Water Quality Improvement Plan for Raccoon River, Iowa Total Maximum Daily Load for Nitrate and Escherichia coli Prepared by K.E. Schilling and C.F. Wolter Iowa Department of Natural Resources, Geological Survey 109 Trowbridge Hall, Iowa City, IA 52242-1319 With contributions from D.E. Christiansen and D. J. Schnoebelen United States Geological Survey 400 South Clinton Street Iowa City, IA 52244 M. K. Jha Center for Agriculture and Rural Development Iowa State University Ames, IA 50011 Iowa Department of Natural Resources Watershed Improvement Section 2008 1 TABLE OF CONTENTS EXECUTIVE SUMMARY .............................................................................................12 1.0 INTRODUCTION.....................................................................................................18 2.0 DESCRIPTION AND HISTORY OF THE RACCOON RIVER ........................21 2.1 Raccoon River Watershed.....................................................................................22 2.2 Stream Network and Watershed Delineations ......................................................23 2.3 Soils.......................................................................................................................25 2.4 Land Use ...............................................................................................................25 2.5 Climate..................................................................................................................27 2.6 Hydrology .............................................................................................................28 2.7 Historical Changes in Raccoon River Streamflow ...............................................30 3.0 TOTAL MAXIMUM DAILY LOAD (TMDL) FOR NITRATE .........................31 3.1 Problem Identification ..........................................................................................31 3.1.1 Class “C” impairment at City of Des Moines ..........................................32 3.1.2 Class “C” impairment at City of Panora .................................................34 3.1.3 Temporal Patterns of Nitrate Concentrations ..........................................35 3.1.4 Spatial Patterns of Nitrate Concentrations and Loads.............................37 3.1.5 Qualified Volunteer Monitoring ...............................................................41 3.2 Pollution Source Assessment................................................................................45 3.2.1 Point Sources ............................................................................................45 3.2.2 Livestock Feeding Operations ..................................................................49 3.2.3 MS4 Permits..............................................................................................49 3.2.4 Nonpoint Sources......................................................................................49 3.3 TMDL Approach and Target ................................................................................53 3.3.1 Waterbody Pollutant Loading Capacity ...................................................53 3.3.2 Modeling Approach ..................................................................................54 3.3.3 TMDL Target ............................................................................................54 3.3.4 Margin of Safety........................................................................................55 3.4 TMDL for Nitrate at City of Des Moines .............................................................55 3.4.1 Existing Load ............................................................................................55 3.4.2 Departure from Load Capacity.................................................................56 3.4.3 Seasonal Variation....................................................................................58 3.4.4 Pollutant Allocation..................................................................................59 3.5 TMDL for Nitrate at City of Panora .....................................................................59 3.5.1 Existing Load ............................................................................................59 3.5.2 Departure from Load Capacity.................................................................61 3.5.3 Seasonal Variation....................................................................................62 3.5.4 Pollutant Allocation..................................................................................63 3.6 Nitrate Loads in Raccoon River Subwatersheds...................................................63 2 4.0 TOTAL MAXIMUM DAILY LOAD (TMDL) FOR E.COLI ..............................65 4.1 Problem Identification ..........................................................................................65 4.1.1 Indicator Bacteria Impairment in the Raccoon River, from mouth to confluence with the North and South Raccoon rivers (IA 04-RAC-0010-1&2)..66 4.1.2 Indicator Bacteria Impairment in the North Raccoon River Near Sac City, (IA 04-RAC-0040-5 & 6)............................................................69 4.1.3 Indicator Bacteria Impairment in the North Raccoon River near Jefferson, from Buttrick Creek to Short Creek (IA 04-RAC-0040-1)..................71 4.1.4 Temporal Patterns of E.coli Concentrations ............................................72 4.1.5 Spatial Patterns of E.coli Concentrations ................................................75 4.1.6 Rationale for Basin-wide TMDL for Indicator Bacteria ..........................78 4.2 Pollution Source Assessment................................................................................79 4.2.1 Point Sources ............................................................................................79 4.2.2 Livestock Feeding Operations ..................................................................83 4.2.3 MS4 Permits..............................................................................................83 4.2.4 Nonpoint Sources......................................................................................83 4.3 TMDL Approach and Target ................................................................................85 4.3.1 Waterbody Pollutant Loading Capacity ...................................................85 4.3.2 Modeling Approach ..................................................................................86 4.3.3 TMDL Target ............................................................................................86 4.3.4 Margin of Safety........................................................................................87 4.4 TMDL for E.coli at City of Des Moines (IA 04-RAC-0010-1&2).......................87 4.4.1 Existing Load ............................................................................................87 4.4.2 Departure from Load Capacity.................................................................88 4.4.3 Seasonal Variation....................................................................................90 4.4.4 Pollutant Allocation..................................................................................91 4.5 TMDL for E.coli Impairment in the North Raccoon river Near Sac City (IA 04-RAC-0040-5 & 6).....................................................................92 4.5.1 Existing Load ............................................................................................92 4.5.2 Departure from Load Capacity.................................................................93 4.5.3 Pollutant Allocation .................................................................................93 4.6 TMDL for E.coli Impairment in the North Raccoon river Near Jefferson (IA 04- RAC-0040-1) ...............................................................................................................94 4.6.1 Existing Load ............................................................................................94 4.6.2 Departure from Load Capacity.................................................................94 4.6.3 Pollutant Allocation .................................................................................94 4.7 TMDL for Future Indicator Bacteria Impairments in the Raccoon River ............95 3 5.0 RACCOON RIVER WATERSHED MODEL.......................................................98 5.1 SWAT Model Setup and Description ...................................................................98 5.2 Data Inputs and Model Assumptions..................................................................101 5.3 Model Calibration and Validation ......................................................................106 5.3.1 Streamflow Calibration...........................................................................106 5.3.2 Streamflow Patterns................................................................................110 5.3.3 Nitrate Model Calibration ......................................................................112 5.3.4 Nitrate Loading Patterns ........................................................................114 5.3.5 E.coli Model Calibration ........................................................................123 5.3.6 E.coli Loading Patterns ...........................................................................124 6.0 IMPLEMENTATION PLAN ................................................................................130 6.1 Watershed Scale Load Reduction Scenarios.......................................................130