U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigation Report 2018–5065

Prepared in cooperation with the California State Water Resources Control Board

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

Prioritization of Oil and Gas Fields for Regional Groundwater 

Monitoring Based on a Preliminary Assessment of Petroleum 

Resource Development and Proximity to California’s 

Groundwater Resources
A

B

C

Cover photographs:

Front cover: A, Kern River adjacent to oil and gas field near Bakersfield, California (Photograph taken by David Dillon, U.S. Geological 

Survey).

B, Oil and gas field in southern San Joaquin Valley, California (Photograph taken by Jessica Teunis, U.S. Geological Survey).

Back cover: C, Oil well at sunset in southern San Joaquin Valley, California (Photograph taken by Jessica Teunis, U.S. Geological 

Survey).
Prioritization of Oil and Gas Fields for 

Regional Groundwater Monitoring Based 

on a Preliminary Assessment of Petroleum 

Resource Development and Proximity to 

California’s Groundwater Resources

By Tracy A. Davis, Matthew K. Landon, and George L. Bennett

A product of the California Oil and Gas Regional Groundwater Monitoring 

Program

Prepared in cooperation with the California State Water Resources Control Board

Scientific Investigations Report 2018–5065

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

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Davis, T.A., Landon, M.K., and Bennett, G.L., 2018, Prioritization of oil and gas fields for regional groundwater 

monitoring based on a preliminary assessment of petroleum resource development and proximity to California’s 

groundwater resources: U.S. Geological Survey Scientific Investigations Report 2018–5065, 115 p., 

https://doi.org/10.3133/sir20185065.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors thank the following cooperators and partners for their support: the California State 

Water Resources Control Board; California Division of Oil, Gas, and Geothermal Resources; and 

California Department of Water Resources. Funding for this work was authorized by Senate 

Bill 4 and administered by the California State Water Resources Control Board.

Contents

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

Introduction.....................................................................................................................................................1

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

Conceptual Description of Factors used in Prioritization ..............................................................7

Petroleum-Well Density..............................................................................................................7

Volume of Injection......................................................................................................................7

Vertical Proximity.........................................................................................................................7

Water-Well Density .....................................................................................................................8

Methods...........................................................................................................................................................8

Data Available for Priority Assessment ..........................................................................................12

Calculation of Variables.....................................................................................................................13

Petroleum-Well Density............................................................................................................13

Volume of Injection....................................................................................................................14

Vertical Proximity.......................................................................................................................14

Water-Well Density ...................................................................................................................16

Field Rankings by Variable ................................................................................................................16

Determining Overall Priority Classifications ..................................................................................22

Results of the Preliminary Assessment of Factors for Prioritization...................................................28

Results of the Prioritization Analysis........................................................................................................29

District 1 (Los Angeles Basin)...........................................................................................................53

District 2 (Ventura Basin)...................................................................................................................53

District 3 (Central Coast)....................................................................................................................54

District 4 (South San Joaquin Basin)...............................................................................................75

District 5 (North/Central San Joaquin Basin).................................................................................75

District 6 (Sacramento Basin)...........................................................................................................76

Summary......................................................................................................................................................108

References Cited........................................................................................................................................108

Appendix 1. Statistical Summaries of Data used to Calculate Factors ............................................111

Petroleum-Well Density ..................................................................................................................111

Volume of Injection...........................................................................................................................111

Vertical Proximity..............................................................................................................................112

Comparison of Depths to Top of Perforations for Production versus Injection 

Petroleum Wells .........................................................................................................112

Comparison of Depths to Top of Perforations for Waste Disposal versus 

Non-Waste-Disposal Wells ......................................................................................113
iv

Comparisons of Vertical Proximity Classifications using Separation-Distance 

Calculation Methods 1 and 2....................................................................................114

References Cited...............................................................................................................................115

Contents—Continued

Figures

1. Maps showing groundwater supply and areas of overlap with oil and 

gas production in California........................................................................................................3

2. Map showing California Division of Oil, Gas, and Geothermal Resources district 

boundaries, California Regional Water Quality Control Board boundaries, and the 

location of oil and gas fields in California.................................................................................6

3. Conceptual diagrams of factors that were assessed in the prioritization of oil and 

gas fields for regional groundwater monitoring......................................................................8

4. Diagrams showing methods for calculating petroleum and water well densities..........17

5. Diagram showing the methods used to calculate vertical separation distance 

between petroleum resource development and groundwater resources for each 

oil and gas field in California.....................................................................................................19

6. Maps showing the location of oil and gas fields in California and the method 

number for calculating vertical separation distance for each field...................................20

7. Histograms showing the distribution of data for individual variables calculated for 

California oil and gas fields in the preliminary assessment of petroleum resource 

development and proximity to groundwater resources.......................................................23

8. Diagram showing the decision process and hierarchy of factors considered 

as part of the prioritization analysis in which California oil and gas fields are 

classified as high, moderate, low priority for regional groundwater monitoring ............27

9. Maps showing overall priority classification for oil and gas fields ...................................30

10. Maps of California oil and gas fields showing rankings for each of the variables .........32

11. Boxplots of vertical separation distance values calculated using a combination 

of methods for each oil and gas field with sufficient data by 

California Division of Oil, Gas, and Geothermal Resources district...................................46

12. Maps of oil and gas fields in district 1, Los Angeles Basin, showing classifications.....55

13. Maps of oil and gas fields in district 2, Ventura Basin, showing classifications.............60

14. Maps of oil and gas fields in district 3, Central Coast, showing classifications..............65

15. Maps of oil and gas fields in district 4, San Joaquin Basin—South, showing 

classifications .............................................................................................................................78

16. Maps of oil and gas fields in district 5, San Joaquin Basin—North/Central, 

showing classifications .............................................................................................................88

17. Maps of oil and gas fields in district 6, Sacramento Valley, showing classifications.....98
v

Tables

1. Counts of California Division of Oil, Gas, and Geothermal Resources 

petroleum wells statewide and in each DOGGR district and water wells 

overlying and adjacent to oil and gas fields in California.................................. external file

2. Ranges of values used to rank California oil and gas fields into high, 

moderate, and low risk categories for individual variables measuring 

petroleum-well density, volume of injection, vertical proximity, and 

water-well density in the preliminary assessment of petroleum 

resource development and proximity to groundwater resources.................... external file

3. Vertical proximity classifications and median separation 

distance between petroleum resource development and groundwater 

resources calculated for California oil and gas fields using a combination 

of methods ................................................................................................................. external file

4. Number of California oil and gas fields that had sufficient data to classify 

fields based on vertical proximity of petroleum resource development to 

groundwater resources into categories of close, moderate, and far and the 

percent of the total number of fields for each California Division of Oil, 

Gas, and Geothermal Resources district and statewide ................................... external file

5. Summary of results from the prioritization analysis of California oil and 

gas fields for regional monitoring and the preliminary assessment of 

petroleum resource development and proximity to groundwater resources 

for each California Division of Oil, Gas, and Geothermal Resources 

district and statewide .............................................................................................. external file

6A. Calculated values and rankings for variables and factors, respectively, 

measuring petroleum resource development and proximity to 

groundwater resources in California oil and gas fields classified as 

high priority................................................................................................................ external file

6B. Calculated values and rankings for variables and factors, respectively, 

measuring petroleum resource development and proximity to 

groundwater resources in California oil and gas fields classified as 

moderate priority ...................................................................................................... external file

6C. Calculated values and rankings for variables and factors, respectively, 

measuring petroleum resource development and proximity to 

groundwater resources in California oil and gas fields classified as 

low priority ................................................................................................................. external file

1–1. Summary of the number and age of petroleum, injection, waste disposal, 

and abandoned wells and production and injection volumes for each oil 

and gas field in California........................................................................................ external file

1–2. Volume of water production and injection for California oil and gas 

wells outside the administrative field boundaries .............................................. external file

1–3. Statistical summary of depth data for petroleum wells and water wells 

for each California oil and gas field....................................................................... external file

1–4. Statistical summary of land surface elevations for petroleum wells and 

water wells for each California oil and gas field................................................. external file

1–5. Results of Wilcoxon rank-sum statistical tests comparing depth to top 

of perforations intervals (TOP) data for production versus injection 

petroleum wells in the preliminary assessment of vertical proximity 

of petroleum resource development to groundwater resources for 

California oil and gas fields..................................................................................... external file
vi

1–6. Results of Wilcoxon rank-sum statistical tests comparing depth to top 

of perforation intervals data for waste-disposal wells versus non-waste-disposal 

injection wells in the preliminary assessment of vertical proximity of 

petroleum resource development to groundwater resources for 

California oil and gas fields..................................................................................... external file

1–7. Vertical proximity classifications for California oil and gas fields based 

on median separation distance values calculated using 

method 1 versus method 2 ...................................................................................... external file

Tables—Continued

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Volume

barrel (bbl; petroleum, 1 barrel=42 gal) 0.1590 cubic meter (m3) 

million barrel 158,987 cubic meter (m3) 

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

Flow rate

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

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

or micrograms per liter (μg/L). One milligram per liter is equivalent to 1 part per million (ppm); 

1 microgram per liter is equivalent to 1 part per billion (ppb).

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).
vii

Abbreviations

α significance level

AI air injection

BFW base of freshwater

bls below land surface

CalWIMS California Well Information Management System

CCST California Council on Science and Technology

COGG California Oil, Gas, and Groundwater cooperative program

DDW Division of Drinking Water (SWRCB)

DH dry hole

DOGGR California Division of Oil, Gas, and Geothermal Resources

DWR California Department of Water Resources

EOR enhanced oil recovery

EPA U.S. Environmental Protection Agency

GD gas disposal

GIS geographical information system

GS gas storage

H Humboldt

IQR interquartile range

LG liquid gas

LSE land surface elevation

OB observation

M Mount Diablo

MMB million barrels

MTRS meridian, township, range, and section

na not available

PLSS Public Land Survey System

PM pressure maintenance

RGMP Regional Groundwater Monitoring Program

RPD relative percent difference

S San Bernardino

SB 4 California Senate Bill 4 of 2013

SC cyclic steam

SF steam flood

SWRCB California State Water Resources Control Board
viii

TD total depth

TDS total dissolved solids

TOP top of first perforated interval in a well

UIC underground injection control

USGS U.S. Geological Survey

WD waste-water disposal

WS water source

Abbreviations—Continued
Prioritization of Oil and Gas Fields for Regional 

Groundwater Monitoring Based on a Preliminary 

Assessment of Petroleum Resource Development and 

Proximity to California’s Groundwater Resources

By Tracy A. Davis, Matthew K. Landon, and George L. Bennett

Abstract

The California State Water Resources Control Board 

initiated a regional monitoring program in July 2015 to 

determine where and to what degree groundwater quality may 

be adversely impacted by oil and gas development activities. 

A key issue in the implementation of the regional groundwater 

monitoring program is that each year, detailed characterization 

work can be done in only a few of California’s 487 onshore oil 

and gas fields. The first step in monitoring groundwater near 

petroleum development is to prioritize oil and gas fields using 

consistent statewide analysis of available data that indicate 

potential risk of groundwater to oil and gas development. 

The U.S. Geological Survey compiled data for four 

factors that characterize the intensity of petroleum resource 

development and proximity to groundwater resources: 

petroleum-well density, volume of water injected in oil 

fields, vertical proximity of groundwater resources to oil 

and gas resource development, and water-well density. An 

overall priority ranking for each field was determined by 

computing summary metrics, analyzing statewide distributions 

of summary metrics for all oil and gas fields, using those 

distributions to define relative categories of potential risk for 

each factor, and combining relative risk rankings for different 

factors into an overall priority ranking. This preliminary 

assessment does not represent an evaluation of groundwater 

risk to oil and gas development, which needs to be based on 

detailed analysis and data related to development activities 

including well stimulation, well integrity issues, produced 

water ponds, and underground injection.

Based on the prioritization analysis, 22 percent 

(107 fields) of the total number of oil and gas fields in 

California were ranked as high priority, 23 percent (114 fields) 

as moderate priority, and 55 percent (266 fields) as low 

priority. These results indicate that between 100 and 200 oil 

fields are principal candidates for the next steps in the regional 

monitoring program. The land area of fields that ranked 

high priority accounted for 41 percent of the total field area 

(3,392 square miles). More than half of the high priority fields 

were in the southern San Joaquin Valley and the Los Angeles 

Basin. Some of the larger fields tended to have higher rankings 

because of greater intensity of petroleum development, 

sometimes coupled with proximity to groundwater resources. 

The U.S. Geological Survey, in collaboration with the 

California State Water Resources Control Board and other 

agencies, has begun regional groundwater monitoring near oil 

and gas fields selected for study through the California Oil, 

Gas, and Groundwater cooperative program. Groundwater 

monitoring includes compiling, analyzing, and developing 

three-dimensional visualizations of existing data, including 

geological frameworks, salinity mapping, identification of 

surface features that could potentially affect groundwater 

quality, locations and depths of oil/gas and water wells, 

cataloging well-construction integrity issues, and evaluating 

the directions of groundwater flow. These analyses are 

required to determine where existing wells should be 

monitored and where new monitoring wells may need to be 

drilled.

Introduction

As required by California Senate Bill 4 of 2013 (SB 4; 

State of California, 2013), and detailed in “Model Criteria 

for Groundwater Monitoring in Areas of Oil and Gas Well 

Stimulation” (California State Water Resources Control Board, 

2015), the California State Water Resources Control Board 

(SWRCB) initiated a Regional Groundwater Monitoring 

Program (RGMP) to protect waters designated for any 

beneficial use in the vicinity of oil and gas fields in California, 

while prioritizing the monitoring of groundwater that is or has 

the potential to be a source of drinking water (California State 

Water Resources Control Board, 2017b). Factors considered 

for the RGMP include well stimulation treatments and other 

events or activities that have the potential to contaminate 

groundwater, such as an oil and gas well failure or breach. 
2 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Fluids produced or introduced in the well stimulation process, 

underground injection control (UIC) wells, and other oil field 

waste management activities such as produced water ponds are 

examined in the RGMP as part of the process of characterizing 

and monitoring groundwater priority zones. 

Accounting for 6 percent of total United States crude oil 

production in 2015, California ranks third in the nation for oil 

production (U.S. Energy Information Administration, 2016). 

Geospatial data and summaries of the nation’s petroleum 

resources are available from the U.S. Geological Survey 

(USGS) Energy Resources Program National Oil and Gas 

Assessment interactive map (U.S. Geological Survey website, 

accessed March 16, 2017, at https://energy.usgs.gov/OilGas/

AssessmentsData/NationalOilGasAssessment.aspx). The 

characteristics of oil and gas fields in California have been 

documented by the California Department of Conservation’s 

Division of Oil, Gas, and Geothermal Resources (DOGGR; 

California Division of Oil, Gas, and Geothermal Resources, 

1982, 1992, and 1998).

California, one of the most populated states in the 

nation, uses more groundwater (and surface water) than any 

other state (Maupin and others, 2014). In 2010, groundwater 

withdrawals in California averaged 12.7 billion gallons per 

day. In many parts of the State, oil and gas resources overlap 

with or are in lateral proximity to groundwater resources; 

this overlap is depicted in figure 1A with the olive- and 

mauve-colored dots representing areas with both oil and gas 

wells and domestic water wells (California Division of Oil, 

Gas, and Geothermal Resources, 2014; Johnson and Belitz, 

2015). Households in some areas depend heavily on water 

from domestic wells; however, irrigation and public supply 

accounted for 69 and 22 percent (by volume), respectively, 

of total fresh groundwater withdrawal in California in 

2010 (Brandt and others, 2014). Some counties, such as 

Kern, Kings, Fresno, and Los Angeles, have the greatest 

groundwater withdrawals in the State as well as the most 

productive oil fields in the State and the Nation (Gautier and 

others, 2004, 2012; Tennyson and others, 2012; Brandt and 

others, 2014; U.S. Energy Information Administration, 2016; 

figs. 1B, C). Reviews of groundwater resources of California 

are provided by the California Department of Water Resources 

(2003, 2016) and Planert and Williams (1995).

 A key issue in the implementation of the RGMP is that 

the State has 487 onshore oil and gas fields, but detailed 

characterization work can only be done in a few fields each 

year. For planning purposes, a prioritization of oil and gas 

fields is needed for consideration in implementing regional 

groundwater monitoring. During 2014–16, the USGS analyzed 

the limited data related to petroleum resource development 

and proximity to groundwater resources in California. This 

analysis uses a consistent approach for all oil and gas fields 

in the State to develop a relative priority ranking (high, 

moderate, and low priority; shown in fig. 2). The prioritization 

does not represent an evaluation of groundwater risk from oil 

and gas development, which needs to be based on detailed 

data analysis from regional monitoring.

Through the California Oil, Gas, and Groundwater 

(COGG) program, the USGS is cooperating collaboratively 

with the SWRCB to implement the RGMP. The COGG 

program is coordinated with other agencies involved in 

managing groundwater and oil and gas resources, including 

DOGGR, the Regional Water Quality Control Boards 

(RWQCBs), the Bureau of Land Management, and local water 

agencies. 

The SWRCB and nine RWQCBs (fig. 2) assist DOGGR 

districts to ensure operators of oil and gas wells adhere 

to state and federal regulations intended to protect waters 

designated for any beneficial use and to promote transparency 

to the public. The DOGGR oversees drilling, operation, 

maintenance, and plugging and abandonment of oil, gas, and 

geothermal wells in California and regulates injection of fluids 

into fields under the UIC program, which includes permitting, 

inspection, and well integrity tests (California Division of Oil, 

Gas, and Geothermal Resources website, accessed January 11, 

2017, at http://www.conservation.ca.gov/dog). The RWQCBs 

have developed programs to monitor and address surfacewater and groundwater issues related to oil and gas production 

activities, including well stimulation treatments, UIC wells, 

produced-water storage and disposal at the surface, and 

aquifer exemptions (Central Valley Regional Water Quality 

Control Board, 2017; Los Angeles Regional Water Quality 

Control Board, 2017). Records pertaining to these activities 

are uploaded by agencies and operators to Geotracker, the 

SWRCB’s data management system for sites that impact or 

have the potential to impact groundwater (California State 

Water Resources Control Board, 2017a).

Purpose and Scope

The purposes of this report are to provide (1) a statewide 

and subordinate regional view of physical characteristics 

that indicate the potential risk to California’s groundwater 

resources from oil and gas resources in the subsurface and 

(2) a comparative analysis of these characteristics to assign 

priority rankings to California oil and gas fields for regional 

groundwater monitoring. 

This report describes which factors were considered 

in the prioritization of oil and gas fields and methods for 

compiling and synthesizing data from various sources, 

calculating each factor, ranking fields by each factor, and 

combining the rankings into an overall priority classification. 

Ancillary well data that were compiled in the process of 

assembling information on petroleum resource development 

were summarized in tables and include drill and abandonment 

dates, number of abandoned wells in each field, volume of 

water produced, net water or steam injection volume, and 

water injection and production volumes for oil and gas wells 

outside field boundaries. Results of statistical analyses that 

quantify the limitations of the statewide datasets are presented 

in tables and described.
Introduction 3

Sac17-0645_fig 01a

124° 122° 120° 118° 116° 114°

42°

40°

38°

36°

34°

0 25 50 100 MILES

0 25 50 100 KILOMETERS

PACIFIC OCEAN

Data sources: Brandt and others, 2014; California Division of 

Oil, Gas, and Geothermal Resources (DOGGR), 2014; Johnson

and Belitz, 2015

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Density of domestic water wells,

in wells per square mile DOGGR oil and gas wells

With overlap of domestic wells and 

oil and gas wells 0

<3

3 to 10

>10 to 100

>100 New, active, and idle wells

Hydraulically fractured

EXPLANATION

With no overlap

New, active, and idle wells

Hydraulically fractured

San Francisco

Sacramento

Fresno

Bakersfield

Los Angeles

San Diego

Ventura

Santa Maria

Salinas

Redding

A

"

Figure 1. Groundwater supply and areas of overlap with oil and gas production in California: A, density of domestic water wells and 

locations of California Division of Oil, Gas, and Geothermal (DOGGR) oil and gas wells; B, 2010 groundwater withdrawal per county; and 

C, 2010 groundwater withdrawal per county in selected counties and the locations of DOGGR oil and gas wells. 
4 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 1. —Continued

Sac17-0645_fig 01b

124° 122° 120° 118° 116° 114°

42°

40°

38°

36°

34°

San Francisco

Sacramento

Fresno

Bakersfield

Los Angeles

San Diego

Ventura

Santa Maria

Salinas

Redding

"

DEL

NORTE

CO

SISKIYOU CO MODOC CO

HUMBOLDT

CO

TRINITY

CO

SHASTA CO

LASSEN CO

TEHAMA CO

PLUMAS CO

BUTTE

CO

MENDOCINO

CO

GLENN

CO SIERRA CO

YUBA

LAKE CO

CO

NEVADA CO COLUSA

CO

SUTTER

CO

PLACER CO

EL DORADO CO YOLO

CO ALPINE

CO SONOMA

CO NAPA

CO SACRAMENTO

CO

MONO

CO

AMADOR CO

SOLANO

CO CALAVERAS CO

TUOLUMNE CO MARIN

CO SAN JOAQUIN

CO

CONTRA

COSTA CO

STANISLAUS

CO

MARIPOSA

CO

MADERA

CO

SAN

MATEO

CO

MERCED CO

FRESNO CO

SANTA

CLARA

CO

INYO CO

SANTA

CRUZ

CO

SAN BENITO

CO

MONTEREY TULARE CO

KINGS

CO

SAN

BERNARDINO

CO

KERN CO

SAN LUIS

OBISPO CO

SANTA BARBARA

CO

VENTURA

CO

LOS ANGELES

CO

RIVERSIDE CO ORANGE

CO

SAN DIEGO CO IMPERIAL CO

0 25 50 100 MILES

0 25 50 100 KILOMETERS

PACIFIC OCEAN

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

2010 groundwater withdrawal by county, 

in million gallons per day DOGGR oil and gas wells

<25

25 to 100

>100 to 250

>250 to 500

>500 to 750

>750

>250 to 500

>500 to 750

>750

New, active, and idle wells

Hydraulically fractured

EXPLANATION

Data sources: Brandt and others, 2014; California Division of 

Oil, Gas, and Geothermal Resources (DOGGR), 2014; Johnson

and Belitz, 2015

B
Introduction 5

Figure 1. —Continued

Sac17-0645_fig 01c

")

120° 118°

36°

34°

EXPLANATION

Data sources: Brandt and others, 2014; California Division of 

Oil, Gas, and Geothermal Resources (DOGGR), 2014; Johnson

and Belitz, 2015

0 10 20 40 MILES

0 10 20 40 KILOMETERS

2010 groundwater withdrawal by county,

in million gallons per day

<25 >100 to 250

25 to 100 >250 to 500

>500 to 750

>750 

DOGGR oil and gas wells

New, active, and idle wells 

Hydraulically fractured

SANTA

BARBARA CO

SAN LUIS

OBISPO CO

MONTEREY CO

VENTURA CO

KERN CO

SAN

BERNARDINO

CO

INYO CO

TULARE CO

FRESNO CO

SAN

BENITO

CO

MADERA CO

KINGS CO

LOS ANGELES CO

RIVERSIDE CO

SAN DIEGO CO

ORANGE CO

Fresno

Bakersfield

Los Angeles

Ventura

Santa Maria

PACIFIC OCEAN

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

C

CALIFORNIA

Sacramento

San Francisco

San Diego

Redding

Map area Los

Angeles
6 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 2. California Division of Oil, Gas, and Geothermal Resources (DOGGR) district boundaries, California Regional Water Quality 

Control Board (RWQCB) boundaries, and the location of oil and gas fields in California. Sac17-0645_fig 02

124° 122° 120° 118° 116° 114°

42°

40°

38°

36°

34°

0 25 50 100 MILES

0 25 50 100 KILOMETERS

PACIFIC OCEAN

San

Francisco

Bay

Data sources: California Division of Oil, Gas, and Geothermal 

Resources (DOGGR), 2014; California State Water Resources 

Control Board, 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Oil and gas fields (priority classification)

RWQCB boundaries

DOGGR districts

High

Moderate

Low

EXPLANATION

1

2

3

4

5

6

6

5

4

2

1

3

San Francisco

Sacramento

Fresno

Bakersfield

Los Angeles

San

Diego

Ventura

Santa

Maria

Salinas

Redding

North

Coast

Lahontan

Colorado

River

San

Diego

Santa Ana

Los Angeles

Central

Coast

Central Valley

"
Introduction 7

Factors discussed in this report are those used in the 

preliminary assessment and do not include all activities 

related to oil and gas development that have the potential to 

contaminate groundwater, such as produced-water storage 

and disposal at the surface. Hydraulic fracturing and acid well 

stimulation were not considered in the prioritization analysis 

described in this report because the RGMP plans to make an 

overall assessment of the effects of oil and gas development 

on groundwater resources, examining several factors in 

addition to those linked to well stimulation treatments. A 

review of the potential risks of oil and gas well stimulation 

in California was carried out by the California Council on 

Science and Technology (2014, 2015).

Conceptual Description of Factors used in 

Prioritization

Four factors that characterize petroleum resource 

development and proximity to groundwater resources were 

included in the preliminary assessment: petroleum-well 

density, volume of water injected into oil and gas fields, 

vertical proximity of oil and gas development to groundwater 

resources, and density of water wells overlying and adjacent to 

fields. These factors can indicate potential risk of groundwater 

contamination by subsurface processes and activities related 

to oil and gas resource development. Although the effects of 

high density of petroleum wells, fluid injection, and vertical 

and lateral proximity of oil and gas resources to groundwater 

resources could interact to potentially increase the risk to 

groundwater quality, these factors were treated as independent 

variables for the purpose of the prioritization analysis. The 

data sources and how each factor was computed are described 

in the “Methods” section.

Petroleum-Well Density

One factor contributing to potential groundwater risk 

that was available for statewide analysis is density of oil and 

gas wells in each field (fig. 3A). Literature on the effects of 

oil and gas development on groundwater quality has indicated 

that leaky wellbores are the predominant pathway allowing 

contamination (Davies and others, 2014; Dusseault and others, 

2014). The petroleum-well density measurement primarily 

reflects that the more oil and gas wells that are present, the 

greater the risk that some may leak and provide potential 

pathways for contaminants mobilized during oil and gas 

development to move to groundwater. In addition, the density 

of injection wells was analyzed (fig. 3B) because injecting 

fluids and gas into the subsurface increases pressures in certain 

zones; this may in turn spread fluids beyond the intended 

injection zones. Similarly, the density of waste-disposal wells 

was also analyzed (fig. 3B) because injection of oilfield wastes 

into the subsurface has the potential to affect groundwater 

quality and because waste injections generally occur above, 

below, or laterally displaced from the main oilfield production 

zones and may be closer to groundwater resources in some 

cases.

