The overburden aquifer consists of a sand and two till layers. The overburden and bedrock aquifers are hydraulically connected and downward flow gradients have been noted in well clusters. Overburden groundwater flow over the entire site is migrating towards the south/southeast.
The groundwater flow in bedrock appears to take place largely in fracture zones which have a northeast/southwest orientation. Groundwater in bedrock apparently discharges to the unnamed tributary on site from both east and west of the tributary. Additionally, there exist a number of flowing bedrock wells.
Targeted Environmental Media:
 Fractured Bedrock
Not given.
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (Not given)
- Trichloroethene (Not given)
- Pumping Tests
- Pump and Treat
- Other (Monitored Natural Attenuation)
Comments:
Active groundwater extraction in both the shallow and deep aquifers began
in May 1995. In the former source area, only shallow groundwater required extraction and was initially performed as part of a dual vacuum extraction system. Shallow groundwater extraction was converted to an independent system of six wells when the soil remediation
was completed in November 1995. These wells remain operational today and are currently extracting groundwater at a combined flow rate of approximately 4,500 gallons per day. Bedrock groundwater extraction was performed in the downgradient condominium area from
wells LGAW and LGSW from May 1995 to July 1996, at which time EPA supported a temporary shutdown based on attainment of steady-state conditions. As a condition of the shutdown,
the PRPs performed monthly monitoring of VOC concentrations in wells LGAW and LGSW through February 2001, to confirm the persistence of steady-state conditions. At the time of operation, groundwater was extracted from wells LGAW and LGSW at an average combined flow rate of about 110,000 gpd.
TCE and PCE cleanup to 5 ug/L
EPA issued a comfort letter to Home Depot on October 31, 2000, and Home Depot began construction of a large retail building in December 2000 on the northeast corner of the site. A Staples was constructed adjacent to the Home Depot in 2003. During 2002, groundwater monitoring continued and EPA began preparing an Explanation of Significant Differences (ESD) to change the remedy from active pump and treatment to natural attenuation of the groundwater to achieve cleanup levels. The ESD was finalized in 2003. Construction of a 165 unit residential retirement development began on the site in January, 2004. A renewed Groundwater Management Zone (GMZ) permit was approved by the State of NH in November 2007 to ensure that the existing groundwater institutional controls remain in place until cleanup levels are achieved by monitored natural attenuation.
http://cfpub.epa.gov/supercpad/cursites/csitinfo.cfm?id=0101106
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