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Permittee: Metropolitan Council Environmental Services (MCES)

2400 Childs Road

St. Paul, MN 55106

Public Comment Period Begins: May 6, 2015

Period Ends: June 5, 2015

Proposed Action: Met Council–Mississippi Basin Total Phosphorus Permit Issuance

NPDES/SDS Permit Number: MN0070629

*AUID – Assessment Unit Identification

Permitting Contact

Nicole Blasing 7678 College Road, Suite 105

Baxter, MN 56425 Ph. 218-316-3890 Fax 218-828-2594

Permitted Facility Name Discharge Receiving

Water

Receiving Water

Classification

Receiving Water

AUID*

Eagles Point WWTP Mississippi River 2B,3C,4A,4B,5,6 07010206-502

Empire WWTP Mississippi River 2B,3C,4A,4B,5,6 07010206-502

Hastings WWTP Mississippi River 2B,3C,4A,4B,5,6 07010206-501

Metropolitan WWTP Mississippi River 2C,3C,4A,4B,5,6 07010206-504

Seneca WWTP Minnesota River 2C,3C,4A,4B,5,6 07020012-505

National Pollutant Discharge

Elimination System /State Disposal

System (NPDES/SDS) Permit Program

Fact Sheet

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Table of Contents

Purpose and Participation .................................................................................................................. 3-4

Applicable Statutes ............................................................................................................... 3

Purpose ................................................................................................................................. 3

Public Participation ............................................................................................................... 3-4

Overview ............................................................................................................................................ 4

Purpose ................................................................................................................................. 4

Facility Description ............................................................................................................................. 5-9

Background Information ....................................................................................................... 5-7

Facility Locations ...................................................................................................... 5

Permitted Outfall Locations ..................................................................................... 5

Overview Map of Permitted WWTPs ....................................................................... 6

Components and Treatment Technology ............................................................................. 7-9

Current Information ................................................................................................. 7-8

Flow Schematic ........................................................................................................ 8

Changes to Facility or Operation ............................................................................. 8

Significant Industrial Users ...................................................................................... 8

Recent Compliance History ...................................................................................... 8

Recent Monitoring History ...................................................................................... 9

Receiving Water ................................................................................................................................. 10-11

Use Classifications ................................................................................................................. 10

Impairments .......................................................................................................................... 11

Individual NPDES/SDS TP Permit Effluent Limits ............................................................................... 11-12

Proposed Permit Effluent Limit .......................................................................................................... 12-17

Total Phosphorous Water Quality Based Effluent Limit ....................................................... 12-17

Variance ............................................................................................................................................. 17

Total Facility Requirements ............................................................................................................... 17

Nondegredation and Anti-backsliding ............................................................................................... 18

References ......................................................................................................................................... 19

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Purpose and Participation

Applicable Statutes This fact sheet has been prepared according to the Title 40 Federal Code of Regulations (CFR) 124.8 and 124.56 and Minn R. 7001.0100, Subp. 3 in regards to a draft National Pollutant Discharge Elimination System (NPDES)/State Disposal System (SDS) Permit to construct and/or operate wastewater treatment facilities and to discharge into waters of the State of Minnesota. 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. 7000.0650 and Minn. R. 7001.0110, 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. 7000.1900, 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

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MPCA’s Citizens’ Board (Board) for final decision. You may participate in the activities of the Board as provided in Minn. R. 7000.0650.

Comments, petitions, and/or requests must be submitted by the last day of the public comment period to:

Nicole Blasing Minnesota Pollution Control Agency

7678 College Road, Suite 105 Baxter, MN 56425

The Permit will be issued if the MPCA determines that the proposed Permittee 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.

