Water Quality Assessment and Monitoring Study: Analysis of Existing Data on Lake Union/Ship Canal October 2017 Alternative Formats Available Water Quality Assessment and Monitoring Study: Analysis of Existing Data on Lake Union/Ship Canal Prepared for: King County Department of Natural Resources and Parks Wastewater Treatment Division Submitted by: Timothy Clark, Wendy Eash-Loucks, 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 Lake Union/Ship Canal Acknowledgements The authors would like to thank for following people for their contributions to this report: Staff at the King County Environmental Laboratory for field and analytical support. Dawn Duddleson (King County) for her help in completing the literature review. The King County Water Quality and Quantity Group for their insights, especially Sally Abella for her thorough and thoughtful review. Lauran Warner, Frederick Goetz, and Kent Easthouse of the U.S. Army Corps of Engineers. Judy Pickar (project manager), Dean Wilson (science lead), and King County project team members (Bob Bernhard, Mark Buscher, Timothy Clark, Betsy Cooper, Wendy Eash‐Loucks, Elizabeth Gaskill, Martin Grassley, Erica Jacobs, Susan Kaufman‐Una, Lester, Deborah, 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 Lake Union/Ship Canal. Prepared by Timothy Clark, Wendy Eash‐Loucks, 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 Lake Union/Ship Canal Table of Contents Executive Summary ............................................................................................................................................... xii Acronyms and Abbreviations ............................................................................................................................ xx 1.0 Introduction ............................................................................................................................................ 1–1 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 1.4.1 Sources and Quality of Data .................................................................................................. 1–6 1.4.2 Interpreting Box Plots.............................................................................................................. 1–7 2.0 Study Area ................................................................................................................................................ 2–1 2.1 Characteristics ................................................................................................................................... 2–1 2.1.1 Morphology and Shoreline Development ....................................................................... 2–1 2.1.2 Hydrology and Circulation ..................................................................................................... 2–3 2.2 Historical Uses ................................................................................................................................... 2–6 2.3 Current Uses ....................................................................................................................................... 2–7 2.4 Salmon in Lake Union/Ship Canal ............................................................................................ 2–9 2.4.1 Salmon Stocks and Life History Characteristics ........................................................... 2–9 2.4.2 Mortality ..................................................................................................................................... 2–10 2.5 EPA‐Approved Listed Impairments ...................................................................................... 2–12 2.6 Sources and Pathways of Contamination ........................................................................... 2–12 2.6.1 Conceptual Site Model .......................................................................................................... 2–13 2.6.2 Major Ongoing Contaminant Sources and Pathways .............................................. 2–14 2.7 CSO Discharge Sites ...................................................................................................................... 2–15 2.8 Stormwater Discharge Sites ..................................................................................................... 2–20 2.9 Planned and Completed Corrective Actions ...................................................................... 2–20 2.9.1 Historical Contamination Cleanup Areas ..................................................................... 2–20 2.9.2 U.S. Army Corps of Engineers Water Quality Study ................................................. 2–23 3.0 Water Quality .......................................................................................................................................... 3–1 3.1 Sampling Sites and Parameters ................................................................................................. 3–1 3.2 Sampling and Analysis Methodologies ................................................................................... 3–3 King County ii October 2017 Water Quality Assessment and Monitoring Study: Analysis of Existing Data on Lake Union/Ship Canal 3.3 Bacteria ................................................................................................................................................ 3–5 3.3.1 Current Conditions .................................................................................................................... 3–5 3.3.2 Comparison to Criteria ............................................................................................................ 3–6 3.3.3 Long‐Term Trends .................................................................................................................... 3–9 3.4 Physical Parameters .................................................................................................................... 3–10 3.4.1 Temperature ............................................................................................................................. 3–10 3.4.2 Salinity/Conductivity ............................................................................................................ 3–17 3.4.3 Dissolved Oxygen .................................................................................................................... 3–19 3.4.4 Turbidity/Total Suspended Solids/Secchi Transparency ..................................... 3–24 3.4.5 pH and Alkalinity .................................................................................................................... 3–27 3.5 Chlorophyll a ................................................................................................................................... 3–32 3.5.1 Laboratory and Field Method Changes ......................................................................... 3–32 3.5.2 Current Conditions ................................................................................................................. 3–32 3.5.3 Long‐Term Trends ................................................................................................................. 3–35 3.6 Nutrients ........................................................................................................................................... 3–35 3.6.1 Nitrogen ...................................................................................................................................... 3–36 3.6.2 Phosphorus ................................................................................................................................ 3–46 3.6.3 Silica .............................................................................................................................................. 3–52 3.7 Trophic State Indices and Limiting Factors for Phytoplankton ................................ 3–55 3.7.1 Trophic State Indices ............................................................................................................. 3–55 3.7.2 Limiting Factors....................................................................................................................... 3–59 3.7.3 Nitrogen to Total Phosphorus Ratio ............................................................................... 3–60 3.7.4 Phytoplankton Community and Biovolume ................................................................ 3–61 3.8 Metals ................................................................................................................................................