Lithostratigraphic, borehole-geophysical, hydrogeologic, and hydrochemical data from the East Bay Plain, Alameda County, California

Abstract

The U.S. Geological Survey, in cooperation with the East Bay Municipal Utility District, carried out an investigation of aquifer-system deformation associated with groundwater-level changes at the Bayside Groundwater Project near the modern San Francisco Bay shore in San Lorenzo, California. As a part of the Bayside Groundwater Project, East Bay Municipal Utility District proposed an aquifer storage and recovery program for 1 million gallons of water per day. The potential for aquifer-system compaction and expansion, and related subsidence, uplift, or both, resulting from aquifer storage and recovery activities were investigated and monitored in the Bayside Groundwater Project. In addition, baseline analysis of groundwater and substrata properties were performed to assess the potential effect of such activities. Chemical and physical data, obtained from the subsurface at four sites on the east side of San Francisco Bay in the San Lorenzo and San Leandro areas of the East Bay Plain, Alameda County, California, were collected during the study. The results of the study were provided to the East Bay Municipal Utility District and other agencies to evaluate the chemical and mechanical responses of aquifers underlying the East Bay Plain to the future injection and recovery of imported water from the Sierra Nevada of California. Among 4 sites, 14 piezometers and 2 extensometers were installed in 6 boreholes, which ranged in depth from 460 to 1,040 feet. The lithology of drill cuttings, collected at 5- or 10-foot intervals, was described for grain size and any other noticeable features, such as wood or shell fragments. Borehole geophysical logging was performed at each site in the deepest borehole, immediately following drilling. Drill-core samples, totaling 284 feet, were collected at the Bayside site. The drill-core sediment was subsampled to determine pore-water chemistry, vertical hydraulic conductivity, and physical and mechanical properties at different depths. Depositional environment and age were determined by luminescence geochronology and fossil identification. The elemental composition of the drill-core sediments was determined by inductively coupled plasma mass spectroscopy and instrumental neutron activation by abbreviated count analysis. Mineral composition was determined by X-ray diffraction and scanning electron microscopy analysis. Groundwater samples were collected from all 14 piezometers as part of either the USGS Groundwater Ambient Monitoring and Assessment or the USGS National Water Quality Assessment program for water-quality analyses. Sample analytes included nutrients, major and minor ions, trace elements, isotopic ratios of hydrogen and oxygen in water, carbon-14, and tritium. Water-level and aquifer-system-compaction measurements, which indicated diurnal and seasonal fluctuations, were made at the Bayside Groundwater Project site. Slug tests were performed at the Bayside piezometers and nine pre-existing wells to estimate hydraulic conductivity.