National Pollutant Discharge Elimination System /State Disposal System (NPDES/SDS) Permit Program Fact Sheet

Transcription

1 National Pollutant Discharge Elimination System /State Disposal System (NPDES/SDS) Permit Program Fact Sheet Permittee: City of Melrose Facility Name: Melrose WWTF Permit Number: MN First Street NE th Avenue NE Melrose, MN Melrose, MN Current Permit Expiration: May 31, 2013 Public Comment Period Begins: June 10, 2014 Period Ends: July 10, 2014 Receiving Water: Sauk River, Class 2B, 3C, 4A, 4B, 5, 6 Water Proposed Action: Permit Reissuance Permitting Contact Holly Christensen Minnesota Pollution Control Agency 714 Lake Avenue, Suite 220 Detroit Lakes, MN Phone Fax

2 Table of Contents Purpose and Participation... 3 Applicable Statutes Fact Sheet Purpose Public Participation Facility Description... 4 Background Information Topographic Map of Permitted Facility Components and Treatment Technology Table 1. Significant Industrial Users Table 2. Discharge Monitoring Report Summary Receiving Water... 9 Use Classification Impairments, Listings, and Total Maximum Daily Load Studies Existing Permit Effluent Limits Technology Based Effluent Limits State Discharge Requirements Water Quality Based Effluent Limits Table 3. Existing Permit Effluent Limits and Monitoring Proposed Permit Effluent Limits Technology Based Effluent Limits State Discharge Requirements Water Quality Based Effluent Limits Table 4. Reasonable Potential Inputs Table 5. EPA Methods Table 6. Proposed Permit Effluent Limits and Monitoring Additional Requirements Pollutant Minimization Plans Compliance Schedules Variances Industrial Stormwater Coverage Salty Discharge Requirements Additional Monitoring Requirements Priority Pollutants Chronic Whole Effluent Toxicity (WET) Testing Requirements Biosolids Land Application Total Facility Requirements Nondegradation and Anti backsliding

3 Purpose and Participation Applicable Statutes This fact sheet has been prepared according to the Title 40 Federal Code of Regulations (CFR) and and Minn R , subp. 3 in regards to a draft NPDES/SDS permit to construct and/or operate wastewater treatment facilities and to discharge into waters of the State of Minnesota. Fact Sheet Purpose This fact sheet outlines the principal issues related to the preparation of this draft permit and documents the decisions that were made in the determination of the effluent limitations and conditions of this permit. Public Participation You may submit written comments on the terms of the draft permit or on the Commissioner s preliminary determination. 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 specific references 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 to investigate the merits of your position. You may also request that the MPCA Commissioner hold a public informational meeting. A public informational meeting is an informal meeting which the MPCA may hold to help clarify and resolve issues. In accordance with Minn. R and Minn. R , your petition requesting a public informational meeting must identify the matter of concern and must include the following: items 1 through 3 identified above; a statement of the reasons the MPCA should hold the meeting; and the issues you would like the MPCA to address at the meeting. In addition, you may submit a petition for a contested case hearing. A contested case hearing is a formal hearing before an administrative law judge. Your petition requesting a contested case hearing must include a statement of reasons or proposed findings supporting the MPCA decision to hold a contested case hearing pursuant to the criteria identified in Minn. R , subp. 1 and a statement of the issues proposed to be addressed by a contested case hearing and the specific relief requested. To the extent known, your petition should include a proposed list of witnesses to be presented at the hearing, a proposed list of publications, references or studies to be introduced at the hearing, and an estimate 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 1 of this notice. All written comments, requests, and petitions received during the public comment period will be considered in the final decisions regarding the permit. If the MPCA does not receive any written comments, requests, or petitions during the public comment period, the Commissioner or other MPCA staff as authorized by the Commissioner will make the final decision concerning the draft permit. During the public comment period, however, you may request that the draft permit be presented to the 3

