national pollutant discharge elimination system (npdes)/ sheet - mn0020… · receiving water:...

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National Pollutant Discharge Elimination System (NPDES)/

State Disposal System (SDS) Permit Program Fact Sheet

Permit Modification

MN0020761 Permittee: City of Little Falls

900 Hilton Rd PO Box 244 Little Falls, Minnesota 56345

Facility name: Little Falls Wastewater Treatment Facility 900 Hilton Rd

Little Falls, Minnesota 56345 Current permit expiration date: August 31, 2021 Public comment period begins: April 27, 2018 Public comment period ends: June 26, 2018 Receiving water: Mississippi River - Class 1C, 2Bd, 3C, 4A, 4B, 5, 6 Water Permitting contact: Robin Novotny 7678 College Road, Suite 105 Baxter, Minnesota 56425 218-316-3851 [email protected]

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Table of Contents Page

Purpose and participation ....................................................................................................................................................... 4

Applicable statutes .............................................................................................................................................................. 4

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

Public participation ............................................................................................................................................................. 4

Facility description .................................................................................................................................................................. 5

Background information ..................................................................................................................................................... 5

Facility location ................................................................................................................................................................... 5

Outfall location ................................................................................................................................................................... 5

Map of permitted facility .................................................................................................................................................... 6

Components and treatment technology ............................................................................................................................ 6

Flow schematic Existing & Proposed .................................................................................................................................. 8

Changes to facility or operation ........................................................................................................................................ 10

Significant industrial users (SIUs) ...................................................................................................................................... 10

Recent compliance history ................................................................................................................................................ 10

Table 1 Recent monitoring history March 2015 to February 2016 .................................................................................. 10

Receiving water(s) ................................................................................................................................................................. 11

Use classification ............................................................................................................................................................... 11

Table 2 Impairments ......................................................................................................................................................... 11

Total Maximum Daily Load (TMDL) ................................................................................................................................... 12

Existing permit effluent limits ............................................................................................................................................... 12

Technology based effluent limits (TBELs) ......................................................................................................................... 12

Water quality based effluent limits (WQBELs) ................................................................................................................. 12

State Discharge Restriction Limits (SDRs) ......................................................................................................................... 12

Table 3 Existing Permit Effluent Limits & Monitoring ....................................................................................................... 12

Proposed permit effluent limits ............................................................................................................................................ 13

Technology based effluent limits ...................................................................................................................................... 13

Water quality based limits ................................................................................................................................................ 13

State Discharge Restriction Limits (SDRs) ......................................................................................................................... 13

Table 4 Proposed Permit Effluent Limits & Monitoring .................................................................................................... 13

Proposed Total Phosphorus Limit ......................................................................................................................................... 15

Whole Effluent Toxicity and Reasonable Potential ............................................................................................................... 17

Reasonable Potential for Chemical Specific Pollutants(40 CFR §122.44 (d)(1)) ................................................................... 17

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Table 5 Reasonable Potential Analysis .............................................................................................................................. 18

Additional requirements ....................................................................................................................................................... 19

Mercury Minimization Plans (MMP) ................................................................................................................................. 19

Compliance schedules ....................................................................................................................................................... 19

Nitrogen Monitoring Requirements ................................................................................................................................. 19

Salty Monitoring Requirements ........................................................................................................................................ 19

Industrial Stormwater ....................................................................................................................................................... 20

Biosolids ............................................................................................................................................................................ 20

Total facility requirements (TFR)........................................................................................................................................... 20

Nondegredation and anti-backsliding ................................................................................................................................... 20

NPDES/SDS Permit Program Fact Sheet MN0020761 Permit Reissuance of 20

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

Robin Novotny Minnesota Pollution Control Agency 7678 College Road, Suite 105 Baxter, MN 56425


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The permit will be modified 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.

2018 Modified-NPDES/SDS Fact Sheet Changes Available for Public Comment

Section Heading Paragraph Heading Page Number

Permitted Facility Description Paragraph with proposed changes to the wastewater treatment facility. Added updated anti-degradation language

7

Components and treatment technology

Existing and proposed flow diagrams 8 & 9

Proposed Effluent Limits & Monitoring Table 4 removed salty parameters 11-15

Reasonable Potential for Chemical Specific Pollutants

Table 5. Reasonable Potential Analyses updated table with new data

18

Reasonable Potential for Chemical Specific Pollutants

Metals updated reasonable potential paragraph

19

Additional Requirements Salty Discharge Monitoring 19 & 20

Facility Description

Background information Facility location Little Falls Wastewater Treatment Facility (Facility) is located in the NE ¼ of the NE ¼, Section 18, Township 40 North, Range 32 West.

