The Watertown Arsenal Former GSA Property (the Site), Formerly Used Defense Site (FUDS) Project Number D01MA0019_02, is located at 670 Arsenal Street, Watertown, Massachusetts. A 20-25 ft tall retaining wall (northwest side) and chain link fence surround the Site. The southwestern portion of the site, including the compensatory wetlands, is drained by Sawins Pond Brook, flowing eastward toward the Charles River. The northeastern portion of the site, including the Soil Cover area, is drained by a manmade ditch and catch basin that discharges to the Charles River under Greenough Avenue. Currently, the site contains vacant land classified as high to medium density residential due to nearby apartment buildings. 

The parcel was filled to facilitate development during World War II and was subsequently used by the U.S. Army and by the GSA for storing various materials and equipment.  The 11.91-acre GSA Property parcel was part of the former U.S. Army Watertown Arsenal.  The GSA also leased portions of the property to various parties.  A ‘burn area’ was constructed in the northern portion of the property for scrap depleted uranium (DU) waste generated from machining operations at the former Watertown Arsenal. The NRC issued the U.S. Army a license in 1961 for processing the DU within an area at the site referred to as the former burn box area. Within this burn area, DU chips and turnings were coated with oil, placed in a drum, transferred to the site, and placed in a burn box located on a concrete pad surrounded by a chain link fence. The DU material was burned to convert the DU metal into a more chemically stable form. When the burn box container was full, it was welded shut and shipped off-site for appropriate disposal. A new burn box was then placed on the concrete pad. Investigations conducted between 2007 and 2010 identified polychlorinated biphenyls (PCBs) and dioxin in site soil centered on the former burn box. It is suspected that the oil used to coat the DU chips may have contained PCBs. The dioxins may be a result of partially combusted, PCB-containing oil from the burning process. Structures related to former site operations were removed as part of the remedy.

In 2011, a Human Health Risk Assessment (HHRA) characterized potential human health risks associated with future use of the Site as a passive recreational area. The HHRA concluded the Polychlorinated Biphenyl (PCB) Impacted Area could pose risks to human health on presumed exposure to PCBs, antimony, lead, and nickel. An Environmental Risk Assessment occurred after the HHRA.

The Decision Document’s Remedial Action Objective (RAO) is to reduce human health and ecological risks associated with exposure to PCBs, dioxin, and metals in the PCB Impacted Area. The selected remedy included excavating and transporting offsite fill material with PCBs, constructing a soil cover over residual PCB-contaminated fill material, wetland replication (referred to Compensatory Wetlands), and institutional controls. The site achieved construction completion with the completion of the Remedial Action Closeout Report on 30 September 2014. The United States Army Corps of Engineers (USACE) constructed the remedy in accordance with the 2012 Decision Document requirements and the 2013 Remedial Action Work Plan.  Since completion, the USACE has overseen the long term monitoring and completion of the first Five Year Review in 2018. A Grant of Environmental Restriction and Easement (GERE), which includes land use controls limiting site and intrusive activities was also completed.