4 MPCA s Citizens Board (Board) for final decision. You may participate in the activities of the Board as provided in Minn. R Comments, petitions, and/or requests must be submitted by the last day of the public comment period to: Holly Christensen Minnesota Pollution Control Agency 714 Lake Avenue, Suite 220 Detroit Lakes, MN The permit will be reissued if the MPCA determines that the proposed Permittee or Permittees will, with respect to the facility or activity to be permitted, comply or undertake a schedule to achieve compliance with all applicable state and federal pollution control statutes and rules administered by the MPCA and the conditions of the permit and that all applicable 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 Description Background Information Facility Location The Melrose Wastewater Treatment Facility (Facility) is located in the SW 1/4 of Section 35, Township 126 North, Range 33 West, Melrose Township, Stearns County, Minnesota. The Facility is approximately ¼ of a mile to the northeast of the City of Melrose. Outfall Location The outfall (Station SD002) is located immediately to the north of the Facility on the southern side of Sauk River. The PLS coordinates of the outfall are the same as the Facility location: the SW 1/4 of Section 35, Township 126 North, Range 33 West, Melrose Township, Stearns County, Minnesota. Station SD002 is shown on the map on page 5. 4

5 5

6 Components and Treatment Technology Current Information Major components of the Facility include: Collection with gravity and/or Pressure Sewer Influent Flow Meter 2 Flow Equalization Tanks 250,000 gallons total 1 Mechanical Bar Screen 3 Fine Static Screens Grit Removal 3 Primary Clarifiers with chemical and polymer addition for solids settling 2 Trickling Filters each has a 50 foot diameter 4 Cell Activated Sludge Tank contact stabilization, conventional, step feed Phosphorus Removal polymer and ferric chloride addition 3 Secondary Clarifiers 52 foot diameter, 48 foot diameter and 65 foot diameter Chlorination 41,650 gallon tank Dechlorination sulfur dioxide addition 2 Effluent Screw Pumps Postaeration cascade aeration, less than two hours detention time Dissolved Air Flotation Unit 16 foot diameter 3 Anaerobic Digesters complete mixed, heated mesophilic Centrifuge Biosolids Storage Tank 720,000 gallons Biosolids Land Application The existing Facility has a continuous discharge (SD002) to the Sauk River (Class 2B, 3C, 4A, 4B, 5, 6 Water). It is designed to treat an average wet weather flow (AWWF) of 3.0 million gallons per day (MGD) and an average dry weather flow of 2.65 MGD, with a 5 day carbonaceous biochemical oxygen demand concentration of 415 milligrams per liter (mg/l)(based on the AWWF) and a total suspended solids concentration of 456 mg/l. This is a Class A Facility. Waste activated sludge generated in the wastewater treatment process is thickened through a dissolved air flotation thickener. Both primary and waste activated sludge is further processed in three anaerobic digesters. Biosolids are thickened by a centrifuge prior to being pumped to a biosolids storage tank. Stored biosolids are then land applied. One bypass point is known to exist in the disposal system. The bypass is located at the Facility to the southwest of the discharge point, and is kept locked and manually controlled. This point at the Facility is capable of discharging untreated wastewater directly to the Sauk River. The MPCA has evaluated the treatment components of the Facility with regards to the mass limits in the permit. At the time of permit issuance the Facility is operating at less than the permitted AWWF rate of 3.0 mgd and is demonstrating the capability of meeting the effluent mass limit of 3,325 kg/year for total phosphorus. As the Facility approaches it s AWWF it may need infrastructure improvements and/or operational changes to maintain compliance with the mass limits. 6

7 Flow Schematic 7

8 Changes to Facility or Operation There are no planned changes to the Facility or its operation during this five year permit cycle. Significant Industrial Users (SIUs) The Facility has three contributing SIUs. Table 1 lists these SIUs, their processes, their flow contributions, whether there are control mechanisms and limits in place and whether categorical standards apply. Table 1. Significant Industrial Users SIU Process Flow (mgd) Control Mechanism/Limits? Do Categorical Standards Apply? Jennie O Turkey Turkey processing yes no Melrose Dairy Cheese processing yes no Proliant Dairy Whey Protein yes no Recent Compliance History The most recent MPCA inspection of the Facility occurred on June 30, According to the inspection report, a visual inspection was conducted along with a discussion with Mr. Scott Gilbertson, Wastewater Supervisor, and a review of the monthly Discharge Monitoring Reports from April 1, 2009 through May 31, Based on the results of the inspection, there was one violation of the NPDES/SDS permit. On June 1, 2009, the Permittee reported two effluent limit exceedances for total ammonia nitrogen. The calendar month average limits are 1.2 mg/l and 13.6 kg/day. The Facility reported results of 2.1 mg/l and kg/day, respectively. There were no other violations listed in the report. Table 2. Discharge Monitoring Report Summary March 2013 through February

