This digital dataset contains historical geochemical and other information for 580 samples of groundwater from 12 wells located within the Placerita and Newhall Oil Fields in Los Angeles County, southern California. The sampled wells include 5 monitoring wells (Dataset IDs 1-5) associated with a groundwater remediation site, 6 water-supply wells (Dataset IDs 6-11) used to supply groundwater in support of oil production, and 1 well (Dataset ID 12) constructed as an observation well to monitor water-disposal operations. The groundwater remediation site wells represent a subset of a much larger number of monitoring wells that were selected for inclusion in this dataset because they were perforated within the regional groundwater aquifer, and the geochemistry data for these wells include the greatest variety of constituents available in the data source. The numerical water chemistry data, well locations, and well construction information for Dataset IDs 1-5 were compiled from PDFs (Portable Document Format) documents located on the California Department of Toxic Substances Control EnviroStor (DTSC-EnviroStor) website. Water chemistry data for the remaining wells were compiled from a combination of scanned laboratory analysis reports available from the California Geologic Energy Management Division (CalGEM) (Dataset IDs 6-9), analytical reports available as PDFs located on the State Water Resources Control Board GeoTracker (SWRCB-GT) website (Dataset ID 10), and analytical reports located within well history files in CalGEM's online Well Finder (WF) database (Dataset IDs 11-12). The availability of location and well construction information for Dataset IDs 6-12 varied by site. A combination of scanned laboratory analysis reports, CalGEM WF well history files, and California Department of Water Resources Well Completion Reports (CDWR-WCR) were the primary sources of location and well construction information for 5 wells (Dataset IDs 7-10, and 12) and 3 wells (Dataset IDs 8, 10, and 12), respectively. Approximate locations for Dataset IDs 7 and 9 represent meridian, township, range, and section (MTRS) centroids. Google Earth was used to determine the approximate location of Dataset ID 8 based on information from the WCR for that well. No location or well construction information was found for Dataset IDs 6 and 11. Data were manually compiled into two separate files described as follows: 1) a summary data file that includes well identifiers, location, construction, the number of chemistry samples, the period of record, 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 constituents classified into one of the following groups: water-quality indicators, major and minor ions, nutrients, trace elements, naturally occurring radioactive material (NORM), volatile organic compounds (VOCs), and miscellaneous organics compounds. 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.

This digital dataset contains historical geochemical and other information for 45 samples of produced water from 38 sites in the Placerita and Newhall Oil Fields in Los Angeles County, southern 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 17 wells, 6 storage tanks, and 15 unidentifiable sample sources. Well depth, perforation depths, and (or) depths referred to on geochemistry reports as interval of zone produced, are available for all 17 wells. Designated well use and sample descriptions provide further insight about what the samples represent. The well use designation for 13 of the wells is OG (oil/gas). The samples (16) associated with these wells likely represent produced water based on well designation and history, although samples from two wells (Dataset ID 23 and 32) are described as formation water. Four wells have a site type designation of "injectate" based on the current designated well use (INJ, injection; or WD, water disposal), but samples from two of the four wells (Dataset ID 31 and 35) likely represent produced or formation water as well history records indicate that sample collection predated conversion to (Dataset ID 31) or the commencement of (Dataset ID 35) use for water disposal. 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, dissolved organic carbon (DOC), naturally occurring radioactive material (NORM), tracers, semi-volatile organic compounds (SVOCs), 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.

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.

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.

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 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 266 samples of groundwater (GW) from 208 wells located within 3 miles of the Edison, Mountain View, and Ant Hill Oil Fields in Kern County, California. The sampled wells include water-supply wells used primarily for domestic, irrigation, and public uses; however, the specific water-supply use of 27 wells is unknown ('unk'). Three wells with water use denoted as 'WS' (water supply) were documented as having originally been used in support of oil production, or were converted from oil production wells to water-supply wells by the time they were sampled. Numerical water chemistry data were compiled from five data sources: 1) Kern County Public Health Services Department (KCPHSD, 2017), 2) California Department of Conservation's Geologic Energy Management Division (CalGEM) archived analytical reports (CalGEM, 2021), 3) CalGEM Underground Injection Control (UIC) program hard-copy records (CalGEM-UIC, 2017), 4) CalGEM's Well Finder (WF) online database (CalGEM-WF, 2022), and 5) the California State Water Resources Control Board GeoTracker online data portal (SWRCB-GT, 2020). These data sources include varying degrees of location and well construction information. Data were manually compiled into two separate files described as follows: 1) a summary data file (EMA_GW_Summary_Data.xlsx) that includes well identifiers, location, construction, the number of chemistry samples, the period of record, 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 constituents (EMA_GW_Geochemistry.xlsx) classified into one of the following groups: water-quality indicators, major and minor ions, nutrients, trace elements, naturally occurring radioactive material (NORM), and volatile organic compounds (VOCs). Ion (charge) balance calculations and percent error of these calculations were included for samples having a complete suite of major ion analyses. Parameter code, analytical method, reporting level, reporting level type, dilution factor, and supplemental notes were included where available or pertinent. A data dictionary (EMA_GW_Data-Dictionary. xlsx) describes the geochemistry data file and is provided with this data release.

The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board collected produced water and gas samples in the Oxnard Oil Field in Ventura County in August 2018 and the Placerita Oil Field in Los Angeles County in December 2018. 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; and integrated produced water from many 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 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.

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.