U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2018–5082

Prepared in cooperation with the California State Water Resources Control Board and the 

Bureau of Land Management

A product of the California Oil and Gas Regional Groundwater Monitoring Program

Preliminary Groundwater Salinity Mapping Near Selected 

Oil Fields Using Historical Water-Sample Data, Central and 

Southern California
Cover graphic. Oil fields included in this study area and colorized land areas underlying study subregions in central and southern 

California. 
Preliminary Groundwater Salinity Mapping 

Near Selected Oil Fields Using Historical 

Water-Sample Data, Central and Southern 

California

By Loren F. Metzger and Matthew K. Landon

A product of the California Oil and Gas Regional Groundwater Monitoring 

Program

Prepared in cooperation with the California State Water Resources Control Board and the 

Bureau of Land Management

Scientific Investigations Report 2018–5082

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2018

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Suggested citation:

Metzger, L.F., and Landon, M.K., 2018, Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using 

Historical Water-Sample Data, Central and Southern California: U.S. Geological Survey Scientific Investigations 

Report 2018–5082, 54 p., https://doi.org/10.3133/sir20185082.

ISSN 2328-0328 (online)
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Methods...........................................................................................................................................................4

Field Selection Process .......................................................................................................................4

Data Sources.........................................................................................................................................5

Data Processing....................................................................................................................................7

Salinity Data..................................................................................................................................8

Well-Construction Data ............................................................................................................10

Salinity Mapping and Depth-to-TDS Profile Plots.........................................................................10

Results of Salinity Mapping by Geographic Subregion.........................................................................17

Kern Sierran Foothills.........................................................................................................................18

East Kern Valley Floor ........................................................................................................................22

Middle Kern Valley Floor....................................................................................................................26

South Kern Valley Margin..................................................................................................................30

West Kern Valley Floor.......................................................................................................................34

West Kern Valley Margin...................................................................................................................37

Los Angeles Basin ..............................................................................................................................41

Central Coast Basin............................................................................................................................45

Variation in Salinity Vertical Profiles Across Subregions.....................................................................48

Data Limitations and Future Work.............................................................................................................51

References Cited..........................................................................................................................................52

Figures

1. Map showing locations of oil fields included in this report grouped by assigned 

subregion, locations of unanalyzed oil fields, and the Division of Oil, Gas, and 

Geothermal Resources district boundaries .............................................................................3

2. Map showing major geographic and geological features and Division of Oil, Gas, 

and Geothermal Resources district boundaries, central and southern California............9

3. Maps showing the distribution of total dissolved solids in produced water from 

petroleum wells and water from water wells, for selected oil fields in the Kern 

Sierran Foothills subregion, central California ......................................................................19

4. Diagrams showing the vertical distribution of total dissolved solids 

concentrations for mapped oil fields in the Kern Sierran Foothills subregon, 

central California ........................................................................................................................21

Acknowledgments

The authors thank the California State Water Resources Control Board and Bureau of Land 

Management for data and funding for salinity mapping near selected oil fields. We also thank 

the California Division of Oil, Gas, and Geothermal Resources and California Depart-ment 

of Water Resources for providing data and insight. Funding for this work was authorized by 

California Senate Bill 4.
iv

5. Maps showing the distribution of total dissolved solids in produced water from 

petroleum wells and water from water wells, for selected oil fields in the East 

Kern Valley Floor subregion, central California.....................................................................23

6. Diagrams showing the vertical distribution of total dissolved solids 

concentrations for mapped oil fields in the East Kern Valley Floor subregion, 

central California ........................................................................................................................25

7. Maps showing the distribution of total dissolved solids in produced water from 

petroleum wells and water from water wells, for selected oil fields in the Middle 

Kern Valley Floor subregion, central California.....................................................................27

8. Diagrams showing the vertical distribution of total dissolved solids 

concentrations for mapped oil fields in the Middle Kern Valley Floor subregion, 

central California ........................................................................................................................29

9. Maps showing the distribution of total dissolved solids in produced water from 

petroleum wells and water from water wells, for selected oil fields in the South 

Kern Valley Margin subregion, central California.................................................................31

10. Diagrams showing the vertical distribution of total dissolved solids 

concentrations for mapped oil fields in the South Kern Valley Margin subregion, 

central California ........................................................................................................................33

11. Maps showing the distribution of total dissolved solids in produced water from 

petroleum wells and water from water wells, for selected oil fields in the West 

Kern Valley Floor subregion, central California.....................................................................35

12. Diagram showing the vertical distribution of total dissolved solids 

concentrations for mapped oil fields in the West Kern Valley Floor subregion, 

central California ........................................................................................................................37

13. Maps showing the distribution of total dissolved solids in produced water from 

petroleum wells and water from water wells, for selected oil fields in the West 

Kern Valley Margin subregion, central California.................................................................39

14. Diagrams showing the vertical distribution of total dissolved solids 

concentrations for mapped oil fields in the West Kern Valley Margin subregion, 

central California ........................................................................................................................41

15. Maps showing the distribution of total dissolved solids in produced water 

from petroleum wells and water from water wells, for selected oil fields in the 

Los Angeles Basin subregion, southern California...............................................................43

16. Diagrams showing the vertical distribution of total dissolved solids 

concentrations for mapped oil fields in the Los Angeles Basin subregion, 

southern California .....................................................................................................................45

17. Maps showing the distribution of total dissolved solids in produced water from 

petroleum wells and water from water wells, for the Santa Maria Valley oil field, 

Central Coast Basin subregion, central California................................................................46

18. Diagram showing the vertical distribution of total dissolved solids 

concentrations for the Santa Maria oil field, Central Coast Basin subregion, 

central California ........................................................................................................................48

19. Diagram showing generalized distribution of total dissolved solids versus depth 

for the eight geographic subregions, central and southern California .............................49

20. Diagram summarizing aAltitudes of total dissolved solids thresholds, minimum 

top perforation for petroleum wells, and maximum bottom perforfation, well depth, 

or hole depth for water wells, by oil field, central and southern California......................50

Figures—Continued
v

Tables

1. Oil fields listed by Division of Oil, Gas, and Geothermal Resources district and 

geographic region included in reconnaissance salinity mapping, central and 

southern California .......................................................................................................................4

2. Summary by data source of petroleum and water wells compiled for salinity 

mapping, central and southern California ................................................................................6

3. Summary for each oil field of the number of wells, median perforation depth and 

altitude, range and median total dissolved solids (TDS) value, and minimum depths 

to TDS greater than 3,000 and 10,000 mg/L for petroleum and water wells, central and 

southern California .....................................................................................................................11

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

International System of Units to U.S. customary units

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

Volume

liter (L) 33.81402 ounce, fluid (fl. oz)

liter (L) 0.2642 gallon (gal)

Mass

milligram (g) 0.00003527 ounce, avoirdupois (oz)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
vi

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L). One 

milligram per liter is equivalent to 1 part per million (ppm).

Abbreviations

bls below land surface

CB central block

CDWR California Department of Water Resources

COGG California Oil, Gas, and Groundwater Project

DEM digital elevation model

DOGGR Division of Oil, Gas, and Geothermal Resources (California)

EC electrical conductivity

ESI electronic submission of information

GIS geographic information system

GMP groundwater management plan

MTS Maricopa-Tejon subbasin

NEB northeastern block

NWIS National Water Information System

RMP regional monitoring program

RWQCB Regional Water Quality Control Board

SC specific conductance

SSB southern Sierran block

SWB southwestern block

SWRCB State Water Resources Control Board (California)

SWRCB-DDW State Water Resources Control Board Division of Drinking Water (California)

TDS total dissolved solids

UIC Underground Injection Control

USDW underground source of drinking water

USGS U.S. Geological Survey

USGS-PWDB U.S. Geological Survey Produced Waters Database

WDL Water Data Library

WFB west-side fold belt

WRD Water Replenishment District of Southern California
Preliminary Groundwater Salinity Mapping Near Selected 

Oil Fields Using Historical Water-Sample Data, Central 

and Southern California

By Loren F. Metzger and Matthew K. Landon

Abstract

The distribution of groundwater salinity was mapped 

for 31 oil fields and adjacent aquifers and summarized by 

8 subregions across major oil-producing areas of central 

and southern California. The objectives of this study were 

to describe the distribution of groundwater near oil fields 

having total dissolved solids less than 10,000 milligrams per 

liter (mg/L) based on available data and to document where 

data gaps exist. Salinity was represented by the measured 

or calculated concentration of total dissolved solids (TDS) 

in samples of produced water obtained from petroleum 

wells and groundwater obtained from water wells. The 

water chemistry data were used to estimate the minimum 

depths of TDS greater than 3,000 mg/L and greater than 

10,000 mg/L in areas near selected oil fields using historical 

water-chemistry data coupled with available well-location and 

construction information.

The 10,000 mg/L threshold, representing the highest 

level of TDS concentration of water that could be considered 

as a potential source of drinking water, was present in all but 

4 (Jasmin, Kern Bluff, Kern Front, and Mount Poso) of the 

31 individual oil fields. Among petroleum wells, the median 

TDS concentration of produced water ranged from 500 mg/L 

for the Jasmin field to 32,636 mg/L for the Elk Hills field. 

Among water wells, median TDS concentrations, either 

reported or calculated from specific conductance, ranged from 

151 mg/L for wells within 2 miles of the Ten Section field to 

9,750 mg/L for wells within 2 miles of the combined North 

and South Belridge fields.

In general, TDS across the eight geographic subregions 

increased with depth, but the relation of TDS with depth 

varied regionally. The most pronounced increases in TDS with 

depth were across the West Kern Valley Floor and West Kern 

Valley Margin subregions on the west side of the San Joaquin 

Valley, and in the vicinity of the Wilmington field in the Los 

Angeles Basin subregion; in these areas, relatively high TDS 

concentrations greater than 10,000 mg/L were present within 

the upper few hundred to several thousand feet of land surface. 

Total dissolved solids concentrations increased more gradually 

with depth in the Middle Kern Valley Floor subregion, in the 

South Kern Valley Margin subregion, in the vicinity of the 

Montebello and Santa Fe Springs fields in the Los Angeles 

Basin subregion, and in the Central Coast Basin subregion. 

The Kern Sierran Foothills and East Kern Valley Floor 

subregions, on the east side of the San Joaquin Valley, had the 

most gradual increases in TDS with depth. Fields in the East 

Kern Valley Floor subregion generally had groundwater and 

produced water with TDS less than 10,000 mg/L that extended 

to a large depth compared to most other subregions.

Overall, the west side of the San Joaquin Valley in Kern 

County and the Wilmington field in Los Angeles County 

generally have the highest TDS values and the shallowest 

depths to high TDS. High TDS at relatively shallow depths on 

the west side of the San Joaquin Valley may be because of a 

combination of natural conditions and anthropogenic factors. 

In the vicinity of the Wilmington field in the Los Angeles 

Basin subregion, high TDS at relatively shallow depths is 

attributable at least in part to seawater intrusion. Fields on 

the east side of the San Joaquin Valley in Kern County have 

the lowest TDS and greatest depths to TDS greater than 

10,000 mg/L because of their geologic setting adjacent to 

Sierra Nevada recharge areas.

Reconnaissance salinity mapping was limited by 

several factors. The primary limitation was the lack of 

well-construction data for a significant number of water 

wells. Bottom perforation, well depth, or hole depth were 

not available for 35 percent of wells used for salinity 

mapping. A second limitation was variability in data quality. 
2 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Total dissolved solids and specific conductance data were 

compiled from different data sources with varying degrees of 

documentation that ranged from comprehensive to very little 

or none. As a result, it was not always possible to assess the 

quality of the provided data with respect to either conditions 

at each well during sampling or the methodology used for 

sample collection and analysis. A third limitation was the 

lack of wells, either petroleum or water, and associated TDS 

data over large vertical intervals for some fields. As a result, 

the distribution of salinity and the depths at which TDS 

concentration exceeds the 3,000 and 10,000 mg/L thresholds 

could not always be precisely determined. This analysis 

highlights key gaps that need to be filled with additional 

analysis of other sources of information, such as borehole 

geophysical logs and new water sample or geophysical data 

collection.

Introduction

The California State Water Resources Control Board 

(SWRCB) initiated a regional monitoring program (RMP) in 

July 2015, intended to determine where and to what degree 

groundwater quality may be at potential risk from oil and 

gas well stimulation and associated production activities, 

including disposal of produced waters by means of surfacewater ponds and underground injection. Other events or 

activities that have the potential to impact groundwater include 

the breaching of oil and gas well casings. The SWRCB 

also directed the RMP to establish baseline water-quality 

information for all fields and prioritize sampling in areas 

where groundwater is or may be an underground source of 

drinking water (USDW) as defined by the 10,000 milligrams 

per liter (mg/L) total dissolved solids (TDS) concentration 

threshold established by the U.S. Environmental Protection 

Agency (U.S. Environmental Protection Agency, 2017).

The U.S. Geological Survey (USGS) is collaborating 

with the SWRCB to implement the RMP through the 

California Oil, Gas, and Groundwater (COGG) cooperative 

project and coordinating with other agencies involved in 

managing groundwater and oil/gas resources, including the 

Bureau of Land Management, the Regional Water Quality 

Control Boards (RWQCBs), the California Department 

of Conservation’s Division of Oil, Gas, and Geothermal 

Resources (DOGGR), and local water agencies.

Groundwater resources in California that are relatively 

close to the land surface (less than 1,000 feet [ft]) and 

of the highest quality, usually containing TDS less than 

1,000 mg/L, have been tapped for drinking water, irrigation, 

and other beneficial uses. The location, extent, and quality 

of those resources are relatively well understood. The use of 

groundwater resources in deeper zones (greater than 1,000 ft) 

and areas containing poorer quality water has been expanding, 

particularly during recent droughts (California Department 

of Water Resources, 2015a). The oil and gas industry has 

historically been responsible for protecting groundwater in 

California containing less than 3,000 mg/L TDS through 

proper well-construction techniques and avoiding waste 

injection into these zones (Bishop, 2014). As a result, there 

is information in oil and gas well records about the location 

of the “base of fresh water,” or estimates of the depth at 

which 3,000 mg/L TDS is reached (Horsely Witten Group, 

2011). However, there is relatively little information about 

the distribution of groundwater resources containing between 

3,000 and 10,000 mg/L TDS in areas near oil fields.

Purpose and Scope

The objectives of this study were to describe the 

distribution of groundwater near oil fields having TDS less 

than 10,000 mg/L based on available water-sample data and 

to document where data gaps exist. This report presents a 

compilation of water-quality data collected in and around 

31 oil fields in southern and central California (fig. 1); no 

new samples were collected as part of this study. These fields 

were selected for reconnaissance regional salinity mapping 

because water-sample data were available in proximity to 

these fields, and these fields represent a range of geographic 

and hydrogeologic settings across major oil-producing areas of 

central and southern California. 
Introduction 3

Figure 1. Locations of oil fields included in this report grouped by assigned subregion, locations of unanalyzed oil fields, and the 

Division of Oil, Gas, and Geothermal Resources (DOGGR) district boundaries.

KERN

COUNTY

SANTA

BARBARA

COUNTY

LOS

ANGELES

COUNTY

SAN LUIS

OBISPO

COUNTY

Los AngelesLos Angeles

BakersfieldBakersfield

Santa MariaSanta Maria

120°30' 118°30'

36°00'

34°00'

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North 

and 45°30' North

North American Datum of 1983

Pacific Ocean

District 1District 1

District 4District 4

District 3District 3

Data sources: DOGGR, 2014a (district 

boundaries); DOGGR, 2014b (oil field 

boundaries)

EXPLANATION

Oil fields included in this study by subregion

Kern Sierran Foothills

East Kern Valley Floor

Middle Kern Valley Floor

South Kern Valley Margin

West Kern Valley Floor

West Kern Valley Margin

Los Angeles Basin

Central Coast Basin

Oil fields not analyzed

Division of Oil Resources (DOGGR) district 

boundary

Study area CALIFORNIA

Bakersfield

Santa

Maria Los Angeles
4 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Methods

The spatial (areal and vertical) distribution of 

groundwater salinity was analyzed and mapped using available 

data for petroleum and water wells. For this initial salinity 

mapping effort, 31 oil fields were selected, and data from a 

variety of sources were compiled, processed, and attributed.

Field Selection Process

Oil fields included in this reconnaissance salinity 

mapping effort were selected as a subset of fields categorized 

as high and moderate priority fields by Davis and others 

(2018) based on (1) vertical proximity of useable groundwater 

to oil/gas resources, (2) the density of all petroleum wells and 

those used for injection and waste disposal, and (3) the volume 

of produced water re-injected into oil-bearing formations 

via injection and waste-disposal wells. The objective of the 

study by Davis and others (2018) was to support planning of 

regional groundwater monitoring tasks, including prioritizing 

which of the 487 onshore oil and gas fields in California 

should be addressed by this reconnaissance salinity mapping 

study. Davis and others (2018) identified 112 fields as having 

a high priority and 111 fields as having a moderate priority 

for regional monitoring of nearby groundwater. Of these, a 

subset of 31 (26 high, 5 moderate) fields were selected for this 

reconnaissance salinity mapping study: 27 fields in DOGGR 

District 4 (Kern County), 3 fields in DOGGR District 1 (Los 

Angeles), and 1 field in DOGGR District 3 (Central Coast; 

table 1). These fields were chosen because water-sample 

data were available in proximity to these fields and because 

the fields represent a range of geographic and hydrogeologic 

settings across major oil-producing areas of central and 

southern California. For the purposes of salinity mapping, 

individual fields were grouped based on geographic area but 

analyzed at both field and subregional scales. The designated 

subregional groupings and number of individual fields 

assigned to each, denoted in parentheses, include Kern Sierran 

Foothills (seven), East Kern Valley Floor (five), Middle Kern 

Valley Floor (four), South Kern Valley Margin (four), West 

Kern Valley Floor (two), West Kern Valley Margin (five), 

Los Angeles Basin (three), and Central Coast Basin (one; 

fig. 1). Within these subregional groupings, some fields (North 

and South Belridge, North and South Coles Levee) were 

combined because of their proximity and (or) limited data. The 

combination of North Belridge with South Belridge and North 

Coles Levee with South Coles Levee resulted in 31 individual 

fields being treated as 29 aggregated fields for the purposes of 

this report.

Table 1. Oil fields listed by Division of Oil, Gas, and Geothermal 

Resources (DOGGR) district and geographic region included in 

reconnaissance salinity mapping, central and southern California.

