The Sylvester site is a 28-acre property in Nashua, New Hampshire that was once a sand borrow pit. Between the late 1960s and 1979, over 800,000 gallons of organic solvents and other hazardous liquids were dumped there illegally. The site was added to the National Priorities List (NPL), the federal government's list of the most contaminated sites in the country, on September 8, 1983.
The dumping left soil and groundwater contaminated with 28 identified chemicals. These include volatile organic compounds (VOCs) such as benzene, toluene, trichloroethene, and tetrachloroethene, along with chlorinated solvents like chloroform and dichloromethane, and arsenic and other metals. Without cleanup, contaminated groundwater would have threatened drinking water quality for communities in Massachusetts and caused fish kills in the Nashua River.
Cleanup was organized in phases. In 1982, EPA built a slurry wall, a vertical engineered barrier extending down to bedrock, around the 20-acre contamination zone and installed a cap to keep surface water from seeping in. EPA also removed 1,314 drums from the site, and the City of Nashua extended municipal water to the area. A groundwater treatment plant then ran from 1985 to 1996, pulling out 300 gallons per minute, treating it to remove contaminants, and returning clean water to the contained area. That facility destroyed more than 216 tons of VOCs and removed over 90% of contamination before shutting down in December 1996. All remedial construction was completed on April 8, 1992, and the site reached sitewide ready-for-anticipated-reuse status on April 7, 2016.
Today, the site has no current risk to public health or the environment. Human exposure is under control, and contaminated groundwater migration is stabilized with no unacceptable discharge to surface water. The State of New Hampshire monitors groundwater, surface water, and sediment on an annual or biennial basis. Institutional controls, including zoning restrictions, remain in place to prevent land uses that could disturb cleanup components. EPA completed its seventh five-year review on August 28, 2024, confirming that response actions continue to protect human health and the environment in the short term. That review also noted the need to consider adding PFAS compounds as contaminants of concern and updating the groundwater monitoring plan. The site remains on the NPL and has not been deleted.
Community members with questions can contact EPA's Community Involvement Coordinator, Aaron Shaheen, by email or phone. The Remedial Project Manager, Elizabeth Milano, handles technical and cleanup questions. The New Hampshire Department of Environmental Services also maintains involvement through a state contact. Site records are available for public review at the EPA Region 1 office in Boston and at the New Hampshire Department of Environmental Services in Concord.
