The Tinkham's Garage site encompasses 375 acres in Londonderry. The site is bounded by Route 102 to the north, Gilcreast Road to the east, Ross Drive to the southeast, and an unnamed tributary to Beaver Brook to the west.
Areas of the site were used during the 1970s for the disposal of liquid hazardous wastes, including organic solvents and waste oils. In late 1982 and early 1983, several private drinking water wells, surface water, and soils on the site were found to be contaminated with a variety of volatile organic compounds (VOCs). Concentrations of contaminants in the water were sufficient to require the closing of several private wells and the well supplying the Woodland Village Condominiums in early 1983. In September 1983, the site was placed on the National Priorities List.
In 1983, the State and EPA installed a permanent water line from the neighboring Town of Derry, which provided a municipal water supply to all the residences originally shown to have contaminated well water. The remedial investigation/feasibility study was completed in early 1986. EPA signed a Record of Decision (ROD) on the cleanup plan in September 1986, and an Amended ROD (AROD) in March 1989. The AROD called for treatment of contaminated groundwater and soil.
Soil and groundwater remediation commenced in 1995. Soil remedial activities included the processing of contaminated soils in the garage and condominium areas. Soils were treated by an in-situ dual vacuum extraction system that was designed to simultaneously pump groundwater and extract soil vapor. Groundwater remedial activities involved pumping contaminated groundwater from existing bedrock wells located in the condominium area. However, due to achievement of steady-state VOC concentrations in bedrock groundwater, pumping of bedrock wells was discontinued in July 1996.
In June 2002, the potentially responsible parties (PRPs) submitted a Groundwater Management Permit (GMP) application to DES, and the shallow groundwater pumping systems were shutdown. On October 30, 2002, DES issued a GMP that required implementing institutional controls to restrict the use of groundwater within a defined area designated as the Groundwater Management Zone (GMZ). In accordance with the GMP, the PRPs conduct semi-annual groundwater monitoring.
Home Depot Inc. purchased a clean parcel of the site on Route 102 and built a retail facility on the property during the summer and fall of 2002. Remaining portions of the 375 acre site have since been developed into elderly residential housing. These development activities have not had an adverse affect on the clean up of the site.
EPA and DES conducted a quality assurance/quality control audit of the sampling and analysis program at the Tinkham Garage site in 2007. Also, the existing GMP was renewed in the fall of 2007. DES continues to assist EPA in review of the Annual Groundwater Management Permit Report to ensure PRP compliance with GMP requirements.
The third Five-Year Review Report for the site was finalized and released March 2009. Recommendations and follow-up actions noted in the report called for development and implementation of a work plan to assess the nature and extent of 1,4-dioxane contamination in groundwater at and adjacent to the site.
A work plan was finalized in August 2009. The goal of the work plan was to determine if 1,4-dioxane is present at the boundaries of the site and to monitor residential water supply wells located south of the site. In November 2009, the PRP contractor collected samples from the site and nine residential water supply wells. The presence of 1,4-dioxane was not identified at levels in excess of the laboratory specific method detection limit in the nine residential wells.
The Groundwater Management Permit for the site was renewed on December 28, 2012. The permit-required groundwater sampling program remains unchanged with sampling events scheduled for May and November each year and an Annual Groundwater Summary Report to be submitted in January each year.
The next scheduled Five-Year Review will be in 2014. The PRP contractor recently conducted evaluations of three representative bedrock monitoring wells to identify the relative contributions of individual fracture zones within those wells. A report of these evaluations will be forthcoming in the summer of 2014.