Volume of Injection

The volume of injection of fluids into the subsurface 

in or near oil fields was considered a potential risk factor to 

groundwater because injections have the potential to alter 

subsurface fluid movement towards useable groundwater 

and because the injected fluids are sometimes relatively poor 

quality water. Sources of injected waters include produced 

water (often brines) withdrawn along with the extracted 

hydrocarbons in wells withdrawing fluids from oil-bearing 

formations, groundwater withdrawn from non-oil-bearing 

formations, and imported fresh water. Some produced waters 

are mixed with fresh water and treated prior to injection. 

Water is typically injected into formations in oil and gas 

fields for the purposes of subsidence control, enhanced oil 

recovery, and waste disposal (fig. 3B). Categories of injection 

for enhanced recovery include water flooding, steam flooding, 

and cyclic steam injection, the latter involving cyclic injection 

and withdrawal from a single well. Waste disposal is permitted 

only in formations from which no more hydrocarbons can 

be viably recovered and formations that are not potential 

sources of drinking water (U.S. Environmental Protection 

Agency, 2016).

Vertical Proximity

Vertical proximity of petroleum resource development to 

groundwater resources is a measure of the difference in depths 

at which the two resources occur (fig. 3C). Conceptually, the 

farther apart the oil and gas resources and useable groundwater 

are, the less likely it is constituents from oil and gas 

development will move to groundwater. Oil and gas resources 

are generally considered to be separated from groundwater 

resources by large vertical distances. However, in parts of 

California, oil and gas resources are found at shallower 

depths than is common in other parts of the United States 

(California Council on Science and Technology, 2015; Jackson 

and others, 2015), and consequently, at greater proximity to 

usable groundwater. In areas of the State where oil and gas 

resources are thousands of feet below groundwater resources, 

those groundwater resources should, all other factors being 

the same, be less at risk from oil and gas development than 

in areas where petroleum resources are close to groundwater 

resources.
8 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Water-Well Density

Water-well density can be considered to be a factor 

influencing groundwater risk from oil field contamination. 

Water-well density is a surrogate measure of potential 

exposure of water users; more wells can indicate more water 

users who could be exposed should groundwater quality be 

degraded (fig. 3D). Additionally, the density of water wells 

overlying and adjacent to oil and gas fields was used to 

identify areas of lateral overlap of oil and gas development 

activities and currently used groundwater resources. There 

is a greater probability of the proximity of oil and gas 

development to private and public supplies of groundwater, 

as well as to human population, in or near fields with higher 

water-well density compared to fields with lower water-well 

density.

Methods

For this study, data on petroleum wells and water wells 

in California were compiled from various sources. The data 

were used to compute petroleum-well density, volume of 

injection, vertical proximity, and water-well density for each 

oil and gas field. Fields were ranked by each factor based 

on the distribution of data for all oil and gas fields, and the 

priority classifications were assigned to fields based on the 

relative potential risk to groundwater near each field using an 

algorithm that considered all available data. 

Aquifer

Aquifer

EXPLANATION

Water and steam

injection

Water supply

Waste-water

injection

Oil and gas

extraction

Well type

Oil and gas wells

A

Figure 3. Factors that were assessed in the prioritization of oil and gas fields for regional groundwater monitoring: A, oil and gas 

production; B, injection for enhanced oil recovery and waste disposal; C, vertical proximity of petroleum resource development to 

groundwater resources; and D, groundwater withdrawal in and near oil and gas fields.
Methods 9

Figure 3. —Continued

Sac17-0645_fig 03b

Aquifer

Aquifer

EXPLANATION

Water and steam

injection

Water supply

Waste-water

injection

Oil and gas

extraction

Well type

Water and steam injection

B
10 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 3. —Continued

Sac17-0645_fig 03c

Aquifer

Aquifer

EXPLANATION

Water and steam

injection

Water supply

Waste-water

injection

Oil and gas

extraction

Well type

Proximity

C
Methods 11

Figure 3. —Continued

Sac17-0645_fig 03d

Aquifer

Aquifer

EXPLANATION

Water and steam

injection

Water supply

Waste-water

injection

Oil and gas

extraction

Well type

Groundwater wells

D
12 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Data Available for Priority Assessment

The main sources of data available for the prioritization 

assessment were databases provided by DOGGR, the 

California Department of Water Resources (DWR), and the 

SWRCB’s Division of Drinking Water (DDW).

Three datasets downloaded from DOGGR’s geographical 

information system (GIS) mapping website were used for 

mapping locations of oil and gas wells, administrative 

boundaries of oil and gas fields, and DOGGR districts: All 

Wells, Field Boundaries, and District Boundaries (California 

Division of Oil, Gas, and Geothermal Resources, 2014; Davis 

and others, 2018). The geospatial data were downloaded 

December 29, 2014, from http://www.conservation.ca.gov/

dog/maps/Pages/GISMapping2.aspx and are available at 

https://doi.org/10.5066/F7FJ2DV3. The 2014 DOGGR Field 

Boundaries dataset included 514 oil, gas, and geothermal 

fields in California. Offshore and geothermal fields were 

excluded from this assessment, leaving 487 onshore oil and 

gas fields available for analysis.

The State is divided into six DOGGR jurisdictional 

districts, the boundaries of which generally follow county lines 

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

2014; fig. 2). The DOGGR districts are used in this report to 

organize results for oil and gas fields into geographic areas 

and are named by district number and the primary geologic 

basin or region in which oil and gas fields are located: District 

1—Los Angeles Basin, District 2—Ventura Basin, District 

3—Central Coast, District 4—San Joaquin Basin (South), 

District 5—San Joaquin Basin (North/Central), and District 

6—Sacramento Basin.

Water injection and production volumes were compiled 

from DOGGR’s online injection databases available at 

ftp://ftp.consrv.ca.gov/pub/oil/new_database_format/. 

Digital records of water injection and production on a monthly 

basis for all wells were available for the period 1977–2015 

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

2015). The DOGGR production and injection database also 

included oil produced, gas produced and injected, and surface 

pressures; however, these attributes are not summarized in this 

report. 

Information about well construction was not included 

in the 2014 DOGGR All Wells dataset and was compiled 

from other sources. The well data used to calculate vertical 

proximity, including oil and gas well depths and water 

well depths, are available online at https://doi.org/10.5066/

F7FJ2DV3 (Davis and others, 2018). Data sources and 

methods used to attribute wells with depth information are 

described in the metadata associated with this data release and 

are discussed only briefly here. 

Scanned images of records for individual oil and 

gas wells, including geophysical logs, well history, well 

completion reports, and correspondences, were viewed on 

DOGGR’s online Well Finder (http://www.conservation.

ca.gov/dog/Pages/Wellfinder.aspx). For oil and gas production 

wells (excluding injection wells), depths to the top of 

perforated intervals (TOP), depths to base of freshwater 

(BFW), and ancillary data were extracted from these well 

records. For injection wells, depths to TOP and BFW 

were included in the data from DOGGR’s California Well 

Information Management System (CalWIMS) database for 

UIC wells. The Microsoft Access database file was received 

from DOGGR on February 28, 2015, and included information 

pertaining to underground injection and well construction for 

28,462 injection wells.

The depth to BFW was often reported in the DOGGR 

UIC database and scanned well records for individual wells on 

the DOGGR Well Finder. The source and methodology of the 

reported depth to the BFW were generally not documented. 

The data for depths to BFW had larger uncertainties than 

the other variables compiled for this analysis. The BFW is 

historically defined by DOGGR and the Bureau of Land 

Management as the depth in a well where the water in 

overlying aquifers has less than or equal to 3,000 milligrams 

per liter (mg/L or parts per million) of total dissolved solids 

(TDS; California Division of Oil, Gas, and Geothermal 

Resources, 1982, 1992, 1998; Bureau of Land Management, 

2001). The depth to the BFW has generally been estimated 

using qualitative interpretations of borehole geophysical logs 

to estimate the depth to the first sandy zone where TDS is 

greater than overlying zones or using water-quality criteria 

such as the presence of high concentrations of individual 

constituents like boron. Some oil and gas fields have field 

rules that define the criteria for estimating base of freshwater, 

but more commonly, specific criteria for determining the 

BFW within fields are not apparent. Additionally, under 

SB 4, the U.S. Environmental Protection Agency (EPA) 

definition of water potentially useful for drinking water as 

less than 10,000 mg/L TDS has been adopted by California 

as the definition for groundwater that needs to be protected 

for beneficial uses. There are few data available on the 

distribution of groundwater having TDS between 3,000 and 

10,000 mg/L. Despite the uncertainties in TDS value, the 

corresponding BFW, and how it is determined, the BFW 

data are an informative and widely available data source 

for evaluating proximity of oil and gas development to 

groundwater resources, if used with appropriate awareness 

of the limitations. It is assumed that the BFW values were 

determined by oil and gas geologists based on knowledge and 

experience. Because the level of knowledge and experience 

is likely to vary, BFW values in individual wells are likely to 

have substantial uncertainties. However, when aggregated at 

oil field scales, the BFW data are likely to preserve regional 

differences that allow comparison of the relative depths of the 

fresh groundwater systems between oil fields.
Methods 13

The DWR provided about 750,000 scanned images of 

drillers’ logs and well completion reports for water wells in 

California. Using a combination of well selection methods, 

well construction and ancillary data were extracted from 

drillers’ logs for about 67,000 wells and entered into a 

geodatabase. Well locations were approximated from the 

Public Land Survey System (PLSS) designation provided 

by DWR for each scanned log. The PLSS designation lists 

the meridian, township, range, and section (MTRS). The 

PLSS grid system in California consists of three meridians—

Humboldt (H), Mount Diablo (M), and San Bernardino 

(S)—and baselines. Each township is identified by township 

and range designations: township designation indicates the 

location north or south of the baseline; range indicates the 

location east of west of the meridian. Each township is divided 

into 36 numbered sections, each approximately 1 square mile, 

which were further divided into 16 quarter-quarter sections. 

Wells were plotted at the center of the section or quarterquarter section in which each was located as indicated by 

MTRS and location information from the well completion 

report. If a field boundary intersected or contained the center 

of a section, then the wells in that section were considered 

to overlie the field. The scanned images provided by DWR 

are not a complete inventory of all water wells statewide. 

However, the scanned images and the data extracted 

from them are considered, for this analysis, to be the best 

representation of existing water wells near oil and gas wells.

The DDW database of public supply wells supplemented 

the water well data (data available on the SWRCB’s 

Geotracker at https://geotracker.waterboards.ca.gov/gama/

datadownload). This database included well location and 

ancillary data for about 22,000 public supply wells in 

California, of which 3,672 wells were located in or within 

3.1 miles (5 kilometers) of oil and gas fields (table 1). The 

DDW wells were included in well-density calculations but not 

vertical-proximity calculations because well depth information 

was generally not available for these wells.

Calculation of Variables

The intensity of petroleum resource development 

was characterized for each oil and gas field by assessing 

petroleum-well density and volume of injection, and the 

proximity of oil and gas development to groundwater 

resources was characterized by vertical proximity and waterwell density. Multiple variables were considered for each 

factor (table 2). Petroleum-well density was based on three 

variables: density of all petroleum wells, density of injection 

wells, and density of waste-disposal wells. Volume of 

injection was based on two variables: total volume of water 

or steam injection and total volume of water injection for 

waste disposal only. Vertical proximity was assessed by using 

a combination of five methods for calculating the distance 

separating petroleum and groundwater resources. Water-well 

density considered two variables: the density of water wells 

overlying the field and density of water wells adjacent to each 

oil and gas field.

Petroleum-Well Density

Density of all petroleum wells, density of injection 

wells, and density of waste-disposal wells were calculated as 

the number of wells in a field divided by the area of the field 

expressed in units of wells per square mile (wells/mi2; fig. 4A). 

The well densities were calculated using ESRI ArcGIS tools 

and datasets downloaded from the DOGGR GIS Mapping 

website (Davis and others, 2018). The 2014 DOGGR All 

Wells dataset included the locations, well classification, and 

selected information for over 222,000 new, active, idle, or 

plugged petroleum wells in 3,247 sections in California. 

Onshore oil and gas wells from this dataset that plotted within 

the field boundaries were used in density calculations. There 

were about 13,000 petroleum wells that plotted outside of field 

boundaries (appendix table 1–1).

The three variables of petroleum-well density were 

differentiated by well type as indicated in the “GISSymbol” 

column of the 2014 DOGGR All Wells dataset. Major 

categories of wells used for oil and gas extraction or field 

management and the total number of wells for each category 

are listed in table 1. Petroleum wells were grouped in this 

analysis into three categories: production, injection, and other. 

Wells in all three categories were included in the density of 

all petroleum wells. Production wells were those used for oil 

and (or) gas extraction and included two DOGGR well types: 

oil and gas (OG) and dry gas (DG). Injection wells included 

wells used for water, steam, gas, air, and waste injection 

and included the following DOGGR well types: water flood 

(WF), steam flood (SF), cyclic steam (SC), waste-water 

disposal (WD), gas disposal (GD), gas storage (GS), pressure 

maintenance (PM), air injection (AI) and liquid petroleum 

gas (LG). The density of injection wells included all of these 

injection well types. The density of waste-disposal wells 

included only injection wells with the DOGGR well types WD 

and GD. The GD wells, which were primarily in the MidwaySunset field and a few other fields in District 4, represented 

only 4 percent of the waste-disposal wells. Well types SF, 

WF, SC, and AI compose the enhanced oil recovery (EOR) 

category of injection wells. The remaining DOGGR well 

types, dry hole (DH), observation (OB), water source (WS), 

and unknown, were categorized as other.
14 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Volume of Injection

Volume of injection was calculated by the sum of 

monthly injection volumes of water and steam, as reported 

for January 1977 through September 2015 in DOGGR’s 

online injection databases (California Division of Oil, Gas, 

and Geothermal Resources, 2015). Similar to the density 

calculations, the two volume variables were differentiated 

by well type. The total volume of water and steam injection 

considered all wells that inject water or steam for the purposes 

of EOR (WF, SF, and SC wells) and waste disposal (WD 

wells). The total volume of water injection for waste disposal 

considered only WD wells. Volumes were reported by well 

in units of barrels, which are equal to about 42 gallons and 

include steam injection. Volumes calculated for each field 

over the approximate 39 years of record were large and are 

therefore presented in this report as million barrels (MMB).

Vertical Proximity

Vertical proximity was estimated by calculating the 

vertical separation distance between oil and gas development 

and groundwater resources for fields using a combination of 

variables and calculation methods (fig. 5). For all methods, 

vertical proximity is the inverse of the separation distance. 

That is, the smaller the distance between the resources, 

the greater proximity of (or closer) oil and gas production 

activities are to groundwater resources, and therefore, the 

greater potential risk to usable groundwater. Variables used 

to calculate separation distance were depths to TOP and 

BFW extracted from DOGGR well records for oil and gas 

wells, depths to TOP from DOGGR’s UIC database, and 

total well depths (TD) extracted from DWR scanned images 

of well completion reports for water wells. Depth data for 

petroleum and water wells, although painstaking to compile 

into databases, represent best available data for estimating 

vertical proximity on an oil-field scale across the State. The 

availability of data for each of the variables used to calculate 

separation distance, however, varied by oil field, necessitating 

the use of a combination of different calculation methods. 

Statistical summaries of the depth data for each field are 

available in appendix 1 (appendix table 1–3). Statewide, 

the dataset of separation-distance variables included depths 

to TOP for 20,242 oil and gas wells (17,278 injection and 

2,964 production); depths to BFW for 6,202 oil and gas wells 

(5,248 injection and 954 production); and TD for 16,911 water 

wells overlying or adjacent to oil and gas fields (Davis and 

others, 2018). 

The five methods used to calculate separation distance for 

each oil and gas field are shown in figure 5. Each subsequent 

method introduced additional uncertainty making it less robust 

than the previous method; therefore, the method selected to 

define separation distance for each field was the first method 

to have five or more values for depth to TOP for petroleum 

wells, except where noted. Method 1 is the only method for 

calculating separation distance that used data available in the 

same well, which were comparisons of depths to TOP and 

BFW in individual petroleum wells (4,157 of the 20,242 wells 

with depth to TOP also had depth to BFW). For the four 

other methods, data for petroleum wells and water wells were 

compared using a near-neighbor scheme or aggregated at an 

oil-and-gas-field scale. 

For method 1, separation distance for each field was 

calculated by taking the difference between depth to TOP and 

depth to BFW in the same well for all petroleum wells with 

data and then computing the median value:

SEP d d f T ,1 OP BFW M     (1)

where

SEPf,1 is the separation distance for a field using 

method 1,

dTOP is the depth to top of perforated interval for a 

petroleum well,

dBFW is the depth to base of freshwater in the same 

petroleum well, and

M is the median of all values for the field.

In order to calculate separation distance using method 1, 

each well must be attributed with both TOP and BFW depths. 

This method used an imprecisely defined BFW, likely 

representing the depth to the deepest groundwater resources 

with less than 3,000 mg/L TDS. This depth does not represent 

the depth of currently used groundwater. 

For method 2, separation distance for each field was 

calculated by taking the difference between depth to TOP for 

petroleum wells and TD of the nearest and deepest water well 

within 1.25 miles of the petroleum well and then computing 

the median value:

SEP d d f T ,2 OP TD M     (2)

where

SEPf,2 is the separation distance for a field using 

method 2,

dTOP is the depth to top of perforated interval for a 

petroleum well,

dTD is the total well depth of a water well near the 

petroleum well, and

M is the median of all values for the field.
Methods 15

Petroleum wells were matched with the nearest DWR water 

well within 1.25 miles. Sections are not exactly 1 square 

mile, and the distance between their centers, which is where 

water wells are typically plotted, may vary slightly. Using 

the 1.25-mile search radius allows petroleum wells to be 

matched with water wells in an adjacent section even if the 

center of the adjacent section is greater than 1 mile away from 

the petroleum wells. The deepest water well in a section was 

chosen because the calculated separation distance will be a 

minimum distance and is the most protective of groundwater 

quality. In contrast to method 1, the depth of groundwater 

resources in method 2 was represented by the depths of 

groundwater wells in the area. 

For method 3, separation distance for each field was 

calculated by computing the median depth to TOP for all 

petroleum wells in the field and the median depth to BFW and 

then taking the difference between the two medians:

SEP d d f T , , 3   OP M BFW ,M (3)

where

SEPf,3 is the separation distance for a field using 

method 3,

dTOP,M is the median depth to top of perforated 

interval for all petroleum wells in a field, 

and

dBFW,M is the median depth to base of freshwater for 

all petroleum wells in a field.

This approach has uncertainty because it compares data for 

petroleum wells that were potentially in different parts of an 

oil field with varying land surface elevation. Additional steps 

were taken to evaluate the effects of land-surface variations 

on the statistically aggregated results for the field (see 

appendix 1).

For method 4, vertical separation distance for each field 

was calculated by computing the median depth to TOP for all 

petroleum wells in the field and the median TD for water wells 

within 1.25 miles of the petroleum wells and then taking the 

difference between the two medians:

SEP d d f T , , 4   OP M TD M, (4)

where

SEPf,4 is the vertical separation distance for a field 

using method 4,

dTOP,M is the median depth to top of perforated 

interval for all petroleum wells in a field, 

and

dTD,M is the median total well depth for water wells 

near the petroleum wells.

Only one field (Northwest Lost Hills) was attributed 

with vertical separation distance using method 4 (fig. 6A). 

If a field had an overlying water well, the well was usually 

within 1.25 miles of a petroleum well, and method 2 was the 

preferred calculation method.

For method 5, vertical separation distance for each field 

was calculated by computing the median depth to TOP for all 

petroleum wells in the field:

SEP d f T , , 5 = OP M (5)

where

SEPf,5 is the vertical separation distance for a field 

using method 5, and

dTOP,M is the median depth to top of perforated 

interval for all petroleum wells in a field.

Method 5 used only perforation depths for petroleum wells 

because all other sources of depth data for groundwater 

resources were exhausted. This approach represents the 

maximum distance between groundwater and petroleum 

resources by assuming that freshwater overlies the fields and 

the depth to BFW is shallow in comparison to depths to TOP 

for petroleum wells.

A total of 174 oil and gas fields were attributed with 

separation distance using the following combination of 

calculation methods: 77 fields by method 1, 75 fields by 

method 2, 13 fields by method 3, 1 field (Northwest Lost 

Hills) by method 4, and 9 fields by method 5. Fields for 

which separation distance was attributed using method 1 were 

generally the larger fields throughout DOGGR districts 1, 2, 

and 3 (fig. 6A); fields in districts 4 and 5 that are at the center 

of the Central Valley or on the east side; and most of the fields 

that were attributed for district 6 (fig. 6B). Several fields on 

the west side of the Central Valley in districts 4 and 5 used 

methods 2 and 5, indicating data on the depths of freshwater 

resources in the area were generally not available.

All of the separation distance calculation methods 

make the assumption that the minimum depth of oil and gas 

resources in a particular field can be represented by a summary 

of the depths to TOP for petroleum wells with available data. 

Although there are far more oil and gas production wells 

than injection wells statewide, there were more perforationdepth data readily available for injection wells. Data for 

the two categories of wells were combined for separation 

distance calculations because of the lack of data available for 

production wells. Generally, injection wells were shallower 

than production wells for each field (see appendix 1 section 

“Comparison of Depths to Top of Perforations for Production 

versus Injection Petroleum Wells” for more information). 

Therefore, by using depths to TOP that are primarily for 

injection wells, the distance between oil and gas development 

and groundwater resources likely was smaller in some cases 

than if more data were available for production wells. 
16 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

The separation distance calculation methods also 

assume that the maximum depth of usable groundwater can 

be represented by a summary of depth to BFW for petroleum 

wells or by TD for water wells. Methods 1 and 3 estimate the 

vertical distance between oil and gas resources and brackish 

groundwater, as represented by depth to BFW (assumed to 

be the boundary between waters less than and greater than 

3,000 mg/L TDS), which is generally not currently used but 

could presumably be used as a water source in the future. In 

contrast, methods 2 and 4 estimate vertical distance between 

oil and gas resources and TD of water wells, which generally 

pump fresh groundwater. For fields that have no information 

about the depths of groundwater resources that can be used 

for beneficial uses, method 5 estimates separation distance 

using only the depths to TOP for petroleum wells. The use 

of different attributes to define the depth of groundwater 

resources, including depth to BFW and TD of water wells, 

or using only depths to TOP for petroleum wells to calculate 

separation distance, caused variability in the values between 

different methods in some cases, but did not result in different 

classifications of vertical proximity or the overall priority 

classifications for 56 of 81 fields compared (see appendix 1

section “Comparisons of Vertical Proximity Classifications 

using Separation-Distance Calculation Methods 1 and 2”).

For 10 fields, the distance between oil and gas resources 

and BFW (method 1) was greater than the distance between 

petroleum resources and currently used groundwater 

(method 2), and the smaller separation values (greater 

proximity) calculated from method 2 were used in the 

prioritization analysis (appendix table 1–7). Results from 

methods 1 and 2 are preferred to results from methods 3, 4, 

and 5. The BFW values that are recorded in wells that also 

have TOP values permit vertical separation distance to be 

calculated in that well using method 1, which is not possible 

with any of the other separation distance calculation methods 

used in this report. Once these vertical separation distance 

values are calculated for the set of wells having both BFW 

and TOP for an oil and gas field, the resulting dataset likely 

represents one of the better-constrained estimates of vertical 

proximity available. For methods 3, 4, and 5, median values 

were used as the summary statistic of grouped data for each 

field. Vertical separation calculated using methods 3 and 

4 may be less reliable than methods 1 and 2 because there 

are topographic features that result in substantial changes 

in land surface elevation within some fields. Comparisons 

of depths between wells or well types in different parts of a 

field may not be appropriate if land surface elevations differ 

substantially. More information about how the aggregation 

of data for each field (regardless of well type or elevation) 

and use of different variables (depths to TOP and BFW, 

and TD) for estimation of the separation of resources can 

cause variations in separation distance values or the vertical 

proximity classification for some fields is included in 

appendix 1.

Water-Well Density

The density of water wells overlying a field was 

calculated as the number of DWR wells plus DDW wells in a 

field divided by the area of the field (fig. 4B). The density of 

water wells adjacent to each oil and gas field was calculated 

as the number of DWR plus DDW wells within 3.1 miles 

(5 kilometers) of the field boundary (buffer) divided by the 

area of the buffer (fig. 4B). Buffers for oil and gas fields often 

overlap with each other; therefore, the same water well may be 

counted in more than one field’s adjacent water-well density.

Active and idle water wells that are used to withdraw 

water for beneficial uses, such as municipal, domestic, 

irrigation, agricultural, and industrial uses, were included in 

the water-well density calculations. Monitoring wells, other 

uncategorized wells (for example, cathodic protection and 

unknown), and wells for which the section was unknown 

were excluded from the dataset. Some of the DDW wells have 

entries for both the raw and treated sample points; treated 

sample points were excluded from the dataset. A statewide 

count of attributed water wells overlying or adjacent to oil 

and gas fields (dataset available at https://doi.org/10.5066/

F7FJ2DV3) is included in table 1. The DWR data included 

16,911 wells overlying or adjacent (within 3.1 miles) to oil 

and gas fields; the DDW data consisted of 3,672 water wells 

overlying or adjacent to oil and gas fields. The calculation 

of water-well densities used the combined DWR and DDW 

dataset; municipal wells were excluded from the DWR data to 

avoid possibly double-counting municipal wells.

Field Rankings by Variable

Oil and gas fields were grouped into three relative 

categories (high, moderate, or low) of potential risk to 

groundwater resources for each variable representing 

petroleum-well density, volume of injection, vertical 

proximity, and water-well density. When describing results 

of the preliminary assessment, fields with vertical proximity 

are categorized as close, moderate, or far for high, moderate, 

or low (respectively) relative categories of potential risk. 

The boundaries between high and moderate categories and 

between moderate and low categories for each variable were 

chosen based on the statistical distribution of values for all 

oil and gas fields. Percentiles (0, 10th, 25th, 50th, 75th, and 

90th), indicating the percent of the distribution that is equal 

to or below it, were calculated to summarize the distribution 

and group fields into the three categories for each variable. 

