Property Line

0 300 600

SCALE IN FEET

April 2008

98<1

<1

1600170

27<1 <1

14

94140

610

540<1

82190

<1

EHC Treatment Zone

Monitoring well andCT concentration (ug/L)

N

Property Line

0 300 600

SCALE IN FEET

August 2007

36<1

<1

2700620

33<1 <1

17

150380

610

410<1

2.485

<1

EHC Treatment Zone

Monitoring well andCT concentration (ug/L)

N

Property Line

0 300 600

SCALE IN FEET

February 2007

47<1

<1

770140

100011 <1

140

49067

280

4606.4

3798

<1

EHC Treatment Zone

Monitoring well andCT concentration (ug/L)

N

Property Line

0 300 600

SCALE IN FEET

March 2005

ISCR - PRB

38

LIQUID ISCR CASE STUDIES

39

E-ZVI Case Study

40

Baseline Concentrations

41

Approach (cont.)

42

Injection design

December 2004 TCE

Contours

Depth 30-50

Feet

April 2008 TCE

Contours

Depth 30-50

Feet

TCE Concentration (ppb)

≥ 10,000 ppb

1,000 ppb

≥ 100 ppb

≥ 10 ppb

Treatment Area

TCE Groundwater Cleanup Target Level is 3.0 ppb

Monitoring Well with Screen Interval

Multi-Chamber Monitoring Well

Case Study #3 – Patrick AFB, Florida RITS Spring 2009: EZVI Treatment of Chlorinated Solvents 43

44

Concord NWS Case Study

Enhanced Reductive Dechlorination Pilot Test:

• An Enhanced Reductive Dechlorination (ERD) pilot test

was previously conducted in the TCE source area from

2011 to 2014.

• The ERD pilot test used buffered emulsified vegetable oil

substrate which was augmented with dechlorinating

microbial consortium (SDC-9™).

ISCR Pilot Study:

• The test was conducted in the TCE source area wells

(S29MW01 and S29MW03) not affected by the ERD pilot

test.

• The aquifer was first primed for substrate distribution by

fracturing the aquifer using the ELS and bioaugmentation

solution.

• Following confirmation of fracture development, ZVI

suspended in guar was injected into the interval followed

immediately by the lactate, ELS solution and

bioaugmentation culture.

• Monitoring was then conducted to verify the degradation

of TCE.

45

Analytical Results

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

-100 0 100 200 300 400 500 600

Sta

nd

ard

Un

its

Days

ISCR vs Biotic Only Treatment ComparisonpH

S29MW10 - Biotic Only

S29MW11 - Biotic Only

S29MW01 - ISCR

S29MW03 - ISCR

-600

-500

-400

-300

-200

-100

0

100

200

300

400

-100 0 100 200 300 400 500 600

mV

Days

ISCR vs Biotic Only Treatment ComparisonOxidation-Reduction Potential

S29MW10 - Biotic Only

S29MW11 - Biotic Only

S29MW01 - ISCR

S29MW03 - ISCR

46

Analytical Results

47

Concord NWPS – Total Chlorinated Ethenes

CHC (field application rate by weight)

Engineered ISCR-treated plumes degrade with half lives one to two orders of magnitude faster

than that seen under anaerobic natural attenuation

Amended and Unamended Field Half Lives

Amended and Unamended Field Half Lives

5,736 5,7366,648 6,648 6,648

2,112 2,112

456552

14

3

14 13

41

2 2 2 2 2

20

400

20

200

400

50

500

200

1

10

100

1,000

10,000

PCE (10%) PCE (0.5%) TCE (10%) TCE (1%) TCE (0.5%) Vinyl Chloride

(10%)

Vinyl Chloride

(1%)

Carbon

Tetrachloride

(0.5%)

Chloroform

(0.5%)

Half

Lif

e (

ho

urs

)

Anaerobic Natural Attenuation Rates (Alvarez & Ilman, 2006)

Injected PRB Field Half Life

Trench PRB Field Half Life

Granular ZVI (Abiotic)

49

Latest Developments

1. Integrated Emulsified Lecithin + ZVI

• Full-scale application at Concord NWS in 2014

2. Ferox Plus by Hepure

• ZVI plus emulsified vegetable oil (SRS)

3. Magnetic Susceptibility Analysis

• Allows us to determine the capacity of the aquifer to intrinsically support

abiotic ISCR

4. Combined Remedies

• Sequential ISCO/ISCR (Klozur Persulfate /EHC)

• ERH/ISCR (CDMSmith, Hunters Point Naval Shipyard)

50

Bench, Pilot, and Design Optimization

Tests

1. Bench tests typically recommended only for unique combination of CVOCs,

CVOCs that have not been tested before, CVOCs concentrations outside

the previously tested range or unique geochemical conditions (e.g. high

sulfate)

2. Pay close attention to how you scale up from bench test data (i.e. the ratio of

water to soil used in the bench is usually skewed compared to what it is in

the aquifer)

3. Perform pilot test to answer questions around distribution, injectability, and

full-scale design

4. Pilot test must be small enough to be cost effective, and add value to the

full-scale, at the same time broad enough to collect sufficient data. As a

general rule, be prepared to collect a lot more data in the pilot then you will

during full-scale application

51

Lessons Learned

1. Geochemistry is important but it is relatively easy to overcome limiting

geochemical conditions

2. It is important to know where the majority of the target contamination

resides….specially for source and residual source areas

3. Distribution is the key to success, so engage a qualified injection

contractor during the design phase

4. Adopt newer site characterization tools to optimize implementation and

achieve desired goals

5. Employ recommended injection pumps, mixing equipment and

procedures

6. Allow flexibility in the design to address unforeseen conditions in the

field

52

CHAPTER 10 IN SITU CHEMICAL REDUCTION FOR SOURCE REMEDIATION Paul G. Tratnyek,1 Richard L. Johnson,1 Gregory V. Lowry2 and Richard A. Brown3

B.H. Kueper et al. (eds.), Chlorinated Solvent Source Zone Remediation, doi: 10.1007/978-1-4614-6922-3_10, # Springer Science+Business Media New York 2014

Reference Documents

Ravi Srirangam P.E., Ph.D.

Technical Manager, Environmental Solutions

PeroxyChem, LLC

One Commerce Square

2005 Market Street, Suite 3200

Philadelphia, PA 19103

P: 312.480.5250| E:Ravi.Srirangam@peroxychem.com

www.peroxychem.com/remediation

Questions???