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Water well data used for preliminary regional groundwater salinity mapping near selected oil fields in central and southern California

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.