in situ treatment of contaminated soil and groundwater: lessons...

In Situ Treatment of Contaminated Soil and Groundwater:

Lessons Learned from the Field

Presented by Alan Weston, Ph.D. Conestoga-Rovers & Associates

Niagara Falls, NY, USA

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1. Introduction to In Situ Treatment

2. In Situ Technologies

3. Case Studies

4. Conclusion

Agenda

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Treatment of soil or groundwater in place

Achieved by adding reagents or manipulating subsurface conditions

Can be an effective alternative to traditional dig and haul or pump and treat technologies

In Situ Remediation

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Less intrusive, public acceptance

Transition to MNA and closure achieved more

easily

Less disruption to property, use can continue

In Situ Remediation

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Technologies include:

- Monitored natural attenuation (MNA)

- In situ chemical oxidation (ISCO)

- In situ enhanced biodegradation (ISEB)

- Permeable reactive barrier (PRB)

- Air Sparge / Soil vapor extraction (AS/SVE)

- In situ stabilization (ISS)

- Phytoremediation – Wetlands

- Soil Flushing

In Situ Remediation

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3. Case Studies

4. Conclusion

Agenda

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In Situ Chemical Oxidation (ISCO)

•Destruction of of contaminants using oxidizing reagents

•Catalyzed Sodium Persulfate, Fenton’s Reagent, Permanganates or ozone may be used to reduce high concentrations

•Treatability study is recommended determine optimum dosage of reagents

•ISCO is site specific and successful treatment is a function of an effective delivery system

In Situ Technologies

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In Situ Enhanced Biodegradation (ISEB)

Contaminants are metabolized into less toxic or non-toxic compounds by microbes

Biodegradation is enhanced through the addition of carbon/energy sources, electrons acceptors, nutrients and microbial cultures,

Enhanced aerobic conditions favor the biodegradation of BTEX, petroleum hydrocarbons, PAH, oxygenates

Enhanced anaerobic conditions favor the biodegradation of chlorinated solvents


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Air Sparge/Soil Vapor Extraction (AS/SVE)

Vertical sparge wells inject air, into the water table to strip VOC out of groundwater

Air is drawn through the soil by a vacuum

Vertical or horizontal SVE wells installed in the unsaturated zone above sparge zone for vapor collection

Decrease in pressure is created allowing release of vapor.

Extracted gas flow is vented to the atmosphere or treated


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3. Case Studies

4. Conclusion

Agenda

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Case Study #1. Large Scale In Situ Remedial

Action: CRA Self Implementation

Large Site in Illinois was impacted with chlorinated solvents

CRA reviewed site data and performed a remedial technology assessment

ISCO and SVE were the technologies recommended for further consideration for on-Site impacts

Road

AS/Injection Well

SVE Well

Treatment Area

80 ft x 700 ft

On-Site Treatment Area

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Case Study 1

A laboratory treatability study was performed to test ISCO

Results of ISCO testing showed that KMnO4 and catalyzed

Na2S2O8 would be suitable oxidants

Na2S2O8 was chosen for on-Site treatments based on lower

costs, no regulatory issues and sustainability (lower carbon

footprint)

SVE implementation was also recommended

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ISCO performed first

4,000 gallons of catalyzed Na2S2O8 solution was pumped

into each A/S well

167,000 gallons was pumped into horizontal trenches

Personnel from local offices installed trenches and

performed injections with ITG help

1 month after ISCO injection was complete the A/S and SVE

systems were connected

Case Study 1

Percent Reduction

PCE TCE DCE

MW-2 74% 99% 100%

MW-3 - 98% 91%

MW-5 100% 78% -

MW-6 88% 97.5% 100%

MW-7 - 98.5% 99.7%

Results

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Results Greater than 74% removal of all chlorinated solvents

was observed

Horizontal and vertical injections achieved good

dispersal of oxidant in the subsurface

One injection event was required

Lessons Learned

Cost saving obtained by:

