u7Minnesota River and Greater Blue Earth River Basin Total Suspended Solids Total Maximum Daily Load Study January 2020 wq-iw7-47e Authors and contributors: Andrea Plevan, Tetra Tech Jennifer Olson, Tetra Tech Jon Butcher, Tetra Tech Bill Carlson, Tetra Tech Mark Greve, Tetra Tech Scott MacLean, MPCA Paul Davis, MPCA Bottom left cover photo credit: Jim Strudell, MPCA Prepared for: Minnesota Pollution Control Agency 12 Civic Center Plaza, Suite 2165 Mankato, MN 56001 Prepared by: 413 Wacouta Street, Suite 435 Saint Paul, MN 55101 www.tetratech.com Contents Contents ............................................................................................................................................ i Tables ............................................................................................................................................... iii Figures .............................................................................................................................................. iii Abbreviations .................................................................................................................................... v Executive Summary .......................................................................................................................... vii 1. Project Overview ........................................................................................................................1 1.1 Purpose ................................................................................................................................................ 1 1.2 Identification of Water Bodies ............................................................................................................. 3 1.3 Priority Ranking .................................................................................................................................. 12 2. Applicable Water Quality Standards and Numeric Water Quality Targets ................................... 13 3. Previous TMDL Development .................................................................................................... 16 4. Watershed and Water Body Characterization ............................................................................ 22 4.1 Subwatersheds ................................................................................................................................... 23 4.2 Land Cover.......................................................................................................................................... 29 4.3 Current/Historic Water Quality .......................................................................................................... 31 4.3.1 HUC-8 07020004: Hawk–Yellow Medicine Watershed ....................................................... 39 4.3.2 HUC-8 07020005: Chippewa River Watershed ................................................................... 40 4.3.3 HUC-8 07020006: Redwood River Watershed .................................................................... 41 4.3.4 HUC-8 07020007: Minnesota River–Mankato Watershed ................................................. 42 4.3.5 HUC-8 07020008: Cottonwood River Watershed ............................................................... 43 4.3.6 HUC-8 07020009: Blue Earth River Watershed .................................................................. 44 4.3.7 HUC-8 07020010: Watonwan River Watershed ................................................................. 45 4.3.8 HUC-8 07020011: Le Sueur River Watershed ..................................................................... 46 4.3.9 HUC-8 07020012: Lower Minnesota River Watershed ....................................................... 47 4.4 Sediment Sources ............................................................................................................................... 47 4.4.1 Source Assessment Modeling Approach............................................................................. 48 4.4.2 Nonpermitted Sources ........................................................................................................ 49 4.4.3 Permitted Sources ............................................................................................................... 50 4.4.4 Summary of Modeling Results ............................................................................................ 52 5. TSS TMDL Development Approach ............................................................................................ 57 5.1 Loading Capacity ................................................................................................................................ 57 5.1.1 Development of Flow Duration Curves ............................................................................... 57 5.1.2 Development of Load Duration Curves ............................................................................... 59 5.1.3 MNR GBE TSS load capacities vs SMM load capacities ....................................................... 60 Minnesota River and Greater Blue Earth River Basin TSS TMDL Minnesota Pollution Control Agency i 5.2 Percent Reductions ............................................................................................................................ 62 5.3 Lac Qui Parle Boundary Condition ..................................................................................................... 62 5.4 Wasteload Allocation ......................................................................................................................... 62 5.4.1 Municipal and Industrial Wastewater ................................................................................. 63 5.4.2 Construction and Industrial Stormwater ............................................................................ 64 5.4.3 Municipal Separate Storm Sewer Systems ......................................................................... 65 5.5 Margin of Safety ................................................................................................................................. 66 5.6 Load Allocation Methodology ............................................................................................................ 67 5.7 Seasonal Variation .............................................................................................................................. 69 6. TSS TMDL Summaries ............................................................................................................... 70 7. Future Growth Considerations .................................................................................................. 72 7.1 New or Expanding Permitted MS4 WLA Transfer Process ................................................................. 72 7.2 New or Expanding Wastewater.......................................................................................................... 72 8. Reasonable Assurance .............................................................................................................. 73 8.1 Framework ......................................................................................................................................... 73 8.2 Basin, Regional, and Local Entities ..................................................................................................... 75 8.3 Summary of Local Plans ..................................................................................................................... 76 8.4 Basin Wide Nonpoint Source Reduction Activities ............................................................................ 78 9. Monitoring Plan ........................................................................................................................ 83 10. Implementation Strategy Summary ....................................................................................... 85 10.1 Nonpermitted Sources ....................................................................................................................... 87 10.2 Permitted Sources .............................................................................................................................. 89 10.2.1 Construction Stormwater ................................................................................................... 89 10.2.2 Industrial Stormwater ......................................................................................................... 89 10.2.3 MS4s .................................................................................................................................... 90 10.2.4 Wastewater ......................................................................................................................... 90 10.3 Cost .................................................................................................................................................... 90 10.4 Adaptive Management....................................................................................................................... 91 11. Public Participation ............................................................................................................... 92 11.1 Draft Minnesota River Turbidity TMDL Stakeholder Meetings .......................................................... 92 11.2 Greater Blue Earth River Basin Stakeholder Meetings....................................................................... 95 11.3 Public Notice for Comments