Why the technology was selected:
The aquifer is interconnected and relatively permeable, allowing for development of a recirculation cell. The Henry's Law constant for PCE is high, allowing it to be readily stripped from groundwater. The Density Driven Convection (DDC) technology controls vapor emissions at the well head, thereby eliminating concerns associated with the accumulation of fugitive soil vapors within the strip mall. SVE was selected to strip volatile organics from the unsaturated zone.

Date implemented:
October 1999

Final remediation design:
Eleven 4-inch-diameter DDC wells were installed. 5-ft-long lower screens were positioned just above bedrock; 5-ft upper screens were positioned between 20-25 ft bgs. The upper screens straddled the static water level. A bentonite seal was placed outside the well casing separating the two screened intervals. Approximately 10 scfm of air was injected into each well. The drop tubes were positioned approximately 15 ft below the static water level. Vapors produced within the wells were collected and directed through carbon prior to discharge to the atmosphere.

Results to date:
In 10 months, all dissolved PCE concentrations were reduced to levels below the 5 µg/L Rhode Island regulatory requirement. The system was turned off in August of 1999. Compliance monitoring was conducted to evaluate the potential for rebound. PCE concentrations remained below 5 µg/L for four quarters. The state of Rhode Island issued a No Further Action letter in the spring of 2000. The system was decommissioned in April of 2000.

Cost to Design and Implement:
$150,000 (estimated, for all technologies)

Why the technology was selected:
The aquifer is interconnected and relatively permeable, allowing for development of a recirculation cell. The Henry's Law constant for PCE is high, allowing it to be readily stripped from groundwater. The Density Driven Convection (DDC) technology controls vapor emissions at the well head, thereby eliminating concerns associated with the accumulation of fugitive soil vapors within the strip mall. SVE was selected to strip volatile organics from the unsaturated zone.

Date implemented:
October 1999

Final remediation design:
Eleven 4-inch-diameter DDC wells were installed. 5-ft-long lower screens were positioned just above bedrock; 5-ft upper screens were positioned between 20-25 ft bgs. The upper screens straddled the static water level. A bentonite seal was placed outside the well casing separating the two screened intervals. Approximately 10 scfm of air was injected into each well. The drop tubes were positioned approximately 15 ft below the static water level. Vapors produced within the wells were collected and directed through carbon prior to discharge to the atmosphere.

Results to date:
In 10 months, all dissolved PCE concentrations were reduced to levels below the 5 µg/L Rhode Island regulatory requirement. The system was turned off in August of 1999. Compliance monitoring was conducted to evaluate the potential for rebound. PCE concentrations remained below 5 µg/L for four quarters. The state of Rhode Island issued a No Further Action letter in the spring of 2000. The system was decommissioned in April of 2000.

Cost to Design and Implement:
$150,000 (estimated, for all technologies)

Why the technology was selected:
The aquifer is interconnected and relatively permeable, allowing for development of a recirculation cell. The Henry's Law constant for PCE is high, allowing it to be readily stripped from groundwater. The Density Driven Convection (DDC) technology controls vapor emissions at the well head, thereby eliminating concerns associated with the accumulation of fugitive soil vapors within the strip mall. SVE was selected to strip volatile organics from the unsaturated zone.

Date implemented:
October 1999

Final remediation design:
Eleven 4-inch-diameter DDC wells were installed. 5-ft-long lower screens were positioned just above bedrock; 5-ft upper screens were positioned between 20-25 ft bgs. The upper screens straddled the static water level. A bentonite seal was placed outside the well casing separating the two screened intervals. Approximately 10 scfm of air was injected into each well. The drop tubes were positioned approximately 15 ft below the static water level. Vapors produced within the wells were collected and directed through carbon prior to discharge to the atmosphere.

Results to date:
In 10 months, all dissolved PCE concentrations were reduced to levels below the 5 µg/L Rhode Island regulatory requirement. The system was turned off in August of 1999. Compliance monitoring was conducted to evaluate the potential for rebound. PCE concentrations remained below 5 µg/L for four quarters. The state of Rhode Island issued a No Further Action letter in the spring of 2000. The system was decommissioned in April of 2000.

Cost to Design and Implement:
$150,000 (estimated, for all technologies)