Overview Purpose The Metropolitan Council Environmental Services (MCES) Mississippi Basin Total Phosphorous (TP) Permit (Permit) establishes a combined TP limit for five MCES owned and operated Wastewater Treatment Plants (WWTPs) that discharge to, or upstream of, Mississippi River Pools 2, 3 and 4 and Lake Pepin (MCES-Eagles Point WWTP, MCES–Empire WWTP, MCES–Metropolitan WWTP, MCES–Seneca WWTP and MCES–Hastings WWTP). This Permit authorizes the MCES (Permittee) to aggregate the TP Water Quality Based Effluent Limits (WQBEL) among the five WWTPs. The TP limit established in this Permit is intended to allow for efficient long-term planning and use of publicly-owned regional resources in order to achieve the collective TP reduction goals for the Mississippi River Basin and Lake Pepin Watershed. The TP limit represents the sum of the TP WQBEL for the five WWTPs to achieve both the current Wisconsin water quality standards and Minnesota’s eutrophication standards for the Mississippi River and Lake Pepin. Minnesota’s river eutrophication criteria and site specific standards for Lake Pepin are compatible with Wisconsin’s existing TP water quality standard for Pool 3 of the Mississippi River. The TP limit established in this Permit will represent a 71% (393,000 kg/year) reduction of the permitted TP loading from the MCES WWTPs included in this Permit. The 393,000 kg/year reduction in permitted TP loading to the Mississippi River and Lake Pepin is estimated to represent 79% of the total annual TP loading discharged by Minnesota NPDES permitted municipal and industrial WWTPs upstream of Lake Pepin. This Permit does not authorize a discharge of any pollutant other than TP. The Permittee is required to comply with all of the conditions specified in the individual NPDES/SDS permits associated with each WWTP included in this Permit in addition to the requirements of this Permit. The individual NPDES/SDS permits include WWTP specific concentration based TP limits and monitoring requirements.

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Facility Description Background Information Facility Location Table 1. Location of Permitted Facilities

Permitted Outfall Locations Table 2. Permitted Surface Discharge (SD) Stations and Locations

MCES Facility Name Type of Station Individual

NPDES/SDS SD Station

Total Phosphorous

Permit SD Station Number

Station Location

Eagles Point WWTP Effluent to Surface Water

SD002 ----- NW ¼ of SW ¼ of S34, T27N, R21W

Empire WWTP Effluent to Surface Water

SD002 ----- NE ¼ of S17, T115N, R18W

Hastings WWTP Effluent to Surface Water

SD001 ----- SW ¼ of S22, T115N, R17W

Metropolitan WWTP Effluent to Surface Water

SD001 ----- SE ¼ of SE ¼ of S9, T28N, R22W

Seneca WWTP Effluent to Surface Water

SD001 ----- NW ¼ of S18, T27N, R23W

MCES Total Phosphorous- Calculation Station

SD001

MCES Permitted

Facility

Individual NPDES/SDS

Permit Number Facility Location

Eagles Point WWTP MN0029904 NW ¼ of SW ¼ of S34, T27N, R21W

Empire WWTP MN0045845 NE ¼ of S17, T115N, R18W

Hastings WWTP MN0029955 SW ¼ of S22, T115N, R17W

Metropolitan

WWTP

MN0029815 SE ¼ of SE ¼ of S9, T28N, R22W

Seneca WWTP MN0030007 NW ¼ of S18, T27N, R23W

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Overview Map of Permitted Facility

* Additional locational information can be found in the individual NPDES/SDS Permit associated with each WWTP included in this Permit.

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Components and Treatment Technology Current Information A general description of each WWTP included in this Permit is outlined below. Additional information can be found in the individual NPDES/SDS Permits associated with each WWTP.

1. MCES–Eagles Point WWTP (Individual NPDES/SDS Permit Number MN0029904)

The MCES-Eagles Point WWTP is an existing Class A WWTP that is designed to treat an Average Wet Weather (AWW) design flow of 11.9 million gallons per day (mgd). The WWTP consists of two mechanical bar screens, influent pumping, three grit removal units, two primary clarifiers, four activated sludge tanks with ammonia and biological phosphorus removal, two final clarifiers, and ultraviolet disinfection. Biosolids are thickened by a gravity thickener and two gravity belt thickeners and hauled to the MCES-Metropolitan WWTP for further treatment and disposal.

