Site Name: TOWN GARAGE/RADIO BEACON
EPA ID: NHD981063860 EPA Region: 01 Metro Statistical Area: 4760
HOLTON CIRCLE, LONDONDERRY, NH 03053
Operable Unit: 01
ROD ID: EPA/ROD/R01-92/070 ROD Date: 09/30/92
Contaminant: VOCs
Keys: Alternate Water Supply; Carcinogenic Compounds; Chromium; Clean Air Act; Clean Water Act; Contingent Remedy; Direct Contact; Drinking Water Contaminants; Ground Water; Ground Water Monitoring; Institutional Controls; MCLGs; MCLs; Metals; O&M; Safe Drinking Water Act; Solidification/Stabilization; Solvents; State; Standards/Regulations; VOCs; Wetlands
Abstract:
SITE HISTORY/DESCRIPTION: The Town Garage Radio Beacon, NH, site includes the Holton Circle residential development of 23 homes, a town garage area, and an undeveloped hillslope and wetlands area in Londonderry, New Hampshire. Excluding the town garage, land use in the area is predominantly residential. Drinking water is obtained via private bedrock wells, with the exception of nine residents on Holton Circle and residents of the adjacent Isabella Drive development who are connected to a public water supply. The underlying aquifer is a Class IIb aquifer, a potential source of drinking water. From 1940 to 1968, the area was owned by the Department of Defense (DOD), who reportedly used it as a radio beacon facility from 1940 and 1947. In 1968, the property was transferred to the Town of Londonderry. Eight acres of the property were used as a garage to store town vehicles, along with road sand and salt, and to perform routine maintenance on the vehicles; 12 more acres were given to the Londonderry Housing and Redevelopment Authority. Site contamination was discovered in 1984 when Holton Circle residents requested that the state sample their bedrock wells. Resulting investigations showed VOCs at levels above federal and state drinking water standards. The state has continued to monitor the wells onsite and notes that decreasing concentrations of 1,1,1-TCA and increasing concentrations of 1,1-DCE and 1,1-DCA demonstrate that a degradation process is occurring. This ROD addresses a final remedy for the contaminated ground water onsite. No other remedial actions are anticipated for the site. The primary contaminants affecting the ground water are VOCs.
PERFORMANCE STANDARDS OR GOALS: Chemical-specific interim ground water clean -up levels are based on SDWA MCLGs and state standards and include 1,1-DCE 7 ug/l; 1,1,1-TCA 200 ug/l; antimony 6 ug/l; beryllium 4 ug/l; chromium 100 ug/l; and barium 2,000 ug/l. Three years after these levels have been achieved, a risk assessment will be performed to determine whether the levels are protective and, therefore, should be final.
INSTITUTIONAL CONTROLS: Institutional controls in the form of property deed restrictions or local zoning ordinances will be implemented to restrict future ground water use in the town garage and undeveloped hillslope areas. A drainage restriction also will be employed at the town garage to prevent future releases to the ground water.
Remedy:
SELECTED REMEDIAL ACTION: The selected remedial action for this site includes allowing the contaminated ground water in the overburden and bedrock aquifers to naturally attenuate; implementing institutional controls including deed restrictions to prevent future use of ground water; monitoring ground water; and implementing a contigency remedy to provide an alternate water supply to affected residences in the event that contaminants into the drinking water wells reverse their historical trend and concentrations begin to increase beyond the clean-up levels. There are no capital costs associated with this remedy; however the estimated present worth O&M cost for this remedial action is $1,250,000.