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Bourne’s Pond mapping, inlet‑widening benefits and outfall borings move forward, committee told
Summary
Consultant Kristen Rathgen presented Bourne’s Pond watershed mapping and nitrogen‑reduction modeling; staff reported a third Army Corps submittal and a likely December schedule for marine borings to support outfall design and USGS hydrodynamic modeling is being peer reviewed.
The Town of Falmouth’s Water Quality Management Committee on Sept. 11 received a technical briefing on Bourne’s Pond watershed mapping and an update on outfall permitting and marine borings tied to the town’s comprehensive wastewater planning.
Kristen Rathgen of ScienceWears told the committee Bourne’s Pond watershed contains about 1,200 parcels, roughly 970 single‑family homes, and compared Mass. Estuaries Project (MEP) and Cape Cod Commission model outputs (MEP: 4,162 kg nitrogen; Cape tool: 6,306 kg). She explained that using an IA performing at 10 mg/L (the state recommended performance) would yield an estimated 3.1 kg/year nitrogen reduction per single‑family residence versus a larger reduction for sewer connection. "For Bournes Pond, the proposed IA district represents about 20% of the parcels in the watershed and the proposed sewer district represents 25% of the parcels," she said, and noted inlet‑widening modeling by SMAST that estimated about 1,995 kg of equivalent nitrogen reduction for the main embayment if implemented.
Board members asked detailed questions about the Vineyard Sound sampling used in some model scenarios; several members said they wanted a more complete dataset (salinity, dissolved oxygen and seasonality) before drawing strong conclusions from the recent upward trend shown in Vineyard Sound monitoring data. The committee agreed to seek broader datasets and independent analysis to provide context for the SMAST numbers.
Amy (town staff) reported permitting progress on the outfall. She said the project team has made a third submittal to the U.S. Army Corps of Engineers for marine borings and, if the Corps accepts the filing and starts its review, the team plans marine borings in December: one land boring at Kite Park and six offshore borings spaced roughly every 500 feet up to about 3,000 feet offshore, with each casing pushed to about 100 feet to characterize soils for outfall design and cost estimates. "We will do the marine borings in December of this year," Amy said. She also said preliminary USGS hydrodynamic modeling has been run and will be peer reviewed by state water‑resources regulators before the town relies on its findings.
The committee discussed outfall sizing tradeoffs, noting the permit work is currently framed around a roughly 2.0‑million‑gallon‑per‑day maximum but that directional‑drilling design could allow later capacity increases without reboring. Members emphasized the balance between near‑term permitting timelines and the long‑term value of added capacity.
Next steps: committee staff will distribute the broader water‑quality datasets for independent review, provide updated modeling as peer review completes, and proceed with Army Corps permitting and planned December borings if permits proceed on schedule.
