Skokomish River Basin Fecal Coliform Bacteria Total Maximum Daily Load Study April 2001 Publication No. 01-03-014 printed on recycled paper This report is available on the Department of Ecology home page on the World Wide Web at http://www.ecy.wa.gov/biblio/0103014.html For additional copies of this publication, please contact: Department of Ecology Publications Distributions Office Address: PO Box 47600, Olympia WA 98504-7600 E-mail: [email protected] Phone: (360) 407-7472 Refer to Publication Number 01-03-014 The Department of Ecology is an equal opportunity agency and does not discriminate on the basis of race, creed, color, disability, age, religion, national origin, sex, marital status, disabled veteran's status, Vietnam era veteran's status, or sexual orientation. If you have special accommodation needs or require this document in alternative format, please contact Joan LeTourneau, Environmental Assessment Program, at (360)-407-6764 (voice). Ecology's telecommunications device for the deaf (TDD) number at Ecology Headquarters is (360) 407-6006. Skokomish River Basin Fecal Coliform Bacteria Total Maximum Daily Load Study by Keith Seiders, Guy Hoyle-Dodson, and Paul Pickett Environmental Assessment Program Watershed Ecology Section Olympia, Washington 98504-7710 April 2001 Waterbody Numbers: WA-16-1010, WA-16-1013, WA-16-1014, WA-16-1015, WA-16-1016, WA-16-1020, WA-16-1030 Publication No. 01-03-014 printed on recycled paper This page is purposely blank for duplex printing Table of Contents Page List of Figures and Tables...................................................................................................ii List of Acronyms................................................................................................................iii Abstract ............................................................................................................................... v Acknowledgements ............................................................................................................ vi Introduction ......................................................................................................................... 1 Background ................................................................................................................... 1 Problem Description...................................................................................................... 2 Water Quality Standards ............................................................................................... 2 Study Area..................................................................................................................... 4 Land Use ....................................................................................................................... 6 Pollutant Sources........................................................................................................... 6 Project Objectives ......................................................................................................... 7 Water Quality Data..............................................................................................................9 Methods.........................................................................................................................9 Quality Assurance and Quality Control Results ......................................................... 12 Water Quality Monitoring Results .............................................................................. 12 Fecal Coliform TMDL Analysis ....................................................................................... 19 Approach ..................................................................................................................... 19 Seasonal Variation and Critical Conditions ................................................................ 19 Flow Balance............................................................................................................... 22 TMDL Development................................................................................................... 24 FC Load Balance......................................................................................................... 28 FC Load Allocation..................................................................................................... 31 Margin of Safety.......................................................................................................... 35 Monitoring and Implementation.................................................................................. 36 Conclusions and Recommendations.................................................................................. 39 References ......................................................................................................................... 43 Appendices A. Quality Assurance and Quality Control B. Flow Measurement Techniques C. Water Quality Data D. Load Allocation Scenarios Page i List of Figures and Tables Page Figures Figure 1. Skokomish River bacteria TMDL study area ..................................................... 5 Figure 2. Water quality data summary plots ...............................................................13-14 Figure 3. Historical FCmf levels in the Skokomish River at Highway 101..................... 16 Figure 4. Monthly FC values from various data sets ....................................................... 21 Figure 5. Distribution of mean daily flow in the Skokomish River basin ....................... 23 Figure 6. Distribution of mean daily FC load in the Skokomish River basin.................. 29 Figure 7. Distribution of mean daily FC load in the Skokomish River basin at recommended allocation levels......................................................................... 33 Figure 8. Comparison of FC load distributions at study conditions and target conditions ......................................................................................................... 34 Tables Table 1. Skokomish River basin streams on the 1996 and 1998 303(d) lists for FC......... 3 Table 2. Sampling sites for the Skokomish River TMDL water quality study, 1999-2000.......................................................................................................... 10 Table 3. Summary of field and laboratory methods......................................................... 11 Table 4. Study sites not meeting the dissolved oxygen standard of 9.5 mg/L................. 15 Table 5. Calculation of FC target values for the Skokomish River at Highway 106 to protect marine water standards...................................................................... 26 Table 6. Summary statistics for FC during the averaging period and for target reductions........................................................................................................... 27 Table 7. Mean daily values for flow, FC, FC load, flow, and balances at key sites for the study period............................................................................................ 30 Table 8. Recommended FC TMDL load allocations for Skokomish River sub-basins... 32 Page ii List of Acronyms AMV arithmetic mean value BMP best management practices BOD biological oxygen demand cfs cubic feet per second CI confidence interval CV coefficient of variation DO dissolved oxygen DOH Washington State Department of Health EC Escherichia coli (E. coli) Ecology Washington State Department of Ecology EMTS Environmental Monitoring and Trends Section EPA U.S. Environmental Protection Agency FC fecal coliform bacteria FCmf fecal coliform by membrane filter FCmpn fecal coliform by most probable number GIS geographic information system GMV geometric mean value LA load allocation mg/L milligrams per liter mL milliliters ppt parts per thousand QAPP quality assurance project plan RM river mile RMSCV root mean square of the coefficient of variation RPD relative percent difference RSD relative standard deviation STR Statistical Theory of Rollback TMDL Total Maximum Daily Load Tribe Skokomish Indian Tribe TSS total suspended solids USGS U.S. Geological Survey WAC Washington Administrative Code Page iii This page is purposely blank for duplex printing Page iv Abstract A Total Maximum Daily Load (TMDL) study for fecal coliform bacteria (FC) was conducted for the Skokomish River, because FC levels were not meeting fresh water quality standards due to nonpoint source pollution. The goal of the TMDL is to protect public health from pathogens in fresh water and help protect the marine waters of Hood Canal and shellfish harvesting in Annas Bay. The study was a cooperative effort with the Skokomish Tribe, whose Reservation includes part of the watershed. This study precedes the development of a water cleanup plan which will guide activities to better manage FC pollution. The Department of Ecology sampled 18 stream sites from January 1999 through January 2000, seven of which were sampled concurrently by the Skokomish Tribe. Study results confirmed violations of water quality standards for FC and found seven sites where dissolved oxygen did not meet standards. The mean daily FC load was calculated for each site using a 10-month averaging period. Load balances indicate the presence of significant FC sources (52% of the FC load) along the lower mainstem corridors of the Skokomish River and Purdy Creek between the bridges for Highways 106 and 101, and East Bourgault Road. Weaver Creek and Hunter Creek contributed