Outfall location The Facility outfall location (SD004) is located in the NE ¼ of the NE ¼, Section 18, Township 40 North, Range 32 West.


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Map of permitted facility

Components and treatment technology The Little Falls Wastewater Treatment Facility (Facility) is located in the NE ¼ of the NW ¼, Section 18, Township 40 North, Range 32 West, Belle Prairie Township, Morrison County, Minnesota. This is a Class A facility. An existing ethanol facility (now repurposed to manufacture other organic chemicals) discharges its domestic wastewater, ion exchange softener regeneration water, cooling tower bleed and boiler blowdown to the city's sanitary sewer collection system. The Facility discharges continuously (SD 004) to the Mississippi River (Class 1C, 2Bd, 3B, 3C, 4A, 4B, 5, 6 water). The Facility is designed to treat an average wet weather (AWW) flow of 2.4 million gallons per day (mgd), an average annual flow of 1.9 mgd, and an average dry weather (ADW) flow of 1.1 mgd, with a five day carbonaceous biochemical oxygen demand (CBOD5) strength of 177 milligrams per liter (mg/L).


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Major Components of the existing WWTF consist of: 1 Equalization Tank (aerated wet weather tank) 1 Influent Flow Meter (Parshall flume) 1 Bar Screen - Manual 1 Bar Screen - Mechanical 1 Aerated Grit Removal Tank 2 Primary Clarifiers 1 ABF Tower (Activated Biofilter Facility) 2 Intermediate Clarifiers 1 Activated Sludge - contact stabilization, conventional, step feed (two tanks) 2 Final Clarifiers 2 Chlorine Contact Tanks (one follows EQ tank) 1 Dechlorination 1 Postaeration (cascading aeration) 1 Gravity Thickening 2 Aerated Sludge Holding Tanks 1 Centrifuge 1 Lime/Heat Stabilization Sludge Treatment Unit 1 Covered De-Watered Biosolids Storage Area 1 Land Application of Biosolids 1 Odor Control Unit (Ammonia scrubber with a hydrochloric acid feed system and a biofilter) The proposed Facility after construction will consist of influent flow monitoring with a Parshall flume, a mechanically raked screen, a manually raked bypass screen, a vortex grit removal system, a flow equalization basin, two anaerobic selector tanks with mixing, two oxidation ditches set up for biological phosphorus removal, backup chemical phosphorus removal system, two final clarifiers, an ultraviolet light disinfection system followed by cascade aeration prior to discharge. The proposed solids handling will consist of two aerobic digesters, biosolids dewatering with a centrifuge and a rotary press, dewatered biosolids cake storage in a building, and land application of biosolids and/or the biosolid cakes are used by the county landfill. Southeast Lift Station Bypass and West Lift Station Bypass are capable of discharging untreated wastewater to the Mississippi River. Treatment Facility Bypass/Overflow is a bypass point from the flow equalization basin to the outfall pipe. Should the flow equalization basin overflow, wastewater will be routed to a wet weather chlorine contact chamber for disinfection and dechlorination before discharge to the Mississippi River.

Any changes to the Facility that result in an increase in pollutant loading are subject to antidegradation requirements found at Minn. R. 7050.0250 to 7050.0335y

This Permit 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 MPCA that contains effluent limits more stringent than those that would be established by Minn. R. 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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Flow schematic Existing Facility


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Flow Schematic Proposed Facility


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Changes to facility or operation Facility improvements or modifications are required to accommodate phosphorus removal. The Facility shall complete the actions and submit information for these improvements under the terms of the Compliance Schedule under section 5.8.25 of the reissued permit.

The Significant Industrial Users (SIU), Central Minnesota Ethanol Cooperative has taken over operation and ownership of the pretreatment facility. The ethanol facility has installed a closed loop water reuse system and has disconnected the pipe between the City’s WWTF and the ethanol plant which eliminates the pretreatment facility discharge to the City’s WWTF. A major portion of the ethanol plant flow discharging to the WWTF was eliminated. However, the ethanol plant is still discharging from an additional discharge point, domestic wastewater, ion exchange softener regeneration water, cooling tower bleed and boiler blowdown to the city's WWTF. Significant industrial users (SIUs) There are two SIU that contribute process wastewater to the Facility. Anderson Custom Process is a drying process company and contributes 25,000 gallons per day (gpd) of process wastewater. The principle product or raw materials are starches and carbohydrates. The company has a pretreatment agreement with the Facility which includes local limits.