9 Table 2. con t. Receiving Water Use Classification The receiving water (Sauk RIver) is a Class 2B, 3C, 4A, 4B, 5 and 6 Water Water Use Classifications For Waters Of The State Subp. 2. Class 1 waters, domestic consumption. Domestic consumption includes all waters of the state that are or may be used as a source of supply for drinking, culinary or food processing use, or other domestic purposes and for which quality control is or may be necessary to protect the public health, safety, or welfare. Subp. 3. Class 2 waters, aquatic life and recreation. Aquatic life and recreation includes all waters of the state which do or may support fish, other aquatic life, bathing boating or other recreational purposes, and where quality control is or may be necessary to protect aquatic or terrestrial life or their habitats, or the public health, safety, or welfare. Subp. 4. Class 3 waters, industrial consumption. Industrial consumption includes all waters of the state which are or may be used as a source of supply for industrial process or cooling water, or any other industrial or commercial purposes, and for which quality control is or may be necessary to protect the public health, safety, or welfare. Subp. 5. Class 4 waters, agriculture and wildlife. Agriculture and wildlife includes all waters of the state which are or may be used for any agriculture purposes, including stock watering and irrigation, or by waterfowl or other wildlife, and for which quality control is or may be necessary to protect terrestrial life and its habitat or the public health, safety, or welfare. Subp. 6. Class 5 waters, aesthetic enjoyment and navigation. Aesthetic enjoyment and navigation includes all waters of the state which are or may be used for any form of water transportation or navigation, or fire prevention, and for which quality control is or may be necessary to protect the public health, safety, or welfare. Subp. 7. Class 6 waters, other uses. Other uses includes all waters of the state which are or may serve the above listed uses or any other beneficial uses not listed herein, including without limitation any such 9

10 uses in this or any other state, province, or nation of any waters flowing through or originating in this state, and for which quality control is or may be necessary for the above declared purposes, or to conform with the requirements of the legally constituted state or national agencies having jurisdiction over such waters, or any other considerations the agency may deem proper. There are no endangered or threatened species living in the receiving water. Impairments, Listings, and Total Maximum Daily Load (TMDL) Studies Sauk River Chain of Lakes & Eden and Vails TMDL Study Horseshoe Lake, a lake on the Sauk River near Richmond, Minnesota is downstream of this Facility s discharge. Horseshoe Lake was placed on the 2004 MPCA CWA Section 303 (d) TMDL list of impaired waters due to excess nutrients which impede swimming in the lake. Phosphorus is the primary nutrient responsible for excess algal growth in Horseshoe Lake. Federal regulation [40 CFR (d) (1) (i)] restricts mass increases from new and expanding NPDES permitted facilities upstream of impaired waters. This regulation also requires water quality based effluent limits for existing facilities that cause or contribute to a downstream impairment. To address this water quality impairment, a TMDL study of this area has been conducted and a draft report completed. The study determines the capacity to assimilate pollutant loads as the basis for recommendations of wasteload allocation for point sources and load allocation for nonpoint sources within the watershed. An appropriate balance of point and nonpoint source controls that attain water quality objectives were selected with full stakeholder involvement. Based on the results of the TMDL study, this Facility has been assigned a total phosphorus wasteload allocation of 3,325 kilograms per year (kg/year) as a 12 month moving total. This limit will go into effect at the time of permit reissuance. Statewide Mercury TMDL Mercury This permit contains requirements for mercury monitoring. These requirements were added in response to the U.S. Environmental Protection Agency s approval of the Minnesota state wide Mercury Total Maximum Daily Load (TMDL) plan. More information on the TMDL can be found on the MPCA internet site at Specific mercury monitoring requirements are found in the Surface Discharge Stations Chapter of this permit. Those requirements include sampling for total suspended solids via a grab sample taken at the same time as the total and dissolved mercury grab samples are taken. 10

