08/08/2022 SELECT BOARD Minutes - Laserfiche WebLink

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4 Mashpee Select Board Minutes August 8, 2022 APPOINTMENTS & HEARINGS: Presentation on Phosphorus in the, Ponds: De . artmentmmof Natural Resources Director Ashley Fisher: At the request of the Select Board, Ashley Fisher Director of Natural Resources presented an overview of the phosphorus in the Mashpee ponds and lakes. Factors contributing to the problem include, but are not limited to; Lawn fertilizer Storm water runoff Road water runoff Nitrogen from septic and cesspools Waterfowl excrement It was explained that abundant levels of nutrients cause eutrophication which causes harmful algae blooms. Ways to treat and control external nutrient sources internally include; dredging, aeration, and nutrient inactivation. External controls require sewering, berms, bylaws, buffer zones, stormwater prevention and modifications of yard use/green infrastructure. Ms. Fisher reviewed the conditions of each pond recommending remedial strategies as provided; Ashumet Pond; 215 acres with an average depth of 23', maximum depth of 69' having 2.5 miles of heavily developed shoreline. Remedial strategies include in -pond phosphorous inactivation using aluminum and iron salts, geochemical barriers at the plume pond interface and in -pond removal of phosphorus by hypolimnetic extraction. To eliminate the input and inactivate the accumulated phosphorous the geochemical barrier and aluminum sulfate were the chosen options. Past history of Ashumet Pond includes treatments to the Ashumet Valley sewage treatment plant plume, a part of the Military Reservation Plume Response Program. Through the years this included the installation of a geochemical barrier with iron treatments. It has been determined the external loading from residential properties has contributed to the phosphorous levels for the past 10 years. Further treatments would require Mashpee/Falmouth planning and implementation. Santuit Pond is shallow having a maximum depth of 10', on average 6.5'. The shoreline is steep with moderate development and an abandoned cranberry bog recently purchased by the Town to assist in the pond remediation process. The water quality of Santuit Pond is noted to be poor. This watershed enters into the Popponesset Bay system. The Town in collaboration with the Mashpee Wampanoag Tribe is investigating the use of inactivation treatments with aluminum sulfate. The collaboration effort includes the review and implementation of stormwater control measures. The Solar Bees, an aeration system is currently oxygenating the bottom sediment assisting in the limitation of algae growth.