Central Minnesota Ethanol Cooperative discharges domestic wastewater, ion exchange softener regeneration water, cooling tower bleed and boiler blowdown to the Facility. The contribution to the Facility is 20,000 to 25,000 gpd. The company has a pretreatment agreement with the Facility which includes local limits.

Recent compliance history The most recent MPCA inspection of the Facility occurred on May 5, 2015. According to the May 15, 2015, inspection report, there were no violations of the NPDES/SDS Permit No. MN0020761. The report indicates that the Facility appears to be in good working condition and is well maintained and cared for.

Table 1 Recent monitoring history March 2015 to February 2016 Parameter Limit Type Limit Units Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb

CBOD5 CalMoAvg 25 mg/L 7.3 8.6 5.7 3.3 4.9 2.9 3.7 4.4 5.8 3.7 7.1 6.4

CBOD5 CalMoAvg 227 kg/d 23.7 29 23.9 14.2 18.6 10.1 12.1 13.3 21 13.5 23.2 20.2

CBOD5 MxCalWkAvg 40 mg/L 9.1 14 8.9 4.6 8.5 3.8 4.8 7.2 7.5 5.8 11 7.5

CBOD5 MxCalWkAvg 363 kg/d 29.8 48 25.8 19.7 33.5 12.4 16 21.5 29.9 21.2 34.5 24.3

CBOD5 % Removal

MnCalMoAvg 85 % 96.4 96.4 96.7 98.3 97.6 98.5 98.2 98.1 96.8 97.9 96.1 96.8

Chlorine, Residual

DailyMax 0.038 mg/L 0.05 0.05 0.05 0.05 0.05

Fecal Coliform

CalMoGeoMn 200 #/100ml 41 135 55 20 60 24 28

Mercury, Total

CalQtrMax ng/L 2 1.2 1.3 1.3

Nitrogen, Ammonia

CalMoAvg mg/L 8.9 13 2.8 0.35 11 1 1.7 4.1 2.2 4.4 9.3 13

Oxygen, Dissolved

CalMoMin mg/L 0.8 0.8 0.4 0.4 0.2 0.4 0.3 0.3 0.3 0.3 0.4 0.7

pH CalMoMax 9 SU 7.3 7.1 7.1 7 7.1 7 7 7 7.1 7.1 7.2 7.3

pH CalMoMin 6 SU 6.9 6.8 6.6 6.7 6.7 6.6 6.7 6.6 6.7 6.9 7 7

Phosphorus Total

CalMoAvg kg/d 8 15.7 10.1 6.9 7.5 9.3 8.8 8.6 9.3 9 8.2 7.34

Phosphorus Total

CalMoAvg mg/L 2.5 2.1 2.5 1.6 2 2.7 2.7 2.8 2.7 1.8 2.6 2.3

TSS CalMoAvg 30 mg/L 8.9 7.5 6 4.2 4.6 3.4 3.3 4 7.6 5 7.3 9.4

TSS CalMoAvg 272 kg/d 29.3 25.6 25.5 18.7 17.7 12 10.9 12.3 27.6 18.4 23.9 29.4

TSS MxCalWkAvg 45 mg/L 12 7.7 9.2 5.7 7.2 4.7 5.5 4.9 9.5 8 9.3 9.9

TSS MxCalWkAvg 408 kg/d 38.7 31.7 30 26.3 28.7 16.2 18.1 14.8 43.7 29.4 30.4 30.7

TSS % Removal

MnCalMoAvg 85 % 95.4 96.1 96.4 97.6 97.6 98.2 98.4 97.9 95.5 96.8 95.4 95


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Receiving water(s) Use classification The receiving water is the Mississippi River a Class 1C, 2Bd, 3C, 4A, 4B, 5, 6 Water. Minn. R. 7050.0200, Water Use Classifications for Waters of the State Subp. 2. Class 1 waters, domestic consumption. Domestic consumption includes all waters of the state which are or may be used as a source of supply for drinking, culinary or food processing use of 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 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. Table 2 Impairments

