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Mankato city of

Sewage treatment plant, major discharger, Mankato, Minnesota. NPDES permit MN0030171 expired May 31, 2026; its limits still apply. Last 12 months: over a limit once (last March 2026). Source: EPA ECHO, Oct 22, 2026.

Reports due
About 47 days after each period: outfall D133 form A1 monthly (34 values), outfall D133 form A2 monthly (2 values), outfall D133 form A3 monthly (1 value), outfall D133 form A4 monthly (1 value), outfall S138 form A1 monthly (14 values)
Last report on file
August 2026
Oct 2024 – Sep 2025
1 value over a limit, 0 required values missing, 0 of 53 reports late

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

Period endingParameterReportedLimit
March 2026pH, monthly maximum10.2≤ 9 SU

Limits in force (63)

ParameterStatisticLimitMonthsOutfall
Oxygen, dissolved [DO]monthly minimumreport only (mg/L)Apr, MayD133
Oxygen, dissolved [DO]monthly minimum≥ 5 mg/LJan, Feb, Mar, Jun, Jul, Aug, Sep, Oct, Nov, DecD133
pHmonthly minimum≥ 6 SUall yearD133
pHmonthly maximum≤ 9 SUall yearD133
Solids, total suspendedmonthly average≤ 30 mg/Lall yearD133
Solids, total suspendedmonthly maximumreport only (mg/L)May, SepD133
Solids, total suspendedmaximum weekly average≤ 45 mg/Lall yearD133
Solids, total suspendedmonthly average≤ 1277 kg/dall yearD133
Solids, total suspendedmaximum weekly average≤ 1916 kg/dall yearD133
Nitrogen, total [as N]monthly averagereport only (mg/L)all yearD133
Nitrogen, ammonia total [as N]monthly average≤ 62.1 mg/LJan, Feb, Mar, DecD133
Nitrogen, ammonia total [as N]monthly average≤ 20.5 mg/LOct, NovD133
Nitrogen, ammonia total [as N]monthly average≤ 5.6 mg/LJun–SepD133
Nitrogen, ammonia total [as N]monthly average≤ 62.7 mg/LApr, MayD133
Nitrogen, ammonia total [as N]monthly average≤ 2640 kg/dJan, Feb, Mar, DecD133
Nitrogen, ammonia total [as N]monthly average≤ 872 kg/dOct, NovD133
Nitrogen, ammonia total [as N]monthly average≤ 238 kg/dJun–SepD133
Nitrogen, ammonia total [as N]monthly average≤ 2670 kg/dApr, MayD133
Nitrogen, Kjeldahl, total [as N]monthly averagereport only (mg/L)all yearD133
Nitrite + Nitrate total [as N]monthly averagereport only (mg/L)all yearD133
Phosphorus, total [as P]monthly averagereport only (mg/L)all yearD133
Phosphorus, total [as P]monthly maximum≤ 1 Ratioall yearD133
Phosphorus, total [as P]12-month averagereport only (kg/d)all yearD133
Phosphorus, total [as P]monthly average≤ 33.2 kg/dJun–SepD133
Phosphorus, total [as P]year-to-date total≤ 12243 kg/yrall yearD133
Cyanide, total [as CN]monthly maximumreport only (ug/L)all yearD133
Beryllium, total [as Be]monthly maximumreport only (ug/L)all yearD133
Cadmium, total [as Cd]monthly maximumreport only (ug/L)all yearD133
Chromium, total [as Cr]monthly maximumreport only (ug/L)all yearD133
Silver, total [as Ag]monthly maximumreport only (ug/L)all yearD133
Selenium, total [as Se]monthly maximumreport only (ug/L)all yearD133
Coliform, fecal MPN + membrane ftl 44.5 Cmonthly geometric mean≤ 200 #/100mLApr–OctD133
Flow, in conduit or thru treatment plantmonthly averagereport only (MGD)all yearD133
Flow, in conduit or thru treatment plantmonthly maximumreport only (MGD)all yearD133
Flow, in conduit or thru treatment plantmonthly totalreport only (Mgal/mo)all yearD133
Chlorine, total residualdaily maximum≤ .038 mg/Lall yearD133
Solids, total dissolvedmonthly averagereport only (mg/L)Mar, SepD133
Mercury, dissolved [as Hg]monthly maximumreport only (ng/L)May, SepD133
Mercury, total [as Hg]monthly maximumreport only (ng/L)May, SepD133
BOD, carbonaceous [5 day, 20 C]monthly average≤ 22 mg/LJan, Feb, Mar, Jun, Jul, Aug, Sep, Oct, Nov, DecD133
BOD, carbonaceous [5 day, 20 C]monthly average≤ 25 mg/LApr, MayD133
BOD, carbonaceous [5 day, 20 C]maximum weekly average≤ 33 mg/LJan, Feb, Mar, Jun, Jul, Aug, Sep, Oct, Nov, DecD133
BOD, carbonaceous [5 day, 20 C]maximum weekly average≤ 40 mg/LApr, MayD133
BOD, carbonaceous [5 day, 20 C]monthly average≤ 936 kg/dJan, Feb, Mar, Jun, Jul, Aug, Sep, Oct, Nov, DecD133
BOD, carbonaceous [5 day, 20 C]monthly average≤ 1064 kg/dApr, MayD133
BOD, carbonaceous [5 day, 20 C]maximum weekly average≤ 1404 kg/dJan, Feb, Mar, Jun, Jul, Aug, Sep, Oct, Nov, DecD133
BOD, carbonaceous [5 day, 20 C]maximum weekly average≤ 1596 kg/dApr, MayD133
BOD, carb-5 day, 20 deg C, percent removalmonthly average minimum≥ 85 %all yearD133
Solids, suspended percent removalmonthly average minimum≥ 85 %all yearD133
Precipitation, total defined period/inmonthly totalreport only (in)all yearS138
pHmonthly minimumreport only (SU)all yearS138
pHmonthly maximumreport only (SU)all yearS138
Solids, total suspendedmonthly averagereport only (mg/L)all yearS138
Solids, total suspendedmonthly maximumreport only (mg/L)all yearS138
Nitrogen, total [as N]monthly averagereport only (mg/L)all yearS138
Nitrogen, Kjeldahl, total [as N]monthly averagereport only (mg/L)all yearS138
Nitrite + Nitrate total [as N]monthly averagereport only (mg/L)all yearS138
Phosphorus, total [as P]monthly averagereport only (mg/L)all yearS138
Flow, in conduit or thru treatment plantmonthly averagereport only (MGD)all yearS138
Flow, in conduit or thru treatment plantmonthly maximumreport only (MGD)all yearS138
Flow, in conduit or thru treatment plantmonthly totalreport only (Mgal/mo)all yearS138
BOD, carbonaceous [5 day, 20 C]monthly averagereport only (mg/L)all yearS138
BOD, carbonaceous [5 day, 20 C]monthly maximumreport only (mg/L)all yearS138

How strict are these limits?

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

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Your permit document is the final word. As JSON: /api/v1/permits/MN0030171 · MCP: https://passage-data.com/mcp