Why the technology was selected:
Extraction of groundwater and vapors using EFR was selected to reduce the concentrations in soil and groundwater. The idea behind the use of EFR is to remove as much contamination in the shortest time possible to reduce the amount of chemicals added for in-situ chemical oxidation (ISCO). ISCO has been demonstrated at other sites to be an effective technology for the remediation of VOCs. The sandy soils at the site make ISCO particularly appropriate for this site. MNA will be utilized to further remediate contamination in groundwater following active remediation by ISCO and EFR.

Date implemented:
September 11, 2002.

Final remediation design:
EFR is accomplished by applying high levels of vacuum pressure to either monitoring wells or extraction wells through a drop tube applied near the static groundwater table in the well. Each EFR event was about 24 hours long. The EFR events use truck-mounted vacuum equipment and a tank capable of extracting 3,000 gallons. The combined air and liquids are transferred to a treatment system where the liquids are separated with a liquid scrubber/knockout system and discharged to a storage tank. Halogenated vapors are incinerated in a forced air Thermal Oxidation Unit. The extracted water is disposed offsite. ISOTEC's chemical oxidation process was used at the site. It is based on modified Fenton's chemistry using a proprietary catalyst/oxidizer mix (reagent) to produce free radical oxidants and reductants that attack chemical bonds. Injections were performed using both temporary direct push (DP) injection points as well as permanent monitoring wells. Based on the chemistry of the ISOTEC process, it is not necessary to add acids or pH modifiers. The initial Phase 1 pilot study (April 8, 2003 and April 22, 2003)concentrated on remediation of soil and groundwater within an approximate 50-ft elliptical radius centered on the former headwall location where most of the soil and groundwater contamination is concentrated. The target vertical treatment zone included unsaturated soils at the interval of 2-18 ft bgs, saturated soils between 18 and 50 ft bgs, and deeper fractured rock (up to 80 ft bgs). A total of 46 DP points with multiple injection intervals and 12 injection wells were used for the ISCO. Exact spacing is detemined by the concentrations of VOCs in soil and groundwater. Generally, the ISCO reagents were applied at 4-ft intervals in the unsaturated zone and 9-ft intervals in the saturated zone. The injection activity typically occurs under a low pressure condition between 15 and 40 psi, with a few locations noted to be as high as 60-100 psi due to localized tight geology. During the two phase ISCO pilot study (August 25, 2003 and September 25, 2003), 54,190 gallons of ISOTEC reagents were injected to further reduce contaminant concentrations where the Phase 1 pilot was done, and to treat selected hot spots downgradient of the drycleaner and deeper zones of groundwater contamination.

Other technologies used:
Enhanced Fluid Recovery (EFR). This is a remediation technology similar to SVE.

Results to date:
According to reports prepared by EFR contractor Fruits and Associates, Inc., approximately 190 gallons of solvents have been removed. A limited number of soil samples were taken following the Phase 1 ISCO pilot. No soil samples were taken following Phase 2. VOCs in two soil samples were reduced from 105 µg/kg and 87 µg/kg to non-detect in both soil samples. At least 30 days were allowed after the completion of each phase of the chemical injection prior to obtaining soil or groundwater samples. Following the Phase 1 pilot study, average VOCs in groundwater generally decreased by 83 percent based on groundwater samples from 9 monitoring wells compared to baseline concentrations taken April 2003 prior to the Phase 1 pilot study. Following the Phase 2 pilot study, average VOCs generally decreased by 89 percent based on the differences between baseline conditions measured in April 2003 and the post-Phase 2 groundwater samples from 6 wells. Results from well MW-29 are not included because VOCs increased from a baseline of 427 µg/l to 3,166 µg/l following the Phase 2 injection event. In well 5A, even though PCE concentrations dropped from a baseline of 5,500 µg/l to 100 µg/l following the Phase 1 pilot study, it was noted that the PCE concentration in this well had increased to 860 µg/l following the Phase 2 pilot study. Compared to baseline conditons, this still represents an 84 percent reduction in PCE following Phase 2 compared to baseline concentrations prior to any ISCO. The increases noted in wells MW-5A and MW-29 are attributed to desorption of solvents from soil. According to research utilizing Fenton's reagents, Fenton's reactions produce both oxidizing and reducing species. Reductive species are involved in desorbing contamination from VOCs sorbed on soil particles into a dissolved phase in the groundwater. Once the VOC contamination that was associated with the soil has been transferred to a dissolved phase, further ISCO treatments should be more effective in permanently reducing VOC concentrations in groundwater. To estimate the radial effects of influence from chemical injection, water bubbling and rising were observed in nearby monitoring wells. Based on the monitoring wells relative to the injection points, a conservative radial extent of treatment ranging between 5 and 10 ft was observed as reasonable for the site. This means that in areas with highest VOC concentrations, a tighter injection grid of 10 ft would be necessary between injection points while in other less contaminated areas, a 20-ft spacing between injection points would be satisfactory.

Next Steps:
For soils near the former headwall, EFR is being proposed for further treatment. This is the general area where both phases of the pilot study incorporating ISCO were done. The idea here is that ISCO has desorbed VOCs from soil in this area and the EFR should now be more effective in this area. EFR is also proposed for the soil underlying the area where the former drycleaning machines were located. ISCO was never performed under the building where PCE is greater than its cleanup standard of 0.5 mg/kg because of concern that fumes may be released in the building. Further full-scale ISCO is proposed for both the shallow and deeper groundwater aquifers. For the deeper aquifer, it will be necessary to use wells to inject the reagents because of limitations of the geoprobe equipment. For the shallower aquifer, injection points should be adequate in addition to wells. MNA will continue to be evaluated as a remediation technology following the application of the full scale ISCO.

Cost to Design and Implement:
Costs are currently being developed

Why the technology was selected:
Extraction of groundwater and vapors using EFR was selected to reduce the concentrations in soil and groundwater. The idea behind the use of EFR is to remove as much contamination in the shortest time possible to reduce the amount of chemicals added for in-situ chemical oxidation (ISCO). ISCO has been demonstrated at other sites to be an effective technology for the remediation of VOCs. The sandy soils at the site make ISCO particularly appropriate for this site. MNA will be utilized to further remediate contamination in groundwater following active remediation by ISCO and EFR.

Date implemented:
September 11, 2002.

Next Steps:
For soils near the former headwall, EFR is being proposed for further treatment. This is the general area where both phases of the pilot study incorporating ISCO were done. The idea here is that ISCO has desorbed VOCs from soil in this area and the EFR should now be more effective in this area. EFR is also proposed for the soil underlying the area where the former drycleaning machines were located. ISCO was never performed under the building where PCE is greater than its cleanup standard of 0.5 mg/kg because of concern that fumes may be released in the building. Further full-scale ISCO is proposed for both the shallow and deeper groundwater aquifers. For the deeper aquifer, it will be necessary to use wells to inject the reagents because of limitations of the geoprobe equipment. For the shallower aquifer, injection points should be adequate in addition to wells. MNA will continue to be evaluated as a remediation technology following the application of the full scale ISCO.

Cost to Design and Implement:
Costs are currently being developed