Filter Effluent Turbidity Excursion After Backwash

Act on the individual filter, not the combined value. Filter 2 at 0.42 NTU is already above the 0.30 NTU individual-filter limit, and the trend is rising. Combined effluent is compliant only because it is diluted by two clean filters; averaging across filters hides a single-filter failure, and the rule is written against individual filter effluent for exactly this reason.

First 15 minutes:

1. Confirm the reading is real - check the analyzer for fouling, air bubbles, or a bad calibration, and pull a grab sample to compare.
2. If confirmed, take Filter 2 out of service or route it to waste immediately. Filter-to-waste is the correct tool here; the fact that it hasn't been used in two years is a reason to verify valve operation and line flushing before relying on it, not a reason to skip it.
3. Notify the supervisor and document the time, readings, and action.
4. Watch the remaining two filters - they now carry the full load and their loading rate rises.

Do not wait for the combined number to move. By the time dilution fails, the clearwell has already taken on water that will be hard to correct.

Rank by likelihood after a backwash, since the excursion began within 25 minutes of returning the filter to service:

1. Incomplete backwash / media disturbance. Media may not have fully resettled, or the backwash was cut short. Check backwash duration, rate, and the log; look for media in the troughs or a mudball layer. A filter that was fine before backwash and bad after points here first.
2. Filter-to-waste valve did not actually divert flow. Verify valve position and flow, not just the control signal. A stuck valve means dirty water is still reaching the clearwell.
3. Air binding or a cracked/loose media support. Air binding from a low water level during backwash causes channeling. Check for air release at the filter, and check the underdrain and support gravel for disturbance.
4. Coagulation upset. If raw water changed overnight (rain, turnover), the coagulant dose may be wrong and particles are passing. Check raw turbidity, pH, and jar-test or streaming current results.
5. Analyzer fault. Confirm with a grab sample before chasing process changes.

Sequence matters: rule out instrumentation and valve position first, because those are fast to check and a false alarm or a stuck valve changes the response entirely.

This is a judgement call about escalation, not a formula. The defensible position is to escalate now rather than wait out the three hours, because three conditions stack: a confirmed regulatory exceedance, reduced treatment capacity (two filters carrying 6 MGD means each is at 3 MGD against a 1.5 MGD rating - well over design rate), and a single operator who cannot simultaneously troubleshoot the filter and protect the clearwell.

Reasonable actions:

• Call the supervisor or on-call operator immediately on confirming the exceedance. Do not wait for the shift to end.
• If no help is reachable, reduce plant flow to bring the remaining filters back within design loading, even if that means rationing clearwell storage. Protecting water quality outranks production.
• Consider whether the clearwell water already produced needs to be isolated or blended, and tell the supervisor so that decision is made with full information.

Document: time of first high reading, grab-sample confirmation, time filter removed from service, valve/flow verification, notifications made and to whom, flow reductions, and clearwell level trend. The record should let a reviewer reconstruct why each decision was made when it was.