National Pollutant Discharge Elimination System (NPDES)/State Disposal System (SDS) Permit Program Fact SheetPermit ReissuanceMN0030171Permittee:City Of Mankato501 South Victory DriveP.O. Box 3368Mankato, Minnesota 56001Facility name:Mankato Water Resource Recovery Facility701 Pine StreetMankato, Minnesota 56001-2930Current permit expiration date:August 31, 2015Public comment period begins:April 5, 2021Public comment period ends:June 4, 2021Receiving water:Minnesota River - Class 2B, 3C, 4A, 4B, 5, 6 waterPermitting contact:Nancy Heskett7381 Airport View Drive SouthwestRochester, MN [email protected]

Table of ContentsPagePurpose and participation . 3Applicable statutes. 3Purpose. 3Public participation . 3Facility description . 4Background information . 4Facility location. 4Outfall location. 4Map of permitted facility . 4Components and treatment technology. 5Current information . 5Flow schematic . 6Significant industrial users (SIUs) . 6Recent compliance history . 6Recent monitoring history . 6Table 1. Recent Monitoring History. 7Receiving water(s) . 8Use classification . 8Impairments . 8Existing permit effluent limits . 8Technology based effluent limits (TBELs). 8Water quality based effluent limits (WQBELs) . 8State Discharge Restrictions . 9Conditional Effluent Limits. 9Proposed permit effluent limits . 9Additional requirements . 12Total facility requirements (TFR). 13Antidegradation and anti-backsliding . 14

NPDES/SDS Permit Program Fact SheetPermit ReissuanceMN00301713 of 14Purpose and participationApplicable statutesThis fact sheet has been prepared according to the 40 CFR § 124.8 and 124.56 and Minn. R. 7001.0100, subp. 3 inregards to a draft National Pollutant Discharge Elimination System (NPDES)/State Disposal System (SDS) permit toconstruct and/or operate wastewater treatment facilities and to discharge into waters of the State of Minnesota.PurposeThis fact sheet outlines the principal issues related to the preparation of this draft permit and documents the decisionsthat were made in the determination of the effluent limitations and conditions of this permit.Public participationYou may submit written comments on the terms of the draft permit or on the Commissioner’s preliminarydetermination. Your written comments must include the following:1. A statement of your interest in the permit application or the draft permit.2. A statement of the action you wish the Minnesota Pollution Control Agency (MPCA) to take, including specificreferences to sections of the draft permit that you believe should be changed.3. The reasons supporting your position, stated with sufficient specificity as to allow the Commissioner toinvestigate the merits of your position.You may also request that the MPCA Commissioner hold a public informational meeting. A public informational meetingis an informal meeting which the MPCA may hold to help clarify and resolve issues.In accordance with Minn. R. 7000.0650 and Minn. R. 7001.0110, your petition requesting a public informational meetingmust identify the matter of concern and must include the following: items one through three identified above; astatement of the reasons the MPCA should hold the meeting; and the issues you would like the MPCA to address at themeeting.In addition, you may submit a petition for a contested case hearing. A contested case hearing is a formal hearing beforean administrative law judge. Your petition requesting a contested case hearing must include a statement of reasons orproposed findings supporting the MPCA decision to hold a contested case hearing pursuant to the criteria identified inMinn. R. 7000.1900, subp. 1 and a statement of the issues proposed to be addressed by a contested case hearing andthe specific relief requested. To the extent known, your petition should include a proposed list of witnesses to bepresented at the hearing, a proposed list of publications, references or studies to be introduced at the hearing, and anestimate of time required for you to present the matter at hearing.You must submit all comments, requests, and petitions during the public comment period identified on page one of thisnotice. All written comments, requests, and petitions received during the public comment period will be considered inthe final decisions regarding the permit. If the MPCA does not receive any written comments, requests, or petitionsduring the public comment period, the Commissioner or other MPCA staff as authorized by the Commissioner will makethe final decision concerning the draft permit.Comments, petitions, and/or requests must be submitted by the last day of the public comment period to:Nancy HeskettMinnesota Pollution Control Agency7381 Airport View Drive SouthwestRochester, MN 55902

