BACKGROUND

Mystic Lake was treated with alum in the Fall of 2010, after experiencing two cyanobacteria blooms that resulted in the death of over 2 million mussels, including some endangered species. The National Heritage of Endangered Species Program (NHESP) restricted the alum treatment to less than what was originally proposed to control phosphorus release from the sediments of Mystic Lake. Water quality evaluations completed since 2011 have found that the 2010 alum treatment resulted in reduced phosphorus concentrations in the bottom water, but not as much as desired, based on periodic lower water clarity and occasional visible cyanobacteria accumulations. A report commissioned by the Indian Ponds Association recommends another alum treatment for Mystic Lake (Mystic Lake Status Update 2020 by Water Resource Services, Inc.).

 

The Town Council appropriated $195,000 as part of the Fiscal Year 2024 Capital Budget for the Alum Treatment. The Department of Public Works has since received all necessary regulatory approvals to complete the alum treatment up to a concentration of 50 g/m2 . Bids have been opened for the project and one bid was received. The bids were structured such that the contractor provided pricing for various concentrations from 25 g/m2 to 50 g/m2 . Based on the bid results, the maximum concentration that can be achieved with the current appropriation is 35 g/m2 . DPW recommends conducting the treatment at the maximum permitted concentration (50 g/m2 ) to ensure maximum efficacy. The treatment is scheduled to be completed this fall. The contractor is required to complete the treatment between October 16th and December 15th. An additional permit requirement is for the Town to complete a mussel survey of the pond 4 years after the treatment is completed. The anticipated cost for this mussel survey ($12,000) has been included in this request.