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Sewage treatment plant, Custer, South Dakota. NPDES permit SD0023281 expired Mar 31, 2026; its limits still apply. Last 12 months: no values over a limit. Source: EPA ECHO, Oct 22, 2026.
| Parameter | Statistic | Limit | Months | Outfall |
|---|---|---|---|---|
| Temperature, water deg. centigrade | 30-day average | report only (deg C) | all year | 001 |
| Temperature, water deg. centigrade | daily maximum | report only (deg C) | all year | 001 |
| Flow rate | 30-day average | report only (MGD) | all year | 001 |
| Flow rate | daily maximum | report only (MGD) | all year | 001 |
| Oxygen, dissolved [DO] | daily minimum | report only (mg/L) | all year | 001 |
| BOD, 5-day, 20 deg. C | 30-day average | ≤ 30 mg/L | all year | 001 |
| BOD, 5-day, 20 deg. C | maximum 7-day average | ≤ 45 mg/L | all year | 001 |
| pH | daily minimum | ≥ 6 SU | all year | 001 |
| pH | daily maximum | ≤ 9 SU | all year | 001 |
| Solids, total suspended | 30-day average | ≤ 30 mg/L | all year | 001 |
| Solids, total suspended | maximum 7-day average | ≤ 45 mg/L | all year | 001 |
| Nitrogen, total [as N] | 30-day average | report only (mg/L) | all year | 001 |
| Nitrogen, total [as N] | daily maximum | report only (mg/L) | all year | 001 |
| Nitrogen, ammonia total [as N] | 30-day average | report only (mg/L) | all year | 001 |
| Nitrogen, ammonia total [as N] | daily maximum | report only (mg/L) | all year | 001 |
| Nitrogen, nitrate total [as N] | 30-day average | report only (mg/L) | all year | 001 |
| Nitrogen, nitrate total [as N] | daily maximum | report only (mg/L) | all year | 001 |
| Phosphorus, total [as P] | 30-day average | report only (mg/L) | all year | 001 |
| Phosphorus, total [as P] | daily maximum | report only (mg/L) | all year | 001 |
| E. coli, colony forming units [CFU] | 30-day geometric mean | report only (#/100mL) | May–Sep | 001 |
| E. coli, colony forming units [CFU] | daily maximum | report only (#/100mL) | May–Sep | 001 |
| Temperature, water deg. centigrade | value | report only (deg C) | all year | 002 |
| Flow rate | value | report only (MGD) | all year | 002 |
| Conductivity | value | report only (umho/cm) | all year | 002 |
| BOD, 5-day, 20 deg. C | value | report only (mg/L) | all year | 002 |
| pH | daily minimum | report only (SU) | all year | 002 |
| pH | daily maximum | report only (SU) | all year | 002 |
| Solids, total suspended | value | report only (mg/L) | all year | 002 |
| Nitrogen, total [as N] | value | report only (mg/L) | all year | 002 |
| Nitrogen, ammonia total [as N] | value | report only (mg/L) | all year | 002 |
| Nitrogen, nitrite total [as N] | value | report only (mg/L) | all year | 002 |
| Nitrogen, nitrate total [as N] | value | report only (mg/L) | all year | 002 |
| Nitrogen, Kjeldahl, total [as N] | value | report only (mg/L) | all year | 002 |
| Phosphorus, total [as P] | value | report only (mg/L) | all year | 002 |
| Sodium adsorption ratio | value | report only (Ratio) | all year | 002 |
| Chloride [as Cl] | value | report only (mg/L) | all year | 002 |
| Sulfate, total [as SO4] | value | report only (mg/L) | all year | 002 |
| E. coli, colony forming units [CFU] | daily maximum | ≤ 126 #/100mL | all year | 002 |
| Flow, total | value | report only (Mgal) | all year | 002 |
| Duration of Land Application | monthly total | report only (d) | all year | 002 |
| Solids, total dissolved | value | report only (mg/L) | all year | 002 |
| Temperature, water deg. centigrade | 30-day average | report only (deg C) | all year | 004 |
| Temperature, water deg. centigrade | daily maximum | report only (deg C) | all year | 004 |
| Flow rate | 30-day average | report only (MGD) | all year | 004 |
| Flow rate | daily maximum | report only (MGD) | all year | 004 |
| Oxygen, dissolved [DO] | daily minimum | report only (mg/L) | all year | 004 |
| BOD, 5-day, 20 deg. C | 30-day average | ≤ 10 mg/L | all year | 004 |
| BOD, 5-day, 20 deg. C | daily maximum | ≤ 17.5 mg/L | all year | 004 |
| pH | daily minimum | ≥ 6.5 SU | all year | 004 |
| pH | daily maximum | ≤ 9 SU | all year | 004 |
| Solids, total suspended | 30-day average | ≤ 10 mg/L | all year | 004 |
| Solids, total suspended | daily maximum | ≤ 17.5 mg/L | all year | 004 |
| Nitrogen, total [as N] | 30-day average | report only (mg/L) | all year | 004 |
| Nitrogen, total [as N] | daily maximum | report only (mg/L) | all year | 004 |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2.2 mg/L | Jan, Feb | 004 |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2.4 mg/L | Mar | 004 |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2.9 mg/L | Apr | 004 |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 1.4 mg/L | May, Jun | 004 |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 1 mg/L | Jul, Aug | 004 |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 1.6 mg/L | Sep | 004 |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2 mg/L | Oct | 004 |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2.1 mg/L | Nov, Dec | 004 |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 4.9 mg/L | Jan, Feb | 004 |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 5 mg/L | Mar | 004 |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 6 mg/L | Apr | 004 |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 3.5 mg/L | May, Jun | 004 |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 3.1 mg/L | Jul, Aug | 004 |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 3.3 mg/L | Sep | 004 |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 4.1 mg/L | Oct | 004 |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 4.5 mg/L | Nov, Dec | 004 |
| Nitrogen, nitrate total [as N] | 30-day average | report only (mg/L) | all year | 004 |
| Nitrogen, nitrate total [as N] | daily maximum | report only (mg/L) | all year | 004 |
| Phosphorus, total [as P] | 30-day average | report only (mg/L) | all year | 004 |
| Phosphorus, total [as P] | daily maximum | report only (mg/L) | all year | 004 |
| E. coli, colony forming units [CFU] | 30-day geometric mean | ≤ 259 #/100mL | May–Sep | 004 |
| E. coli, colony forming units [CFU] | daily maximum | ≤ 1178 #/100mL | May–Sep | 004 |
Cited limits by parameter: South Dakota's rules and the federal ones.
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Your permit document is the final word. As JSON: /api/v1/permits/SD0023281 · MCP: https://passage-data.com/mcp