Why the technology was selected:
Most effective, feasible methods to remove the source, and to inhibit further migration of chlorinated compounds in groundwater. Access limitations and the low permeability of the silty clay unit influenced this decision. The carbon amendment technology requires little maintenance, and can be readily implemented. Carbon injection can be initiated at a slow rate, and the effects can be monitored to assess the adequacy of the injection rates utilized.

Final remediation design:
PCE-impact soil, to a depth of 14 ft. bgs., was excavated and transported to a landfill. Contactors encountered groundwater, from precipitation and surface run-in during excavation or from the sand-seam that was penetrated, during the soil removal activity and pumped and discharged it to the sanitary sewer. Contractors used carbon injections (molasses) to promote enhanced reductive dechlorination of PCE. 182 Geoprobe injection points were used in a grid-like pattern across the estimated area of impact, sited to intersect the sand seam (12-17 ft. bgs.). A Geoprobe rod was initially used as a well screen and riser for injection of the dilute molasses solution. After 15 Geoprobe borings had been completed, the rod was replaced with a 1-inch temporary PVC pipe. Bentonite pellets were then used to seal the temporary wells. 15-25 gal. of molasses and 25 gal. of water/gal. of molasses were injected during the first event. 10 wells were installed after the first event to facilitate performance monitoring within limits of the plume. 5 follow-up injections of the same size were completed over a six-month period.

Results to date:
Soil removal: Contractors removed 3,125 tons of soil, and disposed of it in an off-site landfill. PCE concentrations were below the soil RCL of 25 mg/kg following the excavation. Groundwater Remediation: Sampling results taken from a 20-month period following completion of soil remediation activities and the initial carbon injection event reveal PCE concentrations at non-detectable levels. An expected increase in PCE breakdown products, such as cis-1,2-DCE and vinyl chloride (VC), occurred. VC concentrations ranged from 0.37 µg/L to 88 µg/L, TCE concentrations occurred at 15 µg/L, and cis-1,2-DCE occurred at 300 µg/L. Observed concentrations of these PCE breakdown products over time suggested that residual contaminant levels would steadily decrease as the reductive dechlorination process continued. Concentrations of the non-toxic, innocuous end-products of dechlorination, ethane and ethene, were detected in four monitoring wells at approximately 1-2 orders of magnitude higher than the ethane and ethene concentrations in wells on the fringe of the plume. This was viewed as evidence that the reductive dechlorination process was going to completion. Site is now closed.

Next Steps:
Site was closed Oct. 4, 2001 without the need for institutional controls. This site did NOT qualify for reimbursement under the WI Dry Cleaner Environmental Response Program (DERP).

Cost to Design and Implement:
$1,150,000 for all technologies

Why the technology was selected:
Most effective, feasible methods to remove the source, and to inhibit further migration of chlorinated compounds in groundwater. Access limitations and the low permeability of the silty clay unit influenced this decision. The carbon amendment technology requires little maintenance, and can be readily implemented. Carbon injection can be initiated at a slow rate, and the effects can be monitored to assess the adequacy of the injection rates utilized.

Final remediation design:
PCE-impact soil, to a depth of 14 ft. bgs., was excavated and transported to a landfill. Contactors encountered groundwater, from precipitation and surface run-in during excavation or from the sand-seam that was penetrated, during the soil removal activity and pumped and discharged it to the sanitary sewer. Contractors used carbon injections (molasses) to promote enhanced reductive dechlorination of PCE. 182 Geoprobe injection points were used in a grid-like pattern across the estimated area of impact, sited to intersect the sand seam (12-17 ft. bgs.). A Geoprobe rod was initially used as a well screen and riser for injection of the dilute molasses solution. After 15 Geoprobe borings had been completed, the rod was replaced with a 1-inch temporary PVC pipe. Bentonite pellets were then used to seal the temporary wells. 15-25 gal. of molasses and 25 gal. of water/gal. of molasses were injected during the first event. 10 wells were installed after the first event to facilitate performance monitoring within limits of the plume. 5 follow-up injections of the same size were completed over a six-month period.