AUID REACH_NAME REACH_DESC USE_CLASS CAT APPRVD

07010104-519 Mississippi River

Little Falls Dam to Swan R

1C, 2Bd, 3C 4A HgF

07010201-501 Mississippi River

End HUC 07010104 (below Swan R) to Two R

1C, 2Bd, 3C 4A HgF


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Total Maximum Daily Load (TMDL) Mercury - The statewide mercury Total Maximum Daily Load (TMDL) was approved March 27, 2007, with the implementation plan approved in 2008. For more information on the Mercury TMDL and implementation plan, refer to http://www.pca.stat.emn.us/publications/wq-wwprm1-16.-pdf. Lake Pepin TMDL – Effluent from the Facility is discharged to the Mississippi River upstream of Lake Pepin, a reservoir on the Mississippi River. In 2002, Lake Pepin was placed on the Federal Clean Water Act Section 303(d) list of impaired waters due to excess nutrients. A TMDL study is currently being developed and a significant portion of the modeling analysis has been completed. Information regarding the proposed total phosphorus Water Quality Based Effluent Limits (WQBEL) that are included in the draft permit is included below under the heading Proposed Total Phosphorus Effluent Limit below. Existing permit effluent limits The limits and monitoring requirements in the current permit are presented in Table 3 and list WQBEL; technology based effluent limits and state discharge restriction limits. Technology Based Effluent Limits (TBELs) The CBOD5, total suspended solids (TSS), potential for Hydrogen (pH), and percent removal limits are technology based limits developed for achieving secondary treatment standards. These limits are specified in 40 CFR § 133.102, Minn. R. 7050.0211 and Minn. R. 7053.0215. Water quality based effluent limits (WQBELs) The total residual chlorine limit is a water quality based effluent limit. This limit is based on the designated use classification of the receiving water. The total residual chlorine limit is the final acute value for chlorine found in Minn. R. 7050.0222. This limit was determined to be necessary to protect the use classification for the receiving water. State discharge restriction limits (SDRs) The fecal coliform bacteria limit is a state discharge limit specified under Minn. R. 7053.0215, subp. 1. Table 3 Existing Permit Effluent Limits and Monitoring

Parameter Limit Units Limit Type Effective Period

Sample Type Frequency Notes

SD004: Surface Discharge Station

CBOD5 227 kg/day CalMoAvg Jan-Dec 24-Hour Flow Composite

3 x Week

CBOD5 25 mg/L CalMoAvg Jan-Dec 24-Hour Flow Composite

3 x Week

CBOD5 363 kg/day MxCalWkAvg Jan-Dec 24-Hour Flow Composite

3 x Week

CBOD5 40 mg/L MxCalWkAvg Jan-Dec 24-Hour Flow Composite

3 x Week

CBOD5 % Removal 85 % MnCalMoAvg Jan-Dec Calculation 3 x Week

Chlorine Residual 0.038 mg/L Daily Maximum

Jan-Dec Grab 1 x Day 4

http://www.pca.stat.emn.us/publications/wq-wwprm1-16.-pdf


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Fecal Coliform 200 #100ml CalMoGeoMn Apr-Oct Grab 3 x Week

Mercury, Total Monitor Only

ng/L CalQrtMax Jan-Dec Grab 1 x Quarter 3

Nitrogen, Ammonia Monitor Only

mg/L CalMoAvg Jan-Dec 24-Hour Flow Composite

1 x Month

Oxygen, Dissolved Monitor Only

mg/L CalMoMn Jan-Dec Grab 1 x Day 1

pH 9 SU CalMoMax Jan-Dec Grab 1 x Day 1

pH 6 SU CalMoMn Jan-Dec Grab 1 x Day 1

Phosphorus, Total Monitor Only

kg/day CalMoAvg Jan-Dec 24-Hour Flow Composite

1 x Week

Phosphorus, Total Monitor Only

mg/L CalMoAvg Jan-Dec 24-Hour Flow Composite

1 x Week

TSS 272 kg/day CalMoAvg Jan-Dec 24-Hour Flow Composite

3 x Week

TSS 30 mg/L CalMoAvg Jan-Dec 24-Hour Flow Composite

3 x Week

TSS 408 kg/day MxCalWkAvg Jan-Dec 24-Hour Flow Composite

3 x Week

TSS 45 mg/L MxCalWkAvg Jan-Dec 24-Hour Flow Composite

3 x Week

TSS % Removal 85 % MnCalMoAvg Jan-Dec Calculation 3 x Week

Proposed permit effluent limits The limits and monitoring requirements for Station SD004 for the draft reissued Permit MN0020761 are presented in Table 4. This table lists water quality based effluent limits; technology based effluent limits, and state discharge restriction limits. In addition, the Facility will be monitoring for the salty parameters. Technology Based Effluent Limits (TBEL) The CBOD5, TSS, pH, and percent removal limits are technology based effluent limits developed for achieving secondary treatment standards. These limits are specified in 40 CFR § 133.102, Minn. R. 7050.0211 and Minn. R. 7053.0215. Water Quality Based Limits (WQBEL) The total phosphorus and total residual chlorine limits are WQBEL. The total residual chlorine limit is the final acute value for chlorine found in Minn. R. 7050.0222. The proposed phosphorus limit is based on Minn. R. 7053.0285, subp. 8, and Minn. R. 7050.0222 to protect downstream waters from eutrophication. State Discharge Restriction Limits (SDRs) The fecal coliform bacteria limit is a state discharge limit as specified in Minn. R. 7053.0125, subp. 1.


