GIS Data
Data
California Groundwater Ambient Monitoring and Assessment (GAMA) Program Shallow Aquifer Assessment Study Unit Grid Cells for Assessment of Groundwater Resources
Watson, E. and Johnson, T.D., 2021, U.S. Geological Survey data release
Related Study Unit(s): California Desert Region Resources Used for Public Supply, Eastern Sacramento Valley and Foothills Groundwater Resources Used for Domestic Supply, Madera-Chowchilla and Kings Sub-basins Groundwater Resources Used for Domestic Supply, Madera-Chowchilla Basin Groundwater Resources Used for Public Supply, Monterey Bay and Salinas Valley Basins Groundwater Resources Used for Public Supply, Monterey Bay, Salinas Valley, and Adjacent Highlands Groundwater Resources Used for Domestic Supply, North San Francisco Bay Basins Groundwater Resources Used for Public Supply, North San Francisco Bay Groundwater Resources Used for Domestic Supply, Northern Sierra Nevada Foothills Groundwater Resources Used for Domestic Supply, Sacramento Metro Groundwater Resources Used for Domestic Supply, Sacramento Valley Groundwater Resources Used for Domestic Supply, Tule-Tulare-Kaweah and Associated Highlands Groundwater Resources Used for Domestic Supply, Western Mojave Desert Groundwater Resources Used for Domestic Supply
ABSTRACT
The California Groundwater Ambient Monitoring and Assessment Program (GAMA) is a statewide assessment of groundwater quality designed to help better understand and identify risks to groundwater resources. GAMA is implemented by the California State Water Resources Control Board. The U.S. Geological Survey (USGS) is the technical lead for the Priority Basin Project (PBP), one of the components of the GAMA Program. Starting in 2012, GAMA began an assessment of water resources in shallow aquifers in California. These shallow aquifers provide water for domestic and small community-supply wells, which are often drilled to shallower depths in the groundwater system than public-supply wells. Shallow aquifers are of interest because shallow groundwater may respond more quickly and be more susceptible to contamination from human activities at the land surface, than the deeper aquifers (USGS, 2018).
To prioritize shallow aquifers, California was divided into 938 groundwater units consisting of California Department of Water Resources (DWR) groundwater basins and highland areas outside of the basins defined by California Groundwater Units (Johnson and Belitz, 2014) or Hydrologic Units (HUC8) from the Watershed Boundary Dataset (USGS and USDA, 2013). The groundwater units were prioritized for sampling based on the number and density of households relying on domestic wells, water-use, and well-location information compiled from well-completion reports submitted to the DWR. The groundwater units were grouped into study units designed to facilitate comparison of groundwater quality between the shallow aquifer systems and the deep aquifer systems assessed by GAMA from 2004 to 2012 (Bennett, 2018). Some study units were further subdivided into study areas. The study units (and study areas when applicable) were divided into equal area polygons (cells) so that all cells within a given study unit (or study area) have an equal area. The GAMA_PBP_SAA_Boundaries shapefile contains the study unit boundaries and the GAMA_PBP_SAA_GridCells shapefile contains the study area grid cells.