Results to date:
Soil removal: Contractors removed 3,125 tons of soil, and disposed of it in an off-site landfill. PCE concentrations were below the soil RCL of 25 mg/kg following the excavation. Groundwater Remediation: Sampling results taken from a 20-month period following completion of soil remediation activities and the initial carbon injection event reveal PCE concentrations at non-detectable levels. An expected increase in PCE breakdown products, such as cis-1,2-DCE and vinyl chloride (VC), occurred. VC concentrations ranged from 0.37 µg/L to 88 µg/L, TCE concentrations occurred at 15 µg/L, and cis-1,2-DCE occurred at 300 µg/L. Observed concentrations of these PCE breakdown products over time suggested that residual contaminant levels would steadily decrease as the reductive dechlorination process continued. Concentrations of the non-toxic, innocuous end-products of dechlorination, ethane and ethene, were detected in four monitoring wells at approximately 1-2 orders of magnitude higher than the ethane and ethene concentrations in wells on the fringe of the plume. This was viewed as evidence that the reductive dechlorination process was going to completion. Site is now closed.

Next Steps:
Site was closed Oct. 4, 2001 without the need for institutional controls. This site did NOT qualify for reimbursement under the WI Dry Cleaner Environmental Response Program (DERP).

Cost to Design and Implement:
$1,150,000 for all technologies

Why the technology was selected:
Most effective, feasible methods to remove the source, and to inhibit further migration of chlorinated compounds in groundwater. Access limitations and the low permeability of the silty clay unit influenced this decision. The carbon amendment technology requires little maintenance, and can be readily implemented. Carbon injection can be initiated at a slow rate, and the effects can be monitored to assess the adequacy of the injection rates utilized.

Final remediation design:
PCE-impact soil, to a depth of 14 ft. bgs., was excavated and transported to a landfill. Contactors encountered groundwater, from precipitation and surface run-in during excavation or from the sand-seam that was penetrated, during the soil removal activity and pumped and discharged it to the sanitary sewer. Contractors used carbon injections (molasses) to promote enhanced reductive dechlorination of PCE. 182 Geoprobe injection points were used in a grid-like pattern across the estimated area of impact, sited to intersect the sand seam (12-17 ft. bgs.). A Geoprobe rod was initially used as a well screen and riser for injection of the dilute molasses solution. After 15 Geoprobe borings had been completed, the rod was replaced with a 1-inch temporary PVC pipe. Bentonite pellets were then used to seal the temporary wells. 15-25 gal. of molasses and 25 gal. of water/gal. of molasses were injected during the first event. 10 wells were installed after the first event to facilitate performance monitoring within limits of the plume. 5 follow-up injections of the same size were completed over a six-month period.

Results to date:
Soil removal: Contractors removed 3,125 tons of soil, and disposed of it in an off-site landfill. PCE concentrations were below the soil RCL of 25 mg/kg following the excavation. Groundwater Remediation: Sampling results taken from a 20-month period following completion of soil remediation activities and the initial carbon injection event reveal PCE concentrations at non-detectable levels. An expected increase in PCE breakdown products, such as cis-1,2-DCE and vinyl chloride (VC), occurred. VC concentrations ranged from 0.37 µg/L to 88 µg/L, TCE concentrations occurred at 15 µg/L, and cis-1,2-DCE occurred at 300 µg/L. Observed concentrations of these PCE breakdown products over time suggested that residual contaminant levels would steadily decrease as the reductive dechlorination process continued. Concentrations of the non-toxic, innocuous end-products of dechlorination, ethane and ethene, were detected in four monitoring wells at approximately 1-2 orders of magnitude higher than the ethane and ethene concentrations in wells on the fringe of the plume. This was viewed as evidence that the reductive dechlorination process was going to completion. Site is now closed.

Next Steps:
Site was closed Oct. 4, 2001 without the need for institutional controls. This site did NOT qualify for reimbursement under the WI Dry Cleaner Environmental Response Program (DERP).

Cost to Design and Implement:
$1,150,000 for all technologies