06/25/2026 CONSERVATION COMMISSION Minutes

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Town of Mashpee Conservation Commission 16 Great Neck Road North Mashpee, MA 02649 Mr. Ladewig explained that the project resulted from a multi-year collaborative effort involving the Mashpee Wampanoag Tribe, the Town of Mashpee, and the Southeast New England Program Network. He stated that Santuit Pond had experienced recurring and prolonged cyanobacteria blooms due to excessive phosphorus levels. He explained that phosphorus enters the pond from both watershed sources and internal loading from pond sediments, with internal loading estimated to contribute more than 70 percent of the annual phosphorus load. The presentation reviewed ongoing efforts to address phosphorus inputs to the pond. It was noted that the Town of Mashpee had been implementing stormwater and wastewater improvements within the watershed to reduce external phosphorus sources. After evaluating dredging alternatives with the Army Corps of Engineers and determining them to be unsuitable, the Mashpee Wampanoag Tribe pursued an in-pond treatment approach. The project received funding through MassDEP's Section 319 Watershed Improvement Grant Program and support from several regional organizations. The proposed treatment would utilize buffered alum consisting of aluminum sulfate and sodium aluminate to bind phosphorus within the pond sediments and prevent its release into the water column. The treatment design included two application zones, with higher treatment rates proposed in the deepest portion of the pond and lower treatment rates proposed in shallower areas below four feet in depth. Treatment would be applied by contractor vessels launched from the Town landing. Materials would either be transferred directly to the vessels or temporarily stored in holding tanks located on existing paved surfaces. Any temporary holding tanks would utilize secondary containment measures to prevent accidental releases. The treatment would be conducted over a two-year period, with the first application anticipated in November 2026 and the second application approximately one year later. The November timing was selected in consultation with the Mashpee Wampanoag Tribe and the Division of Marine Fisheries to minimize impacts to diadromous fisheries. Pre- and post-treatment water quality monitoring would be conducted, and intensive pH monitoring would occur during treatment activities to ensure that pH levels remained within acceptable ranges. Monitoring results would be submitted to both the Commission and the Division of Marine Fisheries following each treatment event. Commission members discussed the proposed treatment and the recommendations contained within the Division of Marine Fisheries comment letter. It was suggested that compliance with all recommendations contained in the Division of Marine Fisheries letter be incorporated as a condition of approval. Questions were raised regarding the effectiveness and expected lifespan of alum treatments, the long-term management of phosphorus within the pond sediments, and the relationship between improved water clarity and aquatic vegetation growth. Mr. Ladewig explained that phosphorus bound by the treatment would remain within the sediments and that watershed improvements would continue to be important in limiting new phosphorus inputs. He also noted that improved water clarity could increase aquatic plant growth, making ongoing invasive species management an important component of overall pond management. 8