Consultant schedules tracer study at Bass Lake clearwell to measure baffling factor and CT

Guy (presenter) told State Water Resources Control Board staff and local plant operators that a modified step‑dose tracer study will be used to measure the baffling factor and the T10 contact time for the Bass Lake clearwell and that the field test is planned for next week.

Guy said the study will use a modified step‑dose tracer method that he described as faster than full step‑dose or slug‑dose tests and that the result will be combined with the tank’s hydraulic residence time to compute a daily T10 value used for plant CT calculations. “This is what we call water age distribution curve,” Guy said when introducing the method, and he explained that EPA practice uses the T10 (the time by which 10% of the exiting water has an age equal to or less than that value) as the basis for ensuring disinfectant exposure.

The presentation laid out specific, test‑day procedures for Bass Lake: the team will operate the plant at a low flow of 300 gallons per minute, hold the clearwell level at 19 feet, and run the tracer test for one hour and 52 minutes. Based on the tank…