GROUNDWATER Resources of the Seattle Metropolitan Area

For the purposes of water supply, the Seattle Metropolitan Area (SMA) ranges from Olympia, WA in the South north to Everett, WA, the Cascade Mountains on the east and Puget Sound on the west.  The area covers approximately, 2000 square miles and 4 counties.  Most of the municipal supply comes from Cascade Mountain runoff but is not sufficient to quench the SMA’s thirst.  Due to climate variations, anticipated changes in the timing of Cascade mountain runoff over the next few decades will likely exacerbate this problem.  Consequently, groundwater plays an increasingly more important role in supplying water to the region.  Groundwater resources within the SMA occur within one of the more complex hydrogeologic environments in the United States.  In addition, water rights (both ground and surface water) are all but totally appropriated and management requires a major effort in understanding the complex flow, withdrawal and apportionment of the groundwater resource.

Although, numerous continental glaciations advanced through the SMA leaving a layer cake distribution of aquifers and aquitards, Cascade mountain glaciers and more recent fluvial depositional processes also contributed to form a highly variable distribution of groundwater resources which have proven difficult to develop, manage and protect from over-appropriation and quality threats.  Water utilities within the SMA are currently looking to enhance available groundwater resources via one or more proactive resource management approaches like aquifer storage and recovery, transfer of water rights from industrial or agricultural to municipal, enhancing well field performance, and even desalination.  As the SMA population is expected to grow significantly in the coming decades, the effective development and management of groundwater resources will determine how the region is able to meet its demand for clean water.