Percentiles were targeted to delineate the boundaries between 

categories, yet the actual bounding values used were often 

rounded to the nearest whole number. The range of values 

that defined the high, moderate, and low categories for each 

variable and the targeted and actual percentiles that were used 

to define the boundaries between each category are shown 

in table 2.
Methods 17

Sac17-0645_fig 04a

118°11'30''

0 0.5 1 2 MILES

0 0.5 1 2 KILOMETERS

117°57'30''

34°4'

33°58'

Well density: the number of wells in the field (n) divided by the field area (A)

n = 802 DOGGR wells

A = 5.7 square miles

Density = 141 wells per square mile

Density of injection wells

n = 97 injection wells

A = 5.7 square miles

Density = 17 wells per square mile

Density of waste-disposal wells

n = 1 waste-disposal well

A = 5.7 square miles

Density = 0.18 wells per square mile

EXPLANATION

DOGGR wells

Other

Production

Injection—enhanced oil recovery

Injection—waste disposal

Density of all petroleum wells

Montebello field

Oil and gas field Petroleum wells are all wells in the California Division of Oil, Gas, and Geothermal Resources (DOGGR) 

2014 All Wells dataset. Injection wells are all injection wells for enhanced oil recovery and waste 

disposal (see table 1 for well types). Waste disposal wells are all injection wells used for waste-water 

and gas disposal.

Data sources: California Division of Oil, Gas, and Geothermal Resources 

(DOGGR), 2014; California State Water Resources Control Board, 2016

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

A

Figure 4. Methods for calculating petroleum and water well densities: A, density of all petroleum wells, injection wells, and wastedisposal wells in the field; and B, density of water wells overlying the field and adjacent to the field.
18 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 4. —Continued

Sac17-0645_fig 04b

118°11'30''

0 0.5 1 2 MILES

0 0.5 1 2 KILOMETERS

117°57'30''

34°4'

33°58'

Density of water wells overlying the field

Number of wells overlying the field (n) 

 divided by the field area (A)

n = 7 water wells

A = 5.7 square miles

Density = 1.2 wells per square mile

Density of water wells adjacent to the field

Number of water wells in the 3.1-mile buffer (n) 

 divided by the buffer area (A)

n = 147 water wells

A = 64 square miles

Density = 2.3 wells per square mile

EXPLANATION

Montebello field

Montebello buffer

DWR well (1 or more)

DDW well

Oil and gas field

3.1-mile buffer

Water wells

PLSS section

Water wells are beneficial-use groundwater wells (excluding public supply wells) attributed from

California Department of Water Resources (DWR) well logs plus public supply wells from the

California State Water Resources Control Board's Division of Drinking Water (DDW) database. DWR 

wells were plotted at the center of the Public Land Survey System (PLSS) section or

the quarter-quarter section in which they are located.

Data sources: California Division of Oil, Gas, and Geothermal Resources 

(DOGGR), 2014; California State Water Resources Control Board, 2016

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

B
Methods 19

Figure 5. Methods used to calculate vertical separation distance between petroleum resource development and groundwater 

resources for each oil and gas field in California.

Sac17-0645_fig 05

Depth to

BFW 

Depth to

TOP 

300 feet

1,000 feet

700 feet

Petroleum well

TD

Depth to

TOP 

300 feet

1,000 feet

700 feet

Petroleum

well

Nearby water well 

Median

depth to

BFW 

Median

depth to

TOP 

300 feet

1,000 feet

700 feet

Petroleum well

Petroleum

wells

Median

TD 

Median

depth to

TOP 

300 feet

1,000 feet

700 feet

Overlying

water wells 

Median

depth to

TOP 

1,000 feet

Petroleum wells

Method 1

Compares depth to top of first perforated interval in a well (TOP) and depth to base of 

freshwater (BFW) in the same petroleum well, then computes the median value for the field

Most robust of the methods

Provided vertical proximity for almost half of the 174 fields that were attributed (77 fields; 

44 percent) 

Method 2

Method 3

Method 4

Method 5

Compares depth to TOP in a petroleum well to total depth (TD) of a water well within 

1.25 miles, then computes the median value for the field 

Groundwater resources are characterized by currently used resources

Provided vertical proximity for almost half of the fields that were attributed (75 fields; 

43 percent)

Compares the median depth to TOP for petroleum wells in the field to the median depth to 

BFW for petroleum wells in the field

Because depths are grouped for the entire field prior to calculating the vertical distance, 

topographic features within a field may make depth comparisons between wells less 

reliable

Provided vertical proximity for 13 fields (7 percent of the attributed fields)

Compares the median depth to TOP for petroleum wells in the field to the median TD for 

water wells overlying the field

Similar to method 3, topographic features within a field may make depth comparisons

between wells less reliable

Provided vertical proximity for only 1 field, because water wells overlying fields

were generally within 1.25 miles of a petroleum well

Computes the median depth to TOP for petroleum wells

Least robust of the methods because the depth of groundwater resources is not taken into 

account

Provided vertical proximity for 9 fields (5 percent of the fields that were attributed)
20 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 6. Location of oil and gas fields in California and the method number for calculating vertical separation distance for each field

in A, California Division of Oil, Gas, and Geothermal Resources (DOGGR) districts 1–5 and B, DOGGR district 6. 

Sac17-0645_fig 06a

121° 120° 119° 118°

37°

36°

35°

34°

Calculation method for separation distance DWR groundwater basins

DOGGR district boundary

County

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

1

2

3

4

5

None

PACIFIC OCEAN

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

TULARE CO

INYO CO

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

FRESNO CO

MADERA CO

KERN CO

LOS ANGELES CO VENTURA CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA BARBARA CO

SAN BERNARDINO CO

District 5

District 1

District 2

District 3

District 4

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION

A
Methods 21

Figure 6. —Continued

Sac17-0645_fig 06b

S

A

N

J

O

A

Q

U I N V A L L E Y

124° 123° 122° 121°

40°

39°

38°

Calculation method for separation distance DWR groundwater basins

DOGGR district boundary

County

1

2

None

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

PACIFIC OCEAN

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 12.5 25 50 KILOMETERS

0 10 20 40 MILES

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map

area

EXPLANATION

District 6

District 5

District 3

MENDOCINO CO

NAPA CO

SOLANO CO

SONOMA CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO SAN

FRANCISCO CO ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS

CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

Sacramento

San Francisco

B
22 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

The range of values that defined each category was 

chosen based on the data distribution shown in histograms 

(figs. 7A–D) and the occurrence of natural breaks, or inflection 

points, in the data. One method for dividing up the fields into 

three categories is to rank the fields by each variable and place 

the lowest ranked one-third of the fields in the low category, 

the middle one-third in the moderate category, and the upper 

one-third in the high category. Another method is to use the 

interquartile range for the moderate category, the lower quarter 

of fields for the low category, and the upper quarter of fields 

for the high category. However, more than half of the fields 

had values of zero for some variables, such as density of 

injection wells and total volume of water or steam injection 

(figs. 7A, B). These variables had left-skewed distributions 

with 50 percent or more of the data having the lowest values 

and a long right tail, for some variables exceeding a range of 

three or four orders of magnitude (for example, total volume 

of water or steam injection had a 50th percentile value of 

6.7 MMB, 90th percentile of 140 MMB, and maximum of 

18,178 MMB). Therefore, the targeted boundary between the 

low and moderate categories was shifted up from the 25th 

or 33rd percentile to the 50th (median) or 75th percentile, 

depending upon which value was closest to break points, or 

inflection points, where the frequency of occurrence of higher 

values decreased substantially. The targeted range of values 

defining the low-risk category was the 0th (minimum) to 

50th percentile for density of all petroleum wells, density of 

injection wells, density of waste-disposal wells, and density of 

water wells overlying the field (table 2). The 50th percentile 

to maximum of separation distance was the targeted range 

of values for defining the low-risk category of inverselyproportion vertical proximity. The range of values defining 

the low category for total volume of water or steam injection, 

total volume of injection for waste disposal, and density of 

water wells adjacent to field was targeted as the minimum 

to 75th percentile. The boundary between the moderate and 

high categories was approximated by the 90th percentile for 

all variables except vertical proximity, so that the high range 

included only the top 10 percent of fields and the moderate 

range included 15–40 percent of the fields. For vertical 

proximity, the boundary between moderate and high riskcategories was approximated by the 25th percentile of the 

separation distance values, so that 25 percent of the fields 

would be in each of the high and moderate categories and 

50 percent of the fields would be in the low category. The 

values that delineated the boundaries between categories 

were often rounded from the targeted percentiles resulting in 

variations in the percentages of fields in each category.

Determining Overall Priority Classifications

Oil and gas fields were ranked for each of the individual 

variables measuring the intensity of oil and gas development 

activities and proximity to groundwater resources. From 

these rankings, a summary classification of high, moderate, 

or low priority was assigned to each oil and gas field. A 

hierarchy based on the expected effect on the imminence of 

groundwater contamination that each of the factors represents 

was developed to determine the order in which they were 

considered (fig. 8). The decision process that was used for 

classifying all oil and gas fields is shown in more detail in 

figure 8. 

The ranking for the factor petroleum-well density was 

determined by the highest ranking assigned among the three 

density variables: density of all petroleum wells, density of 

injection wells, and density of waste-disposal wells. Similarly, 

the ranking for volume of injection was determined by the 

higher ranking assigned between the two volume variables: 

total volume of water or steam injection and total volume of 

water injection for waste disposal only. The ranking for the 

factor water-well density was determined by rankings for 

densities of water wells overlying and adjacent to fields: fields 

ranked high in overlying water-well density or moderate in 

overlying density and high in adjacent water-well density 

were ranked high, fields that had low overlying and adjacent 

water-well densities were ranked low, and all other fields were 

ranked moderate. 

For assignment of the summary priority, vertical 

proximity was considered first, followed by injection volume, 

petroleum-well density, and lastly water-well density (fig. 8). 

Fields that had petroleum resource development closest to 

groundwater resources (vertical separation distance of 1,000 ft 

or less) were categorized as high priority for the purpose of 

identifying where regional groundwater monitoring should 

be implemented first. Fields that had the greatest injection 

volumes (top decile of all fields) were classified as high 

priority. For the other fields, combinations of injection 

volume, petroleum-well densities, and overlying and adjacent 

water-well densities were considered. Fields were not assigned 

to a lower summary priority classification than their ranking 

for the injection volume factor; however, some fields had 

lower summary priority classifications than their ranking for 

the petroleum-well density factor. For example, fields that 

ranked high for petroleum-well density and low for injection 

volume were classified as moderate for summary priority. This 

is because fields with these characteristics generally had high 

petroleum-well density owing to small field size but contained 

few oil and gas wells overall (appendix table 1–1), had no 

records of water injection, and vertical proximity of resources 

was unknown or considered low risk.

Water-well density was factored in to the classifications 

to determine if a field that had intermediate rankings for other 

factors would be moved into the low or high summary priority 

category. The rankings for variables measuring water-well 

density (densities of water wells overlying and adjacent to 

fields) were applied to the overall priority classifications based 

on the algorithm shown in figure 8. Fields ranked moderate 

for injection volume, moderate for petroleum-well density, 

and high for water-well density (either overlying or adjacent) 

were classified as high for summary priority because there 

is potentially substantial lateral overlap of resources. Fields 

ranked low for injection volume, moderate for petroleum-well 

density, and low for overlying and adjacent water-well density 

were classified as low for summary priority. 
Figure 7. Distribution of data for individual variables calculated for California oil and gas fields in the preliminary assessment of petroleum resource to groundwater resources: A, density of all petroleum wells, injection wells, and waste-disposal wells; B, total volume of water and steam injection anfor waste-disposal; C, vertical proximity using combined methods, method 1, and method 2; and D, density of overlying water wells and adjacent wate

259 Low range (<0.02)

Low range (<0.02)

1 2 3 4 5 6 7 8 9 

0 10 20 30 40 50 60 70 80 90 

Low range

(<10)

Number of wells per square mile (wells/mi2)

Number of wells per square mile (wells/mi2)Number of wells per square mile (wells/mi2)

84

37 27 16 9 5 4 8

113

55

33 19 18 18 13 4 14 6 7 3 8 5 2 4 0 

Density of injection wells

Moderate range (0.02 to 6)

58

125

24 21 16 10 12 6 9 4 6 8

Density of waste−disposal wells

Moderate range (0.02 to 2) High range (>2)

1 5 0 2 1 1

286

0 0 0 0 0 

0 1 2 3 4 5 6 7 8 9 

50th percentile = 0.0

100

0

200300

Number of fields

100

0

200300

Number of fields

100

0

200300

Number of fields

50th percentile = 0.0

3 6 1 1 2 2 0 1 

Number of fields with 

Maxi

Number of fields with waste

Max

High range (>6)

4

50th percentile = 10.5

Moderate range (10 to 70)

High range (>70)

Total n

Maxim

A Density of all petroleum wells

90th percentile = 1.6

90th percentile = 6.3

90th percentile = 70.9

EXPLAN

0 Numb

samp
Figure 7. —Continued

Million barrels (MMB)

Number of fields with waste−water injec

Maximum = 2

Number of fields

Volume of waste-water injection

32

10 6 7 2 4 2 1 3 2 1 0 1 0 1 0 2 0 1 2 1 0 1

77

Moderate range (2.5 to 25)

Lowrange

Lowrange

High range (>25)

6 7

0 10 20 30 40 50 60 70 8

1 1 0 0 0 0 0 0 0 0 0 0 0 0 

75th percentile = 2.5 90th percentile = 23.9

B Volume of total water and steam injection

0 10 20 30 40 50 60 70 80 90 110 130 150 170 190

10 11 9 7 5 1 3 5 3 1 2 1 0 3 0 1 2 0 1 0 0 2 0 1

113

Moderate range (10 to 140) High range (>140)

Number of fields with water or steam inje

Maximum = 18

50th percentile = 6.7

0

255075

125150175225250275

100200

300

0

255075

125150175225250275

100200300

3 2 0 0 0 0 0 1 1 1 1 1 0 0 0 

100 120 140 160 180 2

Number of fields

Million barrels (MMB)

90th percentile = 140.0

Low range (<2.5)

Lowrange

EXPLANATION

0 Number of fie

sampled

233261

Low range (<10)
Figure 7. —Continued

Median distance between petroleum resource development and groundwater resources, in feet (ft)

12,000 11,000 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 

6

19

14 13

16

8

20

12

10

7

4 5

9

5 5 6 6 4

1 1 1 0 0 0 1 0

3

7

4

9 8

4

13

8

5 3 3 2 4 3 4 1 2 3 0 1 0 0 0 0 0 0

4

12

8 8 9 7

13

9 9 10 7 5 4 10 3 6 8 3 1 1 3 1 2 1

Low range (>3,000 ft)

Moderate range

(1,000 to 3,000 ft)

Hi

(<

15

0

30

Number of fields

Low range (>3,000 ft)

Moderate range

(1,000 to 3,000 ft)

High r

(<1,0

Moderate

range

(1,000 to 3,000 ft) High ra

(<1,000 

Low range (>3,000 ft)

0 0 

Median distance between petroleum resource development and groundwater resources, in feet (ft)

12,000 11,000 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 

15

0

30

Number of fields

Median distance between petroleum resource development and groundwater resources, in feet (ft)

12,000 11,000 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 

15

0

30

Number of fields

Vertical separation distance using method 1 Number of fields with method 1 separati

C

Vertical separation distance using combined methods Total number of fields with separatio

Vertical separation distance using method 2 Number of fields with method 2 separatio

50th percentile = 2,654 75th percentile = 1,0

0

75th percentile = 1,328

50th percentile = 2,844

0

50th percentile = 3,602 75th percentile = 1,701

EXPLANATION

0 Number of fields

sampled

The high and low ranges are named with respect to vertical proximity, which is inversely proportional to vertical separation distance.
Figure 7. —Continued

0 1 2 3 4 5 6 7 8 9 10

Moderate range (1–8)

Number of fields with overlying water wells = 

Maximum = 67 wells pe

Number of fields with adjacent water wells = 

Maximum = 15 wells pe

Density of water wells adjacent to the field

161

110

56 41

16 15 15 10 10 6 4 7 1 3 5 4 2 3 2 2 3

Number of wells per square mile (wells/mi2)

0 1 2 3 4 5 6 7 8 9 10

Number of wells per square mile (wells/mi2)

162

4

Low

range

(<1)

65 47 31 25 16 20 17 14

200

Density of water wells overlying the field

D

50th percentile = 0.6

75th percentile = 1.9 90th percentile = 4.4

90th percentile = 7.8

8 5 3 10 2 4 7 4 1 2 1 3 2

Moderate range (1 to 8)

Low range (<2) Moderate range (2 to 4) High range (>4)

High range (>8)

Number of fields 0 100

200

Number of fields 0 100

EXPLANATION

0 Number of fields

sampled
Figure 8. Decision process and hierarchy of factors considered as part of the prioritization analysis in which California oil and gas fields are classifipriority for regional groundwater monitoring.

Prioritization analysis decision tree

(Number on line indicates number of fields)

Verti

Wate

Petroleu

Volum

Vertical proximity

1,000 to 3,000 ft >3,000 ft

≤1,000 ft

Volume of injection

Low Moderate

High

Low Petroleum-well density Petroleum-well density 

Moderate

Moderate

Low

Low

High

Moderate

Overlying water-well 

density

Overlying water-well 

density

Moderate

Low Adjacent water-well density

Moderate

High

Low

Adjacent water-well 

density Moderate

High

Low

Low priority Moderate priority High pr

3942

13 1

46

9

2511

6

21

83

183

Fields were ranked by each factor into the high, moderate, and low categories for potential risk to groundwater resources using the threshold values listed in table 3. Rankings were then combined to determine the overall priority classification for each oil and gas field by using the decision process and hierarchy of factors shown in this figure.Vertical proximity classification has an inverse relation with separation distance: smaller distances correspond to greater proximity and higher potential risk categories. The injection-volume classification was determined by the higher ranking of the two volume calculations: total volume of water or steam injection and total volume of waste-water injection. The petroleum-well density classification was determined by the highest ranking of the three well density calculations: all petroleum wells, injection wells, or waste-disposal wells. The water-well density classification was determined using a combination of 

rankings for overlying and adjacent water-well densities. 
28 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Results of the Preliminary Assessment 

of Factors for Prioritization

For each of the variables representing petroleum-well 

density, around 10 percent of the fields were in the high 

category, around 40 percent were in the moderate category, 

and around 50 percent were in the low category (table 2). The 

90th percentile was chosen as the moderate-high boundary 

for the variables representing petroleum-well density because 

the data spanned a wide range and some fields having values 

greater than the 90th percentile had dramatically larger 

petroleum-well densities than most of the fields (fig. 7A). The 

90th percentile selected as the boundary between the high 

and moderate categories was rounded from 6.3 wells/mi2 to 

6 wells/mi2 for density of injection wells and rounded from 

1.6 wells/mi2 to 2 wells/mi2 for density of waste-disposal 

wells. Less than half of the oil and gas fields contained 

injection wells; therefore, the boundary between the moderate 

and low categories for both the density of injection wells and 

density of waste-disposal wells was the smallest non-zero 

value (0.02 wells/mi2), equal to the 53rd and 58th percentiles, 

respectively. The 50th percentile approximated a change in the 

frequency distribution of petroleum-well density values, with 

a relatively large number of fields having densities less than 

10 wells/mi2.

For each of the variables representing volume of 

injection, around 10 percent of the fields were in the high 

category, around 15 percent were in the moderate category, 

and around 75 percent were in the low category (table 2). 

The percentiles for total volume of water or steam injection 

and total volume of water injection for waste disposal were 

calculated from the 464 fields that had data. About half of 

the fields had water or steam injection, and total volumes of 

water injection per field were much greater than volumes of 

waste-water disposal (fig. 7B). The 23 fields that did not have 

any injection or production records available online were 

generally small (up to 3 mi2), contained few wells, and were 

mostly abandoned (fields coded as “na” for injection-volume 

variables; appendix table 1–1); these fields were grouped 

into the low risk category for each of the injection-volume 

variables. The 75th percentile was used for the boundary 

between low and moderate categories for total water or steam 

injection and for volume of waste-water injection because it 

was close to a substantial change in the frequency distribution 

for water injection volumes by field and therefore represented 

a logical threshold for separating fields with lower values from 

those with higher injection volumes (fig. 7B).

About 36 percent of the oil and gas fields were 

assessed for vertical proximity (174 of the 487 fields; fig. 6) 

based on median vertical separation distance between 

petroleum resource development to groundwater resources. 

Separation distance was calculated for oil and gas fields 

with sufficient data using a combination of five methods. 

Separation values from each method, the principal method 

used to define separation, and the resulting classification for 

vertical proximity for each of the 174 fields are presented 

in table 3. Separation distance values were positive if 

petroleum development activities were generally deeper 

than groundwater resources and negative if petroleum 

development activities were shallower than groundwater 

resources. Note that greater potential risk to groundwater 

resources is represented by greater values for the density and 

injection-volume variables, whereas greater potential risk is 

represented by smaller values for vertical separation (that is, 

less distance between petroleum resources and groundwater 

resources, or greater proximity). Separation distance values 

were generally greater as calculated from method 2 than from 

method 1 (fig. 7C). Values for vertical separation had a broad 

distribution, with the most frequently occurring values in 

the central part of the distribution and a longer right tail of 

large separation values (lowest proximity) than the left tail 

(greatest proximity). 

The values that defined the boundaries between ranges 

were round numbers close to the 50th and 25th percentiles 

for the combination of all methods applied and for methods 1 

and 2 (the primary methods that were used to define median 

separation distance for the fields; fig. 7C). The proportion of 

total number of fields with vertical proximity in each of the 

high-, moderate-, and low-risk categories and the proportion 

of total fields in each district and statewide are listed in 

table 4. About 23 percent of fields with oil and gas resources 

closest to groundwater resources (separation distance less than 

1,000 feet [ft]) were classified in the high-risk category for 

vertical proximity, which corresponds to 8 percent of the total 

487 fields (table 4). The next approximately one-third of fields 

with vertical separation distance between 1,000 to 3,000 ft 

were in the moderate-risk category, and the 44 percent of the 

fields with separation greater than 3,000 ft were in the low-risk 

category. The true threshold at which groundwater throughout 

California is less vulnerable to oil and gas development is 

unknown. A vertical distance of 3,000 ft was used in this 

study, classifying about half of the fields with sufficient depth 

data in the low-risk category for vertical proximity.

For density of water wells overlying the field, 10 percent 

of the fields were in the high category, 34 percent were 

in the moderate category, and 56 percent were in the low 

category (table 2). For density of water wells adjacent to 

the field, 12 percent of the fields were in the high category, 

11 percent were in the moderate category, and 77 percent 

were in the low category. About two-thirds of the oil and gas 

fields had at least one overlying water well and nearly all 

fields had at least one adjacent water well within 3.1 miles 

of field administrative boundaries (fig. 7D). Densities of 

overlying water wells were generally greater than densities of 

adjacent water wells. This difference was likely not because 

of greater water use within field boundaries compared 

to just outside the fields, but because water wells were 

plotted at the center of the section in which they are located 

(see “Methods” section titled “Calculation of Variables”). 
Results of the Prioritization Analysis 29

A buffer may contain part of a section, but the wells in that 

section were not included in the well-density calculation 

unless the buffer passed through the center of the section. 

Conversely, administrative boundaries for oil and gas fields 

often traced along section boundaries or bisected a section, 

resulting in more water wells being included in the well 

density overlying the field. Water-well densities spanned a 

relatively narrow range of values compared to the petroleumwell densities (fig. 7D). Values near the 90th percentiles were 

selected as the boundary between the moderate and high 

categories for density of overlying water wells and density 

of adjacent water wells because use of the 90th percentiles 

resulted in a clear separation of fields having substantially 

higher well densities. For overlying water-well density, the 

50th percentile approximated the boundary between low and 

moderate categories, above which the frequency of occurrence 

of values gradually declined. In contrast, the 75th percentile 

approximated the boundary between low and moderate 

categories for adjacent water-well density, because it was an 

approximate inflection point in the frequency distribution of 

adjacent well-density values.

Results of the Prioritization Analysis

The prioritization analysis is a statewide reconnaissance 

assessment of potential risk to groundwater from oil and gas 

development using existing data for the purpose of identifying 

where regional monitoring should be implemented first. A 

preliminary analysis of petroleum resource development 

and the proximity to California’s groundwater resources was 

followed by classification of oil and gas fields into overall 

priority classes. 

Petroleum resource development and proximity to 

groundwater resources were assessed for oil and gas fields 

using a combination of rankings of calculated values for 

variables delineating petroleum-well density, volume of 

injection, vertical proximity, and water-well density. Based 

on variable-specific rankings for density of all petroleum 

wells (fig. 9A), injection wells (fig. 9B), and waste-disposal 

wells (fig. 9C), 84 fields had high petroleum-well density, 

218 fields had moderate petroleum-well density, and 185 fields 

had low petroleum-well density (table 5). Based on variablespecific rankings for total volume of water and steam injection 

(fig. 9D) and total volume of waste-water injection (fig. 9E), 

62 fields were classified in the high category for volume of 

injection, 75 fields had moderate volume of injection, and 

350 fields had low volume of injection. Of the 174 fields with 

vertical separation distance values, 39 fields were classified 

in the high-risk category for vertical proximity of oil and gas 

resource development to groundwater resources (greatest 

proximity), 58 fields were in the moderate-risk category, 

and 77 fields were in the low-risk category (table 4; fig. 11). 

Based on rankings for density of water wells overlying the 

field (fig. 9F) and density of water wells adjacent to the field 

(fig. 9G), 67 fields had high water-well density, 158 fields had 

moderate water-well density, and 262 fields had low waterwell density. Only four fields had no overlying or adjacent 

water wells; two of these fields were categorized as high 

priority based on high petroleum-well density and moderate 

volume of injection. Calculated values for the individual 

variables and the rankings for factors used in the prioritization 

analysis are listed in tables 6A–C. 

The prioritization of fields for regional groundwater 

monitoring resulted in 107 fields classified as high overall 

priority, 114 fields as moderate priority, and 266 fields as 

low priority (table 5; fig. 10). On an area-weighted basis, 

41 percent of the aggregated field area ranked high priority, 

30 percent ranked moderate, and 29 percent ranked low. Of the 

107 high priority fields, 39 fields (36 percent) were classified 

as high priority based on vertical proximity, 42 fields were 

classified as high priority based on high volume of injection, 

and the other 26 fields classified as high priority had moderate 

volume of injection coupled with high petroleum-well density 

or had a combination of moderate and high risk classifications 

for petroleum-well density and water-well density (table 6A; 

fig. 8). Often, fields that had petroleum resource development 

vertically closest to groundwater resources also had high 

petroleum-well density: 28 of 39 of the fields that had the 

greatest vertical proximity also had high petroleum-well 

density or high volume of injection. 