2. MCES–Empire WWTP (Individual NPDES/SDS Permit Number MN0045845)

The MCES-Empire WWTP is an existing Class A WWTP that is designed to treat an AWW design flow of 28.61 mgd. The WWTP consists of an influent pumping station, three mechanical fine screens, two vortex grit removal tanks, six primary clarifiers, five anaerobic/anoxic selector basins for biological phosphorus removal, ferric chloride addition, five activated sludge basins, eight secondary clarifiers, three ultraviolet light (UV) disinfection units, and an effluent pumping station. Solids processing consists of three gravity belt thickeners for waste activated sludge and two gravity thickening tanks for primary sludge. The thickened primary and secondary sludge are combined and treated in three primary anaerobic digesters and two secondary anaerobic digesters. Digested solids are further processed in two belt filter presses and the dewatered solids are stored on two storage pads. Filtrate from the solids treatment dewatering processes is discharged to four filtrate equalization tanks prior to being returned to the anaerobic/anoxic tanks or the activated sludge basins. Biosolids from this process are Class B and land applied.

3. MCES–Hastings WWTP (Individual NPDES/SDS Permit Number MN0029955) The MCES-Hastings WWTP is an existing Class B WWTP that is designed to treat an AWW design flow of 2.69 mgd. The WWTP consists of a mechanical bar screen, screenings compactor, magnetic flow meter, two aerated grit removal units, two primary clarifiers, two four-pass aeration tanks (for a total of eight basins) with fine bubble diffusion, two final clarifiers, a disinfection contact chamber using sodium hypochlorite and dechlorination with sodium bisulfite solution. Primary and secondary sludges are blended and gravity thickened. Thickened sludge is loaded out and transferred to the MCES-Metropolitan WWTP for further treatment and disposal.

4. MCES–Metropolitan WWTP (Individual NPDES/SDS Permit Number MN0029815) The MCES-Metropolitan WWTP is an existing Class A WWTP that is designed to treat an AWW design flow of 314 mgd. The WWTP consists of mechanical bar screens, grit removal, primary clarifiers, an activated sludge system with biological phosphorus removal, final clarifiers, chlorine disinfection, and dechlorination equipment. Odors are treated using biofilters and chemical scrubbers. Sludge treatment consists of thickening by gravity or flotation, polymer addition, dewatering using roll presses, centrifuges, fluidized bed incineration or land application. Ash from the incinerator is conveyed to storage silos for disposal or beneficial reuse.

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5. MCES-Seneca WWTP (Individual NPDES/SDS Permit Number MN0030007) The MCES-Seneca WWTP is an existing Class A WWTP that is designed to treat an AWW design flow of 38 mgd. The WWTP consists of three mechanical bar screens, grit removal, two primary clarifiers, seven activated sludge basins with single stage nitrification and biological phosphorus removal, six final clarifiers, chlorination, dechlorination, and cascade effluent aeration with pure oxygen injection. Chemical addition is used for phosphorus removal as a backup to the biological phosphorus removal. Biosolids are managed by thickening and dewatering prior to incineration.

Flow Schematic A flow schematic for each WWTP included in this Permit can be found in the individual NPDES/SDS permit associated with each WWTP. Changes to Facility or Operation There are no changes to a facility or operations of the WWTPs included in this Permit. Any changes to a facility or its operation will be included in the individual NPDES/SDS permit associated with each WWTP. Significant Industrial Users (SIUs) A review of the SIUs that discharge to each WWTP included in this Permit was not completed as part of the permit issuance process. Any SIU that discharges to a WWTP covered by this Permit will be reviewed as part of the re-issuance of the individual permit associated with each WWTP. Recent Compliance History The Seneca, Metropolitan, Empire, and Eagles Point WWTP’s individual permits include 12 month moving average phosphorous limits of 1.0 mg/L. The Hastings WWTP’s individual permit includes a schedule to attain compliance with a final 12 month moving average phosphorous limit of 1.0 mg/L. The Eagles Point, Empire, Metropolitan, and Seneca WWTP’s have not reported a phosphorus limit violation within the past five years. The current permit for the Hastings WWTP does not have an assigned phosphorous limit.

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Recent Monitoring History Tables 3 includes the 2014 calendar month average and calendar year average effluent TP values in mg/L and Table 4 includes the 2014 TP load summary in kg/month and kg/year for each MCES Facility included in the MCES TP Permit.

Table 3. 2014 Total Phosphorus Concentration Values in mg/L.