NPDES/SDS Permit Program Fact SheetPermit ReissuanceMN00301714 of 14The permit will be reissued if the MPCA determines that the proposed Permittee or Permittees will, with respect to thefacility or activity to be permitted, comply or undertake a schedule to achieve compliance with all applicable state andfederal pollution control statutes and rules administered by the MPCA and the conditions of the permit and that allapplicable requirements of Minn. Stat. ch. 116D and the rules promulgated thereunder have been fulfilled.More detail on all requirements placed on the facility may be found in the Permit document.Facility descriptionBackground informationFacility locationThis Facility is an existing municipal wastewater treatment facility that treats wastewater from the communities ofMankato, North Mankato, Eagle Lake, Madison Lake, South Bend Township, Skyline, and Lake Washington SanitarySewer District. The Facility is located in the SE ¼ of Section 6, Township 108 North, or approximately one mile southeastof the Highway 14/169 interchange on the north side of Mankato.Outfall locationThe continuous discharge outfall for this Facility (SD 001 in the permit) is located in the SE ¼ of Section 6, Township 108North, or approximately one mile southeast of the Highway 14/169 interchange on the north side of Mankato.Map of permitted facility

NPDES/SDS Permit Program Fact SheetPermit ReissuanceMN00301715 of 14Components and treatment technologyCurrent informationThe existing facility has a continuous discharge from SD 001. This is a Class A facility.The facility is designed to treat:- An average wet weather (AWW) flow of 11.25 million gallons per day (MGD);an average dry weather (ADW) flow of 6.0 MGD;a peak hourly wet weather (PHWW) flow of 36.0 MGD;a peak instantaneous wet weather (PIWW) flow of 42.0 MGD;an annual average flow of 9.38 MGD;five-day carbonaceous biochemical oxygen demand (CBOD5 ) of 160 milligrams per liter (mg/L).The facility consists of preliminary treatment (two mechanical bar screens, two vortex grit removal units, two gritconcentrators and two grit dewatering units); flow equalization (three equalization basins); primary treatment (twoprimary clarifiers); secondary treatment (four complete mix-activated sludge aeration basins and three secondaryclarifiers); tertiary treatment (a phosphorus removal process consisting of a high rate chemical/physical precipitationprocess, which consists of two microsand ballast assisted flocculation processes and two lamella clarification processes;cloth media filters; a chlorine contact basin and three rapid mix chambers and disinfection (two chlorination contacttanks and a dechlorination tank). The facility also includes a recycled water pumping station. Sludge treatment consistsof two dissolved air floatation thickening tanks, two belt filter presses that include a gravity thickener phase and a pressphase, and three primary anaerobic digesters and one secondary anaerobic digester. On-site biosolids storage consistsof a dewatered solids bunker. Biosolids are land applied to approved sites.The proposed facility will maintain the existing discharge at SD 001. It will also remain a Class A facility and will maintaindesign parameters and flow values above.The proposed facility will maintain the two mechanical bar screens(to be replaced), two vortex grit removal units, twogrit concentrators as well as the two grit dewatering units as well as the addition of a washer/compactor system. Thethree equalization basins, two primary clarifiers, four complete mix-activated sludge aeration basins and threesecondary clarifiers will remain with work being done to replace the aeration basin walkways and electrical systems. Thephosphorus removal process of high rate chemical/physical precipitation process consisting of two microsand ballastassisted flocculation processes, two lamella clarification processes and cloth media filters will remain. The chlorinecontact basin, dechlorination basin and the reuse return building will be demolished and replaced and a new chemicalfeed building will be added. The dissolved air floatation tanks will be replaced with a rotary drum and new thickeningsystem, the two primary digesters and single secondary digester will be replaced with three new anaerobic digesters,digester three will be retrofit to a sludge storage tank, work will include expansion of onsite biosolids storage. Theseptage receiving station will also be expanded.The facility has an existing and will maintain an agreement to provide a portion of the disinfected tertiary recycled waterfrom the facility for use as non-contact cooling water at the Mankato Energy Center (MEC). The amount of recycledwater supplied to the MEC will vary due to energy demand, operational status of the MEC, and seasonal and dailyconditions affecting the cooling efficiency and evaporation rate of water at the MEC cooling towers. Up to three-fourthsof the cooling water will be lost to evaporation. The remaining water will be returned to the facility and commingledwith treated effluent prior to dechlorination and discharge to the Minnesota River via SD 001.

