Final - Bitterroot Watershed Total Maximum Daily Loads and Water Quality Improvement Plan December 2014 Steve Bullock, Governor Tracy Stone-Manning, Director DEQ Document Number C05-TMDL-04aF Prepared by: Water Quality Planning Bureau Watershed Management Section Contributors: Water Quality Planning Bureau Watershed Management Section Mindy McCarthy, Nutrients Project Manager Christian Schmidt, Previous Nutrients Project Manager Jordan Tollefson, Project Coordinator and Temperature Project Manager Information Management and Technical Services Section Kyle Flynn, Project Modeler Mike Van Liew, Previous Modeler U.S. Environmental Protection Agency Peter Brumm, Metals Project Manager Montana Department of Environmental Quality Water Quality Planning Bureau 1520 E. Sixth Avenue P.O. Box 200901 Helena, MT 59620-0901 Suggested citation: Montana DEQ and U.S. EPA Region 8. 2014. Bitterroot Watershed Total Maximum Daily Loads and Water Quality Improvement Plan. Helena, MT: Montana Dept. of Environmental Quality. ACKNOWLEDGEMENTS DEQ would like to acknowledge multiple entities for their contributions in the development of the TMDLs contained in this document. This project was a joint effort with the Montana Office of the U.S. Environmental Protection Agency (EPA). DEQ would like to thank the EPA staff that contributed to the completion of this project. Peter Brumm was a vital member of this project, serving as the project manager for the metals TMDLs in Section 6.0 and authoring Section 2.0, the Bitterroot Watershed Project Area Description, as well as creating all maps contained in Appendix A. DEQ would also like to thank Jessica Clarke with our Monitoring and Assessment Section who conducted water quality monitoring in support of the metals and nutrients TMDLs; and Carrie Greeley, an administrative assistant, for her time and effort formatting this document. A consulting firm, Tetra Tech, Inc., provided support with temperature field data collection, data analysis, and modeling for Mill Creek, and authored Section 7.0 in the document, as well as authored Attachment A, Modeling Water Temperature in Mill Creek. DEQ would also like to thank the Bitterroot Water Forum and Gil Gale from the Bitterroot National Forest for their input and assistance throughout development of these TMDLs. Draft versions of source assessment reports and this document were sent to stakeholders for review and input. The involvement of all reviewers led to improvements in this document and is greatly appreciated. Bitterroot Watershed Total Maximum Daily Loads and Water Quality Improvement Plan – Table of Contents TABLE OF CONTENTS Acronym List ................................................................................................................................................ xi Document Summary ............................................................................................................................... DS-1 1.0 Project Overview .................................................................................................................................. 1-1 1.1 Why We Write TMDLs ...................................................................................................................... 1-1 1.2 Water Quality Impairments and TMDLs Addressed by this Document ........................................... 1-2 1.3 What This Document Contains ........................................................................................................ 1-6 2.0 Bitterroot Watershed Project Area Description .................................................................................. 2-1 2.1 Physical Characteristics .................................................................................................................... 2-1 2.1.1 Location ..................................................................................................................................... 2-1 2.1.2 Topography ............................................................................................................................... 2-1 2.1.3 Geology ..................................................................................................................................... 2-1 2.1.4 Soil ............................................................................................................................................. 2-2 2.1.5 Surface Water ........................................................................................................................... 2-3 2.1.6 Groundwater ............................................................................................................................. 2-4 2.1.7 Climate ...................................................................................................................................... 2-4 2.2 Ecological Characteristics ................................................................................................................. 2-5 2.2.1 Ecoregion .................................................................................................................................. 2-5 2.2.2 Fire ............................................................................................................................................ 2-6 2.2.3 Aquatic and Terrestrial Life ....................................................................................................... 2-7 2.3 Cultural Characteristics .................................................................................................................... 2-7 2.3.1 Population ................................................................................................................................. 2-7 2.3.2 Transportation Networks .......................................................................................................... 2-8 2.3.3 Land Ownership ........................................................................................................................ 2-8 2.3.4 Land Cover and Use .................................................................................................................. 2-9 2.3.5 Point Sources .......................................................................................................................... 2-10 3.0 Montana Water Quality Standards ...................................................................................................... 3-1 3.1 Stream Classifications and Designated Beneficial Uses ................................................................... 3-1 3.2 Numeric and Narrative Water Quality Standards ............................................................................ 3-3 4.0 Defining TMDLs and Their Components .............................................................................................. 4-1 4.1 Developing Water Quality Targets ................................................................................................... 4-2 4.2 Quantifying Pollutant Sources ......................................................................................................... 4-2 4.3 Establishing the Total Allowable Load ............................................................................................. 4-3 4.4 Determining Pollutant Allocations ................................................................................................... 4-3 12/3/2014 Final i Bitterroot Watershed Total Maximum Daily Loads and Water Quality Improvement Plan – Table of Contents 4.5 Implementing TMDL Allocations ...................................................................................................... 4-5 5.0 Nutrient TMDL Components ................................................................................................................ 5-1 5.1 Nutrient Effects on Beneficial Uses .................................................................................................. 5-1 5.2 Stream Segments of Concern .......................................................................................................... 5-1 5.3 Water Quality Assessment Method and Information Sources ........................................................ 5-3 5.4 Water Quality Targets ...................................................................................................................... 5-4 5.4.1 Nutrient Water Quality Standards ............................................................................................ 5-4 5.4.2 Nutrient Target Values .............................................................................................................. 5-4 5.4.3 Existing Conditions and Comparison to Targets ....................................................................... 5-7 5.4.4 Nutrient TMDL Development Summary ................................................................................. 5-18 5.5 Source Assessment, TMDL, and Allocation Approaches ................................................................ 5-19 5.5.1 Source Assessment Approach ................................................................................................. 5-19 5.5.2 TMDL and Allocation Approach .............................................................................................. 5-23 5.6 Source Assessments, TMDLs, and Allocations for Each Stream..................................................... 5-26 5.6.1 Threemile Creek .....................................................................................................................