- Use of sodium persulfate

- Field implementation

performed by CRA personnel

no need specialists

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Case Study #2. Treatment of

Metals in Groundwater

Groundwater at a site was contained lead and silver

Source area concentrations exceeded local regulatory

criteria and posed a water quality risk to a downgradient

creek

A treatability study was performed to test reducing

agents for their ability to precipitate these compounds

from groundwater

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Treatability Study Results

0

5000

10000

15000

20000

25000

30000

Con

trol

Na Dith

ionite

Na Metab

isulfite

Na Sulfid

e

Ca Polys

ulfid

e

Al

Ba

Be

Cu

Pb

g

Ni

Ag

Zn

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Full Scale Application

Sodium sulfide injections were performed at 30 injection

wells in the primary source zone at the Site

Increased sulfide was observed in all monitoring wells

indicating that the injected materials reached these

wells

In all the treatment areas, dissolved lead and silver

were reduced to non-detect levels by the 1-month

sampling event

Levels of total lead and silver had increased by the 1-

month sampling event due to suspended particulates

Dissolved iron increased in the wells treated by the

sodium sulfide injection. Soluble ferrous iron is

produced under reducing conditions

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Lessons Learned

Sodium sulfide is effective for the precipitation of lead

and silver in groundwater

Presence of light metal sulfides can interfere with

dissolved metals analysis

Any perturbation to the groundwater (e.g. sampling)

has the potential to resuspend metals sulfides in the

groundwater

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• Former chemical manufacturing facility in Michigan

• Various chlorinated solvents in groundwater

• Emulsified soy lactate was injected to stimulate

biodegradation of chlorinated compounds

Case Study 3 - Anaerobic Biodegradation of

Chlorinated Solvents

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Injection Layout

Soy Lactate Barrier

Injections by direct push

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-50

0

50

100

150

200

Mar-10 May-10 Jun-10 Aug-10 Sep-10 Nov-10

time

[VO

C]

(ug

/L)

0

1000

2000

3000

4000

5000

6000

[c-1

,2-D

CE

]

1,1-DCE

1,2-DDP

TCE

VC

Ethene

c-1,2-DCE

Monitoring Results

Injection Performed

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Strongly reducing conditions were created throughout

the treatment area

Reductions in chlorinated CVOC concentrations

occurred after 90 days and after 180 days

Reductions in concentrations of breakdown products

such as cis-1,2-DCE were observed

The presence of dissolved ethane and ethene indicated

that complete biodegradation of the chlorinated

compounds was occurring

Results

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Lessons Learned

Emulsified soy lactate is effective in stimulating reductive

dechlorination

The performance of a laboratory treatability study and

careful design of the field implementation can lead to a

smooth, problem free treatment

Results

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Case Study 4: iSOC PRB for BTEX

Site in Texas had BTEX In groundwater

In situ submerged oxygen curtain (iSOC) units

were installed at the Site in order prevent further

migration of the BTEX plume by treating the BTEX

at the perimeter of the plume.

The iSOC units were placed as a barrier,

downgradient of the BTEX source area.

Nutrients were injected into the iSOC wells

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iSOC Barrier

Location of iSOC Barrier

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Results

Concentrations of oxygen in groundwater in iSOC

wells >30 mg/L

Benzene and petroleum hydrocarbon

concentrations showed an immediate decrease

after the iSOC system was started

A cycle of decreasing concentrations followed by

rebound has been observed and is expected to

continue until LNAPL has been removed from the

capillary fringe

Concentrations downgradient of the barrier are low

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Results

Lessons learned

LNAPL can be treated by in situ enhanced

biodegradation, however it takes time

Requires operation of the iSOC treatment system

until LNAPL has been removed

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3. Case Studies

4. Conclusion

Agenda

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In situ treatment has the potential to complete treatment

efficiently and cost effectively

An understanding of site conditions is required in order

to determine whether in situ technologies are

appropriate for the site

Necessary to determine which in situ technology is right

for the site

Safe and effective application of the technology can be

performed by CRA

Conclusion

in situ treatment of contaminated soil and groundwater: lessons...

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