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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1. Introduction to In Situ Treatment
2. In Situ Technologies
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
In Situ Technologies
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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
In Situ Technologies
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1. Introduction to In Situ Treatment
2. In Situ Technologies
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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1. Introduction to In Situ Treatment
2. In Situ Technologies
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