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.

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.

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.

DWR continuous groundwater level measurements contains continuous time-series data from automated recorders at sites operated by the Department of Water Resources. Readings are taken at 15-minute to one-hour intervals. Some of the readings are relayed to the California Data Exchange Center. However, most of the monitoring sites are visited once every month or two, when readings are off-loaded from data recorders, then finalized and published. Wells monitored for this dataset are located within Butte, Colusa, Glenn, Mendocino, Modoc, Sacramento, San Joaquin, Shasta, Siskiyou, Solano, Sutter, Tehama, Yolo, and Yuba Counties. Water-level measurements are the principal source of information about changes in groundwater storage and movement in a basin, and how these are affected by various forms of recharge (e.g., precipitation, seepage from streams, irrigation return) and discharge (e.g., seepage to streams, groundwater pumping). Water-level monitoring involves "continuous" or periodic measurements. Continuous monitoring makes use of automatic water-level sensing and recording instruments that are programmed to make scheduled measurements in wells. This provides a high-resolution record of water-level fluctuations. Resulting hydrographs can accurately identify the effects of various stresses on the aquifer system and provide measurements of maximum and minimum water levels in aquifers. Continuous monitoring may be the best technique to use for monitoring fluctuations in groundwater levels during droughts and other critical periods when hydraulic stresses may change at relatively rapid rates, or when real-time data are needed for making water management decisions [see usgs reference](https://ca.water.usgs.gov/sustainable-groundwater-management/groundwater-levels-california.html).

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 Department of Water Resources (DWR) Enterprise Monitoring Well Network dataset contains information regarding wells monitored by DWR. The wells included in this dataset have been completed, a well completion report (WCR) has been submitted through the Online System for Well Completion Reports (OSWCR), and have been registered either through the California Statewide Groundwater Elevation Monitoring (CASGEM) Online System or the Sustainable Groundwater Management Act (SGMA) Portal’s Monitoring Network Module (MNM). This dataset will be updated on a monthly basis.

The Department of Water Resources (DWR) Enterprise Monitoring Well Network dataset contains information regarding wells monitored by DWR. The wells included in this dataset have been completed, a well completion report (WCR) has been submitted through the Online System for Well Completion Reports (OSWCR), and have been registered either through the California Statewide Groundwater Elevation Monitoring (CASGEM) Online System or the Sustainable Groundwater Management Act (SGMA) Portal’s Monitoring Network Module (MNM). This dataset will be updated on a monthly basis.

The Drinking Water Surveillance Program (DWSP) monitors water quality at selected municipal drinking water systems for scientific and research purposes. DWSP is a voluntary partnership that compliments the regulatory monitoring that must be done by the drinking water systems. DWSP monitors for inorganic, organic and radiological parameters. Water quality data are available by individual years.

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 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.