MCES

Facility

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Yr

Avg

Eagles

Point

WWTP

1.06 0.85 1.12 0.81 0.67 0.58 1.17 0.7 0.34 0.32 0.42 0.39 0.703

Empire

WWTP

0.19 0.21 0.24 0.22 0.28 0.76 0.39 1.11 0.39 0.23 0.23 0.23 0.373

Hastings

WWTP

3.92 3.66 3.21 3.28 3.09 3.45 3.42 3.44 3.6 3.82 3.85 3.71 3.537

Metro

WWTP

0.3 0.6 0.4 0.4 0.3 0.3 0.2 0.2 0.3 0.3 0.2 0.3 0.317

Seneca

WWTP

0.73 0.91 0.65 0.65 1.16 0.81 0.55 0.7 0.65 0.39 0.57 0.5 0.689

Table 4. 2014 Total Phosphorous Load in kg/month and kg/year.

MCES

Facility

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Yr

Sum

Eagles

Point

WWTP

571 393 582 428 367 320 635 363 165 161 211 202 4,398

Empire

WWTP

219 215 287 267 369 1093 519 1335 434 264 255 264 5,521

Hasting

s

WWTP

651 538 562 557 569 639 581 581 580 628 613 615 7,114

Metro

WWTP

5,63

0

10,16

0

7,89

5

9,05

0

7,82

5

8,82

3

4,97

2

4,31

8

6,05

6

5,96

9

3,73

2

5,70

0

80,13

0

Seneca

WWTP

1,82

4

2,040 1,65

7

1,65

7

3,26

0

2,40

8

1,51

1

1,82

5

1,59

6

963 1,34

9

1,22

8

21,31

8

Aggregate 2013 Load (kg/yr)

118,481

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Receiving Waters Use Classifications Table 5. Receiving Water Use Classification for Each Permitted Facility

*AUID – Assessment Unit Identification

Class 2 waters, aquatic life and recreation. Aquatic life and recreation includes all waters of the state that support or may support fish, other aquatic life, bathing, boating, or other recreational purposes and for which quality control is or may be necessary to protect aquatic or terrestrial life or their habitats or the public health, safety, or welfare. Class 3 waters, industrial consumption. Industrial consumption includes all waters of the state that 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. Class 4 waters, agriculture and wildlife. Agriculture and wildlife includes all waters of the state that are or may be used for any agricultural 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. Class 5 waters, aesthetic enjoyment and navigation. Aesthetic enjoyment and navigation includes all waters of the state that 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. Class 6 waters, other uses and protection of border waters Other uses includes all waters of the state that serve or may serve the uses in subparts 2 to 6 or any other beneficial uses not listed in this part, including without limitation any such 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 declared purposes in this part, to conform with the requirements of the legally constituted state or national agencies having jurisdiction over such waters, or for any other considerations the agency may deem proper.

MCES Permitted

Facility

Discharge

Receiving Water

Receiving Water

Classification

Receiving Water

AUID*

Eagles Point WWTP Mississippi River 2B,3C,4A,4B,5,6 07010206-502

Empire WWTP Mississippi River 2B,3C,4A,4B,5,6 07010206-502

Hastings WWTP Mississippi River 2B,3C,4A,4B,5,6 07010206-501

Metropolitan WWTP Mississippi River 2C,3C,4A,4B,5,6 07010206-504

Seneca WWTP Minnesota River 2C,3C,4A,4B,5,6 07020012-505

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Impairments Listed below are the impairments associated with phosphorous that are downstream of the WWTPs included in this Permit. There are other impairments including mercury, polychlorinated biphenyl (PCB) in fish tissue, perfluorooctane sulfonate (PFOS) in fish tissue, fecal coliform, and turbidity in addition to the impairments listed below. The additional impairments will be addressed in the individual NPDES/SDS permit associated with each WWTP.

Table 6. TP Impairments Downstream of Permitted Facilities

Downstream Impairments

Number of

Impaired

Reaches TMDL Status

Minnesota River

Oxygen, Dissolved 1

The Lower Minnesota River – Low Dissolved Oxygen TMDL has

been approved by U.S. EPA. The Seneca WWTP is the only

WWTP upstream of this impairment and the discharge was not

assigned a WLA because it is located outside of the TMDL’s

project area.

