This release contains borehole geophysical electrical log data (elogs), total dissolved solids sample data (TDS), and geostatistical program files used to estimate the salinity distribution in groundwater above and in the vicinity of the Montebello Oil Field, located near Los Angeles, California, USA. Original data are drawn from a variety of publicly available sources and are combined here for use in geostatistical simulation and estimation. The extent of the estimation area is a 3-mile buffer zone surrounding the Montebello Oil Field administrative boundary, and the subsurface aquifer region lying above locally mapped oil-bearing units. The data compilation and analysis were done as part of the California State Water Resources Control Board Oil and Gas Regional Monitoring Program and the associated USGS California Oil, Gas, and Groundwater (COGG) Program.

The U.S. Geological Survey (USGS) and California State University-Sacramento, in cooperation with the California State Water Resources Control Board and U.S. Bureau of Land Management, compiled and analyzed data for mapping groundwater salinity in selected oil and gas fields in California. The data for the Midway-Sunset (MWSS) oil field includes digitized borehole geophysical data, geochemical analyses of produced water samples from oil and gas wells, core sample analysis from select wells, and groundwater total dissolved solids (TDS) estimations with the related geophysical log data. These data have been compiled from many sources and span several decades. The geochemical data include ion concentrations and TDS which are attributed with the sample date, geological formation, and perforation depths. These data have been in archived scanned pages of historical lab analyses on the Division of Oil, Gas, and Geothermal Resources (DOGGR) website. The borehole geophysical data has been provided by California Division of Oil, Gas, and Geothermal Resources (DOGGR). These data were compiled primarily to create groundwater salinity maps to assist in regional groundwater monitoring as part of the California State Water Resources Control Board's Program of Regional Monitoring of Water Quality in Areas of Oil and Gas Production and the USGS California Oil, Gas, and Groundwater (COGG) program.

The U.S. Geological Survey (USGS) and California State University-Sacramento, in cooperation with the California State Water Resources Control Board and U.S. Bureau of Land Management, compiled and analyzed data for mapping groundwater salinity in selected oil and gas fields in California. The data for the Midway-Sunset (MWSS) oil field includes digitized borehole geophysical data, geochemical analyses of produced water samples from oil and gas wells, core sample analysis from select wells, and groundwater total dissolved solids (TDS) estimations with the related geophysical log data. These data have been compiled from many sources and span several decades. The geochemical data include ion concentrations and TDS which are attributed with the sample date, geological formation, and perforation depths. These data have been in archived scanned pages of historical lab analyses on the Division of Oil, Gas, and Geothermal Resources (DOGGR) website. The borehole geophysical data has been provided by California Division of Oil, Gas, and Geothermal Resources (DOGGR). These data were compiled primarily to create groundwater salinity maps to assist in regional groundwater monitoring as part of the California State Water Resources Control Board's Program of Regional Monitoring of Water Quality in Areas of Oil and Gas Production and the 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.

