spokane river watershed nonpoint source phosphorus reduction plan December 2011 2011 Table of Contents List of Acronyms ................................................................................................................x Using this Plan ................................................................................................................. xii Executive Summary .................................................................................................... ES-1 Chapter 1 Spokane River Watershed Nonpoint Source Phosphorus Background and Issues ...................................................................................... 1-1 1.1 Introduction .......................................................................................................... 1-1 1.2 Background .......................................................................................................... 1-3 1.2.1 Spokane Watershed Water Quality Considerations ................................. 1-3 1.2.2 Spokane River DO TMDL Development ................................................. 1-4 1.3 Purpose ................................................................................................................. 1-5 1.4 Phosphorus Control Approach ............................................................................. 1-5 1.5 Watershed Description ......................................................................................... 1-7 1.5.1 Study Area ................................................................................................ 1-7 Chapter 2 Spokane River DO TMDL Identification of Nonpoint Source Phosphorus Loads ................................................................................. 2-1 2.1 Introduction .......................................................................................................... 2-1 2.2 Summary of Nonpoint Source Phosphorus Sources ............................................ 2-2 2.3 Summary of Phosphorus Wasteload and Load Allocations ................................. 2-2 2.3.1 Point Source Phosphorus Wasteload Allocations ..................................... 2-2 2.3.2 Nonpoint Source Phosphorus Load Allocations ....................................... 2-3 Chapter 3 Subbasin Assessment Nonpoint Source Phosphorus ................................ 3-1 3.1 Watershed Nonpoint Source Phosphorus ............................................................. 3-1 3.2 Lower Spokane River Subbasin ........................................................................... 3-4 3.2.1 Lower Spokane River Subbasin Characteristics ....................................... 3-4 3.2.2 Lower Spokane River Subbasin Land Use ............................................... 3-5 3.2.3 Lower Spokane River Subbasin Pollution Sources .................................. 3-7 3.3 Upper Spokane River WA Subbasin - Nonpoint Source Phosphorus ................. 3-7 3.3.1 Upper Spokane River WA Subbasin Characteristics ............................... 3-7 3.3.2 Upper Spokane River WA Subbasin Land Use ........................................ 3-8 3.3.3 Upper Spokane River WA Subbasin Pollution Sources ......................... 3-10 3.4 Little Spokane River Subbasin - Nonpoint Source Phosphorus ........................ 3-10 3.4.1 Little Spokane River Subbasin Characteristics ...................................... 3-10 3.4.2 Little Spokane River Subbasin Land Use ............................................... 3-11 3.5 Hangman Creek Subbasin - Nonpoint Source Phosphorus ................................ 3-13 3.5.1 Hangman Creek Subbasin Characteristics .............................................. 3-13 3.5.2 Hangman Creek Subbasin Land Use ...................................................... 3-14 3.5.3 Hangman Creek Subbasin Pollution Sources ......................................... 3-16 3.6 Upper Spokane River ID Subbasin - Nonpoint Source Phosphorus .................. 3-16 3.6.1 Upper Spokane River ID Subbasin Characteristics ................................ 3-16 3.6.2 Upper Spokane River ID Subbasin Land Use ........................................ 3-18 3.6.3 Upper Spokane River ID Subbasin Pollution Sources ........................... 3-19 Spokane River Watershed Nonpoint Source Phosphorus Reduction Plan Page i 3.7 Coeur d’Alene Lake Subbasin - Nonpoint Source Phosphorus ......................... 3-19 3.7.1 Coeur d’Alene Lake Subbasin Characteristics ....................................... 3-19 3.7.2 Coeur d’Alene Lake Subbasin Land Use ............................................... 3-21 3.7.3 Coeur d’Alene Lake Subbasin Pollution Sources .................................. 3-22 3.8 Upper Coeur d’Alene River Subbasin - Nonpoint Source Phosphorus ............. 