New London Submarine Base

Overview

New London Submarine Base sits on 576 acres along the eastern bank of the Thames River in Groton and Ledyard, Connecticut. The U.S. Navy has operated the base for submarine operations, and waste from those activities contaminated soil, sediment, and groundwater across multiple disposal areas, including three landfills, chemical storage sites, and tank farms. The site was added to the National Priorities List (NPL) on August 30, 1990, meaning the federal government formally identified it as a priority cleanup location under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).

Contaminants found at the site include heavy metals such as arsenic, lead, cadmium, and mercury, as well as volatile organic compounds (VOCs) like trichloroethene and benzene. Polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pesticides including DDT and dieldrin, and dioxins have also been detected. These contaminants appear in soil, groundwater, surface water, sediment, and solid waste across more than a dozen distinct areas of the base. From 1957 to 1973, waste including spent battery acids and pesticides was buried below the water table in an 11-acre landfill near wetlands, which became a major concern.

The U.S. Navy leads the investigation and cleanup, with oversight from the EPA and the Connecticut Department of Energy and Environmental Protection (DEEP). The site has been divided into 16 operable units, each targeting a specific area or contamination type. Of 40 originally identified sites, 39 have been cleaned up or closed. All three landfills have been capped, contaminated soil and sediment have been excavated, and eight removal actions have been completed. Several operable units have finished remedial action, including the Area A Landfill, Torpedo Shops, and Area A Wetland. Others remain in operation and maintenance phases. Four operable units, covering Sites 26, 27, 28, and Sites 10 and 11, do not yet have decision documents, with estimated decisions expected between September and November 2027. The Navy also completed a preliminary assessment for per- and polyfluoroalkyl substances (PFAS) in 2020, and that investigation is ongoing.

Human exposure is currently under control, with no unacceptable exposure pathways identified. Groundwater contamination migration has been stabilized. Institutional controls restrict the site to industrial use only, prohibit residential development, and require ongoing groundwater and sediment monitoring. The most recent five-year review was completed on December 17, 2021, and the next is estimated between December 2026 and February 2027. Construction is not yet complete across the entire site, and it has not been removed from the NPL.

Community members can stay involved through the Navy's Restoration Advisory Board, which holds public meetings on cleanup activities. The Navy also issues a newsletter about environmental cleanup at the base. Site records are available at the EPA Superfund website, the Town of Groton Public Library, Bill Library in Ledyard, and the Naval Submarine Base Public Works Office in Groton.