Results of a monitoring program of continuous water levels and physical water properties at the Operable Unit 1 area of the Savage Municipal Well Superfund site, Milford, New Hampshire, water years 2000-03

The Milford-Souhegan glacial-drift (MSGD) aquifer, in south-central New Hampshire, is an important source of industrial, commercial, and domestic water. The MSGD aquifer was also an important source of drinking water for the town of Milford until it was found to contain high concentrations of volatile organic compounds (VOCs) in the Savage and Keyes municipal-supply wells in the early 1980s. A VOC plume was found to cover part of the southwestern half of the MSGD aquifer. In September 1984, the site was designated a Superfund site, called the Savage Municipal Well Superfund site. The primary source area of contaminants was a former tool manufacturing facility (called the OK Tool facility, and now called the Operable Unit 1 (OU1) area) that disposed of solvents at the surface and in the subsurface. The facility was closed in 1987 and removed in 1998. A low-permeability containment barrier wall was constructed and installed in the overburden (MSGD aquifer) in 1998 to encapsulate the highest concentrations of VOCs, and a pump-and-treat remediation facility was also added. Remedial operations of extraction and injection wells started in May 1999.

A network of water-level monitoring sites was implemented in water year 2000 (October 1, 1999, through September 30, 2000) in the OU1 area to help assess the effectiveness of remedial operations to mitigate the VOC plume, and to evaluate the effect of the barrier wall and remedial operations on the hydraulic connections across the barrier and between the overburden and underlying bedrock. Remedial extraction and injections wells inside and outside the barrier help isolate ground-water flow inside the barrier and the further spreading of VOCs. This report summarizes both continuous and selected periodic manual measurements of water level and physical water properties (specific conductance and water temperature) for 10 monitoring locations during water years 2000-03. Additional periodic manual measurements of water levels were made at four nearby monitoring wells. Water levels are referenced to periods of remedial extraction and injection operations.

Remedial extraction inside the barrier in the overburden causes water-level drawdowns in interior (inside the barrier) monitoring wells but also exterior (outside the barrier) monitoring wells. Drawdowns were observed in the following descending sequence at: interior overburden wells, interior underlying bedrock wells, exterior underlying bedrock wells, and exterior overburden wells.