The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board collected produced water and gas samples in the Poso Creek, Midway-Sunset, and Buena Vista Oil Fields in Kern County in 2020 and 2021. Sampled sites included oil wells; injectate from tanks, pipelines, and injection wells where produced water from many wells, after removal of oil, is stored or transported before underground injection; and integrated produced water from multiple oil wells collected from pipelines before oil removal. This digital dataset contains the site information, analyzing laboratories and methods, and water and gas chemistry and quality-control results for these samples. Chemistry results include concentrations of dissolved noble and hydrocarbon gases and their isotopic composition; concentrations of inorganic constituents including salinity, major and minor ions, trace elements, and nutrients; dissolved organic carbon and optical properties of dissolved organic carbon; stable isotopes of water, strontium dissolved in water, and carbon in dissolved inorganic carbon; and radium isotopes. Samples were analyzed in the field and by eight laboratories operated or contracted by the USGS.

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.

As part of the California State Water Resources Control Board’s Oil and Gas Regional Monitoring Program , the U.S. Geological Survey collected groundwater and quality-control (QC) samples during September 2016–February 2017 from 14 water-production wells located within a one-mile buffer zone of and in the Fruitvale Oil field, Kern County, California. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds, naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon, dissolved standard and hydrocarbon gases, and dissolved noble and atmospheric gases. In total, 235 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-lab comparisons were collected at approximately 10 percent of the wells. The water well and associated quality-control sample data are presented in this data release.

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 and associated quality control (QC) samples for an RMP study of the Santa Fe Springs (SFSP) Oil Field during April 2021 through April 2024. Groundwater samples collected in 2021-2024 were from twenty-seven monitoring wells, two irrigation wells, three public supply wells and a fire hydrant located within the Santa Fe Springs Oil Field study area. 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, and dissolved noble gases and atmospheric gases. In total, 261 constituents, water-quality indicators, or properties were measured. QC samples analyzed for the Santa Fe Springs Oil Field study area include five field blanks, one equipment blank, six VOC source solution blanks, four replicates, and four VOC spikes.

An investigation was done by the U.S. Geological Survey, in cooperation with the California State Water Resources Control Board's Program of Regional Groundwater Monitoring of Water Quality in Areas of Oil and Gas Production, to assess the effects of oil and gas production activities on nearby groundwater resources. During November 2016–September 2017, 30 samples were collected at groundwater wells and 1 sample was collected at a surface-water site. This dataset contains site information and water chemistry results for samples collected near the Lost Hills and North and South Belridge oil fields, Kern County, California. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds, naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon, low molecular weight organic acids, dissolved standard and hydrocarbon gases, and dissolved noble and atmospheric gases. Quality-control samples including replicates; source-solution, equipment, and field blanks; laboratory spikes; and split samples for interlab comparisons were collected and summarized in this data release.

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 for the Placerita Oil Field study area, the area within the Placerita Oil Field administrative boundary and the surrounding three-mile buffer zone in Los Angeles County, California. Sixteen groundwater samples were collected from June 2018 through November 2018 from three public-supply wells, two monitoring wells, three irrigation wells, two oil-field water supply wells, and one domestic well. Samples were collected using established groundwater data-collection protocols and procedures. Samples were 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) characteristics, (9) dissolved standard and hydrocarbon gases (methane through hexane), (10) dissolved noble gases and atmospheric gases, and (11) low molecular weight organic acids. In total, 229 constituents, water-quality indicators, or properties were measured. Quality-control (QC) samples were used to assess the quality of laboratory results. QC samples were collected for all oil fields assessed by the Regional Monitoring Program during the general time period (within three months) of groundwater samples that were collected for the Placerita Oil Field study area and include four replicates, three field blanks, one equipment blank, four source-solution blanks, three laboratory-matrix spikes, and two samples collected to verify results of environmental samples that arrived at the laboratory above the recommended temperature for preventing degradation of VOCs and nutrients.

An investigation was done by the U.S. Geological Survey, in cooperation with the California State Water Resources Control Board's Program of Regional Groundwater Monitoring of Water Quality in Areas of Oil and Gas Production, to assess the effects of oil and gas production activities on nearby groundwater resources. During November 2016–September 2017, 30 samples were collected at groundwater wells and 1 sample was collected at a surface-water site. This dataset contains site information and water chemistry results for samples collected near the Lost Hills and North and South Belridge oil fields, Kern County, California. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds, naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon, low molecular weight organic acids, dissolved standard and hydrocarbon gases, and dissolved noble and atmospheric gases. Quality-control samples including replicates; source-solution, equipment, and field blanks; laboratory spikes; and split samples for interlab comparisons were collected and summarized in this data release.

The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board collected produced water samples for analysis of volatile organic compounds (VOCs) in the eight California oil fields of Fruitvale, Lost Hills, North Belridge, Orcutt, Placerita, South Belridge, Midway-Sunset, and Buena Vista from 2016 to 2020. Sampled sites included oil wells; injectate from tanks, pipelines, and injection wells where produced water from many wells, after removal of oil, is stored or transported prior to underground injection; integrated produced water from many oil wells collected from pipelines before oil removal; and surface disposal ponds where produced water, after removal of oil, is disposed of. This digital dataset contains the site information, analyzing laboratories and methods, and water and gas chemistry and quality-control results for these samples. Chemistry results include concentrations of VOCs, low molecular weight organic acids, and supporting data on chloride, alkalinity, and sample temperatures for comparison to VOC data. Samples were analyzed in the field and by three laboratories operated or contracted by the USGS.

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 Oil and Gas Regional Groundwater Monitoring Program the U.S. Geological Survey collected and analyzed groundwater and associated quality control (QC) samples to assess regional groundwater quality overlying and adjacent to the Orcutt Oil Field during September 2017 through March 2018. Groundwater samples were collected from 15 groundwater monitoring, irrigation and production wells located within a three-mile buffer zone overlying and surrounding the Orcutt Oil Field administrative boundary in Santa Barbara 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, naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon, low molecular weight organic acids, dissolved standard and hydrocarbon gases, and dissolved noble and atmospheric gases. In total, 294 constituents and water-quality indicators were measured. QC samples including replicates; source-solution, equipment, and field blanks; laboratory spikes; and split samples for interlab comparisons were collected at approximately 10 percent of the wells and results are 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_OrcuttGW for definitions of fields within these data files.