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Table 4 Proposed Permit Effluent Limits & Monitoring

Parameter

Discharge limitations Monitoring requirements

Quantity

/Loading

avg.

Quantity

/Loading

max.

Quantity

/Loading

units

Quality

/Conc. min.

Quality

/Conc. avg.

Quality

/Conc. max.

Quality/

Conc.

units Frequency Sample type

Effective

period

CBOD5 227

CalMoAvg

363

MaxCalWkAvg

kg/day 25

CalMoAvg

40

MaxCalWkAvg

mg/L 3 times

per week

24-Hour Flow

Composite

Jan-Dec (Sep-

Aug) (Oct-

Sep)

CBOD5 %

Removal

85

MnCalMoAvg

percent 3 times

per week

Calculation Jan-Dec (Sep-

Aug) (Oct-

Sep)

Chlorine

Residual

0.038 daily

maximum

mg/L once per

day

24-Hour Flow

Composite

Jan-Dec (Sep-

Aug) (Oct-

Sep)

Fecal

Coliform

200

CalMoGeoM

organisms

per 100

milliliter

3 times

per week

Grab Apr-Oct

Flow Monitor only.

CalMoTot

MG Monitor

only.

CalMoAvg

Monitor only.

CalMoMax

MGD once per

day

Measurement,

Continuous

Jan-Dec (Sep-

Aug) (Oct-

Sep)

Mercury,

Dissolved

Monitor only.

CalMoMax

ng/L once per

month

Grab May, Sep

Mercury,

Total

Monitor only.

CalMoMax

ng/L once per

month

Grab May, Sep

Nitrite Plus

Nitrate

Monitor

only.

CalMoAvg

mg/L once per

month

24-Hour Flow

Composite

Jan-Dec (Sep-

Aug) (Oct-

Sep)

Nitrogen,

Ammonia

Monitor

only.

CalMoAvg

mg/L once per

month

24-Hour Flow

Composite

Jan-Dec (Sep-

Aug) (Oct-

Sep)

Nitrogen,

Kjeldahl

Monitor

only.

CalMoAvg

mg/L once per

month

24-Hour Flow

Composite

Jan-Dec (Sep-

Aug) (Oct-

Sep)

Nitrogen,

Total

Monitor

only.

CalMoAvg

mg/L once per

month

24-Hour Flow

Composite

Jan-Dec (Sep-

Aug) (Oct-

Sep)

Oxygen,

Dissolved

Monitor

only.

CalMoMn

mg/L once per

day

Grab Jan-Dec (Sep-

Aug) (Oct-

Sep)


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Parameter

Discharge limitations Monitoring requirements

Quantity

/Loading

avg.

Quantity

/Loading

max.

Quantity

/Loading

units

Quality

/Conc. min.

Quality

/Conc. avg.

Quality

/Conc. max.

Quality/

Conc.

units Frequency Sample type

Effective

period

pH 6.0 CalMoMn 9.0

CalMoMax

SU once per

day

Grab Jan-Dec (Sep-

Aug) (Oct-

Sep)

Phosphorus,

Total

Monitor only.

CalMoTot

kg/mo Monitor

only.

CalMoAvg

mg/L once per

week

24-Hour Flow

Composite

Jan-Dec (Sep-

Aug) (Oct-

Sep)

TSS 272

CalMoAvg

408

MaxCalWkAvg

kg/day 30

CalMoAvg

45

MaxCalWkAvg

mg/L 3 times

per week

24-Hour Flow

Composite

Jan-Dec (Sep-

Aug) (Oct-

Sep)

TSS) %

Removal

85

MnCalMoAvg

percent 3 times

per week

Calculation Jan-Dec (Sep-

Aug) (Oct-

Sep)

TSS grab

(Mercury)

Monitor only.

CalMoMax

mg/L once per

month

Grab May, Sep

Proposed Total Phosphorus Effluent Limit The Facility has an AWW design flow of 2.4 mgd. The current permit does not include a total phosphorus limit. This area of the Mississippi is located in the north river nutrient region, and therefore, has total phosphorus (TP) and Chlorophyll-a (Chl-a) criteria of 50 micrograms per liter (µg/L) and 7 µg/L, respectively. Water samples used for water quality eutrophication assessments consist of TP and Chl-a samples (n ≥ 12 TP and Chl-a, each) collected during June-September, representing at least two years of data within the last 10 years. Water quality impairments result when both TP and Chl-a exceed their respective criteria concentrations. For this assessment, samples used were collected approximately 12 miles downstream of Little Falls WWTF, along the Mississippi River.

