Presentation on theme: "Air Force Plant 4 Superfund Site Evaluation of SVE Combined with ERH for the Remediation of TCE Source Material Jeffrey Ragucci SWS 6262 – Soil Contamination."— Presentation transcript:
1 Air Force Plant 4 Superfund Site Evaluation of SVE Combined with ERH for the Remediation of TCE Source MaterialJeffrey RagucciSWS 6262 – Soil Contamination & RemediationNovember 2014
2 Contaminant Overview Trichloroethylene (TCE) Manmade chemical solvent Colorless liquid with chemical formula C2Cl3HPast uses: cosmetics, drugs, pesticidesCurrent uses: metals degreaser, adhesives, paints, varnishes
3 Contaminant OverviewWhen released to soil, TCE will exist in four phases:Dense Nonaqueous Phase Liquid (DNAPL)Dissolved phase in soil waterGas phase in soil vaporSorbed phase on aquifer solids
4 TCE Remediation Technologies Pump and treat - groundwaterExtraction of groundwater using pumps and conventional wells followed by ex situ treatmentAdvantagesEasy to permit, design, operateLow startup costsDisadvantagesLong-term operation results in high total cost
5 TCE Remediation Technologies Excavation - soil, groundwaterPhysical removal of soil and water, with ex situ treatment or offsite disposalAdvantagesEquipment readily availableEffective for small releasesProven and reliableDisadvantagesPotential for worker or offsite exposureDifficult and/or costly in unstable soils, below water table, or close to structuresMoves contamination from one location to another rather than eliminating it
6 TCE Remediation Technologies In Situ Chemical Reduction (ISCR) - soil, groundwaterZero valent iron (ZVI) used to cause reductive dechlorinationAdvantagesSimple to implement and equipment readily availableCan achieve results similar to thermal but at lower costDisadvantagesAdding water and clay reduces compressive strength of soil, possibly requiring post- treatment capping and/or soil stabilizationSites must be free of surface or buried obstructions
7 TCE Remediation Technologies In Situ Chemical Oxidation (ISCO) - soil, groundwaterChemical oxidants injected to cause in situ degradationAdvantagesSimple to implement and equipment readily availableDisadvantagesMultiple rounds of injections often requiredPreferential flow paths preventing uniform reactant distributionHigh costs of oxidantsPossible side effects such elevated levels of sulfate or trace metals
8 TCE Remediation Technologies In Situ Biological Treatment - soil, groundwaterAddition of a soluble carbon source or electron donor promotes reductive dechlorinationAdvantagesSimple to implement and equipment readily availableDisadvantagesMultiple rounds of injections often requiredPreferential flow paths prevent uniform distributionLong term implementation and monitoring often requiredPossible side effects such as elevated levels of arsenic, heavy metals and methane
9 TCE Remediation Technologies Soil vapor extraction (SVE) - soilExtraction of soil gas from the vadose zone using vacuum pumps and conventional wells followed by ex situ treatmentAdvantagesEasy to permit, design, operateLow startup costsDisadvantagesLong-term operation results in high total cost
10 TCE Remediation Technologies Thermal treatment - soil, groundwaterHeating of subsurface causing in situ destruction by pyrolysis, and/or followed by recovery of vapor or liquidAdvantagesHigh levels of contaminant removal, including DNAPL and from low permeability zonesDisadvantagesHigh technical skill requiredHigh cost, energy use, and carbon footprintIncomplete heating may result in untreated areasLarge number of vertical borings needed
11 Air Force Plant 4 Site 760 acre property Operated by government contractors since World War II for production of military aircraftTCE used for metals degreasingTCE source area present below Building 181 from former disposal pit and spillsPlume extending across site known as Eastern Parking Lot (EPL) plumeAdditional contaminants onsite, but this report focuses on Building 181 source areaEPA Record of Decision requiring remediation at the site
15 Treatment SelectionPump and treat - groundwater only. Conclusion: eliminated.Excavation - not feasible due to buildings on active facility. Conclusion: eliminated.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.In Situ Chemical Oxidation (ISCO) - cost estimate of $2,000,000. Less effective on DNAPL. Risk of non-uniform treatment. Conclusion: eliminated.In Situ Biological Treatment - cost estimate of $3,700,000 to $7,000,000. Ineffective on DNAPL. Conclusion: eliminated.
16 Treatment Selection Soil Vapor Extraction (SVE) Effective on highly permeable soil. Terrace Alluvium conductivity is 13 to 132 ft/day.Pilot test demonstrated effectiveness.Cost estimate based on pilot study: $612,000.Conclusion: selected due to demonstrated effectiveness and cost. However, unable to treat groundwater.
17 Treatment SelectionThermal Treatment - Electrical Resistive Heating (ERH)Installation of electrodes into subsurface. Electricity passing through soil generates heat, turning DNAPL and groundwater containing dissolved TCE into soil vapor.Soil vapor captured by SVE system and treated.Pilot test demonstrated effectiveness.Cost based on actual implementation: $2,500,000.Conclusion: selected due to demonstrated effectiveness. Cost comparable to other technologies considered.
18 ImplementationSVE system installed as an immediate response actionSVE system expanded2002 concentrations:Source area soil: up to 2770 mg/kg (cleanup goal of 11.5 mg/kg)Dissolved phase: up to 129 mg/L (cleanup goal of 10 mg/L)DNAPL still presentERH system implemented
19 ERH System 98 electrodes 14 temperature monitoring points (TMPs) 12 monitoring wellsAdditional SVE wells installedLinked to existing SVE system
23 Results Mean soil concentrations: 90% reduction to 0.184 mg/kg Mean groundwater concentrations: 88% reduction to 4.1 mg/L2008 Five Year Review - concentrations in groundwater rebounding to mg/L, exceeding cleanup goal
24 Lessons Learned Problem: DNAPL was not fully removed Reason: insufficient power (and thus heating) was applied to the subsurfaceRoot cause: reliance upon conductivity assessment from 2001 pilot study. Prior to full implementation in 2002, a full conductivity assessment was not conducted.Lack of sufficient pre-design work
25 What Now? Not feasible to re-install $2,500,000 ERH system ISCO and in situ biological treatment previously eliminated due to inability to treat large volume of DNAPL and costLikely effective in treating residual DNAPLCost reduced due to smaller treatment volume