01/09/2023 SELECT BOARD Minutes - Laserfiche WebLink

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7 Mashpee Select Board Minutes January 9, 2023 M114 1111'111111�11 iq� Intl mr.. 8.epTqgLt11qtiyps. (continued) It Lorcs Lov, yt 11 C 41111110 1# 1 Santult Pond that have contributed to potential environmental and hw-nan health impacts. There is a direct relationship between the severity of the algal blooms and the concentration of phosphorus that increases dramatically during the warm summer months. Phosphorus is noted to derive from the watershed, from septic systems, fertilizer, waterfowl and stormwater runoff Most of the phosphorus entering the pond is accumulated in the top layer of sediment. A significant portion of the phosphorus is not readily available for uptake by the algae however, the mixing of the sediment releases a considerable amount which is made available for use in the eutrophication process. Mixing processes include swimming, motorboat activity and other activities of like. The majority of the suspension of phosphorus derives from motor boat activity. The top 1.6 is the active layer for phosphorus. In phosphorus -rich waters studies have shown that 78-80% of phosphorus is within the top is of the sediment. The majority of the suspension or mixing can be related to motor boat activity if the lake has a high level of motor boat activity and if the water body is considered shallow with resistance to wind and pressure changes. Santuit Pond is a shallow pond with depths ranging from 5 to 9 feet. Motors as small as 10hp cause a mixing depth of 1.8 meters or approximately 6 feet. It is therefore recommended the use of internal combustion motor boats in Santuit Pond be restricted to 5hp. Ms. Mas stressed the need to use the tools within the tool box that are available for use. To address the sourcm of phosphorus intemally you would minimize resuspension, especially at the top layer of sediment, limit phosphorus release using alum and remove sediment by dredging. External measures include watershed management, stormwater runoff practices, fertilizer reduction measures, septic system functions, sewening an the use of solar bees, I In addition, bylaws, regulations and policies must be reviewed. This would include identifying opportunities and recommendation as well as water quality protection and enhancing climate resilience. The recommendation in this outreach session to remediate Santuit Pond plans to reduce the potential for resuspension by limiting horsepower on Santuit Pond. Studies have shown a suspension depth of 6 feet with 10 hp engines, and a mixing depth of 10 feet with 28 hp engines. Electric motors at or below the threshold would be allowed on the pond as would non -motorized boats. As a community, actions to remediate Santuit Pond would require a variety of procedures and trials. The issues within the pond did not happen overnight, and they will not go away overnight. Engagements may take decades to improve upon the pond for future generations.