Lake Pepin and Mississippi River Eutrophication Total Maximum Daily Load Report April 2021 wq-iw9-22e Authors and contributors: Lake Pepin Legacy Alliance Minnesota Pollution Control Minnesota Department of Agency Natural Resources Mike McKay Anna Bosch Rob Burdis Rylee Main Wayne Cords Scot Johnson Mac Becco Duane Duncanson Megan Moore Jinny Fricke LimnoTech, Inc. Lee Ganske Wisconsin Department of Natural Resources Nicholas Grewe Marco Graziani Kevin Kirsch Hans Holmberg Steven Heiskary Patrick Oldenburg Dendy Lofton Scott Maclean John Sullivan Todd Redder Cathy Malakowsky Scott Wade Hafiz Munir Metropolitan Council Joe DePinto Rachel Olmanson Kent Johnson Wendy Larson Norman Senjem Cathy Larson Ed Verhamme Glenn Skuta Judy Sventek Mike Trojan Dave Wall Minnesota Department of Agriculture Dennis Wasley Larry Gunderson Lake Pepin TMDL Science Justin Watkins Advisory Panel Lake Pepin TMDL Stakeholder Chris Zadak Advisory Committee Lake Pepin Watershed Phosphorus TMDLs Minnesota Pollution Control Agency Contents List of Tables ........................................................................................................................................ v List of Figures ....................................................................................................................................... v Acronyms .......................................................................................................................................... viii Executive Summary ............................................................................................................................. 1 1. Project Overview ...................................................................................................................... 1 1.1. Project Purpose and History................................................................................................................. 1 1.2. Identification of Waterbodies .............................................................................................................. 3 1.3. Priority Ranking .................................................................................................................................... 6 2. Applicable Water Quality Standards and Numeric Water Quality Targets ................................. 7 2.1. State of Minnesota Designated Uses ................................................................................................... 7 2.2. State of Minnesota Water Quality Standards and Criteria for Listing ................................................. 8 3. Watershed and Waterbody Characterization .......................................................................... 11 3.1. Lake Pepin and Impaired Stream Reaches ......................................................................................... 11 3.2. Watershed Characteristics ................................................................................................................. 13 3.2.1. Land Use .............................................................................................................................. 17 3.2.2. Hydrology ............................................................................................................................ 19 3.3. Historic and Current Water Quality Conditions of Impaired Waters ................................................. 22 3.3.1. Mississippi River – Lake Pepin ............................................................................................. 22 3.3.2. Twin Cities Metropolitan Area ............................................................................................ 26 3.3.3. Minnesota River Basin ........................................................................................................ 27 3.4. Phosphorus Source Summary ............................................................................................................ 30 3.4.1. Municipal and Industrial Wastewater ................................................................................. 32 3.4.2. Regulated Stormwater ........................................................................................................ 36 3.4.3. Permitted Confined Animal Feeding Operations ................................................................ 39 3.4.4. Nonpoint Sources ................................................................................................................ 41 3.4.5. Natural Background ............................................................................................................ 45 4. Modeling Approach ................................................................................................................ 47 4.1. Water Quality Model .......................................................................................................................... 47 4.1.1. Baseline Loads ..................................................................................................................... 50 4.1.2. Scenario Development ........................................................................................................ 51 4.1.3. Modeling to Develop WLAs ................................................................................................. 54 4.2. Relationships to Other TMDLs ........................................................................................................... 54 5. TMDL Development ................................................................................................................ 56 5.1. Loading Capacity ................................................................................................................................ 60 Lake Pepin Watershed Phosphorus TMDLs Minnesota Pollution Control Agency iii 5.1.1. Lake Pepin and Pool 2 ......................................................................................................... 60 5.1.2. Impaired Stream AUID – Crow River to Upper St. Anthony Falls ........................................ 60 5.2. Wasteload Allocation Methodology .................................................................................................. 62 5.2.1. Permitted Municipal and Industrial Wastewater ............................................................... 62 5.2.2. Regulated MS4 Stormwater ................................................................................................ 65 5.2.3. Regulated Construction and Industrial Stormwater ........................................................... 67 5.3. Load Allocation Methodology ............................................................................................................ 67 5.4. Margin of Safety ................................................................................................................................. 68 5.5. Reserve Capacity ................................................................................................................................ 68 5.5.1. Minnesota Reserve Capacity ............................................................................................... 69 5.5.2. Wisconsin Reserve Capacity ................................................................................................ 70 5.6. Boundary Conditions .......................................................................................................................... 70 5.7. Seasonal Variation .............................................................................................................................. 73 5.8. Tribal Lands ........................................................................................................................................ 73 6. Reasonable Assurance ............................................................................................................ 75 6.1. Framework ......................................................................................................................................... 75 6.2. Basin, Regional and Local Entities ...................................................................................................... 79 6.3. Summary of Local Plans ..................................................................................................................... 83 6.4. Example Basin-wide Source Reduction Activities and Tools .............................................................. 84 6.5. Future Developments ......................................................................................................................... 95 7. Monitoring Plan ...................................................................................................................... 97 8. Implementation Strategy Summary ...................................................................................... 100 8.1. The Minnesota Nutrient Reduction Strategy ................................................................................... 100 8.2. The Minnesota Watershed Approach .............................................................................................. 103 8.3. Permitted Sources ............................................................................................................................ 103 8.3.1. Construction Stormwater ................................................................................................. 103 8.3.2. Industrial Stormwater ......................................................................................................