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Farm Pond advisory group presents lake assessment, outlines future alum treatment criteria
Summary
The Farm Pond Advisory Committee presented a nearly finished lake management assessment identifying high internal phosphorus and describing criteria (e.g., Secchi depth under 2 meters for six weeks or repeated cyanobacteria closures) that would trigger potential alum treatment estimated at under $200,000 applied incrementally.
The Sherborn Conservation Commission received a near-final Farm Pond Lake Management Assessment from Catherine Rocchio of the Farm Pond Advisory Committee, who said the document will be submitted to the state soon and begins community education on potential internal-phosphorus mitigation.
Rocchio explained the report finds high phosphorus levels likely driven by sediments releasing phosphorus from the pond bottom and outlines potential alum treatment as one remediation option, though FPAC does not intend to pursue alum this budget cycle. FPAC is developing decision criteria that would prompt treatment — for example, sustained Secchi disc clarity of less than 2 meters for six weeks or multiple cyanobacteria blooms that close the pond — and estimated that full treatment could cost under $200,000 to be applied in incremental doses over time.
Commissioner Steve Scrimshaw emphasized the mechanism of internal loading, noting it can create a cycle where algal growth reduces oxygen penetration, expanding anoxic zones and releasing more phosphorus; FPAC also noted rising temperatures may accelerate that process. The committee said it will prepare educational materials and one-page handouts for abutters and the public and plans outreach presentations, including to the Select Board and community events, before any formal request for funding or action.
