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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). 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. These grid cells can be found in the GAMA_PBP_SAA_GridCells shapefile included in this Data Release.

The Depletions of Interconnected Surface Water (ISW) dataset has been established to provide technical resources in support of Groundwater Sustainability Agencies (GSAs) as they develop and update their Groundwater Sustainability Plans (GSPs) under the Sustainable Groundwater Management Act (SGMA). The Department of Water Resources will post information and resources here, including three technical papers which provide informational resources to help identify, understand, and communicate the nature, occurrence, and estimation of depletions of ISW.

The Depletions of Interconnected Surface Water (ISW) dataset has been established to provide technical resources in support of Groundwater Sustainability Agencies (GSAs) as they develop and update their Groundwater Sustainability Plans (GSPs) under the Sustainable Groundwater Management Act (SGMA). The Department of Water Resources will post information and resources here, including three technical papers which provide informational resources to help identify, understand, and communicate the nature, occurrence, and estimation of depletions of ISW.

The California Groundwater Ambient Monitoring and Assessment Program (GAMA) is a statewide, comprehensive assessment of groundwater quality designed to help better understand and identify risks to groundwater resources. GAMA is being implemented by the California State Water Resources Control Board. The USGS is the technical lead for the Priority Basin Project (PBP), one of the components of the GAMA Program. The initial focus of the GAMA Priority Basin Project in 2004 to 2012 was on assessment of water-quality in groundwater resources used for public drinking water supply (Belitz and others, 2003; 2015). Groundwater basins and sub-basins (472 in total) were prioritized based upon a number of factors (Belitz and others 2003). Two hundred and twenty-seven of these basins and additional areas outside of basins were subsequently grouped into 35 study units comprising 87 Study Areas. The basin and sub-basin boundaries, local geology, local knowledge, and watershed data were used to define the Study Areas. The Study Areas each were divided into equal-area grid cells collectively referred as a "study area grid". The number and size of cells generated for each Study Area was based upon the size of the area being sampled, and the number of public-supply wells available to sample. Three Study Areas contained an insufficient number of public-supply wells for division into a study area grid and were instead directly sampled. The number of cells in a study area grid ranged from 7 to 122 (median 20), and the size of the cells ranged from 4 to 471 km2 (median 25 km2). Additional information about the design of individual study area grids can be found in the reports listed below. The 87 Study Areas are collected and assembled here into one GIS dataset.