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 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.

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.

This digital dataset contains geochemical and other information for 1,209 samples of groundwater from 343 wells located within 3-miles of the Buena Vista, Elk Hills, Midway-Sunset, and North and South Coles Levee oil fields in the southwestern San Joaquin Valley of central California. Data were compiled by the U.S. Geological Survey (USGS) from preexisting datasets and transferred manually 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 geochemical and other information for 1,209 samples of groundwater from 343 wells located within 3-miles of the Buena Vista, Elk Hills, Midway-Sunset, and North and South Coles Levee oil fields in the southwestern San Joaquin Valley of central California. Data were compiled by the U.S. Geological Survey (USGS) from preexisting datasets and transferred manually 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.

This digital dataset contains historical geochemical and other information for 100 samples of groundwater from 71 wells located within 3 miles of the Poso Creek Oil Field in Kern County, California. An additional 12 wells in the Poso Creek study area, but co-located within 3 miles of the adjacent Rosedale and Rosedale Ranch Oil Fields, were not included in this data release; these data are planned for a future data release associated with those fields. The sampled wells include water-supply wells used primarily for domestic, irrigation, and industrial uses. Numerical water chemistry data were compiled from two data sources: 1) Kern County Public Health Services Department (KCPHSD) PDF (Portable Document Format) files, and 2) the Eastside Water Management Area (EWMA) Groundwater Sustainability Plan (GSP) Chapter. These data sources include varying location and well-construction information. Locations for most of the wells represent either well-specific coordinates provided in the KCPHSD PDFs, approximate locations determined using ArcGIS (GIS, Geographic Information System) software based on descriptive information or location maps in the KCPHSD PDFs, parcel centroid coordinates determined from a GIS parcel shapefile (KERN PARCEL) based on parcel numbers provided by either the KCPHSD or EWMA data source, or approximate locations from Google Earth based on visual identification of well locations. For two wells (Dataset_IDs 1 and 2) coordinates represent the locations provided by the California Department of Water Resources Water Data Library (CDWR WDL) as those particular wells are located in that database in association with water-level measurement data. For three wells (Dataset_IDs 22, 30, and 42) having limited information, locations represent meridian, township, range, section, and quarter-quarter section (MTRSQQ) centroids. Information on well construction was compiled from California Department of Water Resources Well Completion Reports (CDWR-WCR) included with the PDFs located on the KCPHSD website, or located on the CDWR Well Completion Reports Map Application website. Well construction from CDWR-WCRs was available for 53 of the 71 wells. For one well (Dataset_ID 5), a WCR could not be located, however, well construction information was available in the EWMA GSP. 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), 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, 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 100 samples of groundwater from 71 wells located within 3 miles of the Poso Creek Oil Field in Kern County, California. An additional 12 wells in the Poso Creek study area, but co-located within 3 miles of the adjacent Rosedale and Rosedale Ranch Oil Fields, were not included in this data release; these data are planned for a future data release associated with those fields. The sampled wells include water-supply wells used primarily for domestic, irrigation, and industrial uses. Numerical water chemistry data were compiled from two data sources: 1) Kern County Public Health Services Department (KCPHSD) PDF (Portable Document Format) files, and 2) the Eastside Water Management Area (EWMA) Groundwater Sustainability Plan (GSP) Chapter. These data sources include varying location and well-construction information. Locations for most of the wells represent either well-specific coordinates provided in the KCPHSD PDFs, approximate locations determined using ArcGIS (GIS, Geographic Information System) software based on descriptive information or location maps in the KCPHSD PDFs, parcel centroid coordinates determined from a GIS parcel shapefile (KERN PARCEL) based on parcel numbers provided by either the KCPHSD or EWMA data source, or approximate locations from Google Earth based on visual identification of well locations. For two wells (Dataset_IDs 1 and 2) coordinates represent the locations provided by the California Department of Water Resources Water Data Library (CDWR WDL) as those particular wells are located in that database in association with water-level measurement data. For three wells (Dataset_IDs 22, 30, and 42) having limited information, locations represent meridian, township, range, section, and quarter-quarter section (MTRSQQ) centroids. Information on well construction was compiled from California Department of Water Resources Well Completion Reports (CDWR-WCR) included with the PDFs located on the KCPHSD website, or located on the CDWR Well Completion Reports Map Application website. Well construction from CDWR-WCRs was available for 53 of the 71 wells. For one well (Dataset_ID 5), a WCR could not be located, however, well construction information was available in the EWMA GSP. 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), 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, 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 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 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.