Since 2009, the [California Statewide Groundwater Elevation Monitoring (CASGEM) Program](https://water.ca.gov/programs/groundwater-management/groundwater-elevation-monitoring--casgem) has tracked seasonal and long-term groundwater elevation trends in groundwater basins statewide. The program’s mission is to establish a permanent, locally-managed program of regular and systematic monitoring in all of California's alluvial groundwater basins. Senate Bill x7-6, passed by the legislature in 2009, established collaboration between local monitoring parties and DWR to collect statewide groundwater elevations, to be made available to the public. In response to the law, we developed the CASGEM program. Collecting and evaluating these groundwater data on a statewide scale is a fundamental step toward improving management of California's groundwater resources. The CASGEM program relies and builds upon the many previously established local long-term groundwater monitoring and management programs. Our role is to coordinate the CASGEM program, to work cooperatively with local entities, and to maintain the collected elevation data in a readily and widely available public database.

The DWR Periodic Groundwater Levels dataset contains seasonal and long-term groundwater level measurements collected by the Department of Water Resources and cooperating agencies in groundwater basins statewide. It also includes data collected through the Sustainable Groundwater Management Act (SGMA) Portal’s Monitoring Network Module (MNM), and the CASGEM (California Statewide Groundwater Elevation Monitoring) Program. Most measurements are taken manually twice per year to capture the peak high and low values in groundwater elevations. However, the dataset also includes measurements recorded more frequently, monthly, weekly, or daily. This resource also included daily measurements from DWR's automated monitoring network of groundwater sites. For DWRs holdings of groundwater level measurements recorded at more frequent intervals (e.g., hourly), please refer to DWR's “Continuous Groundwater Level Measurements” dataset. For additional information regarding DWR groundwater levels data collection please visit DWR's Groundwater Management website (https://www.water.ca.gov/Programs/Groundwater-Management). The source data can also be accessed directly from two websites. The Water Data Library (http://wdl.water.ca.gov) provides anonymous access to this and other data sets. The CASGEM online system (https://www.casgem.water.ca.gov/OSS) provides authenticated access to only the the periodic groundwater measurements. This dataset is maintained primarily in the DWR Enterprise Water Management database and contains information specific to the location of groundwater level monitoring wells and groundwater level measurements collected at these wells. The Stations resource identifies well location coordinates and other supplementary items about the well type. Measurements resources includes information about the time/date a measurement was collected, the entity collecting the measurement, a measurement indicating the depth to groundwater, and quality information about the measurement. The Well Perforations resources contains well construction information identifying the well's screened intervals (not available for all wells).

The Groundwater Sustainability Plan (GSP) Monitoring dataset contains the monitoring sites and associated groundwater level, subsidence or streamflow measurements collected by Groundwater Sustainability Agencies (GSA) during implementation of their GSP. All data is submitted to the Department of Water Resources (DWR) through the Sustainable Groundwater Management Act (SGMA) Portal’s Monitoring Network Module (MNM). The GSP Regulations established the monitoring network criteria (23 CCR § 354.34) and the data and reporting standard for monitoring sites and measurements (23 CCR § 352.4). The data fields associated with these datasets were created by DWR to ensure that GSAs electronically submit monitoring site and measurement data which meets the GSP Regulation’s data and reporting standards. For additional information regarding GSAs, GSPs, and SGMA related monitoring, please view DWR’s SGMA Portal Resources at https://sgma.water.ca.gov/portal/.

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 domestic-supply (shallow) aquifers in California. These 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. Domestic-supply 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 domestic-supply 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. Version Notes: This Data Release supersedes the data release published in 2020 (version 1). This data release was updated to include study units sampled since the initial publication. Also, report references for all version 1 study units have been updated to reflect the most recent publications for each study unit. In addition, study unit names were updated to be listed as the full name instead of the study unit abbreviations used in version 1. Minor revisions were also made to the metadata text. The version 1 data release may be obtained by contacting the dataset Point of Contact.

The Groundwater Sustainability Plan (GSP) Monitoring dataset contains the monitoring sites and associated groundwater level, subsidence or streamflow measurements collected by Groundwater Sustainability Agencies (GSA) during implementation of their GSP. All data is submitted to the Department of Water Resources (DWR) through the Sustainable Groundwater Management Act (SGMA) Portal’s Monitoring Network Module (MNM). The GSP Regulations established the monitoring network criteria (23 CCR § 354.34) and the data and reporting standard for monitoring sites and measurements (23 CCR § 352.4). The data fields associated with these datasets were created by DWR to ensure that GSAs electronically submit monitoring site and measurement data which meets the GSP Regulation’s data and reporting standards. For additional information regarding GSAs, GSPs, and SGMA related monitoring, please view DWR’s SGMA Portal Resources at https://sgma.water.ca.gov/portal/.