Water quality suggest nutrient data are meeting eutrophication criteria. TP and Chl-a concentrations were 53 µg/L (n = 64) and 3 µg/L (n = 12), respectively. Even though TP is slightly over the nutrient criteria, it is not considered impaired because only one nutrient parameter is elevated. Under low flow conditions, point sources are typically the dominant source of nutrient loading. The 80th percent flow exceedence low flow condition and associated TP loading was used to identify point source impacts on the receiving water. The United States Geological Survey (USGS) gage (05267000) and surface monitoring station (S000-150) data, located on the Mississippi River near Royalton, MN (approximately 12 miles downstream from Little Falls WWTF), were used.

The data demonstrates that under low flow conditions, when point sources are the most significant contributor, the receiving water is meeting its nutrient criteria. Given that the current actual load is greater than the proposed effluent limit, it is reasonable to conclude that the recommended limit will result in a decrease in ambient TP, thereby not causing or contributing to an exceedance of the pending river eutrophication standards in the immediate receiving water. As such, more restrictive TP limits protective of the immediate receiving water in the Mississippi River are not necessary.


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In 2002, Lake Pepin was placed on the federal Clean Water Act Section 303(d) list of impaired waters due to excess nutrients. A Total Maximum Daily Load (TMDL) study is currently being developed and a significant portion of the modeling analysis has been completed. Phosphorus is the primary nutrient responsible for excess algal growth in Lake Pepin. Federal law [40 CFR 122.44(d)] restricts mass increases upstream of impaired waters and states that all NPDES dischargers that have the reasonable potential (RP) to cause or contribute to downstream impaired waters are required to have a WQBEL. When determining RP, the Code of Federal Regulations also states that the MPCA shall use procedures which account for existing controls on point and nonpoint sources of pollution. Permittees are found to have RP for TP if: 1) they discharge upstream of a nutrient impaired waterbody, 2) they discharge at TP concentrations greater than the ambient target, and 3) there is no geographical barrier capable of trapping a significant mass of nutrients between the outfall and the impairment. For all reasons listed above, Little Falls is found to have RP for TP upstream of Lake Pepin. Therefore, Little Falls is required to have a TP WQBEL. It is recommended that the city of Little Falls receive a 2,653 kg/yr TP WQBEL which was derived from a draft TMDL waste load allocation (WLA) as described below. Draft WLAs in combination with other point and nonpoint reductions are sufficient to meet draft criteria in Lake Pepin designed to support the designated uses of this water resource.

A computer water-quality model for Lake Pepin was developed by MPCA modeling consultant, LimnoTech, to evaluate

site specific eutrophication criteria and the reductions necessary to achieve these criteria (LimnoTech, 2009). The

standards for Lake Pepin were determined to be 0.100 mg/L TP and 0.028 mg/L Chl-a (Heiskary and Wasley, 2012).

These standards were adopted in Minnesota Rule 7505.0222. Within the model, all major sources of TP upstream of

Lake Pepin were considered, and 21 separate scenarios were developed. Scenario 21 achieved compliance with the

criteria and predicted that the following TP reductions from tributaries would be necessary: HSPF modeled reductions

from the Minnesota River, 50% from the Cannon River, 20% from the Mississippi River upstream of Lock and Dam 1 and

20% from the St. Croix River. During the modeling process, MPCA staff simultaneously developed draft WLAs,

compatible with reductions in scenario 21 for all NPDES dischargers within the contributing basin of Lake Pepin. All

simulations represented point sources on a 12-month basis.

Categorical WQBELs using AWWDF or Maximum Daily Flow were developed for NPDES WWTFs in the Lake Pepin Basin

using the general formula below:

General Formula:

MM WLA = (AWWDF x 0.8 mg/L TP x 3.785 L/gal x 365 days/yr)

City of Little Falls WWTP WLA:

2,653 kg/yr TP = (2.4 mgd x 0.8 mg/L x 3.785 L/gal x 365 days/yr)

These values are then implemented in permits as 12 – month rolling total kg/day mass values. Limits are evaluated on a

monthly basis to ensure compliance.

This analysis demonstrates the facility does not have the potential to cause or contribute to river eutrophication impairment in the Mississippi River – Brainerd Watershed, under permitted effluent conditions. Existing limits are sufficient for the immediate and downstream waters to meet RES. Nonetheless, it was determined that the facility has RP to cause or contribute to the excess nutrient impairment in Lake Pepin and is therefore required to have a WQBEL. The recommended TP effluent limit (2,653 kg/yr) in the draft permit is a WQBEL derived from the draft WLA which in turn is derived from the water quality standard that the receiving water must meet to support designated uses.


