Dual Vapor Extraction at Tinkham's Garage Superfund Site, Londonderry, NH

Site Name:

Tinkham's Garage Superfund Site

Location:

Londonderry, NH

Period of
Operation:

November 22, 1994 to September 29, 1995

Cleanup
Type:

Full scale

Vendor:

Joleen Kealey
Project Manager
Terra Vac, Inc.
213 Rear Broadway
Methuen, MA 01844
Tel: (978) 688- 5280

Technology:
Dual Vapor Extraction (DVE)

- 33 DVE wells divided into 25 shallow DVE wells, screened in the overburden, and 8 deep DVE wells, screened in the upper bedrock and overburden; five existing pilot test wells were left in place and used for vapor extraction; the wells were distributed over three manifold lines
- SVE vacuum at blower - 5 in Hg (=68 in WC)
- SVE flow rate - 500 scfm, average
- Vapors treated using activated carbon; recovered groundwater treated using air stripping to meet the Derry POTW pre-treatment standards; off-gas from air stripper treated using vapor phase carbon

Cleanup Authority:
CERCLA
- ROD signed 1985
- ROD amended March 1989

EPA RPM:
James DiLorenzo
U.S. EPA Region 1 (MC:HBO)
One Congress Street, Suite 1100
Boston, MA 02114- 2023
Tel: (617) 918-1247
E-mail: dilorenzo.jim@epa.gov
Additional Contacts:
None

Contaminants:
Chlorinated Solvents
- Tetrachloroethene (PCE) and trichloroethene (TCE)
- Site investigations found total VOCs as high as 652 ppm in soil and 42 ppm in groundwater

Waste Source:
Discharges of liquids and sludge to surface soils

Type/Quantity of Media Treated:
Soil and Groundwater/9,000 cubic yards of soil treated
- Overburden consisting of inorganic and organic silty clay and sand grading to fine and medium-grained sand; weathered metamorphic bedrock at approximately 14 feet bgs
- Depth to groundwater - 5 to 6 feet bgs
- Hydraulic conductivity - range 1 ft/d to 10 ft/d

Purpose/Significance of Application:
Use of DVE to treat soil and groundwater contaminated with chlorinated solvents, including PCE and TCE

Regulatory Requirements/Cleanup Goals:
- ROD specified 1 ppm total VOCs for soil and 5 ppb each for PCE and TCE in groundwater

Results:
- Soil cleanup goals were achieved within ten months of operation; groundwater cleanup goals were not achieved at the conclusion of DVE system operation and pump-and-treat has been implemented as the site
- Approximately 53 pounds of VOCs were removed by the DVE system:
- vapor extraction removed approximately 48 pounds; averaging 0.17 pounds per day
- groundwater extraction removed approximately 5 pounds of VOCs (recovered in the aqueous phase); averaging 0.016 pounds per day
- The majority of VOCs recovered were PCE and TCE
- VOCs extracted in the vapor phase were reduced from concentrations as high 16 ppm to below 1 ppm (the soil cleanup goal)
- Concentrations of VOCs in groundwater in the source area decreased by over 99% in one well and by 64% in a second well. However, total VOCs concentrations in groundwater remained above the cleanup goals and ranged from 29 to 237 ppb in the source area

Cost Factors:
- The actual cost for the project, not including permitting and oversight, was $1.5 million, or $170/cy (based on 9,000 cy of soil treated).
- This cost includes an adjustment for inflation

Description:
The Tinkham's Garage Superfund site includes 375 acres of residential and undeveloped land in Londonderry, NH. Site investigations in 1981 found soil and groundwater contaminated with VOCs, including PCE, and TCE, resulting from unauthorized surface discharges of liquids and sludge in 1978 and 1979. Several source areas were identified at the site including areas near a condominium complex and a one acre area located behind Tinkham's Garage ("Garage Area"). The original 1985 ROD for the site specified excavation of contaminated soil with onsite treatment by either thermal aeration, composting, or soil washing. As a result of the pre-design and pilot studies, the ROD was amended in March 1989 to require the treatment of contaminated soil by DVE. For cost purposed, VOC impacted soil was consolidated for treatment. Contaminated soil from the various areas at the site was excavated and hauled to the Garage Area, where it was and spread and compacted in place.

The DVE system consisted of 33 DVE wells divided into 25 shallow DVE wells, screened in the overburden, and 8 deep DVE wells, screened in the upper bedrock and overburden. Five existing pilot test wells were left in place and used for vapor extraction. The wells were distributed over three manifold lines to provide the greatest coverage over the area of contamination. After 10 months of operation, approximately 53 pounds of VOCs were removed by the DVE system, with SVE removing about 48 pounds and groundwater extraction removing about 5 pounds. The soil cleanup goals were achieved. VOCs extracted in the vapor phase were reduced from concentrations as high as 16 ppm to below 1 ppm (the soil cleanup goal). However, total VOCs concentrations in groundwater remained above the cleanup goals. According to Terra Vac, DVE was not intended to achieve groundwater remediation goals; rather the extraction and treatment of groundwater was necessary to target and remediate soil contamination located within the saturated zone. A pump and treat system is currently operating at the site to provide a long term migration control remedy for groundwater. The actual cost to treat the soil was $1.5 million, or $170/cy (based on 9,000 cy of soil treated).