11 Existing Permit Effluent Limits Technology Based Effluent Limits (TBELs) The total suspended solids, ph, and percent removal limits are TBELs developed for achieving secondary treatment standards. These limits are specified in 40 CFR and Minn. R and Minn. R State Discharge Requirements (SDRs) The calendar month average total phosphorus limit and the fecal coliform limit are state discharge requirements. There are no drinking water intakes within 25 miles of the discharge point; a year round fecal coliform is not applicable. Water Quality Based Effluent Limits (WQBELs) The residual chlorine, carbonaceous biochemical oxygen demand, ammonia nitrogen, and dissolved oxygen limits are WQBELs. The residual chlorine limit is the final acute value for chlorine found in Minn. R These limits are the limits that were determined to be necessary to protect the use classification for the receiving water. 11

12 Table 3. Existing Permit Effluent Limits and Monitoring 12

13 Proposed Permit Effluent Limits Technology Based Effluent Limits (TBELs) The total suspended solids, ph, and percent removal limits are technology based limits developed for achieving secondary treatment standards. These limits are specified in 40 CFR and Minn. R and Minn. R State Discharge Requirements (SDRs) The calendar month average total phosphorus limit and the fecal coliform limit are state discharge requirements. There are no drinking water intakes within 25 miles of the discharge point; a year round fecal coliform is not applicable. Water Quality Based Effluent Limits (WQBELs) The residual chlorine, carbonaceous biochemical oxygen demand, ammonia nitrogen, dissolved oxygen, and the annual mass total phosphorus limits are WQBELs. The residual chlorine limit is the final acute value for chlorine found in Minn. R These limits are the limits that were determined to be necessary to protect the use classification for the receiving water. Background The discharge is located on the Sauk River. This portion of the Sauk River has a water classification of 2B, 3C, 4A, 4B, 5, and 6. The Permittee has submitted four chronic whole effluent toxicity (WET) tests and two priority pollutant scans since The average dry weather (ADW) design flow is used to calculate WQBELs under critical low flow stream conditions. The ADW for this Facility is 2.65 mgd. The low flow condition is defined by the once in ten year weekly average flow (7Q 10 ), which is determined to be 5.26 mgd (8.15 cubic feet per second). The analysis below is based on data submitted to date. Reasonable Potential for Chemical Specific Pollutants (40CFR122.44(d)(1)) Federal regulations require MPCA to evaluate the discharge to determine whether the discharge has the reasonable potential to cause 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 the reasonable potential to cause, or contribute to an excursion of an applicable water quality standard. Projected effluent quality (PEQ) derived from effluent monitoring data is compared to Preliminary Effluent Limits (PELs) determined from mass balance inputs. Both determinations account for effluent variability. Where PEQ exceeds the PEL, there is reasonable potential to cause or contribute to a water quality standards excursion. When reasonable potential is indicated the permit must contain a WQBEL for that pollutant. The priority pollutant scan information of the effluent was evaluated using reasonable potential procedures. The Agency staff could only find two priority pollutant scans for this Facility. Since there 13

14 were only two data points for all of the pollutants, MPCA did not do a reasonable potential analysis. There were too few data points to do the analysis for the priority pollutant scan pollutants. From the table below mercury and chronic WET testing indicated no reasonable potential to cause or contribute to an excursion above the applicable water quality standard. Therefore, no effluent limits are needed. Mercury Monitoring results of the effluent include 19 data points at a calculated CV of 0.6. PEQ is derived as an upper bound value from the highest value measured (0.7 ng/l), and the determined variability (CV = 0.6) and number of data points (19). The PEL calculation assumes that the background mercury concentration is at the water quality standard (6.9 ng/l) when the listed stream impairment is for fish consumption advice, and no local river water column analytical data exist. To assure that the discharge does not cause or contribute to a water quality standards excursion for mercury impaired waters, the numeric water quality standard (6.9 ng/l) is applied at the point of discharge for the mass balance equation for the subsequent PEL calculations. Where PEQ exceeds the PEL, there is reasonable potential to cause or contribute to a water quality standards excursion. Since PEQ does not exceed the PEL in this case, reasonable potential to cause or contribute to an excursion above water quality standards is not indicated. A WQBEL is not needed. The following table contains the inputs to the reasonable potential analysis for mercury and chronic WET testing. The analysis is made with effluent data that is expressed as total metal. These pollutants were evaluated on the basis of analytical measurements that made evident the need for a full determination. Where PEQs exceed PELs, a WQBEL is needed. 14