NPDES/SDS Permit Program Fact SheetPermit ReissuanceMN00301716 of 14Flow schematicSignificant industrial users (SIUs)This Facility receives process wastewater from 16 SIUs; Ameripride Linen & Apparel, Archer Daniels Midland, AssociatedFinishing Inc., CAB Construction, CHS Oilseed Processing, Coloplast Corporation, D&K Powder Coating, Hiniker Company,Jones Metal Products Inc., Kato Engineering, Mankato Energy Center LLC, Pro-Fabrication, Thin-Film Technology,Viessman Incorporated, Wispak Incorporated, and Xcel Energy. The Permittee has delegated authority to operate itsown pretreatment program under 40 CFR § 403. Pollutants of concern are monitored and controlled through contractsadministered by the Facility to the SIU’s.Recent compliance historyA compliance Evaluation Inspection (CEI) was conducted at the facility on July 29, 2019. Violations were cited for threereleases of wastewater over the period of December 1, 2016, through June 30, 2019, which included failure toimmediately report the releases and to submit sampling results. In addition, incorrect limit types were calculated andreported and exceedances of the limits for fecal coliform were noted on monitoring stations WS 004 and WS 007. Aletter of Warning was issued, and following discussion of all the violations and submittal of amended DMRs for the fecalcoliform reporting, no further action was required.A Desk Audit Report was conducted of the facility’s pretreatment program on September 25, 2020. No requirementswere found to be non-compliant during the inspection.Recent monitoring historyThe following table shows the average monthly reported values by the Facility from January through December 2020.Where no number is given in the Limit and Units column, the Facility is required to monitor only; no limit is required inthe permit.

NPDES/SDS Permit Program Fact SheetPermit ReissuanceTable 1. Recent Monitoring HistoryParameterBeryllium, TotalCBOD5LimitUnitsug/L22 mg/LLimit TypeSingleValTCalMoAvgCBOD525 mg/LCalMoAvgCBOD5936 kg/dCalMoAvgCBOD51,064 kg/dCalMoAvgCBOD533 mg/LMxCalWkAvgCBOD540 mg/LMxCalWkAvgCBOD51,404 kg/dMxCalWkAvgCBOD51,596 kg/dMxCalWkAvgCBOD5, % Removal85 %Cadmium, Totalug/LChlorine, Total Residual 0.038 mg/LChromium, Totalug/LCopper, Totalug/LCyanide, Totalug/LFecal Coliform200 #/100mlFlowmgdFlowmgdFlowMgalMercury, Totalng/LNitrite Plus Nitratemg/LNitrogen, Ammonia5.6 mg/LNitrogen, Ammonia20.5 mg/LNitrogen, Ammonia62.1 mg/LNitrogen, Ammonia62.7 mg/LNitrogen, Ammonia238 kg/dNitrogen, Ammonia872 kg/dNitrogen, Ammonia2,640 kg/dNitrogen, Ammonia2,670 kg/dNitrogen, Kjeldahlmg/LNitrogen, Nitratemg/LOxygen, Dissolvedmg/LOxygen, Dissolved5 mg/LpH9 SUpH6 SUPhosphorus, Totalkg/dPhosphorus, Total43.1 kg/dPhosphorus, Total1 ratioPhosphorus, Total8,895.60 kg/yrSelenium, Totalug/LSilver, Totalug/LSolids, Total Dissolvedmg/LTSS30 mg/LTSS1,277 kg/dTSS45 mg/LTSS1,916 kg/dTSS, % Removal85 %MN00301717 of oMax7.5797.402CalMoTot173.779 MoMax0.375 0.3717SeasTDTot1653.218 106.3142984.6835.79998

