The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board compiled and analyzed historical produced water chemistry data and ancillary oil well information at the Buena Vista, McKittrick, and Cymric Oil Fields in the southwestern San Joaquin Valley (SWSJV), Kern County, California. Historical water chemistry data provide information on the salt mass balance of produced water disposed of on land, and in particular, chloride which is a conservative, nonreactive tracer. Data were compiled from the California Geologic Energy Management Division (CalGEM) Underground Injection Control (UIC) scans of laboratory results for produced water samples, the CalGEM Well Finder database for oil and gas wells, and historical documents (Rogers, 1917; WZI; 1988). The SWSJV_geochem.csv dataset supplements previously compiled chemistry data by the USGS at the Midway-Sunset, Elk Hills, North Belridge, South Belridge, and Lost Hills Oil Fields (cross-referenced in this data release). The Fall1953_volumes_chemistry.csv dataset contains Fall 1953 water production volumes by lease and produced water sample results compiled from Rickett and Reaves (1954a-d) to provide a spatial understanding of historical disposal on land.

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.

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.

This digital dataset contains historical geochemical and other information for 271 samples of produced water from 143 sites in or near the San Ardo Oil Field in Monterey County, central California. Produced water is a term used in the oil industry to describe water that is produced from oil wells as a byproduct along with the oil and gas. The locations from which these historical samples have been collected include 101 wells; three wells (DataSet_ID 118 ,125, and 130) are located outside of the administrative boundary, but closer to San Ardo (within 3 miles) than any other oil field, and therefore they were included in this dataset. Well depth, perforation depths, and (or) depths referred to on geochemistry reports as interval of zone produced, are available for 97 of these wells. Additional sample sites include 11 storage tanks, and 31 unidentifiable sample sources. Designated well use and sample descriptions provide further insight about what the samples represent. The well use designation of most of the wells (79) is OG (oil/gas) and the samples (188) associated with these wells represent produced water. Samples from two wells (Dataset ID 28 and 130) are described as formation water. One well (Dataset ID 30) was drilled as a water-source well (WS) and used to supply groundwater in support of oil production at the time it was sampled, but later converted to an injection well. Another well (Dataset ID 103) was originally drilled as an oil well, but later abandoned and converted to an irrigation well prior to sampling. Eighteen wells have a site type designation of "injectate" based on the sample description combined with the designated well use at the time of sample collection (SF, steam flood; WD, water disposal; or WF, water flood). Most of the historical samples associated with injectate sites may represent water that originated from sources other than the wells at which they were collected. However, samples from two of these wells (Dataset ID 16 and 76) likely represent produced water as they were sampled prior to the wells being used for injection. Limited information is available about historical samples from storage tanks and unidentifiable sample sources, but these may represent pre- or post-treated composite samples of produced water from single or multiple wells. The numerical water chemistry data were compiled by the U.S. Geological Survey (USGS) from scanned laboratory analysis reports available from the California Geologic Energy Management Division (CalGEM). Sample site characteristics, such as well construction details, were attributed using a combination of information provided with the scanned laboratory analysis reports and well history files from CalGEM Well Finder. The compiled data are divided into two separate data files described as follows: 1) a summary data file identifying each site by name, the site location, basic construction information, and American petroleum Institute (API) number (for wells), the number of chemistry samples, period of record, sample description, and the geologic formation associated with the origin of the sampled water, or intended destination (formation into which water was to intended to be injected for samples labeled as injectate) of the sample; and 2) a data file of geochemistry analyses for selected water-quality indicators, major and minor ions, nutrients, and trace elements, parameter code and (or) method, reporting level, reporting level type, and supplemental notes. A data dictionary was created to describe the geochemistry data file and is provided with 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.

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.

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.

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.

This digital dataset contains historical geochemical and other information for 255 samples of groundwater from 41 wells located within 3-miles of the San Ardo Oil Field in Monterey County, central California. Data were compiled from preexisting datasets into two separate data files described as follows: 1) a summary data file identifying each well, it's location, basic well construction, the number of chemistry samples and period of record, and data sources; and 2) a data file of geochemistry analyses for selected water-quality indicators, major and minor ions, nutrients, and trace elements, plus parameter code and (or) method, reporting level, reporting level type, and supplemental notes. A data dictionary was created to describe the geochemistry data file and is provided with this data release.

This digital dataset contains historical geochemical and other information for 89 samples of produced water from 84 sites in the Santa Maria Valley Oil Field in Santa Barbara County, California. Produced water is a term used in the oil industry to describe water that is produced from oil wells as a byproduct along with the oil and gas. Additionally, 3 samples from 3 sites that represent source water used in support of oil production were included in this dataset, for a total of 92 samples and 87 sites, respectively. The locations from which these historical samples have been collected include 27 wells, 2 reservoirs, 10 storage tanks, and 49 unidentifiable sample sources. Well depth, perforation depths, and (or) depths referred to on geochemistry reports as interval of zone produced, are available for 25 of the 27 wells. Designated well use and sample descriptions provide further insight about what the samples represent. The well use designation for 23 of the wells is OG (oil/gas). The 27 samples associated with these wells likely represent produced water based on well designation and history. One of the 27 samples is a composite from two wells represented by Dataset ID 46. Three wells have a site type designation of "injectate" based on the current designated well use (WD, water disposal; or WF, water flood). The samples associated with these sites are of unknown origin, but likely represent produced water from OG wells in the Santa Maria Valley Oil Field. The two reservoir samples (Dataset_ID 53 and 54) are freshwater sources that were used in support of oil production, including one reservoir (Dataset_ID 54) described as supplied by groundwater wells. Limited information is available about historical samples from storage tanks and unidentifiable sample sources. These samples may represent pre- or post-treated composite samples of produced water from single or multiple wells. The numerical water chemistry data were compiled by the U.S. Geological Survey (USGS) from the following sources: scanned laboratory analysis reports available from the California Geologic Energy Management Division (CalGEM) Underground Injection Control (UIC) program, analytical reports located within well history files in CalGEM's online Well Finder (WF) database, analytical reports available as PDFs (Portable Document Format) documents located on the State Water Resources Control Board GeoTracker (SWRCB-GT) website, and data compiled by the USGS for the National Produced Water Geochemical Database (USGS PWDB). Sample site characteristics, such as well construction details, were attributed using a combination of information provided with the scanned laboratory analysis reports and well history files from CalGEM Well Finder. The compiled data are divided into two separate data files described as follows: 1) a summary data file identifying each site by name, the site location, basic construction information, and American Petroleum Institute (API) number (for wells), the number of chemistry samples, period of record, sample description, and the geologic formation associated with the origin of the sampled water, or intended destination of the sample (formation into which water was to intended to be injected for samples labeled as injectate), specific sample dates for each site, and an inventory of which constituent groups were sampled on each date; and 2) a data file of geochemistry analyses for selected water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds (VOCs), hydrocarbons, and organic acids. Ion (charge) balance calculations and percent error of these calculations were included for samples having a complete suite of major ion analyses. Analytical method, reporting level, reporting level type, and supplemental notes were included where available or pertinent. A data dictionary was created to describe the geochemistry data file and is provided with this data release.