[See figure 1 for locations of DOGGR districts, geographic subregions, and oil 

fields. Subregions are listed in the order presented in the report]

Subregion Field

DOGGR District 4

Kern Sierran Foothills Jasmin

Kern Sierran Foothills Kern Bluff

Kern Sierran Foothills Kern Front

Kern Sierran Foothills Kern River

Kern Sierran Foothills Mount Poso

Kern Sierran Foothills Poso Creek

Kern Sierran Foothills Round Mountain

East Kern Valley Floor Edison

East Kern Valley Floor Fruitvale

East Kern Valley Floor Mountain View

East Kern Valley Floor Rosedale

East Kern Valley Floor Rosedale Ranch

Middle Kern Valley Floor Canfield Ranch

Middle Kern Valley Floor Greeley

Middle Kern Valley Floor Rio Bravo

Middle Kern Valley Floor Ten Section

South Kern Valley Margin San Emidio Nose

South Kern Valley Margin Tejon

South Kern Valley Margin Wheeler Ridge

South Kern Valley Margin Yowlumne

West Kern Valley Floor Coles Levee, North and South

West Kern Valley Margin Belridge, North and South

West Kern Valley Margin Cymric

West Kern Valley Margin Elk Hills

West Kern Valley Margin Lost Hills

DOGGR District 1

Los Angeles Basin Montebello

Los Angeles Basin Santa Fe Springs

Los Angeles Basin Wilmington

DOGGR District 3

Central Coast Basin Santa Maria Valley
Methods 5

Data Sources

Sources of water-quality data included DOGGR, the 

California Department of Water Resources (CDWR), the 

SWRCB, the USGS, and the Water Replenishment District of 

Southern California (WRD). The number of wells from each 

of these data sources and period of record is summarized in 

table 2. These data sources included widely varying degrees 

of documentation, ranging from detailed information about 

sample type and methodology to little or no supporting 

information. Given the uncertainty of data quality, it was 

not possible to screen out all unrepresentative samples. For 

the purposes of this report, petroleum wells are defined as 

including all wells installed in support of developing oil and 

gas resources, including oil and gas recovery, injection, and 

water source wells. Petroleum well samples were screened 

to omit samples representing injectate, tank, or composite 

samples where the sample was not collected from a specific 

well. Although samples derived from drill stem tests (DSTs) 

or Johnson formation testers (JFTs) are not considered to 

be as representative of formation water as produced-water 

samples, owing to possible mixing with fluids used for well 

construction, these samples were retained for the sake of 

consistency with similar efforts at characterizing salinity 

across oil fields (Gillespie and others, 2017). For water-well 

samples, care was taken to omit samples not representing 

groundwater, such as pore-water samples obtained from 

the unsaturated zone above the water table. Other samples, 

particularly from relatively shallow water wells (bottom 

perforation, completion depth, or hole depth less than 200 ft), 

appear to represent sources such as perched groundwater or 

infiltration from surface impoundments, which may not be 

representative of regional groundwater conditions. However, 

given the uncertainty in being able to distinguish regional 

from local effects of salinity at the scales used for this report, 

samples from shallow water wells were retained as part of the 

salinity mapping effort.

The Division of Oil, Gas, and Geothermal Resources 

was the primary source of TDS data for petroleum wells 

and consisted of two separate databases. The first was 

the Underground Injection Control (UIC) database, from 

DOGGR’s California Well Information Management System 

(CalWIMS). The database includes information on each 

well, including location, type, status, construction, geologic 

formation, and water analyses. Data were provided by 

DOGGR in the form of a Microsoft Access file on February 

28, 2015, containing information on more than 13,000 wells in 

the study area used primarily for injection (water flood, steam 

flood, or cyclic steam) in support of petroleum production 

activities. Water-sample data in the UIC database is limited 

to TDS and boron for both produced and injectate waters. 

Injectate analyses were not used for salinity mapping because 

that water can be a mixture of produced waters, wastewater, 

or water mixed with chemicals that is unrepresentative of the 

formation into which it is injected. Although documentation 

of the reported TDS values was not available, the values are 

referred to as “zone water” in the dataset and are understood to 

represent water sampled in the injection zone prior to injection 

(Curtis Welty, DOGGR, written commun., June 22, 2015). 

Many of the sample data values appear to be non-unique, 

with just 289 values representing TDS for all 13,219 studyarea wells in the UIC database. For 9 of the 31 oil fields 

analyzed for this report, more than 50 percent of the UIC 

wells in each field were represented by a single TDS value. 

The highest percentages of wells represented by a single 

TDS value were associated with Kern River field (1,719 of 

1,868 wells), Rio Bravo field (11 of 12 wells), and Yowlumne 

field (38 of 42 wells) at 92 percent, 92 percent, and 90 percent, 

respectively. The reporting of a limited number of identical 

values for numerous wells indicates that most of the TDS data 

do not represent unique analytical results. The TDS values 

may have been assigned to UIC wells based on location or 

other factors such as the geologic formation corresponding 

to the depth of injection. A detailed assessment to determine 

possible commonalities of wells with identical TDS values 

was beyond the scope to this study. In cases where it was not 

possible to distinguish actual versus assigned TDS values, 

only wells having a unique TDS value not associated with 

any other well within the same field were retained for salinity 

mapping. As a result of this approach, the report used a total of 

114 UIC wells (table 2).

The second DOGGR database that was used for this 

report is the Oil and Gas Online Data website (http://www.

conservation.ca.gov/dog), which includes separate archives 

of water analyses and well completion reports for petroleum 

wells. The archive of water analyses includes scanned copies 

of analyses for oil-field waters, but the archive is limited to 

District 4 (ftp://ftp.consrv.ca.gov/pub/oil/chemical_analysis). 

In addition to TDS data, many of these analyses include 

results for inorganic constituents, trace elements, and 

nutrients. The DOGGR Well Finder, an online archive of well 

completion reports, includes information on location, geology, 

well construction, and documentation of well modifications 

throughout each well’s history (http://www.conservation.

ca.gov/dog/Pages/Wellfinder.aspx). The DOGGR Well Finder 

was also used for wells in the UIC database that were lacking 

data for depth to top of perforated interval. Gillespie and 

others (2017) used the DOGGR archives to compile water 

sample and related data for about 580 wells as part of a 

previous study to evaluate groundwater salinity in the southern 

San Joaquin Valley. Many of the 580 wells in the report by 

Gillespie and others (2017), plus additional wells compiled as 

part of the COGG project, were used for the salinity mapping 

presented in this report, for a total of 764 wells from the 

DOGGR-online data sources (table 2). Records obtained from 

the DOGGR archives generally included sample date, depth 

of the tested interval, and source of the water (Gillespie and 

others, 2017). Where available, sample source is indicated in 

the USGS data release accompanying this report (Metzger and 

others, 2018).
6 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

A third source of data for petroleum wells was the 

SWRCB’s GeoTracker database. This is a website data portal 

that contains information on facilities having the potential 

to affect groundwater quality (http://geotracker.waterboards.

ca.gov/search.asp). GeoTracker includes water analyses from 

petroleum wells specifically compiled as part of monitoring 

impacts from oil and gas production activities. Total dissolved 

solids data were retrieved from GeoTracker for 11 wells in the 

study area (table 2).

The fourth and final data source for petroleum wells 

was the USGS National Produced Waters Geochemical 

Database (USGS-PWDB), administered by the USGS Energy 

Resources Program. This database is a nationwide compilation 

of various individual databases and reports (Blondes and 

others, 2014). It contains geochemical data for produced-water 

samples plus ancillary well information. The USGS-PWDB 

contains data for inorganic (including TDS), trace element, 

and physical parameters for petroleum wells in California 

from 1937 to 1980. This database contains information on 

272 wells in the oil fields mapped for this report, including an 

undetermined number of wells that are also in the DOGGR 

archives (table 2). For the version (v2.1) of the USGSPWDB available at the time salinity maps were originally 

created, approximately 40 percent of the petroleum well 

entries for California were lacking data for top perforation, 

15 percent had no sample date, and about 10 percent were 

duplicates. The information is neither independently verified 

nor systematically checked for inconsistencies, but errors are 

corrected when noted by database users (Blondes and others, 

Table 2. Summary by data source of petroleum and water wells compiled for salinity mapping, central and southern California.

[Numbers in parenthesis represent the value shown as a percentage of the corresponding total number of wells. Abbreviations: CDWR-WDL, California 

Department of Water Resources, Water Data Library; DOGGR, California Division of Oil, Gas, and Geothermal Resources; DOGGR-UIC, California Division 

of Oil, Gas, and Geothermal Resources, Underground Injection Control; SWRCB, California State Water Resources Control Board; SWRCB-DDW, California 

State Water Resources Control Board, Division of Drinking Water; TDS, total dissolved solids; USGS-NWIS, U.S. Geological Survey, National Water 

Information System; USGS-PWDB, U.S. Geological Survey, Produced Waters Database; WRD, Water Replenishment District of Southern California; 

%, percent]

Primary database1 Well type

Number 

of 

wells

Number of 

wells with 

construction 

data2

Number and 

percentage of wells 

with multiple TDS3

entries

Number and percentage of 

wells wholly or partially 

represented by TDS calculated 

from specific conductance

Period of record 

for wells used in 

salinity mapping

DOGGR-UIC Petroleum 114 111 None None 1952–2013

DOGGR-online data Petroleum 764 763 100 (13%) None 1930–2014

SWRCB-GeoTracker Petroleum 11 11 2 (18%) None 2015

USGS-PWDB Petroleum 4

272 241 63 (23%) None 51937–80

CDWR-WDL Water 6

2,182 1,202 966 (44%) 797 (36%) 1930–2014

SWRCB-DDW Water 7

430 302 387 (90%) 27 (6%) 1978–2014

SWRCB-GeoTracker Water 8 8 8 (100%) None 2014–16

SWRCB-miscellaneous Water 98 68 None8 None 1994–2015

USGS-NWIS Water 9

698 612 225 (32%) 325 (46%) 1927–2014

WRD Water 10130 130 122 (94%) 3 (2%) 1998–2013

TOTALS 114,677 123,418 131,867 (40%) 1,152 (25%) —

1

Some wells have records in multiple databases.

2

Top perforation for petroleum wells, and bottom perforation, well depth, or hole depth for water wells.

3

Reported TDS or calculated TDS from specific conductance; wells with multiple values represented by the median.

4

Includes an undetermined number of wells that are also in the DOGGR archives.

5

Information on sample dates incomplete, so period of record may be longer.

6

Includes 74 wells that are also in other listed data sources.

7

Includes 100 wells that are also in other listed data sources.

8

Multiple records available for an undetermined number of wells. Only most recent analysis used for salinity mapping.

9

Includes six wells that are also in other listed data sources.

10Includes 81 wells that are also in other listed data sources.

11Number of unique wells, not counting those present in multiple data sources: 1,131 petroleum and 3,546 water wells.

12Number of unique wells, not counting those present in multiple data sources: 1,096 petroleum and 2,322 water wells.

13Number of unique wells, not counting those present in multiple data sources: 159 petroleum and 1,708 water wells.
Methods 7

2014). The latest version of this database (v2.3) includes data 

for top perforation for several wells for which this information 

was previously unavailable (Blondes and others, 2017). 

These additional data were included in this report and salinity 

maps modified as necessary. The DOGGR archives were 

also queried for wells missing data for top perforation, which 

resulted in locating data for top perforation for all but 31 of the 

272 USGS-PWDB wells used for salinity mapping.

The first source for water-well data was a CDWR 

database referred to as the Water Data Library (WDL). This 

source contains inorganic chemistry data for groundwater 

and surface-water samples dating back to 1930. The WDL is 

a publicly accessible online database that can be searched by 

map-based interface, by county, or by site (station name or 

number; California Department of Water Resources, 2015b). 

Data in the WDL for TDS and specific conductance (primarily 

laboratory measurements) for 2,182 wells were used for 

salinity mapping, including 74 wells that are also in the other 

water-well databases (table 2). Well-construction information 

is not available in this database; however, bottom perforation, 

well depth, and (or) hole depth data for 1,202 of the CDWRsampled wells were found in well drillers’ logs compiled by 

CDWR and in USGS National Water Information System 

(NWIS) and SWRCB databases.

The SWRCB was the second major source of waterwell data, comprised of several individual sources including 

the SWRCB Division of Drinking Water (SWRCB-DDW), 

GeoTracker, and miscellaneous sources. The SWRCB-DDW 

database contains water analyses for public-supply wells 

located throughout the State (California State Water Resources 

Control Board, 2015). Total dissolved solids and specific 

conductance data for 430 public-supply wells available in 

the SWRCB-DDW database were used for salinity mapping 

(table 2). Although well-construction data is not available 

in the SWRCB-DDW geochemical database, a separate 

database referred to as the California Drinking Water Source 

Assessment and Protection Program (CADWSAP), obtained 

from the SWRCB in 2015, contains limited well-construction 

data (top perforation and screen length) for 191 of the 

SWRCB-DDW wells used for salinity mapping. Depth to 

bottom perforation for these particular wells was estimated as 

the sum of depth to top perforation and screen length based 

on the assumption that the screened interval was continuous. 

Well-construction information for an additional 111 wells was 

located in other data sources used for this report. The SWRCB 

GeoTracker database contains water analyses for samples 

from monitoring wells in areas requiring cleanup as a result 

of activities that have affected or may affect groundwater 

quality (California State Water Resources Control Board, 

2016). This database includes TDS and specific conductance 

data for eight wells used for salinity mapping (table 2). 

Miscellaneous SWRCB data sources accounted for TDS and 

specific conductance data from 98 wells used for monitoring 

or water supply in support of oil and gas production. These 

miscellaneous data sources included electronic submission 

of information (ESI) reports, groundwater management plans 

(GMP), and historical data sets submitted to the SWRCB by 

oil and gas producers. The ESI and GMP documents included 

well-construction information for most of the wells used for 

salinity mapping.

The third source of data for water wells used for salinity 

mapping was the USGS NWIS, a repository for the storage 

of all data collected by the USGS to document, describe, and 

measure water-resource conditions (U.S. Geological Survey, 

2015). Total dissolved solids and specific conductance data 

are available for 698 wells used for salinity mapping, of 

which 612 wells had pertinent construction information, 

either bottom perforation depth, completed well depth, or hole 

depth (table 2). The NWIS also contains well-construction 

information for 700 WDL wells having TDS and specific 

conductance data used for salinity mapping.

The WRD database was the fourth and final source of 

data from water wells used for salinity mapping. Data were 

provided by WRD in the form of a Microsoft Access file on 

August 7, 2013. This dataset represents a compilation of 

location, well type, construction, geologic formation, and 

inorganic chemical analyses from various sources, including 

USGS, CDWR, WRD, and local water agencies for about 

2,500 wells located in the Los Angeles Basin. For the 

purposes of this report, TDS and specific conductance data 

from 130 wells located in and around the Montebello, Santa 

Fe Springs, and Wilmington fields, including 81 wells also 

available in the previously described data sources, were used 

for salinity mapping (table 2).

 The resulting data compiled for this study, including 

metadata, are available as a USGS data release (Metzger and 

others, 2018).

Data Processing

Salinity datasets were assembled for all wells having 

TDS or specific conductance data and organized by well type: 

(1) production and injection petroleum wells and (2) water 

wells (supply and monitoring). In addition to TDS and specific 

conductance, pertinent information extracted and compiled 

for both well types included data source, well identifier, 

relevant oil field, well location, well-construction information 

(particularly perforation depths), and land-surface altitude. 

Land-surface altitudes were estimated using a USGS 30-meter 

digital elevation model (DEM) in ArcGIS based on well 

location. For petroleum wells, depth to the top perforation was 

the primary well-construction attribute of interest because it 

potentially represents the closest depth of oil/gas production 

activities to overlying aquifers. For water wells, depth to the 

bottom perforation was the primary well-construction attribute 

of interest because it potentially represents the maximum 

depth at which water may be currently extracted for beneficial 

use. Although sample data from water and petroleum wells 

may represent mixtures of water from large vertical perforated 

intervals, the bottom perforations of water wells and top 

perforations of petroleum wells are the bounding values for 

the depths those samples represent.
8 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Salinity Data

Total dissolved solids and specific conductance data 

compiled for the salinity datasets represent all values that were 

available at the time reconnaissance salinity mapping was 

undertaken for this report. For the purposes of data processing 

and mapping, data for petroleum and water wells were handled 

separately, but within each dataset, wells were grouped 

regardless of well subtype or data source. For example, all 

petroleum wells, whether identified as being used for injection 

and obtained from the UIC database or identified as being 

used for production and obtained from the USGS-PWDB or 

DOGGR-Well Finder, were combined into a single dataset. 

Among the data available were multiple TDS and (or) specific 

conductance analyses from different sampling dates. For 

petroleum wells, approximately 14 percent of wells included 

TDS and (or) specific conductance for more than one date. 

For water wells, approximately 48 percent of wells included 

data for multiple dates, with about 9 percent of such wells 

(314) having TDS and (or) specific conductance spanning at 

least 25 years (Metzger and others, 2018). For those particular 

wells, mapped TDS values represent the median for the 

entire record, irrespective of the beginning and ending date 

or overall length of record. These median values are included 

in the USGS data release for this study (Metzger and others, 

2018). For the SWRCB-miscellaneous data, time-series data 

exist but were not readily available for salinity mapping; 

the data used represented the most recently measured TDS 

or specific conductance data reported (table 2). For all other 

data sources, mapped TDS values represent a single discrete 

sample for a particular date (some dates in the USGS-PWDB 

are not specified).

As noted previously, TDS data were not available 

for all wells. Although TDS data were available for all 

petroleum wells used for salinity mapping, approximately 

25 percent of water wells were lacking TDS data for all or 

at least some sample dates. Specific conductance, a measure 

of water’s ability to conduct an electrical current, is a good 

approximation of the salinity of natural waters (Drever, 1982). 

For water wells wholly (no samples with TDS analyses) 

or partially (selected dates within period of record without 

TDS analyses) lacking reported TDS, specific conductance 

was used to calculate TDS. A simple linear regression 

model (ordinary least squares; Helsel and Hirsch, 2002) was 

developed for each of four combinations of hydrogeologic 

province (Belitz and others, 2003) and DOGGR district 

where the two coincided: (area 1) the Transverse and Selected 

Peninsular Ranges hydrogeologic province and DOGGR 

District 1, (area 2) the San Joaquin Valley part of the Central 

Valley hydrogeologic province and DOGGR District 4, 

(area 3) the Sierra Nevada hydrogeologic province and 

DOGGR District 4, and (area 4) the Southern Coast Ranges 

hydrogeologic province and DOGGR District 3 (fig. 2). 

The simple linear regression models for areas 1, 2, 3, and 

4 used approximately 38,110, 8,010, 165, and 8,674 pairs 

of data from all data sources for 7,001, 3,526, 137, and 

3,048 wells, respectively, located throughout the four areas 

irrespective of oil field. Data pairs used to derive this relation 

were included in the regression model only if (1) TDS was 

less than 50,000 mg/L, (2) computed values for TDS were 

within 25 percent of measured values for TDS, and (3) TDS 

ranged between 0.55 and 0.81 percent of the value of specific 

conductance. The third criteria used to qualify the data used 

in this report represents the expected range of the ratio of 

TDS to specific conductance for most natural waters and is 

a recommended quality-assurance check for computed TDS 

(Friedman and Erdmann, 1982). Slightly different ranges 

for this ratio have been cited for use as a general qualityassurance check (0.55–0.75; Hem, 1985) and for measured 

TDS determined by residue on evaporation at 180 °C (0.55–

0.86; Friedman and Erdmann, 1982). The resulting regression 

equations for the four areas (area 1, equation 1; area 2, 

equation 2; area 3, equation 3; area 4, equation 4), with the 

intercept set to zero and R-squared values between 0.98 and 

1, were used to calculate TDS for analyses in the water-well 

salinity dataset based on reported specific conductance:

TDS = 0.6888SC (1)

TDS = 0.718SC (2)

TDS = 0.6527SC (3)

TDS = 0.6825SC (4)

where

SC is the reported specific conductance in 

microsiemens per centimeter (μS/cm) at 

25 °C, and

TDS is the calculated TDS in mg/L.