Pepin Lake

Nutrient/Eutrophication

Biological Indicators 1

The draft Lake Pepin – Excess Nutrients TMDL is on hold until a

site specific water quality standard is approved in connection

with the next iteration of Minnesota Rules Chapter 7050. All

five facilities and their associated discharges are located within

the TMDL project area. As a result a pre-TMDL WQBEL was

developed for the five MCES Facilities included in this permit.

Individual NPDES/SDS TP Permit Effluent Limits The Seneca, Metropolitan, Eagles Point, and Empire WWTP’s individual NPDES/SDS permits currently include a 1.0 mg/L, 12 month moving average, TP limit and currently meet the limit by biological phosphorous removal. The Hastings WWTP individual NPDES/SDS permit currently does not include a phosphorous limit as it has not been required by Minn. R. 7053.0255. Individually, the Hastings WWTP discharge does not affect the trophic status of a lake and/or has not expanded. To expedite the permit re-issuance process, MCES has accepted a phosphorous limit of 1.0 mg/L, 12 Month Moving Average. The Hastings WWTP individual NPDES/SDS Permit is currently up for re-issuance. The draft individual NPDES/SDS Permit includes a final TP limit of 1.0 mg/L, 12 Month Moving Average with a schedule to attain compliance with the final TP limit. Upon issuance of this Permit the current phosphorous concentration limits included in the individual NPDES/SDS Permits associated with each WWTP will be retained in each respective Permit. The phosphorous loading limits that are currently in each individual NPDES/SDS Permit will be removed when the individual Permits are re-issued. Upon final issuance, the Permittee will be required to maintain compliance with the combined TP WQBEL established in this Permit.

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Table 7. Phosphorous limit included in the individual NPDES/SDS permit associated with each MCES WWTP

Proposed Permit Effluent Limit Total Phosphorous Water Quality Based Limit

Overview and Applicable Standards For this Permit, the MPCA has determined the phosphorus loading reductions required to achieve both Wisconsin’s water quality standards and Minnesota’s eutrophication standards for the Mississippi River and Lake Pepin (Table 8). The intent is to develop a TP WQBEL that will allow for long term planning and faster implementation by authorizing MCES to coordinate and manage TP loads amongst a number of their WWTPs.

Table 8. Minnesota eutrophication standards for rivers, Mississippi River Pools and Lake Pepin (Heiskary and Wasley 2012). Concentrations expressed as summer averages. Source of data for assessment noted.

Permitted Facility Name

12 month moving

average limit in mg/L

12 month moving total limit in

kg/year

draft 12 month moving average

limit in mg/L

Eagles Point WWTP 1.0 16,440

Empire WWTP 1.0 39,525

Hastings WWTP ----- ----- 1.0

Metropolitan WWTP 1.0 431,077

Seneca WWTP 1.0 52,560

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River/Pool Site TP (mg/L) Chl-a (ug/L)

Rivers

Miss. @Anoka1

UM‐872 0.100 18

Lake St. Croix3 SC‐0.3 0.40 14

Minn.

@Jordan1

MI‐39 0.150 35

Pools & Pepin

Pool 12 UM‐847 0.100 35

Pool 24 UM‐815 0.125 35

Pool 34

UM-796 0.100 35

Pepin (Pool 4)5 4 fixed sites 0.100 28

Pools 5‐86 Near‐dam 0.100 35

1 River eutrophication criteria‐based.

2 Minimize frequency of severe blooms. Upstream criteria provide additional protection for Pool 1.

3 MN lake eutrophication criteria‐based. Based on modeling St. Croix outlet (SC‐0.3).

4 Minimize frequency of severe blooms & meet Pepin requirements. LD3 TP standard same as current WI standard.

5. TP consistent with WI standard. Lake Pepin criteria assessed based on lake‐wide mean from 4 monitoring sites.

6 Minimize frequency of severe blooms; upstream P requirements benefit lower pools. WI TP standard of 0.100 mg/L applies to Pools 5‐8.

