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Richland County Utilities & Services

Sewage treatment plant, major discharger, Irmo, South Carolina. NPDES permit SC0046621 expired Mar 31, 2023; its limits still apply. Last 12 months: over a limit 6 times (last August 2026). Source: EPA ECHO, Oct 22, 2026.

Reports due
About 29 days after each period: form 1 monthly (31 values), form 2 quarterly (4 values), form 3 monthly (2 values), form 4 quarterly (2 values)
Last report on file
August 2026
Oct 2024 – Sep 2025
7 values over a limit, 0 required values missing, 0 of 32 reports late

Last 12 months (Oct 1, 2025 – Sep 30, 2026)

Period endingParameterReportedLimitOver by
November 2025Phosphorus, total [as P], monthly average1.95≤ 1.38 mg/L41%
November 2025Phosphorus, total [as P], weekly average4.21≤ 2.07 mg/L103%
November 2025Solids, total suspended, weekly average72≤ 45 mg/L60%
January 2026E. coli, daily maximum687≤ 349 MPN/100mL97%
March 2026E. coli, daily maximum1554≤ 349 MPN/100mL345%
August 2026E. coli, daily maximum921≤ 349 MPN/100mL164%

Limits in force (43)

ParameterStatisticLimitMonths
Oxygen demand, ultimatemonthly average≤ 4009 lb/dall year
Oxygen demand, ultimateweekly average≤ 6014 lb/dall year
Oxygen, dissolved [DO]minimum≥ 5 mg/Lall year
BOD, 5-day, 20 deg. Cmonthly average≤ 30 mg/Lall year
BOD, 5-day, 20 deg. Cweekly average≤ 45 mg/Lall year
BOD, 5-day, 20 deg. Cmonthly average≤ 1501 lb/dall year
BOD, 5-day, 20 deg. Cweekly average≤ 2252 lb/dall year
pHminimum≥ 6 SUall year
pHmaximum≤ 8.5 SUall year
Solids, total suspendedmonthly average≤ 30 mg/Lall year
Solids, total suspendedweekly average≤ 45 mg/Lall year
Solids, total suspendedmonthly average≤ 1501 lb/dall year
Solids, total suspendedweekly average≤ 2252 lb/dall year
Nitrogen, total [as N]monthly averagereport only (mg/L)all year
Nitrogen, total [as N]weekly averagereport only (mg/L)all year
Nitrogen, total [as N]monthly averagereport only (lb/d)all year
Nitrogen, total [as N]weekly averagereport only (lb/d)all year
Nitrogen, ammonia total [as N]monthly average≤ 17.13 mg/LMar–Oct
Nitrogen, ammonia total [as N]monthly average≤ 20 mg/LJan, Feb, Nov, Dec
Nitrogen, ammonia total [as N]weekly average≤ 25.69 mg/LMar–Oct
Nitrogen, ammonia total [as N]weekly average≤ 30 mg/LJan, Feb, Nov, Dec
Nitrogen, ammonia total [as N]monthly average≤ 857 lb/dMar–Oct
Nitrogen, ammonia total [as N]monthly average≤ 1001 lb/dJan, Feb, Nov, Dec
Nitrogen, ammonia total [as N]weekly average≤ 1286 lb/dMar–Oct
Nitrogen, ammonia total [as N]weekly average≤ 1502 lb/dJan, Feb, Nov, Dec
Phosphorus, total [as P]monthly average≤ 1.38 mg/Lall year
Phosphorus, total [as P]weekly average≤ 2.07 mg/Lall year
Phosphorus, total [as P]monthly average≤ 69 lb/dall year
Phosphorus, total [as P]weekly average≤ 103.5 lb/dall year
Flow, in conduit or thru treatment plantmonthly averagereport only (MGD)all year
Flow, in conduit or thru treatment plantweekly averagereport only (MGD)all year
Chlorine, total residualmonthly average≤ .5 mg/Lall year
Chlorine, total residualdaily maximum≤ 1 mg/Lall year
Chlorine, total residualmonthly average≤ 25.02 lb/dall year
Chlorine, total residualdaily maximum≤ 50.04 lb/dall year
E. coli30-day geometric mean≤ 126 MPN/100mLall year
E. colidaily maximum≤ 349 MPN/100mLall year
E. coli30-day geometric mean≤ 126 MPN/100mLall year
E. colidaily maximum≤ 800 MPN/100mLall year
BOD, 5-day, percent removalmonthly average minimum≥ 85 %all year
Solids, suspended percent removalmonthly average minimum≥ 85 %all year
%Effect Static Renewal 7 Day Chronic Ceriodaphnia dubiamonthly average≤ 25 %all year
%Effect Static Renewal 7 Day Chronic Ceriodaphnia dubiadaily maximum≤ 40 %all year

How strict are these limits?

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

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On EPA ECHO: Facility report · DMR history

Your permit document is the final word. As JSON: /api/v1/permits/SC0046621 · MCP: https://passage-data.com/mcp