Subsets of wells and their associated data for the 

31 oil fields and surrounding buffer areas within 2 miles of 

administrative field boundaries included 1,131 petroleum 

wells and 3,546 water wells (table 3). A small number of 

wells (26) were represented by multiple (2–3) discrete 

samples collected at unique depths within the same well. 

The petroleum wells selected for the mapped fields were 

located within the administrative boundaries of each field. 

These boundaries mark the areal extent, both on and offshore, 

of an oil or gas field within which all producing wells are 

located. Petroleum wells in the Wilmington field (Los Angeles 

Basin subregion) identified as being located offshore were 

omitted from salinity mapping. The water wells selected for 

the mapped fields were located both within and outside the 

administrative field boundaries (version dated November 19, 
Methods 9

GARLOCK FAULT

SAN ANDREAS FAULT

SANTA YNEZ FAULT

SAN GABRIEL FAULT

WHITE WOLF FAULT

Basin and Range

Sierra

Nevada

Mojave

Desert

Transverse and Selected

Peninsular ranges

Data sources: DOGGR, 2014a 

(district boundaries); DOGGR, 2014b 

(oil field boundaries)

Belitz and others, 2003 

(hydrogeologic provinces)

120°30' 118°30'

36°00'

34°00'

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

Pacific Ocean

NWB

NEB

CB

SWB

SSB

MTS

WFB

District 1District 1

District 4District 4

District 3District 3

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

EXPLANATION

Oil fields included in this study by subregion

Kern Sierran Foothills

East Kern Valley Floor

Middle Kern Valley Floor

South Kern Valley Margin

West Kern Valley Floor

West Kern Valley Margin

Los Angeles Basin

Central Coast Basin

Division of Oil, Gas, and Geothermal 

Resources (DOGGR) District boundary

Significant fault

SWB

CB

NEB

SSB

WFB

MTS

NWB

San Joaquin Valley features

Geologic structure boundary

Southern Sierran block

West-side fold belt

Maricopa-Tejon subbasin

Bakersfield Arch

Los Angeles Basin features

Geologic structure boundary

Southwestern block

Central block

Northeastern block

Northwestern block

Southern Coast Ranges

San Joaquin Valley

Central Valley

(San Joaquin Valley part)

Figure 2. Major geographic and geological features and Division of Oil, Gas, and Geothermal Resources (DOGGR) district boundaries, 

central and southern California. Broader colorized land areas underlying study subregions represent hydrogeologic provinces.
10 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

2014, and downloaded December 1, 2014, from http://www.

conservation.ca.gov/dog/maps/Pages/GISMapping2.aspx) to a 

distance of up to 2 miles. The exception was the Wilmington 

field, where well selection was limited to a 1-mile buffer area 

to avoid including what would have constituted a majority 

of water wells within the administrative field boundaries of 

several adjacent unmapped fields with a 2-mile buffer. The 

designation of a buffer area around each mapped field was 

done with the idea that the effects of oil and gas activities 

could laterally extend some distance outward beyond 

administrative field boundaries. Where mapped fields were 

adjacent or in proximity with each other, overlapping buffer 

areas resulted in some water wells being used for salinity 

mapping for more than one field. A geographic information 

system (GIS) and its associated ArcGIS tools was used to 

delineate the areal extent of the buffers and identify which 

wells were located within administrative field boundaries 

and the surrounding buffer area for each mapped field. The 

resulting data compiled for this study, including metadata, are 

available as a USGS data release (Metzger and others, 2018).

Well-Construction Data

Wells that were compiled as part of the data processing 

step, but that were missing pertinent information needed 

for salinity mapping, were referred to as unattributed. For 

petroleum wells, the top perforation was not available for a 

relatively small number of wells, ranging from about 1 percent 

(Edison and Fruitvale fields) up to 40 percent (Santa Fe 

Springs field) for 12 of the 29 aggregated fields (table 3). 

For the remaining 17 aggregated fields, top perforation was 

known for all petroleum wells. For the purposes of this 

report, petroleum wells missing top perforation (unattributed) 

information were assigned a value representing the median 

top perforation for all attributed wells located within the same 

field as the unattributed wells.

Unattributed water wells were dealt with somewhat 

differently than petroleum wells. Bottom perforation was 

the preferred attribute for water wells, but it was available 

for only 36 percent (1,268) of the 3,546 compiled water 

wells. An additional 197 wells (including 191 with SWRCBDDW as the primary TDS data source and 2 wells with 

CDWR-WDL as the primary TDS data source, but also 

available in SWRCB-DDW) had top perforation and reported 

screen length data from which an approximate bottom 

perforation could be estimated. Wells lacking any perforation 

information but having completed well depth and (or) hole 

depth numbered 857. Given that for most water wells the 

completed well depth and hole depth are typically not much 

deeper than the bottom perforation, these were considered 

acceptable substitutions. Even allowing for estimated bottom 

perforation and completed well or hole depth substitutions, 

1,224 (35 percent) of all water wells compiled had insufficient 

construction information. Instead of perforation data, or 

acceptable alternatives, values representing the median bottom 

perforation for attributed wells were assigned to all of the 

1,224 unattributed wells on a field-by-field basis (table 3). 

A number of the salinity mapped fields, particularly in Kern 

County, share the same water wells within overlapping 

buffer areas. For the purposes of this report, each field and 

its associated well data were treated independently. As a 

result, the median value assigned to unattributed water wells 

was as much as several hundred feet different in adjacent 

fields despite having overlapping buffer areas. However, in 

comparison with depths of petroleum wells, these uncertainties 

in estimated water-well depths had relatively little effect on 

aggregate salinity profiles for oil field areas.

Salinity Mapping and Depth-to-TDS Profile Plots

The results of this reconnaissance salinity mapping 

study are displayed through a series of maps and profile 

plots. ArcGIS was used to determine which wells to include 

for mapping salinity for each priority oil/gas field based on 

geographic location as described earlier. Once wells were 

assigned to the relevant field, or fields in the case of water 

wells located within overlapping buffer areas, they were 

categorized based on depth (perforation depth, or well or 

hole depth instead of bottom perforation for water wells) and 

TDS concentration. Depth classifications portrayed as top 

perforation (petroleum wells) or bottom perforation, well 

depth, or hole depth (water wells) relative to land surface 

include less than 1,000 ft, 1,000–2,000 ft, 2,001–5,000 ft, and 

greater than 5,000 ft. On the salinity maps, these depths are 

represented by a triangle, circle, square, and inverted triangle, 

respectively. Total dissolved solids classifications and their 

corresponding descriptions (shown in parentheses) include less 

than 1,000 mg/L (fresh), 1,000–3,000 mg/L (mildly saline), 

3,001–10,000 mg/L (moderately saline), and greater than 

10,000 mg/L (very saline, if less than 35,000 mg/L, to brine, 

if greater than 35,000 mg/L; Stanton and others, 2017). These 

categories are represented on the salinity maps by the depth 

symbols colored blue, green, orange, and red, respectively. 

Salinity maps for all subregions show petroleum and water 

wells on separate figures to help distinguish well type, depth, 

and TDS classifications where well density is high.
Table 3. Summary for each oil field of the number of wells, median perforation depth and altitude, range and median total dissolved solids (TDS) valuTDS greater than 3,000 and 10,000 mg/L for petroleum and water wells, central and southern California`[Values for water wells in some adjacent fields may be identical owing to mapping wells shared by overlapping buffer areas. Depths are below land surface. Altitudes are referenVertical Datum of 1988 (NAVD 88). Total dissolved solids minimum, maximum, and median values highlighted in orange and red represent values greater than 3,000 and 10,00Abbreviations: bls, below land surface; DOGGR, California Division of Oil, Gas, and Geothermal Resources; ft, feet; mg/L, milligram per liter; na, not applicable; >, greater th

Subregion Field1 Well type Number of wells

Wells 

with 

construction 

data

Percentage 

of wells with 

construction 

data

Median 

perforation 

depth

(ft)2

Median 

perforation 

altitude

(ft)3

Petroleum 

well 

highest top perforation 

altitude

(ft)

Water well 

lowest bottom 

perforation 

altitude 

(ft)4

TDS 

minimum

(mg/L)

TDS 

maximum

(mg/L)

TDS 

median

(mg/L)

DOGGR District 4

Kern Sierran 

Foothills Jasmin Water 42 23 55 61,602 –1,066 — –2,993 212 1,010 341

Kern Sierran 

Foothills Jasmin Petroleum 3 3 100 2,784 –2,062 –1,896 — 482 6,090 500

Kern Sierran 

Foothills Kern Bluff Water 33 17 52 461 116 — –1,336 146 2,384 459

Kern Sierran 

Foothills Kern Bluff Petroleum 7 7 100 1,070 –339 –44 — 572 1,300 644

Kern Sierran 

Foothills Kern Front Water 159 92 58 6686 –180 — –1,142 139 2,077 445

Kern Sierran 

Foothills Kern Front Petroleum 31 31 100 2,321 –1,665 –853 — 386 2,318 1,049

Kern Sierran 

Foothills Kern River Water 123 80 65 670 –161 — –1,336 111 2,384 295

Kern Sierran 

Foothills Kern River Petroleum 82 82 100 941 –322 501 — 240 25,500 745

Kern Sierran 

Foothills Mount Poso Water 13 7 54 6600 493 — –244 115 2,480 372

Kern Sierran 

Foothills Mount Poso Petroleum 42 41 98 1,660 –468 619 — 206 4,566 1,391

Kern Sierran 

Foothills Poso Creek Water 121 76 63 920 –385 — –1,371 130 3,712 297

Kern Sierran 

Foothills Poso Creek Petroleum 57 57 100 2,558 –1,857 –377 — 570 13,100 1,341

Kern Sierran 

Foothills

Round Mountain Water 14 6 43 6308 255 — 116 160 2,480 750

Kern Sierran 

Foothills

Round Mountain Petroleum 17 17 100 1,675 –622 –82 — 854 16,300 2,150
Subregion Field1 Well type Number of wells Wells with construc- tion data Percentage of wells with construction data Median perfo- ration depth (ft)2 Median perfo- ration altitude (ft)3 Petroleum well highest top perforation altitude (ft) Water well lowest bottom perforation altitude (ft)4 TDS mini- mum (mg/L) TDS maximum (mg/L) TDS median (mg/L) 

DOGGR District 4—Continiued East Kern Valley Floor Edison Water 507 280 55 600 –74 — –1,730 125 3,060 550 

East Kern Valley Floor Edison Petroleum 67 66 99 3,415 –2,841 291 — 444 20,775 1,664 East Kern Valley Floor Fruitvale Water 456 321 70 583 –182 — –752 97 2,377 242 

East Kern Valley Floor Fruitvale Petroleum 98 97 99 3,624 –3,220 –2,404 — 632 24,930 3,699 East Kern Valley Floor Mountain View Water 570 285 50 600 –129 — –1,537 92 3,060 459 

East Kern Valley Floor Mountain View Petroleum 40 40 100 6,099 –5,646 –2,459 — 900 39,900 4,880 East Kern Valley Floor Rosedale Water 146 91 62 6526 –181 — –722 110 2,377 332 

East Kern Valley Floor Rosedale Petroleum 4 4 100 4,836 –4,481 –3,095 — 28,000 38,515 31,882 East Kern 

Valley Floor

Rosedale Ranch Water 150 95 63 6610 –231 — –1,142 118 3,712 524

East Kern 

Valley Floor

Rosedale Ranch Petroleum 43 42 98 4,161 –3,789 –2,878 — 5,550 33,106 24,867

Table 3. Summary for each oil field of the number of wells, median perforation depth and altitude, range and median total dissolved solids (TDS) valuTDS greater than 3,000 and 10,000 mg/L for petroleum and water wells, central and southern California`—Continued[Values for water wells in some adjacent fields may be identical owing to mapping wells shared by overlapping buffer areas. Depths are below land surface. Altitudes are referenVertical Datum of 1988 (NAVD 88). Total dissolved solids minimum, maximum, and median values highlighted in orange and red represent values greater than 3,000 and 10,00Abbreviations: bls, below land surface; DOGGR, California Division of Oil, Gas, and Geothermal Resources; ft, feet; mg/L, milligram per liter; na, not applicable; >, greater th
Subregion Field1 Well type Number of wells

Wells 

with 

construction 

data

Percentage 

of wells with 

construction 

data

Median 

perforation 

depth

(ft)2

Median 

perforation 

altitude

(ft)3

Petroleum 

well 

highest top perforation 

altitude

(ft)

Water well 

lowest bottom 

perforation 

altitude 

(ft)4

TDS 

minimum

(mg/L)

TDS 

maximum

(mg/L)

TDS 

median

(mg/L)

DOGGR District 4—Continiued

Middle Kern 

Valley Floor

Canfield Ranch Water 120 96 80 6606 –266 — –452 92 826 187

Middle Kern 

Valley Floor

Canfield Ranch Petroleum 20 20 100 7,914 –7,567 –2,815 — 2,902 38,141 28,403

Middle Kern 

Valley Floor

Greeley Water 135 77 57 6510 –167 — –466 96 2,690 317

Middle Kern 

Valley Floor

Greeley Petroleum 23 22 96 11,390 –11,054 –2,865 — 10,825 39,029 19,815

Middle Kern 

Valley Floor

Rio Bravo Water 81 43 53 6422 –90 — –461 104 2,690 271

Middle Kern 

Valley Floor

Rio Bravo Petroleum 24 17 71 6,417 –6,089 –3,791 — 13,968 41,693 25,035

Middle Kern 

Valley Floor

Ten Section Water 45 38 84 688 –342 — –493 91 826 151

Middle Kern 

Valley Floor

Ten Section Petroleum 4 4 100 2,986 –2,661 –1,979 — 12,077 30,600 21,324

South Kern 

Valley Margin

San Emidio 

Nose Water 110 40 36 61,200 –673 — –2,058 424 3,042 1,094

South Kern 

Valley Margin

San Emidio 

Nose Petroleum 5 4 80 8,376 –7,823 –4,454 — 13,709 21,974 19,333

Table 3. Summary for each oil field of the number of wells, median perforation depth and altitude, range and median total dissolved solids (TDS) valuTDS greater than 3,000 and 10,000 mg/L for petroleum and water wells, central and southern California`—Continued[Values for water wells in some adjacent fields may be identical owing to mapping wells shared by overlapping buffer areas. Depths are below land surface. Altitudes are referenVertical Datum of 1988 (NAVD 88). Total dissolved solids minimum, maximum, and median values highlighted in orange and red represent values greater than 3,000 and 10,00Abbreviations: bls, below land surface; DOGGR, California Division of Oil, Gas, and Geothermal Resources; ft, feet; mg/L, milligram per liter; na, not applicable; >, greater th
Subregion Field1 Well type Number of wells Wells with construc- tion data Percentage of wells with construction data Median perfo- ration depth (ft)2 Median perfo- ration altitude (ft)3 Petroleum well highest top perforation altitude (ft) Water well lowest bottom perforation altitude (ft)4 TDS mini- mum (mg/L) TDS maximum (mg/L) TDS median (mg/L) 

DOGGR District 4—Continiued South Kern Valley Margin Tejon Water 68 40 59 1,070 –238 — –1,065 271 2,090 425 

South Kern Valley Margin Tejon Petroleum 15 15 100 5,370 –4,213 –994 — 1,084 21,700 7,000 South Kern Valley Margin Wheeler Ridge Water 50 22 44 61,109 –370 — –1,065 258 2,685 825 

South Kern Valley Margin Wheeler Ridge Petroleum 47 41 87 3,889 –2,383 519 — 3,749 46,139 21,944 South Kern Valley Margin Yowlumne Water 81 36 44 61,099 –514 — –2,058 350 3,800 1,192 South Kern Valley Margin Yowlumne Petroleum 1 1 100 4,202 –3,650 –3,650 — 17,000 17,000 17,000 West Kern Valley Floor Coles Levee, North and South Water 111 92 83 422 –128 — –841 105 9231,000 380 

West Kern Valley Floor Coles Levee, North and South Petroleum 18 18 100 8,815 –8,419 –1,249 — 4,508 36,985 24,549 West Kern 

Valley Margin

Belridge, North 

and South Water 82 51 62 238 253 — –226 2,300 48,000 9,750

West Kern 

Valley Margin

Belridge, North 

and South Petroleum 131 128 98 965 –384 552 — 560 48,262 19,506

Table 3. Summary for each oil field of the number of wells, median perforation depth and altitude, range and median total dissolved solids (TDS) valuTDS greater than 3,000 and 10,000 mg/L for petroleum and water wells, central and southern California`—Continued[Values for water wells in some adjacent fields may be identical owing to mapping wells shared by overlapping buffer areas. Depths are below land surface. Altitudes are referenVertical Datum of 1988 (NAVD 88). Total dissolved solids minimum, maximum, and median values highlighted in orange and red represent values greater than 3,000 and 10,00Abbreviations: bls, below land surface; DOGGR, California Division of Oil, Gas, and Geothermal Resources; ft, feet; mg/L, milligram per liter; na, not applicable; >, greater th
Subregion Field1 Well type Number of wells

Wells 

with 

construction 

data

Percentage 

of wells with 

construction 

data

Median 

perforation 

depth

(ft)2

Median 

perforation 

altitude

(ft)3

Petroleum 

well 

highest top perforation 

altitude

(ft)

Water well 

lowest bottom 

perforation 

altitude 

(ft)4

TDS 

minimum

(mg/L)

TDS 

maximum

(mg/L)

TDS 

median

(mg/L)

DOGGR District 4—Continued

West Kern 

Valley Margin

Cymric Water 4 1 25 8542 –73 — –73 901 11,900 2,359

West Kern 

Valley Margin

Cymric Petroleum 33 32 97 1,895 –999 225 — 1,607 29,000 16,767

West Kern 

Valley Margin

Elk Hills Water 84 70 83 6332 9 — –516 110 9231,000 1,438

West Kern 

Valley Margin

Elk Hills Petroleum 151 148 98 3,287 –2,603 –266 — 4,638 50,005 32,636

West Kern 

Valley Margin

Lost Hills Water 59 49 73 304 2 — –719 165 23,000 4,100

West Kern 

Valley Margin

Lost Hills Petroleum 66 66 100 1,720 –1,332 325 — 5,657 85,000 31,336

DOGGR District 1

Los Angeles 

Basin Montebello Water 261 180 69 336 –118 — –1,267 176 2,514 512

Los Angeles 

Basin Montebello Petroleum 3 3 100 5,500 –5,130 –2,123 — 25,677 27,583 25,690

Los Angeles 

Basin Santa Fe Springs Water 202 145 72 450 –319 — –1,363 200 2,490 580

Los Angeles 

Basin Santa Fe Springs Petroleum 5 3 60 5,991 –5,837 –4,197 — 13,059 33,000 18,114

Table 3. Summary for each oil field of the number of wells, median perforation depth and altitude, range and median total dissolved solids (TDS) valuTDS greater than 3,000 and 10,000 mg/L for petroleum and water wells, central and southern California`—Continued[Values for water wells in some adjacent fields may be identical owing to mapping wells shared by overlapping buffer areas. Depths are below land surface. Altitudes are referenVertical Datum of 1988 (NAVD 88). Total dissolved solids minimum, maximum, and median values highlighted in orange and red represent values greater than 3,000 and 10,00Abbreviations: bls, below land surface; DOGGR, California Division of Oil, Gas, and Geothermal Resources; ft, feet; mg/L, milligram per liter; na, not applicable; >, greater th
Subregion Field1 Well type Number of wells Wells with construc- tion data Percentage of wells with construction data Median perfo- ration depth (ft)2 Median perfo- ration altitude (ft)3 Petroleum well highest top perforation altitude (ft) Water well lowest bottom perforation altitude (ft)4 TDS mini- mum (mg/L) TDS maximum (mg/L) TDS median (mg/L) 

DOGGR District 1—Continued Los Angeles Basin Wilmington Water 330 244 74 282 –265 — –1,869 204 48,250 1,070 

Los Angeles Basin Wilmington Petroleum 118 111 94 3,124 –3,109 –2,318 — 10,258 38,886 30,957 DOGGR District 3 Central Coast Basin Santa Maria Valley Water 471 373 79 6238 –52 — –1,199 127 6,840 901 

Central Coast Basin Santa Maria Valley Petroleum 6 6 100 4,798 –4,702 –1,683 — 8,000 84,891 24,742 — TOTALS Water 103,546 102,322 65 — — — — — — — 

— TOTALS Petroleum 111,161 1,126 97 — — — — — — — 

1Includes 2-mile buffer area around administrative boundaries of field with the exception of Wilmington where a 1-mile buffer was applied. 2Median of top perforation for petroleum wells and bottom perforation for water wells. Well or hole depth used in lieu of bottom perforation for individual water wells. 3Median of top perforation altitude for petroleum wells and bottom perforation altitude for water wells. Based on wells having reported top perforation for petroleum wells and 

or hole depth for water wells. 4Includes well depth or hole depth in lieu of bottom perforation. For several fields (Tejon and Wheeler Ridge), same well applies. 5Value collectively represents both water and petroleum wells within each field and is the minimum depth from average land-surface altitude at the wells, rounded to the neare

6Represents well or hole depth in lieu of sufficient perforation data. 7Not applicable. Threshold not encountered. 8Represents a single value.9Represents same well located within South Coles Levee field and adjacent to, but within buffer area, of Elk Hills field.10Total number of unique wells and not the sum of each field because some water wells were mapped more than once where buffer areas overlap adjacent mapped fields.11Includes 25 wells with a total of 52 unique sample depths.