Wisconsin’s TP standard of 0.100 mg/L at Lock and Dam 3 (also the river eutrophication standard in Minnesota) appears to be the most restrictive reach based on the reduction scenarios considered in the Lake Pepin modeling effort that was completed in 2009 (shown in Table 9 and Figure 2). Wisconsin’s current TP standard of 0.100 mg/L for large rivers applies to all reaches of the Mississippi River. It is important to note that Wisconsin’s regulations do not include the evaluation of response variables (i.e. chlorophyll‐a, BOD, DO flux) to determine whether rivers are impaired due to eutrophication. As a result, phosphorus is the only target for development of effluent limits or TMDLs at Lock and Dam 3. This simplifies the process somewhat since chlorophyll‐a (measure of algal production) or other response variables of river eutrophication standards in Minnesota do not need to be considered for this Permit.

Table 9. Estimated long-term summer average total phosphorous (mg/L) based on reduction scenarios applied to 1985-2006 baseline years.

Scenario St.

Croix

Minn LD1* LD2* LD3* Upper

LP

Lower

LP

Overall

LP

Outlet

LP

2 0.045 0.285 0.110 0.215 0.170 0.153 0.152 0.153 0.169

4 0.036 0.141 0.088 0.161 0.126 0.113 0.110 0.111 0.120

17 0.036 0.141 0.088 0.122 0.100 0.093 0.092 0.092 0.102

20 0.036 0.148 0.088 0.152 0.121 0.111 0.109 0.110 0.121

21 0.036 0.139 0.088 0.120 0.099** 0.094 0.094 0.094 0.105***

Standard 0.040 0.150 0.100 0.125 0.100 0.100 0.100 * LD1 = Lock & Dam 1, LD2 = Lock & Dam 2, LD3 = Lock & Dam 3

**Excess TP available from 0.099 to 0.1 mg/L at Lock and Dam 3 is available for point sources not included in original model.

***Outlet of Lake Pepin is controlled by internal loading in lower lake. May need additional non‐

point reductions to meet 0.10 mg/L.

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Figure 2. Locations of MCES WWTPs (starred) in reference to navigational pools and the lock and dam locations of the Mississippi River.

2009 Model Results Scenario 21 of the available model runs meets the 0.100 mg/L target at Lock and Dam 3. In scenario 21, all MCES WWTPs in the model domain (Pool 2 through Pool 4 of the Mississippi River) had mass allocations based on the WWTPs AWWDF and 0.3 mg/L to meet applicable standards (Figure 2). Since the initial 2009 modeling, the MPCA has established WQBELs upstream of Lake Pepin calculated from facility design flow and effluent concentration assumptions related to facility type and size. This “categorical” approach (Table 10) is designed to achieve the necessary balance of wasteload allocations (WLAs) among approximately 540 wastewater dischargers upstream of Lake Pepin. Generally, larger facilities are allocated loads based on more restrictive effluent concentration assumptions.

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Table 10. Lake Pepin Categorical WLA Assumptions

Type Category Design Flow Category Effluent Concentration

Assumptions Extra Large Municipal XLM Average Wet Weather Design Flow

≥20mgd 0.3 mg/L

Major Municipal MM Average Wet Weather Design Flow ≥1 but <20 mgd

0.8 mg/L

Large Municipal LM Average Wet Weather Design Flow ≥0.2 to 0.3 but < 1 mgd

1.0 mg/L

Small Municipal Pond SMP Average Wet Weather Design Flow <0.2 mgd

2.0 mg/L

Small Municipal Mechanical

SMM Average Wet Weather Design Flow <0.3 mgd

3.5 mg/L

Industrial High Concentration

LIHC Maximum Flow 1.0 mg/L

Industrial Low Concentration

LILC Maximum Flow Actual effluent concentration plus a margin of safety

Table 11 includes the TP allocations for the five MCES WWTPs that are included in the Met Council–Mississippi Basin TP Permit based on the categorical approach. Given that all the facilities listed in Table 11 are in close proximity to each other, changes in their individual allocations are not expected to change the model output for Lock and Dam 3. The Blue Lake and St. Croix Valley WWTPs are not included in this Met Council–Mississippi Basin TP Permit due to local water quality considerations. Table 11. Comparison of original model domain, Lake Pepin categorical and revised model domain TP WLAs of scenario for five MCES WWTPs. The final TP WQBEL for the five MCES WWTPs included in this Permit are in the shaded boxes.