Fields were classified as having overall moderate or 

low priority primarily based on a combination of moderate 

and low rankings for three of the major factors considered: 

volume of injection, petroleum-well density, and waterwell density (table 6B, C; fig. 8). A total of 43 fields that 

had moderate injection volume were classified as moderate 

priority (table 6B). For the 337 remaining fields that had 

low injection volume, overall priority classifications were 

based on rankings for well densities: 71 fields were classified 

as moderate priority based on a synthesis of rankings for 

petroleum-well density and water-well density; 183 fields 

that had low petroleum-well density were classified as low 

priority (table 6C); and 83 fields that had moderate petroleumwell density and low water-well density were classified as 

low priority. Whereas petroleum resource development and 

vertical proximity often co-occurred, high water-well density 

was generally not in areas with greatest density of oil and 

gas production activities. Only 13 fields had high waterwell density and also were ranked high for either volume of 

injection or petroleum-well density. On average, low priority 

fields presented the least amount of risk to groundwater 

resources based on low volume of injection and low or 

moderate petroleum-well density (table 6C). Results of the 

prioritization analysis, including maps of fields, their priority 

classification, and rankings for each factor, are summarized in 

more detail by DOGGR district.
30 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 9. California oil and gas fields showing rankings for each of the variables: A, density of all petroleum wells; B, density of 

injection wells; C, density of waste-disposal wells; D, total volume of water and steam injection; E, total volume of water injection for 

waste disposal; F, density of water wells overlying the field; and G, density of water wells adjacent to the field.

121° 120° 119° 118°

37°

36°

35°

34°

Density of all petroleum wells, in wells per square mile (mi2) DWR groundwater basins

DOGGR district boundary

County

High (>70 wells/mi2) Low (<10 wells/mi2)

Moderate (10 to 70 wells/mi2)

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

District 5

District 1

District 2

District 3

District 4

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION

Sac17-0645_fig 9a1

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

FRESNO CO

MADERA CO

KERN CO

LOS ANGELES CO VENTURA CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA BARBARA CO

SAN BERNARDINO CO

TULARE CO

INYO CO

A
Results of the Prioritization Analysis 31

Figure 9. —Continued

Sac17-0645_fig 9a2

124° 123° 122° 121°

40°

39°

38°

Density of all petroleum wells, in wells per square mile (mi2) DWR groundwater basins

DOGGR district boundary

County

Moderate (10 to 70 wells/mi2 Moderate (10 to 70 wells/mi ) 2

Low (>10 wells/mi2 Low (>10 wells/mi ) 2

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 12.5 25 50 KILOMETERS

0 10 20 30 40 50 MILES

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Redding

San Diego

Sacramento

Los Angeles

San Francisco Map

area

CALIFORNIA

EXPLANATION

District 6

District 5

District 3

SAN

FRANCISCO CO

MENDOCINO CO

SONOMA CO

NAPA CO

SOLANO CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

A—Continued
32 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 9. —Continued

Sac17-0645_fig 9b1

121° 120° 119° 118°

37°

36°

35°

34°

Density of injection wells, in wells per square mile (mi2) DWR groundwater basins

DOGGR district boundary

County

High (>6 wells/mi2) Low (<0.02 wells/mi2)

Moderate (0.02 to 6 wells/mi2)

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

District 5

District 1

District 2

District 3

District 4

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

FRESNO CO

MADERA CO

KERN CO

LOS ANGELES CO VENTURA CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA

BARBARA CO

SAN BERNARDINO CO

TULARE CO

INYO CO

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION

B
Results of the Prioritization Analysis 33

Figure 9. —Continued

Sac17-0645_fig 9b2

124° 123° 122° 121°

40°

39°

38°

Density of injection wells, in wells per square mile (mi2) DWR groundwater basins

DOGGR district boundary

Moderate Moderate (0.02 to 6 0.02 to 6 wells/mi wells/mi2) County

Low (<0.02 wells/mi2 Low (<0.02 wells/mi ) 2 High (>6 wells/mi ) 2 High (>6 wells/mi ) 2

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 12.5 25 50 KILOMETERS

0 10 20 40 MILES

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map

area

CALIFORNIA

EXPLANATION

District 6

District 5

District 3

SAN

FRANCISCO CO

MENDOCINO CO

SONOMA CO

NAPA CO

SOLANO CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

B—Continued
34 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 9. —Continued

Sac17-0645_fig 9c1

121° 120° 119° 118°

37°

36°

35°

34°

TULARE CO

INYO CO

Density of waste-disposal wells, in wells per square mile (mi2) DWR groundwater basins

DOGGR district boundary

County

High (>2 wells/mi2) Low (<0.02 wells/mi2)

Moderate (0.02 to 2 wells/mi2)

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

SAN BERNARDINO CO

KERN CO

LOS ANGELES CO VENTURA CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA

BARBARA CO

TULARE CO

INYO CO

FRESNO CO

MADERA CO

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

District 5

District 1

District 2

District 3

District 4

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION

C
Results of the Prioritization Analysis 35

Figure 9. —Continued

Sac17-0645_fig 9c2

SAN

FRANCISCO CO

MENDOCINO CO

SONOMA CO

NAPA CO

SOLANO CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

124° 123° 122° 121°

40°

39°

38°

Density of waste-disposal wells, in wells per square mile (mi2) DWR groundwater basins

DOGGR district boundary

County

Moderate (0.02 to 2 wells/mi2)

Low (<0.02 wells/mi2)

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 12.5 25 50 KILOMETERS

0 10 20 40 MILES

EXPLANATION

District 6

District 5

District 3

C—Continued

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Redding

San Diego

Sacramento

Los Angeles

San Francisco Map

area

CALIFORNIA
36 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 9. —Continued

Sac17-0645_fig 9d1

121° 120° 119° 118°

37°

36°

35°

34°

Total volume of water and steam injection, in million barrels (MMB) DWR groundwater basins

DOGGR district boundary

County

High (>140 MMB) Low (<10 MMB)

Moderate (10 to 140 MMB)

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

SAN BERNARDINO CO

KERN CO

LOS ANGELES CO VENTURA CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA

BARBARA CO

TULARE CO

INYO CO

FRESNO CO

MADERA CO

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

District 5

District 1

District 2

District 3

District 4

D

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014
Results of the Prioritization Analysis 37

Figure 9. —Continued

Sac17-0645_fig 9d2

124° 123° 122° 121°

40°

39°

38°

DWR groundwater basins

DOGGR district boundary

County

Low (<10 MMB)

Total volume of water and steam injection

Moderate (10 Moderate (10 to 140 MMB)

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

0 12.5 25 50 KILOMETERS

0 10 20 40 MILES

EXPLANATION

District 6

District 5

District 3

SAN

FRANCISCO CO

MENDOCINO CO

SONOMA CO

NAPA CO

SOLANO CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

D—Continued

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Redding

San Diego

Sacramento

Los Angeles

San Francisco Map

area

CALIFORNIA
38 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 9. —Continued

Sac17-0645_fig 9e1

121° 120° 119° 118°

37°

36°

35°

34°

Total volume of water injection for waste disposal, in million barrels (MMB) DWR groundwater basins

DOGGR district boundary

County

High (>25 MMB) Low (<2.5 MMB)

Moderate (2.5 to 25 MMB)

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

SAN BERNARDINO CO

KERN CO

LOS ANGELES CO VENTURA CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA

BARBARA CO

TULARE CO

INYO CO

FRESNO CO

MADERA CO

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

District 5

District 1

District 2

District 3

District 4

E

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION
Results of the Prioritization Analysis 39

Figure 9. —Continued

Sac17-0645_fig 9e2

124° 123° 122° 121°

40°

39°

38°

DWR groundwater basins

DOGGR district boundary

County

Total volume of water injection for waste disposal, in million barrels (MMB)

High (>25 MMB) Low (<2.5 MMB)

Moderate (2.5 to 25 MMB)

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 12.5 25 50 KILOMETERS

0 10 20 40 MILES

EXPLANATION

District 6

District 5

District 3

SAN

FRANCISCO CO

MENDOCINO CO

SONOMA CO

NAPA CO

SOLANO CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

E—Continued

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Redding

San Diego

Sacramento

Los Angeles

San Francisco Map

area

CALIFORNIA
40 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 9. —Continued

Sac17-0645_fig 9f1

121° 120° 119° 118°

37°

36°

35°

34°

Density of water wells overlying the field, in wells per square mile (mi2) DWR groundwater basins

DOGGR district boundary

County

High (>8 wells/mi2) Low (<1 well/mi2)

Moderate (1 to 8 wells/mi2)

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

SAN BERNARDINO CO

KERN CO

LOS ANGELES CO VENTURA CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA

BARBARA CO

TULARE CO

INYO CO

FRESNO CO

MADERA CO

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

District 5

District 1

District 2

District 3

District 4

F

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION
Results of the Prioritization Analysis 41

Figure 9. —Continued

Sac17-0645_fig 9f2

124° 123° 122° 121°

40°

39°

38°

DWR groundwater basins

DOGGR district boundary

County

Low (<1 well/mi2)

Density of water wells overlying the field, in wells per square mile (mi2)

High (>8 wells/mi2)

Moderate (1 to 8 wells/mi2)

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 12.5 25 50 KILOMETERS

0 10 20 40 MILES

EXPLANATION

District 6

District 5

District 3

SAN

FRANCISCO CO

MENDOCINO CO

SONOMA CO

NAPA CO

SOLANO CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

F—Continued

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Redding

San Diego

Sacramento

Los Angeles

San Francisco Map

area

CALIFORNIA
42 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 9. —Continued

Sac17-0645_fig 9g1

121° 120° 119° 118°

37°

36°

35°

34°

Density of water wells adjacent to the field, in wells per square mile (mi2) DWR groundwater basins

DOGGR district boundary

County

High (>4 wells/mi2) Low (<2 wells/mi2)

Moderate (2 to 4 wells/mi2)

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

SAN BERNARDINO CO

KERN CO

LOS ANGELES CO VENTURA CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA

BARBARA CO

TULARE CO

INYO CO

FRESNO CO

MADERA CO

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

District 5

District 1

District 2

District 3

District 4

G

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION
Results of the Prioritization Analysis 43

Sac17-0645_fig 9g2

124° 123° 122° 121°

40°

39°

38°

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

DWR groundwater basins

DOGGR district boundary

County

Low (<2 wells/mi2)

Density of water wells adjacent to the field, in wells per square mile (mi2)

High (>4 wells/mi2)

Moderate (2 to 4 wells/mi2)

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

0 12.5 25 50 KILOMETERS

0 10 20 40 MILES

SAN

FRANCISCO CO

MENDOCINO CO

SONOMA CO

NAPA CO

SOLANO CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

EXPLANATION

District 6

District 5

District 3

G—Continued

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Redding

San Diego

Sacramento

Los Angeles

San Francisco Map

area

CALIFORNIA

Figure 9. —Continued
44 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 10. Overall priority classification for oil and gas fields in A, California Division of Oil, Gas, and Geothermal Resources (DOGGR) 

districts 1–5 and B, DOGGR district 6.

Sac17-0645_fig 10a

121° 120° 119° 118°

37°

36°

35°

34°

Priority classifications DWR groundwater basins

DOGGR district boundary

County

High Low

Moderate

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Map area

CALIFORNIA

SAN BENITO CO

SANTA

CLARA CO

STANISLAUS CO

MERCED CO

MONTEREY CO

FRESNO CO

MADERA CO

KERN CO

VENTURA CO LOS ANGELES CO

ORANGE CO

KINGS CO

SAN LUIS OBISPO CO

SANTA BARBARA CO

SAN BERNARDINO CO

TULARE CO

INYO CO

Data sources: California Department of Water Resources (DWR), 2003, 2016; 

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

District 5

District 1

District 2

District 3

District 4

0 15 30 60 MILES

0 15 30 60 KILOMETERS

EXPLANATION

A
Results of the Prioritization Analysis 45

Figure 10. —Continued

Sac17-0645_fig 10b

SAN

FRANCISCO CO

124° 123° 122° 121°

40°

39°

38°

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

2014; California Department of Water Resources (DWR), 2003; California State 

Water Resources Control Board, 2016; Davis and others, 2017

Priority classifications DWR groundwater basins

DOGGR district boundary

County

High Low

Moderate

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 12.5 25 50 KILOMETERS

0 10 20 40 MILES

Redding

San Diego

Sacramento

Los Angeles

San Francisco

Redding

San Diego

Sacramento

Los Angeles

San Francisco

CALIFORNIA

EXPLANATION

District 6

District 5

District 3

MENDOCINO CO

SONOMA CO

NAPA CO

SOLANO CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS CO

SACRAMENTO CO

SAN JOAQUIN CO

STANISLAUS

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

Sacramento

San Francisco

B
46 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 11. Vertical separation distance values calculated using a combination of methods for each oil and gas field with sufficient 

data by California Division of Oil, Gas, and Geothermal Resources (DOGGR) district: A, district 1; B, district 2; C, district 3; D, district 4; 

E, district 5; and F, district 6.

Sac17-0645_fig 11a

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

−1,000

−2,000

High

Moderate

Low

A

30 48 180 12 48 62 952 75 48 7 31 15 15 127 12 9 17 10 6 6 120 6 10 25 5 6

Distance between petroleum resource development and groundwater resources, in feet

Yorba Linda

Montebello

Inglewood

West Newport

Richfield

Torrance

Wilmington

Long Beach

Brea-Olinda

Los Angeles Downtown

Las Cienegas

East Coyote

Dominguez

Huntington Beach

Seal Beach

Sansinena

West Coyote

Rosecrans

Bandini

San Vicente

Santa Fe Springs

Howard Townsite

Playa Del Rey

Beverly Hills

East Los Angeles

Cheviot Hills

 322

1,0081,0661,124

1,124

1,7241,7441,8612,3142,5572,5782,5882,6082,7102,7102,8463,0933,5253,9714,2724,3524,3965,1625,8646,1297,6268,426

5

50th percentile

 (median)

Number of observations 90th percentile

Sample value

Median value

75th percentile

25th percentile

10th percentile

EXPLANATION

Note: The depth of petroleum resource development 

was estimated from the depth to first perforated 

interval (TOP) for petroleum wells in each field, and 

depth of groundwater resources was estimated by 

depth to base of freshwater in petroleum wells 

(method 1; brown boxplots) or total depth of water 

wells overlying the field (method 2; tan boxplots). For 

fields with no groundwater data, separation 

distance was calculated from depths to TOP for 

petroleum wells (method 5; white boxplots). 

Methods 3 and 4 values are not shown. 
Results of the Prioritization Analysis 47

Figure 11. —Continued

Sac17-0645_fig 11bPiru

Oxnard

Summerland

Tapia

Placerita

Newhall

Ojai

Oakridge

Bardsdale

Ramona

Aliso Canyon

Hasley Canyon

Honor Rancho

Ventura

Oak Canyon

Castaic Hills

South Mountain

Saticoy

Rincon

San Miguelito

West Montalvo

Newhall−Potrero

−236

 120 386 768 808

1,0041,4762,6642,8323,0483,1113,3553,9083,9344,6694,9715,7206,3506,5176,8207,8687,868

High

Moderate

Low

6 58 6 10 44 12 33 13 12 10 5 5 6 32 6 6 5 5 22 45 11 6

B

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

−1,000

−2,000

Distance between petroleum resource development and groundwater resources, in feet

120

EXPLANATION

5

50th percentile

 (median)

Number of observations 90th percentile

Sample value 75th percentile

25th percentile

10th percentile

Median value

Note: The depth of petroleum resource development 

was estimated from the depth to first perforated 

interval (TOP) for petroleum wells in each field, and 

depth of groundwater resources was estimated by 

depth to base of freshwater in petroleum wells 

(method 1; brown boxplots) or total depth of water 

wells overlying the field (method 2; tan boxplots). For 

fields with no groundwater data, separation 

distance was calculated from depths to TOP for 

petroleum wells (method 5; white boxplots). 

Methods 3 and 4 values are not shown. 
48 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 11. —Continued

Sac17-0645_fig 11c

High

Moderate

Low

C

0

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

−1,000

−2,000

Distance between petroleum resource development and groundwater resources, in feet

 486 7251,0001,1631,7421,7902,1912,5422,6373,519

Paris Valley

Arroyo Grande

San Ardo

Zaca

Lynch Canyon

Cat Canyon

Casmalia

Orcutt

Santa Maria Valley

Lompoc

6 15 17 5 23 6 14 34 5 8 486

EXPLANATION

5

50th percentile

 (median)

Number of observations 90th percentile

Sample value 75th percentile

25th percentile

10th percentile

Median value

Note: The depth of petroleum resource development 

was estimated from the depth to first perforated 

interval (TOP) for petroleum wells in each field, and 

depth of groundwater resources was estimated by 

depth to base of freshwater in petroleum wells 

(method 1; brown boxplots) or total depth of water 

wells overlying the field (method 2; tan boxplots). For 

fields with no groundwater data, separation 

distance was calculated from depths to TOP for 

petroleum wells (method 5; white boxplots). 

Methods 3 and 4 values are not shown. 
Results of the Prioritization Analysis 49

Figure 11. —Continued

Sac17-0645_fig 11d

5 1,265 12 9 1,249 7 50 25 46 15 30 115 5 42 568 39 6 17 16 15 358 25 25 15 5 14 5 8 6 −503 −312 −243 −72 −29 −19

2880127224307308366432458470570598638692750

1,0481,0761,1001,3481,7801,806

1,874

High

Moderate

Low

D

0

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

−1,000

−2,000

Distance between petroleum resource development and groundwater resources, in feet

Comanche Point

South Belridge

Tejon Hills

Jasmin

Kern River

Kern Bluff

Poso Creek

Round Mountain

Kern Front

Deer Creek

Mount Poso

Midway-Sunset

North Deer Creek

Fruitvale

Lost Hills

Chico Martinez

North Belridge

Devils Den

Rosedale Ranch

Cymric

McKittrick

Asphalto

Edison

Tejon

Blackwells Corner

Trico Gas

Semitropic

Ant Hill

Bowerbank

2

EXPLANATION

5

50th percentile

 (median)

Number of observations 90th percentile

Sample value 75th percentile

25th percentile

10th percentile

Median value

Note: The depth of petroleum resource development 

was estimated from the depth to first perforated 

interval (TOP) for petroleum wells in each field, and 

depth of groundwater resources was estimated by 

depth to base of freshwater in petroleum wells 

(method 1; brown boxplots) or total depth of water 

wells overlying the field (method 2; tan boxplots). For 

fields with no groundwater data, separation 

distance was calculated from depths to TOP for 

petroleum wells (method 5; white boxplots). 

Methods 3 and 4 values are not shown. 
50 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 11d2

High

Moderate

Low

D—Continued

0

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

−1,000

−2,000

Distance between petroleum resource development and groundwater resources, in feet

1,9482,2862,3152,5902,7122,9673,0643,4923,6183,7123,8464,3824,6145,1915,2475,5055,7456,0726,6126,6857,220

7,494

7,9148,1258,2248,2349,03211,559

1,948

EXPLANATION

Buttonwillow Gas

Antelope Hills

Belgian Anticline

McDonald Anticline

Buena Vista

Mountain View

Rosedale

Rose

Pleito

Union Avenue

Wheeler Ridge

North Shafter

Bellevue

Greeley

West Bellevue

Elk Hills

Canfield Ranch

Ten Section

Strand

North Tejon

Canal

North Coles Levee

Paloma

South Coles Levee

San Emidio Nose

Yowlumne

Rio Bravo

Rio Viejo

25 18 8 14 11 21 6 14 7 5 8 22 11 14 8 220 23 11 6 5 6 52 16 7 7 18 11 5

5

50th percentile

 (median)

Number of observations 90th percentile

Sample value 75th percentile

25th percentile

10th percentile

Median value

Note: The depth of petroleum resource development 

was estimated from the depth to first perforated 

interval (TOP) for petroleum wells in each field, and 

depth of groundwater resources was estimated by 

depth to base of freshwater in petroleum wells 

(method 1; brown boxplots) or total depth of water 

wells overlying the field (method 2; tan boxplots). For 

fields with no groundwater data, separation 

distance was calculated from depths to TOP for 

petroleum wells (method 5; white boxplots). 

Methods 3 and 4 values are not shown. 

Figure 11. —Continued
Results of the Prioritization Analysis 51

Sac17-0645_fig 11e

High

Moderate

Low

E

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

−1,000

0

−2,000

Distance between petroleum resource development and groundwater resources, in feet

208

EXPLANATION Burrel

East Extension Coalinga

Southeast Burrel

Gill Ranch Gas

Guijarral Hills

Kettleman North Dome

Pleasant Valley

Hollister

Pyramid Hills

Coalinga

Raisin City

Chowchilla Gas

Jacalitos

Riverdale

Helm

San Joaquin

6 16 1,054 30 6 14 5 15 36 10 7 9 16 24 15 5 208 444 699 1,910 1,963 2,212 3,069 4,467 4,558 5,639 5,790 6,006 6,024 6,683 7,444 7,609

5

50th percentile

 (median)

Number of observations 90th percentile

Sample value 75th percentile

25th percentile

10th percentile

Median value

Note: The depth of petroleum resource development 

was estimated from the depth to first perforated 

interval (TOP) for petroleum wells in each field, and 

depth of groundwater resources was estimated by 

depth to base of freshwater in petroleum wells 

(method 1; brown boxplots) or total depth of water 

wells overlying the field (method 2; tan boxplots). For 

fields with no groundwater data, separation 

distance was calculated from depths to TOP for 

petroleum wells (method 5; white boxplots). 

Methods 3 and 4 values are not shown. 

Figure 11. —Continued
52 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 11f

High

Moderate

Low

F

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

−1,000

0

−2,000

Distance between petroleum resource development and groundwater resources, in feet

6 21 11 7 14 6 12 6 6 7 9 7 37 15 10 11 32 10 7 12 5 5 52 13 5 13 6 8 6 927

EXPLANATION

Todhunters Lake Gas

River Island Gas

Half Moon Bay

Millar Gas

Bounde Creek Gas

Sycamore Gas

Pleasant Creek Gas

Los Medanos Gas

Vernalis Gas

Willows-Beehive Bend Gas

Rice Creek Gas

Maine Prairie Gas

West Thornton-Walnut Grove Gas

Rio Vista Gas

Sutter Buttes Gas

Grizzly Bluff Gas

Brentwood

French Camp Gas

Bunker Gas

Grimes Gas

Lindsay Slough Gas

South Oakley Gas

Lathrop Gas

East Brentwood Gas

Denverton Creek Gas

Union Island Gas

Malton−Black Butte Gas

Livermore

La Honda

927957

1,2211,3081,6861,7012,2922,3002,4142,5112,6352,6452,8442,9183,0183,2763,3403,4503,6023,6604,1684,3425,1485,8037,0997,3837,8738,8049,506

5

50th percentile

 (median)

Number of observations 90th percentile

Sample value 75th percentile

25th percentile

10th percentile

Median value

Note: The depth of petroleum resource development 

was estimated from the depth to first perforated 

interval (TOP) for petroleum wells in each field, and 

depth of groundwater resources was estimated by 

depth to base of freshwater in petroleum wells 

(method 1; brown boxplots) or total depth of water 

wells overlying the field (method 2; tan boxplots). For 

fields with no groundwater data, separation 

distance was calculated from depths to TOP for 

petroleum wells (method 5; white boxplots). 

Methods 3 and 4 values are not shown. 

Figure 11. —Continued
Results of the Prioritization Analysis 53

District 1 (Los Angeles Basin)

District 1 covers the southern end of California from the 

international boundary to San Bernardino County (fig. 12A). 

The 67 oil and gas fields in district 1 represent the smallest 

aggregated field area of the districts (214 mi2; table 5) and are 

primarily within the coastal plain of Los Angeles and Orange 

Counties. The Los Angeles Basin is centered on a northwesttrending syncline bordered by the Newport-Inglewood fault 

zone in the southwest and the Whittier fault zone in the 

northeast (Beyer, 1995). There is a long history of intensive 

oil and gas development in the Los Angeles Basin. Gautier 

and others (2012) estimated a mean of 3.2 billion barrels 

of remaining oil in the most productive oil fields in the Los 

Angeles Basin. Enhanced oil recovery techniques have been 

used in many of these fields to recover remaining oil. The Los 

Angeles Basin coincides with the Coastal Plain of Los Angeles 

and Coastal Plain of Orange County groundwater basins, 

which are separated by the Los Angeles-Orange County 

line (California Department of Water Resources, 2016). The 

northeastern parts of these coastal groundwater basins are 

considered to have higher recharge to underlying deposits, and 

the central and western parts of the groundwater basins are 

areas in which groundwater percolation is impeded by lower 

permeability deposits and groundwater is confined (California 

Department of Water Resources, 2015). Eleven district 1 fields 

are in or near the San Gabriel Valley groundwater basin and 

Upper Santa Ana Valley groundwater basin in San Bernardino 

and Riverside Counties (fig. 12A).

For district 1, 37 percent of the fields (25 fields) were 

classified as high priority, 19 percent (13 fields) were 

moderate, and 43 percent (29 fields) were low (table 5). 

High overall priority classification was primarily based on 

high intensity of petroleum resource development and, for a 

few fields, vertical proximity to groundwater resources. Of 

the 25 fields in district 1 classified as high overall priority, 

24 fields had high petroleum-well density and moderate or 

high volume of injection, 4 fields had close vertical proximity 

of resources, and none had high water-well density (table 6A; 

figs. 12A–E). For fields with high volume of injection, oil field 

injection volumes were predominantly for the purposes of 

enhanced oil recovery. High-priority fields were generally the 

largest fields that accounted for the majority of the district’s 

field area. By area, 79 percent of the total area of district 1 oil 

and gas fields was classified as high priority, 7 percent was 

moderate, and 14 percent was low (table 5). Otherwise, fields 

had physical characteristics that indicated moderate to low 

risk to groundwater resources. Vertical proximity of petroleum 

resource development to groundwater resources was most 

frequently moderate and low. Water-well density was typically 

low in and near oil and gas fields, particularly at fields along 

the edges of the groundwater basins.

Petroleum resource development in district 1 was 

relatively far from groundwater resources compared to oil 

and gas fields in other districts. Of the 67 fields in district 

1, 4 fields were classified in the high-risk category based on 

vertical proximity, 16 fields were in the moderate category, 

13 fields were in the low category, and 34 fields had 

insufficient data to evaluate this factor (table 4; fig. 12D). 

Median vertical separation distances for district 1 fields 

were typically between 1,000 and 8,500 ft (fig. 11). Many 

of the smaller fields had insufficient data to evaluate vertical 

proximity and had low intensity of petroleum resource 

development based on low petroleum-well density and little or 

no water injection compared with larger fields. The availability 

of depth to BFW data was greater in district 1 than in most 

other districts (except district 6): vertical separation distance 

for almost half of the fields was calculated using BFW data, 

and these fields were mostly in the moderate risk category 

for vertical proximity (figs. 6 and 11). Water-well density for 

the fields was most frequently low (fig. 12E); water wells 

were primarily public supply wells located in the central 

part of the Coastal Plain of Los Angeles and Coastal Plain 

of Orange County groundwater basins, whereas oil and gas 

fields are located along the edges of the groundwater basins. 