Table 3. Summary for each oil field of the number of wells, median perforation depth and altitude, range and median total dissolved solids (TDS) valuTDS greater than 3,000 and 10,000 mg/L for petroleum and water wells, central and southern California`—Continued[Values for water wells in some adjacent fields may be identical owing to mapping wells shared by overlapping buffer areas. Depths are below land surface. Altitudes are referenVertical Datum of 1988 (NAVD 88). Total dissolved solids minimum, maximum, and median values highlighted in orange and red represent values greater than 3,000 and 10,00Abbreviations: bls, below land surface; DOGGR, California Division of Oil, Gas, and Geothermal Resources; ft, feet; mg/L, milligram per liter; na, not applicable; >, greater th
Results of Salinity Mapping by Geographic Subregion 17

In addition to regional-scale maps, profile plots of 

TDS concentration versus perforation depth, represented as 

altitude above the North American Vertical Datum of 1988 

(NAVD 88), were created for each field and grouped by 

subregion. Depths corresponding to the TDS concentrations 

were depicted as altitudes rather than depth below land surface 

(bls) to account for variations in both land-surface elevation 

and geological structural changes within fields and to be able 

to more directly compare differences in vertical distribution 

of TDS concentrations between nearby fields. Petroleum 

wells were generally represented by black symbols, with the 

exception of wells having uncertain locations and plotted 

based on township, range, and section to the corresponding 

centroid. A total of 27 wells having approximate locations 

were distinguished using a gray symbol. Water wells located 

within versus outside the administrative field boundaries were 

distinguished by using different symbol colors, red and green, 

respectively. Finally, the profile plots show the approximate 

altitude at which TDS concentration exceeds the 3,000 and 

10,000 mg/L thresholds. These are primarily based on the 

shallowest depth at which TDS equal to or greater than those 

concentrations is encountered. For some fields, denoted by 

an asterisk (*) on figures 6, 8, 10, 14, and 16, the altitudes of 

these thresholds were determined using regression analysis 

of TDS concentration versus perforation altitude. These were 

used for fields where the R-square value was 0.6 or greater 

and where these altitudes corresponded reasonably well with 

visually determined altitudes.

Results of Salinity Mapping by 

Geographic Subregion

Results of the salinity mapping in each of the studied 

fields are summarized in table 3, which shows (1) the number 

of wells with TDS data by type (petroleum and water) 

mapped for each field; (2) the number and percentage of 

wells with known top (petroleum wells) or bottom (water 

wells) perforation, well depth, or hole depth; (3) the median 

perforation depth in feet below land surface; (4) the mean 

perforation altitude relative to NAVD 88; (5) the minimum, 

maximum, and median TDS value for each field by well type; 

and (6) the approximate depth to TDS threshold values of 

3,000 and 10,000 mg/L.

Among the 31 individual fields or 29 aggregated fields 

studied (including combined entries for the North and South 

Coles Levee fields and the North and South Belridge fields), 

the median TDS concentration of produced water from 

petroleum wells ranged from 500 mg/L (for the Jasmin field in 

the Kern Sierran Foothills subregion) to 32,636 mg/L (for the 

Elk Hills field in West Kern Valley Margin subregion; table 3). 

Median TDS concentrations in produced water from petroleum 

wells were less than 10,000 mg/L in 11 of 29 aggregated 

fields, including 8 fields with median TDS concentrations 

less than 3,000 mg/L; these fields were located in the eastern 

part of the San Joaquin Valley in Kern County, specifically 

the Kern Sierran Foothills and East Kern Valley Floor 

subregions. Among fields having median TDS concentrations 

less than both threshold values, Kern Bluff and Kern Front 

in the Kern Sierran Foothills were the only fields where the 

maximum TDS concentration in produced water was less 

than 3,000 mg/L, at 1,300 mg/L (7 wells) and 2,318 mg/L 

(31 wells), respectively.

Among water wells, median TDS concentrations, either 

reported as TDS or calculated from specific conductance 

using equations 1–4, were less than 10,000 mg/L for all 

fields, ranging from 151 mg/L (for wells within 2 miles of the 

Ten Section field in Middle Kern Valley Floor subregion) to 

9,750 mg/L (for wells within 2 miles of the combined North 

and South Belridge fields in the West Kern Valley Margin 

subregion; table 3). The combined North and South Belridge 

fields and Lost Hills field were the only fields for which the 

median TDS concentration in water from wells was greater 

than 3,000 mg/L. However, the maximum TDS concentration 

in water wells was greater than 3,000 in 13 fields and 

greater than 10,000 mg/L in 6 fields. The three highest TDS 

concentrations among all wells used for reconnaissance 

salinity mapping were 87,500 mg/L (from water wells in 

the vicinity of the Elk Hills field in the West Kern Valley 

Margin subregion) and 161,730 and 231,000 mg/L (from 

overlapping buffer areas of the Elk Hills and the South 

Coles Levee fields in the West Kern Valley Margin and 

West Kern Valley Floor subregions, respectively; Metzger 

and others, 2018). These exceptionally high TDS values in 

groundwater in the southwestern San Joaquin Valley may 

be associated with infiltration from produced water disposal 

ponds (Bean and Logan, 1983). Alternatively or in addition, 

high TDS values may be the result of perched water subject 

to evaporative pumping or agricultural drainage ponds (Swain 

and Duell, 1993).

Results of reconnaissance salinity mapping for each of 

the eight geographic subregions (Kern Sierran Foothills, East 

Kern Valley Floor, Middle Kern Valley Floor, South Kern 

Valley Margin, West Kern Valley Floor, West Kern Valley 

Margin, Los Angeles Basin, and Central Coast Basin) are 

described in more detail below through a series of maps and 

field-specific depth-to-TDS profile plots grouped by subregion.
18 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Kern Sierran Foothills

Located to the north of Bakersfield, California, on the 

eastern side of the southern San Joaquin Valley (fig. 1), the 

Kern Sierran Foothills subregion includes the following 

seven oil fields: Jasmin, Kern Bluff, Kern Front, Kern River, 

Mount Poso, Poso Creek, and Round Mountain. These 7 fields 

included a widely varying number of petroleum and water 

wells with TDS data for each field; petroleum wells numbered 

between 3 (Jasmin) and 82 (Kern River), and within-field or 

assigned water wells located within 2 miles of administrative 

boundaries numbered between 6 (Round Mountain) and 

92 (Kern Front; table 3). The number of wells having 

perforation and (or) depth information (attributed) by type 

ranged from 98 percent (Mount Poso) to 100 percent (all other 

fields) of petroleum wells and 43 percent (Round Mountain) to 

65 percent (Kern River) of water wells.

Geologically, the Kern Sierran Foothills subregion 

coincides with the eastern part of a feature referred to as the 

Bakersfield Arch, a ridge of southwest-plunging basement 

rock (Sierran metamorphic and plutonic rocks) that separates 

two structural regions of the San Joaquin Valley, the southern 

Sierran block (SSB) and the Maricopa-Tejon subbasin (MTS; 

Bartow, 1991; Hosford Scheirer, 2007, chap. 5; fig. 2). The 

sedimentary rock that overlies this geologic feature consists 

primarily of sandstone and siltstone of Tertiary age and 

younger (Bartow and Pittman, 1983). The thickness of these 

deposits increases from about 1,000 feet (ft) at the eastern 

edge of the Mount Poso field to close to 8,000 ft at the western 

edge of the Poso Creek field (Hosford Scheirer, 2007, chap. 7). 

The primary stratigraphic units associated with these deposits, 

in ascending order and from older to younger, include the 

Walker Formation, Famoso sand of Edwards (1943), Vedder 

Sand, Freeman Silt–Jewett Sand, Round Mountain Silt 

(a member of the Monterey Formation), Santa Margarita 

Sandstone, the Chanac Formation, and the Kern River 

Formation. On the western side of this subregion, beginning in 

the vicinity of the Kern River field and increasing in thickness 

towards the west, is an additional formation of marine origin 

referred to as the Etchegoin, situated between the Chanac 

Formation (below) and the Kern River Formation (above). 

In the eastern part of the Kern Sierran Foothills subregion, 

roughly coinciding with the Round Mountain field and eastern 

part of the Mount Poso field, the Round Mountain Silt, Santa 

Margarita Sandstone, and the Chanac Formation pinch out 

and are replaced with the Olcese Sand, a formation that is 

commonly more saline than both the overlying and underlying 

units (Hosford Scheirer, 2007, chap. 13; Gillespie and others, 

2017). The Kern River Formation is nonmarine in origin and 

contains the most productive hydrocarbon-bearing intervals 

in the subregion (Hosford Scheirer, 2007, chap. 13). It has 

a maximum thickness of about 2,500 ft at its western edge 

(Bartow, 1983). Most water wells used for salinity mapping 

were completed at depths of less than 2,000 ft bls, with the 

deepest well perforated at just over 2,300 ft bls; therefore, 

most if not all are located within the Kern River Formation. In 

comparison, the deepest petroleum wells in the Kern Sierran 

Foothills subregion used for salinity mapping extend into the 

Famoso and Vedder sands beneath the Kern River field.

Groundwater in the Kern Sierran Foothills subregion can 

be characterized as having relatively low TDS concentrations 

(less than 3,000 mg/L), particularly in and around the Kern 

River and Kern Front fields, where many of the wells were 

shallow (less than 1,000 ft bls; figs. 3A–B). Total dissolved 

solids concentrations were generally higher in water from 

wells in the Round Mountain, Poso Creek, and Mount Poso 

fields, with a number of wells having concentrations between 

1,000 and 10,000 mg/L. Jasmin field, the most northerly field 

of the Kern Sierran Foothills subregion, included the deepest 

petroleum and water wells based on median perforation depth 

but the lowest overall TDS concentrations. Median TDS 

concentrations in produced water ranged from 500 mg/L 

(Jasmin field) to 2,150 mg/L (Round Mountain field). For 

water wells, median TDS concentrations in groundwater 

ranged from 295 mg/L (Kern River field) to 750 mg/L (Round 

Mountain field).

Profile plots of the vertical distribution of TDS show 

that produced-water samples generally have higher TDS than 

water-well samples, but there is considerable overlap in TDS 

concentrations between the two well types (fig. 4). The lower 

end of the range of TDS values in samples from petroleum 

wells overlaps the upper end of the range of TDS values in 

samples from water wells for all fields. The profile plots also 

show little to no separation (close vertical proximity) between 

the altitudes of perforations for petroleum and water wells for 

most of the fields. This is particularly true in the Kern River 

field and its adjacent buffer area, where the median altitude 

of the top perforation for mapped petroleum wells is –322 ft 

compared to a median altitude of the bottom perforation for 

mapped water wells of –161ft. For six of the seven fields 

and adjacent buffer areas, the shallowest top perforations of 

petroleum wells and deepest bottom perforations of water 

wells overlap (table 3). This means that a number petroleum 

wells are perforated closer to land surface than some water 

wells, although the majority of the water wells in question are 

located within the buffer area and outside of the administrative 

field boundaries. This vertical proximity may be the result 

of perforation placement with respect to where recoverable 

oil is located. In some fields, petroleum well perforations 

do not necessarily coincide with where oil is structurally or 

stratigraphically trapped, but rather where oil may be present 

as a result of upward migration. If a pathway is available 

for upward migration, oil has a tendency to ride on top of 

the water table as it fluctuates, thereby allowing it to reach 

altitudes corresponding with the perforation depths of water 

wells (Jan Gillespie, written commun., 2016). The largest 

vertical contrast is in the Kern Front and Poso Creek fields 

where the separation between the median perforation altitudes 

of petroleum and water wells is about 1,500 ft.
Results of Salinity Mapping by Geographic Subregion 19

Tulare County

Kern County

Kern RiverKern River

RattlesnakeRattlesnake Creek

Creek RancheriaRancheria

Poso CreekPoso Creek

Little Creek

Dyer CreekDyer Creek

Creek

Five DogFive Dog

Monotti Creek

Dead Ox Creek

Wildcat

Creek

Arrastre Creek

Coarse Gold River

White

Creek

99

155

155

178

184

118 224

99

65

46

99

43

43

58

58

119°15' 119°00'

35°45'

35°30'

0 2 4 6 KILOMETERS

0 2 4 6 MILES

Round

 Mountain

Kern

 Bluff

Mount

 Poso

Kern

 Front

Poso Creek

Jasmin

Kern

 River

A

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

3,001–10,000

>10,000

Figure 3. Distribution of total dissolved solids in A, produced water from petroleum wells, and B, water from water wells, for selected 

oil fields in the Kern Sierran Foothills subregion, central California.
20 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Tulare County

Kern County

Kern RiverKern River

RattlesnakeRattlesnake Creek

Creek RancheriaRancheria

Poso CreekPoso Creek

Little Creek

Dyer CreekDyer Creek

Creek

Five DogFive Dog

Monotti Creek

Dead Ox Creek

Wildcat

Creek

Arrastre Creek

Coarse Gold River

White

Creek

99

155

155

178

184

118 224

99

65

46

99

43

43

58

58

119°15' 119°00'

35°45'

35°30'

0 2 4 6 KILOMETERS

0 2 4 6 MILES

Round

 Mountain

Kern

 Bluff

Mount

 Poso

Kern

 Front

Poso Creek

Jasmin

Kern

 River

B

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

3,001–10,000

>10,000

Figure 3. —Continued
Results of Salinity Mapping by Geographic Subregion 21

Altitude, in feet above North Americam Datum of 1988

−6,000

−5,000

−4,000

−3,000

−2,000

−1,000

0

1,000

2,000

−6,000

−5,000

−4,000

−3,000

−2,000

−1,000

0

1,000

2,000

−6,000

−5,000

−4,000

−3,000

−2,000

−1,000

0

1,000

2,000

Total dissolved solids (TDS), in milligrams per liter (mg/L)

Total dissolved solids (TDS), in milligrams per liter (mg/L)

10 100 1,000 10,000 100,000

10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000

EXPLANATION

Range of land-surface altitudes at wells

Approximate minimum depth of TDS >3,000 mg/L 

Approximate minimum depth of TDS >10,000 mg/L

3,000 mg/L TDS concentration

Petroleum well (top perforation)

Water well within field (bottom perforation)

Water well outside field (bottom perforation)

Round Mountain

Kern River Mount Poso Poso Creek

Jasmin Kern Bluff Kern Front

−6,000

−5,000

−4,000

−3,000

−2,000

−1,000

0

1,000

2,000

−6,000

−5,000

−4,000

−3,000

−2,000

−1,000

0

1,000

2,000

−6,000

−5,000

−4,000

−3,000

−2,000

−1,000

0

1,000

2,000

−6,000

−5,000

−4,000

−3,000

−2,000

−1,000

0

1,000

2,000

10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000

Figure 4. Vertical distribution of total dissolved solids concentrations for mapped oil fields in the Kern Sierran Foothills subregon, 

central California.
22 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Median TDS concentrations for both petroleum and water 

wells in all seven fields were less than 3,000 mg/L, indicating 

that the water was fresh to mildly saline. In addition, TDS 

concentrations for all mapped wells in the Kern Bluff and 

Kern Front fields were less than 3,000 mg/L. Total dissolved 

solids concentrations were between 3,000 and 10,000 mg/L in 

7 percent of all petroleum wells (16 of 239) in the subregion 

used for mapping. These were distributed among five fields: 

Kern River (six), Round Mountain (three), Mount Poso 

(three), Poso Creek (three), and Jasmin (one; fig. 3A). Except 

for one water well located in the Poso Creek field buffer area, 

samples from water wells had TDS concentrations less than 

3,000 mg/L, with the majority (87 percent) of those less than 

1,000 mg/L (fig. 3B). Total dissolved solids concentrations 

greater than 10,000 mg/L were present in produced water 

from three petroleum wells in the Kern River field (including 

one well having samples from three distinct depths) and one 

petroleum well each in the Poso Creek and Round Mountain 

fields (Metzger and others, 2018). The top perforations or 

sample depths corresponding with these high TDS values 

ranged in altitude from about –1,000 to –5,000 ft. Based on 

this limited set of data points and using the shallowest depth of 

TDS greater than 10,000 mg/L as the criteria for designating 

where this threshold is met, an altitude of –1,000 ft is the 

approximate minimum depth of this threshold in the Kern 

River and Round Mountain fields, and –2,000 ft is the 

approximate minimum depth of this threshold in the Poso 

Creek field (fig. 4). These depths are 700 (Kern River field) to 

1,200 ft (Round Mountain field) below the deepest overlying 

(within-field) water wells but may not represent the deepest 

or typical depth of USDW in this subregion. According to 

Gillespie and others (2017), USDW extends to depths as 

great as 6,000 ft. This is supported by the profile plot for the 

Kern River field (fig. 4), which shows samples from four 

petroleum wells with TDS concentrations between 3,000 and 

10,000 mg/L. The top perforation of these particular wells 

ranged from –4,200 to –5,100 ft, placing them within the 

Vedder Sand unit, which in the Kern River, Kern Front, and 

Mount Poso fields is characterized by waters having relatively 

low salinity (Fisher and Boles, 1990).

