A 3.7-mile stretch of the Lower Neponset River in Boston and Milton, Massachusetts is listed on the National Priorities List (NPL), the federal registry of the most contaminated sites in the country. The NPL listing happened in March 2022. The main concern is polychlorinated biphenyls (PCBs) in river sediment. PCBs are industrial chemicals linked to health and ecological risks. EPA is leading the cleanup work and has divided it into phases.
Phase 1 covers the river from the confluence of Mother Brook to the Tileston and Hollingsworth Dam. Sampling for Phase 1 finished in November 2023. EPA then completed a final Engineering Evaluation and Cost Analysis report to look at cleanup options. A public comment period on the preferred cleanup plan ran from June 13 to August 1, 2025, and a virtual public hearing took place on July 9, 2025. Phase 2 sampling covers the area downstream to the Walter Baker Chocolate Dam and is expected to wrap up in 2025.
The Remedial Investigation (RI) involves collecting sediment cores, testing water quality, sampling fish and mussels for tissue analysis, characterizing the ecology, and testing floodplain soil. EPA has stated that human exposure to contamination is not yet under control because there is not enough data and the response only recently began. The Massachusetts Department of Public Health has issued a Freshwater Fish Consumption Advisory and a Recreational Use Fact Sheet because people still fish along the river and the PCB contamination likely poses risks to both human health and the environment.
Two short-term removal actions are also underway alongside the main investigation. One is at the Lewis Chemical removal site and the other is the Riverside Square PCBs removal investigation. These are targeted actions meant to address specific contamination sources while the broader cleanup planning continues.
Community members can get involved through the site's Community Advisory Group (CAG), which holds monthly meetings open to residents of Hyde Park, Mattapan, Dorchester, and Milton. The CAG gives neighbors a regular way to ask questions and stay informed as the cleanup moves forward.