3-22 3.8.1 Upper Coeur d’Alene River Subbasin Characteristics ........................... 3-23 3.8.2 Upper Coeur d’Alene River Subbasin Land Use ................................... 3-23 3.8.3 Upper Coeur d’Alene River Subbasin Pollution Sources ....................... 3-24 3.9 South Fork Coeur d’Alene River Subbasin - Nonpoint Source Phosphorus ..... 3-25 3.9.1 South Fork Coeur d’Alene River Subbasin Characteristics ................... 3-25 3.9.2 South Fork Coeur d’Alene River Subbasin Land Use ............................ 3-26 3.9.3 South Fork Coeur d’Alene River Subbasin Pollution Sources ............... 3-27 3.10 St. Joe River Subbasin - Nonpoint Source Phosphorus ................................... 3-27 3.10.1 St. Joe River Subbasin Characteristics ................................................. 3-27 3.10.2 St. Joe River Subbasin Land Use ......................................................... 3-29 3.10.3 St. Joe River Subbasin Pollution Sources ............................................. 3-30 3.11 Pend Oreille Lake Subbasin - Nonpoint Source Phosphorus ........................... 3-30 3.11.1 Pend Oreille Lake Subbasin Characteristics ......................................... 3-30 3.11.2 Pend Oreille Lake Subbasin Land Use ................................................. 3-30 3.11.3 Pend Oreille Lake Subbasin Pollution Sources .................................... 3-31 3.12 Conclusions ...................................................................................................... 3-31 Chapter 4 Spokane River Watershed – Nonpoint Source Phosphorus .................... 4-1 4.1 Water Quality Report Screening .......................................................................... 4-1 4.2 Report and Data Credibility Assessment ............................................................. 4-1 4.3 Nonpoint Source Phosphorus Database ............................................................... 4-2 4.4 Summary of Phosphorus Dataset ......................................................................... 4-2 4.4.1 Data Count ................................................................................................ 4-2 4.4.2 Average Total Phosphorus Concentration ................................................ 4-5 4.4.3 Total Phosphorus Loading ................................................................................ 4-8 4.4.4 Septic System Density ............................................................................ 4-10 4.5 Groundwater Total Phosphorus Data Analysis .................................................. 4-12 4.6 Groundwater Orthophosphorus Data Analysis .................................................. 4-14 4.7 Surface Water Total Phosphorus Data Analysis ................................................ 4-17 4.8 Surface Water Orthophosphorus Data Analysis ................................................ 4-18 4.9 Prioritization of Nonpoint Source Phosphorus Sources and Subbasins ............. 4-19 4.10 Nonpoint Source Phosphorus Data Gaps ......................................................... 4-20 4.10.1 Groundwater ......................................................................................... 4-20 4.10.2 Surface Water ....................................................................................... 4-21 4.10.3 Data and Analysis Gap Prioritization ................................................... 4-22 4.11 Nonpoint Source Phosphorus Recommended Studies ..................................... 4-22 Chapter 5 Watershed Conditions and Supplemental Data ........................................ 5-1 5.1 Screening-Level Field Reconnaissance ............................................................... 5-1 5.2 Field Data Collection ........................................................................................... 5-3 5.2.1 Deep Creek Field Data Collection and Phosphorus Loading Summary .. 5-3 5.2.2 Eaglewood Field Data Collection and Phosphorus Loading Summary ... 5-6 Spokane River Watershed Nonpoint Source Phosphorus Reduction Plan Page ii Chapter 6 Spokane River Watershed – Groundwater Nonpoint Source Phosphorus Advanced Analysis ........................................................................ 6-1 6.1 Groundwater Analytical Methods and Tools for Nonpoint Source Phosphorus Assessment ..................................................................................................... 6-1 6.2 Applicability and Feasibility of Groundwater Techniques for Spokane River Watershed ...................................................................................................... 6-1 6.3 Selection of Groundwater Analysis Techniques for Application to Spokane River Watershed .....................................................................................................