East Kern Valley Floor

Encompassing the area around the city of Bakersfield, 

Calif., on the eastern side of the southern San Joaquin Valley 

(fig. 1), the East Kern Valley Floor subregion includes 

the following five oil fields: Edison, Fruitvale, Mountain 

View, Rosedale, and Rosedale Ranch. Wells used for 

mapping salinity across these 5 fields numbered between 

4 (Rosedale) and 98 (Fruitvale) petroleum wells and between 

146 (Rosedale) and 570 (Mountain View) water wells within 

or assigned to each field (table 3). The number of wells 

attributed with construction information by type ranged from 

98 percent (Rosedale Ranch) to 100 percent (Mountain View 

and Rosedale) of petroleum wells and 50 percent (Mountain 

View) to 70 percent (Fruitvale) of water wells.

Geologically, the East Kern Valley Floor subregion 

is located along and to the south of the Bakersfield Arch 

(fig. 2). The Rosedale, Rosedale Ranch, and Fruitvale fields 

straddle the crest of the Bakersfield Arch. The Edison and 

the Mountain View fields are located to the southeast of the 

Bakersfield Arch, and entirely within the Maricopa-Tejon 

subbasin (MTS). Depth to basement rock in the vicinity of 

the Rosedale, Rosedale Ranch, and Fruitvale fields ranges 

from about 8,000 to 12,000 ft bls (Hosford Scheirer, 2007, 

chap. 7). The overlying strata are similar to but deeper than 

fields to the northeast, owing to the greater depth to basement 

rock. In contrast to the Kern Sierran Foothills subregion, the 

Etchegoin and Kern River Formations are generally thicker 

in the East Kern Valley Floor subregion. This subregion 

also has an additional unit not present in the Kern Sierran 

Foothills subregion, referred to as the Fruitvale shale of Miller 

and Bloom (1939; a member of the Monterey Formation), 

situated between the Round Mountain Silt (below) and the 

Santa Margarita Sandstone (above; Hosford Scheirer, 2007, 

chap. 7). The nonmarine Chanac Formation is the principal 

hydrocarbon reservoir for the Rosedale Ranch and Fruitvale 

fields (Hosford Scheirer, 2007, chap. 13). The Fruitvale 

shale of Miller and Bloom (1939) is the principal reservoir 

in the Rosedale field (Division of Oil, Gas, and Geothermal 

Resources, 1998). In the vicinity of the Edison and Mountain 

View fields, depth to basement ranges between about 4,000 

to 10,000 ft bls (Hosford Scheirer, 2007, chap. 7). The 

Walker, Vedder, Freeman-Jewett, Olcese, Round Mountain, 

Fruitvale, Santa Margarita, Chanac, and Kern River 

stratigraphic units are present to various extents and tapped 

as hydrocarbon reservoirs in the Edison and Mountain View 

fields (Department of Oil, Gas, and Geothermal Resources, 

1998). Additionally, fractured schist, which forms part of 

the basement surface, also serves as a hydrocarbon reservoir 

under parts of both of these fields (Division of Oil, Gas, and 

Geothermal Resources, 1998; Hosford Sheirer, 2007, chap. 5).

Groundwater in the East Kern Valley Floor subregion 

can be characterized as spanning a greater range of TDS 

concentrations than the adjacent Kern Sierran Foothills 

subregion. Total dissolved solids concentrations in samples 

from most wells (70 percent) were less than 10,000 mg/L 

(figs. 5A–B). Total dissolved solids greater than 10,000 mg/L 

were only in samples from petroleum wells having relatively 

deep top perforations or sample depths greater than 

2,000 ft bls. Many of these wells are located in the Rosedale 

Ranch, Rosedale, and Mountain View fields. Median TDS 

concentrations in produced water from petroleum wells ranged 

from 1,664 mg/L (Edison) to 31,882 mg/L (Rosedale). For 

samples from water wells, median TDS concentrations ranged 

from 242 mg/L (Fruitvale) to 550 mg/L (Edison; table 3).
Results of Salinity Mapping by Geographic Subregion 23

Kern RiverKern River

RattlesnakeRattlesnake

Creek

Creek RancheriaRancheria

Poso CreekPoso Creek

CalienteCaliente

Creek

Walker

Basin

Creek

ComancheComanche

Creek

178

184

118

224

99

99

58

58

65

178

223

99

119

118

166

184

5

119°10' 119°00' 118°50'

35°30'

35°15'

0 2 4 6 MILES

0 2 4 6 KILOMETERS

Rosedale

 Ranch

Fruitvale Rosedale

Edison

Mountain

 View

A

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

3,001–10,000

>10,000

Wells having uncertainty with respect to location

Figure 5. Distribution of total dissolved solids in A, produced water from petroleum wells, and B, water from water wells, for selected 

oil fields in the East Kern Valley Floor subregion, central California.
24 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Kern RiverKern River

RattlesnakeRattlesnake

Creek

Creek RancheriaRancheria

Poso CreekPoso Creek

Basin

Creek

ComancheComanche

Creek

178

184

118

224

99

99

58

58

65

178

223

99

119

118

166

184

5

119°10' 119°00' 118°50'

35°30'

35°15'

0 2 4 6 MILES

0 2 4 6 KILOMETERS

Rosedale

 Ranch

Fruitvale

Rosedale

Edison

Mountain

 View

B

CalienteCaliente

Creek

Walker

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

3,001–10,000

>10,000

Figure 5. —Continued
Results of Salinity Mapping by Geographic Subregion 25

Profile plots of the vertical distribution of TDS show 

that produced-water samples generally had much higher TDS 

concentrations than water-well samples, as evidenced by 

relatively little overlap between the two well types (fig. 6). The 

exception is the Edison field, where approximately 40 percent 

of TDS concentrations in produced-water samples were 

similar (less than 3,000 mg/L) to all samples from withinfield water wells, possibly owing to the relatively shallow 

perforation depths (less than 2,000 ft bls) of those particular 

petroleum wells. The Edison field had the smallest vertical 

separation (about 2,800 ft) between mapped petroleum and 

water wells based on median altitudes of well perforation and 

(or) completed well depth (water wells; table 3). For several 

dozen petroleum wells in the Edison field, the top perforation 

was higher than the bottom perforation of numerous water 

wells, including some located within the administrative field 

boundaries (figs. 5, 6). Profile plots for the other four fields 

show larger vertical separation between the median perforation 

altitudes of petroleum and water wells. The largest vertical 

contrast is in the Mountain View field, where the separation 

between the median perforation altitudes of petroleum and 

water wells was about 5,500 ft (table 3).

Median TDS concentrations for both petroleum and 

water wells were less than 3,000 mg/L for only one of five 

fields (Edison). For all other fields, only water wells had 

median TDS concentrations less than 3,000 mg/L (table 3). 

Total dissolved solids concentrations were between 3,000 and 

10,000 mg/L in 32 percent of petroleum wells (81 of 252) in 

the East Kern Valley Floor subregion used for mapping. These 

petroleum wells were distributed among 4 fields: Fruitvale 

(57), Mountain View (13), Edison (8), and Rosedale Ranch 

(3; fig. 5A). Except for three water wells, two in the buffer 

area of Rosedale Ranch and one within the overlapping buffer 

areas of the Edison and Mountain View fields, samples from 

water wells had TDS concentrations less than 3,000 mg/L, 

with the majority (92 percent) of those less than 1,000 mg/L 

(fig. 5B). Total dissolved solids concentrations were greater 

than 10,000 mg/L in produced water from all petroleum 

wells in Rosedale, all but three petroleum wells in Rosedale 

Ranch, and approximately one-quarter of all petroleum 

wells in Mountain View. Smaller proportions of petroleum 

wells in both the Edison and Fruitvale fields, about 20 and 

5 percent, respectively, had TDS concentrations greater 

than 10,000 mg/L. The top perforations or sample depths 

corresponding with these high TDS values ranged in altitude 

from about –2,500 to –10,000 ft. In comparison, water wells 

were generally perforated at altitudes above –1,000 ft with 

the exception of the Edison field where the deepest bottom 

perforation was at about –1,700 ft (fig. 6). Using either the 

shallowest depth of TDS greater than 10,000 mg/L based 

on the actual perforation depth, or predicted depth based 

on regression analysis (Rosedale and Rosedale Ranch), the 

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

Total dissolved solids (TDS), in milligrams per liter (mg/L)

10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000

EXPLANATION

Range of land-surface altitudes at wells

Approximate minimum depth of TDS >3,000 mg/L 

Approximate minimum depth of TDS >10,000 mg/L

3,000 mg/L TDS concentration

Petroleum well (top perforation)

Petroleum well (top perforation), location uncertain

Water well within field (bottom perforation)

Water well outside field (bottom perforation)

Minimum depths to 3,000 and 10,000 mg/L TDS 

determined at least in part from regression −10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000

Rosedale* Rosedale Ranch*

Edison Fruitvale Mountain View

Altitude, in feet above North Americam Datum of 1988

Figure 6. Vertical distribution of total dissolved solids concentrations for mapped oil fields in the East Kern Valley Floor subregion, 

central California.
26 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

approximate minimum depth of TDS greater than 10,000 mg/L 

ranges from an altitude of about –1,300 ft (1,900 ft bls) 

in Rosedale to about –5,200 ft (5,600 ft bls) in Mountain 

View. All samples from water wells had TDS concentrations 

below the 10,000 mg/L threshold. Only a few water wells 

had TDS concentrations greater than 3,000 mg/L, with the 

highest concentration of about 3,800 mg/L in a sample from 

a well located almost 2 miles north of the Rosedale Ranch 

field (fig. 5B).

Middle Kern Valley Floor

The Middle Kern Valley Floor subregion is in the center 

of the southern San Joaquin Valley to the west of Bakersfield, 

Calif. (fig. 1), and includes the following four oil fields: 

Canfield Ranch, Greeley, Rio Bravo, and Ten Section. These 

four fields included a relatively small number of petroleum 

wells (4–24) within each field in comparison to the number of 

water wells located within or assigned to each field (45–135; 

table 3). The number of wells attributed by type ranged from 

71 percent (Rio Bravo) to 100 percent (Canfield Ranch and 

Ten Section) of petroleum wells and 53 percent (Rio Bravo) to 

84 percent (Ten Section) of water wells (table 3).

Geologically, the Middle Kern Valley Floor subregion 

overlies (Greeley) or is on the periphery of (Rio Bravo, Ten 

Section, and Canfield Ranch) the southwestern extent of the 

Bakersfield Arch (fig. 2). Depth to basement rock increases 

north to south from about 13,000 to 17,000 ft bls (Hosford 

Scheirer, 2007, chap. 7). The overlying strata from oldest 

to youngest are the Kreyenhagen Formation, Vedder Sand, 

Freeman Silt–Jewett Sand, member units of the Monterey 

Formation (Round Mountain Silt, Fruitvale shale of Miller and 

Bloom [1939], Stevens sand of Eckis [1940], and Reef Ridge 

Shale), the Chanac Formation (confined to eastern part of the 

subregion), the Etchegoin Formation, and the San Joaquin 

Formation (Gillespie and others, 2017; Hosford Scheirer, 

2007, chap. 13). The Monterey Formation is the primary 

hydrocarbon reservoir in the Middle Kern Valley Floor 

subregion, specifically the Fruitvale shale of Miller and Bloom 

(1939) in the Canfield Ranch, Greeley, and Ten Section fields, 

and Round Mountain Silt in the Rio Bravo field (Division 

of Oil, Gas, and Geothermal Resources, 1998). Additional 

hydrocarbon reservoirs include the Vedder and Jewett Sands 

in the Greeley and Rio Bravo fields, and the Etchegoin 

Formation in the Rio Bravo field (Division of Oil, Gas, and 

Geothermal Resources, 1998).

Groundwater in the Middle Kern Valley Floor 

subregion can be characterized as having a large contrast in 

TDS concentrations across all fields, owing to significant 

differences in depths between petroleum and water wells. All 

except two wells perforated at depths greater than 2,000 ft bls 

yielded samples with TDS concentrations greater than 

10,000 mg/L (figs. 7A–B). In contrast, all wells perforated 

at depths less than 1,000 ft bls yielded samples with TDS 

concentrations less than 3,000 mg/L, with the vast majority 

of those less than 1,000 mg/L. Median TDS concentrations 

in produced water were greater than 10,000 mg/L in all four 

fields, ranging from 19,815 mg/L (Greeley) to 28,403 mg/L 

(Canfield Ranch). For water wells, median TDS concentrations 

in groundwater were fresh in all four fields, ranging from 

151 mg/L (Ten Section) to 317 mg/L (Greeley; table 3).

Profile plots of the vertical distribution of TDS show 

that produced-water samples in the four mapped Middle 

Kern Valley Floor subregion fields all had much higher TDS 

concentrations than water-well samples, as evidenced by 

the complete lack of overlap between where samples plot 

for the two well types (fig. 8). In addition, the profile plots 

show a large vertical separation based on the median altitude 

of top perforation of petroleum wells versus median bottom 

perforation, completed well depth, or hole depth for water 

wells, ranging from about 2,300 ft for Ten Section to about 

10,900 ft for Greeley (fig. 8; table 3).

Total dissolved solids concentrations less than 

10,000 mg/L were present in all samples from water wells but 

in only 3 percent (2 of 71) of produced-water samples from 

petroleum wells. Overall, TDS concentrations in produced 

water ranged from 2,902 mg/L from a well in Canfield Ranch 

to 41,693 mg/L from a well in Rio Bravo (table 3). The top 

perforation of these wells ranged from altitudes of –2,000 to 

about –11,500 ft. In comparison, all water-well samples had 

TDS concentrations less than 3,000 mg/L and were from wells 

perforated at altitudes between 500 and –500 ft (fig. 8). Based 

on a combination of linear regression analysis (R-squared 

values between 0.57 and 0.84) and visual assessment, the 

approximate minimum depth marking the 10,000 mg/L 

threshold ranges from an altitude of about –2,000 ft (2,300 bls) 

in Ten Section to about –3,800 ft (4,100 bls) in Rio Bravo 

(table 3). Similarly, the approximate minimum depth of the 

3,000 mg/L threshold ranges from an altitude of about –700 ft 

(1,000 ft bls) in Ten Section to about –1,300 ft (1,600 ft bls) 

in Greeley. These altitudes for the 3,000 mg/L threshold in the 

four fields are deeper than the bottom perforation, completed 

well depth, or hole depth of all water wells used for salinity 

mapping in the Middle Kern Valley Floor subregion.
Results of Salinity Mapping by Geographic Subregion 27

Kern RiverKern River

43

58

65

223

119

5

99

58

43

119

5

119°15' 119°05'

35°30'

35°15'

0 2 3 4 KILOMETERS

0 2 3 4 MILES

A

Greeley

Rio

 Bravo

 Ten

 Section

Canfield

 Ranch

1

1

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

3,001–10,000

>10,000

Wells having uncertainty with respect to location

Figure 7. Distribution of total dissolved solids in A, produced water from petroleum wells, and B, water from water wells, for selected 

oil fields in the Middle Kern Valley Floor subregion, central California.
28 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Figure 7. —Continued

Kern RiverKern River

43

58

65

223

119

5

99

58

43

119

5

119°15' 119°05'

35°30'

35°15'

0 2 3 4 KILOMETERS

0 2 3 4 MILES

B

Greeley

Rio

 Bravo

 Ten

 Section

Canfield

 Ranch

1

1

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

3,001–10,000

>10,000
Results of Salinity Mapping by Geographic Subregion 29

Total dissolved solids (TDS), in milligrams per liter (mg/L)

10 100 1,000 10,000 100,000

EXPLANATION

Range of land-surface altitudes at wells

Approximate minimum depth of TDS >3,000 mg/L 

Approximate minimum depth of TDS >10,000 mg/L

3,000 mg/L TDS concentration

Petroleum well (top perforation)

Petroleum well (top perforation), location uncertain

Water well within field (bottom perforation)

Water well outside field (bottom perforation)

Minimum depths to 3,000 and 10,000 mg/L TDS 

determined at least in part from regression

10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000

Ten Section*

−12,000

−10,000

−8,000

−6,000

−4,000

−2,000

0

2,000

−12,000

−10,000

−8,000

−6,000

−4,000

−2,000

0

2,000

Canfield Ranch* Greeley*

−12,000

−10,000

−8,000

−6,000

−4,000

−2,000

0

2,000

Rio Bravo*

−12,000

−10,000

−8,000

−6,000

−4,000

−2,000

0

2,000

Total dissolved solids (TDS), in milligrams per liter (mg/L)

Altitude, in feet above North Americam Datum of 1988

Figure 8. Vertical distribution of total dissolved solids concentrations for mapped oil fields in the Middle Kern Valley Floor subregion, 

central California.
30 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

South Kern Valley Margin

Situated across the southern end of the San Joaquin 

Valley and bordering the junction of three geologic provinces 

(the Sierra Nevada, Transverse and Selected Peninsular 

Ranges, and Southern Coast Ranges; fig. 1), the South Kern 

Valley Margin subregion includes the following four oil fields: 

San Emidio Nose, Tejon, Wheeler Ridge, and Yowlumne. 

Wells used for mapping salinity across these 4 fields numbered 

between 1 (Yowlumne) and 47 (Wheeler Ridge) petroleum 

wells and between 50 (Wheeler Ridge) and 110 (San Emidio 

Nose) water wells within or assigned to each field (table 3). 

The number of wells attributed with depth data ranged from 

80 percent (San Emidio Nose) to 100 percent (Tejon and 

Yolumne) of petroleum wells and 36 percent (San Emidio 

Nose) to 59 percent (Tejon) of water wells (table 3).

Geologically, the South Kern Valley Margin subregion 

resides within the MTS (fig. 2), an area characterized by 

Cenozoic deposits that increase in thickness from the southeast 

towards the northwest (Hosford Scheirer, 2007, chap. 7). 

The thickness of these deposits, and thus depth to underlying 

basement rock, ranges from about 12,000 ft near the eastern 

end of the Tejon field to about 22,000 ft in the vicinity of the 

Yowlumne field (Hosford Scheirer, 2007, chap. 13). The White 

Wolf Fault separates the Tejon and Wheeler Ridge fields to 

the southeast from the San Emidio and Yowlumne fields to the 

northwest (fig. 2). The most productive hydrocarbon-bearing 

zones common to both the Tejon and Wheeler Ridge fields 

from oldest to youngest include the Freeman Silt–Jewett Sand, 

Olcese Sand, Round Mountain Silt, Fruitvale shale of Miller 

and Bloom (1939), and Santa Margarita Sandstone (Division 

of Oil, Gas, and Geothermal Resources, 1998). The most 

productive hydrocarbon-bearing zone common to both the 

San Emidio and Yowlumne fields is the Monterey Formation, 

particularly the Reef Ridge Shale (Division of Oil, Gas, and 

Geothermal Resources, 1998).

Groundwater in the South Kern Valley Margin subregion 

has a wide range of TDS concentrations. Total dissolved 

solids concentrations in samples from most wells (87 percent) 

were less than 10,000 mg/L (figs. 9A–B). This included 

about 29 percent (20 of 68) of petroleum wells and all (309) 

water wells. Total dissolved solids concentrations were 

generally highest across the Yowlumne, Wheeler Ridge, and 

San Emidio Nose fields, owing to the majority of petroleum 

wells in those fields yielding produced-water samples with 

concentrations more than 10,000 mg/L. Comparatively 

low TDS concentrations (less than 1,000 mg/L) were 

prevalent in samples from water wells within northern parts 

of the buffer areas for the Tejon and Wheeler Ridge fields 

(fig. 9B). In addition, about 30 percent of water wells with 

bottom perforation, completed well depth, or hole depth 

between 1,000 and 2,000 ft bls near the San Emidio Nose 

field yielded samples with TDS concentrations less than 

1,000 mg/L. Median TDS concentrations in produced water 

ranged from 7,000 mg/L (Tejon) to 21,944 mg/L (Wheeler 

Ridge). For water wells, median TDS concentrations in 

groundwater ranged from 425 mg/L (Tejon) to 1,192 mg/L 

(Yowlumne; table 3).

