Total Coliform Routine and Repeat Sample Count

ScopeRestoring a water system after a flood or a main break ends in sampling, and the load is a federal table plus a multiplier. This calculator looks up the routine total coliform samples per month from 40 CFR 141.857(b) -- all 33 population bands, 2 samples at 1,001-2,500 people up to 480 at 3,960,001 or more, reproduced because it is public-domain regulation and its steps are regulatory choices, not a curve -- then counts the repeat samples, the E. coli analyses, and whether a Level 1 treatment technique trigger has been crossed. Every total-coliform-positive sample needs at least 3 repeats collected the same day within 24 hours of notification, and every positive is analyzed for E. coli. A town of 15,000 is in the 12,901-17,200 band, 15 samples a month; with 2 positives it owes 6 repeat bottles within 24 hours and 2 E. coli analyses, and because it takes fewer than 40 samples it is judged on the count rule: 2 positives trigger a Level 1 assessment. A city of 45,000 takes 50 samples and is judged on the percentage: 3 positives is 6.0% of routine samples, 5.1% counting the 9 repeats, over the 5.0% line either way; 2 positives would not trigger. A system that fails to collect every required repeat has triggered a Level 1 assessment regardless of the results. Systems serving 1,000 or fewer people are routed to 141.854 and the state. It does not address seasonal start-up, repeat sample siting, the E. coli MCL, or the conduct of an assessment, and states with primacy may be more stringent and set their own return-to-service rules. 40 CFR 141 Subpart Y, the state primacy agency, and the operator of record govern.

Formula or tableroutine samples per month = the 40 CFR 141.857(b) row for the population served (33 bands, 1,001-2,500 -> 2 through 3,960,001 or more -> 480); repeats = 3 per TC-positive sample within 24 h; E. coli analyses = every TC-positive sample; Level 1 = more than 5.0% TC-positive (routine and repeat) at 40 or more samples a month, or 2 or more TC-positive below 40, or any required repeat not taken.

Source and edition40 CFR 141.857(b), 141.858(a)-(b), and 141.859(a)(1), the Revised Total Coliform Rule (Subpart Y), read at law.cornell.edu on 2026-09-30; the 141.857(b) table is federal regulation and is reproduced in full. The state primacy agency governs.

Free accessThe Code of Federal Regulations is public domain; the monitoring-frequency table is transcribed in full and was checked row by row against the Cornell LII copy.

What governsEstimate. Operator of record and primacy agency govern.

API field namespopulation_served, tc_positive_count, positive_repeat_count, routine_samples_taken, routine_samples_per_month, repeat_samples_required, ecoli_analyses_required, tc_positive_pct_routine

• Community-system table the 141.857(b) population table; systems serving 1,000 or fewer follow 141.854 (non-community ground water), 141.855 (community ground water) or 141.856 (surface water) and are routed there; until 2026-10-17 all were sent to 141.85440 CFR 141.857(b); 141.854-141.856 checked on ecfr.gov 2026-10-17
• Percentage includes repeats TC-positive routine and repeat samples over all samples taken in the month40 CFR 141.859(a)(1)(i)
• Every repeat is required failing to collect any required repeat is a Level 1 trigger regardless of results40 CFR 141.859(a)(1)(iii)