Mashpee engineers report test glitch, sand-bed options and a renewed debate over phasing

GHD engineer Mark Dranville told the Mashpee Sewer Commission on July 16 that a main-process performance test for the Phase 1 facility identified a single component that failed because of a chemical-feed issue and that a partial re-test is planned; most other test elements passed.

The presentation covered construction progress across six contracts, the status of six pumping stations and planning for recharge capacity at existing sand beds. Dranville said Contract 1 (the treatment facility and admin building) shows siding and interior-wall work underway and that, overall, the program is tracking near its projected schedule despite some lag in pay‑application paperwork.

Why it matters: the town will soon confront capacity and environmental constraints as it brings new neighborhoods online. Dranville said Phase 2 will leave the plant close to capacity and that adding recharge capacity is important to connect additional properties without building new sand beds.

Key technical details and next steps

- Sand-bed staging: Dranville said existing sand beds currently handle about 120,000 gallons per day per stage. Phase 2 will provide two stages; GHD is investigating whether one or two additional stages can be accommodated in the existing beds to avoid constructing new recharge beds.

- Groundwater mounding and vernal pools: modeling shows local groundwater mounding near sand beds (the largest mound near the beds could be roughly 3½ feet). A wetland scientist inspected nearby vernal pools and reported no species likely to be sensitive to the small increases projected; Dranville said the state may nonetheless require baseline and ongoing monitoring.

- Infiltration limits and testing: the current allowable loading rate cited was 7 gallons per day per square foot. Doubling flow would require permission for about 14 gpd/sq ft; Dranville said state regulators have required field testing using wastewater (not clean water) to demonstrate higher infiltration rates and that there is a precedent in Falmouth.

- PFAS and plume concerns: Dranville reported the project team reviewed updated plume data from the nearby base and concluded proposed effluent discharge at the Wequoit recharge site is unlikely to affect known groundwater plumes.

- Funding: the select board authorized submission of a Project Evaluation Form to the State Revolving Fund; the PEF is due July 24. Dranville estimated the Phase 3 effort at roughly $150 million.

Points of contention

Commissioners pressed staff on phasing and water-quality priorities. One commissioner urged faster work on the upper Great Neck area and described the "top mile" above Great Pines as a remaining, significant source of nitrogen to the river that the current phasing schedule treats as a later phase. That commissioner argued the town should address that section sooner rather than deferring it to future decades.

Dranville replied that the town has voted to proceed with Phase 3 (Wequoit area) and that Phase 4 (which will include parts of Pompanesett and Wequoit as described in earlier plans) remains the next phase after 3; he said staff will revisit the revised phasing plan with the select board and sewer commissioners before submission.

Concerns about nearby site work

A commissioner reported deep excavation and soil removal at the town transfer station, close to the sand-bed area, and asked staff to check with the DPW director. Wastewater staff agreed to investigate and report back.

What happens next

Staff will submit the PEF to SRF and pursue DEP review of any proposed increases in infiltration rates and any required vernal‑pool monitoring. The commission will revisit phasing with the select board and follow up at future meetings. The continuance request for the flow‑neutral bylaw application was approved; that public hearing was rescheduled for Aug. 20, 2026.

Attributions: direct quotes and technical findings in this report are based on the presentation and exchanges led by Mark Dranville (GHD) and the commissioners and staff who questioned him.