Profile plots of the vertical distribution of TDS show 

that concentrations in produced-water samples were almost 

all higher than water-well samples. Some produced-water 

samples from the Tejon field had TDS overlapping with values 

in water-well samples. In the two fields with a relatively 

high number of produced-water samples, Tejon and Wheeler 

Ridge, produced-water samples showed increasing TDS 

concentration with depth. In the Wheeler Ridge field, several 

petroleum wells were perforated at a higher altitude than 

associated water wells; this is because land-surface elevations 

differ by up to 1,500 ft between the hills in the western part of 

the field, where many of the petroleum wells are located, and 

the more gently sloping and lower elevations several miles 

to the north, outside of the administrative field boundaries, 

where many of the water wells are located (fig. 10). For the 

remaining three fields, the vertical separation based on the 

individual (Yowlumne, with only one well) or median altitude 

of top perforation of petroleum wells versus median bottom 

perforation, completed well depth, or hole depth for water 

wells ranged from about 3,100 ft for Yowlumne to about 

7,100 ft for San Emidio Nose (fig. 10; table 3).

Total dissolved solids concentrations exceeded 

10,000 mg/L in produced-water samples from all petroleum 

wells in the San Emidio Nose and Yowlumne fields, in 

produced-water samples from about three-quarters of 

the petroleum wells in the Wheeler Ridge field, and in 

produced-water samples from one-third of the petroleum 

wells in the Tejon field. Petroleum wells having TDS 

greater than 10,000 mg/L were perforated at altitudes of 

500 to –11,000 ft. Using either the shallowest depth of TDS 

greater than 10,000 mg/L based on the actual perforation 

depth, or predicted depth based on regression analysis 

(San Emidio Nose), the approximate minimum depth of 

TDS greater than 10,000 mg/L ranges from an altitude 

of about 500 ft (1,200 ft bls) in Wheeler Ridge to about 

–4,500 ft (5,000 ft bls) in San Emidio Nose. Groundwater 

samples from water wells had TDS concentrations generally 

less than 3,000 mg/L, with the exception of maximum 

concentrations of 3,800 mg/L and 3,042 mg/L in samples 

from water wells located in the buffer areas of the Yowlumne 

and San Emidio Nose fields, respectively (figs. 9B, 10). 

Based on these concentrations, the shallowest depth of TDS 

greater than 3,000 mg/L ranges from an altitude of about 

500 ft (1,200 ft bls) in Wheeler Ridge to about –1,500 ft 

(2,000 ft bls) in San Emidio Nose (fig. 10; table 3). The 

reported 3,000 and 10,000 mg/L thresholds in Wheeler Ridge 

are at the same depth, owing to the lack of samples with TDS 

concentrations between 3,000 and 10,000 mg/L from wells 

perforated shallower than the shallowest well having a TDS 

concentration greater than 10,000 mg/L (fig. 10).
Results of Salinity Mapping by Geographic Subregion 31

Ventura County

Kern CountyKern County Los Angeles

 County

Kern

River

Cuddy

Creek

Gorman Creek

Los AlamosCreek

Deadman

Creek

Seymour

Creek

AmargosaAmargosa

Creek

LockwoodLockwood Creek

North

Creek

Fork

LockwoodLockwood

Muddy

Creek

ComancheComanche Creek

Walker

Basin

Creek

166

5

166

5

118

223 223

184 224

43

99

99

119 119

119°15' 119°00'

35°15'

34°45'

0 4 6 8 KILOMETERS

0 4 6 8 MILES

A

2

2

Wheeler

 Ridge Tejon

San

 Emidio

 Nose

Yowlumne

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

3,001–10,000

>10,000

Wells having uncertainty with respect to location

Figure 9. Distribution of total dissolved solids in A, produced water from petroleum wells, and B, water from water wells, for selected 

oil fields in the South Kern Valley Margin subregion, central California.
32 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Figure 9. —Continued

Ventura County

Kern CountyKern County Los Angeles

 County

Kern

River

Cuddy

Creek

Gorman Creek

Los Alamos

Creek

Deadman

Creek

Seymour

Creek

AmargosaAmargosa

Creek

LockwoodLockwood Creek

North

Creek

Fork

LockwoodLockwood

Muddy

Creek

ComancheComanche Creek

Walker

Basin

Creek

166

5

166

5

118

223 223

184 224

43

99

99

119 119

119°15' 119°00'

35°15'

34°45'

0 4 6 8 KILOMETERS

0 4 6 8 MILES

B

2

2

Wheeler

 Ridge

Tejon

San

 Emidio

 Nose

Yowlumne

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

3,001–10,000

>10,000
Results of Salinity Mapping by Geographic Subregion 33

Total dissolved solids (TDS), in milligrams per liter (mg/L)

10 100 1,000 10,000 100,000

EXPLANATION

Range of land-surface altitudes at wells

Approximate minimum depth of TDS >3,000 mg/L 

Approximate minimum depth of TDS >10,000 mg/L

3,000 mg/L TDS concentration

Petroleum well (top perforation)

Petroleum well (top perforation), location uncertain

Water well within field (bottom perforation)

Water well outside field (bottom perforation)

Minimum depths to 3,000 and 10,000 mg/L TDS 

determined at least in part from regression

10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000

−12,000

−10,000

−8,000

−6,000

−4,000

−2,000

0

2,000

−12,000

−10,000

−8,000

−6,000

−4,000

−2,000

0

2,000

−12,000

−10,000

−8,000

−6,000

−4,000

−2,000

0

2,000

−12,000

−10,000

−8,000

−6,000

−4,000

−2,000

0

2,000

Yowlumne

San Emidio Nose* Tejon Wheeler Ridge

Total dissolved solids (TDS), in milligrams per liter (mg/L)

Altitude, in feet above North Americam Datum of 1988

Figure 10. Vertical distribution of total dissolved solids concentrations for mapped oil fields in the South Kern Valley Margin subregion, 

central California.
34 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

West Kern Valley Floor

The West Kern Valley Floor subregion is located slightly 

west of the center of the southern San Joaquin Valley floor 

(fig. 1) and includes the North and South Coles Levee fields. 

These two oil fields were combined for the purposes of salinity 

mapping because of their proximity as adjoining fields. The 

North and South Coles Levee fields directly abut the Elk 

Hills field in the adjacent West Kern Valley Margin subregion 

to the west; thus for the purposes of salinity mapping, these 

fields share many of the same within- and outside-field water 

wells (45) as a result of overlapping 2-mile buffer areas. Total 

dissolved solids and (or) specific conductance analyses were 

available for 18 petroleum wells and 111 water wells (table 3). 

All petroleum wells and 83 percent of water wells were 

attributed with perforation or well depth information (table 3).

Geologically, the West Kern Valley Floor subregion 

resides at the junction of three structural regions of the 

southern San Joaquin Valley, the SSB, MTS, and west-side 

fold belt (WFB; Bartow, 1991). This junction also coincides 

with the west end of the Bakersfield Arch (Bartow, 1991). The 

thickness of Cenozoic strata in this subregion ranges between 

16,000 and 20,000 ft and generally increases from north to 

south (Hosford Scheirer, 2007, chap. 7). The most productive 

hydrocarbon-bearing zones include the Kreyenhagen, 

Monterey, and Etchegoin Formations in North Coles Levee 

and the Etchegoin and San Joaquin Formations in South Coles 

Levee (Division of Oil, Gas, and Geothermal Resources, 

1998). Among these formations, the Monterey is the only 

reservoir for petroleum; the others are reservoirs for natural 

gas (Division of Oil, Gas, and Geothermal Resources, 1998).

Groundwater in the West Kern Valley Floor subregion 

can be characterized as having a large contrast in TDS 

concentrations particularly among samples from water wells 

(figs. 11A–B). Median TDS concentrations were 380 mg/L 

for samples from water wells to 24,549 mg/L in producedwater samples from petroleum wells (table 3). The majority 

of petroleum wells (16 of 18) had TDS concentrations 

greater than 10,000 mg/L (fig. 11A). Total dissolved solids 

concentrations in samples from most water wells (102 of 

111) were less than 10,000 mg/L. Total dissolved solids 

concentrations from the remaining nine water wells (not 

all visible on fig. 11B because five wells plot in the same 

locations as other wells), were as high as 231,000 mg/L 

(table 3). All of these nine wells were outside of and to the 

southwest of the administrative field boundaries (fig. 11B). 

The source of high TDS concentrations in samples from these 

water wells is unknown but could potentially be associated 

with infiltration of evaporatively concentrated produced 

water from formerly used, unlined disposal ponds, as has 

been discussed in previous studies in the region (Bean and 

Logan, 1983). Degradation of water quality may also be 

associated with agricultural practices including the application 

of imported water for irrigation, resulting in downward 

leaching of salts from the root zone to the water table and 

infiltration of evaporatively concentrated irrigation water from 

agricultural sumps (Swain and Duell, 1993). Regardless of the 

source, data in this area indicate that depth to groundwater is 

shallow, and salinity, as represented by electrical conductivity 

(EC), is elevated. Contour maps from 2013 (the latest year 

available) and earlier indicated that depth to water in much 

of the West Kern Valley Floor subregion was 10–15 ft bls, 

and even shallower at 5–10 ft bls to the southwest, coinciding 

with the highest TDS samples from water wells (California 

Department of Water Resources, 2017). Electrical conductivity 

of shallow groundwater in this subregion was as high as 

20,000 microsiemens per centimeter (μS/cm; California 

Department of Water Resources, 2017).

A profile plot of the vertical distribution of TDS shows 

overlap between TDS values of produced water and waterwell samples, owing to the very large range of TDS values for 

groundwater from water wells, particularly those outside of the 

North and South Coles Levee fields, coupled with a relatively 

narrow range of TDS values for produced waters (fig. 12). 

The shallowest depth for petroleum wells with TDS greater 

than 10,000 mg/L was at an altitude of –1,200 ft. This altitude 

corresponds to a depth of about 1,500 ft bls and translates 

into vertical separation of about 700 ft between the shallowest 

top perforation for a mapped petroleum well and the deepest 

bottom perforation or completed well depth for a mapped 

within-field water well. Total dissolved solids concentrations 

of groundwater from water wells within these fields were less 

than 3,000 mg/L, with the exception of samples from three 

water wells with concentrations up to almost 5,300 mg/L. 

These wells were relatively shallow with completed depths 

between 52 and 682 ft (Metzger and others, 2018). Based on 

TDS concentrations of samples from petroleum and water 

wells located within the administrative boundaries of the 

North and South Coles Levee fields, thresholds for 3,000 

and 10,000 mg/L are at about 300 ft (near land surface) and 

–1,200 ft (1,500 ft bls), respectively (fig. 12).
Results of Salinity Mapping by Geographic Subregion 35

Kern RiverKern River

43

119

5

119

5

119°20' 119°15'

35°20'

35°15'

0 2 3 KILOMETERS

0 2 3 MILES

A

1

1

South Coles Levee

North Coles Levee

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

3,001–10,000

>10,000

Figure 11. Distribution of total dissolved solids in A, produced water from petroleum wells, and B, water from water wells (not all 

wells visible because five wells plot in the same locations as other wells), for selected oil fields in the West Kern Valley Floor subregion, 

central California.
36 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Kern RiverKern River

43

119

5

119

5

119°20' 119°15'

35°20'

35°15'

0 2 3 KILOMETERS

0 2 3 MILES

B

1

1

South Coles Levee

North Coles Levee

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

3,001–10,000

>10,000

Figure 11. —Continued
Results of Salinity Mapping by Geographic Subregion 37

West Kern Valley Margin

The West Kern Valley Margin subregion represents 

the western side of the southern San Joaquin Valley (fig. 1) 

and includes the following five oil fields: North Belridge, 

South Belridge, Cymric, Elk Hills, and Lost Hills. North and 

South Belridge were combined for the purposes of salinity 

mapping because of the proximity of these fields and limited 

availability of TDS data from water wells. Wells used for 

mapping salinity across these 5 fields numbered between 

33 (Cymric) and 151 (Elk Hills) petroleum wells and between 

4 (Cymric) and 84 (Elk Hills) water wells within or assigned 

to each individual or aggregated field (table 3). The number 

of wells attributed by type ranged from 97 percent (Cymric) 

to 100 percent (Lost Hills) of petroleum wells and 25 percent 

(Cymric) to 83 percent (Elk Hills) percent of water wells 

(table 3). For water wells used to map salinity in the Cymric 

field, construction information was unavailable for three out 

of four wells, including two wells located in a part of the 

Cymric field’s 2-mile buffer area where it overlaps the South 

Belridge field. In the absence of construction information, and 

for the purposes of salinity profile plots, the three unattributed 

Cymric water wells were assigned alternative values for 

bottom perforation. Unattributed water wells included in the 

profile plot for Cymric were assigned the bottom perforation 

value (542 ft bls) representing the single water well within 

2 miles of the Cymric field having known construction 

information. Similarly unattributed water wells included in 

the profile plot for the combined North and South Belridge 

fields were assigned the median bottom perforation value 

(238 ft bls) representing all water wells in the North and South 

Belridge fields (table 3). As with other fields having a high 

proportion of unattributed wells used for the reconnaissance 

salinity mapping, the assignment of alternative values to 

represent depths results in some uncertainty as to the vertical 

distribution of TDS in the Cymric and combined North and 

South Belridge fields.

Geologically, the West Kern Valley Margin occupies 

the southern part of the WFB (fig. 2). This structural block is 

bounded on the west and south sides by the Southern Coast 

Ranges geographic province and the San Andreas fault zone. 

The WFB is characterized by extensive folding and faulting 

and variable stratigraphy (Bartow, 1991). Depth to basement 

and thickness of overlying Mesozoic and Cenozoic deposits 

increases substantially from southeast to northwest, ranging 

from about 20,000 ft at the eastern end of the Elk Hills field 

to about 40,000 ft near the northern end of the North Belridge 

field (Hosford Scheirer, 2007, chap. 7). The most productive 

hydrocarbon reservoirs in the subregion are associated with 

Cenozoic deposits and include, from oldest to youngest, the 

Tumey, Temblor, Monterey, Etchegoin, and Tulare Formations 

(Division of Oil, Gas, and Geothermal Resources, 1998).

Groundwater in the West Kern Valley Margin subregion 

has relatively high TDS concentrations, often greater than 

10,000 mg/L, compared to other subregions. Total dissolved 

solids concentrations in samples were less than 10,000 mg/L 

in 14 percent (54 of 381) of petroleum wells and about 

74 percent (164 of 222) of water wells (figs. 13A–B). Large 

contrasts in TDS concentrations were present in samples 

from petroleum wells, particularly in the Cymric field and 

combined North and South Belridge fields, where minimum 

TDS concentrations were 1,607 and 560 mg/L, respectively, 

and maximum concentrations were 29,000 and 48,262 mg/L, 

respectively (table 3). Median TDS concentrations in produced 

water ranged from 16,767 mg/L (Cymric) to 32,636 mg/L 

(Elk Hills). Large contrasts in TDS also were present for 

water wells; median concentrations for the West Kern Valley 

Margin subregion were higher than for any other subregion, 

ranging from 1,438 mg/L (Elk Hills) to 9,750 mg/L (combined 

North and South Belridge fields). Total dissolved solids 

concentrations greater than 3,000 mg/L in samples from water 

wells were prevalent within and outside the administrative 

field boundaries for Lost Hills and the combined North 

and South Belridge fields (fig. 13B). Significant contrasts 

in the areal distribution of TDS were evident for Elk Hills; 

Total dissolved solids (TDS), in milligrams per liter (mg/L)

EXPLANATION

Range of land-surface altitudes at wells

Approximate minimum depth of TDS >3,000 mg/L 

Approximate minimum depth of TDS >10,000 mg/L

3,000 mg/L TDS concentration

Petroleum well (top perforation)

Water well within field (bottom perforation)

Water well outside field (bottom perforation)

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000 Coles Levee, North and South

10 100 1,000 10,000 100,000 1,000,000

Altitude, in feet above

North Americam Datum of 1988

Figure 12. Vertical distribution of total dissolved solids concentrations for mapped oil fields in the West Kern Valley Floor subregion, 

central California.
38 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

concentrations generally were greater than 3,000 mg/L in 

samples from water wells located on the south side of Elk 

Hills, in comparison to less than 3,000 mg/L in samples from 

water wells on the north side of Elk Hills.

Similar to the West Kern Valley Floor subregion, the 

source of moderately saline to very saline TDS in the West 

Kern Valley Margin subregion could also be the result of 

agricultural practices or oil production activities (Bean and 

Logan, 1983; Swain and Duell, 1993). Because many of 

the affected water wells are relatively shallow (less than 

200 ft bls), areas of TDS greater than 3,000 mg/L may be 

indicative of localized perched aquifers. Contour maps 

available from CDWR for 2013 and earlier years indicated 

shallow groundwater and elevated EC in the 2-mile buffer 

area southeast of Elk Hills (including the overlapping 

2-mile buffer area shared with the West Kern Valley Floor 

subregion) and within the 2-mile buffer area east of Lost 

Hills (California Department of Water Resources, 2017). 

Depth to water was generally 5–20 ft bls southeast of Elk 

Hills and east of Lost Hills. Electrical conductivity of shallow 

groundwater to the southeast of Elk Hills was generally 4,000–

10,000 μS/cm (California Department of Water Resources, 

2017). Electrical conductivity of shallow groundwater to 

the east of the Lost Hills field and south of Highway 46 was 

generally less than 2,000 to 10,000 μS/cm, but east of the 

Lost Hills field and north of Highway 46, EC was 10,000 to 

greater than 20,000 μS/cm (California Department of Water 

Resources, 2017).

Profile plots of the vertical distribution of TDS show 

considerable overlap in concentrations from petroleum 

and water wells. In fields having petroleum and withinfield water wells (all except Cymric), vertical separation 

between petroleum and within-field water wells is minimal 

to nonexistent because a number of petroleum wells were 

perforated at similar and even shallower depths than water 

wells. As discussed earlier, the juxtaposition of petroleumand water-well vertical proximity may not necessarily 

coincide with where oil is structurally or stratigraphically 

trapped, but rather where oil may be present as a result of 

upward migration. The Tulare Formation is the shallowest 

hydrocarbon reservoir, present within 1,000 ft of land 

surface with a thickness of several hundred feet. As such, at 

least some within-field water wells, the majority of which 

are designated as monitoring wells, may be perforated or 

completed at altitudes corresponding with perforation depths 

of petroleum wells. Total dissolved solids concentrations 

in water-well samples largely coincided with the low end 

of TDS concentrations in produced water in the North and 

South Belridge, Cymric, and Lost Hills fields (fig. 14). 

Elk Hills field is a notable exception because the range of 

TDS concentrations in samples from water wells greatly 

exceeded the overall range of produced water concentrations. 

