High Resolution Hydrogeologic Characterization of the Central & West Coast Groundwater Basins, Los Angeles County

Historic analysis by geologists from both the oil industry and academia have resulted in the delineation of the complex geologic structures which make up the oil fields of the Coastal Plain of Los Angeles County. The geologic history of the deep consolidated materials are better known than the younger unconsolidated materials that comprise the numerous groundwater bearing units. Since the first regional groundwater assessment of the Coastal Plain (Mendenhall, W.C., 1905 [USGS]), numerous studies have been conducted which have enhanced the overall understanding of the aquifers and groundwater movement. By incorporating thousands of data records including water and oil well logs, the California Department of Water Resources was able to produce one of the most widely used publication for the area entitled Bulletin No. 104, Planned Utilization of the Ground Water Basins of the Coastal Plain of Los Angeles County, Appendix A – Ground Water Geology. While heavily referenced, this document should be utilized more for guidance. Since the late 1990’s and continuing today, the United States Geological Survey and the Water Replenishment District of Southern California have been implementing recent technologies to better characterize the unconsolidated materials which make up the Coastal Plain groundwater basin in order to understand the horizontal and vertical connectedness of the large scale aquifer system. This recent work has included the drilling of deep (up to 3,000 feet) boreholes, application of advanced geophysical logging, construction of nested monitoring wells, and sophisticated geochemical analyses along with implementation of a host of other tools/technologies that have resulted in the extensive collection of high resolution three-dimensional hydrogeologic data for aquifer characterization in greater detail. This presentation will present the tools currently being utilized to improve the understanding of the Central and West Coast Groundwater Basins.