High overall priority classification for district 1 fields was 

based on the intensity of oil and gas development, and with 

the exception of a few fields with close vertical proximity to 

groundwater resources, these fields were not classified as high 

risk based on proximity to groundwater resources.

District 2 (Ventura Basin)

District 2 encompasses Ventura County and the western 

part of Los Angeles County in southern California. The 

70 fields in district 2 have an aggregated field area of 309 mi2

in the coastal valley and surrounding foothills of the western 

Transverse Ranges between the Topatopa Mountains in the 

north and the Santa Monica Mountains in the south (fig. 13A). 

The Ventura Basin is the main structural downwarp that 

formed in the major fold and thrust belt system, trapping oil 

accumulations along several anticlinal structures that have 

varying degrees of deformation (Keller, 1995). Cumulative 

production in Ventura Basin through 1990 was approximately 

2,640 million barrels of oil, 4.64 trillion cubic feet of gas, 

and 160 million barrels of total natural gas liquids. District 2 

fields are primarily in or near the Santa Clara River Valley, a 

few fields are in Ventura River Valley, Los Posas Valley, San 

Fernando Valley, Simi Valley, Conejo, Pleasant Valley, Ojai 

Valley, and Upper Ojai Valley groundwater basins, and two 

fields are in Montecito and Carpinteria groundwater basins 

in Santa Barbara County. The other oil and gas fields in the 

Santa Barbara coastal plain are part of the Ventura Basin but 

are within the boundary of district 3. The most productive 

groundwater aquifers of the Santa Clara River Valley 

generally consist of layers of alluvium deposited between 

the Pliocene and Holocene epochs with groundwater present 

under unconfined, semi-confined, and confined conditions 

(California Department of Water Resources, 2015).
54 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

For district 2, 19 percent of the fields (13 fields) were 

classified as high priority, 30 percent (21 fields) were 

moderate, and 51 percent (36 fields) were low (table 5; 

fig. 13A). High overall priority classification was primarily 

based on high petroleum-well density, including some of 

the highest densities of injection wells and waste-disposal 

wells in the state. Eleven of the 13 high-priority fields in the 

district had high petroleum-well density and high or moderate 

volume of injection wells (table 6A; figs. 13B, C). Densities 

of injection and waste-disposal wells in the State were up to 

43 wells/mi2 (San Miguelito field) and 11 wells/mi2 (Placerita 

field), respectively. Other than injection wells used for EOR 

or waste disposal, district 2 contained about 35 percent of the 

gas storage wells and more than half of the dry hole wells 

in California. Although well densities were high for some 

fields in the district, fields were more frequently classified as 

moderate and low overall priority. By area, 23 percent of the 

total area of district 2 oil and gas fields was ranked as high 

priority, 52 percent was moderate, and 24 percent was low. 

The percentage of moderate-priority fields (by count and by 

area) in district 2 was greater than for other districts. Moderate 

overall priority classification was characterized by moderate 

petroleum-well density, moderate and low volume of injection, 

moderate and low vertical proximity of resources, and low 

water-well density. This combination may indicate that most 

fields in district 2 were small, produced little petroleum, and 

did not have petroleum resource development near where 

groundwater resources are currently used. 

Median vertical separation distances for fields varied 

throughout district 2, but most oil and gas fields in the district 

were deep and had large vertical distances from groundwater 

(fig. 13D). Of the fields in district 2, 5 fields were classified 

in the high-risk category for vertical proximity, 6 fields were 

in the moderate category, 15 were in the low category, and 

44 fields had insufficient data to evaluate vertical proximity 

(table 4). Median vertical separation distance (shown in 

fig. 11) varied from a potential overlap of resources to 7,900 ft 

separation. Water-well density was low for most fields 

throughout the district (fig. 13E). Many of the groundwater 

wells were in the alluvial groundwater basins in the center 

of the valleys, whereas oil and gas fields were more often 

in the mountainous regions outside or at the edges of the 

groundwater basins.

District 3 (Central Coast)

District 3 includes counties along the central coast 

of California from Santa Barbara to Santa Clara County 

(fig. 10A). The 39 fields in the district have an aggregated field 

area of 264 mi2 (table 5). There were about 12,600 DOGGR 

oil and gas wells in the district, including 11,000 production 

wells and 1,350 injection wells (table 1). Injection wells 

are primarily steam injection, water flood, and waste 

disposal. District 3 fields are primarily in the Santa Maria 

Basin (Stanley, 1995) that coincides with the Santa Maria, 

San Antonio Creek Valley, and Santa Ynez River Valley 

groundwater basins; in the Cuyama Basin (Tennyson, 1995) 

that coincides with the Cuyama Valley groundwater basin; 

and in the Salinas Basin (Stanley, 1995) that coincides with 

the Salinas Valley groundwater basin in the north portion 

of the district (California Department of Water Resources, 

2016). There are a few fields along the Santa Barbara coastal 

plain, some of which are gas fields or used for gas storage. 

Much of the petroleum that has been produced is from 

reservoirs in Miocene sandstones, and indications of oil and 

gas at the surface, such as tar sands and seeps, are known in 

certain areas. In the Santa Maria Basin, oil accumulations are 

generally heavy and from reservoirs in the Miocene Monterey 

Formation trapped in anticlines or by an unconformity and 

from Pliocene sandstone reservoirs above an unconformity 

(Tennyson, 1996). In the Salinas Basin, fields such as San 

Ardo, Paris Valley, and King City fields have oil trapped 

in anticlines; the other fields in the Salinas Basin have 

stratigraphic petroleum traps (Stanley, 1995). The source 

rock for petroleum in the Salinas Basin is believed to be the 

Monterey Formation, from which heavy oil, minor amounts of 

gas, and large volumes of water have been produced.

For district 3, 36 percent of the oil and gas fields 

(14 fields) were classified as high priority, 21 percent (8 fields) 

were moderate, and 44 percent (17 fields) were low (table 5; 

fig. 14A). District 3 contains the fewest number of fields 

among all the districts, but some fields are larger, giving an 

aggregated field area (264 mi2) that is greater than the 67 fields 

in district 1 (214 mi2). By area, 80 percent of the total area of 

district 3 oil and gas fields ranked as high priority, 7 percent 

was moderate, and 13 percent was low. High priority fields 

in district 3 were generally characterized as large fields with 

moderate to high petroleum-well density. Because the fields 

were larger (up to 60 mi2) and had moderate to high density of 

injection wells, fields also tended to have high water injection 

volumes (total and waste-disposal). Twelve of the fourteen 

high priority fields were in the high risk category for water 

injection volumes and included fields with some of the highest 

waste-water disposal volumes in the State (table 6A). The rest 

of the 25 fields classified as moderate and low priority were 

small compared to other fields in the district (field areas less 

than 5 mi2) and mostly had moderate to low petroleum-well 

density, low volume of injection, unknown vertical proximity, 

and moderate to low water-well density (tables 6A–B). 

Of the fields in district 3, 2 fields were classified as high 

risk based on vertical proximity, 7 fields were moderate, 

1 field was low, and 29 fields had insufficient data to evaluate 

this factor (table 5; fig. 14D). District 3 fields had mostly 

low water-well density (26 fields), some fields had moderate 

density (13 fields), and no fields in the district had high 

water-well density (fig. 14E). There were a couple fields 

(Santa Maria Valley and Cat Canyon) in the middle of the 

Santa Maria groundwater basins that had several overlying 

water wells, yet had low or moderate water-well density 

and moderate risk from vertical proximity; these fields were 

classified as high priority based on high volume of injection 

rather than proximity of petroleum resource development to 

groundwater resources.
Results of the Prioritization Analysis 55

Figure 12. Oil and gas fields in district 1, Los Angeles Basin, showing classifications for A, overall priority; B, petroleum-well density; 

C, volume of injection; D, vertical proximity; and E, water-well density.

Sac17-0645_fig 12a

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

SAN

GABRIEL

VALLEY

COASTAL

PLAIN OF

LOS ANGELES

COASTAL

PLAIN OF

ORANGE

COUNTY

SAN

JUAN

VALLEY

SAN FERNANDO VALLEY

RAYMOND

UPPER 

SANTA

ANA

VALLEY

District 1

118°20'

34°10'

33°50'

33°40'

34°

118° 117°40'

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

642 424

422

682 134 054 136

568

322

232

394

012

782

849

258

622

620

208

618

414

412

688

728

320

740

502

504

316

554

704

640

674

804 068

034 426

478

666

496

378

838

796

820

630

660

396

836

078 076

070

180 178 856

598 360

362 572

440

142

240

364

376

382

324

522

014

DWR groundwater basins

County

DWR groundwater subbasins

Priority classifications

High Moderate Low

EXPLANATION

Numbers in priority classifications indicate the field codes

Field

name

Field

code

Alondra

Anaheim

Bandini

Beverly Hills

Boyle Heights

Brea-Olinda

Buena Park, East

Buena Park, West

Cheney Ranch Gas

Cheviot Hills

Chino-Soquel

Coyote, East

Coyote, West

Dominguez

El Segundo

Esperanza

Gaffey

012

014

034

054

068

070

076

078

134

136

142

178

180

208

232

240

258

Field

name

Field

code

Howard Townsite

Huntington Beach

Hyperion

Inglewood

Kraemer

Kraemer, Northeast

Kraemer, West

La Mirada

Lapworth

Las Cienegas

Lawndale

Leffingwell

Long Beach

Long Beach Airport

Los Angeles City

Los Angeles Downtown

Los Angeles, East

316

320

322

324

360

362

364

376

378

382

394

396

412

414

422

424

426

Mahala

Montebello

Newgate

Newport

Newport, West

Olive

Playa Del Rey

Potrero

Prado-Corona

Richfield

Rosecrans

Rosecrans, East

Rosecrans, South

Rowland

Salt Lake

Salt Lake, South

Sansinena

440

478

496

502

504

522

554

568

572

598

618

620

622

630

640

642

660

Santa Fe Springs

San Vicente

Sawtelle

Seal Beach

Sherman

Sunset Beach

Talbert

Torrance

Turnbull

Union Station

Walnut

Whittier

Whittier Heights, North

Wilmington

Yorba Linda

666

674

682

688

704

728

740

782

796

804

820

836

838

849

856

Field

name

Field

code

Field

name

Field

code

A

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983
56 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 12b

SAN

GABRIEL

VALLEY

COASTAL

PLAIN OF

LOS ANGELES

COASTAL

PLAIN OF

ORANGE

COUNTY

SAN

JUAN

VALLEY

SAN FERNANDO VALLEY

RAYMOND

UPPER 

SANTA

ANA

VALLEY

118°20'

34°10'

33°50'

33°40'

34°

118° 117°40'

DWR groundwater basins

County

DWR groundwater subbasins

Petroleum-well density

High Moderate Low

EXPLANATION

Numbers in petroleum-well density classifications indicate the field codes

Field

name

Field

code

Alondra

Anaheim

Bandini

Beverly Hills

Boyle Heights

Brea-Olinda

Buena Park, East

Buena Park, West

Cheney Ranch Gas

Cheviot Hills

Chino-Soquel

Coyote, East

Coyote, West

Dominguez

El Segundo

Esperanza

Gaffey

012

014

034

054

068

070

076

078

134

136

142

178

180

208

232

240

258

Field

name

Field

code

Howard Townsite

Huntington Beach

Hyperion

Inglewood

Kraemer

Kraemer, Northeast

Kraemer, West

La Mirada

Lapworth

Las Cienegas

Lawndale

Leffingwell

Long Beach

Long Beach Airport

Los Angeles City

Los Angeles Downtown

Los Angeles, East

316

320

322

324

360

362

364

376

378

382

394

396

412

414

422

424

426

Mahala

Montebello

Newgate

Newport

Newport, West

Olive

Playa Del Rey

Potrero

Prado-Corona

Richfield

Rosecrans

Rosecrans, East

Rosecrans, South

Rowland

Salt Lake

Salt Lake, South

Sansinena

440

478

496

502

504

522

554

568

572

598

618

620

622

630

640

642

660

Santa Fe Springs

San Vicente

Sawtelle

Seal Beach

Sherman

Sunset Beach

Talbert

Torrance

Turnbull

Union Station

Walnut

Whittier

Whittier Heights, North

Wilmington

Yorba Linda

666

674

682

688

704

728

740

782

796

804

820

836

838

849

856

Field

name

Field

code

Field

name

Field

code

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

LOS ANGELES CO

SAN BERNARDINO CO

LOS ANGELES CO

ORANGE CO

RIVERSIDE CO

District 1

320

504

502

740

728

688

412

208

414

849

782

012

426

362

142

440

572

478

836

660

630

070

856

598

180 178 376

076

522

360

364

240

396

666

394

232

258

322

620

622

618

316

568

324

682 136

134 054 642

674

382

378

078

496

014

838

796

820

424

422 640

704

804

068

034

554

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

B

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Figure 12. —Continued
Results of the Prioritization Analysis 57

Sac17-0645_fig 12c

118°20'

34°10'

33°50'

33°40'

34°

118° 117°40'

DWR groundwater basins

County

DWR groundwater subbasins

Volume of injection

High Moderate Low

EXPLANATION

Numbers in volume of injection classifications indicate the field codes

Field

name

Field

code

Alondra

Anaheim

Bandini

Beverly Hills

Boyle Heights

Brea-Olinda

Buena Park, East

Buena Park, West

Cheney Ranch Gas

Cheviot Hills

Chino-Soquel

Coyote, East

Coyote, West

Dominguez

El Segundo

Esperanza

Gaffey

012

014

034

054

068

070

076

078

134

136

142

178

180

208

232

240

258

Field

name

Field

code

Howard Townsite

Huntington Beach

Hyperion

Inglewood

Kraemer

Kraemer, Northeast

Kraemer, West

La Mirada

Lapworth

Las Cienegas

Lawndale

Leffingwell

Long Beach

Long Beach Airport

Los Angeles City

Los Angeles Downtown

Los Angeles, East

316

320

322

324

360

362

364

376

378

382

394

396

412

414

422

424

426

Mahala

Montebello

Newgate

Newport

Newport, West

Olive

Playa Del Rey

Potrero

Prado-Corona

Richfield

Rosecrans

Rosecrans, East

Rosecrans, South

Rowland

Salt Lake

Salt Lake, South

Sansinena

440

478

496

502

504

522

554

568

572

598

618

620

622

630

640

642

660

Santa Fe Springs

San Vicente

Sawtelle

Seal Beach

Sherman

Sunset Beach

Talbert

Torrance

Turnbull

Union Station

Walnut

Whittier

Whittier Heights, North

Wilmington

Yorba Linda

666

674

682

688

704

728

740

782

796

804

820

836

838

849

856

Field

name

Field

code

Field

name

Field

code

SAN

GABRIEL

VALLEY

COASTAL

PLAIN OF

LOS ANGELES

COASTAL

PLAIN OF

ORANGE

COUNTY

SAN

JUAN

VALLEY

SAN FERNANDO VALLEY

RAYMOND

UPPER 

SANTA

ANA

VALLEY

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

District 1

LOS ANGELES CO

ORANGE CO

RIVERSIDE CO

SAN BERNARDINO CO

LOS ANGELES CO

502

504

320

014

522

078 076

180

396

666

622

620

316

568

324

382 424 804 068

034 426

478 378

422 640

704

682 642

674

054 136 134

554

618 178

598

856

070

660

836

796

838 820

630

360

240

142

440

572

362

414

412

849

782

208 012

394

232

322

728

688

496

376

364

258

740

C

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Figure 12. —Continued
58 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 12d

SAN

GABRIEL

VALLEY

COASTAL

PLAIN OF

LOS ANGELES

COASTAL

PLAIN OF

ORANGE

COUNTY

SAN

JUAN

VALLEY

SAN FERNANDO VALLEY

RAYMOND

UPPER 

SANTA

ANA

VALLEY

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

118°20'

34°10'

33°50'

33°40'

34°

118° 117°40'

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Vertical Proximity

Close Moderate Far Unknown

EXPLANATION

Numbers in vertical proximity classifications indicate the field codes

DWR groundwater basins

County

DWR groundwater subbasins

Field

name

Field

code

Alondra

Anaheim

Bandini

Beverly Hills

Boyle Heights

Brea-Olinda

Buena Park, East

Buena Park, West

Cheney Ranch Gas

Cheviot Hills

Chino-Soquel

Coyote, East

Coyote, West

Dominguez

El Segundo

Esperanza

Gaffey

012

014

034

054

068

070

076

078

134

136

142

178

180

208

232

240

258

Field

name

Field

code

Howard Townsite

Huntington Beach

Hyperion

Inglewood

Kraemer

Kraemer, Northeast

Kraemer, West

La Mirada

Lapworth

Las Cienegas

Lawndale

Leffingwell

Long Beach

Long Beach Airport

Los Angeles City

Los Angeles Downtown

Los Angeles, East

316

320

322

324

360

362

364

376

378

382

394

396

412

414

422

424

426

Mahala

Montebello

Newgate

Newport

Newport, West

Olive

Playa Del Rey

Potrero

Prado-Corona

Richfield

Rosecrans

Rosecrans, East

Rosecrans, South

Rowland

Salt Lake

Salt Lake, South

Sansinena

440

478

496

502

504

522

554

568

572

598

618

620

622

630

640

642

660

Santa Fe Springs

San Vicente

Sawtelle

Seal Beach

Sherman

Sunset Beach

Talbert

Torrance

Turnbull

Union Station

Walnut

Whittier

Whittier Heights, North

Wilmington

Yorba Linda

666

674

682

688

704

728

740

782

796

804

820

836

838

849

856

Field

name

Field

code

Field

name

Field

code

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA LOS ANGELES CO

ORANGE CO

RIVERSIDE CO

SAN BERNARDINO CO

LOS ANGELES CO

District 1

782

849

320

728

688

412

414

208

324

682 136 134 054

674

704

640 422

382

424 804

068

034 426

666

836

660

070

856

598

522

180 178

820 478 378

838

796 630

642

618

622

554

316

568

012

394

322

232

504

502

740

258

496

376

396

078 076

014

364

360

362

240

142

440

572

D

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

620

Figure 12. —Continued
Results of the Prioritization Analysis 59

Sac17-0645_fig 12e

118°20'

34°10'

33°50'

33°40'

34°

118° 117°40'

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Water-well density

Field

name

Field

code

Alondra

Anaheim

Bandini

Beverly Hills

Boyle Heights

Brea-Olinda

Buena Park, East

Buena Park, West

Cheney Ranch Gas

Cheviot Hills

Chino-Soquel

Coyote, East

Coyote, West

Dominguez

El Segundo

Esperanza

Gaffey

012

014

034

054

068

070

076

078

134

136

142

178

180

208

232

240

258

Field

name

Field

code

Howard Townsite

Huntington Beach

Hyperion

Inglewood

Kraemer

Kraemer, Northeast

Kraemer, West

La Mirada

Lapworth

Las Cienegas

Lawndale

Leffingwell

Long Beach

Long Beach Airport

Los Angeles City

Los Angeles Downtown

Los Angeles, East

316

320

322

324

360

362

364

376

378

382

394

396

412

414

422

424

426

Mahala

Montebello

Newgate

Newport

Newport, West

Olive

Playa Del Rey

Potrero

Prado-Corona

Richfield

Rosecrans

Rosecrans, East

Rosecrans, South

Rowland

Salt Lake

Salt Lake, South

Sansinena

440

478

496

502

504

522

554

568

572

598

618

620

622

630

640

642

660

Santa Fe Springs

San Vicente

Sawtelle

Seal Beach

Sherman

Sunset Beach

Talbert

Torrance

Turnbull

Union Station

Walnut

Whittier

Whittier Heights, North

Wilmington

Yorba Linda

666

674

682

688

704

728

740

782

796

804

820

836

838

849

856

Field

name

Field

code

Field

name

Field

code

High Moderate Low

EXPLANATION

Numbers in water-well density classifications indicate the field codes

DWR groundwater basins

County

DWR groundwater subbasins

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

LOS ANGELES CO

ORANGE CO

RIVERSIDE CO

SAN BERNARDINO CO

LOS ANGELES CO

SAN

GABRIEL

VALLEY

COASTAL

PLAIN OF

LOS ANGELES

COASTAL

PLAIN OF

ORANGE

COUNTY

SAN

JUAN

VALLEY

SAN FERNANDO VALLEY

RAYMOND

UPPER 

SANTA

ANA

VALLEY

District 1

E

502

504

740

728

688

412

414

208

622 012

034 426

478 378

820

836

666

396

496

376

078

660

070

142

240

360

364

362

440

180 572 178 856

598

522

076

838

796 630

394

232

322

554

324

136

134 054

382 424

682

674 640 422

804 068

642

618

316

568

849

782

258

320

014

704

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

620

Figure 12. —Continued
60 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 13. Oil and gas fields in district 2, Ventura Basin, showing classifications for A, overall priority; B, petroleum-well density; 

C, volume of injection; D, vertical proximity; and E, water-well density.

Sac17-0645_fig 13a

DOGGR district boundary

Priority classifications

Field

name

Field

code

Aliso Canyon

Bardsdale

Beverly Hills

Big Mountain

Bouquet Canyon

Cabrillo

Canada Larga

Canton Creek

Cascade

Castaic Hills

Castaic Junction

Chaffee Canyon

Charlie Canyon

Cheviot Hills

Conejo

Del Valle

El Rio

El Segundo

Eureka Canyon

Fillmore

010

036

054

056

064

091

102

110

120

124

126

130

132

136

170

198

230

232

242

246

Field

name

Field

code

Hasley Canyon

Holser

Honor Rancho

Hopper Canyon

Horse Meadows

Hyperion

Inglewood

Las Llajas

Las Posas

Long Canyon

Lyon Canyon

Mission

Montalvo, West

Moorpark

Moorpark West

Newhall

Newhall-Potrero

Oak Canyon

Oak Park

Oakridge

298

304

308

310

312

322

324

384

386

416

438

468

476

484

485

498

500

508

512

514

Oakview

Oat Mountain

Ojai

Oxnard

Pacoima

Piru

Piru Creek

Placerita

Playa Del Rey

Ramona

Ramona, North

Rincon

Rincon Creek

Salt Lake

San Miguelito

Santa Clara Avenue

Santa Paula

Santa Susana

San Vicente

Saticoy

516

519

520

530

531

546

548

550

554

586

588

600

601

640

658

662

670

672

674

678

Saugus

Sawtelle

Sespe

Sherman

Shiells Canyon

Simi

Somis

South Mountain

Summerland

Tapia

Tapo, North

Tapo Canyon, South

Tapo Ridge

Temescal

Timber Canyon

Torrey Canyon

Ventura

Wayside Canyon

West Mountain

680

682

694

704

708

710

712

714

724

742

744

746

748

764

774

784

814

824

830

Field

name

Field

code

Field

name

Field

code

High Moderate Low

EXPLANATION

Numbers in priority classifications indicate the field codes

DWR groundwater basins County

DWR groundwater subbasins

OJAI

VALLEY

UPPER

OJAI

VALLEY

MONTECITO

CARPINTERIA

VENTURA

RIVER VALLEY

LOWER VENTURA

RIVER VALLEY

LOS POSAS

VALLEY

PLEASANT

VALLEY

HIDDEN

VALLEY

THOUSAND

OAKS AREA

CONEJO RUSSELL

VALLEY

MALIBU

VALLEY

COASTAL PLAIN

OF LOS

ANGELES

SIMI VALLEY

SAN FERNANDO

VALLEY

SANTA CLARA

RIVER VALLEY

SANTA PAULA

SANTA CLARA

RIVER VALLEY

UPPER

VENTURA

RIVER

OJAI

VALLEY

UPPER

OJAI

VALLEY

MONTECITO

CARPINTERIA

VENTURA

RIVER VALLEY

LOWER VENTURA

RIVER VALLEY

LOS POSAS

VALLEY

PLEASANT

VALLEY

HIDDEN

VALLEY

THOUSAND

OAKS AREA

CONEJO RUSSELL

VALLEY

MALIBU

VALLEY

COASTAL PLAIN

OF LOS

ANGELES

SIMI VALLEY

SAN FERNANDO

VALLEY

SANTA CLARA

RIVER VALLEY

SANTA PAULA

SANTA CLARA

RIVER VALLEY

UPPER

VENTURA

RIVER

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

694

310 546

548

764

508 124

132 742

308 824

064

680

298

198

500

498

519

384 710

512

708 036

246

774

670

102

520

520

601

724

600

814

476

230

662

530

091

416

712

170

386

678

830 714

658

130

784 514

746

484 056

485

672

744 242

010 120

468

531

312

704

640

674 682

136

324

554

322

232

054

550 438

586

304 588

126

110

516 748

34°30'

34°

119°30' 119°0' 118°30'

District 2

District 3

District 1

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

VENTURA CO

VENTURA CO

SANTA BARBARA CO

LOS ANGELES CO

ORANGE CO

A

Topatopa Mountains

Santa Monica Mountains

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983
Results of the Prioritization Analysis 61

Sac17-0645_fig 13b

34°30'

34°

119°30' 119°0' 118°30'

VENTURA CO

VENTURA CO

SANTA BARBARA CO

LOS ANGELES CO

ORANGE CO

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29° 30’ and 45° 30’; North American Datum of 1983

Petroleum-well density

Field

name

Field

code

Aliso Canyon

Bardsdale

Beverly Hills

Big Mountain

Bouquet Canyon

Cabrillo

Canada Larga

Canton Creek

Cascade

Castaic Hills

Castaic Junction

Chaffee Canyon

Charlie Canyon

Cheviot Hills

Conejo

Del Valle

El Rio

El Segundo

Eureka Canyon

Fillmore

010

036

054

056

064

091

102

110

120

124

126

130

132

136

170

198

230

232

242

246

Field

name

Field

code

Hasley Canyon

Holser

Honor Rancho

Hopper Canyon

Horse Meadows

Hyperion

Inglewood

Las Llajas

Las Posas

Long Canyon

Lyon Canyon

Mission

Montalvo, West

Moorpark

Moorpark West

Newhall

Newhall-Potrero

Oak Canyon

Oak Park

Oakridge

298

304

308

310

312

322

324

384

386

416

438

468

476

484

485

498

500

508

512

514

Oakview

Oat Mountain

Ojai

Oxnard

Pacoima

Piru

Piru Creek

Placerita

Playa Del Rey

Ramona

Ramona, North

Rincon

Rincon Creek

Salt Lake

San Miguelito

Santa Clara Avenue

Santa Paula

Santa Susana

San Vicente

Saticoy

516

519

520

530

531

546

548

550

554

586

588

600

601

640

658

662

670

672

674

678

Saugus

Sawtelle

Sespe

Sherman

Shiells Canyon

Simi

Somis

South Mountain

Summerland

Tapia

Tapo, North

Tapo Canyon, South

Tapo Ridge

Temescal

Timber Canyon

Torrey Canyon

Ventura

Wayside Canyon

West Mountain

680

682

694

704

708

710

712

714

724

742

744

746

748

764

774

784

814

824

830

Field

name

Field

code

Field

name

Field

code

High Moderate Low

EXPLANATION

Numbers in petroleum-well density classifications indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

