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City of Great Falls

Sewage treatment plant, major discharger, Great Falls, Montana. NPDES permit MT0021920 expired Aug 31, 2024; its limits still apply. Last 12 months: no values over a limit. Source: EPA ECHO, Oct 22, 2026.

Reports due
About 28 days after each period: form A monthly (36 values), form Q quarterly (2 values), form S1 twice a year
Last report on file
August 2026
Oct 2024 – Sep 2025
0 values over a limit, 0 required values missing, 0 of 18 reports late

Limits in force (42)

ParameterStatisticLimitMonths
Temperature, water deg. centigrademonthly averagereport only (deg C)all year
Temperature, water deg. centigradedaily maximumreport only (deg C)all year
Flow ratedaily averagereport only (MGD)all year
Flow ratedaily maximumreport only (MGD)all year
Flow ratedaily averagereport only (MGD)all year
Flow ratedaily maximumreport only (MGD)all year
Oxygen, dissolved [DO]single samplereport only (mg/L)all year
BOD, 5-day, 20 deg. Cmonthly average≤ 25 mg/Lall year
BOD, 5-day, 20 deg. C7-day average≤ 40 mg/Lall year
BOD, 5-day, 20 deg. Cmonthly average≤ 2773 lb/dall year
BOD, 5-day, 20 deg. C7-day average≤ 4437 lb/dall year
BOD, 5-day, 20 deg. Cmonthly averagereport only (mg/L)all year
pHinstantaneous minimumreport only (SU)all year
pHinstantaneous maximumreport only (SU)all year
Solids, total suspendedmonthly average≤ 30 mg/Lall year
Solids, total suspended7-day average≤ 45 mg/Lall year
Solids, total suspendedmonthly average≤ 3328 lb/dall year
Solids, total suspended7-day average≤ 4991 lb/dall year
Solids, total suspendedmonthly averagereport only (mg/L)all year
Oil and grease, hexane extr methodinstantaneous maximum≤ 10 mg/Lall year
Nitrogen, total [as N]monthly averagereport only (mg/L)Jul–Sep
Nitrogen, total [as N]monthly averagereport only (lb/d)Jul–Sep
Nitrogen, ammonia total [as N]monthly averagereport only (mg/L)all year
Nitrogen, Kjeldahl, total [as N]monthly averagereport only (mg/L)Jul–Sep
Nitrite + Nitrate total [as N]monthly averagereport only (mg/L)all year
Nitrite + Nitrate total [as N]daily maximumreport only (mg/L)all year
Phosphorus, total [as P]monthly averagereport only (mg/L)Jul–Sep
Phosphorus, total [as P]monthly averagereport only (lb/d)Jul–Sep
Arsenic, total recoverablemonthly average≤ 19.8 ug/Lall year
Arsenic, total recoverabledaily maximum≤ 19.8 ug/Lall year
Lead, total recoverablemonthly averagereport only (ug/L)all year
E. coli, MTEC-MF30-day geometric mean≤ 126 CFU/100mLApr–Oct
E. coli, MTEC-MF30-day geometric mean≤ 630 CFU/100mLJan, Feb, Mar, Nov, Dec
E. coli, MTEC-MF7-day geometric mean≤ 252 CFU/100mLApr–Oct
E. coli, MTEC-MF7-day geometric mean≤ 1260 CFU/100mLJan, Feb, Mar, Nov, Dec
Cyanide, total recoverablemonthly average≤ 19.9 ug/Lall year
Cyanide, total recoverabledaily maximum≤ 19.9 ug/Lall year
BOD, 5-day, percent removalminimum≥ 85 %all year
Solids, suspended percent removalminimum≥ 85 %all year
Oil and grease visualvaluereport only (N=0;Y=1)all year
Pass/Fail Static Renewal 48Hr Acute Ceriodaphnia dubiavaluereport only (pass=0;fail=1)all year
Pass/Fail Static Renewal 96Hr Acute Pimephales Promelasvaluereport only (pass=0;fail=1)all year

How strict are these limits?

Cited limits by parameter: Montana's rules and the federal ones.

Check this month's numbers Email me before each report is due

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On EPA ECHO: Facility report · DMR history

Your permit document is the final word. As JSON: /api/v1/permits/MT0021920 · MCP: https://passage-data.com/mcp