15 Table 4. Reasonable Potential Inputs Parameter Hg (ng/l) WET(TUc) Max Measured Value # data points PEQ Plant flow ADW (mgd) Rec. water flow, 7Q10(mgd) Background Conc Continuous Std (cs) ppm hard Maximum Std (ms) ppm hard Final Acute Value (FAV) 4900 na 408 ppm hard Mass Balance cs Mass Balance ms Coeff of Variation (CV) Long Term Avg cs Long Term Avg ms Preliminary Effl limits: Daily Max Monthly Ave (2x/month) na Reasonable Potential PEQ>Daily max PEQ>Montly Ave PEQ> FAV Final Reasonable Potential FALSE FALSE FALSE No Notes: background for mercury set to chronic WQS because of the statewide Hg TMDL FALSE na na No 15

16 Reasonable Potential Conclusions for Mercury and Chronic WET testing Reasonable potential to cause or contribute to the excursion above a water quality standard has not been indicated for either mercury or chronic WET testing. See monitoring recommendations shown below. The following EPA Inorganic Analytical Methods (EPA 600/ ) and EPA Organic Analytical Methods (40 CFR 136; Oct. 26, 1984) apply: Table 5. EPA Methods Pollutant Monitoring Frequency EPA Method Method Detection Level Total and dissolved mercury 2X/yr ng/l Mercury Minimization Plan Existing municipal major facilities with no reasonable potential to exceed the applicable mercury standard: 1. Will not be assigned an interim or a final mercury limit. 2. Will be assigned twice annual effluent total and dissolved mercury and concurrent TSS grab sample monitoring throughout the five year permit cycle. 3. Will be required to submit a new or updated Mercury Minimization Plans (MMP) to the MPCA within 180 days of permit reissuance/issuance. Whole Effluent Toxicity (WET) The Permittee has chronic WET monitoring as a requirement. The Permittee has chronic WET testing because the ratio of the 7Q10 low flow of the receiving water compared to the Facility s ADW flow is less than or equal to 20:1. The Facility has a chronic monitoring TUc (Toxic Unit chronic) monitoring threshold value of or rounded to 2.9 TUc. A reasonable potential evaluation was done on the chronic WET tests to determine if there was cause to exceed the WET monitoring threshold value of 2.9 TUc. No reasonable potential was found to exceed the monitoring threshold of 2.9 TUc. Because no reasonable potential has been found, a monitoring threshold value of 2.9 TUc has been established. The 2.9 TUc is a monitoring threshold value, not a WET limit. Annual WET testing is required once per year. If the permit exceeds five years, an additional WET test for each year that exceeds the five year permit cycle is required. If the monitoring threshold value of 2.9 TUc is exceeded for any one WET test, the Facility will perform two WET retests to determine if a Toxicity Reduction Evaluation is needed. 16