Loading Source Permitted

Flow

(MGD)

Original

Model

Domain TP

Load

(MT/yr)

Lake Pepin

Categorical

TP Load

(MT/yr)

Revised

Model

Domain TP

Load

(MT/yr)

Effluent

Concentration

Assumption

for Revised

Model

Domain Load

(mg/L)

Metro WWTP 314.0 130.1 130.1 120.55 0.2779

Eagle’s Point

WWTP

11.90 4.9 13.2 8.22 0.50

Hastings WWTP 2.69 1.1 3.0 2.97 0.80

Empire WWTP 28.60 11.9 11.9 11.85 0.30

Seneca WWTP 38.00 15.7 15.7 15.75 0.30

MCES TP WQBEL* 395.2 163.8 173.9 159.3

*The Blue Lake WWTP was not included due to trapping losses/temporary storage in the lower Minnesota River and its potential impact on the river eutrophication status of lower Minnesota River. The St. Croix Valley WWTP was not included due to trapping losses in Lake St. Croix and wasteload allocation of Lake St. Croix TMDL.

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Other point sources directly to or near the model domain

Approximately 21 WWTPs in Minnesota and 3 WWTPs in Wisconsin discharge directly to the model domain and were not included in model runs since they were considered small. Future eutrophication total maximum daily load (TMDLs) will require WLAs for all facilities discharging phosphorus upstream of Lake Pepin and impaired Mississippi River Pools. Based on model scenario 21, 183 MT/yr of TP is available for WLAs within the model domain. 159.3 MT/yr of TP was allocated to the MCES WWTPs listed in Table 11 resulting in 23.7 MT/yr of TP for the remaining WWTPs that discharge within the model domain. WQBELs for the remaining dischargers within the model domain will be developed for each discharge as their individual NPDES/SDS permits are reissued. Point sources not directly to the model domain will also need allocations. Estimates for point source loads throughout the Lake Pepin watershed, including the model domain but excluding 7 headwater watersheds, are approximately 600 MT/yr.

Proposed Monthly TP Limit for Met Council–Mississippi Basin TP Permit (excludes Blue Lake and St. Croix Valley WWTPs) Federal regulation 40 CFR 122.45(d) requires monthly average limits for all continuously discharging publicly owned treatment works unless it is impracticable. The term impracticable is not well defined. Therefore, EPA Region V and the MPCA are currently in negotiations to further clarify this term as it may apply to TP limits in wastewater NPDES Permits within Minnesota. If an annual WLA is converted to a monthly average limit, the EPA has advocated for the use of methods published in the Technical Support Document (TSD) for Water Quality-Based Toxics Control to account for treatment variability (EPA/505/2-90-001, U.S. EPA 1991). To expedite the issuance of the Met Council–Mississippi Basin TP Permit, a monthly mass TP limit has been added to the Permit. The statistical procedures described in EPA’s TSD manual can be used to convert annual mass WLAs into a monthly limit. The EPA Region V has assessed TP effluent data from major facilities in Minnesota to derive a monthly multiplier to be applied to WLAs to calculate monthly limits. The MPCA has selected a standard monthly multiplier when needed to apply for WQBELs for lake and river eutrophication standards. This is similar to the approach used by Wisconsin except that the multiplier for Minnesota is more conservative then the “3.0” multiplier used by Wisconsin. The monthly limit is expressed as a daily average load. Proposed TP annual WLA = 159,349 kg/yr (159.3 MT/yr) Conversion to monthly limit: Daily WLA = 159,349 kg ÷ 365 days = 436.6 kg/day Monthly limit = Daily WLA * monthly multiplier = 436.6 kg/day * 2.1 = 916.8 kg/day

The MPCA did not include any concentration limits for the umbrella permit. This is consistent with the application of lake based WQBELS for lakes with large watersheds. TP concentration limits for the Metropolitan, Hastings, Eagles Point, Empire and Seneca WWTPs will be included in the individual NPDES/SDS Permits associated with each WWTP. As the overall flow from the five MCES WWTPs in the Permit increases, the flow-weighted mean concentration of the five MCES WWTPs will have to decrease to meet the monthly mass limit (Table 12).