This digital dataset is comprised of three separate data files that contain total dissolved solids, well construction, and well identifying information for 3,546 water wells used to map salinity in and around 31 southern and central California oil fields. Salinity mapping was done for 27 fields located in the southern San Joaquin Valley of Kern County (North Belridge, South Belridge, Canfield Ranch, North Coles Levee, South Coles Levee, Cymric, Edison, Elk Hills, Fruitvale, Greely, Jasmin, Kern Bluff, Kern Front, Kern River, Lost Hills, Mount Poso, Mountain View, Poso Creek, Rio Bravo, Rosedale, Rosedale Ranch, Round Mountain, San Emidio Nose, Tejon, Ten Section, Wheeler Ridge, and Yowlumne), 3 fields in the LA Basin of Los Angeles County (Montebello, Santa Fe Springs, and Wilmington), and 1 field in the central coast area of Santa Barbara and San Luis Obispo Counties (Santa Maria Valley). Unlike petroleum wells, water wells both within and adjacent to oil fields of interest were used for salinity mapping. Water wells within an area (buffer) of 2-miles from the administrative field boundaries, with the exception of the Wilmington oil field with a buffer of 1-mile, were used for salinity mapping. Water wells located within overlapping buffer areas of adjacent oil fields were assigned to multiple fields for the purpose of being able to map salinity on a field-by-field basis. The dataset includes total dissolved solids (TDS) analyses from 1927 to 2016. Many of the analyses represent TDS concentrations that were calculated, as part of the salinity mapping, from specific conductance (SC) in lieu of reported TDS concentrations. Approximately 30 percent of the mapped water wells are wholly or partially derived from SC. In addition, approximately 50 percent of the water wells have TDS or SC analyses from more than one unique sample date. For wells having multiple analyses TDS represents the median value for the entire period of record, irrespective of whether it is from reported, calculated, or a combination of both TDS types. This dataset also includes ancillary data in the form of bottom perforation depth, well depth, or hole depth, land-surface elevation at the well head, and well location and identifier information. Bottom perforation depth was missing for about 65 percent of all water wells used for salinity mapping and were assigned a alternative value for plotting purposes. Where available, well depth or hole depth were used in lieu of bottom perforation depth. For water wells lacking bottom perforation, well depth, or hole depth (40 percent), the bottom perforation was estimated based on screen length when available (5 percent), or when the median bottom perforation or median well depth for all wells associated with an individual field is provided as an approximation for the purpose of vertical plotting (35 percent). Summary data about each well used for salinity mapping is contained in the file called Water_Wells_Summary_Data. Detailed information about all individual TDS values including those used for determining median TDS values, are contained in the file called Water_Wells_All_Data. Data used for the development of linear regression equations for calculating TDS from specific conductance in lieu of reported TDS values are contained in the file called Water_Wells_Regress_Data.

This digital dataset is comprised of three separate data files that contain total dissolved solids, well construction, and well identifying information for 3,546 water wells used to map salinity in and around 31 southern and central California oil fields. Salinity mapping was done for 27 fields located in the southern San Joaquin Valley of Kern County (North Belridge, South Belridge, Canfield Ranch, North Coles Levee, South Coles Levee, Cymric, Edison, Elk Hills, Fruitvale, Greely, Jasmin, Kern Bluff, Kern Front, Kern River, Lost Hills, Mount Poso, Mountain View, Poso Creek, Rio Bravo, Rosedale, Rosedale Ranch, Round Mountain, San Emidio Nose, Tejon, Ten Section, Wheeler Ridge, and Yowlumne), 3 fields in the LA Basin of Los Angeles County (Montebello, Santa Fe Springs, and Wilmington), and 1 field in the central coast area of Santa Barbara and San Luis Obispo Counties (Santa Maria Valley). Unlike petroleum wells, water wells both within and adjacent to oil fields of interest were used for salinity mapping. Water wells within an area (buffer) of 2-miles from the administrative field boundaries, with the exception of the Wilmington oil field with a buffer of 1-mile, were used for salinity mapping. Water wells located within overlapping buffer areas of adjacent oil fields were assigned to multiple fields for the purpose of being able to map salinity on a field-by-field basis. The dataset includes total dissolved solids (TDS) analyses from 1927 to 2016. Many of the analyses represent TDS concentrations that were calculated, as part of the salinity mapping, from specific conductance (SC) in lieu of reported TDS concentrations. Approximately 30 percent of the mapped water wells are wholly or partially derived from SC. In addition, approximately 50 percent of the water wells have TDS or SC analyses from more than one unique sample date. For wells having multiple analyses TDS represents the median value for the entire period of record, irrespective of whether it is from reported, calculated, or a combination of both TDS types. This dataset also includes ancillary data in the form of bottom perforation depth, well depth, or hole depth, land-surface elevation at the well head, and well location and identifier information. Bottom perforation depth was missing for about 65 percent of all water wells used for salinity mapping and were assigned a alternative value for plotting purposes. Where available, well depth or hole depth were used in lieu of bottom perforation depth. For water wells lacking bottom perforation, well depth, or hole depth (40 percent), the bottom perforation was estimated based on screen length when available (5 percent), or when the median bottom perforation or median well depth for all wells associated with an individual field is provided as an approximation for the purpose of vertical plotting (35 percent). Summary data about each well used for salinity mapping is contained in the file called Water_Wells_Summary_Data. Detailed information about all individual TDS values including those used for determining median TDS values, are contained in the file called Water_Wells_All_Data. Data used for the development of linear regression equations for calculating TDS from specific conductance in lieu of reported TDS values are contained in the file called Water_Wells_Regress_Data.