17 Table 6. Proposed Effluent Limits and Monitoring 17

18 Table 6. Continued 18

19 Additional Requirements Pollutant Minimization Plans Mercury Minimization Plan This permit contains requirements for mercury monitoring and for submittal of a Mercury Minimization Plan (MMP) or updated MMP. These requirements are in response to the U.S. Environmental Protection Agency s approval of the Minnesota state wide Mercury TMDL plan. Compliance Schedules There is no compliance schedule included in this permit. Variances There are no variances included in this permit. Industrial Stormwater Coverage On April 5, 2010, the Industrial Stormwater General Permit (MNR050000) was issued. This permit addresses stormwater discharges associated with industrial activity for facilities that discharge stormwater to waters of the state, including Municipal Separate Storm Sewer Systems. The General Permit also addressed stormwater discharges associated with industrial activities at facilities that provide on site infiltration of industrial stormwater discharges associated with the facility. For both industrial and municipal wastewater facilities, in lieu of obtaining coverage under both the General Permit and the individual NPDES permit, the MPCA has added the necessary industrial stormwater requirements language and limits and monitoring to this permit so that coverage under this NPDES permit alone will cover both permits. An additional discharge station (SD003) has been created within this permit with specific limits and monitoring, and a Discharge Monitoring Report is required to be submitted annually. There is also an Industrial Stormwater Chapter specific to this Facility. The Inspection Report, Annual Report, and the Benchmark Monitoring Factsheet can be found on the MPCA s website and must be used to ensure compliance with the limits and monitoring requirements for the Facility. Salty Discharge Requirements Because this Facility has a receiving water stream flow to effluent dilution ration of less than 5:1, and has a salty waste stream from concentrating treatment technologies (e.g. reverse osmosis, ion exchange, membrane filtration, etc.) or food processing industries using density based (saline) sorting processes, the Facility is required to monitor for salty discharge parameters. Monitoring of Bicarbonates, Calcium, Chloride, Hardness, Magnesium, Potassium, Sodium, Dissolved Solids, Specific Conductance, and Sulfate shall be sampled once per month from the effluent waste stream (SD002). The Permittee may request a reduction in monitoring if, after two years of data, the monitoring does not indicate a reasonable potential to exceed a limit. If monitoring results indicate a reasonable potential for any of the parameters, the Permittee will be required to submit an application for permit modification and, if necessary, a compliance schedule will be added to the Permit to ensure progress towards meeting the water quality standards. 19

20 Additional Monitoring Requirements This draft permit requires additional monitoring for nitrite plus nitrate nitrogen and total Kjeldahl nitrogen, at a frequency of two times per year for the five year term of the permit. Total dissolved solids is part of this monitoring; however, it is also a requirement of the salty discharge monitoring sampling (once per month). The data will be recorded on a custom supplemental form provided by the MPCA and must be submitted with the discharge monitoring report. These additional parameters are being added to every permitted municipal facility with an average wet weather design flow of 100,000 gallons per day or greater. Priority Pollutants Priority pollutant monitoring on the effluent is required three times during the life of the permit. Sampling events are required to be completed at least one year apart. This permit includes requirements to fulfill the priority pollutant monitoring requirements in the current U.S. Environmental Protection Agency (EPA) application form (EPA Form A). Chronic Whole Effluent Toxicity (WET) Testing Requirements An annual requirement to submit chronic toxicity test batteries is required in this permit. The first set of annual chronic WET results are due one year from the end of the first calendar quarter following permit reissuance and annually thereafter. The test batteries are due by December 31 st of each year. Biosolids Land Application This permit requires biosolids to be treated to meet specific standards, and specifies monitoring, recordkeeping, reporting, and general requirements for biosolids that are applied to the land. Unless they are exceptional quality biosolids, sites to which biosolids are applied are approved by the MPCA by the procedures found in Minn. R Total Facility Requirements (TFR) All NPDES permits issued in the State of Minnesota contain certain conditions that remain the same regardless of the size, location, or type of discharge. The standard conditions satisfy the requirements outlined in 40 CFR These conditions are listed in the Total Facility Requirements chapter of an NPDES permit. These requirements cover a wide range of areas including recordkeeping, sampling, equipment calibration, equipment maintenance, reporting, facility upsets, bypass, solids handling, changes in operation, facility inspections, and permit reissuance. Nondegradation and Anti Backsliding In accordance with MPCA rules regarding nondegradation for all waters that are not Outstanding Resource Value Waters, nondegradation review is required for any new or expanded significant discharge (Minn. R ). A significant discharge is 1) a new discharge (not in existence before January 1, 1988) that is greater than 0.2 MGD to any water other than a Class 7 water or 2) an expanded discharge that expands by greater than 0.2 MGD that discharges to any water other than a Class 7 water or 3) a new or expanded discharge containing any toxic pollutant at a mass loading rate likely to increase the concentration of the toxicant in the receiving water by greater than one percent over the baseline quality. The flow rate used to determine significance is the design average wet weather flow. The January 1, 1988 design average wet weather flow for this Facility is 2.5 MGD. 20

21 This Permit also complies with Minn. R regarding anti backsliding. Any point source discharger of sewage, industrial, or other wastes for which a NPDES permit has been issued by the MPCA that contains effluent limits more stringent than those that would be established by parts to shall continue to meet the effluent limits established by the permit, unless the permittee establishes that less stringent effluent limits are allowable pursuant to federal law, under section 402(o) of the Clean Water Act, United States Code, title 33, section