Positive Coliform Sample With a Holding-Time Problem

It is not valid for compliance. Collected 09:15, plated 19:05 - 9 hours 50 minutes against an 8-hour maximum holding time. Ice in the cooler does not extend the hold time. The result cannot be used to satisfy a monitoring requirement or to drive a compliance determination.

What that means in practice:

• You are one routine sample short for the month unless a replacement is collected at a representative site within the compliance period. A sampling gap becomes a monitoring violation on its own.
• Do not erase it. Record the result with the invalidity and the reason, notify NJDEP, and get the lab's concurrence in writing. Lab QA problems are worth a paper trail.
• Take repeats around the site anyway. They cost almost nothing, they are good practice after a positive, and they protect you if NJDEP decides the invalidation was not justified.
• Treat the field chlorine as real. The invalid result says nothing reliable about the bacteriology, but 0.04 mg/L where the system normally holds 0.5–0.9 mg/L is a fact about the distribution system that does not depend on a plate count. That residual is the actual finding of the day.

Invalidating a result does not invalidate a problem.

Work from the tap outward.

At the tap:

• Re-measure with a fresh DPD kit. Check reagent age, check that the tap was flushed before testing, and check whether the sample point is on a long dead-leg or an unflushed faucet aerator.
• Ask about recent plumbing work, a new water softener, or a shut-off valve left closed.

On the main:

• Residuals at the two nearest hydrants and at taps up and down the main. Look for a dead end, a low-flow loop, a recently isolated section, or a storage tank with poor turnover.
• Look at pressure records for the last 72 hours.

Cross-connection - the leading suspect:

• That RPZ assembly failed a survey and was never reinspected. Is it still there? Bypassed? Removed? Testable assemblies require annual testing by a certified tester; find out who owns it and who tested it last.
• Check for direct connections to irrigation, boiler feed, carbonators at the soda fountain, and hose bibs with submerged hoses. These are exactly the fixtures that produce a positive coliform sample plus a chlorine demand plus an earthy or chlorinous odor.

Saturday's break:

• Was the 6-inch main dewatered below 20 psi? Was it disinfected after repair, flushed, and did it get two consecutive absent coliform samples before being returned to service? A 400-foot distance is well within the zone of influence.

Order matters: chase the chlorine loss first, because a bacteriological problem usually follows a residual problem rather than the other way around.

Two or more routine total coliform positives in the same month trigger a Level 1 assessment, regardless of whether the repeats were clean. Absent repeats prevent an MCL violation; they do not prevent the assessment.

Requirements:

• Repeat samples for each positive must have been collected within 24 hours of notification - verify that the clock was actually met.
• Complete the Level 1 assessment within 30 days, using a qualified person and the state's form, and submit it to NJDEP. Missing the deadline or the submission is itself a treatment technique violation.
• The assessment is not a formality. It has to examine: sampling sites and technique, chlorine residual patterns and fluctuations, pressure loss and main breaks, cross-connection control, storage tank turnover and stratification, and any treatment or flow change during the period. Then it must name specific corrective actions with a schedule.

Given this system's history - a failed backflow assembly, a Saturday main break, a 0.04 mg/L residual - the assessment should center on cross-connection control and distribution integrity, not on the laboratory. If the corrective actions do not address the failed RPZ, the assessment is not honest and the next positives will look exactly like these.