This dataset contains groundwater salinity information for boreholes which had terminated at least 5m and no more than 50m above bedrock. The bores have been extracted predominantly from the Groundwater Management System (GMS) and the State Observation Bore Network (SOBN). It should be noted that the analysis undertaken with the salinity data was only of a preliminary nature and should be treated with a critical approach. Local validation of the data (e.g. screen depths) needs to be undertaken in detail. The dataset was compiled by GHD to inform the report 'Potential Influences of Geological Structures on Groundwater Flow Systems' for DEPI's Secure Allocation Future Entitlements (SAFE) Project.

The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board compiled and analyzed data for the purpose of mapping groundwater salinity in selected oil and gas fields in California. The data for the Fruitvale and Rosedale Ranch oil fields include well construction data, digitized borehole geophysical data, geochemical analyses of water samples from oil and gas wells and groundwater wells, geological formation depths, and the groundwater total dissolved solids (TDS) calculations used in an accompanying manuscript. These data have been compiled from many sources and span several decades. The well construction data includes attributes such as the date drilling began (spud date), well depth, the depth of top producing perforation, and borehole orientation. These data have been in archived scanned pages in raster format on the Division of Oil, Gas, and Geothermal Resources (DOGGR) website. Similarly, the borehole geophysical data, measured by oil companies, has been archived in raster format. This project has converted the borehole geophysical data from selected oil and gas wells into a computer readable numerical format. The geochemical analyses have also been archived in scanned formats, but now have been compiled into numerical datasets in additional data releases by Metzger and others (2018) and Gans and others (2018). All of the data compiled and analyzed are part of the California State Water Resources Control Board's Program of Regional Monitoring of Water Quality in Areas of Oil and Gas Production and the USGS California Oil, Gas, and Groundwater (COGG) program.

The U.S. Geological Survey (USGS) in cooperation with the California State Water Resources Control Board compiled and analyzed data for the purpose of mapping groundwater salinity in selected oil and gas fields in California. The data for the Fruitvale and Rosedale Ranch oil fields include well construction data, digitized borehole geophysical data, geochemical analyses of water samples from oil and gas wells and groundwater wells, geological formation depths, and the groundwater total dissolved solids (TDS) calculations used in an accompanying manuscript. These data have been compiled from many sources and span several decades. The well construction data includes attributes such as the date drilling began (spud date), well depth, the depth of top producing perforation, and borehole orientation. These data have been in archived scanned pages in raster format on the Division of Oil, Gas, and Geothermal Resources (DOGGR) website. Similarly, the borehole geophysical data, measured by oil companies, has been archived in raster format. This project has converted the borehole geophysical data from selected oil and gas wells into a computer readable numerical format. The geochemical analyses have also been archived in scanned formats, but now have been compiled into numerical datasets in additional data releases by Metzger and others (2018) and Gans and others (2018). All of the data compiled and analyzed are part of the California State Water Resources Control Board's Program of Regional Monitoring of Water Quality in Areas of Oil and Gas Production and the USGS California Oil, Gas, and Groundwater (COGG) program.