Total dissolved solids concentrations ranged from 110 to 

231,000 mg/L (table 3), including samples from five water 

wells, all located outside of the field and within the 2-mile 

buffer area, with concentrations greater than 50,000 mg/L 

(fig. 13B). Three of these five wells are also located in the 

overlapping 2-mile buffer area of the West Kern Valley Floor 

subregion. Although somewhat less than concentrations in 

water-well samples from Elk Hills, high TDS greater than 

10,000 mg/L in samples from water wells were also prevalent 

both within and outside of the combined North and South 

Belridge fields and the Lost Hills field. For the combined 

North and South Belridge fields, approximately 49 percent of 

water wells had TDS greater than 10,000 mg/L. For the Lost 

Hills field, approximately 15 percent of water wells had TDS 

greater than 10,000 mg/L. An analysis of salinity versus depth 

for the North Belridge field by Gillespie and others (2017) 

noted a salinity reversal with decreasing salinity as depth 

increased below about –6,500 ft (7,000 ft bls). Although not 

readily apparent based on this report’s analysis of combined 

TDS data from North and South Belridge, a similar effect is 

evident for the Cymric and Elk Hills fields, albeit at much 

shallower depths. Total dissolved solids concentrations 

in petroleum wells appear to peak at about –4,000 ft 

(5,000 ft bls) and –2,000 ft (3,000 ft bls) in Cymric and Elk 

Hills, respectively, and subsequently decline with increasing 

depth (fig. 14). Salinity reversals in other San Joaquin Valley 

oil fields beyond the scope of this study have been noted by 

other researchers and ascribed to differences in water origin 

(Gillespie and others, 2017).

No individual or aggregated field in the West Kern 

Valley Margin had median TDS concentrations less than 

10,000 mg/L for petroleum wells (table 3). However, all 

fields did have median TDS less than 10,000 mg/L for water 

wells, including Elk Hills and Cymric with median TDS less 

than 3,000 mg/L (table 3). Petroleum wells with TDS greater 

than 10,000 mg/L were perforated over a broad range of 

altitudes between 500 and –8,600 ft (fig. 14). In comparison, 

all water wells with well-construction information that were 

used for mapping salinity in the subregion were perforated 

or completed at altitudes between 500 ft (less than 50 ft bls) 

and –800 ft (1,100 ft bls). Using the shallowest depth of 

TDS greater than 10,000 mg/L based on actual perforation 

depth, the approximate minimum depth of TDS greater than 

10,000 mg/L ranges from an altitude of about 500 ft (100 ft 

bls) in the combined North and South Belridge fields to about 

–1,100 ft (1,800 ft bls) in Elk Hills field. Except for Elk Hills, 

the depths of the 3,000 and 10,000 mg/L thresholds were 

similar, owing to the lack of samples with TDS concentrations 

between 3,000 and 10,000 mg/L from wells shallower than 

the shallowest well having a TDS concentration greater 

than 10,000 mg/L.
Results of Salinity Mapping by Geographic Subregion 39

San Luis

Obispo County

Kern CountyKern County

Poso CreekPoso Creek

Chico

MartinezMartinez Creek

Creek

Creek

Zemorra

Diego

San

Broad Creek

Kern

River 119

43

43

46

46

33

58

58

33

33

5

166

119°45' 119°30' 35°45'

34°15'

0 4 6 8 KILOMETERS

0 4 6 8 MILES

A

2

2

South

Belridge

Cymric

Elk HillsElk Hills

North

Belridge

Lost

Hills

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

3,001–10,000

>10,000

Wells having uncertainty with respect to location

Figure 13. Distribution of total dissolved solids in A, produced water from petroleum wells, and B, water from water wells, for selected 

oil fields in the West Kern Valley Margin subregion, central California.
40 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Figure 13. —Continued

San Luis

Obispo County

Kern CountyKern County

Poso CreekPoso Creek

Chico

MartinezMartinez Creek

Creek

Creek

Zemorra

Diego

San

Broad Creek

Kern

River 119

43

43

46

46

33

58

58

33

33

5

166

119°45' 119°30' 35°45'

34°15'

0 4 6 8 KILOMETERS

0 4 6 8 MILES

B

2

2

South

Belridge

Cymric

Elk HillsElk Hills

North

Belridge

Lost

Hills

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

3,001–10,000

>10,000
Results of Salinity Mapping by Geographic Subregion 41

Los Angeles Basin

The Los Angeles Basin subregion occupies the relatively 

flat and broad expanse of central and southern Los Angeles 

County, extending from mountains of the Transverse and 

Selected Peninsular Ranges hydrogeologic province on the 

north and west to the Pacific Ocean on the south (fig. 1). 

Oil fields mapped as part of this reconnaissance salinity 

mapping effort included Montebello, Santa Fe Springs, 

and Wilmington. Wells used for mapping salinity across 

these 3 fields numbered between 3 (Montebello) and 

118 (Wilmington) petroleum wells and between 202 (Santa Fe 

Springs) and 330 (Wilmington) water wells within or adjacent 

to each field (table 3). Petroleum wells in the Wilmington 

field identified as being located offshore were not included in 

salinity mapping. Water wells included in salinity mapping 

for the Wilmington field were limited to those located within 

1 mile of the field’s administrative boundaries, as opposed 

to the 2-mile buffer area used for all other mapped fields, to 

exclude what would have constituted a majority of water wells 

located within nearby unmapped fields to the north and west 

of Wilmington. The number of attributed wells ranged from 

60 percent (Santa Fe Springs) to 100 percent (Montebello) of 

petroleum wells and 69 percent (Montebello) to 74 percent 

(Wilmington) of water wells (table 3).

Geologically, the Los Angeles Basin subregion can 

be characterized as a deep sedimentary basin surrounded 

by east-to-west trending hills and mountains that form the 

Transverse and Selected Peninsular Ranges and are composed 

of crystalline rocks (Bilodeau and others, 2007). The Los 

Angeles Basin subregion is divided into four structural 

blocks because of faulting: the Southwestern Block (SWB), 

the Northwestern Block (NWB), the Central Block (CB), 

and the Northeastern Block (NEB; Beyer, 1988, Yerkes and 

others, 1965). The three oil fields included in this report are 

located in the SWB (Wilmington), the CB (Santa Fe Springs), 

and the NEB (Montebello; fig. 2). Basement rock within 

the Los Angeles Basin subregion consists of metamorphic 

and igneous rock of Precambrian to Late Cretaceous age 

(Yerkes and others, 1965). The overlying strata consist of 

marine and nonmarine sedimentary and volcanic rock of Late 

Cretaceous to recent age with a maximum thickness of about 

31,000 ft approximately midway between the Wilmington and 

Montebello fields, within the CB (Yerkes and others, 1965). 

The primary hydrocarbon reservoirs in the subregion are the 

Puente Repetto and Pico Formations (Division of Oil, Gas, and 

Geothermal Resources, 1992). In the Wilmington field, some 

oil production also occurs beneath the Puente Formation from 

fractured basement rock referred to as Catalina Schist (Beyer, 

1988; Division of Oil, Gas, and Geothermal Resources, 1992). 

Above the Pico Formation resides non-hydrocarbon-bearing 

upper (San Pedro Formation) and lower (Lakewood Formation 

and recent alluvium) aquifer systems tapped by water-supply 

wells (Reichard and others, 2003).

Figure 14. Vertical distribution of total dissolved solids concentrations for mapped oil fields in the West Kern Valley Margin subregion, 

central California.

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

Total dissolved solids (TDS), in milligrams per liter (mg/L)

Total dissolved solids (TDS), in milligrams per liter (mg/L)

EXPLANATION

Range of land-surface altitudes at wells

Approximate minimum depth of TDS >3,000 mg/L 

Approximate minimum depth of TDS >10,000 mg/L

3,000 mg/L TDS concentration

Petroleum well (top perforation)

Petroleum well (top perforation), location uncertain

Water well within field (bottom perforation)

Water well outside field (bottom perforation)

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

−10,000

−8,000

−4,000

−6,000

−2,000

0

2,000

10 100 1,000 10,000 1,000,000 100,000 10 100 1,000 10,000 1,000,000 100,000 10 100 1,000 10,000 1,000,000 100,000

10 100 1,000 10,000 1,000,000 100,000

Lost Hills

Belridge, North and South Cymric Elk Hills

Altitude, in feet above North Americam Datum of 1988
42 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Groundwater near the studied fields in the Los Angeles 

Basin subregion has a large contrast in TDS based on well 

depth and location, particularly within and adjacent to the 

Wilmington field. Total dissolved solids concentrations 

in produced-water samples from all 126 petroleum wells 

used for salinity mapping were greater than 10,000 mg/L 

(table 3; figs. 15A–B). These mapped petroleum wells all had 

top perforation depths greater than 2,000 ft bls (fig. 15A). 

In contrast, some of the highest TDS concentrations were 

associated with samples from water wells having either 

bottom perforation or completed well depth less than 

1,000 ft bls and were located in or near the Wilmington field 

(fig. 15B). Total dissolved solids concentrations were greater 

than 10,000 mg/L in samples from 20 percent (66 of 330) of 

water wells in the Wilmington area used for salinity mapping. 

An additional 15 percent (50 of 330) of water wells in the 

Wilmington area had TDS concentrations between 3,000 and 

10,000 mg/L. Median TDS concentrations in produced water 

ranged from 18,114 mg/L (Santa Fe Springs) to 30,957 mg/L 

(Wilmington). For water wells, median TDS concentrations 

in water samples ranged from 512 mg/L (Montebello) to 

1,070 mg/L (Wilmington; table 3). These median values 

are somewhat higher than but still comparable to averages 

of upper and lower aquifer median TDS concentrations 

in the Central Groundwater Basin (401 mg/L), which 

includes the Montebello and Santa Fe Springs oil fields, 

and the West Coast Groundwater Basin (688 mg/L), which 

includes the Wilmington oil field, based on water supply and 

monitoring wells sampled as part of a study by Reichard and 

others (2003).

Profile plots of the vertical distribution of TDS show 

that produced-water samples generally had much higher 

TDS concentrations than water-well samples, as evidenced 

by limited overlap between the two well types (fig. 16). The 

exception is the Wilmington field, where the overall range 

of TDS concentrations in produced-water samples from 

petroleum wells overlaps the upper end of the range of TDS 

values in samples from water wells. Total dissolved solids 

concentrations in samples from about one-third (61 of 180) of 

water wells within the Wilmington field were similar (greater 

than 10,000 mg/L) to the TDS concentrations of produced 

water from petroleum wells, including samples from two water 

wells (one within the field and the other within the 1-mile 

buffer area) that exceeded the maximum TDS concentration of 

produced water, with TDS concentrations up to 48,250 mg/L 

(fig. 16; table 3). Among the three fields, Wilmington also had 

the smallest vertical separation, with a difference of about 

2,800 ft between the median top perforation for petroleum 

wells and median bottom perforation, completed well depth, 

or hole depth for water wells. For Montebello and Santa Fe 

Springs, the vertical separation based on median depths was 

about 5,000 and 5,500 ft, respectively.

Top perforation depths for petroleum wells used for 

salinity mapping were all greater than 2,000 ft bls, ranging 

from 2,300 to 8,100 ft bls (fig. 16). In comparison, bottom 

perforation, completed well depth, or hole depth for withinfield water wells were all less than 2,000 ft bls, ranging from 

about 10 to 1,900 ft bls.

Using either the shallowest depth of TDS greater 

than 10,000 mg/L based on the actual perforation depth, 

or predicted depth based on regression analysis (Santa Fe 

Springs), the approximate minimum depth of TDS greater 

than 10,000 mg/L ranges from an altitude of about 0 ft 

(approximately 0 ft bls) in Wilmington to about –4,200 ft 

(4,400 bls) in Santa Fe Springs (fig. 16; table 3). For the 

3,000 mg/L and 10,000 mg/L thresholds, the approximate 

minimum depths in Wilmington were similar (the approximate 

minimum depth lines on fig. 16 overlap), owing to similar well 

depths over the entire range of TDS concentrations in samples 

from water wells. For the Montebello and Santa Fe Springs 

fields, the 3,000 mg/L threshold is much shallower than the 

10,000 mg/L threshold, at about –1,100 ft (1,500 ft bls) and 

–900 ft (1,100 ft bls), respectively. Widespread elevated TDS 

concentrations at shallow depths in the Wilmington area, 

particularly in wells closest to the coast, is attributable at 

least in part to seawater intrusion as a result of groundwater 

pumping, which lowered water levels below sea level and 

induced the inland movement of seawater (Reichard and 

others, 2003; Land and others, 2004). Beginning in the 

1950s, efforts were made to address seawater intrusion by 

injecting imported water into aquifers to create a hydraulic 

barrier. Over time, a combination of reduced groundwater 

pumping and artificial injection resulted in increasing water 

levels. However, despite these efforts, geophysical-log and 

water-quality analyses indicate that in parts of the West Coast 

Groundwater Basin, high salinity water persists in aquifers 

of the Lakewood Formation and overlying alluvium (above 

about 400 ft bls) and is increasing in parts of deeper aquifers 

(below about 700 ft bls) of the San Pedro Formation (Land 

and others, 2004). Additional possible sources of saline water 

include (1) disposal of oil-field brine water into sumps, natural 

channels, or onto the land surface, all common practices 

during the early development of oil in Wilmington and other 

fields in the West Coast Groundwater Basin; (2) groundwater 

contamination at depth from possible migration of 

contamination through abandoned or failed well casing; and 

(3) deep circulation of connate water (Land and others, 2004).
Results of Salinity Mapping by Geographic Subregion 43

Los Angeles County

Orange County

Channel

Compton

Los Angeles River

Rio HondoRio Hondo

San Gabriel

Creek

La

Brea

Creek

Coyote Creek

Moody

Carbon Creek

Rio HondoRio Hondo

River

DominguezDominguez

Creek

Mirada

Creek

42

60

90

72

22

19

10

710

10

710

101

5

19

605

60

110

90

91

5

1 1

710

22

405

1

47

110

110

118°15' 118°00'

34°00'

33°45'

0 1 3 4 KILOMETERS

0 1 3 4 MILES

A

2

2

Pacific Ocean

Santa Fe

 Springs

MontebelloMontebello

Wilmington

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

3,001–10,000

>10,000

Wells having uncertainty with respect to location

Figure 15. Distribution of total dissolved solids in A, produced water from petroleum wells, and B, water from water wells, for selected 

oil fields in the Los Angeles Basin subregion, southern California.
44 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Los Angeles County

Orange County

Channel

Compton

Los Angeles River

Rio HondoRio Hondo

San Gabriel

Creek

La

Brea

Creek

Coyote Creek

Moody

Carbon Creek

Rio HondoRio Hondo

River

DominguezDominguez

Creek

Mirada

Creek

42

110

110

60

90

72

22

19

10

710

10

710

101

5

19

605

60

110

90

91

5

1 1

710

22

405

1

47

118°15' 118°00'

34°00'

33°45'

0 1 3 4 KILOMETERS

0 1 3 4 MILES

B

2

2

Pacific Ocean

Santa Fe Springs

MontebelloMontebello

Wilmington

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

3,001–10,000

>10,000

Figure 15. —Continued
Results of Salinity Mapping by Geographic Subregion 45

Central Coast Basin

The Central Coast Basin subregion is in Santa Barbara 

and San Luis Obispo Counties (fig. 1). This subregion contains 

a number of active oil fields, but for the reconnaissance 

salinity mapping, the Santa Maria Valley field was the sole 

focus. Wells used for salinity mapping in the Santa Maria 

Valley field included 6 petroleum wells and 471 water wells 

located either within the administrative field boundaries or 

the surrounding 2-mile buffer area. All petroleum wells and 

79 percent of water wells were attributed with perforation and 

(or) well depth information (table 3).

Geologically, the Santa Maria Valley field in the Central 

Coast Basin subregion overlies a broad structural depression 

(syncline) bordered on all but the west side by hills that form 

the surface expression of regional uplift (anticlines; Worts, 

1951). Basement consists of metamorphic and igneous rock 

of the Franciscan Formation (Worts, 1951). Overlying strata 

from older to younger are a combination of consolidated 

rock (the Monterey Formation and interbedded volcanics, the 

Sisquoc Formation, and Foxen Mudstone) and unconsolidated, 

water-bearing deposits (Careaga Sand, the Paso Robles 

Formation, the Orcutt Formation, and alluvium; Worts, 1951). 

The thickness of these consolidated and unconsolidated strata 

increases from northeast to southwest across the subregion, 

attaining a maximum thickness of about 10,000 ft along the 

axis of the Santa Maria Valley syncline, just north of but 

roughly parallel to Orcutt Creek (figs. 17A–B; Woodring and 

Bramlette, 1950; Worts, 1951). The principal hydrocarbon 

reservoirs include the Monterey, Sisquoc, and Foxen 

Formations, with additional production obtained from the 

Point Sal and Franciscan Formations (Division of Oil, Gas, 

and Geothermal Resources, 1992).

Median TDS concentrations near the Santa Maria Valley 

oil field ranged from 900 mg/L for samples from water wells 

to 24,742 mg/L in produced-water samples from petroleum 

wells (table 3). The majority of petroleum wells (five of six) 

had TDS concentrations greater than 10,000 mg/L (fig. 17A). 

The one exception had a TDS concentration between 

3,000 and 10,000 mg/L and was the shallowest of the six 

petroleum wells, with a top perforation between 1,000 and 

2,000 ft bls versus greater than 2,000 ft bls for all other 

mapped petroleum wells (fig. 17A). Total dissolved solids 

concentrations in samples from nearly all water wells (467 of 

471) were less than 3,000 mg/L (fig. 17B). For the remaining 

four water wells (one within the field and three just outside 

of the administrative boundaries), TDS concentrations were 

between 3,000 and 10,000 mg/L. These particular wells 

were relatively shallow (well or hole depth instead of bottom 

perforation less than 200 ft bls) and were located in the 

western part of the Santa Maria Valley field.

−8,000

−7,000

−3,000

−5,000

−1,000

0

2,000

−4,000

−6,000

−2,000

1,000

−7,000

−3,000

−5,000

−1,000

0

−4,000

−6,000

−2,000

1,000

−7,000

−3,000

−5,000

−1,000

0

−4,000

−6,000

−2,000

1,000

Total dissolved solids (TDS), in milligrams per liter (mg/L)

EXPLANATION

Range of land-surface altitudes at wells

Approximate minimum depth of TDS >3,000 mg/L 

Approximate minimum depth of TDS >10,000 mg/L

3,000 mg/L TDS concentration

Petroleum well (top perforation)

Petroleum well (top perforation), location uncertain

Water well within field (bottom perforation)

Water well outside field (bottom perforation)

Minimum depths to 3,000 and 10,000 mg/L TDS 

determined at least in part from regression

−8,000

2,000

−8,000

2,000

10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000 10 100 1,000 10,000 100,000

Montebello Santa Fe Springs* Wilmington

Altitude, in feet above

North Americam Datum of 1988

Figure 16. Vertical distribution of total dissolved solids concentrations for mapped oil fields in the Los Angeles Basin subregion, 

southern California. [The approximate minimum depths of TDS to 3,000 and 10,000 mg/L in Wilmington were similar, so the approximate 

minimum depth lines overlap.]
46 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Figure 17. Distribution of total dissolved solids in A, produced water from petroleum wells, and B, water from water wells, for the 

Santa Maria Valley oil field, Central Coast Basin subregion, central California.