NPDES/SDS Permit Program Fact SheetPermit ReissuanceMN00301718 of 14Receiving water(s)Use classificationThis Facility discharges to the Minnesota River. This water is classified as a 2B, 3C, 4A, 4B, 5, 6 water. This classificationindicates that the body of water is capable of sustaining aquatic life and recreation. More information on theclassification of waters can be found in Minn. R. 7050.0140.ImpairmentsStatewide Mercury TMDL - A Total Maximum Daily Load (TMDL) has been completed to address mercury, statewide. TheFacility has not shown reasonable potential to exceed the water quality standard of 6.9 nanograms per liter (ng/l), butmust continue to monitor for total mercury and report the results to the MPCA.Lower Minnesota River Low Dissolved Oxygen TMDL - The Facility was assigned loading based on discharge monitoringreport records during low stage river events plus an estimated 20-year growth projection of the community. Althoughthere is an individual waste load allocation (WLA) in the Lower Minnesota River Low Dissolved Oxygen TMDL, this TMDLsWLA’s are implemented in accordance with the Minnesota River Basin: General Phosphorus Permit (General Permit).According to Appendix B of the General Permit, this Facility has a calculated phosphorous limit of 1,800 lbs/yr. TheFacility must comply with Appendix B, Part 1 and must use a trade ratio of 1.1 to 1. However, proposed RiverEutrophication Standard (RES) limits for the permit will render the WLA for the General Phosphorus Permit obsolete, asthe RES limits are more restrictive. The Permittee is still required to maintain coverage because they sell phosphoruscredits under the General Permit and their buyers’ permits have not been reissued with more restrictive RES limits.Draft South Metro Mississippi TMDL Turbidity Impairment - The draft WLA for this TMDL is 466,105 kg/year and 1,277kg/day for total suspended solids (TSS). WLAs were calculated based on the permitted average wet weather design flow(AWWDF) and the existing permitted TSS concentration limit of 30 mg/L. The draft WLA is equivalent to the Facility’scurrent permitted TSS effluent limit. The draft TSS WLA for this Facility is 0.164 tons/day of TSS.Draft Minnesota River Turbidity TMDL – This TMDL is currently underway to address 18 impairments on the MinnesotaRiver and its tributaries. The draft WLA for this Facility is 1,277 kg/day TSS, which is equal to the current permit limit.WLAs were calculated based on the permitted AWWDF and the existing permitted TSS concentration limit of 30 mg/L.Draft Lake Pepin Excess Nutrients TMDL -The discharge is located within the project area and as a result, a stafflimnologist has reviewed the current phosphorous limit that is included in the permit and developed a pre-TMDL waterquality based effluent limit (WQBEL) for this Facility.Existing permit effluent limitsTechnology based effluent limits (TBELs)Limits for five-day carbonaceous biochemical oxygen demand (CBOD5) (applicable April-May), TSS and percent removalare technology based limits, as specified by 40 CFR §133.102 and Minn. R. 7053.0215 to meet minimum secondarytreatment levels.Water quality based effluent limits (WQBELs)The limits for CBOD5 (applicable June-March), ammonia and total residual chlorine (TRC) are water quality based limits.The TRC limit is the final acute value for chlorine found in Minn. R. 7050.0222. This limit is determined to be necessary toprotect the use classification of the receiving water. The seasonal dissolved oxygen limit has been applied pursuant toMinn. R. 7053.0205, subpart 8. The 8895.6 kg/year and the 43.1 kg/day phosphorus limits are WQBELs applicable underMinn. R. 7053.0205, subp. 8 and Minn. R. 7050.0222 and have been applied to protect downstream waters fromeutrophication.

NPDES/SDS Permit Program Fact SheetPermit ReissuanceMN00301719 of 14State Discharge RestrictionsThe 1.0 mg/L limit for phosphorus was applied to meet discharge restrictions specified under Minn. R. 7053.0255. Thelimit for fecal coliform was developed to meet state discharge restrictions specified under Minn. R. 7053.0215, subp. 1,requiring the Facility to meet minimum secondary treatment levels.Conditional Effluent LimitsThe Facility operates under conditional effluent limits (Minn. R. 7050.0213). Conditional Effluent Limits are defined astwo or more different sets of limits for a parameter that apply to a facility’s discharge within the same effective perioddue to a conditional situation that does not meet the definition of Variability of Operation.Under the conditional effluent limit requirements, monitoring for the parameters of Beryllium, Cadmium, Chromium,Cyanide, Selenium, and Silver are required only when the Facility accepts leachate from the Northern States Power (NSP)ash disposal site.Proposed permit effluent limitsThe Permittee has been authorized to reuse treated effluent from the Facility. Potential uses for the reused effluentinclude irrigation, landscaping, vehicle and equipment washing, internal equipment cooling, cooling towers, industrialuses (including those in which the water may come into contact with workers), pipeline testing, air conditioning, toiletand urinal flushing, priming drain traps, structural firefighting, decorative fountains, commercial laundries, consolidationand backfill around potable water pipelines, artificial snow making, commercial car washes (including unheated handwashes), industrial boiler feed, soil compaction, mixing concrete, dust control, cleaning of roads, sidewalks and outdoorwork areas, and flushing sanitary sewers. Other uses not specifically listed above may be allowed on a case-by-case basiswithout permit modification, with prior MPCA approval. Wastewater that is reused is effluent from the treatment plantthat is filtered and subsequently disinfected to a higher level and has stringent limits for total coliform bacteria andturbidity. Wastewater that does not meet these limits is not reused.Technology based effluent limitsLimits for CBOD5 (applicable April-May), TSS and percent removal are specified under Minn. R. 7053.0215, Supb. 1,requiring the Facility to meet minimum secondary treatment levels.Water quality based limitsThe limits for CBOD5 (applicable June-March) are applicable under Minn. R. 7053.0225. The seasonal ammonia limits areapplicable under Minn. R. 7053.0205, subp. 8 and Minn. R. 7050, subp. 0220 and have been applied to the Facility toprotect downstream waters from ammonia toxicity. The Total Residual Chlorine limit is the final acute value for chlorinefound in Minn. R. 7053.0205. This limit is determined to be necessary to protect the use classification of the receivingwater. The 33.2 kg/day seasonal Phosphorus limit and the 12,434 kg/year calendar year to date limit are WQBELsapplicable under Minn. R. 7053.0205, subp. 8 and Minn. R. 7050.0222 and have been applied to protect downstreamwaters from eutrophication. The WQBELs are more restrictive than the Minnesota River Basin Low Dissolved OxygenWaste load Allocation for this Facility.State Discharge Restrictions (SDRs)The limit for fecal coliform has been developed to meet state discharge restrictions specified under Minn. R. 7053.0215,subp. 1, requiring the Facility to meet minimum secondary treatment levels.The proposed limit and monitoring requirements for the facility are found in the limits and monitoring table in theaccompanying draft permit document.

