Vashon- Maury Island Water Resources - A Retrospective of Contributions & Highlights December 2013 Department of Natural Resources and Parks Water and Land Resources Division Science and Technical Support Section King Street Center, KSC-NR-0600 201 South Jackson Street, Suite 600 Seattle, WA 98104 http://www.kingcounty.gov/environment/wlr/science-section.aspx Alternate Formats Available 206-477-4807 TTY Relay: 711 Vashon-Maury Island Water Resources - A Retrospective of Contributions & Highlights Submitted by: King County Department of Natural Resources and Parks Water and Land Resources Division Scientific and Technical Support Section Water Quality and Quantity Data Group - Hydrologic Services http://www.kingcounty.gov/environment/waterandland.aspx Prepared by: S. Bilir With contributions from: E. Ferguson (Vashon-Maury Island Groundwater Protection Program information) and C. DeGasperi (Quartermaster Harbor Nitrogen Management Study information). Citation: King County. 2013. Vashon-Maury Island Water Resources – A Retrospective of Contributions & Highlights. Prepared by King County Department of Natural Resources and Parks, Water and Land Resources Division, Science and Technical Support Section. Seattle, Washington. December. Front page photo credit: L. Larkin Vashon-Maury Island Water Resources – A Retrospective of Contributions & Highlights Table of Contents List of Figures ...................................................................................................................................................................... iii List of Tables ........................................................................................................................................................................ v List of Appendices .............................................................................................................................................................. v Index of Abbreviations & Acronyms ............................................................................................................................. vi Executive Summary ..................................................................................................................................................... ES-1 1.0. Introduction ......................................................................................................................................................... 1 1.1 Overview and Purpose of this Report ............................................................................................ 1 1.2 General Setting ..................................................................................................................................... 2 1.2.1 Geography ................................................................................................................................ 2 1.2.2 Topography .............................................................................................................................. 3 1.2.3 Geology ..................................................................................................................................... 3 1.2.4 Land Use and Cover .............................................................................................................. 3 1.3 Legal Setting .......................................................................................................................................... 3 1.3.1 State Regulatory Framework ............................................................................................... 3 1.3.2 Local Regulatory Framework ............................................................................................... 4 2.0. Technical Activities and Reports ..................................................................................................................... 5 2.1 Carr Report: Water Resources Study ............................................................................................ 5 2.2 Ground Water Management Plan : Area Characterization ....................................................... 7 2.3 King County Groundwater Protection Program ......................................................................... 9 2.3.1 Ambient Groundwater Monitoring Study ........................................................................ 9 2.3.2 Watershed Plan ..................................................................................................................... 10 2.3.3 Water Resources Evaluation ............................................................................................. 10 2.4 Quartermaster Harbor Nitrogen Management Study .............................................................. 21 2.4.1 Sustainability Indicator Development and Monitoring ................................................. 25 3.0. Island-Wide Climate Conditions ................................................................................................................... 26 3.1 Air Temperature ................................................................................................................................ 27 3.2 Precipitation ........................................................................................................................................ 29 3.3 Stream Flows ...................................................................................................................................... 36 King County Science and Technical Support Section i December 2013 Vashon-Maury Island Water Resources – A Retrospective of Contributions & Highlights Table of Contents (CONTINUED) 4.0. Island-Wide Water Resources ...................................................................................................................... 41 4.1 Water Resources Usage .................................................................................................................. 41 4.2 Groundwater Quantity Monitoring ............................................................................................... 45 4.2.1 Aquifer Zones ........................................................................................................................ 45 4.2.2 Groundwater Level Responses and Trends ................................................................... 47 4.2.3 Groundwater Contour Maps ............................................................................................. 49 4.3 Island – Wide Hydrologic Water Budget .................................................................................... 54 4.4 Water Quality on Vashon-Maury Island ....................................................................................... 57 4.4.1 Marine Water Quality in Quartermaster Harbor ........................................................ 58 4.4.2 Freshwater Surface Water Quality .................................................................................. 60 4.4.3 Vashon-Maury Island‘s Groundwater Quality................................................................ 73 5.0. Summary of Scientific Findings ....................................................................................................................... 84 5.1 Findings for Climatic Conditions .................................................................................................... 84 5.2 Findings of the Island-wide Hydrologic Budget .......................................................................... 85 5.3 Findings for Island-Wide Water Resources ................................................................................ 85 5.3.1 Water Usage .......................................................................................................................... 85 5.3.2 Groundwater Quantity ....................................................................................................... 86 5.3.3 Marine Water Quality ......................................................................................................... 87 5.3.4 Freshwater Surface Water Quality .................................................................................. 87 5.3.5 Groundwater Quality .......................................................................................................... 88 6.0. Moving Forward ................................................................................................................................................ 89 6.1 Future Sustainability Monitoring .................................................................................................... 89 6.2 Key Challenges ................................................................................................................................... 89 6.2.1 Continuing to Engage and Educate Islanders ................................................................. 89 6.2.2 Implications of the Earth Justice Challenge .................................................................... 90 6.2.3 Adapting to a Changing Climate ....................................................................................... 90 6.2.4 Uncertainties Affecting Water Resources ...................................................................... 91 7.0. References .......................................................................................................................................................... 93 King County Science and Technical Support Section ii December 2013 Vashon-Maury Island Water Resources – A Retrospective