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Town of Mashpee Conservation Commission <br /> 16 Great Neck Road North <br /> Mashpee, MA 02649 <br /> Ms. Thornbrugh began the questioning, commending the upgrade but asking for clarification about the <br /> nitrogen calculations. She confirmed that the nitrogen level remained relatively high due to the small lot size <br /> but sought assurance that the project complied with Regulation 30, which allows the Commission discretion to <br /> impose stricter nitrogen limits where appropriate. She also raised questions about the Area of Critical <br /> Environmental Concern (ACEC) mapping, noting inconsistencies between state and town GIS layers, both <br /> showing the ACEC boundary very close to or potentially overlapping the site. <br /> Ms. Thornbrugh said her intent was to ensure due diligence, particularly since the proposed system would be <br /> located in the velocity flood zone (VE) and near groundwater, and she wanted to confirm that all possible <br /> environmental protections were being applied to the design. <br /> 41 Seconsett Island Road -Nitrogen Reduction and Regulatory Consideration <br /> Ms. Thornbrugh raised questions about whether the nitrogen output of the proposed septic system could be <br /> further reduced. Mr. Dibb explained that, depending on the sensitivity of the site and regulatory limits, the <br /> nitrogen could theoretically be lowered from 18 parts per million to as low as five. He clarified that nitrogen <br /> reduction beyond the system's design would largely depend on minimizing fertilizer use on lawns or adopting <br /> alternative systems such as composting toilets, though on this small lot there would be limited practical gains. <br /> The Board of Health had already determined the proposed system represented the best feasible option for the <br /> property, and no structural changes to the house were proposed. <br /> Ms. Thornbrugh also inquired about the Area of Critical Environmental Concern (ACEC) mapping, <br /> noting slight discrepancies between state and town GIS layers. Mr. Dibb clarified that the official ACEC <br /> boundary is defined by mean low water and that the slight differences in GIS representation did not affect <br /> compliance. <br /> Additional questions addressed the design of the system itself. The impervious barrier used in the leach field <br /> was confirmed to be a buried vertical liner, preventing horizontal effluent movement toward the house. The <br /> leach field would be slightly raised, about one foot above existing grade,helping to reduce slope toward the <br /> roadway and improve stability. Commissioners confirmed that no walls or above-ground structures were <br /> proposed, and the design complied with all Coastal Bank setback requirements under the revised Regulation <br /> 25, rendering any waiver request unnecessary. <br /> 41 Seconsett Island Road—Driveway and Stormwater Management <br /> Commissioners then turned to site access and stormwater management. Ms. Thornbrugh asked whether the <br /> driveway had to be fully paved, expressing concern that impermeable pavement could channel stormwater <br /> runoff directly toward the shoreline. Mr. Dibb explained that paving provided traction, stability, and reduced <br /> erosion risk on the steep slope. He suggested that alternatives such as permeable pavers or gravel could be <br /> considered for a small portion of the driveway closest to the water while maintaining sufficient stability for <br /> vehicle access. <br /> Ms. Godfrey asked whether the septic tanks and IA system components were secured against flooding or <br /> buoyancy. Mr. Dibb confirmed that buoyancy calculations had been conducted, showing the tanks' weight <br /> exceeded the upward buoyant force by factors of three to four. Securing the tank covers with bolts or other <br /> fasteners would prevent them from floating during storm events, a standard measure in velocity zones. <br /> 25 <br />