724

600

658 814

601

520

516

520

774

670

714

246

036 708

242

130 784 514

531

704

550

680 064

308

824

500

498

438

120

312 468

010

384 519

512 710 484

712

386

170 530

091

662 230

476

485

746

056

672

748 744

310 546

764

110

508

132

742 124

298

198 126 586

588

304

694

830

102

416

678

548

640

674

054

324

554

322

232

136 682

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

District 2

District 1

District 3

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

B

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Figure 13. —Continued
62 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 13c

District 2

District 1

34°30'

34°

119°30' 119°0' 118°30'

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29° 30’ and 45° 30’; North American Datum of 1983

Volume of injection

Field

name

Field

code

Aliso Canyon

Bardsdale

Beverly Hills

Big Mountain

Bouquet Canyon

Cabrillo

Canada Larga

Canton Creek

Cascade

Castaic Hills

Castaic Junction

Chaffee Canyon

Charlie Canyon

Cheviot Hills

Conejo

Del Valle

El Rio

El Segundo

Eureka Canyon

Fillmore

010

036

054

056

064

091

102

110

120

124

126

130

132

136

170

198

230

232

242

246

Field

name

Field

code

Hasley Canyon

Holser

Honor Rancho

Hopper Canyon

Horse Meadows

Hyperion

Inglewood

Las Llajas

Las Posas

Long Canyon

Lyon Canyon

Mission

Montalvo, West

Moorpark

Moorpark West

Newhall

Newhall-Potrero

Oak Canyon

Oak Park

Oakridge

298

304

308

310

312

322

324

384

386

416

438

468

476

484

485

498

500

508

512

514

Oakview

Oat Mountain

Ojai

Oxnard

Pacoima

Piru

Piru Creek

Placerita

Playa Del Rey

Ramona

Ramona, North

Rincon

Rincon Creek

Salt Lake

San Miguelito

Santa Clara Avenue

Santa Paula

Santa Susana

San Vicente

Saticoy

516

519

520

530

531

546

548

550

554

586

588

600

601

640

658

662

670

672

674

678

Saugus

Sawtelle

Sespe

Sherman

Shiells Canyon

Simi

Somis

South Mountain

Summerland

Tapia

Tapo, North

Tapo Canyon, South

Tapo Ridge

Temescal

Timber Canyon

Torrey Canyon

Ventura

Wayside Canyon

West Mountain

680

682

694

704

708

710

712

714

724

742

744

746

748

764

774

784

814

824

830

Field

name

Field

code

Field

name

Field

code

High Moderate Low

EXPLANATION

Numbers in injection classifications indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

VENTURA CO

VENTURA CO

SANTA BARBARA CO

LOS ANGELES CO

ORANGE CO

694

246

774

670

520

724

516

508

304 586 198

298 308

824

064

550

438

498

010 120

531

682 136

324

054

674

640

704

554

322

232

312 468

680

742

132

124

126

500

514

744

746

672

748 242

130 784

384 519

710 512 484 485

712

714 830

678

814 416

600

658

170

091

530

662 230

476 386

056

764 588

310 546

708 036

110

548

102

601

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

District 3

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

C

Figure 13. —Continued
Results of the Prioritization Analysis 63

Figure 13. —Continued

Sac17-0645_fig 13d

District 2

District 1

34°30'

34°

119°30' 119°0' 118°30'

VENTURA CO

VENTURA CO

SANTA BARBARA CO

ORANGE CO

LOS ANGELES CO

Unknown

Vertical proximity

Field

name

Field

code

Aliso Canyon

Bardsdale

Beverly Hills

Big Mountain

Bouquet Canyon

Cabrillo

Canada Larga

Canton Creek

Cascade

Castaic Hills

Castaic Junction

Chaffee Canyon

Charlie Canyon

Cheviot Hills

Conejo

Del Valle

El Rio

El Segundo

Eureka Canyon

Fillmore

010

036

054

056

064

091

102

110

120

124

126

130

132

136

170

198

230

232

242

246

Field

name

Field

code

Hasley Canyon

Holser

Honor Rancho

Hopper Canyon

Horse Meadows

Hyperion

Inglewood

Las Llajas

Las Posas

Long Canyon

Lyon Canyon

Mission

Montalvo, West

Moorpark

Moorpark West

Newhall

Newhall-Potrero

Oak Canyon

Oak Park

Oakridge

298

304

308

310

312

322

324

384

386

416

438

468

476

484

485

498

500

508

512

514

Oakview

Oat Mountain

Ojai

Oxnard

Pacoima

Piru

Piru Creek

Placerita

Playa Del Rey

Ramona

Ramona, North

Rincon

Rincon Creek

Salt Lake

San Miguelito

Santa Clara Avenue

Santa Paula

Santa Susana

San Vicente

Saticoy

516

519

520

530

531

546

548

550

554

586

588

600

601

640

658

662

670

672

674

678

680

682

694

704

708

710

712

714

724

742

744

746

748

764

774

784

814

824

830

Field

name

Field

code

Field

code

High Moderate Far

EXPLANATION

Numbers in vertical proximity classifications indicate the field codes

Saugus

Sawtelle

Sespe

Sherman

Shiells Canyon

Simi

Somis

South Mountain

Summerland

Tapia

Tapo, North

Tapo Canyon, South

Tapo Ridge

Temescal

Timber Canyon

Torrey Canyon

Ventura

Wayside Canyon

West Mountain

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

OJAI

VALLEY

UPPER

OJAI

VALLEY

MONTECITO

CARPINTERIA

VENTURA

RIVER VALLEY

LOWER VENTURA

RIVER VALLEY

LOS POSAS

VALLEY

PLEASANT

VALLEY

CONEJO

HIDDEN

VALLEY

THOUSAND

OAKS AREA

RUSSELL

VALLEY

MALIBU

VALLEY

COASTAL

PLAIN

OF

LOS ANGELES

SIMI VALLEY

SAN FERNANDO

VALLEY

SANTA CLARA

RIVER VALLEY

SANTA PAULA

SANTA CLARA

RIVER VALLEY

UPPER

VENTURA

RIVER

OJAI

VALLEY

UPPER

OJAI

VALLEY

MONTECITO

CARPINTERIA

VENTURA

RIVER VALLEY

LOWER VENTURA

RIVER VALLEY

LOS POSAS

VALLEY

PLEASANT

VALLEY

CONEJO

HIDDEN

VALLEY

THOUSAND

OAKS AREA

RUSSELL

VALLEY

MALIBU

VALLEY

COASTAL

PLAIN

OF

LOS ANGELES

SIMI VALLEY

SAN FERNANDO

VALLEY

SANTA CLARA

RIVER VALLEY

SANTA PAULA

SANTA CLARA

RIVER VALLEY

UPPER

VENTURA

RIVER

724

600

520 774

102

516

310 546

508

586

588

764

304

548

500

124742

298

498

674

640

704

136 682 054

554

322

232

308

824

132

198 126

550

438

064 680

531

312 468

010 120

519

324

714 830

036

678

416

670

130 514

744

746

710

384 056

484 512 485

246

672

748 242

784

694

708

814

476 230

530

662

091

170

386

712

658

110

601

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

District 3

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

D

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983
64 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Figure 13. —Continued

Sac17-0645_fig 13e

34°30'

34°

119°30' 119°0' 118°30'

District 2

District 1

VENTURA CO

VENTURA CO

SANTA BARBARA CO

ORANGE CO

LOS ANGELES CO

Water-well density

Field

name

Field

code

Aliso Canyon

Bardsdale

Beverly Hills

Big Mountain

Bouquet Canyon

Cabrillo

Canada Larga

Canton Creek

Cascade

Castaic Hills

Castaic Junction

Chaffee Canyon

Charlie Canyon

Cheviot Hills

Conejo

Del Valle

El Rio

El Segundo

Eureka Canyon

Fillmore

010

036

054

056

064

091

102

110

120

124

126

130

132

136

170

198

230

232

242

246

Field

name

Field

code

Hasley Canyon

Holser

Honor Rancho

Hopper Canyon

Hyperion

Inglewood

Las Llajas

Las Posas

Long Canyon

Lyon Canyon

Mission

Montalvo, West

Moorpark

Moorpark West

Newhall

Newhall-Potrero

Oak Canyon

Oak Park

Oakridge

298

304

308

310

322

324

384

386

416

438

468

476

484

485

498

500

508

512

514

Oakview

Oat Mountain

Ojai

Oxnard

Pacoima

Piru

Piru Creek

Placerita

Playa Del Rey

Ramona

Ramona, North

Rincon

Rincon Creek

Salt Lake

San Miguelito

Santa Clara Avenue

Santa Paula

Santa Susana

San Vicente

Saticoy

516

519

520

530

531

546

548

550

554

586

588

600

601

640

658

662

670

672

674

678

680

682

694

704

708

710

712

714

724

742

744

746

748

764

774

784

814

824

830

Field

name

Field

code

Field

code

High Moderate Low

EXPLANATION

Numbers in water-well density classifications indicate the field codes

Saugus

Sawtelle

Sespe

Sherman

Shiells Canyon

Simi

Somis

South Mountain

Summerland

Tapia

Tapo, North

Tapo Canyon, South

Tapo Ridge

Temescal

Timber Canyon

Torrey Canyon

Ventura

Wayside Canyon

West Mountain

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

OJAI

VALLEY

UPPER

OJAI

VALLEY

MONTECITO

CARPINTERIA

VENTURA

RIVER VALLEY

LOWER VENTURA

RIVER VALLEY

LOS POSAS

VALLEY

PLEASANT

VALLEY

CONEJO

HIDDEN

VALLEY

THOUSAND

OAKS AREA

RUSSELL

VALLEY

MALIBU

VALLEY

COASTAL PLAIN

OF LOS

ANGELES

SIMI VALLEY

SAN FERNANDO

VALLEY

SANTA CLARA

RIVER VALLEY

SANTA PAULA

SANTA CLARA

RIVER VALLEY

UPPER

VENTURA

RIVER

OJAI

VALLEY

UPPER

OJAI

VALLEY

MONTECITO

CARPINTERIA

VENTURA

RIVER VALLEY

LOWER VENTURA

RIVER VALLEY

LOS POSAS

VALLEY

PLEASANT

VALLEY

CONEJO

HIDDEN

VALLEY

THOUSAND

OAKS AREA

RUSSELL

VALLEY

MALIBU

VALLEY

COASTAL PLAIN

OF LOS

ANGELES

SIMI VALLEY

SAN FERNANDO

VALLEY

SANTA CLARA

RIVER VALLEY

SANTA PAULA

SANTA CLARA

RIVER VALLEY

UPPER

VENTURA

RIVER

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

724

601

600 658 814

516

520

670

774

708

714 830

678 416

230 662

530 170

712

485 484 512

056

514

744 242

784 130 748

672

310 546

764

710

746

386

091

476

694

246

036 102

548 588

304 586

110

508

498

438

500

198 126 680 064

308

824

298

124742

550

531

704

640

674

054 136

324

554

322

232

682

120 010

384 519

468

132

0 2.5 5 10 MILES

0 2.5 5 10 KILOMETERS

District 3

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

E

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983
Results of the Prioritization Analysis 65

Figure 14. Oil and gas fields in district 3, Central Coast, showing classifications for A, overall priority; B, petroleum-well density; 

C, volume of injection; D, vertical proximity; and E, water-well density.

Sac17-0645_fig 14a1

VENTURA CO

KERN CO

SAN LUIS OBISPO CO

SANTA BARBARA CO

121° 120°30' 120° 119°30'

35°

34°30'

0 3 6 12 MILES

0 3 6 12 KILOMETERS

District 3

District 4

SANTA YNEZ

RIVER VALLEY

SAN ANTONIO

CREEK VALLEY

SANTA

MARIA

CUYAMA

VALLEY

HUASNA

VALLEY

GOLETA MONTECITO

CARPINTERIA

District 2

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Priority classifications

Field

name

Field

code

Alegria

Arroyo Grande

Asphalto

Barham Ranch

Belgian Anticline

Buena Vista

Canada Larga

Capitan Oil

Capitola Park

Careaga Canyon

006

028

032

038

042

080

102

114

115

116

Field

name

Field

code

Casmalia

Cat Canyon

Cuyama, Central

Cuyama, South

Elk Hills

Elwood

Four Deer

Glen Annie Gas

Goleta

Gonyer Anticline

122

128

186

188

228

234

250

268

270

272

Guadalupe

Harris Canyon, NV

Huasna

Jesus Maria

La Goleta Gas

Las Varas Canyon

Lompoc

Lopez Canyon

Los Alamos

Mesa

286

295

318

334

368

388

410

418

420

462

486

524

594

601

632

668

711

724

760

860

Field

name

Field

code

Field

code

High Moderate Low

EXPLANATION

Numbers in priority classifications indicate the field codes

Morales Canyon

Orcutt

Refugio Cove Gas

Rincon Creek

Russell Ranch

Santa Maria Valley

Sisquoc Ranch

Summerland

Temblor Hills

Zaca

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

594114 006

388

334

234

860

188

632

038 420 410

116

122

524 128

250 295

268

270

724

601

368

462

711

668

318

418

028

286

186

115 486

272

102

080

228 032 042 760

A

CALIFORNIA

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983
66 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 14a2

0 3 6 12 MILES

0 3 6 12 KILOMETERS

121°30' 121° 120°30'

36°30'

36°

District 5

District 3

Priority classifications

Field

name

Field

code

Bitterwater

Cantua Creek

Cantua Nueva

Coalinga

Coalinga, East Extension

058

112

113

150

152

Field

name

Field

code

Guijarral Hills

Jacalitos

Kettleman North Dome

King City

Kreyenhagen

288

326

348

350

366

Lynch Canyon

Merritt Gas

Monroe Swell

Paris Valley

Pleasant Valley

436

448

474

534

558

580

644

800

806

Field

name

Field

code

Field

code

High Moderate Low

EXPLANATION

Numbers in priority classifications indicate the field codes

Quinado Canyon

San Ardo

Turk Anticline

Vallecitos

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

644

436

150

113

800

806

058

474

112

326

366

288

558

348

152

448

534

580

350

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

SAN CARPOFORO

VALLEY

ARROYO DE LA

CRUZ VALLEY

SAN LUIS OBISPO 

CO

KERN CO

KINGS CO

FRESNO CO

SAN BENITO CO

MONTEREY CO

SALINAS

VALLEY

BITTER

WATER

VALLEY

HERNANDEZ

VALLEY

PEACH

TREE

VALLEY

CARMEL

VALLEY

LOCKWOOD

VALLEY

VALLECITOS

CREEK

VALLEY

SAN JOAQUIN

VALLEY

SAN CARPOFORO

VALLEY

ARROYO DE LA

CRUZ VALLEY

SAN BENITO

RIVER

VALLEY

CHOLAME

VALLEY

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

A—Continued

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Figure 14. —Continued
Results of the Prioritization Analysis 67

Sac17-0645_fig 14b1

121° 120°30' 120° 119°30'

35°

34°30'

0 3 6 12 MILES

0 3 6 12 KILOMETERS

District 3

District 4 VENTURA CO SANTA BARBARA CO

District 2

SANTA YNEZ

RIVER VALLEY

SAN ANTONIO

CREEK VALLEY

SANTA

MARIA

CUYAMA

VALLEY

HUASNA

VALLEY

GOLETA MONTECITO

CARPINTERIA

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014 SAN LUIS OBISPO CO KERN CO

006 594 114

860

038 420

128

388

270

234 368

462

724

601

268

711

115

042

228

032

102 080

760

418

318

028

188

632

486

668

286

524

122

334 295

410

250

116

186

272

B

Petroleum-well density

Field

name

Field

code

Alegria

Arroyo Grande

Asphalto

Barham Ranch

Belgian Anticline

Buena Vista

Canada Larga

Capitan Oil

Capitola Park

Careaga Canyon

006

028

032

038

042

080

102

114

115

116

Field

name

Field

code

Casmalia

Cat Canyon

Cuyama, Central

Cuyama, South

Elk Hills

Elwood

Four Deer

Glen Annie Gas

Goleta

Gonyer Anticline

122

128

186

188

228

234

250

268

270

272

Guadalupe

Harris Canyon, NW

Huasna

Jesus Maria

La Goleta Gas

Las Varas Canyon

Lompoc

Lopez Canyon

Los Alamos

Mesa

286

295

318

334

368

388

410

418

420

462

486

524

594

601

632

668

711

724

760

860

Field

name

Field

code

Field

code

High Moderate Low

EXPLANATION

Numbers in petroleum-well density classifications indicate the field codes

Morales Canyon

Orcutt

Refugio Cove Gas

Rincon Creek

Russell Ranch

Santa Maria Valley

Sisquoc Ranch

Summerland

Temblor Hills

Zaca

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Figure 14. —Continued
68 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 14b2

0 3 6 12 MILES

0 3 6 12 KILOMETERS

121°30' 121° 120°30'

36°30'

36°

District 5

District 3

SAN LUIS OBISPO 

CO

KERN CO

KINGS CO

FRESNO CO

SAN BENITO CO

MONTEREY CO

SALINAS

VALLEY

BITTER

WATER

VALLEY

HERNANDEZ

VALLEY

PEACH

TREE

VALLEY

CARMEL

VALLEY

LOCKWOOD

VALLEY

VALLECITOS

CREEK

VALLEY

SAN JOAQUIN

VALLEY

SAN CARPOFORO

VALLEY

ARROYO DE LA

CRUZ VALLEY

SAN BENITO

RIVER

VALLEY

CHOLAME

VALLEY

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

644

448 436

534

350

474

058

806

112

150

152

288

558

326

366

348

113

800

580

Petroleum-well density

Field

name

Field

code

Bitterwater

Cantua Creek

Cantua Nueva

Coalinga

Coalinga, East Extension

058

112

113

150

152

Field

name

Field

code

Guijarral Hills

Jacalitos

Kettleman North Dome

King City

Kreyenhagen

288

326

348

350

366

Lynch Canyon

McCool Ranch

Monroe Swell

Paris Valley

Pleasant Valley

436

448

474

534

558

580

644

800

806

Field

name

Field

code

Field

code

High Moderate Low

EXPLANATION

Numbers in petroleum-well density classifications indicate the field codes

Quinado Canyon

San Ardo

Turk Anticline

Vallecitos

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

B—Continued

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Figure 14. —Continued
Results of the Prioritization Analysis 69

Sac17-0645_fig 14c1

VENTURA CO

KERN CO

SAN LUIS OBISPO CO

SANTA BARBARA CO

121° 120°30' 120° 119°30'

35°

34°30'

0 3 6 12 MILES

0 3 6 12 KILOMETERS

District 3

District 4

SANTA YNEZ

RIVER VALLEY

SAN ANTONIO

CREEK VALLEY

SANTA

MARIA

CUYAMA

VALLEY

HUASNA

VALLEY

GOLETA MONTECITO

CARPINTERIA

234 368 268

388 270 114

410 420 038 860

334

122

524

295

116

250

668

286

188

186

632

486

418

028

318 272

102 080

760 228 042 032

115

128 711

594 006

462

724

601

District 2

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

DOGGR district boundary

DWR groundwater basins

County

Volume of injection

High Moderate Low

EXPLANATION

Numbers in volume of injection classifications indicate the field codes

Field

name

Field

code

Alegria

Arroyo Grande

Asphalto

Barham Ranch

Belgian Anticline

Buena Vista

Canada Larga

Capitan Oil

Capitola Park

Careaga Canyon

006

028

032

038

042

080

102

114

115

116

Field

name

Field

code

Casmalia

Cat Canyon

Cuyama, Central

Cuyama, South

Elk Hills

Elwood

Four Deer

Glen Annie Gas

Goleta

Gonyer Anticline

122

128

186

188

228

234

250

268

270

272

Guadalupe

Harris Canyon, NV

Huasna

Jesus Maria

La Goleta Gas

Las Varas Canyon

Lompoc

Lopez Canyon

Los Alamos

Mesa

286

295

318

334

368

388

410

418

420

462

486

524

594

601

632

668

711

724

760

860

Morales Canyon

Orcutt

Refugio Cove Gas

Rincon Creek

Russell Ranch

Santa Maria Valley

Sisquoc Ranch

Summerland

Temblor Hills

Zaca

Field

name

Field

code

Field

code

Field

name

C

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Figure 14. —Continued
70 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 14c2

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

0 3 6 12 MILES

0 3 6 12 KILOMETERS

121°30' 121° 120°30'

36°30'

36°

SAN LUIS OBISPO 

CO

KERN CO

KINGS CO

FRESNO CO

SAN BENITO CO

MONTEREY CO

District 5

District 3

SALINAS

VALLEY

BITTER

WATER

VALLEY

HERNANDEZ

VALLEY

PEACH

TREE

VALLEY

CARMEL

VALLEY

LOCKWOOD

VALLEY

VALLECITOS

CREEK

VALLEY

SAN JOAQUIN

VALLEY

SAN CARPOFORO

VALLEY

ARROYO DE LA

CRUZ VALLEY

SAN BENITO

RIVER

VALLEY

CHOLAME

VALLEY

644

150

326

558

288

348

366

152

448 436

534

580

350

474

058

806

112

113

800

C—Continued

DOGGR district boundary

DWR groundwater basins

County

Volume of injection

Field

name

Field

code

Bitterwater

Cantua Creek

Cantua Nueva

Coalinga

Coalinga, East Extension

058

112

113

150

152

Field

name

Field

code

Guijarral Hills

Jacalitos

Kettleman North Dome

King City

Kreyenhagen

288

326

348

350

366

Lynch Canyon

McCool Ranch

Monroe Swell

Paris Valley

Pleasant Valley

436

448

474

534

558

580

644

800

806

Field

name

Field

code

Field

code

High Moderate Low

EXPLANATION

Numbers in volume of injection classifications indicate the field codes

Quinado Canyon

San Ardo

Turk Anticline

Vallecitos

Field

name

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Figure 14. —Continued
Results of the Prioritization Analysis 71

Sac17-0645_fig 14d1

VENTURA CO

KERN CO

SAN LUIS OBISPO CO

SANTA BARBARA CO

121° 120°30' 120° 119°30'

35°

34°30'

0 3 6 12 MILES

0 3 6 12 KILOMETERS

District 3

District 4

SANTA YNEZ

RIVER VALLEY

SAN ANTONIO

CREEK VALLEY

SANTA

MARIA

CUYAMA

VALLEY

HUASNA

VALLEY

GOLETA MONTECITO

CARPINTERIA

668

524

122

334 295 250

116

410

128

486

632

188

115

272

102

080

760 042 032 228

186

711

860

038

006 594 114 388 270

234

462

724

601

268 368

420

286

028

418

318

D

Unknown

District 2

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Vertical proximity

Field

name

Field

code

Alegria

Arroyo Grande

Asphalto

Barham Ranch

Belgian Anticline

Buena Vista

Canada Larga

Capitan Oil

Capitola Park

Careaga Canyon

006

028

032

038

042

080

102

114

115

116

Field

name

Field

code

Casmalia

Cat Canyon

Cuyama, Central

Cuyama, South

Elk Hills

Elwood

Four Deer

Glen Annie Gas

Goleta

Gonyer Anticline

122

128

186

188

228

234

250

268

270

272

Guadalupe

Harris Canyon, NW

Huasna

Jesus Maria

La Goleta Gas

Las Varas Canyon

Lompoc

Lopez Canyon

Los Alamos

Mesa

286

295

318

334

368

388

410

418

420

462

486

524

594

601

632

668

711

724

760

860

Field

name

Field

code

Field

code

Close Moderate Far

EXPLANATION

Numbers in vertical proximity classifications indicate the field codes

Morales Canyon

Orcutt

Refugio Cove Gas

Rincon Creek

Russell Ranch

Santa Maria Valley

Sisquoc Ranch

Summerland

Temblor Hills 

Zaca

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Figure 14. —Continued
72 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 14d2

0 3 6 12 MILES

0 3 6 12 KILOMETERS

121°30' 121° 120°30'

36°30'

36° Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

644

448 436

534

580

350

474

058

806

112

150 152

326

366

558

288

348

113

800

D—Continued

Unknown

Vertical proximity

Field

name

Field

code

Bitterwater

Cantua Creek

Cantua Nueva

Coalinga

Coalinga, East Extension

058

112

113

150

152

Field

name

Field

code

Guijarral Hills

Jacalitos

Kettleman North Dome

King City

Kreyenhagen

288

326

348

350

366

Lynch Canyon

McCool Ranch

Monroe Swell

Paris Valley

Pleasant Valley

436

448

474

534

558

580

644

800

806

Field

name

Field

code

Field

code

Close Moderate Far

EXPLANATION

Numbers in vertical proximity classifications indicate the field codes

Quinado Canyon

San Ardo

Turk Anticline

Vallecitos

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

SAN LUIS OBISPO 

CO

KERN CO

KINGS CO

FRESNO CO

SAN BENITO CO

MONTEREY CO

District 5

District 3

SALINAS

VALLEY

BITTER

WATER

VALLEY

HERNANDEZ

VALLEY

PEACH

TREE

VALLEY

CARMEL

VALLEY

LOCKWOOD

VALLEY

VALLECITOS

CREEK

VALLEY

SAN JOAQUIN

VALLEY

SAN CARPOFORO

VALLEY

ARROYO DE LA

CRUZ VALLEY

SAN BENITO

RIVER

VALLEY

CHOLAME

VALLEY

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Figure 14. —Continued
Results of the Prioritization Analysis 73

Sac17-0645_fig 14e1

VENTURA CO

KERN CO

SAN LUIS OBISPO CO

SANTA BARBARA CO

121° 120°30' 120° 119°30'

35°

34°30'

0 3 6 12 MILES

0 3 6 12 KILOMETERS

District 3

District 2

District 4

SANTA YNEZ

RIVER VALLEY

SAN ANTONIO

CREEK VALLEY

SANTA

MARIA

CUYAMA

VALLEY

HUASNA

VALLEY

GOLETA MONTECITO

CARPINTERIA

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Water-well density

Moderate Low

EXPLANATION

Numbers in water-well density classifications indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Alegria

Arroyo Grande

Asphalto

Barham Ranch

Belgian Anticline

Buena Vista

Canada Larga

Capitan Oil

Capitola Park

Careaga Canyon

006

028

032

038

042

080

102

114

115

116

Field

name

Field

code

Casmalia

Cat Canyon

Cuyama, Central

Cuyama, South

Elk Hills

Elwood

Four Deer

Glen Annie Gas

Goleta

Gonyer Anticline

122

128

186

188

228

234

250

268

270

272

Guadalupe

Harris Canyon, NV

Huasna

Jesus Maria

La Goleta Gas

Las Varas Canyon

Lompoc

Lopez Canyon

Los Alamos

Mesa

286

295

318

334

368

388

410

418

420

462

486

524

594

601

632

668

711

724

760

860

Morales Canyon

Orcutt

Refugio Cove Gas

Rincon Creek

Russell Ranch

Santa Maria Valley

Sisquoc Ranch

Summerland

Temblor Hills

Zaca

Field

name

Field

code

Field

code

Field

name

228

080

272

486

632

188

186

128

668

524

122

116

250 334 295

410 420 038

006 594 114 388 270

268 368

462

724

601

234

286

028

418

318

711

860

115

760

102

042 032

E

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Figure 14. —Continued
74 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 14e2

806

058

350

580

534

436

326

150 152

112 800

113

558

288

348

366

644

448

474

0 3 6 12 MILES

0 3 6 12 KILOMETERS

121°30' 121° 120°30'

36°30'

36° Redding

Sacramento

San Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

SAN LUIS OBISPO 

CO

KERN CO

KINGS CO

FRESNO CO

SAN BENITO CO

MONTEREY CO

District 5

District 3

SALINAS

VALLEY

BITTER

WATER

VALLEY

HERNANDEZ

VALLEY

PEACH

TREE

VALLEY

CARMEL

VALLEY

LOCKWOOD

VALLEY

VALLECITOS

CREEK

VALLEY

SAN JOAQUIN

VALLEY

SAN CARPOFORO

VALLEY

ARROYO DE LA

CRUZ VALLEY

SAN BENITO

RIVER

VALLEY

CHOLAME

VALLEY

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Water-well density

Field

name

Field

code

Bitterwater

Cantua Creek

Cantua Nueva

Coalinga

Coalinga, East Extension

058

112

113

150

152

Field

name

Field

code

Guijarral Hills

Jacalitos

Kettleman North Done

King City

Kreyenhagen

288

326

348

350

366

Lynch Canyon

McCool Ranch

Monroe Swell

Paris Valley

Pleasant Valley

436

448

474

534

558

580

644

800

806

Field

name

Field

code

Field

code

Moderate Low

EXPLANATION

Numbers in water-well density classifications indicate the field codes

Quinado Canyon

San Ardo

Turk Anticline

Vallecitos

Field

name

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

E—Continued

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

Figure 14. —Continued
Results of the Prioritization Analysis 75

District 4 (South San Joaquin Basin)

District 4 encompasses the south zone of the San Joaquin 

Basin in central California that is bounded by the Temblor 

Range in the west and by the Sierra Nevada in the east (for 

description of south, central, and north zones, see Hosford 

Scheirer, 2007). The boundary within the San Joaquin Basin 

between district 4 and district 5 is defined by the Kern-Kings 

County line and Tulare-Fresno County line (fig. 10A). The 

102 fields of district 4 have an aggregated field area of 962 mi2

(table 5). District 4 fields are within the southern part of the 

San Joaquin Valley groundwater basin (fig. 15A; California 

Department of Water Resources, 2016). The southern San 

Joaquin Valley groundwater basin is composed of eroded 

materials from the surrounding mountains that deposited into 

the valley, primarily Coast Range alluvium underlain by the 

Corcoran Clay confining unit on the western side of the valley 

and alluvium from the Sierra Nevada on the east side (Faunt, 

2009; California Department of Water Resources, 2015). 

