Jeffrey Ragucci
SWS 6262 – Soil Contamination
& Remediation
November 2014

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Trichloroethylene (TCE)
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Manmade chemical solvent
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Colorless liquid with chemical formula C
2
Cl
3
H
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Past uses: cosmetics, drugs, pesticides
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Current uses: metals degreaser, adhesives, paints, varnishes

•
When released to soil, TCE will exist in four phases:
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Dense Nonaqueous Phase Liquid (DNAPL)
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Dissolved phase in soil water
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Gas phase in soil vapor
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Sorbed phase on aquifer solids

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Pump and treat - groundwater
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Extraction of groundwater using pumps and conventional wells followed by ex situ treatment
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Advantages
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Easy to permit, design, operate
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Low startup costs
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Disadvantages
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Long-term operation results in high total cost

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Excavation - soil, groundwater
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Physical removal of soil and water, with ex situ treatment or offsite disposal
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Advantages
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Equipment readily available
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Effective for small releases
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Proven and reliable
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Disadvantages
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Potential for worker or offsite exposure
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Difficult and/or costly in unstable soils, below water table, or close to structures
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Moves contamination from one location to another rather than eliminating it

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In Situ Chemical Reduction (ISCR) - soil, groundwater
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Zero valent iron (ZVI) used to cause reductive dechlorination
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Advantages
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Simple to implement and equipment readily available
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Can achieve results similar to thermal but at lower cost
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Disadvantages
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Adding water and clay reduces compressive strength of soil, possibly requiring posttreatment capping and/or soil stabilization
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Sites must be free of surface or buried obstructions

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In Situ Chemical Oxidation (ISCO) - soil, groundwater
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Chemical oxidants injected to cause in situ degradation
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Advantages
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Simple to implement and equipment readily available
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Disadvantages
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Multiple rounds of injections often required
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Preferential flow paths preventing uniform reactant distribution
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High costs of oxidants
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Possible side effects such elevated levels of sulfate or trace metals

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In Situ Biological Treatment - soil, groundwater
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Addition of a soluble carbon source or electron donor promotes reductive dechlorination
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Advantages
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Simple to implement and equipment readily available
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Disadvantages
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Multiple rounds of injections often required
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Preferential flow paths prevent uniform distribution
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Long term implementation and monitoring often required
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Possible side effects such as elevated levels of arsenic, heavy metals and methane

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Soil vapor extraction (SVE) - soil
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Extraction of soil gas from the vadose zone using vacuum pumps and conventional wells followed by ex situ treatment
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Advantages
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Easy to permit, design, operate
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Low startup costs
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Disadvantages
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Long-term operation results in high total cost

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Thermal treatment - soil, groundwater
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Heating of subsurface causing in situ destruction by pyrolysis, and/or followed by recovery of vapor or liquid
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Advantages
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High levels of contaminant removal, including
DNAPL and from low permeability zones
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Disadvantages
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High technical skill required
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High cost, energy use, and carbon footprint
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Incomplete heating may result in untreated areas
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Large number of vertical borings needed

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760 acre property
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Operated by government contractors since World War II for production of military aircraft
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TCE used for metals degreasing
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TCE source area present below Building 181 from former disposal pit and spills
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Plume extending across site known as Eastern Parking Lot (EPL) plume
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Additional contaminants onsite, but this report focuses on Building 181 source area
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1996 - EPA Record of Decision requiring remediation at the site

Building 181
EPL Plume

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Pump and treat - groundwater only. Conclusion: eliminated.
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Excavation - not feasible due to buildings on active facility. Conclusion: eliminated.
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In Situ Chemical Reduction (ISCR) - cost estimate of $2,500,000 to $6,000,000.
Unable to perform soil mixing for application. Decreases compressive strength of soil, risking surface structures. Conclusion: eliminated.
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In Situ Chemical Oxidation (ISCO) - cost estimate of $2,000,000. Less effective on
DNAPL. Risk of non-uniform treatment. Conclusion: eliminated.
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In Situ Biological Treatment - cost estimate of $3,700,000 to $7,000,000. Ineffective on DNAPL. Conclusion: eliminated.

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Soil Vapor Extraction (SVE)
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Effective on highly permeable soil. Terrace Alluvium conductivity is 13 to 132 ft/day.
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Pilot test demonstrated effectiveness.
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Cost estimate based on pilot study: $612,000.
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Conclusion: selected due to demonstrated effectiveness and cost. However, unable to treat groundwater.

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Thermal Treatment - Electrical Resistive Heating (ERH)
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Installation of electrodes into subsurface. Electricity passing through soil generates heat, turning DNAPL and groundwater containing dissolved TCE into soil vapor.
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Soil vapor captured by SVE system and treated.
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Pilot test demonstrated effectiveness.
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Cost based on actual implementation: $2,500,000.
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Conclusion: selected due to demonstrated effectiveness. Cost comparable to other technologies considered.

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1993 - SVE system installed as an immediate response action
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2000 - SVE system expanded
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2002 concentrations:
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Source area soil: up to 2770 mg/kg (cleanup goal of 11.5 mg/kg)
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Dissolved phase: up to 129 mg/L (cleanup goal of 10 mg/L)
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DNAPL still present
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2002 - ERH system implemented

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98 electrodes
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14 temperature monitoring points (TMPs)
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12 monitoring wells
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Additional SVE wells installed
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Linked to existing SVE system

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Mean soil concentrations: 90% reduction to 0.184 mg/kg
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Mean groundwater concentrations: 88% reduction to 4.1 mg/L
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2008 Five Year Review - concentrations in groundwater rebounding to 20-50 mg/L, exceeding cleanup goal

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Problem: DNAPL was not fully removed
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Reason: insufficient power (and thus heating) was applied to the subsurface
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Root cause: reliance upon conductivity assessment from 2001 pilot study.
Prior to full implementation in 2002, a full conductivity assessment was not conducted.
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Lack of sufficient pre-design work

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Not feasible to re-install $2,500,000 ERH system
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ISCO and in situ biological treatment previously eliminated due to inability to treat large volume of DNAPL and cost
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Likely effective in treating residual DNAPL
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Cost reduced due to smaller treatment volume