CITY OF MASON CITY

NPDES permit IA0057169 · Major POTW · administratively continued, expires 2026-07-31 · EPA's file as of 2026-09-19

Check this month's numbers before you file
Watch this permit — $79 a month. Every Monday, from EPA's newest files: the next report due and when, whether EPA's file holds your last one, any change to this permit's limits or status, and the renewal date.

This permit expired on 2026-07-31 and is administratively continued: its last limits keep applying until a new permit is issued, and EPA still expects the reports.

EPA's record, 2025-09-01 to 2026-08-31

0values over a limit
0required values missing, on 0 form(s)
0of 11 forms filed late

Last period with anything received: 2026-07-31.

Reporting

Reports are due about 15 days after each monitoring period ends (the most common figure among IA permits in EPA's filings — check your permit).

Limits in force (101)

OutfallParameterStatisticLimitMonths
001Oxygen, dissolved [DO]DAILY MN >= 4.5 mg/L Feb
001Oxygen, dissolved [DO]DAILY MN >= 5 mg/L Jun
001Oxygen, dissolved [DO]DAILY MN >= 4.5 mg/L May
001Oxygen, dissolved [DO]DAILY MN >= 5 mg/L Jul
001Oxygen, dissolved [DO]DAILY MN >= 4.5 mg/L Nov
001Oxygen, dissolved [DO]DAILY MN >= 4.5 mg/L Oct
001Oxygen, dissolved [DO]DAILY MN >= 4.5 mg/L Dec
001Oxygen, dissolved [DO]DAILY MN >= 4.5 mg/L Mar
001Oxygen, dissolved [DO]DAILY MN >= 4.5 mg/L Jan
001Oxygen, dissolved [DO]DAILY MN >= 4.5 mg/L Apr
001Oxygen, dissolved [DO]DAILY MN >= 5 mg/L Aug
001Oxygen, dissolved [DO]DAILY MN >= 5 mg/L Sep
001BOD, 5-day, 20 deg. C30DA AVG report only all year
001BOD, 5-day, 20 deg. CDAILY MX report only all year
001BOD, 5-day, 20 deg. C30DA AVG report only all year
001BOD, 5-day, 20 deg. CDAILY MX report only all year
001pHDAILY MN >= 6.4 SU all year
001pHDAILY MX <= 9 SU all year
001pH30DA AVG report only all year
001pHDAILY MX report only all year
001Solids, total suspended30DA AVG <= 30 mg/L all year
001Solids, total suspended7 DA AVG <= 45 mg/L all year
001Solids, total suspended30DA AVG <= 3728 lb/d all year
001Solids, total suspended7 DA AVG <= 5592 lb/d all year
001Solids, total suspended30DA AVG report only all year
001Solids, total suspendedDAILY MX report only all year
001Solids, total suspended30DA AVG report only all year
001Solids, total suspendedDAILY MX report only all year
001Nitrogen, total [as N]30DA AVG <= 934.8 lb/d all year
001Nitrogen, total [as N]DAILY MX <= 1530.1 lb/d all year
001Nitrogen, total [as N]30DA AVG report only all year
001Nitrogen, total [as N]DAILY MX report only all year
001Nitrogen, total [as N]30DA AVG report only all year
001Nitrogen, total [as N]DAILY MX report only all year
001Nitrogen, ammonia total [as N]30DA AVG <= 2.2 mg/L Jul
001Nitrogen, ammonia total [as N]30DA AVG <= 2 mg/L Aug
001Nitrogen, ammonia total [as N]30DA AVG <= 2.5 mg/L Sep
001Nitrogen, ammonia total [as N]30DA AVG <= 2.2 mg/L Jun
001Nitrogen, ammonia total [as N]30DA AVG <= 4.1 mg/L Oct
001Nitrogen, ammonia total [as N]30DA AVG <= 9 mg/L Jan
001Nitrogen, ammonia total [as N]30DA AVG <= 5.1 mg/L Mar
001Nitrogen, ammonia total [as N]30DA AVG <= 3.2 mg/L May
001Nitrogen, ammonia total [as N]30DA AVG <= 6.1 mg/L Nov
001Nitrogen, ammonia total [as N]30DA AVG <= 6.5 mg/L Dec
001Nitrogen, ammonia total [as N]30DA AVG <= 3.7 mg/L Apr
001Nitrogen, ammonia total [as N]30DA AVG <= 10.3 mg/L Feb
001Nitrogen, ammonia total [as N]DAILY MX <= 11.5 mg/L Jul
