Faculty Advisor

Jeff Tepper

Area of Study

Science and Mathematics

Publication Date

Summer 2016


This project seeks to characterize the chemical and isotopic compositions of groundwater and surface water in portions of Pierce and King Counties, with the goal of using these results to determine the water sources of local lakes. Specifically of interest are lakes studied by Puget Sound students over the past ~10 years where water analyses appear to define a mixing line, likely between surface runoff and the shallow groundwater (Figures 1, 2, and 3). Existing data pertain only to surface water from the lakes while data pertaining to groundwater is patchy or nonexistent and includes only a few of the parameters needed to define the groundwater endmember. The hydrogeology of the Puget Lowlands is largely a reflection of its glacial past. Aquifers in this area are predominantly made up of glacial deposits and can be generalized into three units: (1) the shallow aquifer system (SAS), (2) the sea level aquifer (SLA) which may be hydrologically connected to the SAS, and (3) the deep aquifer system (DAS) which is almost entirely confined. This project aims to characterize the groundwater from all three aquifers using elemental analysis and stable isotopes to answer the following questions: (1) What is the cause of high Mg2+ and SO4 concentrations in groundwater? (2) Can observed chemical variations in the lakes be explained by mixing? If so, are the variations due to different proportions of groundwater inflow or to inputs of chemically different groundwater, or to both? (3) Can regional groundwater patterns be identified using existing and generated data?


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