The California State Water Resources Control Board (State Water Board) initiated the Oil and Gas Regional Monitoring Program (RMP) to assess effects of oil and gas development on groundwater designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in cooperation with the State Water Board, and in partnership with other State and local agencies. The USGS collected and analyzed groundwater, surface water, and associated quality control (QC) samples in the Elk Hills study area during June 2017–April 2018. The Elk Hills study area includes the Elk Hills and North Coles Levee Oil Fields and a five-kilometer buffer zone surrounding the administrative boundaries of the two oil fields in Kern County, California. Water samples were collected from twenty-six monitoring wells, four irrigation wells, two public supply wells, and one managed recharge pond. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds (VOCs), naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon (DOC) characteristics, dissolved standard and hydrocarbon gases (methane through hexane), and dissolved noble and atmospheric gases. Over 200 constituents and water-quality indicators were measured. Quality-control samples collected as part of this study included replicates, field blanks, equipment blanks, source-solution blanks, and matrix spikes.

In cooperation with the California State Water Resources Control Board’s oil and gas Regional Monitoring Program, the U.S. Geological Survey collected and analyzed groundwater and associated quality control (QC) samples during June 2017 – August 2017. Groundwater samples were collected from one public supply well, four monitoring wells, and nine irrigation wells located within a three- mile buffer zone overlying and surrounding the Oxnard oil field administrative boundary in Ventura County, California. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon (DOC), low molecular weight organic acids, dissolved standard and hydrocarbon gases, and dissolved noble and atmospheric gases. Approximately 280 constituents and water-quality indicators were measured. Quality-control samples including replicates; source-solution, equipment, and field blanks; laboratory spikes; and split samples for inter-laboratory comparisons were collected and summarized in this data release. A data dictionary was created to describe the data tables and is provided with this data release. Please refer to this data dictionary file called COGG_Data_Dictionary_OxnardGW for definitions of fields within these data files.

In cooperation with the California State Water Resources Control Board’s oil and gas Regional Monitoring Program, the U.S. Geological Survey collected and analyzed groundwater and associated quality control (QC) samples during June 2017 – August 2017. Groundwater samples were collected from one public supply well, four monitoring wells, and nine irrigation wells located within a three- mile buffer zone overlying and surrounding the Oxnard oil field administrative boundary in Ventura County, California. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon (DOC), low molecular weight organic acids, dissolved standard and hydrocarbon gases, and dissolved noble and atmospheric gases. Approximately 280 constituents and water-quality indicators were measured. Quality-control samples including replicates; source-solution, equipment, and field blanks; laboratory spikes; and split samples for inter-laboratory comparisons were collected and summarized in this data release. A data dictionary was created to describe the data tables and is provided with this data release. Please refer to this data dictionary file called COGG_Data_Dictionary_OxnardGW for definitions of fields within these data files.

The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board (State Water Board) compiled and analyzed data for mapping groundwater salinity, characterizing aquifer systems, and documenting the effects of oil field water injection in the Elk Hills Elk Hills, Buena Vista, and Coles Levee Oil Fields, San Joaquin Valley, California. Data provided in this data release include borehole geophysical data, geochemical analyses of water samples, hydrologic data, geological formation depths, and information on observed well log resistivity anomalies—interpreted to be from injection for disposal of produced water from oil wells or from natural causes. The data reported here were used in an accompanying interpretive manuscript describing aquifer salinity and the effects of produced water disposal in the study area. The geochemical data were compiled for water samples from 14 water source wells to supply groundwater for oil and gas operations and one groundwater monitoring well. The constituents compiled from geochemical data sources included water-quality indicators and detected concentrations of major ions, minor ions, and trace elements. The data represent several decades and most originated from oil and gas producers which are archived in scanned pages in raster format on the California Geologic Energy Management Division (CalGEM) website. The data were compiled into computer readable numerical data sets for the related study. Other data, such as interpolated surfaces of geologic layers, were created for the study based on information in drilling records and are provided here. All the data and the associated manuscript are part of the State Water Board Oil and Gas Regional Monitoring Program and the associated USGS California Oil, Gas, and Groundwater (COGG) Program.

The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board (State Water Board) compiled and analyzed data for mapping groundwater salinity, characterizing aquifer systems, and documenting the effects of oil field water injection in the Elk Hills Elk Hills, Buena Vista, and Coles Levee Oil Fields, San Joaquin Valley, California. Data provided in this data release include borehole geophysical data, geochemical analyses of water samples, hydrologic data, geological formation depths, and information on observed well log resistivity anomalies—interpreted to be from injection for disposal of produced water from oil wells or from natural causes. The data reported here were used in an accompanying interpretive manuscript describing aquifer salinity and the effects of produced water disposal in the study area. The geochemical data were compiled for water samples from 14 water source wells to supply groundwater for oil and gas operations and one groundwater monitoring well. The constituents compiled from geochemical data sources included water-quality indicators and detected concentrations of major ions, minor ions, and trace elements. The data represent several decades and most originated from oil and gas producers which are archived in scanned pages in raster format on the California Geologic Energy Management Division (CalGEM) website. The data were compiled into computer readable numerical data sets for the related study. Other data, such as interpolated surfaces of geologic layers, were created for the study based on information in drilling records and are provided here. All the data and the associated manuscript are part of the State Water Board Oil and Gas Regional Monitoring Program and the associated USGS California Oil, Gas, and Groundwater (COGG) Program.