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Table 12. Flow-weighted mean concentration needed for the five MCES WWTPs in the Permit to meet monthly mass limit at four flow levels.

Monthly limit (kg/day)

Flow description Flow (mgd) TP concentration to meet limit at designated flow (mg/L)

916.8 Ave. wet weather design flow 395.2 0.61

916.8 Recent high flow (2012) 227.0 1.07

916.8 Recent avg flow (2010-12) 214.0 1.13

916.8 Average design flow 319.7 0.76

Summary: Proposed TP Limits for Met Council–Mississippi Basin TP Permit (excludes Blue Lake and St. Croix Valley WWTPs) It is assumed that one unit of TP from any of these five WWTPs has the same impact on Lock and Dam 2 and 3 (monitoring locations for Pools 2 and 3) and as a result it is expected that there will not be any localized impacts from each individual discharge. The MPCA considers the phosphorus load from the Seneca WWTP to be a direct discharge to Pool 2 for the purposes of this review. The Blue Lake WWTP is not included in this analysis due to trapping losses/temporary storage in the lower Minnesota River and its potential impact on the river eutrophication status of lower Minnesota River and potential for the discharge to affect

compliance with future river eutrophication standards in the Minnesota. St. Croix Valley was not included

due to complicated trapping mechanisms in Lake St. Croix and to maintain consistency with the assumptions and requirements of the Lake St. Croix Excess Nutrients TMDL. The MPCA has developed a combined TP WQBEL of 159.3 MT/yr (159,349 kg/year), 12 month moving total, for the following MCES WWTPs: Metro, Hastings, Eagles Point, Empire and Seneca. The Permit also includes an additional monthly combined TP limit of 916.8 kg/day. Although the Permit will include a calendar month average effluent limit of 916.8 kg/day, it is notable that actually discharging a cumulative loading of that magnitude for more than one or two months during a 12 month period will required dramatically reduced cumulative effluent loadings to be achieved during subsequent months in order to achieve compliance with the 12 month moving total effluent limit of 159.3 MT/year. As a result the 159.3 MT/year annual loading limit is likely to drive operational decisions with respect to treatment and targeted effluent concentrations.

Variance

There are no variances to a Clean Water Act requirement included in this Aggregate TP Permit.

Total Facility Requirements (TFR)

All NPDES/SDS 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 § 122.41, Minn. R. 7001.0150 and Minn. R. 7001.1090. These conditions are listed in the Total Facility Requirements chapter of the NPDES/SDS 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 modification and reissuance.

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Nondegredation and Anti-Backsliding In accordance with the Minnesota Pollution Control Agency rules regarding nondegredation for all waters (that are not Outstanding Resource Value Waters [ORVW]), nondegredation review is required for any new or expanded significant discharge (Minn. R. 7050.0185). A significant discharge is 1) a new discharge (not in existence before January 1, 1988) that is greater than 200,000 gallons per day (gpd) or 2) an expanded discharge that expands by greater than 200,000 gpd that discharges to any non-ORVW 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. This Permit also complies with Minn. R. 7053.0275 regarding anti-backsliding.

Any point source discharger of sewage, industrial, or other wastes for which a NPDES permit has been issued by the agency that contains effluent limits more stringent than those that would be established by parts 7053.0215 to 7053.0265 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 1342.

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References

Heiskary, S. and D. Wasley. 2012. Mississippi River Pools 1 through 8: Developing River, Pool

and Lake Pepin Eutrophication Criteria. MPCA St. Paul 83 pp. LTI. 2009. Upper Mississippi River-Lake Pepin Quality Model. Development, Calibration and Application.

Prepared for MPCA. LimnoTech, Ann Arbor, MI. Tetra tech. 2009. Minnesota River Basin Turbidity TMDL Scenario Report. Prepared for MPCA. Tetra Tech,

Research Triangle Park, NC U.S. EPA, 1991. Technical support document for water quality-based toxics control. EPA/505/2-90-001,

PB91-127415, 335 pp

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