Water Quality Assessment and Monitoring Study: Analysis of Existing Data on the Duwamish Estuary October 2017 Alternative Formats Available Water Quality Assessment and Monitoring Study: Analysis of Existing Data on the Duwamish Estuary Prepared for: King County Department of Natural Resources and Parks Wastewater Treatment Division Submitted by: Chris Magan, Timothy Clark, Kate Macneale, Martin Grassley, Bob Bernhard, and Dean Wilson King County Water and Land Resources Division Department of Natural Resources and Parks Water Quality Assessment and Monitoring Study: Analysis of Existing Data on the Duwamish Estuary Acknowledgements The authors would like to thank for following people for their contributions to this report: Dawn Duddleson (King County) for her help in completing the literature review. The King County Water Quality and Quantity Group for their insights and guidance. King County project team members: Judy Pickar (project manager), Dean Wilson (science lead), Bob Bernhard, Mark Buscher, Timothy Clark, Betsy Cooper, Wendy Eash‐Loucks, Elizabeth Gaskill, Martin Grassley, Erica Jacobs, Susan Kaufman‐Una, Deborah Lester, Kate Macneale, Chris Magan, Bruce Nairn, Sarah Ogier, Erika Peterson, John Phillips, Cathie Scott, Jim Simmonds, Jeff Stern, Dave White, Mary Wohleb, and Olivia Wright. The project’s Science and Technical Review Team members—Virgil Adderley, Mike Brett, Jay Davis, Ken Schiff, and John Stark—for guidance and review of this report. Citation King County. 2017. Water Quality Assessment and Monitoring Study: Analysis of Existing Data on the Duwamish Estuary. Prepared by Chris Magan, Timothy Clark, Kate Macneale, Martin Grassley, Bob Bernhard, and Dean Wilson, Water and Land Resources Division. Seattle, Washington. King County i October 2017 Water Quality Assessment and Monitoring Study: Analysis of Existing Data on the Duwamish Estuary Table of Contents 1.1 King County Wastewater System ............................................................................................... 1‐1 1.2 CSO Control Program ...................................................................................................................... 1‐3 1.3 Water Quality Assessment and Monitoring Study .............................................................. 1‐3 1.4 Scope and Content of this Report ............................................................................................... 1‐6 Geographic Limits ....................................................................................................................... 1‐6 Approaches to Data Analysis ................................................................................................. 1‐6 Interpreting Box Plots............................................................................................................... 1‐8 2.1 Green‐Duwamish River Watershed .......................................................................................... 2‐1 2.2 Characteristics .................................................................................................................................... 2‐4 Historical and Current Configurations .............................................................................. 2‐4 Physical Characteristics of the Duwamish Estuary ...................................................... 2‐5 Hydrology of the Duwamish Estuary ................................................................................. 2‐6 2.3 Historical and Current Uses ......................................................................................................... 2‐8 Commercial and Industrial Uses .......................................................................................... 2‐8 Other Human Uses ...................................................................................................................... 2‐9 Animals and Their Habitats .................................................................................................... 2‐9 2.4 Contaminant Sources and Pathways ..................................................................................... 2‐10 2.5 King County CSO Discharge Sites ............................................................................................ 2‐14 Discharge Site Descriptions ................................................................................................. 2‐14 Average Annual Discharge Frequencies and Volumes ............................................ 2‐16 2.6 Historical Contamination Cleanup Sites .............................................................................. 2‐17 Harbor Island ............................................................................................................................. 2‐17 Lockheed West Seattle ........................................................................................................... 2‐20 Lower Duwamish Waterway .............................................................................................. 2‐21 2.7 EPA‐Approved Listed Impairments ....................................................................................... 2‐22 King County ii October 2017 Water Quality Assessment and Monitoring Study: Analysis of Existing Data on the Duwamish Estuary 3.1 Sampling Sites and Parameters .................................................................................................. 3‐1 3.2 Sampling and Analysis Methodologies .................................................................................... 3‐4 3.3 Bacteria ................................................................................................................................................. 3‐5 Current Conditions ..................................................................................................................... 3‐6 Comparison to Criteria ............................................................................................................. 3‐7 Long‐term Trends .................................................................................................................... 3‐10 Discussion ................................................................................................................................... 3‐13 3.4 Physical Parameters ..................................................................................................................... 3‐13 Temperature .............................................................................................................................. 3‐13 Dissolved Oxygen ..................................................................................................................... 3‐23 Salinity .......................................................................................................................................... 3‐31 Conductivity ............................................................................................................................... 3‐35 pH .................................................................................................................................................... 3‐39 Alkalinity ..................................................................................................................................... 3‐44 Total Suspended Solids ......................................................................................................... 3‐45 Turbidity ...................................................................................................................................... 3‐48 3.5 Nutrients ............................................................................................................................................ 3‐51 Nitrogen ....................................................................................................................................... 3‐51 Phosphorus ................................................................................................................................. 3‐60 3.6 Metals .................................................................................................................................................. 3‐65 Current Conditions .................................................................................................................. 3‐66 Comparison to Criteria .......................................................................................................... 3‐67 3.7 Organic Compounds...................................................................................................................... 3‐70 Current Conditions .................................................................................................................. 3‐70 Comparison to Water Quality Criteria ............................................................................ 3‐72 4.1 Data Evaluated ................................................................................................................................... 4‐1 4.2 Duwamish Estuary ........................................................................................................................... 4‐2 Physical Structure ....................................................................................................................... 4‐2 Sediment Chemistry .................................................................................................................. 4‐4 4.3 Green River Watershed .................................................................................................................