1. 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 & Remediation
November 2014

2. Contaminant Overview Trichloroethylene (TCE) Manmade chemical solvent
Colorless liquid with chemical formula C2Cl3H
Past uses: cosmetics, drugs, pesticides
Current uses: metals degreaser, adhesives, paints, varnishes

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

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

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

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

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

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

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

10. TCE Remediation Technologies
Thermal treatment - soil, groundwater
Heating of subsurface causing in situ destruction by pyrolysis, and/or followed by recovery of vapor or liquid
Advantages
High levels of contaminant removal, including DNAPL and from low permeability zones
Disadvantages
High technical skill required
High cost, energy use, and carbon footprint
Incomplete heating may result in untreated areas
Large 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 aircraft
TCE used for metals degreasing
TCE source area present below Building 181 from former disposal pit and spills
Plume extending across site known as Eastern Parking Lot (EPL) plume
Additional contaminants onsite, but this report focuses on Building 181 source area
EPA Record of Decision requiring remediation at the site

12. Air Force Plant 4

13. Source Area and EPL Plume
Building 181

14. Cross Section of Site

15. Treatment Selection
Pump 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 Selection
Thermal 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. Implementation
SVE system installed as an immediate response action
SVE system expanded
2002 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 present
ERH system implemented

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

20. ERH Example

21. ERH Example

22. ERH Example

23. Results Mean soil concentrations: 90% reduction to 0.184 mg/kg
Mean groundwater concentrations: 88% reduction to 4.1 mg/L
2008 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 subsurface
Root 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 cost
Likely effective in treating residual DNAPL
Cost reduced due to smaller treatment volume

26. Questions?