Other alluvial deposits include flood-basin deposits along 

the axis of the valley and buried-river channel deposits of 

Pleistocene age.

For district 4, 40 percent of the fields (41 fields) were 

classified as high priority, 28 percent (29 fields) were 

moderate, and 31 percent (32 fields) were low (table 5; 

fig. 15A). District 4 contained almost half of the fields that 

had high overall priority classifications for the state, and 

these fields accounted for a majority of the aggregated field 

area. By area, 70 percent of the total area of district 4 oil and 

gas fields ranked as high priority, 24 percent was moderate, 

and 6 percent was low. High overall priority classification 

in the district was characterized by commonly co-occurring 

high petroleum-well density, high injection volume, and high 

vertical proximity of petroleum resource development to 

groundwater resources (figs. 15B–D). District 4 also had the 

most fields with high water-well density (fig. 15E), next to 

district 6. Some areas within the district, such as the center of 

the groundwater basins, had fields classified as high priority 

based on moderate petroleum-well density and high waterwell density. Fields that had small vertical separation distance 

between petroleum and groundwater resources were located 

along the western and eastern edges of the San Joaquin Valley, 

and fields that had moderate and great separation distances 

were located on the valley floor where groundwater use was 

the highest.

Vertical proximity of petroleum resources to groundwater 

resources in district 4 was classified as close for 23 fields, 

moderate for 14 fields, far for 23 fields, and 42 fields had 

insufficient data to evaluate vertical proximity (table 4; 

fig. 15D). There were seven fields in the State that had median 

vertical separation distance less than 0 ft, indicating potential 

overlap of oil and gas resources and groundwater resources; 

six of these fields were located in district 4 (the other field is 

Piru in district 2; table 6A), and with the exception of one field 

(South Belridge), are located along the east side of the Kern 

County groundwater basin (fig. 15D). Some fields in which 

hydraulic fracturing and well stimulation have been used 

(California Council on Science and Technology, 2015) were 

among the fields in the high risk category based on vertical 

proximity. For example, median vertical separation distances 

for North Belridge, South Belridge, and Lost Hills fields were 

470 ft, –312 ft (overlap), and 432 ft, respectively (fig. 11). In 

contrast, separation distance for Elk Hills field was greater: 

median distance between petroleum resource development and 

groundwater resources was 5,505 ft. The EOR injection wells 

in the Elk Hills field were deeper (6,300 ft median depth to 

TOP) than in the other district 4 fields; however, perforation 

depths for waste-disposal wells were much shallower (608 ft 

median depth to TOP; appendix table 1–3). The proportion 

of fields (with available data) in the high-risk category for 

vertical proximity was 20 percent or less for each district, 

with the exception of district 4, where 38 percent of the 

fields were classified in the high-risk category for vertical 

proximity (table 4). Small separation distances between 

petroleum resource development and groundwater resources, 

in combination with high petroleum-well density and injection 

volume, resulted in district 4 having the highest percentage of 

fields classified as high priorities for consideration for regional 

monitoring than any of the other districts.

District 5 (North/Central San Joaquin Basin)

District 5 encompasses the north and central zones of the 

San Joaquin Basin from Kings County to Stanislaus County 

(fig. 10A). There are 41 oil and gas fields in the district; these 

fields have an aggregated area of 425 mi2 (table 5). There are 

about 14,000 DOGGR new, active, idle, and plugged oil and 

gas wells in the district, of which about 12,000 are oil and gas 

production wells and about 1,500 are injection wells (table 1). 

In the north zone of the of the San Joaquin Basin, fields in 

Madera, Merced, and Stanislaus Counties and a few fields in 

Fresno County produce nonassociated gas from Cretaceous, 

Eocene, and Miocene sandstones (Hosford Scheirer, 2007). 

In the central zone of the basin, oil and gas fields are located 

in Fresno, Kings, and San Benito Counties. District 5 fields 

are within the San Joaquin Valley groundwater basin and 

in nearby basins to the west, such as the Gilroy-Hollister 

Valley and Kettleman Plain groundwater basins (California 

Department of Water Resources, 2015; fig. 16A). The north 

zone coincides with the Delta-Mendota, Madera, Chowchilla, 

Merced, Turlock, and Modesto subbasins, which compose part 

of the San Joaquin River hydrologic region. The Tulare Lake, 

Westside, and Kings groundwater subbasins, along with the 

Kern County, Tule, and Kaweah subbasins included in district 

4 (fig. 15A), compose part of the Tulare Lake hydrologic 

region and account for about 38 percent of average annual 

groundwater extraction in the State (California Department of 

Water Resources, 2015). 
76 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

For district 5, 24 percent of the fields (10 fields) 

were classified as high priority, 24 percent were moderate 

(10 fields), and 51 percent were low (21 fields; table 5; 

fig. 16A). Fields that had high overall priority classification 

accounted for almost half of the aggregated field area for 

the district. By area, 46 percent of the total area of district 

5 oil and gas fields was ranked as high priority, 22 percent 

was moderate, and 32 percent was low. High overall priority 

classification was primarily based on either high volume of 

injection or high vertical proximity of resources, and these 

fields were located in the central zone of the San Joaquin 

Basin (exception is the Hollister field, which is outside the 

basin boundary). Although most injection wells were water 

flood and steam injection (table 1), injection volumes were 

predominantly waste-water disposal (tables 6A–C); exceptions 

were Coalinga, East Extension of Coalinga, and North Tejon, 

which had injection for both EOR and waste disposal. For 

a few fields in the western region of Kings groundwater 

subbasin, high priority classifications were based on moderate 

petroleum-well density in an area with high water-well 

density. Fields in district 5 were more frequently characterized 

by moderate or low petroleum-well density (39 of 41 fields) 

and low volume of injection (30 fields; figs. 16B, C). Eleven 

of the 13 gas fields in the district and located in the north 

zone of the San Joaquin Basin were classified as low priority 

based on low intensity of petroleum resource development 

with almost no water injection and moderate to low water-well 

density (table 6C).

Vertical proximity of petroleum resource development to 

groundwater resources in district 5 was classified as close for 

3 fields, moderate for 3 fields, far for 10 fields, and 25 fields 

had insufficient data to evaluate (table 4; fig. 16D). Two of 

the fields that ranked in the high-risk category for vertical 

proximity (Hollister and Pyramid Hills) were classified in 

the low and moderate categories for all of the other factors 

(table 6A). The third field in the high-risk category, Coalinga, 

also had high petroleum-well density and volume of injection. 

One of the high-priority fields in the district, Kettleman North 

Dome, was classified in low category for vertical proximity 

(7,444 ft median separation distance) and in the high category 

for total volume of waste-water disposal (39 MMB). However, 

vertical separation distance was calculated using mostly 

production well data for which median depth to TOP was 

8,300 ft, whereas median depth to TOP for waste-disposal 

wells was much shallower at about 1,100 ft (appendix 

table 1–3). Results from preliminary assessment of petroleum 

resource development at Kettleman North Dome suggest there 

may be few injection wells injecting large volumes of wastewater and at shallower depths than reflected in the vertical 

proximity assessment. This comparison of TOP-depths by 

well type exemplifies how the vertical proximity analysis 

does not represent separation distance of groundwater from 

all petroleum development activities within a field and further 

investigation is necessary on a field scale for evaluating 

vulnerability of groundwater to oil and gas development.

District 6 (Sacramento Basin)

District 6 covers the northern part of California, bounded 

in the west by the Pacific Ocean and in the north and east 

by the State boundaries (fig. 2). The boundary in central 

California between district 5 and district 6 is roughly defined 

by the Stanislaus-San Joaquin County line. District 6 also 

borders the northern end of district 3 near the San Francisco 

Bay region. Collectively, the 168 oil and gas fields in district 6 

represent the largest area of any district (1,216 mi2). District 6 

fields are primarily within the Sacramento Basin and are 

generally used for developing natural gas resources; 11 fields 

are outside of the basin and in or near the coastal valleys to 

the west of the basin. Hosford Scheirer and others (2007) 

estimated a mean of 534 billion cubic feet of natural gas and 

323 thousand barrels of natural gas liquids in the Sacramento 

Basin that are recoverable; more than 80 percent of the 

natural gas is contained in the Upper Cretaceous rocks of the 

Dobbins-Forbes and Winters-Domengine petroleum systems. 

More than 9 trillion cubic feet of natural gas have already been 

produced in the basin. The Sacramento Basin coincides with 

the Sacramento Valley groundwater basin and the northern 

subbasins of the San Joaquin Valley groundwater basin 

(fig. 17A; California Department of Water Resources, 2016). 

Primary groundwater producing formations in the Sacramento 

Valley groundwater basin are composed of alluvial fan 

deposits and volcanic flow deposits derived from erosion of 

the Coast Ranges and Klamath Mountains to the northwest 

and west, Lassen Peak to the northeast, and the Sierra Nevada 

to the east (California Department of Water Resources, 2015). 

The few fields outside of the Sacramento Basin are within the 

boundaries of the coastal Eureka Plain and Eel River Valley 

groundwater basins of Humboldt County, and in or near Santa 

Rosa Valley, Suisun-Fairfield Valley, Petaluma Valley, Clayton 

Valley, Pittsburg Plain, Livermore Valley, and Half Moon Bay 

Terrace groundwater basins surrounding the San Francisco 

Bay region (California Department of Water Resources, 2015).

For district 6, 2 percent of the fields (4 fields) were 

classified as high priority, 20 percent (33 fields) were 

moderate, and 78 percent (131 fields) were low (table 5; 

fig. 17A). District 6 had the most oil and gas fields of the 

districts by count and area, but these fields are mostly used for 

gas extraction and have comparatively less intense petroleum 

resource development, characterized by moderate to low 

petroleum-well density (fig. 17B), virtually no injection 

for enhanced oil recovery, and comparatively low injection 

volume for waste-water disposal (fig. 17C). By area, 5 percent 

of the total area of district 6 oil and gas fields ranked as high 

priority, 40 percent was moderate, and 55 percent was low. 

High overall priority classification was based on vertical 

proximity (two fields), water-injection volume (one field), or 

moderate petroleum-well density in areas with high water-well 

density (one field; table 6A). More than half of the fields in the 

state with high water-well density were in district 6, and the 

majority of these fields were classified as low priority based 

on low volume of injection and low petroleum-well density. 
Results of the Prioritization Analysis 77

Fields in which there were injection activities (gas storage or 

waste disposal) were classified as high or moderate priority, 

based on lateral proximity to currently used groundwater 

resources. In general, injection volumes in the district were 

low relative to other districts: only 8 district-6 fields were 

classified as high or moderate for injection volumes.

For district 6 oil and gas fields, 2 fields were classified 

in the high-risk category for vertical proximity, 12 were in 

the moderate-risk category, 15 were in the low-risk category, 

and 139 had insufficient data to evaluate (table 4; fig. 17D). 

Few fields in district 6 were attributed with vertical proximity, 

because fields generally consisted of oil and gas production 

wells, for which there was a lack of available depth data 

(table 1; appendix table 1–3). Where known, petroleum 

resource development was generally thousands of feet deeper 

than groundwater resources: median vertical separation 

distance ranged from 927 ft to 9,506 ft (fig. 11). 

Whereas district 6 fields generally had moderate to low 

potential risk to groundwater sources based on volume of 

injection, petroleum-well density, and vertical proximity, 

the majority of fields (131 of 168 fields) were characterized 

by moderate to high water-well density (table 5; fig. 17E). 

Fields in California that had high density of overlying or 

adjacent water wells were located in the Sacramento and San 

Joaquin Valleys (figs. 11F, G), and more than half of the fields 

classified in the high-risk category for water-well density 

were in district 6. Because water wells were generally present 

throughout the State (fig. 1A), and all potentially beneficialuse waters adjacent to oil fields have protected-groundwater 

status in California, water-well density was only a deciding 

factor in the overall priority classification for fields that had 

intermediate rankings for other factors. As a result, 27 of the 

37 fields in district 6 that had high water-well density were 

low priority for regional monitoring based on low volume 

of injection and low petroleum-well density (tables 5 and 

6C). However, 32 fields were classified as moderate priority 

because they had moderate petroleum-well density (sometimes 

coupled with moderate injection volume) and moderate to high 

water-well density (table 6B). 
78 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 15a

120° 119°

36°

District 2

35°

District 5 District 4

District 4

District 2

District 3

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

060

702

274 096

280

160

756

115 146

648

222

018

244

696

628

488

650

221

652

375

834

560 832

758

752

754

808

860 038

486

188

720

342

798

490

608 858

428

544

156

158

532

102

042

762

454

272

186

632

711

432

040

020

450

117

022

024

700

140

759

760

716 104

080

228 032

582

190

479

095 052

050

336

256

626

624

238

046 044 446

106

372

374

617

699

698

602

697

260

690 822

092

566

338

340

220

332

066

792

790

794

210

346

578

204

826

434

288

348 344

296

196

768

330

328

194

FRESNO CO

KERN CO

LOS ANGELES CO

SANTA BARBARA CO

SAN LUIS OBISPO CO

VENTURA CO

KINGS CO

FRESNO CO

TULARE CO

TULE

KAWEAH

SALINAS

VALLEY

CUYAMA

VALLEY

WHITE WOLF

SANTA MARIA

SANTA

YNEZ RIVER

VALLEY

SAN ANTONIO

CREEK VALLEY

TULARE LAKE

WESTSIDE

SAN

JOAQUIN

VALLEY

A

Temblor

Range

Sierra

Nevada

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

558

Figure 15. Oil and gas fields in district 4, San Joaquin Basin—South, showing classifications for A, priority; B, petroleum-well density; 

C, volume of injection; D, vertical proximity; and E, water-well density.
Results of the Prioritization Analysis 79

sac17-0645_fig 15aContinued

Priority classifications

High Moderate Low

EXPLANATION

Numbers in priority classifications indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name Fieldcode

Ant Hill

Antelope Hills

Antelope Hills, North

Antelope Plains Gas

Asphalto

Barham Ranch

Beer Nose

Belgian Anticline

Bellevue

Bellevue, West

Belridge, North

Belridge, South

Blackwells Corner

Bowerbank

Buena Vista

Buttonwillow Gas

Cal Canal Gas

Calders Corner

Capitola Park

Canal

Canfield Ranch

Capitola Park

Carneros Creek

Chico Martinez

Cienaga Canyon

Coles Levee, North

Coles Levee, South

Comanche Point

Cuyama, Central

018

020

022

024

032

038

040

042

044

046

050

052

060

066

080

092

095

096

102

104

106

115

117

140

146

156

158

160

186

Field

name Fieldcode

Cuyama, South

Cymric

Deer Creek

Deer Creek, North

Devils Den

Dudley Ridge Gas

Dyer Creek

Eagle Rest

Edison

Edison, Northeast

Elk Hills

English Colony

Fruitvale

Garrison City Gas

Gonyer Anticline

Goosloo

Greeley

Guijarral Hills

Harvester Gas

Jasmin

Jasmin, West

Jerry Slough

Kern Bluff

Kern Front

Kern River

Kernsumner

Kettleman City

Kettleman Middle Dome

Kettleman North Dome

188

190

194

196

204

210

220

221

222

224

228

238

256

260

272

274

280

288

296

328

330

332

336

338

340

342

344

346

348

Lakeside

Lakeside, South

Landslide

Los Lobos

Lost Hills

Lost Hills, Northwest

McClung

McDonald Anticline

McKittrick

Monument Junction

Morales Canyon

Mount Poso

Mountain View

Paloma

Pioneer

Pleasant Valley

Pleito

Poso Creek

Pyramid Hills

Railroad Gap

Rio Bravo

Rio Viejo

Rose

Rosedale

Rosedale Ranch

Round Mountain

Russell Ranch

San Emidio Nose

San Emidio

San Emidio Creek

372

374

375

428

432

434

446

450

454

479

486

488

490

532

544

558

560

566

578

582

602

608

617

624

626

628

632

648

650

652

690

696

697

698

699

700

702

711

716

720

752

754

756

758

759

760

762

766

768

790

792

794

798

808

822

826

832

834

858

860

Field

name Fieldcode

Field

code

Semitropic

Seventh Standard

Shafter

Shafter, Southeast Gas

Shafter, North

Shale Flats Gas

Shale Point Gas

Sisquoc Ranch

Rose

Rosecrans, East

Tejon

Tejon Flats

Tejon Hills

Tejon, North

Temblor East

Temblor Hills

Temblor Ranch

Ten Section

Terra Bella

Trico Gas

Trico Gas, Northwest

Tulare Lake

Union Avenue

Valpredo

Wasco

Welcome Valley

Wheeler Ridge

White Wolf

Yowlumne

Zaca

Field

name

Figure 15. —Continued
80 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 15b

120° 119°

36°

District 2

35°

District 5 District 4

District 4

District 2

District 3

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

696

158

080 532

102

272

486

711

860

038

632

188

186

760

140

020

450

117

024

060

700 702

224

490

160

756

808

754

752

758 832

608 858

428

544

650

221

146 115

652

834

375

648

626

044

238

446 720

104

046

256

340

338

566

488

220

330

617

699

328

194

768

196

628

336 018

222

759 190 762

042 454 582

228

066

156 766 106

372

374

716 342

798

274 096

602

280 624

296

792

790

346

578

204 434

432

690

697

092

822

260 332 698

826

040

022

050

052

095

479

326

348 794 344

210

032

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

TULE

KAWEAH

SALINAS

VALLEY

CUYAMA

VALLEY

WHITE WOLF

SANTA MARIA

SANTA

YNEZ RIVER

VALLEY

SAN ANTONIO

CREEK VALLEY

TULARE LAKE

WESTSIDE

SAN

JOAQUIN

VALLEY

KERN CO

LOS ANGELES CO

SANTA BARBARA CO

SAN LUIS OBISPO CO

VENTURA CO

KINGS CO

FRESNO CO

TULARE CO

B

Temblor

Range

Sierra

Nevada

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

CALIFORNIA

558

Figure 15. —Continued
Results of the Prioritization Analysis 81

sac17-0645_fig 15bContinued

Petroleum-well density

High Moderate Low

EXPLANATION

Numbers in petroleum-well density classifications indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name Fieldcode

Ant Hill

Antelope Hills

Antelope Hills, North

Antelope Plains Gas

Asphalto

Barham Ranch

Beer Nose

Belgian Anticline

Bellevue

Bellevue, West

Belridge, North

Belridge, South

Blackwells Corner

Bowerbank

Buena Vista

Buttonwillow Gas

Cal Canal Gas

Calders Corner

Capitola Park

Canal

Canfield Ranch

Capitola Park

Carneros Creek

Chico Martinez

Cienaga Canyon

Coles Levee, North

Coles Levee, South

Comanche Point

Cuyama, Central

018

020

022

024

032

038

040

042

044

046

050

052

060

066

080

092

095

096

102

104

106

115

117

140

146

156

158

160

186

Field

name Fieldcode

Cuyama, South

Cymric

Deer Creek

Deer Creek, North

Devils Den

Dudley Ridge Gas

Dyer Creek

Eagle Rest

Edison

Edison, Northeast

Elk Hills

English Colony

Fruitvale

Garrison City Gas

Gonyer Anticline

Goosloo

Greeley

Guijarral Hills

Harvester Gas

Jasmin

Jasmin, West

Jerry Slough

Kern Bluff

Kern Front

Kern River

Kernsumner

Kettleman City

Kettleman Middle Dome

Kettleman North Dome

188

190

194

196

204

210

220

221

222

224

228

238

256

260

272

274

280

288

296

328

330

332

336

338

340

342

344

346

348

Lakeside

Lakeside, South

Landslide

Los Lobos

Lost Hills

Lost Hills, Northwest

McClung

McDonald Anticline

McKittrick

Monument Junction

Morales Canyon

Mount Poso

Mountain View

Paloma

Pioneer

Pleasant Valley

Pleito

Poso Creek

Pyramid Hills

Railroad Gap

Rio Bravo

Rio Viejo

Rose

Rosedale

Rosedale Ranch

Round Mountain

Russell Ranch

San Emidio Nose

San Emidio

San Emidio Creek

372

374

375

428

432

434

446

450

454

479

486

488

490

532

544

558

560

566

578

582

602

608

617

624

626

628

632

648

650

652

690

696

697

698

699

700

702

711

716

720

752

754

756

758

759

760

762

766

768

790

792

794

798

808

822

826

832

834

858

860

Field

name

Field

code

Field

code

Semitropic

Seventh Standard

Shafter

Shafter, Southeast Gas

Shafter, North

Shale Flats Gas

Shale Point Gas

Sisquoc Ranch

Rose

Rosecrans, East

Tejon

Tejon Flats

Tejon Hills

Tejon, North

Temblor East

Temblor Hills

Temblor Ranch

Ten Section

Terra Bella

Trico Gas

Trico Gas, Northwest

Tulare Lake

Union Avenue

Valpredo

Wasco

Welcome Valley

Wheeler Ridge

White Wolf

Yowlumne

Zaca

Field

name

Figure 15. —Continued
82 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 15c

120° 119°

36°

District 2

35°

District 5 District 4

District 4

District 2

District 3

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

KERN CO

LOS ANGELES CO

SANTA BARBARA CO

SAN LUIS OBISPO CO

VENTURA CO

KINGS CO

FRESNO CO

TULARE CO

188

711

860

038

186

632

486

272

102

080 532

115 146 428

544

650221652

834

375

858 648

608

560 832 758 754

752

756

160

490

222

224

018

628

336

340

628

338

342

798

716

274

488

220

328

196

194

768

790

792

296

794 344

210

346

578

204

434

617

690 822

092 698

699

697

602 626

624

238

044 046

720

104

228 156 766

582 454 042

760

762

190 479

095

052

140

117

450

020

024

022

040

700 702

060

826

050

106

446

280 096

696

256

260

332

066

432

348

288

330

566

374

372 158

808

032

C

Temblor

Range

Sierra

Nevada

TULE

KAWEAH

SALINAS

VALLEY

CUYAMA

VALLEY

WHITE WOLF

SANTA MARIA

SANTA

YNEZ RIVER

VALLEY

SAN ANTONIO

CREEK VALLEY

TULARE LAKE

WESTSIDE

SAN

JOAQUIN

VALLEY

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

558

Figure 15. —Continued
Results of the Prioritization Analysis 83

sac17-0645_fig 15cContinued

Volume of injection

High Moderate Low

EXPLANATION

Numbers in volume of injection indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name Fieldcode