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Whole Effluent Toxicity and Reasonable Potential The discharge is located on the Mississippi River within a reach not designated as an ORVW. The ADW design flow is used to calculate WQBEL under critical low flow stream conditions. The ADW for this Facility is 1.1 mgd. The low flow condition is defined by the once in 10 year weekly average flow (7Q10), which is determined to be 442.7925 mgd (685 cubic feet per second [cfs]). The dilution ratio is 402.5:1 river low flow to effluent flow at the ADW flow. The discharger has submitted four whole effluent toxicity (WET) test batteries and three priority pollutant scans since 2008. The analysis below is based on data submitted to date. Reasonable Potential for Chemical Specific Pollutants (40 CFR § 122.44(d)(1)) Federal regulations require the 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) etermined 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 limit for that pollutant. The Facility submitted three priority pollutant scans during the past permit cycle. The priority pollutant scan information of the effluent was evaluated using reasonable potential procedures. All of the organic priority pollutants were below the level of detection. Since these pollutants were at low enough levels not to be detected, reasonable potential to cause or contribute to a water quality standards excursion is not indicated. The priority pollutant scans did find concentrations of total copper (Cu), total arsenic (As) and total zinc (Zn) above reporting level concentrations. Reasonable Potential evaluations were done for total copper, total arsenic and total zinc based on priority pollutant scan data. Reasonable potential evaluations were also performed on total mercury (Hg) based on past quarterly sampling of total mercury of the Facility’s effluent. From the table below total arsenic, total copper, total zinc and total mercury indicated no reasonable potential to cause or contribute to an excursion above the applicable water quality standard. No effluent limits are needed.


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Table 5. Reasonable Potential Analyses

Total Mercury Monitoring results of the effluent include 20 data points at a calculated coefficient of variable (CV) of 0.4403. Projected effluent quality is derived as an upper bound value from the highest value measured (5.8 nanograms per liter [ng/l]), and the determined variability (CV = 0.4403) and number of data points (20). 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 preliminary effluent limit calculations. Metals

Parameter

Bicarb as

HCO3(mg/L)

Hardness

(mg/L)

Class 2 Cl

(mg/L)

Class 3 Cl

(mg/L)

Sulfate

(mg/L)

Total

Dissolved

Salts (mg/L)

Specific

Conductance(

umhos/cm) Hg (ng/L)

Max Measured Value 356 292 110 110 38 504 907 3

# data points 16 16 16 16 16 16 16 10

PEQ 427.2 321.2 121 121 45.6 554.4 997.7 3.9

Plant flow ADW (mgd) 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1

Rec. water flow, 7Q10 (mgd) 577.892696 577.8927 577.8926955 577.8927 577.892696 577.892696 577.8926955 577.8926955

Background concentration,

Mississippi River 163 206 0 0 5 190 389 6.9

Chronic standard (cs) 305 500 230 250 1000 700 1000 6.9

162

ppm hard

Maximum standard (ms) NA NA 860 NA NA NA NA 2400

162

ppm hard

Final acute value (FAV) NA NA 1720 NA NA NA NA 4900

170

ppm hard

Mass balance -cs 74905.69 154954.96 121062.11 131589.25 523730.21 268632.07 321993.12 6.90

Mass balance -ms 0.00 0.00 452667.02 0.00 0.00 0.00 0.00 1259631.83

Coefficient of variation 0.33180 0.18207 0.11890 0.11890 0.28618 0.10571 0.14080 0.32558

Long term avg-cs 65188.32 143508.03 105625.56 125139.69 464466.56 256894.86 303403.33 6.02

Long term avg-ms 0.00 0.00 346061.18 0.00 0.00 0.00 0.00 633116.28

Preliminary effl. limits:

Daily max. 131206.45 214887.60 138164.03 163689.59 857577.99 326450.16 416208.11 11.98

Monthly avg. (2 x month) 92878.21 175752.77 120837.51 143162.03 632939.37 289629.88 355505.74 8.53

Reasonable Potential

PEQ > Daily max. FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

PEQ > Monthly avg. FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

PEQ > FAV NA NA FALSE NA NA NA NA FALSE

Final Reasonable Potential No No No No No No No No

Notes

Mississippi River- 1C, 2Bd, 3C, 4A, 4B, 5,and 6

Sodium is 43.93% of total cations. As such, no sodium limit needed.