001Nitrogen, ammonia total [as N]DAILY MX <= 13 mg/L Aug
001Nitrogen, ammonia total [as N]DAILY MX <= 13.8 mg/L Sep
001Nitrogen, ammonia total [as N]DAILY MX <= 14.7 mg/L Jun
001Nitrogen, ammonia total [as N]DAILY MX <= 16 mg/L Oct
001Nitrogen, ammonia total [as N]DAILY MX <= 15.6 mg/L Jan
001Nitrogen, ammonia total [as N]DAILY MX <= 15 mg/L Mar
001Nitrogen, ammonia total [as N]DAILY MX <= 15.4 mg/L May
001Nitrogen, ammonia total [as N]DAILY MX <= 14.9 mg/L Nov
001Nitrogen, ammonia total [as N]DAILY MX <= 16.2 mg/L Dec
001Nitrogen, ammonia total [as N]DAILY MX <= 15.9 mg/L Apr
001Nitrogen, ammonia total [as N]DAILY MX <= 14.6 mg/L Feb
001Nitrogen, ammonia total [as N]30DA AVG <= 196.3 lb/d Jul
001Nitrogen, ammonia total [as N]30DA AVG <= 179 lb/d Aug
001Nitrogen, ammonia total [as N]30DA AVG <= 228 lb/d Sep
001Nitrogen, ammonia total [as N]30DA AVG <= 215.7 lb/d Jun
001Nitrogen, ammonia total [as N]30DA AVG <= 336.5 lb/d Oct
001Nitrogen, ammonia total [as N]30DA AVG <= 738.9 lb/d Jan
001Nitrogen, ammonia total [as N]30DA AVG <= 445 lb/d Mar
001Nitrogen, ammonia total [as N]30DA AVG <= 304.4 lb/d May
001Nitrogen, ammonia total [as N]30DA AVG <= 502.8 lb/d Nov
001Nitrogen, ammonia total [as N]30DA AVG <= 535.5 lb/d Dec
001Nitrogen, ammonia total [as N]30DA AVG <= 328.7 lb/d Apr
001Nitrogen, ammonia total [as N]30DA AVG <= 852.1 lb/d Feb
001Nitrogen, ammonia total [as N]DAILY MX <= 1429.1 lb/d Jul
001Nitrogen, ammonia total [as N]DAILY MX <= 1615.5 lb/d Aug
001Nitrogen, ammonia total [as N]DAILY MX <= 1714.9 lb/d Sep
001Nitrogen, ammonia total [as N]DAILY MX <= 1807.7 lb/d Jun
001Nitrogen, ammonia total [as N]DAILY MX <= 1966.8 lb/d Oct
001Nitrogen, ammonia total [as N]DAILY MX <= 1908.1 lb/d Jan
001Nitrogen, ammonia total [as N]DAILY MX <= 1842.7 lb/d Mar
001Nitrogen, ammonia total [as N]DAILY MX <= 1901 lb/d May
001Nitrogen, ammonia total [as N]DAILY MX <= 1838.4 lb/d Nov
001Nitrogen, ammonia total [as N]DAILY MX <= 1999.4 lb/d Dec
001Nitrogen, ammonia total [as N]DAILY MX <= 1965 lb/d Apr
001Nitrogen, ammonia total [as N]DAILY MX <= 1788.7 lb/d Feb
001Nitrogen, Kjeldahl, total [as N]30DA AVG report only all year
001Nitrogen, Kjeldahl, total [as N]DAILY MX report only all year
001Nitrogen, Kjeldahl, total [as N]30DA AVG report only all year
001Nitrogen, Kjeldahl, total [as N]DAILY MX report only all year
001Phosphorus, total [as P]30DA AVG report only all year
001Phosphorus, total [as P]DAILY MX report only all year
001Phosphorus, total [as P]30DA AVG report only all year
001Phosphorus, total [as P]DAILY MX report only all year
001Phosphorus, total [as P]30DA AVG report only all year
001Phosphorus, total [as P]DAILY MX report only all year
001Phosphorus, total [as P]30DA AVG report only all year
001Phosphorus, total [as P]DAILY MX report only all year
001E. coliGEO MEAN <= 126 #/100mL Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov
001Toxicity [acute], Ceriodaphnia dubiaDAILY MX <= 1 N=0;Y=1 all year
001Toxicity [acute], Pimephales promelas [Fathead Minnow]DAILY MX <= 1 N=0;Y=1 all year
001BOD, carbonaceous [5 day, 20 C]30DA AVG <= 25 mg/L all year
001BOD, carbonaceous [5 day, 20 C]7 DA AVG <= 40 mg/L all year
001BOD, carbonaceous [5 day, 20 C]30DA AVG <= 3107 lb/d all year
001BOD, carbonaceous [5 day, 20 C]7 DA AVG <= 4971 lb/d all year

Built from EPA's ECHO bulk files. EPA's file, not the permit document, is the source: read your permit. Check a report before you file it · All states