Abstract: Geographic Information System Data Base for Geohydrologic Assessments, South San Francisco Bay and Peninsula Area, California

John L. Fio, David A. Leighton

Information on the spatial distribution of geologic, hydrologic, chemical, water-use, and land-use data is necessary to assess ground-water resources. These data are collected by many local, State, and Federal agencies. Because this information is distributed among many sources, it is difficult to compile for assessment purposes. For this reason, a geographic information system data base was developed by the U.S. Geological Survey for the geohydrologic assessment of the ground-water resources in the south San Francisco Bay and Peninsula area, California.

A geographic information system data base is useful because it spatially collates interrelated data from different sources. For example, volumes of pumpage reported by individual water districts indicate that more than 186 × 10⁶ m³ of ground water were withdrawn in 1990. Lithologic and well-construction data indicate that most of this pumpage is from wells screened in two zones; shallow (depths <45 m below land surface) and deep (depths >60 m below land surface). The shallow and deep zones are separated by an interval of predominantly fine-grained sediment. Information from digital maps of land-surface topography, depth to bedrock, and lithology were used where the distribution of sediment thickness and storage capacity were calculated. These calculati ns indicate that storage is greatest in parts of Alameda and Santa Clara Counties, but previous studies indicate that pumpage is limited in these areas by potential saltwater contamination and subsidence of the land surface.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California