No acute WET limit needed

No wild rice known to be downstream

Salty background from Scott Kyse'rs arc maps

mercury background set the the chronic WQS due to the TMDL

Only 1 priority pollutant scans available to use after the ethanol plant was removed from the waste stream


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Table 5 contains the inputs to the reasonable potential analysis for Bicarbonate, Hardness, Class 2 Chloride, Class 3 Chloride, Sulfate, Total Dissolved Salts, Specific Conductance, and Total Mercury. Reasonable potential to cause or contribute to the excursion above the water quality standards/criterion has not been indicated for the salty parameter WQSs/WQC, the acute WET tests, or for total mercury WQS. No reasonable potential exists for any of these parameters. This facility does not have reasonable potential for any salty parameters. Environmental Analysis and Outcomes (EAO) staff recommend discontinuing salty parameter monitoring for this Permitee.

Whole Effluent Toxicity (WET) Minn. R. 7053.0215, subp. 1 “Minimum secondary treatment for municipal point source and other point source dischargers of sewage”, specifies that the discharge shall not be acutely toxic or exceed the final acute value, unless the effluent satisfies acute whole effluent toxicity test conditions (i.e. - less than 50 percent mortality for a sensitive organism). A discharge that exceeds mortality requirements of the rule requires a permit limit for WET. The Facility has submitted four acute WET tests since 2008. The acute toxicity (TUa) units determined for each of the tests were all less than 0.9999 TUa. Therefore, no RP for acute toxicity is indicated pursuant to Minn. R. 7053.0215, subp. 1 and no effluent limit is needed. The recommendation for the permit is to include annual WET monitoring requirements.

Additional Requirements Mercury Minimization Plans (MMP) The draft permit contains requirements for mercury monitoring and for submittal of a Mercury Minimization Plan (MMP) or updated MMP. These requirements were added in response to the U. S. Environmental Protection Agency’s (EPA) approval of the Minnesota statewide Mercury TMDL plan. Specific mercury monitoring requirements are found in the Surface Discharge Station Chapters of this permit. These requirements include sampling for TSS via a grab sample taken at the same time as the mercury grab samples are taken. Compliance Schedules This Facility has been assigned a new WQBEL for TP (2,653 kg/yr). Because this Facility is not capable of achieving this limit at permit issuance, this draft permit contains a compliance schedule to allow the time needed to secure funding, evaluate the design, and build for advance nutrient removal technology. This permit contains a schedule to attain compliance with the final mass limit the schedule can be found in section 5.7.27. The Facility will be required to attain compliance with the WQBEL no later than August 31, 2021. Nitrogen Monitoring Requirements The draft Permit includes influent and effluent monitoring for Ammonia Nitrogen, Nitrite plus Nitrate-Nitrogen, Total Kjeldahl Nitrogen, and Total Nitrogen at a frequency of one time per month for the five-year term of the Permit. There is no nitrogen limit in the Permit. Salty Discharge Monitoring In recent years, the MPCA staff became aware of issues associated with “salty discharges” from industrial and municipal discharges. As a result, the MPCA staff began to request additional monitoring for these facilities and also began assigning effluent limits to facilities that have data showing a reasonable potential to exceed a water quality standard. All industrial and municipal facilities with continuous, periodic/seasonal, or intermittent waste flows where the receiving water stream flow to effluent design flow dilution ratio under low flow conditions is less than 5:1 will be required to monitor effluent for the following parameters: chloride, Ca and Mg hardness as CaCO3, specific conductance, total dissolved solids, sulfates as SO4, bicarbonates (HCO3), sodium, calcium, magnesium, and potassium.


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The existing ethanol facility (now repurposed to manufacture other organic chemicals) discharges its domestic wastewater, ion exchange softener regeneration water, cooling tower bleed, and boiler blowdown to the city's sanitary sewer collection system. The ethanol plant has gone to a closed loop system and disconnected the discharge pipe leading to the WWTF. Industrial Stormwater On April 5, 2015, 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. This Facility has applied for and obtained a Certification of No Exposure; therefore, this permit includes language regarding the No Exposure exclusion. Biosolids This draft reissued Permit authorizes the Permittee to store and land applies domestic wastewater treatment biosolids in accordance with the provisions in this draft permit and Minn. R. ch. 7041.

Total Facility Requirements

All NPDES/SDS Permits issued by 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 outlines in 40 CFR § 122.41, Minn. R. 7001.0150 and 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, bypasses, solids handling, changes in operation, Facility inspections, and permit modification and reissuance.

Antidegradation and anti-backsliding Any changes to the Facility that result in an increase in pollutant loading are subject to anti-degradation requirements found at Minn. R. 7050.0250 to 7050.0335.

This Permit 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 MPCA that contains effluent limits more stringent than those that would be established by Minn. R. 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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