Santa Ynez River

San Antonio Creek

Creek Orcutt

Oso Flaco

Creek

Santa Maria River

Nipomo Creek

Mehlschau Creek

Temettate

Creek

Suey CreekSuey Creek

Cuyama

River

Cr

Alamo

Huasna River

Los

Arroyo Grande

Creek

Berros Creek

166

1

1

166

135

101

135

1

1

101

135

Santa Barbara County

San Luis Obispo County

1

120°30' 120°20'

35°00'

34°45'

0 1 3 4 KILOMETERS

0 1 3 4 MILES

A

2

2

Pacific Ocean

Santa Maria Valley

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

3,001–10,000

>10,000
Results of Salinity Mapping by Geographic Subregion 47

Santa Ynez River

San Antonio Creek

Creek Orcutt

Oso Flaco

Creek

Santa Maria River

Nipomo Creek

Mehlschau

Creek

Temettate

Creek

Suey CreekSuey Creek

Cuyama

River

Cr

Alamo

Huasna River

Los

Arroyo Grande

Creek

Berros Creek

166

1

1

166

135

101

135

1

101

135

1

1

Santa Barbara County

San Luis Obispo County

120°30' 120°20'

35°00'

34°45'

B

Pacific Ocean

Santa Maria Valley

Base from U.S. Geological Survey digital elevation data, 2016, 1:1,500,000

Albers Equal-Area Conic projection, standard parallels are 29°30' North and 

45°30' North

North American Datum of 1983

0 1 3 4 KILOMETERS

0 1 32 4 MILES

2

Data sources: California Division 

of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014b (oil 

field boundaries)

EXPLANATION

Oil field

Field buffer area

Well perforation depth, in feet below land surface

<1,000

1,000–2,000

2,001–5,000

>5,000

Total dissolved solids, in milligrams per liter

<1,000

1,000–3,000

3,001–10,000

>10,000

Figure 17. —Continued
48 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

A profile plot of the vertical distribution of TDS in 

the Santa Maria Valley field shows that concentrations in 

produced-water samples were higher than in water-well 

samples (fig. 18). The profile plot shows a significant vertical 

separation of about 4,600 ft based on the median altitude 

of top perforation for petroleum wells and median bottom 

perforation, completed well depth, and hole depth for 

water wells. The profile plot also shows a relatively small 

vertical separation, about 500 ft, between the shallowest 

top perforation for petroleum wells and deepest bottom 

perforation or completed well depth for within-field water 

wells. However, the TDS value of 8,000 mg/L in produced 

water from the shallowest mapped petroleum well was still 

less than the USDW threshold of 10,000 mg/L (table 3). The 

shallowest depth with TDS greater than 10,000 mg/L was 

at an altitude of –3,900 ft (4,100 ft bls). In comparison, the 

shallowest depth with TDS greater than 3,000 mg/L was at 

an altitude of about 0 ft (200 ft bls; table 3). Concentrations 

in excess of this threshold were limited to four water wells 

in the western part of the Santa Maria Valley field. Seawater 

intrusion is not believed to be a factor based on water-quality 

sampling of several monitoring wells along the western edge 

of the Santa Maria Valley field (GEI Consultants, 2013). Deep 

percolation of applied water for irrigation containing salts 

and nutrients flushed out of the root zone may be a source of 

elevated TDS concentrations (GEI Consultants, 2013).

Variation in Salinity Vertical Profiles 

Across Subregions

In general, TDS across the eight geographic subregions 

increased with depth, but the relation of TDS with depth 

varied regionally (fig. 19). The generalized depth profiles 

for each subregion shown in figure 19 are the best fit lines 

for the aggregated data for each subregion, plotted on a semi 

logarithmic scale (logarithmic x axis for TDS and linear y 

axis for depth). Because of differences in data availability, 

distributions, and uncertainties between the subregions, 

generalized profiles are presented to conceptualize relative 

differences in TDS-depth profiles between subregions. More 

precise and quantitative regional relations between TDS and 

depth will require more complete datasets.

In general, TDS values sharply increased over relatively 

small vertical depths near the land surface in the West Kern 

Valley Floor and West Kern Valley Margin subregions on the 

west side of the San Joaquin Valley and the Wilmington field 

part of the Los Angeles Basin subregion (fig. 19); relatively 

high TDS concentrations were present within the upper 

few hundred to several thousand feet of land surface. For 

these subregions, TDS concentrations were relatively high 

throughout the range of depths for which TDS data were 

available, including most of the shallowest produced waters 

and some overlying and adjacent well-water samples. The 

Total dissolved solids (TDS), in milligrams per liter (mg/L)

EXPLANATION

Range of land-surface altitudes at wells

Approximate minimum depth of TDS >3,000 mg/L 

Approximate minimum depth of TDS >10,000 mg/L

3,000 mg/L TDS concentration

Petroleum well (top perforation)

Water well within field (bottom perforation)

Water well outside field (bottom perforation)

−6,000

−2,000

−3,000

−1,000

−5,000

−4,000

0

2,000

1,000

10 100 1,000 10,000 100,000 1,000,000

Santa Maria Valley

Altitude, in feet above

North Americam Datum of 1988

Figure 18. Vertical distribution of total dissolved solids concentrations for the Santa Maria oil field, Central Coast Basin subregion, 

central California.
Variation in Salinity Vertical Profiles Across Subregions 49

depths of some well-water and produced-water samples in 

these subregions overlapped or had relatively little vertical 

separation. Some groundwater samples had TDS greater 

than 10,000 mg/L in western Kern County because of a 

combination of natural conditions and anthropogenic factors 

(Bean and Logan, 1983), and in the Wilmington field part of 

the Los Angeles subregion because of seawater intrusion and 

other factors (Land and others, 2004).

Total dissolved solids concentrations increased more 

gradually with depth, with intermediate slopes, in the 

Middle Kern Valley Floor and South Kern Valley Margin 

subregions, the Montebello and Santa Fe Springs fields in 

the Los Angeles Basin subregion, and Central Coast Basin 

subregion. In these areas, produced waters primarily had TDS 

concentrations greater than 10,000 mg/L, water-well samples 

primarily had TDS less than 3,000 mg/L, and groundwater 

and produced-water samples were generally thousands of feet 

apart vertically.

The Kern Sierran Foothills and East Kern Valley Floor 

subregions, on the east side of the San Joaquin Valley, had the 

most gradual increases in TDS with depth. Concentrations of 

TDS in available water samples were not typically greater than 

10,000 mg/L even in the deepest petroleum wells sampled 

in the Kern Sierran Foothills subregion, consistent with the 

mapping results of Gillespie and others (2017), which showed 

maximum depths to 10,000 mg/L TDS on the east side of the 

southern San Joaquin Valley. Groundwater and producedwater samples were in relatively close vertical proximity 

in the Kern Sierran Foothills subregion. Fields in the East 

Kern Valley Floor subregion generally had groundwater and 

produced water with TDS less than 10,000 mg/L extending 

to a large depth compared to most other subregions, but most 

of the deeper produced-water samples had TDS more than 

10,000 mg/L.

Depth below land surface, in feet

Total dissolved solids, in milligrams per liter

9,000

12,000

6,000

0

3,000

15,000

1 10 100 1,000 10,000 100,000 1,000,000

Kern Sierran Foothills

East Kern Valley Floor

Middle Kern Valley Floor

South Kern Valley Margin

West Kern Valley Floor

West Kern Valley Margin

Los Angeles Basin

Wilmington

Montebello/Santa Fe Springs

Central Coast Basin

(Santa Maria Valley)

EXPLANATION

Figure 19. Generalized distribution of total dissolved solids versus depth for the eight geographic subregions, central and southern 

California.
50 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

Overall, the west side of the San Joaquin Valley in Kern 

County and the Wilmington field in Los Angeles County, 

in proximity to the Pacific Ocean, generally had the highest 

TDS values and the shallowest depths to high TDS. Fields 

on the east side of the San Joaquin Valley in Kern County 

had the lowest TDS and greatest depths to TDS more than 

10,000 mg/L because of their geologic setting adjacent to 

Sierra Nevada recharge areas (Gillespie and others, 2017). 

The San Joaquin Valley floor and southern margin settings in 

Kern County, Los Angeles Basin subregion inland oil fields 

(Montebello and Santa Fe Springs), and the Central Coast 

Basin subregion Santa Maria Valley oil field had intermediate 

TDS depth profiles with relatively low TDS in groundwater 

at shallow depths and relatively high TDS in produced water 

at large depths and varying degrees of vertical separation of 

these contrasting sample types.

The 10,000 mg/L threshold, representing the highest level 

of TDS concentration of water that could be considered as a 

potential source of drinking water (USDW), was present in all 

but 4 (Jasmin, Kern Bluff, Kern Front, and Mount Poso) of the 

31 individual oil fields (29 aggregated fields). In some of the 

fields where the 10,000 mg/L threshold was encountered, it 

was at relatively shallow depths. For all five mapped fields in 

the West Kern Valley Margin subregion, TDS concentrations 

greater than 10,000 mg/L were present in wells within 2,000 ft 

of land surface, including within 200 ft of land surface in 

North and South Belridge (combined) and Lost Hills (fig. 20; 

table 3). Other than fields in the West Kern Valley Margin 

subregion, parts of the Wilmington field in the Los Angeles 

Basin subregion also had TDS concentrations greater than 

10,000 mg/L within 200 ft of land surface. Selected fields in 

other subregions, including Kern River (Kern Sierran Foothills 

subregion), Rosedale (East Kern Valley Floor subregion), 

and Wheeler Ridge (South Kern Valley Margin subregion), 

had USDW thresholds that were within 2,000 ft bls 

(fig. 20; table 3).

Jasmin

Kern Bluff

Kern FrontKern River

Mount Poso

Poso Creek

 Round Mountain

Edison

Fruitvale

Mountain View

Rosedale

Rosedale Ranch

Canfield Ranch

Greeley

Rio Bravo

Ten Section

San Emidio Nose

Tejon

Wheeler Ridge

Yowlumne

Coles Levee, North & South

Belridge North & South

Cymric

Elk Hills

Lost Hills

Montebello

Santa Fe Springs

Wilmington

Santa Maria Valley

−8,000

−7,000

−6,000

−5,000

−4,000

−3,000

−2,000

−1,000

0

1,000

2,000

Field

Subregion

Kern Sierran Foothills East Kern Valley Floor

Middle Kern

Valley Floor

South Kern

Valley Margin

West Kern

Valley Margin

Los Angeles

Basin

Central

Coast

Basin

West

Kern

Valley

Floor

TDS >3,000 mg/L not encounteredTDS >3,000 mg/L not encountered

Depths to total dissolved solids (TDS) thresholds, minimum petroleum-well top perforation, and 

maximum water-well bottom perforation by field

Altitude, in feet above

North Americam Datum of 1988

EXPLANATION

Depth to TDS >3,000 milligrams per liter (mg/L) indeterminate or uncertain

Depth to TDS >3,000 mg/L

Depth to TDS >10,000 mg/L

Average land-surface altitude of within-field mapped wells

Deepest water-well bottom perforation, well depth, or hole depth

Shallowest petroleum-well top perforation

Figure 20. Altitudes of total dissolved solids (TDS) thresholds, minimum top perforation for petroleum wells, and maximum bottom 

perforfation, well depth, or hole depth for water wells, by oil field, central and southern California.
Data Limitations and Future Work 51

The proximity of the depth interval where petroleum 

wells are perforated for production or injection to the depth 

of where water wells are perforated or completed varies 

substantially between different oil fields and thus indicates 

regional differences in the proximity of groundwater having 

TDS less than 10,000 mg/L and oil-field waters. The data 

compiled for this analysis differs from that of Davis and others 

(2018), who compared the depths of oil/gas and water wells, 

in that this analysis focuses only on those wells having TDS 

values. In a number of mapped fields in this analysis, the 

highest top perforation for petroleum wells is shallower than 

the deepest bottom perforation or completed well depth for 

water wells. A number of fields in the Kern Sierran Foothills, 

East Kern Valley Floor, South Kern Valley Margin, and 

West Kern Valley Margin subregions have petroleum wells 

perforated at comparable or even higher depths than where 

water wells, located both within and outside administrative 

field boundaries, are perforated or completed including 

Kern River, Poso Creek, Edison, North and South Belridge 

(combined), Elk Hills, and Lost Hills (fig. 20). Fields where 

this applies only to buffer wells, and thus the areal separation 

between petroleum wells and water wells used for salinity 

mapping may be upwards of 2 miles, include Jasmin, Kern 

Bluff, Kern Front, Mount Poso, Tejon, Wheeler Ridge, and 

Cymric (no within-field water wells for either Wheeler Ridge 

or Cymric). All of these fields may represent areas where oil 

and gas extraction activities are located in relative proximity 

to groundwater of potential beneficial use, consistent with 

conclusions of Davis and others (2018) using data sets that 

did not include water quality. As noted earlier in this report, 

vertical proximity of petroleum and water wells may be 

the result of perforation placement with respect to where 

recoverable oil is located. In some fields, petroleum well 

perforations do not necessarily coincide with where oil is 

structurally or stratigraphically trapped, but rather where oil 

may be present as a result of upward migration. Provided that 

oil has a pathway by which to migrate to the water table, it can 

reach altitudes corresponding with the perforation depths of 

water wells (Jan Gillespie, written commun., 2016).

Data Limitations and Future Work

The primary limitation of the reconnaissance salinity 

mapping was the lack of well-construction data for a 

substantial number of wells having salinity data. Bottom 

perforation, the key metric for water wells, was not readily 

available for 64 percent of wells used for salinity mapping. 

Instead of bottom perforation and for the purposes of this 

study, completed well depth or hole (drill) depth were 

acceptable alternatives. In combination with wells where 

depth to bottom perforation was estimated based on depth 

to top perforation plus screen length, the number of water 

wells lacking useful construction information (unattributed) 

was reduced to 35 percent (table 3). However, even with 

alternative values, five fields (Round Mountain, San Emidio 

Nose, Wheeler Ridge, Yowlumne, and Cymric) had less than 

50 percent of water wells attributed (table 3). Construction 

data for petroleum wells was significantly more complete. 

Top perforation, the key metric for petroleum wells, was 

not readily available for just 3 percent of wells used for 

salinity mapping, with no field having less than 60 percent of 

wells attributed.

A second limitation of this study involved variability 

in data quality and selection of data used for mapping. Total 

dissolved solids and specific conductance data for both 

petroleum and water wells were compiled from a variety of 

data sources with varying amounts of documentation about 

sampling methodology ranging from comprehensive to 

very little or none. As a result, it was not always possible to 

assess how representative these data were of regional aquifer 

conditions. A few sample types were omitted, including 

injectate, tank, or composite samples from petroleum wells, 

because these samples could not be assigned to unique 

locations spatially. Analyses from drill stem test (DSTs) or 

Johnson formation testers (JFTs) in petroleum well boreholes 

collected during the drilling process were retained; in some 

cases, these sample results could be influenced by the presence 

of drilling fluids in the sample. Pore-water samples obtained 

from the unsaturated zone above the water table were omitted 

because they do not reflect saturated groundwater conditions 

and could be influenced by surface or soil processes. Other 

samples, particularly from relatively shallow water wells 

possibly representing perched groundwater or infiltration from 

surface impoundments, may not reflect regional groundwater 

conditions. However, given the uncertainty in being able to 

distinguish regional from local effects of salinity at the scales 

used for this report, samples from shallow water wells were 

retained as part of the salinity mapping effort.

Determination of depths in each field for TDS thresholds 

was a third data limitation. Both the 10,000 and 3,000 mg/L 

TDS thresholds should be considered as rough approximations 

given that, even within administrative field boundaries, 

TDS concentrations in samples from some petroleum and 

water wells with comparable depths were lower than the 

threshold concentrations. This indicates significant withinfield variations, possibly attributable to factors such as 

geology; localized areas of wastewater injection; impacts 

from produced-water disposal ponds, irrigation return flow, 

or seawater intrusion; the assignment of median perforation 

or well depth to wells lacking construction information; or 

sample bias (samples that may represent a particular time 

period, data source, or may simply not be representative of the 

formation). Specifically, with respect to geology, variations 

in TDS concentrations may reflect water originating from 

different formations or mixtures of water from shallow and 

deeper sources. For example, the relatively shallow wells in 

the Kern River field of the Kern Sierran Foothills subregion 

may be drawing water from younger fluvial sediments with 

lower TDS versus deeper wells in other fields that may be 

predominantly drawing water from stratigraphically deeper 

units with higher TDS (Coburn and Gillespie, 2002).
52 Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data

This reconnaissance salinity analysis does not consider 

changes in salinity that may be occurring in the subsurface 

over time. Rather, for wells having TDS data (reported or 

converted from specific conductance) for multiple sample 

dates or multiple values on the same date, the median value 

was selected for salinity mapping, provided that the well 

perforation or sample depth was the same or a similar (within 

100 ft vertical depth) for all analyses. Because the period 

of record is variable for each well (see data in Metzger and 

others, 2018), there is an implicit assumption that salinity is 

constant for time. Over a century of activities related to both 

oil production and groundwater pumping for beneficial use, 

older data may be more likely to reflect undisturbed formation 

conditions than recent analysis. In the absence of adequate 

documentation or information with respect to conditions 

at each well, TDS data were not screened on the basis of 

sample date.

Reconnaissance salinity mapping for additional priority 

fields using the approach applied for this study is continuing. 

These reconnaissance assessments may be refined through 

more detailed assessments for monitored oil fields or groups 

of oil fields in the future as part of the regional monitoring 

program. As part of ongoing and future salinity mapping, 

it is anticipated that well attribution will continue to be an 

important task in the ongoing effort to refine reconnaissance 

salinity maps through more detailed analysis as part of 

regional monitoring in and near priority oil fields or groups of 

fields. Additional efforts might also focus on acquiring more 

salinity data and applying more rigorous screening of available 

data to screen out values that may not be representative of 

regional aquifer conditions. Additional water-sample data 

exist that were not available in digital format at the time this 

study was conducted. More of these data may be available in 

numerical databases in the future. Future efforts to develop a 

more comprehensive understanding of the three-dimensional 

distribution of salinity near oil fields will need to incorporate 

a broader array of techniques, including analysis of oil and 

gas well borehole resistivity and ancillary logs, and surface 

and airborne geophysical (electromagnetic) data in selected 

areas to help fill in salinity patterns between locations of 

wells or boreholes with measured or modeled data. These 

additional approaches may become feasible as part of regional 

monitoring efforts at the scale of priority oil fields or groups of 

oil fields.

References Cited

Bartow, J.A., 1991, The Cenozoic evolution of the 

San Joaquin Valley, California: U.S. Geological 

Survey Professional Paper 1501, 40 p., 

https://pubs.er.usgs.gov/publication/pp1501.

Bartow, J.A., and Pittman, G.M., 1983, The Kern River 

Formation, southeastern San Joaquin Valley, California: 

U.S. Geological Survey Bulletin 1529–D, 17 p., 

https://pubs.er.usgs.gov/publication/b1529D.

Bean, R.T., and Logan, J., 1983, Lower Westside water 

quality investigation, Kern County: prepared for California 

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Metzger and Landon—Preliminary Groundwater Salinity Mapping Near Selected Oil Fields Using Historical Water-Sample Data, Central and Southern California— Scientific Investigations Report 2018–5082

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20185082