NPDES/SDS Permit Program Fact SheetPermit ReissuanceMN003017110 of 14Reasonable Potential for Chemical Specific Pollutants (40CFR§122.44(d) (1))Federal regulations require the MPCA to evaluate the discharge to determine whether it has the reasonable potential tocause or contribute to a violation of water quality standards. The Agency must use acceptable technical procedures,accounting for variability (coefficient of variation, or CV), when determining whether the effluent causes, has thereasonable potential to cause, or contribute to an excursion of an applicable water quality standard. Projected effluentquality (PEQ) derived from effluent monitoring data is compared to Preliminary Effluent Limits (PELs) determined frommass balance inputs. Both determinations account for effluent variability. Where PEQ exceeds the PEL, there isreasonable potential to cause or contribute to a water quality standards excursion. When reasonable potential isindicated, the permit must contain a Water Quality Based Effluent Limit (WQBEL) for that pollutant.Whole Effluent Toxicity - The discharge is located on the Minnesota River. This portion of the Minnesota River has thefollowing water classification: 2B, 3C, 4A, 4B, 5, and 6. The Permittee has chronic Whole Effluent Toxicity (WET)monitoring as a requirement. The Permittee has chronic WET testing because the ratio of the 7Q10 low flow (the lowestconsecutive seven-day flow that a river experiences on average at least once every ten years) of the receiving watercompared to the Facility’s average dry weather (ADW) flow is less than or equal to 20:1.The monitoring threshold value of 9.9 toxicity units, chronic (TUc) has been updated to 10.4 TUc because of updatedinformation on updated 7Q10 receiving water flow. A reasonable potential evaluation was attempted on the chronicWET tests to determine if there was cause to exceed the WET monitoring threshold value of 10.4 TUc. Because all fourchronic WET tests done during the last permit cycle had 1.0 TUc for all organisms tested, there was no reasonablepotential to cause or contribute to a chronic WET WQBEL. Because no reasonable potential has been found, amonitoring threshold value of 10.4 TUc has been established. The 10.4 TUc is a monitoring threshold value, not a WETlimit.Priority Pollutants - The priority pollutant scan information of the effluent was evaluated using reasonable potentialprocedures. All but chloroform of the organic priority pollutants were below the level of detection. Since thesepollutants were at low enough levels not to be detected, reasonable potential to cause or contribute to a water qualitystandards excursion is not indicated.Total arsenic, free cyanide, chloroform, total copper, total selenium, total zinc, and total mercury indicated noreasonable potential to cause or contribute to an excursion above the applicable water quality standard. The Facility alsomonitored for total silver, total cadmium and total chromium in their effluent. Cadmium, chromium and silver data wereall below reporting levels. As such, no reasonable potential evaluation could be done for these three metals. No effluentlimits are needed.Mercury- Monitoring results of the effluent include 17 data points at a calculated coefficient of variation

NPDES/SDS Permit Program Fact Sheet MN0030171 Permit Reissuance 3 of 14 . Purpose and participation . Applicable statutes This fact sheet has been prepared according to the 40 CFR § 124.8 and 124.56 and Minn. R. 7001.0100, subp. 3 in regards to a draft National Pollutant Discharge Elimination System (NPDES