05/21/2026 CONSERVATION COMMISSION Minutes

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Town of Mashpee Conservation Commission 16 Great Neck Road North Mashpee, MA 02649 NOI 68 Waterway, Robert C. & Beth Ann Junkin. Proposed demolition of the existing dwelling and reconstruction of a new flood compliant dwelling in the same footprint. (Representative: Cape & Islands Engineering, Inc.) (cont. 4.23 / 5.07) 43- 3413 Mark Dibb of Cape &Islands Engineering appeared on behalf of Robert C. and Beth Ann Junkin for the continued Notice of Intent application for demolition of the existing dwelling and reconstruction of a new flood-compliant dwelling within the same footprint at 68 Waterway. He stated that the project had previously been continued from April 23 and May 7, and that the applicant had submitted updated materials in response to prior Commission comments. Mr. Dibb stated that the applicant had provided an updated plan addressing Regulation 31 compliance, in addition to the previously submitted Regulation 25 compliance statement. He explained that the applicant reviewed the 2007 wooden retaining wall plan,which included a planting plan for a ten-foot strip along the bulkhead. After reviewing existing site conditions,he stated that the ten-foot planted strip did not presently exist, and the updated plan now included planting details to enhance that area with mixed grasses and native shrubs,including species, quantities, and spacing. Mr. Dibb also stated that the applicant submitted the record plan showing groundwater elevation at approximately 2.3 feet, which had been requested in connection with stormwater drainage design for roof runoff. He stated that 25-year HydroCAD stormwater calculations had also been provided, with a minor adjustment to the proposed plastic infiltrator structure based on the model selected. He stated that the proposed stormwater systems were designed for the 25-year storm event. Floor plans were also submitted. Commission discussion focused primarily on the property's location within a DEP wellhead protection zone,nitrogen loading, groundwater elevation, and the proposed dewatering system. One commissioner noted that the final nitrogen calculation was approximately 13.17 parts per million and stated that, in light of the prior hearing discussion on 31 Nick Trail,he had similar cumulative effects concerns because the property was located within a wellhead protection area. The commissioner also raised concerns regarding the high groundwater elevation and the proposed dewatering basin, including the lack of site-specific detail regarding when it would be used, how deep the excavation would be,where discharged water would flow, and whether water could migrate toward the adjacent waterway or over the bulkhead. Mr. Dibb stated that the dewatering system would be used only if needed during construction and would function as a filtering mechanism for groundwater encountered during excavation. He explained that the system would remove sediment and fines before allowing water to flow back toward the low point of the site, likely into the vegetated buffer along the bulkhead,where it would infiltrate. He stated that if water reached the bulkhead, the bulkhead included drainage components. He also stated that construction equipment contamination, such as a hydraulic leak, would be addressed through separate contractor protocols. Commissioners further discussed whether additional conditions should be imposed to address dewatering and water quality concerns, including requiring water to be pumped off-site if the dewatering basin filled or if infiltration was inadequate. Concerns were raised that, given the shallow groundwater and proximity to the creek, water released from the dewatering system could move downgradient toward the bulkhead and adjacent water resource area. Mr. Dibb stated that the foundation appeared shallow and that significant dewatering might not be necessary,but agreed to provide additional clarification regarding the slab elevation, foundation depth, groundwater elevation, anticipated excavation depth, and whether dewatering would be needed. Discussion also addressed whether mitigation plantings should be installed before construction to help provide a vegetated buffer and assist with erosion control,runoff interception, and water retention during construction. Conservation staff stated that early installation of the planting area could help create a buffer between any dewatering discharge and the adjacent waterway and would provide additional protection against erosion. Commissioners further discussed the existing septic system,its age, and the nitrogen calculation. The Chair stated that he was generally more comfortable with the 13.17 parts per million calculation than the higher nitrogen calculation discussed in the prior hearing,but suggested that the existing septic system components should be inspected and verified before or after construction to ensure they remained in proper working condition,particularly given the age of the system and 8