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Airport reports PFOS monitoring update; consultants propose treat‑and‑return option for geothermal wells
Summary
PFOS status report No.18 submitted early to MassDEP; consultants found a spike at the Sandpits stockpile and recommend additional soil accounting and potential treatment of geothermal loop water to avoid spreading contamination.
Town and airport environmental staff briefed the commission on PFAS/PFOS work at the airport and nearby sites, including recent sampling, investigation and planned technical steps. The airport received and completed Immediate Response Action (IRA) status report No. 18 on Aug. 24, 2025, which will be submitted to the Massachusetts Department of Environmental Protection (MassDEP) by the Oct. 1 reporting deadline.
Environmental coordinator Madison Collins said a notable finding in the latest sampling was a new detection at the Sandpits stockpile — from non‑detect to 942 parts per trillion (ppt) — prompting Weston Consultants to perform more detailed soil accounting and forensics to understand the source. Weston has also completed groundwater sampling at Statue Park; Collins said groundwater flows north to south, from Old South Road toward Airport Gas, consistent with historical results.
Commissioners discussed treatment options for the airport’s geothermal open‑loop wells. Consultant Rich Lassen summarized three approaches: (1) decommission geothermal and replace heating/cooling, (2) convert to a closed‑loop system (which would require many additional boreholes and be less efficient), or (3) install a water treatment system to treat the well water before it goes through the heat exchanger and is returned to the ground. Commissioners favored pursuing a treat‑and‑return design as the first task, to mitigate plume movement and show progress on Phase 4 obligations to MassDEP.
Weston was assigned follow‑up work including (a) completing the PFAS fingerprint/forensic analysis, (b) providing the soil accounting for the Sandpits finding, and (c) developing a task order to design a filtration/treatment system sized for the geothermal wells, including an allowance for a future tie‑in to treat groundwater from the plume near the T‑hangars if later required. Staff noted that all treatment technologies generate a waste stream (spent resin or GAC) that will require off‑site disposal and budget for lifecycle operations.
Collins also reported the airport’s water bottle deliveries program and an ongoing bid process to clean the ARCTIC (apparatus) truck, with Clean Harbors among bidders. MassDEP confirmed receipt of a requested extension package on the Phase 4 schedule and is reviewing it.
