Barnstable County, Massachusetts: drinking water report. Barnstable County encompasses Cape Cod, with about 215,000 year-round residents and a summer…
Barnstable County encompasses Cape Cod, with about 215,000 year-round residents and a summer population that more than doubles. Every drop of drinking water comes from the sole-source Cape Cod Aquifer – a glacial sand and gravel formation designated by the EPA as the only source of drinking water for the region. Joint Base Cape Cod (formerly Otis Air National Guard Base) occupies the upper portion of the Cape, directly over the aquifer's recharge zone.
Joint Base Cape Cod has been a Superfund site since 1989. According to the EPA's 2024 remediation progress report, the base has documented contamination from AFFF, fuel spills, and munitions testing that has affected the aquifer through multiple contaminant plumes. PFAS concentrations in groundwater near the fire training area exceed 1,000 ppt – among the highest documented at any military installation in the Northeast.
The contamination plumes extend for miles downgradient, affecting public water supply wells in Mashpee, Falmouth, Bourne, and Sandwich. A 2024 Massachusetts DEP compliance report found that eight Cape Cod water systems have installed PFAS treatment or blended supplies to meet the state's MCL of 20 ppt for combined PFAS.
Cape Cod's sole-source aquifer means there is no alternative water supply – protecting and treating the aquifer is the only option. Water systems across the mid and upper Cape have been investing in treatment, but the plumes from Joint Base Cape Cod are long-lived and continue to migrate.
Check your water for current data at your address. For PFAS at Cape Cod concentrations, reverse osmosis provides the highest household removal rate. Our water filter guide covers systems with certified PFAS performance. Get your detailed report for trends, and visit our Massachusetts page for statewide context.