City to notify residents after TTHM running average briefly exceeded Department of Health limit

The Department of Public Works reported that the city’s running average for total trihalomethanes (TTHMs) briefly rose above the New York State Department of Health reporting threshold after a large quarterly measurement.

The commissioner explained that a December sample measured 145 (units as per DOH reporting) and that a subsequent, recent sample measured 18; because the DOH uses a running average, the calculated running average reached approximately 80.55, which exceeds the reporting level of 80. The commissioner said the exceedance was likely caused by disturbance related to the Loughborough (Library) Lake Dam work, which churned organic material and temporarily raised TTHM formation during chlorination.

Under Department of Health rules the city has 30 days from notification to send letters to affected customers. The commissioner said he will draft a letter emphasizing that this is not an emergency, that recent measurements are much lower, and that the running average was driven by the single high reading. He is exploring including the notice with water bills to reduce postage costs; if that is not feasible, the city will mail the notices separately.

Staff also noted that nutrients and upstream sources (e.g., runoff from neighboring jurisdictions) can influence organic growth in the lake and that the city is working to limit those inputs. The council did not vote on any remedial action during the pre‑agenda meeting; the commissioner said he will explain the issue again at the regular meeting.