01/06/2020 BOARD OF SELECTMEN Agenda Packet

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Town of Mashpeu Departmentof Natural Resources 16 Great Neck Road North M ash pee, MA 02549 ry. S Richard York, Director Date:January 2, 2020 To: Rodney Collins,Town Manager From: Richard York, DNR Director Re: Santuit Pond Update- Remediation Cc: Wayne Taylor,Assistant Town Manager,Terrie Cook,Administrative Assistant The cyanobacteria bloom in Santuit Pond is dying off as it has in winter in the past,.and the advisory was removed by.the Health Department on 12-13-19. As you know, the blooms that were controlled by the SolarBee water circulators returned to Santuit Pond 'in 2017 after an extreme rain event-with 7" of rain July 7, 2017 due to phosphorous and other nutrients in runoff. The blooms occurred again-in 2018 and 2019. Extreme rain events and higher annual rainfall in 2018 and 2019 probably also caused the blooms in those years. Analysis of our water Quality Monitoring data and rainfall data indicates that the bloom in 2018 occurred after the water warmed following 9" of rain on March 2--4, 2018. In 2019,there were events with over an inch of rain in 15 minutes. The annual rainfall was much higher than normal in years 2017, 2018 and 2019 as recorded by the USGS weather station at Mashpee Neck Landing. There was about twice and much rain in the summer of 2017 compared to the summer of 2015. The SolarBee water circulators are needed to reduce the phosphorous load from the sediments (most'of the phosphorous load is in the sediments), but another approach for blooms from nutrients, in stormwater runoff is required. Removal of the algae from the pond would control the bloom and remove the nutrients contained in the algae. The Conservation and Natural Resources Departments are working on two algae removal methods that could be used to eliminate another cyanobacteria bloom this year: 1) Removal of algae,with plankton nets, and 2) Transferring water from the pond to old cranberry bogs that the Town controls in the Santuit Pond Reserve, We are working on the use of both of these methods this winter. The cyanobacteria die off in the winter and are replaced by blooms of diatoms which do not have toxins. When the diatoms die in in late spring and decompose, nutrients including phosphorous can be released into the water to fuel the cyanobacteria blooms. Removal of these this winter blooms could prevent cyanobacteria blooms later in the year. Removal of algae with plankton nets is a common method. I tested this yesterday with a 53 micron mesh plankton net and had over 95% removal of the algae from Santuit Pond. A finer mesh net could remove all of the algae. The bog method i_nvvlves transferring pond water to the bog by removing boards and allowing a portion of the pond to drain in to the bogs. The board are replaced and the water in the bog drains through the sand trapping the algae in the sand. The process can be repeated to remove more algae from the pond. We are researching other technology that could be used if these methods are not effective.