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Falmouth outlines offshore outfall plan, EIR schedule and anti‑degradation sampling results
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Summary
DPW staff described a proposed tertiary‑treated outfall 2,300 feet offshore, a two‑year anti‑degradation sampling program, and modeling work; staff said the outfall plus expanded sewering is expected to yield a net nitrogen reduction of more than 12,000 kg/year but additional evaluations (DO, pH, disinfection) remain.
Amy Lowell, the water superintendent, presented the town's conceptual outfall plan, anti‑degradation evaluation and permitting timeline.
Lowell said the proposed outfall would discharge tertiary‑treated wastewater with ultraviolet disinfection about 2,300 feet south of Grama Tides in Nantucket Sound, beyond the 20‑foot depth contour and beyond eelgrass habitat. The town completed a two‑year sampling program in 2024–2025 to support an anti‑degradation evaluation and is preparing a draft environmental impact report (EIR) for submission to MEPA this spring.
The presentation showed that relocating the town's current groundwater discharge (about 2,941 kg/year) and enabling substantial additional sewering would create a net reduction of more than 12,000 kg/year of nitrogen in the Sound under the town's minimum sewer‑conversion scenario (the town cited ~16,890 kg/yr avoided by sewering areas shown in the 2022 plan; the outfall adds about 1,930 kg/yr from relocated treated flow at much lower concentration).
Ambient sampling at the proposed site met Class SA criteria for most parameters; arsenic concentrations in the sound samples exceeded the SA criterion but arsenic was not detected in the plant effluent and is not attributed to the proposed discharge. Lowell said the town must still evaluate and possibly modify treatment to meet surface‑water permit criteria for dissolved oxygen, pH/alkalinity and disinfection standards before any discharge begins.
The town contracted SMAST and is having UMass Dartmouth produce dispersion modeling and shellfish classification analyses; Lowell said she expects model results by month end. The town is coordinating with DEP, EPA, CZM and other regulators and will seek required determinations under the Interbasin Transfer Act where applicable; USGS modeling of aquifer impacts was completed as a bracketing exercise and showed relatively small simulated effects.
Lowell said the town anticipates submitting the draft EIR in May and expects surface‑water/NPDES permitting in 2027; the town plans to request design funding at the April 2027 town meeting and construction funding in April 2028, with an earliest finish in 2030 and a late finish in 2032 depending on permitting and funding.
Next steps: regulatory review meeting in April, model results to be shared with regulators and the public, and continued work on anti‑degradation and interbasin transfer evaluations.
