Remediation Status: In groundwater monitoring

Why the technology was selected:
Bioremediation was selected as a final active groundwater remedy to polish the remaining groundwater contamination that the pump & treat system had failed to remove. The pilot study objective was to determine if an anaerobic enviornment could be created to degrade the PCE to daughter products that would be degraded into innocuous products when they migrated into the aerobic portion of the aquifer.

Date implemented:
September 14 - November 5, 1998: Excavtion & onsite treatment of contaminated soil. December 8, 1999: Pump & treat system begins operation. May 2004: Enhanced bioremediation inititated.

Final remediation design:
The bioremediation system utilized recovered groundwater that was treated and then mixed with potassium lactate. The potassium lactate/groundwater solution was re-injected via the recovery trench system in order to create anaerobic conditions and degradet the contaminants via reductive dechlorination.

Results to date:
Enhanced bioremediation was conducted at the site from May 2004 until December 2007. Durng that time twelve (12) injection events of 60% potassium lactate solution were conducted. Potassium lactate injection volumes ranged from three (3) to twenty-four (24) gallons. Total potassium lactate injection volume for the project was 139 gallons. An estimated 90,000 gallons of groundwater was extracted, treated and re-injected during this period. The groundwater extraction system ran at an average rate of 0.97 gpm. Potassium lactate injection resulted in the the creation of PCE daughter products TCE, Cis 1,2-DCE and Trans 1,2-DCE in groundwater in the treatment area. Contaminants were not detected in concentrations exceeding cleanup target levels in groundwater samples collected during the last five consecutive groundwater monitoring events (February and July of 2007, January and March of 2008 and in January of 2009.

Next Steps:
A Site Rehabilitation Completion Order was issued for this site on August 7, 2009.

Cost to Design and Implement:
Soil excavation & treatment; 350,000 Other remedial efforts: 243,200

Why the technology was selected:
Pump & treat was initially selected to remediate contaminated groundwater at the site because the contaminant source area was small in size and a well vault had been installed during the excavation. The pump & treat system had a dual purpose: recover and treat contaminated groundwater and provide hydraulic containment of the contaminant plume.

Date implemented:
September 14 - November 5, 1998: Excavtion & onsite treatment of contaminated soil. December 8, 1999: Pump & treat system begins operation. May 2004: Enhanced bioremediation inititated.

Final remediation design:
A groundwater recovery system was installed via trench box (6 ft x 20 ft x 14 ft) at the base of the excavation to a total depth of 34 ft bgs into the top of a weathered limestone. Three sets of 20-foot horizontal 6-inch diameter perforated PVC pipes were installed in the trench box at depth of 34, 24 and 18 ft bgs. Both ends of the pipes were fitted with 6-inch risers and backfilled. The trench box was then lined with geotextile fabric and backfilled with #57 stone. The excavtion was then backfilled with treated soil. The pump and treat system consists of a Grunfos 5E5 submersible pump with a design flow rate of 4-5 gpm. The system was operated only during the wet season. Extracted water is treated with two 200-lb. liquid G.A.C. units. Design operating flow rate for the pump & treat system was 1.5 gpm. Treated groundwater was discharged to an infiltration gallery.

Next Steps:
A Site Rehabilitation Completion Order was issued for this site on August 7, 2009.

Cost to Design and Implement:
Soil excavation & treatment; 350,000 Other remedial efforts: 243,200

Why the technology was selected:
Pump & treat was initially selected to remediate contaminated groundwater at the site because the contaminant source area was small in size and a well vault had been installed during the excavation. The pump & treat system had a dual purpose: recover and treat contaminated groundwater and provide hydraulic containment of the contaminant plume.

Date implemented:
September 14 - November 5, 1998: Excavtion & onsite treatment of contaminated soil. December 8, 1999: Pump & treat system begins operation. May 2004: Enhanced bioremediation inititated.

Final remediation design:
A groundwater recovery system was installed via trench box (6 ft x 20 ft x 14 ft) at the base of the excavation to a total depth of 34 ft bgs into the top of a weathered limestone. Three sets of 20-foot horizontal 6-inch diameter perforated PVC pipes were installed in the trench box at depth of 34, 24 and 18 ft bgs. Both ends of the pipes were fitted with 6-inch risers and backfilled. The trench box was then lined with geotextile fabric and backfilled with #57 stone. The excavtion was then backfilled with treated soil. The pump and treat system consists of a Grunfos 5E5 submersible pump with a design flow rate of 4-5 gpm. The system was operated only during the wet season. Extracted water is treated with two 200-lb. liquid G.A.C. units. Design operating flow rate for the pump & treat system was 1.5 gpm. Treated groundwater was discharged to an infiltration gallery.

Results to date:
The pump & treat system operated intermittently (during the wet season) from December 8, 1999 to November 7, 2002. Total operation time during that period was approximately 18.5 months. Average pumping rate was 0.93 gpm. The highest contaminant influent concentration detected was 660 ug/l PCE. The sytem recovered and treated over 600,000 gallons of contaminated groundwater. Operating flow rate for the pump & treat system is approximately 1.5 gpm. The system is operated only during the wet season. Initial influent concentrations for the pump & treat system were as high as 660 µg/L PCE. During the latest operation period, influent concentrations were as high as 440 µg/L PCE. Through December 2, 2001, a total of 392,381 gallons of water had been treated by the system. Contaminants were not detected in concentrations exceeding cleanup target levels in groundwater samples collected during the last five consecutive groundwater monitoring events (February and July of 2007, January and March of 2008 and in January of 2009.

Next Steps:
A Site Rehabilitation Completion Order was issued for this site on August 7, 2009.

Cost to Design and Implement:
Soil excavation & treatment; 350,000 Other remedial efforts: 243,200

Why the technology was selected:
Excavation was selected over soil vapor extraction because the building that housed the drycleaning operation had been razed and the contaminated soil was accessible to excvation.

Date implemented:
September 14 - November 5, 1998: Excavtion & onsite treatment of contaminated soil. December 8, 1999: Pump & treat system begins operation. May 2004: Enhanced bioremediation inititated.

Final remediation design:
Soil Excavation & Treatment: Sheet piling was utilized to stablize the northern boundary of the property. A total of 3,250 cubic yards of soil was excavated ( 30 ft x 30 ft x 20 ft bgs) with a 2:2 slope - total excavated area 70 ft x 110 ft. Soil with detectable levels of PCE was stockpiled in a bermed area with a leachate collection system. Parallel 4-inch screened PVC pipes were installed horizontally, 1 foot from the bottom of the treatment pile with valves installed on both ends of the piping to allow vacuum or a passive vent to the atmospher to be applied to the soil pile. SVE pipes were then alternated between passive air, air recovery, and air injection points. Two 4-inch diameter pipes were installed along the length of the pile 5 feet from the bottom of the pile. The treatment pile continaed approxiamtley 1,750 cubic yards of soil (108 ft x 40 ft x 8 ft). The pile was covered with visqueen to prevent short circuiting frm teh atmosphere. Longitudinal piping was used for air input and the transverse pipes were used for air recovery. During the treatment period, air input and recovery pies were alternated. Recovered leachate was treated using air strippers and then discharged to an exfiltration gallery.

Results to date:
Excavation began 9/14/98. Onsite soil treatment 9/30/98 to 11/5/98.

Next Steps:
A Site Rehabilitation Completion Order was issued for this site on August 7, 2009.

Cost to Design and Implement:
Soil excavation & treatment; 350,000 Other remedial efforts: 243,200