Monthly Sampling: A Missed Sample and a Positive Repeat
Your system serves 350 people, which puts you in a monitoring category requiring 2 routine total-coliform samples per month. It is the 28th of the month. You have collected one routine sample so far. The one you collected came back positive for total coliform (E. coli absent). Your state requires repeat samples within 24 hours of being notified, and you were notified this morning. You also realize you will not be able to collect the second routine sample before month-end because the only certified sampler (you) is covering a family emergency tomorrow. Your chlorine residual at the positive site was 0.2 mg/L; elsewhere it is 0.8 mg/L.
1. Sort out which obligations are triggered right now and in what priority, given the positive result, the missed routine sample, and the low residual.
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Three separate obligations, in priority order:
- Repeat samples (highest priority, 24-hour clock). The positive total-coliform result triggers repeat sampling - typically the original site plus one upstream and one downstream (confirm your state's exact count). This is due within 24 hours of notification, i.e., by tomorrow morning. This is the clock that matters most.
- The missed routine sample. You are short one routine sample for the month. A missed routine sample is a monitoring violation in most states, reported on the monthly operating report. It is serious but does not carry the same immediate 24-hour deadline as the repeat. You should still try to collect it, or document why you could not and notify the agency.
- The low residual (0.2 mg/L) at the positive site. This is the likely cause of the positive and must be investigated and corrected - flushing, checking for stagnation or a cross-connection. It is not a separate sampling deadline but it is the root cause you must address.
Priority: repeats first (clock is running), then residual investigation, then resolve the missed routine with the agency.
2. You cannot personally collect the second routine sample before month-end. What are your options, and which is the right call?
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Options:
- Let it go and report it as missed. Honest but creates a monitoring violation and may trigger additional sampling requirements.
- Arrange for another certified sampler (a neighboring system's operator, a contract sampler, or a trained backup) to collect it before month-end. Best outcome if feasible on short notice.
- Collect it late - a sample collected after month-end does not count for that month in most programs, so late collection does not cure the miss, though it shows good faith.
Right call: Try hardest for the certified-backup option first, since it avoids the violation entirely. If that fails, report the missed sample accurately to the primacy agency, explain the circumstance, and accept the consequence. Do not backdate or fabricate a sample - falsifying monitoring data is far worse than a missed sample and is a serious violation. The judgment being tested is honesty over convenience.
3. Suppose the repeat samples come back positive as well. How does the situation change?
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A positive repeat changes the classification significantly.
- Repeat positive = the system has a confirmed coliform problem, not a one-off. This typically escalates to a Level 1 assessment (or your state's equivalent) - a structured review of the system to find and fix the cause: treatment, distribution, cross-connections, sampling sites, residuals.
- If any sample is positive for E. coli, it becomes an acute situation with immediate public-notice requirements (often within 24 hours) and possible boil-water notice.
- Corrective actions must be identified and completed, and you may face increased monitoring until you demonstrate the problem is resolved.
- The low residual at the positive site is now the leading suspect - stagnation, a dead end, or a cross-connection. Flushing and residual restoration become part of the corrective action, documented for the assessment.
So the situation moves from "one positive, do repeats" to "confirmed problem, formal assessment, corrective action, and possibly public notice." The exam wants you to recognize that escalation and act on it rather than treating the second positive as routine.