Minnehaha Creek E. Coli Bacteria / Lake Hiawatha Nutrients Total Maximum Daily Load October 2013 Prepared for U.S. Environmental Protection Agency -- Region 5 Minnesota Pollution Control Agency Minnehaha Creek Watershed District Prepared by Tetra Tech, Inc. 1468 West Ninth Street, Suite 620 Cleveland, OH 44113 Minnehaha Creek / Lake Hiawatha Total Maximum Daily Load Table of Contents Acronyms and Abbreviations .....................................................................................................................v TMDL Summary ......................................................................................................................................... vi Executive Summary ................................................................................................................................ viii 1. Overview ..........................................................................................................................................1 2. Background Information ................................................................................................................1 2.1 Population .....................................................................................................................................4 2.2 Municipal Boundaries ...................................................................................................................5 2.3 Land Use / Land Cover .................................................................................................................7 2.4 Soils ...............................................................................................................................................9 2.5 Climate ........................................................................................................................................11 2.6 Geology .......................................................................................................................................12 2.7 Topography .................................................................................................................................12 3. Targets .......................................................................................................................................... 14 3.1 Priority Ranking ..........................................................................................................................14 3.2 Applicable Water Quality Criteria ..............................................................................................14 3.2.1 Minnehaha Creek ..............................................................................................................14 3.2.2 Lake Hiawatha ...................................................................................................................15 3.3 Spatial Distribution of Pollutants ...............................................................................................16 3.4 Critical Conditions ......................................................................................................................20 3.4.1 Seasonal Variation .............................................................................................................20 3.4.2 Inter-annual Variation .......................................................................................................20 3.5 TMDL Reduction Needs ..............................................................................................................24 4. Source Assessment .................................................................................................................... 25 4.1 Point Sources ..............................................................................................................................25 4.1.1 Bacteria ..............................................................................................................................25 4.1.2 Total Phosphorus ...............................................................................................................27 4.2 Nonpoint Sources ........................................................................................................................30 4.2.1 Bacteria ..............................................................................................................................30 4.2.2 Total Phosphorus ...............................................................................................................30 4.3 Upstream Boundary Load (upstream load from Lake Minnetonka) ...........................................31 4.4 Subwatershed Approach..............................................................................................................32 5. Linkage Analysis ......................................................................................................................... 34 5.1 Flow ............................................................................................................................................34 5.1.1 Hydrograph Separation......................................................................................................35 5.1.2 Base Flow Conditions and Conductivity ...........................................................................35 5.1.3 Stormwater ........................................................................................................................41 5.2 Lake Hiawatha ............................................................................................................................42 5.2.1 Data Summary ...................................................................................................................42 5.2.2 Residence Time Analysis ..................................................................................................44 5.3 Watershed Loading and Response ..............................................................................................46 5.3.1 Bacteria ..............................................................................................................................46 5.3.2 Total Phosphorus ...............................................................................................................49 -i - Minnehaha Creek / Lake Hiawatha Total Maximum Daily Load 6. TMDL Development ..................................................................................................................... 55 6.1 Bacteria (Minnehaha Creek) .......................................................................................................55 6.1.1 Loading Capacity ..............................................................................................................55 6.1.2 Allocations ........................................................................................................................56 6.1.3 Margin of Safety ................................................................................................................57 6.2 Phosphorus (Lake Hiawatha) .....................................................................................................58 6.2.1 Loading Capacity ..............................................................................................................58 6.2.2 Allocations ........................................................................................................................59 6.2.3 Margin of Safety ................................................................................................................65 7. Reasonable Assurance and Implementation Strategies ......................................................... 65 7.1 MPCA Stormwater Program .......................................................................................................65 7.2 MCWD Water Resources Management Plan ..............................................................................67 7.3 Funding .......................................................................................................................................68 7.4 Implementation Activities ............................................................................................................69 7.5 Schedule and Tracking ................................................................................................................72 7.6 Adaptive Management .................................................................................................................72 7.7 Monitoring Activities ...................................................................................................................73 7.8 Future Implementation Activity Recommendations ....................................................................74 7.8.1 Multi-scale Analysis ..........................................................................................................75 7.8.2 BMP Performance Curves .................................................................................................78 7.8.3 Opportunities and Constraints (Level of Implementation Curves) ...................................82 7.8.4 Summary ...........................................................................................................................89 7.9 Costs ............................................................................................................................................90 8. Public Participation ....................................................................................................................