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Sewage treatment plant, major discharger, Mason City, Iowa. NPDES permit IA0057169 expired Jul 31, 2026; its limits still apply. Last 12 months: no values over a limit. Source: EPA ECHO, Oct 22, 2026.
| Parameter | Statistic | Limit | Months |
|---|---|---|---|
| Oxygen, dissolved [DO] | daily minimum | ≥ 4.5 mg/L | Feb |
| Oxygen, dissolved [DO] | daily minimum | ≥ 5 mg/L | Jun |
| Oxygen, dissolved [DO] | daily minimum | ≥ 4.5 mg/L | May |
| Oxygen, dissolved [DO] | daily minimum | ≥ 5 mg/L | Jul |
| Oxygen, dissolved [DO] | daily minimum | ≥ 4.5 mg/L | Nov |
| Oxygen, dissolved [DO] | daily minimum | ≥ 4.5 mg/L | Oct |
| Oxygen, dissolved [DO] | daily minimum | ≥ 4.5 mg/L | Dec |
| Oxygen, dissolved [DO] | daily minimum | ≥ 4.5 mg/L | Mar |
| Oxygen, dissolved [DO] | daily minimum | ≥ 4.5 mg/L | Jan |
| Oxygen, dissolved [DO] | daily minimum | ≥ 4.5 mg/L | Apr |
| Oxygen, dissolved [DO] | daily minimum | ≥ 5 mg/L | Aug |
| Oxygen, dissolved [DO] | daily minimum | ≥ 5 mg/L | Sep |
| BOD, 5-day, 20 deg. C | 30-day average | report only (mg/L) | all year |
| BOD, 5-day, 20 deg. C | daily maximum | report only (mg/L) | all year |
| BOD, 5-day, 20 deg. C | 30-day average | report only (lb/d) | all year |
| BOD, 5-day, 20 deg. C | daily maximum | report only (lb/d) | all year |
| pH | daily minimum | ≥ 6.4 SU | all year |
| pH | daily maximum | ≤ 9 SU | all year |
| pH | 30-day average | report only (SU) | all year |
| pH | daily maximum | report only (SU) | all year |
| Solids, total suspended | 30-day average | ≤ 30 mg/L | all year |
| Solids, total suspended | 7-day average | ≤ 45 mg/L | all year |
| Solids, total suspended | 30-day average | ≤ 3728 lb/d | all year |
| Solids, total suspended | 7-day average | ≤ 5592 lb/d | all year |
| Solids, total suspended | 30-day average | report only (mg/L) | all year |
| Solids, total suspended | daily maximum | report only (mg/L) | all year |
| Solids, total suspended | 30-day average | report only (lb/d) | all year |
| Solids, total suspended | daily maximum | report only (lb/d) | all year |
| Nitrogen, total [as N] | 30-day average | ≤ 934.8 lb/d | all year |
| Nitrogen, total [as N] | daily maximum | ≤ 1530.1 lb/d | all year |
| Nitrogen, total [as N] | 30-day average | report only (mg/L) | all year |
| Nitrogen, total [as N] | daily maximum | report only (mg/L) | all year |
| Nitrogen, total [as N] | 30-day average | report only (lb/d) | all year |
| Nitrogen, total [as N] | daily maximum | report only (lb/d) | all year |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2.2 mg/L | Jul |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2 mg/L | Aug |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2.5 mg/L | Sep |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 2.2 mg/L | Jun |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 4.1 mg/L | Oct |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 9 mg/L | Jan |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 5.1 mg/L | Mar |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 3.2 mg/L | May |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 6.1 mg/L | Nov |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 6.5 mg/L | Dec |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 3.7 mg/L | Apr |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 10.3 mg/L | Feb |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 11.5 mg/L | Jul |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 13 mg/L | Aug |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 13.8 mg/L | Sep |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 14.7 mg/L | Jun |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 16 mg/L | Oct |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 15.6 mg/L | Jan |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 15 mg/L | Mar |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 15.4 mg/L | May |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 14.9 mg/L | Nov |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 16.2 mg/L | Dec |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 15.9 mg/L | Apr |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 14.6 mg/L | Feb |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 196.3 lb/d | Jul |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 179 lb/d | Aug |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 228 lb/d | Sep |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 215.7 lb/d | Jun |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 336.5 lb/d | Oct |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 738.9 lb/d | Jan |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 445 lb/d | Mar |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 304.4 lb/d | May |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 502.8 lb/d | Nov |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 535.5 lb/d | Dec |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 328.7 lb/d | Apr |
| Nitrogen, ammonia total [as N] | 30-day average | ≤ 852.1 lb/d | Feb |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1429.1 lb/d | Jul |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1615.5 lb/d | Aug |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1714.9 lb/d | Sep |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1807.7 lb/d | Jun |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1966.8 lb/d | Oct |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1908.1 lb/d | Jan |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1842.7 lb/d | Mar |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1901 lb/d | May |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1838.4 lb/d | Nov |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1999.4 lb/d | Dec |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1965 lb/d | Apr |
| Nitrogen, ammonia total [as N] | daily maximum | ≤ 1788.7 lb/d | Feb |
| Nitrogen, Kjeldahl, total [as N] | 30-day average | report only (mg/L) | all year |
| Nitrogen, Kjeldahl, total [as N] | daily maximum | report only (mg/L) | all year |
| Nitrogen, Kjeldahl, total [as N] | 30-day average | report only (lb/d) | all year |
| Nitrogen, Kjeldahl, total [as N] | daily maximum | report only (lb/d) | all year |
| Phosphorus, total [as P] | 30-day average | report only (mg/L) | all year |
| Phosphorus, total [as P] | daily maximum | report only (mg/L) | all year |
| Phosphorus, total [as P] | 30-day average | report only (lb/d) | all year |
| Phosphorus, total [as P] | daily maximum | report only (lb/d) | all year |
| Phosphorus, total [as P] | 30-day average | report only (mg/L) | all year |
| Phosphorus, total [as P] | daily maximum | report only (mg/L) | all year |
| Phosphorus, total [as P] | 30-day average | report only (lb/d) | all year |
| Phosphorus, total [as P] | daily maximum | report only (lb/d) | all year |
| E. coli | geometric mean | ≤ 126 #/100mL | Mar–Nov |
| Toxicity [acute], Ceriodaphnia dubia | daily maximum | ≤ 1 N=0;Y=1 | all year |
| Toxicity [acute], Pimephales promelas [Fathead Minnow] | daily maximum | ≤ 1 N=0;Y=1 | all year |
| BOD, carbonaceous [5 day, 20 C] | 30-day average | ≤ 25 mg/L | all year |
| BOD, carbonaceous [5 day, 20 C] | 7-day average | ≤ 40 mg/L | all year |
| BOD, carbonaceous [5 day, 20 C] | 30-day average | ≤ 3107 lb/d | all year |
| BOD, carbonaceous [5 day, 20 C] | 7-day average | ≤ 4971 lb/d | all year |
Cited limits by parameter: Iowa'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/IA0057169 · MCP: https://passage-data.com/mcp