The California State Water Resources Control Board (State Water Board) initiated the Regional Groundwater Monitoring Program (RMP) to assess effects of oil and gas development on groundwater designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in cooperation with the State Water Board, and in partnership with other State and local agencies. The USGS collected and analyzed groundwater and associated quality control (QC) samples during September 2014 through October 2018. Groundwater samples collected in 2017-18 were from eight public supply wells, eight monitoring wells and one irrigation well located within the Montebello Oil Field study area, a three-mile buffer zone overlying and surrounding the Montebello Oil Field administrative boundary in Los Angeles County, California. Groundwater from four additional monitoring wells was collected in the Montebello Oil Field study area as part of the exploratory phase of the RMP; those sites were sampled in 2014. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions; nutrients; trace elements, volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs); naturally-occurring radioactive material; geochemical and age-dating tracers; dissolved organic carbon (DOC) characteristics; dissolved standard and hydrocarbon gases (methane through hexane); and dissolved noble gases and atmospheric gases. In total, 286 constituents, water-quality indicators, or properties were measured. QC samples collected as part of the Montebello Oil Field study area include one replicate, two equipment blanks and two source-solution blanks. Additional QC samples collected from study areas for which sampling was done during December 2017 through October 2018 include three replicates, three spikes, two field blanks, and two source-solution blanks.

The California State Water Resources Control Board (State Water Board) initiated the Regional Groundwater Monitoring Program (RMP) to assess effects of oil and gas development on groundwater designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in cooperation with the State Water Board, and in partnership with other State and local agencies. The USGS collected and analyzed groundwater and associated quality control (QC) samples during September 2014 through October 2018. Groundwater samples collected in 2017-18 were from eight public supply wells, eight monitoring wells and one irrigation well located within the Montebello Oil Field study area, a three-mile buffer zone overlying and surrounding the Montebello Oil Field administrative boundary in Los Angeles County, California. Groundwater from four additional monitoring wells was collected in the Montebello Oil Field study area as part of the exploratory phase of the RMP; those sites were sampled in 2014. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions; nutrients; trace elements, volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs); naturally-occurring radioactive material; geochemical and age-dating tracers; dissolved organic carbon (DOC) characteristics; dissolved standard and hydrocarbon gases (methane through hexane); and dissolved noble gases and atmospheric gases. In total, 286 constituents, water-quality indicators, or properties were measured. QC samples collected as part of the Montebello Oil Field study area include one replicate, two equipment blanks and two source-solution blanks. Additional QC samples collected from study areas for which sampling was done during December 2017 through October 2018 include three replicates, three spikes, two field blanks, and two source-solution blanks.

The California State Water Resources Control Board (State Water Board) initiated the Oil and Gas Regional Monitoring Program (RMP) to assess effects of oil and gas development on groundwater (GW) designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in cooperation with the State Water Board, and in partnership with other State and local agencies. The USGS collected and analyzed groundwater and associated quality control (QC) samples in the Midway-Sunset and Buena Vista Oil Fields (MSBV) study area during March 2018 - April 2019. Groundwater samples were collected from seven irrigation, one domestic, and ten monitoring wells located within and near the administrative boundaries of the Midway-Sunset and Buena Vista Oil Fields in Kern County, California. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds (VOCs), naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon (DOC), dissolved standard and hydrocarbon gases (methane through hexane), and dissolved noble and atmospheric gases. Two hundred and twenty constituents and water-quality indicators were measured; one hundred and twenty are reported here. QC samples collected as part of the Midway-Sunset and Buena Vista Oil Fields study included replicates, source-solution blanks, field blanks, and laboratory spikes.

The California State Water Resources Control Board (State Water Board) initiated the Oil and Gas Regional Monitoring Program (RMP) to assess effects of oil and gas development on groundwater (GW) designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in cooperation with the State Water Board, and in partnership with other State and local agencies. The USGS collected and analyzed groundwater and associated quality control (QC) samples in the Midway-Sunset and Buena Vista Oil Fields (MSBV) study area during March 2018 - April 2019. Groundwater samples were collected from seven irrigation, one domestic, and ten monitoring wells located within and near the administrative boundaries of the Midway-Sunset and Buena Vista Oil Fields in Kern County, California. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds (VOCs), naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon (DOC), dissolved standard and hydrocarbon gases (methane through hexane), and dissolved noble and atmospheric gases. Two hundred and twenty constituents and water-quality indicators were measured; one hundred and twenty are reported here. QC samples collected as part of the Midway-Sunset and Buena Vista Oil Fields study included replicates, source-solution blanks, field blanks, and laboratory spikes.

The California State Water Resources Control Board (State Water Board) initiated the Oil and Gas Regional Monitoring Program (RMP) to assess effects of oil and gas development on groundwater designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in cooperation with the State Water Board, and in partnership with other State and local agencies. The USGS collected and analyzed groundwater (GW) and surface water (SW) for the San Ardo Oil Field study area, the area within the San Ardo Oil Field administrative boundary and the surrounding five-kilometer buffer zone, in Monterey County, California. Eighteen groundwater, two stream, and two spring samples were collected from March 2019 through May 2021. Groundwater samples were collected from one public-supply well, five monitoring wells, two irrigation wells, one livestock well, five oil-field water supply wells, and four domestic wells. Samples were collected using established water data-collection protocols and procedures and analyzed for (1) water-quality indicators, (2) major and minor ions, (3) nutrients, (4) trace elements, (5) volatile organic compounds (VOCs), (6) naturally-occurring radioactive material (radium isotopes), (7) geochemical and age-dating tracers, (8) dissolved organic carbon (DOC), (9) dissolved standard and hydrocarbon gases (methane through hexane), and (10) dissolved noble gases and atmospheric gases. In total, 185 constituents, water-quality indicators, or properties are included in this data release. Quality-control (QC) samples were used to assess the quality of laboratory results.