DBP Running Averages, Missing Monitoring and a CCR Deadline
A 3,400-connection community system treats its own surface water and has just completed its fourth quarter of Stage 2 DBP monitoring at the location with the highest TTHM. Quarterly results at that site: TTHM 0.062, 0.081, 0.074 and 0.069 mg/L; HAA5 0.041, 0.048, 0.052 and 0.044 mg/L. The system's TOC removal ratio came in at 1.05 against a required 1.00. The Consumer Confidence Report is due July 1. The operator also finds that the monthly raw-water alkalinity and TOC sample needed to demonstrate the TOC removal ratio was not collected in November, and that two weeks of daily finished-water chlorine residual readings in December are missing because the colorimeter was out for repair. No one recorded the gap at the time.
1. Compute the DBPR running annual averages and determine the compliance position.
Read the worked answer
TTHM LRAA = (0.062 + 0.081 + 0.074 + 0.069) / 4 = 0.0715 mg/L, below the 0.080 mg/L MCL. HAA5 LRAA = (0.041 + 0.048 + 0.052 + 0.044) / 4 = 0.0463 mg/L, below the 0.060 mg/L MCL. No DBP violation, despite the second quarter at 0.081 mg/L - the MCL is a running annual average of four consecutive quarters at each monitoring location, not a single-sample limit.
Two things matter as much as the arithmetic:
- The average must be computed and reported at the highest location, and the reportable figure is both the highest LRAA and the range of quarterly values.
- One quarter at 0.081 mg/L means the system is roughly one poor quarter away from a violation. Treat it as an early warning and look at coagulation and TOC removal performance, storage turnover and elevated water temperature before it becomes a Tier 2 notice. The TOC removal ratio of 1.05 against 1.00 is compliant but thin - the same weak coagulation that puts TOC at the margin is what puts TTHM at the margin.
2. How do you handle the missed November TOC/alkalinity sample and the two-week residual gap?
Read the worked answer
Both are monitoring/recordkeeping violations. Handle them honestly and immediately.
- Do not reconstruct or estimate values. Fabricated or back-filled regulatory data is a far more serious problem than the gap.
- Notify EGLE in writing now, describing what was missed, why, and what has been changed. Report the monitoring violation as required for the period.
- Issue Tier 3 public notice within 30 days of learning of each violation, and disclose the violations in the CCR that covers the period.
- Fix the underlying practices: the TOC/alkalinity sample goes on a compliance calendar with a named backup; institute a second-person check of required monthly samples.
- For the residual gap, the obligation to measure daily does not lapse because an instrument failed. A portable colorimeter, DPD tablets or a borrowed meter exists precisely for this. Sample where the meter failed and document which method was used and why.
The compliance judgement being tested is that missing data is a violation in its own right - you cannot remedy it later, so the only defensible response is disclosure plus a control that prevents recurrence.
3. The board wants to push the CCR back until the missing December records are rebuilt. What do you tell them, and what must the CCR contain for these results?
Read the worked answer
The CCR deadline is fixed: it must be delivered to customers by July 1 for the prior calendar year. Missing records are not grounds for delay - the notice exists to tell people what happened, including what was not monitored. Only a state-approved alternative is even arguable, and this situation does not qualify. Delaying creates a separate violation on top of the monitoring one.
Contents for this reporting year:
- Source water type and, for surface water, source water assessment information.
- Detected DBP results as the highest LRAA and the range of quarterly values for TTHM and HAA5, with the MCLs, the units, and a plain-language definition of a running annual average - so a reader does not misread the 0.081 mg/L quarter as a violation.
- The TOC removal compliance statement.
- Each violation, with the mandatory health-effects language for that violation type, what was not monitored and when, and what the system is doing about it.
Do not invent a DBP violation you do not have, and do not omit the monitoring violation because the water quality data look acceptable. Report the truth, in both directions.