CONCEPTUAL ASSESSMENT OF THE CALIFORNIA COAST BASINS PRINCIPAL AQUIFER IN CONTEXT OF A NATIONAL-EXTENT HYDROGEOLOGIC FRAMEWORK MODEL

The Water Mission Area of the U.S. Geological Survey (USGS) has undertaken the development of a National-Extent Hydrogeologic Framework (NEHF) of the United States. This project is in support of the USGS mission to deliver nationally consistent assessments of water supplies for human and ecological needs and identify factors that influence water availability. The project objectives are to develop a consistent understanding and representation of the subsurface hydrogeology of the United States and construct a quantitative, three-dimensional framework of the nation. The NEHF is designed to be a living framework that is useful at multiple scales and for multiple purposes and can be both a source of information for hydrogeologic investigations and a repository for updated information. The NEHF will focus on previously mapped principal aquifers and secondary hydrogeologic regions. One of these principal aquifers is the California Coastal Basins aquifer (CACB), which occupies multiple basins in proximity to the California coast. California’s largest population centers are located in the CACB, and available potable groundwater is used for public supply, irrigation, and domestic supply. The CACBs are also a source of oil and gas production.

This paper presents a conceptual approach for representing the CACB in the context of the NEHF. The CACB consists primarily of alluvial deposits, marine sediment, and volcanic rocks that occupy structural depressions caused by deformation of the Earth’s crust. The distribution of primary aquifer materials throughout the CACB are evaluated with respect to spatial and stratigraphic relationships within individual basins, texture and age of materials, and previously defined hydrogeologic provinces of California. The thickness and extent of the primary aquifer materials are then quantified using data from existing geologic, hydrogeologic, and groundwater-flow models, where available, or are generalized based on the hydrogeologic understanding of the CACB. This conceptual approach allows for integration of this highly complex principal aquifer into the NEHF and provides a quantitative framework for use in future hydrogeologic investigations in California.