Falmouth committee maps ‘geo‑boundaries’ for Waquoit Bay watersheds, weighing sewers against upgraded septic systems

The Town of Falmouth Water Quality Management Committee on Aug. 28 reviewed proposed “geo‑boundaries” that would define where advanced septic systems (IAs) or sewer hookups must be installed to meet Total Maximum Daily Load (TMDL) nitrogen limits.

Kristen, the committee’s presenter, said Falmouth’s portion of the Eel Pond sub‑embayment contains about 1,440 parcels and that, under the Massachusetts Estuaries Project (MEP) baseline, the town’s planned sewer ring would meet the regulatory removal target for that specific area. “So the proposed sewer district is 58% of the parcels within that portion of the watershed,” she said, citing the GHD allocation and MEP numbers used for planning.

Why that conclusion matters: the committee is using the MEP model as the regulatory baseline for adaptive management and permitting, but newer estimates from the Cape Cod Commission—referred to in the meeting as the MVP dataset—show higher present‑load estimates. That discrepancy produces very different counts of how much additional nitrogen must be removed, and therefore whether to rely on sewering, IAs, or a combination.

The technical tradeoffs surfaced repeatedly. Using the committee’s planning assumptions (IAs performing at roughly 10 milligrams per liter), Kristen said an upgraded IA would remove about 2.7 kilograms of nitrogen per single‑family home per year on average; a sewered home yields a larger per‑home reduction (about 4.4 kilograms by the committee’s estimate). But members and residents noted that the MEP assumes a 35‑gallon‑per‑day water‑use proxy while the MVP’s measured water‑use is higher—pushing estimated current loads up.

“We can rerun the MEP using a higher effluent number,” the presenter said, but cautioned that changing the model would raise the target baseline the town must meet. Select Board member Doug Brownfeld asked whether the MVP numbers are closer to reality; committee members emphasized that adaptive management lets Falmouth implement a first stage (sewering plus some IAs), monitor results and, if necessary, expand measures in later five‑year review cycles.

Public commenters pressed for additional tools. Maggie McGaugh and other residents urged rapid deployment of a urine‑diversion (UD) pilot and stricter setback rules for new construction near surface waters; the committee said geoboundaries would target new construction and upgrades for IAs or UDs but rejected a blanket 1,000‑foot rule as impractical without further mapping.

The committee also discussed lot screening, engineering limits, and potential leaching‑field waivers: members noted Board of Health waivers can allow leaching‑field reductions in remedial cases to accommodate IA modules but that engineering and permitting costs will vary and must be estimated. Jed Coldstone and others argued for re‑running models with higher effluent assumptions to better match measured conditions, while others said consistency with the regulatory baseline permits adaptive management and progress tracking.

Next steps and context: the committee will continue mapping geo‑boundaries for other watersheds, present running tallies of parcels and estimated nitrogen reductions with each presentation, and rely on monitoring records to decide whether to expand sewering or IA deployment under adaptive management.