THREE-DIMENSIONAL REPRESENTATION OF GLACIAL TILL HETEROGENEITY AND POTENTIAL PERCHED CONDITIONS IN THE HYDROGEOLOGIC FRAMEWORK OF SEATTLE, WASHINGTON

A well-developed understanding of the local geologic structure and hydrologic conditions is necessary for building an effective groundwater model. We aim to understand how groundwater in the Seattle area responds to sea-level rise using a groundwater flow model. Previous groundwater work in Seattle has suffered from large errors related to the oversimplification of geologic units within the study area. The geology of the Seattle area is complex and composed of a series of glacial and interglacial deposits overlying volcanic units. The spatial extent of the glacial sediment is highly variable with localized clay deposits creating perched aquifer units. We have used 3-D modeling software and borehole data to improve the hydrogeologic framework for the Seattle area by creating a lithologic model accounting for anisotropy and heterogeneity in hydraulic conductivity. The hydrogeologic framework developed in this study will be used with a numerical groundwater flow model to forecast groundwater responses to future sea levels and climatic conditions. The results will be used to identify areas at risk of groundwater hazards exacerbated by sea level rise and study changing groundwater-surface water interactions with climate change.