09/18/2025 CONSERVATION COMMISSION Minutes

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Town of Mashpee Conservation Commission 16 Great Neck Road North Mashpee, MA 02649 Pre/Post-Hearing Agenda: Not Discussed Approval of Draft Minutes: Chair Cook stated that there were no draft minutes that were ready to be approved. DISCUSSION Discussion: (Public Comment solicited for each discussion - *3 minutes per comment) Water Quality: Issues and initiatives (ongoing discussion item) o No new updates. Discussion • Submittal Requirements Update o No new updates. Discussion • Regulation 30: Consensus o Commission then turned to Regulation 30, specifically the nitrogen concentration standard. Currently, the standard is set at 19 parts per million (ppm), though existing regulations allow for a sliding scale of 5 to 18 ppm depending on site-specific conditions. Commissioners discussed whether the 19 ppm standard should be lowered, citing urgent concerns about water quality in impaired areas of town. o One commissioner explained that while nitrogen calculation sheets from the Cape Cod Commission are widely used, they may not accurately reflect what is actually discharged into groundwater. For example, calculations assume 2.5 occupants per household, but homes with more bedrooms may legally house more people, increasing nitrogen loading beyond the assumptions. The commissioner noted that effluent concentrations directly beneath diffusers can be much higher than the calculated lot- wide average—sometimes exceeding 35 ppm—and that some systems are placed just a few feet above groundwater. o Other commissioners raised questions about seasonal occupancy, enforcement consistency, and fairness to engineers preparing applications. They stressed the importance of having a clear standard or formula so applicants know what benchmarks must be met. Some suggested revisiting or refining the Cape Cod Commission's 2017 technical bulletin, while others felt Mashpee might need to create its own nitrogen formula tailored to local conditions. o Concerns were raised about potential legal challenges if the Commission imposed unattainable standards. Staff reminded the Commission that existing regulations already permit a range down to 5 ppm, and technology exists to achieve those levels in some cases. Members discussed the possibility of convening engineers to advise on current and emerging septic technologies. One suggestion was to invite Brian Horsley of Aztec's Joint Base septic testing center to a future quarterly meeting to provide insight into how Innovative/Alternative (I/A) systems are performing and evolving.