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Curlew Valley Subbasin Assessment and Total Maximum Daily Loads

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Curlew Valley Subbasin Assessment and Total Maximum Daily Loads Curlew Valley Subbasin Assessment and Total Maximum Daily Loads 2019 Hydrologic Unit Code 16020309 Final State of Idaho Department of Environmental Quality April 2019 Printed on recycled paper, DEQ April 2019, PID TM86, CA code 62074. Costs associated with this publication are available from the State of Idaho Department of Environmental Quality in accordance with Section 60-202, Idaho Code. Curlew Valley Subbasin Assessment and Total Maximum Daily Loads 2019 April 2019 Prepared by Hannah Harris Idaho Department of Environmental Quality Pocatello Regional Office 444 Hospital Way #300 Pocatello, ID 83201 (208) 236-6160 Curlew Valley Subbasin Assessment and TMDLs Table of Contents List of Tables ................................................................................................................................. iv List of Figures ................................................................................................................................. v Abbreviations, Acronyms, and Symbols ...................................................................................... vii Executive Summary ..................................................................................................................... viii Subbasin at a Glance .................................................................................................................. ix Key Findings ............................................................................................................................... x Public Participation .................................................................................................................. xiv 1 Introduction .................................................................................................................................. 1 1.1 Regulatory Requirements ...................................................................................................... 1 2 Subbasin Assessment—Subbasin Characterization ..................................................................... 2 3 Subbasin Assessment—Water Quality Concerns and Status ....................................................... 4 3.1 Water Quality Limited Assessment Units Occurring in the Subbasin .................................. 4 3.1.1 Assessment Units ............................................................................................................ 5 3.1.2 Listed Waters .................................................................................................................. 5 3.2 Applicable Water Quality Standards and Beneficial Uses .................................................... 5 3.2.1 Beneficial Uses in the Subbasin ..................................................................................... 6 3.2.2 Water Quality Criteria to Support Beneficial Uses ........................................................ 6 3.3 Summary and Analysis of Existing Water Quality Data ....................................................... 7 3.3.1 Status of Beneficial Uses .............................................................................................. 12 3.3.2 Assessment Unit Summary ........................................................................................... 12 4 Subbasin Assessment—Pollutant Source Inventory .................................................................. 19 4.1 Point Sources ....................................................................................................................... 19 4.2 Nonpoint Sources ................................................................................................................ 19 4.3 Pollutant Transport .............................................................................................................. 20 5 Subbasin Assessment—Summary of Past and Present Pollution Control Efforts ..................... 21 6 Total Maximum Daily Loads ..................................................................................................... 23 6.1 Instream Water Quality Targets .......................................................................................... 24 6.1.1 Design Conditions ........................................................................................................ 24 6.1.2 Target Selection ............................................................................................................ 25 6.1.3 Water Quality Monitoring Points ................................................................................. 26 6.2 Load Capacity ..................................................................................................................... 27 6.3 Estimates of Existing Pollutant Loads ................................................................................ 27 6.3.1 Sediment Loads ............................................................................................................ 27 6.3.2 Nutrient Loads .............................................................................................................. 28 6.3.3 E. coli Concentrations ................................................................................................... 29 iii FINAL April 2019 Curlew Valley Subbasin Assessment and TMDLs 6.4 Load Allocations and Wasteload Allocations ..................................................................... 29 6.4.1 Margin of Safety ........................................................................................................... 34 6.4.2 Seasonal Variation ........................................................................................................ 34 6.4.3 Reasonable Assurance .................................................................................................. 34 6.4.4 Natural Background ...................................................................................................... 35 6.4.5 Construction Stormwater and TMDL Wasteload Allocations ...................................... 35 6.5 Implementation Strategies ................................................................................................... 35 6.5.1 Time Frame ................................................................................................................... 36 6.5.2 Approach ....................................................................................................................... 36 6.5.3 Responsible Parties ....................................................................................................... 36 6.5.4 Implementation Monitoring Strategy ........................................................................... 37 6.5.5 Pollutant Trading .......................................................................................................... 37 7 Conclusions ................................................................................................................................ 38 References Cited ........................................................................................................................... 40 GIS Coverages ........................................................................................................................... 42 Glossary ........................................................................................................................................ 43 Appendix A. Beneficial Uses ........................................................................................................ 47 Existing Uses ............................................................................................................................. 47 Designated Uses ........................................................................................................................ 47 Undesignated Surface Waters and Presumed Use Protection ................................................... 47 Appendix B. Water Quality Criteria ............................................................................................. 49 Appendix C. Stormwater Runoff Types ....................................................................................... 50 Municipal Separate Storm Sewer Systems ................................................................................ 50 Industrial Stormwater Requirements ......................................................................................... 50 Construction Stormwater ........................................................................................................... 51 Appendix D. Pollutant Trading ..................................................................................................... 53 Trading Components ................................................................................................................. 53 Watershed-Specific Environmental Protection ......................................................................... 53 Trading Framework ................................................................................................................... 54 Appendix E. Public Participation and Public Comments ............................................................. 55 Appendix F. Distribution List ....................................................................................................... 57 List of Tables Table A. Water bodies and pollutants for which TMDLs were developed. ................................. xii Table B. Curlew Valley pollutant targets. ...................................................................................
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