Falmouth committee hears watershed plan update outlining sewers, nitrogen‑removing septic systems and monitoring to meet state limits

Amy, the committee's watershed presenter, told the Water Quality Management Committee that the state’s watershed permit regulations passed in 2023 require towns to prepare watershed plans and apply for watershed permits for all designated nitrogen‑sensitive areas by 2030.

The presentation said the town aims to have an internal draft watershed management plan by the end of 2026 and to phase implementation through 2050, combining sewer extensions in dense areas with nitrogen‑removing septic systems and targeted complementary measures such as aquaculture and permeable reactive barriers. Funding for preparing the draft plan was appropriated at the November 2025 town meeting and the town is working with GHD and Science Wares to develop the plans.

Why it matters: the draft maps and models show how much nitrogen must be removed to meet Total Maximum Daily Load (TMDL) limits for impaired coastal ponds, and the choices the town makes now—what to sewer, where to require on‑lot nitrogen reduction, and how to credit alternatives—will affect costs, timelines and permitting with the state Department of Environmental Protection (DEP).

Amy said the planning approach uses a preferred plan that assumes nitrogen‑removing septic systems (previously called IAs) can achieve roughly 10 milligrams per liter (a planning assumption she characterized as roughly a 60 percent reduction) and a preferred contingency scenario that assumes something like 12 mg/L for conservative crediting. She said: "The watershed permit regulations were passed in 2023. They designated the watersheds to ponds with total maximum daily load limits" and that the town has committed to preparing watershed plans and applying for permits by 2030.

The presentation showed Fiddler's Cove and Rand's Canal as examples: a smaller watershed such as Fiddler's Cove could meet the TMDL under the preferred assumptions, while larger watersheds (Great Pond, McCoy Bay) will likely require phased actions spread over many years and may not be fully resolved within the 20‑year implementation horizon without additional measures. The DEP, Amy said, requires a contingency compliance plan that assumes conservative credits (for example, septic systems performing at ~19 mg/L and zero credit for alternatives), which leads to much larger—and much more expensive—districts.

Public members and committee members pressed on a few points. Dan Walsh (Precinct 3) asked who determines which credits are 'agreed upon'; Amy replied that the planning team and technical consultants will provide the technical basis and that detailed credit assumptions can be discussed with the Board of Health and DEP. Earl Barnhart of the Green Center said some source‑separation technologies (composting or urine‑diversion systems) can remove much more nitrogen and asked that the plan explicitly allow property owners to install such options. He said: "I would like these plans to specifically state that if a house is required and mandated to put in an IA ... the property owner has the choice to install one of these other source separation systems that do as well or better than the mandated IAs." Amy said five‑year updates and pilot projects are opportunities to add new technologies to the plan if they secure agreed‑upon credits.

Several speakers raised freshwater phosphorus as a separate concern. Joyce Bach of Friends of Cedar Lake warned that "an even bigger problem for freshwater ponds is too much phosphorus" and asked how future phosphorus removal would be accommodated if the town mandates nitrogen removal now. Committee members said freshwater pond committees are examining phosphorus options and that potential phosphorus add‑ons to systems would be part of future discussions.

Amy emphasized the need for monitoring and adaptive phasing: sentinel station data, town monitoring, and third‑party sources such as the Buzzards Bay Coalition will inform whether the preferred plan is achieving the expected reductions. She also stressed that planning will include coordination with the Board of Health, Department of Public Works, Planning Department and the Select Board, and that public outreach—potentially by precinct—will follow as plans firm up.

Next steps: the committee agreed to move draft materials forward to the Select Board to request DEP feedback on the RME approach and asked staff and consultants to refine maps, assumptions and outreach plans. Amy also noted a public information meeting on the outfall project scheduled for July 15 at Falmouth High School auditorium.