Ant Hill

Antelope Hills

Antelope Hills, North

Antelope Plains Gas

Asphalto

Barham Ranch

Beer Nose

Belgian Anticline

Bellevue

Bellevue, West

Belridge, North

Belridge, South

Blackwells Corner

Bowerbank

Buena Vista

Buttonwillow Gas

Cal Canal Gas

Calders Corner

Capitola Park

Canal

Canfield Ranch

Capitola Park

Carneros Creek

Chico Martinez

Cienaga Canyon

Coles Levee, North

Coles Levee, South

Comanche Point

Cuyama, Central

018

020

022

024

032

038

040

042

044

046

050

052

060

066

080

092

095

096

102

104

106

115

117

140

146

156

158

160

186

Field

name Fieldcode

Cuyama, South

Cymric

Deer Creek

Deer Creek, North

Devils Den

Dudley Ridge Gas

Dyer Creek

Eagle Rest

Edison

Edison, Northeast

Elk Hills

English Colony

Fruitvale

Garrison City Gas

Gonyer Anticline

Goosloo

Greeley

Guijarral Hills

Harvester Gas

Jasmin

Jasmin, West

Jerry Slough

Kern Bluff

Kern Front

Kern River

Kernsumner

Kettleman City

Kettleman Middle Dome

Kettleman North Dome

188

190

194

196

204

210

220

221

222

224

228

238

256

260

272

274

280

288

296

328

330

332

336

338

340

342

344

346

348

Lakeside

Lakeside, South

Landslide

Los Lobos

Lost Hills

Lost Hills, Northwest

McClung

McDonald Anticline

McKittrick

Monument Junction

Morales Canyon

Mount Poso

Mountain View

Paloma

Pioneer

Pleasant Valley

Pleito

Poso Creek

Pyramid Hills

Railroad Gap

Rio Bravo

Rio Viejo

Rose

Rosedale

Rosedale Ranch

Round Mountain

Russell Ranch

San Emidio Nose

San Emidio

San Emidio Creek

372

374

375

428

432

434

446

450

454

479

486

488

490

532

544

558

560

566

578

582

602

608

617

624

626

628

632

648

650

652

690

696

697

698

699

700

702

711

716

720

752

754

756

758

759

760

762

766

768

790

792

794

798

808

822

826

832

834

858

860

Field

name

Field

code

Field

code

Semitropic

Seventh Standard

Shafter

Shafter, Southeast Gas

Shafter, North

Shale Flats Gas

Shale Point Gas

Sisquoc Ranch

Rose

Rosecrans, East

Tejon

Tejon Flats

Tejon Hills

Tejon, North

Temblor East

Temblor Hills

Temblor Ranch

Ten Section

Terra Bella

Trico Gas

Trico Gas, Northwest

Tulare Lake

Union Avenue

Valpredo

Wasco

Welcome Valley

Wheeler Ridge

White Wolf

Yowlumne

Zaca

Field

name

Figure 15. —Continued
84 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 15d

120° 119°

36°

District 2

35°

District 5 District 4

District 4

District 2

District 3

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

TULE

KAWEAH

SALINAS

VALLEY

CUYAMA

VALLEY

WHITE WOLF

SANTA MARIA

SANTA

YNEZ RIVER

VALLEY

SAN ANTONIO

CREEK VALLEY

TULARE LAKE

WESTSIDE

SAN

JOAQUIN

VALLEY

KERN CO

LOS ANGELES CO

SANTA BARBARA CO

SAN LUIS OBISPO CO

VENTURA CO

KINGS CO

FRESNO CO

TULARE CO

D

Temblor

Range

Sierra

Nevada

288

348 344

210

346

794

296

578

204

434

432

050

052

190

140

042

760

762

095

092

066

032

454

080

274 096

106

104

102

046 044

372

340

338

336

342

490

808 160

754

752

758

832 560

756

716

374

532

158

156

582

690

697

698

699

566

488

628

018

602

720

766

696 626

256

798 224

222

624

238

332 260

617

822

040

022

020

280

220

330

328

196

194

768

228

858

544

650 652 221

375

834

608

648

428

272

486

632

186

188

711

038

860

146 115

450

117

024

060

702

700

826

792

790

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

CALIFORNIA

558

Figure 15. —Continued
Results of the Prioritization Analysis 85

sac17-0645_fig 15dContinued

Vertical proximity

Close Far

Moderate Unknown

EXPLANATION

Numbers in vertical proximity indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name Fieldcode

Ant Hill

Antelope Hills

Antelope Hills, North

Antelope Plains Gas

Asphalto

Barham Ranch

Beer Nose

Belgian Anticline

Bellevue

Bellevue, West

Belridge, North

Belridge, South

Blackwells Corner

Bowerbank

Buena Vista

Buttonwillow Gas

Cal Canal Gas

Calders Corner

Capitola Park

Canal

Canfield Ranch

Capitola Park

Carneros Creek

Chico Martinez

Cienaga Canyon

Coles Levee, North

Coles Levee, South

Comanche Point

Cuyama, Central

018

020

022

024

032

038

040

042

044

046

050

052

060

066

080

092

095

096

102

104

106

115

117

140

146

156

158

160

186

Field

name

Field

code

Cuyama, South

Cymric

Deer Creek

Deer Creek, North

Devils Den

Dudley Ridge Gas

Dyer Creek

Eagle Rest

Edison

Edison, Northeast

Elk Hills

English Colony

Fruitvale

Garrison City Gas

Gonyer Anticline

Goosloo

Greeley

Guijarral Hills

Harvester Gas

Jasmin

Jasmin, West

Jerry Slough

Kern Bluff

Kern Front

Kern River

Kernsumner

Kettleman City

Kettleman Middle Dome

Kettleman North Dome

188

190

194

196

204

210

220

221

222

224

228

238

256

260

272

274

280

288

296

328

330

332

336

338

340

342

344

346

348

Lakeside

Lakeside, South

Landslide

Los Lobos

Lost Hills

Lost Hills, Northwest

McClung

McDonald Anticline

McKittrick

Monument Junction

Morales Canyon

Mount Poso

Mountain View

Paloma

Pioneer

Pleasant Valley

Pleito

Poso Creek

Pyramid Hills

Railroad Gap

Rio Bravo

Rio Viejo

Rose

Rosedale

Rosedale Ranch

Round Mountain

Russell Ranch

San Emidio Nose

San Emidio

San Emidio Creek

372

374

375

428

432

434

446

450

454

479

486

488

490

532

544

558

560

566

578

582

602

608

617

624

626

628

632

648

650

652

690

696

697

698

699

700

702

711

716

720

752

754

756

758

759

760

762

766

768

790

792

794

798

808

822

826

832

834

858

860

Field

name Fieldcode

Field

code

Semitropic

Seventh Standard

Shafter

Shafter, Southeast Gas

Shafter, North

Shale Flats Gas

Shale Point Gas

Sisquoc Ranch

Rose

Rosecrans, East

Tejon

Tejon Flats

Tejon Hills

Tejon, North

Temblor East

Temblor Hills

Temblor Ranch

Ten Section

Terra Bella

Trico Gas

Trico Gas, Northwest

Tulare Lake

Union Avenue

Valpredo

Wasco

Welcome Valley

Wheeler Ridge

White Wolf

Yowlumne

Zaca

Field

name

Figure 15. —Continued
86 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 15e

120° 119°

36°

District 2

35°

District 5 District 4

District 4

District 2

District 3

Redding

Sacramento

San Francisco

San Diego

Los Angeles Map area

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

018

020

032

040

042

044

060

066

080

092

095

096

104

106

115

117 140

160

190

194

204

221

222

256

260

272

274

280

328

332

340

336

338

372

428 375

432

450

454

479

479

490

022

050

156

196

758

224

434

532

544 560

566

602

608

624

626

648

690

696

700

702

158 374

716 720

752

756

760

762

766

768

790

808

822

826

046

330

832

834

858

617

102

146

346

210

344

578

296

792

794

288

558

486

632

711

188

860

186

348

220

488

582

228

052

699

446

652 650

697 024

342

754

628

628

038

KERN CO

LOS ANGELES CO

SANTA BARBARA CO

SAN LUIS OBISPO CO

VENTURA CO

KINGS CO

FRESNO CO

TULARE CO

TULE

KAWEAH

SALINAS

VALLEY

CUYAMA

VALLEY

WHITE WOLF

SANTA MARIA

SANTA

YNEZ RIVER

VALLEY

SAN ANTONIO

CREEK VALLEY

TULARE LAKE

WESTSIDE

SAN

JOAQUIN

VALLEY

E

Temblor

Range

Sierra

Nevada

698

238

798

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

CALIFORNIA

Figure 15. —Continued
Results of the Prioritization Analysis 87

sac17-0645_fig 15eContinued

Water-well density

High Moderate Low

EXPLANATION

Numbers in water-well density indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Ant Hill

Antelope Hills

Antelope Hills, North

Antelope Plains Gas

Asphalto

Barham Ranch

Beer Nose

Belgian Anticline

Bellevue

Bellevue, West

Belridge, North

Belridge, South

Blackwells Corner

Bowerbank

Buena Vista

Buttonwillow Gas

Cal Canal Gas

Calders Corner

Capitola Park

Canal

Canfield Ranch

Capitola Park

Carneros Creek

Chico Martinez

Cienaga Canyon

Coles Levee, North

Coles Levee, South

Comanche Point

Cuyama, Central

018

020

022

024

032

038

040

042

044

046

050

052

060

066

080

092

095

096

102

104

106

115

117

140

146

156

158

160

186

Field

name

Field

code

Cuyama, South

Cymric

Deer Creek

Deer Creek, North

Devils Den

Dudley Ridge Gas

Dyer Creek

Eagle Rest

Edison

Edison, Northeast

Elk Hills

English Colony

Fruitvale

Garrison City Gas

Gonyer Anticline

Goosloo

Greeley

Guijarral Hills

Harvester Gas

Jasmin

Jasmin, West

Jerry Slough

Kern Bluff

Kern Front

Kern River

Kernsumner

Kettleman City

Kettleman Middle Dome

Kettleman North Dome

188

190

194

196

204

210

220

221

222

224

228

238

256

260

272

274

280

288

296

328

330

332

336

338

340

342

344

346

348

Lakeside

Lakeside, South

Landslide

Los Lobos

Lost Hills

Lost Hills, Northwest

McClung

McDonald Anticline

McKittrick

Monument Junction

Morales Canyon

Mount Poso

Mountain View

Paloma

Pioneer

Pleasant Valley

Pleito

Poso Creek

Pyramid Hills

Railroad Gap

Rio Bravo

Rio Viejo

Rose

Rosedale

Rosedale Ranch

Round Mountain

Russell Ranch

San Emidio Nose

San Emidio

San Emidio Creek

372

374

375

428

432

434

446

450

454

479

486

488

490

532

544

558

560

566

578

582

602

608

617

624

626

628

632

648

650

652

690

696

697

698

699

700

702

711

716

720

752

754

756

758

759

760

762

766

768

790

792

794

798

808

822

826

832

834

858

860

Field

name Fieldcode

Field

code

Semitropic

Seventh Standard

Shafter

Shafter, Southeast Gas

Shafter, North

Shale Flats Gas

Shale Point Gas

Sisquoc Ranch

Rose

Rosecrans, East

Tejon

Tejon Flats

Tejon Hills

Tejon, North

Temblor East

Temblor Hills

Temblor Ranch

Ten Section

Terra Bella

Trico Gas

Trico Gas, Northwest

Tulare Lake

Union Avenue

Valpredo

Wasco

Welcome Valley

Wheeler Ridge

White Wolf

Yowlumne

Zaca

Field

name

Figure 15. —Continued
88 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 16a

LIVERMORE

VALLEY

121° 120°

37°

36°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

District 3

District 4

District 5

District 6

Kettleman

Plain

KINGS CO

FRESNO CO

SAN BENITO CO

MADERA CO

MARIPOSA CO

TUOLUMNE CO

MERCED CO

STANISLAUS CO

SAN

JOAQUIN

CO

SANTA CLARA CO

ALAMEDA CO

CONTRA COSTA 

CO

MONTEREY CO

SAN LUIS OBISPO CO KERN CO

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

A

SAN JOAQUIN VALLEY

LIVERMORE

VALLEY

SANTA

CLARA

VALLEY

GILROYHOLLISTER

VALLEY

SALINAS

VALLEY

PANOCHE

VALLEY

LOS BANOS

CREEK

VALLEY

CHOLAME

VALLEY

LOCKWOOD

VALLEY

VALLECITOS CREEK

VALLEY

CORRALITOS

VALLEY

CARMEL

VALLEY

QUIEN

SABE

VALLEY

SANTA

ANA

VALLEY

TRES PINOS

VALLEY

SAN BENITO RIVER 

VALLEY

DRY LAKE VALLEY

BITTER WATER VALLEY

HERNANDEZ

VALLEY

PEACH TREE

VALLEY

UPPER SANTA

ANA VALLEY

SUNOL

VALLEY

302

676

204

432

434

790

826

802

456

392 390

786

816

818

404

314

787

149

413

346

210

344

578

296

792

831

794

366

326

288

558

152

150

292

800 112

113

656

134

100

248

086

084

809

614

300

584

654

266

470

144

467

058

806

513

350

436

448

474

580

644

534 348

051

457

459

302

676

204

432

434

790

826

802

456

392 390

786

816

818

404

314

787

149

413

346

210

344

578

296

792

831

794

366

326

288

558

152

150

292

800 112

113

656

134

100

248

086

084

809

614

300

584

654

266

470

144

467

058

806

513

350

436

448

474

580

644

534 348

051

457

459

Base modified from U.S. Geological Survey and other Federal and 

State digital data, various scales; Albers Equal-Area Conic projection, 

standard parallels are 29°30’ N. and 45°30’ N.; North American 

Datum of 1983

Redding

Sacramento

San

Francisco

San Diego

Los Angeles

Map area

CALIFORNIA 616 254

Figure 16. Oil and gas fields in district 5, San Joaquin Basin—North/Central, showing classifications for A, priority; B, petroleum-well 

density; C, volume of injection; D, vertical proximity; and E, water-well density.
Results of the Prioritization Analysis 89

sac17-0645_fig 16aContinued

Priority classifications

High Moderate Low

EXPLANATION

Numbers in priority classifications indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Ash Slough Gas

Bitterwater

Burrel

Burrel, Southeast

Camden

Cantua Creek

Cantua Nueva

Cheney Ranch Gas

Chowchilla Gas

Collegeville, East

Coalinga

Coalinga, East Extension

Devils Den

Dudley Ridge Gas

Five Points

French Camp Gas 

Gill Ranch Gas

051

058

084

086

100

112

113

134

144

149

150

152

204

210

248

254

266

Field

name

Field

code

Guijarral Hills

Hanford

Harvester Gas

Helm

Hollister

Hospital Nose Gas

Jacalitos

Kettleman North Dome

Kettleman Middle Dome

Deer Creek

King City

Kreyenhagen

Lathrop Gas

Lathrop Southeast Gas

Livermore

Lone Tree Creek Gas

Lost Hills

288

292

296

300

302

314

326

344

346

348

350

366

390

392

404

413

432

Lost Hills, Northwest

Lynch Canyon

McCool Ranch

McMullin Ranch Gas

Merrill Avenue Gas

Merrill Avenue, Southeast, Gas

Mint Road Gas

Moffat Ranch Gas

Monroe Swell

Oakdale Gas

Paris Valley

Pleasant Valley

Pyramid Hills

Quinado Canyon

Raisin City

Riverdale

Roberts Island Gas

434

436

448

456

457

459

467

470

474

513

534

558

578

580

584

614

616

644

654

656

676

786

787

790

792

794

800

802

806

809

816

818

826

831

Field

name

Field

code

Field

code

San Ardo

San Joaquin

San Joaquin Gas, Northwest

Sargent

Tracy Gas

Tracy, West, Gas

Trico Gas

Trico Gas, Northwest

Tulare Lake

Turk Anticline

Union Island Gas

Vallecitos

Van Ness Slough

Vernalis Gas

Vernalis, Southwest Gas

Welcome Valley

Westhaven

Field

name

Figure 16. —Continued
90 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 16b

LIVERMORE

VALLEY

121° 120°

37°

36°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

302

204

432

434

790

826

802

456

616

392 390 254

786

816

818

404

314

787

149

413

346

210

344

578

296

792

831

794

366

326

288

558

152 150

292

800 112

113

656

134

100

248

086

084

809

614

300

584

654

266

470

144

467

058

806

513

350

436

448

474

580

644

676

534 348

051

457

459

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

District 3

District 4

District 5

District 6

KINGS CO

FRESNO CO

SAN BENITO CO

MADERA CO

MARIPOSA CO

TUOLUMNE CO

MERCED CO

STANISLAUS CO

SAN

JOAQUIN

CO

SANTA CLARA CO

ALAMEDA CO

CONTRA COSTA 

CO

MONTEREY CO

SAN LUIS OBISPO CO KERN CO

B

SAN JOAQUIN VALLEY

LIVERMORE

VALLEY

SANTA

CLARA

VALLEY

GILROYHOLLISTER

VALLEY

SALINAS

VALLEY

PANOCHE

VALLEY

LOS BANOS

CREEK

VALLEY

CHOLAME

VALLEY

LOCKWOOD

VALLEY

VALLECITOS CREEK

VALLEY

CORRALITOS

VALLEY

CARMEL

VALLEY

QUIEN

SABE

VALLEY

SANTA

ANA

VALLEY

TRES PINOS

VALLEY

SAN BENITO RIVER 

VALLEY

DRY LAKE VALLEY

BITTER WATER VALLEY

HERNANDEZ

VALLEY

PEACH TREE

VALLEY

UPPER SANTA

ANA VALLEY

SUNOL

VALLEY

Kettleman

Plain

Redding

Sacramento

San

Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and 

State digital data, various scales; Albers Equal-Area Conic projection, 

standard parallels are 29°30’ N. and 45°30’ N.; North American 

Datum of 1983

Figure 16. —Continued
Results of the Prioritization Analysis 91

sac17-0645_fig 16bContinued

EXPLANATION

Petroleum-well density

High Low

Moderate 

Numbers in petroleum-well density indicate the field codes

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Ash Slough Gas

Bitterwater

Burrel

Burrel, Southeast

Camden

Cantua Creek

Cantua Nueva

Cheney Ranch Gas

Chowchilla Gas

Collegeville, East

Coalinga

Coalinga, East Extension

Devils Den

Dudley Ridge Gas

Five Points

French Camp Gas 

Gill Ranch Gas

051

058

084

086

100

112

113

134

144

149

150

152

204

210

248

254

266

Field

name

Field

code

Guijarral Hills

Hanford

Harvester Gas

Helm

Hollister

Hospital Nose Gas

Jacalitos

Kettleman North Dome

Kettleman Middle Dome

Deer Creek

King City

Kreyenhagen

Lathrop Gas

Lathrop Southeast Gas

Livermore

Lone Tree Creek Gas

Lost Hills

288

292

296

300

302

314

326

344

346

348

350

366

390

392

404

413

432

Lost Hills, Northwest

Lynch Canyon

McCool Ranch

McMullin Ranch Gas

Merrill Avenue Gas

Merrill Avenue, Southeast, Gas

Mint Road Gas

Moffat Ranch Gas

Monroe Swell

Oakdale Gas

Paris Valley

Pleasant Valley

Pyramid Hills

Quinado Canyon

Raisin City

Riverdale

Roberts Island Gas

434

436

448

456

457

459

467

470

474

513

534

558

578

580

584

614

616

644

654

656

676

786

787

790

792

794

800

802

806

809

816

818

826

831

Field

name

Field

code

Field

code

San Ardo

San Joaquin

San Joaquin Gas, Northwest

Sargent

Tracy Gas

Tracy, West, Gas

Trico Gas

Trico Gas, Northwest

Tulare Lake

Turk Anticline

Union Island Gas

Vallecitos

Van Ness Slough

Vernalis Gas

Vernalis, Southwest Gas

Welcome Valley

Westhaven

Field

name

Figure 16. —Continued
92 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 16c

LIVERMORE

VALLEY

121° 120°

37°

36°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

District 3

District 4

District 5

District 6

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014 KINGS CO FRESNO CO

SAN BENITO CO

MADERA CO

MARIPOSA CO

TUOLUMNE CO

MERCED CO

STANISLAUS CO

SAN

JOAQUIN

CO

SANTA CLARA CO

ALAMEDA CO

CONTRA COSTA 

CO

MONTEREY CO

SAN LUIS OBISPO CO KERN CO

302

204

432

434

790

826

802

456

616

392 390 254

786

816

818

404

314

787

149

413

346

210

344

578

296

792

831

794

366

326

288

558

152 150

292

800 112

113

656

134

100

248

086

084

809

614

300

584

654

266

470

144

467

058

806

513

350

436

448

474

580

644

676

534 348

051

457

459

C

SAN JOAQUIN VALLEY

LIVERMORE

VALLEY

SANTA

CLARA

VALLEY

GILROYHOLLISTER

VALLEY

SALINAS

VALLEY

PANOCHE

VALLEY

LOS BANOS

CREEK

VALLEY

CHOLAME

VALLEY

LOCKWOOD

VALLEY

VALLECITOS

CREEK

VALLEY

CORRALITOS

VALLEY

CARMEL

VALLEY

QUIEN

SABE

VALLEY

SANTA

ANA

VALLEY

TRES PINOS

VALLEY

SAN BENITO RIVER 

VALLEY

DRY LAKE VALLEY

BITTER WATER VALLEY

HERNANDEZ

VALLEY

PEACH TREE

VALLEY

UPPER SANTA

ANA VALLEY

SUNOL

VALLEY

Kettleman

Plain

Base modified from U.S. Geological Survey and other Federal and 

State digital data, various scales; Albers Equal-Area Conic projection, 

standard parallels are 29°30’ N. and 45°30’ N.; North American 

Datum of 1983

Redding

Sacramento

San

Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Figure 16. —Continued
Results of the Prioritization Analysis 93

sac17-0645_fig 16cContinued

Numbers in volume of injection indicate the field codes

EXPLANATION

Volume of injection

High

Moderate 

Low DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Ash Slough Gas

Bitterwater

Burrel

Burrel, Southeast

Camden

Cantua Creek

Cantua Nueva

Cheney Ranch Gas

Chowchilla Gas

Collegeville, East

Coalinga

Coalinga, East Extension

Devils Den

Dudley Ridge Gas

Five Points

French Camp Gas 

Gill Ranch Gas

051

058

084

086

100

112

113

134

144

149

150

152

204

210

248

254

266

Field

name

Field

code

Guijarral Hills

Hanford

Harvester Gas

Helm

Hollister

Hospital Nose Gas

Jacalitos

Kettleman North Dome

Kettleman Middle Dome

Deer Creek

King City

Kreyenhagen

Lathrop Gas

Lathrop Southeast Gas

Livermore

Lone Tree Creek Gas

Lost Hills

288

292

296

300

302

314

326

344

346

348

350

366

390

392

404

413

432

Lost Hills, Northwest

Lynch Canyon

McCool Ranch

McMullin Ranch Gas

Merrill Avenue Gas

Merrill Avenue, Southeast, Gas

Mint Road Gas

Moffat Ranch Gas

Monroe Swell

Oakdale Gas

Paris Valley

Pleasant Valley

Pyramid Hills

Quinado Canyon

Raisin City

Riverdale

Roberts Island Gas

434

436

448

456

457

459

467

470

474

513

534

558

578

580

584

614

616

644

654

656

676

786

787

790

792

794

800

802

806

809

816

818

826

831

Field

name

Field

code

Field

code

San Ardo

San Joaquin

San Joaquin Gas, Northwest

Sargent

Tracy Gas

Tracy, West, Gas

Trico Gas

Trico Gas, Northwest

Tulare Lake

Turk Anticline

Union Island Gas

Vallecitos

Van Ness Slough

Vernalis Gas

Vernalis, Southwest Gas

Welcome Valley

Westhaven

Field

name

Figure 16. —Continued
94 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 16d

LIVERMORE

VALLEY

121° 120°

37°

36°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

District 3

District 4

District 5

District 6

KINGS CO

FRESNO CO

SAN BENITO CO

MADERA CO

MARIPOSA CO

TUOLUMNE CO

MERCED CO

STANISLAUS CO

SAN

JOAQUIN

CO

SANTA CLARA CO

ALAMEDA CO

CONTRA COSTA 

CO

MONTEREY CO

SAN LUIS OBISPO CO KERN CO

302

204

432

434

790

826

802

456

392 390

786

816

818

404

314

787

149

413

346

210

344

578

296

792

831

794

366

326

288

558

152

150

292

800 112

113

656

134

100

248

086

084

809

614

300

584

654

266

470

144

467

058

806

513

350

436

448

474

580

644

676

534 348

051

457

459

D

Kettleman

Plain

SAN JOAQUIN VALLEY

LIVERMORE

VALLEY

SANTA

CLARA

VALLEY

GILROYHOLLISTER

VALLEY

SALINAS

VALLEY

PANOCHE

VALLEY

LOS BANOS

CREEK

VALLEY

CHOLAME

VALLEY

LOCKWOOD

VALLEY

VALLECITOS

CREEK

VALLEY

CORRALITOS

VALLEY

CARMEL

VALLEY

QUIEN

SABE

VALLEY

SANTA

ANA

VALLEY

TRES PINOS

VALLEY

SAN BENITO RIVER 

VALLEY

DRY LAKE VALLEY

BITTER WATER VALLEY

HERNANDEZ

VALLEY

PEACH TREE

VALLEY

UPPER SANTA

ANA VALLEY

SUNOL

VALLEY

Redding

Sacramento

San

Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Base modified from U.S. Geological Survey and other Federal and 

State digital data, various scales; Albers Equal-Area Conic projection, 

standard parallels are 29°30’ N. and 45°30’ N.; North American 

Datum of 1983

616 254

Figure 16. —Continued
Results of the Prioritization Analysis 95

sac17-0645_fig 16dContinued

Field

name

Field

code

Ash Slough Gas

Bitterwater

Burrel

Burrel, Southeast

Camden

Cantua Creek

Cantua Nueva

Cheney Ranch Gas

Chowchilla Gas

Collegeville, East

Coalinga

Coalinga, East Extension

Devils Den

Dudley Ridge Gas

Five Points

French Camp Gas 

Gill Ranch Gas

051

058

084

086

100

112

113

134

144

149

150

152

204

210

248

254

266

Field

name

Field

code

Guijarral Hills

Hanford

Harvester Gas

Helm

Hollister

Hospital Nose Gas

Jacalitos

Kettleman North Dome

Kettleman Middle Dome

Deer Creek

King City

Kreyenhagen

Lathrop Gas

Lathrop Southeast Gas

Livermore

Lone Tree Creek Gas

Lost Hills

288

292

296

300

302

314

326

344

346

348

350

366

390

392

404

413

432

Lost Hills, Northwest

Lynch Canyon

McCool Ranch

McMullin Ranch Gas

Merrill Avenue Gas

Merrill Avenue, Southeast, Gas

Mint Road Gas

Moffat Ranch Gas

Monroe Swell

Oakdale Gas

Paris Valley

Pleasant Valley

Pyramid Hills

Quinado Canyon

Raisin City

Riverdale

Roberts Island Gas

434

436

448

456

457

459

467

470

474

513

534

558

578

580

584

614

616

644

654

656

676

786

787

790

792

794

800

802

806

809

816

818

826

831

Field

name

Field

code

Field

code

San Ardo

San Joaquin

San Joaquin Gas, Northwest

Sargent

Tracy Gas

Tracy, West, Gas

Trico Gas

Trico Gas, Northwest

Tulare Lake

Turk Anticline

Union Island Gas

Vallecitos

Van Ness Slough

Vernalis Gas

Vernalis, Southwest Gas

Welcome Valley

Westhaven

Field

name

Numbers in vertical proximity indicate the field codes

EXPLANATION

Vertical proximity

Close Far

Moderate Unknown

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Figure 16. —Continued
96 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 16e

LIVERMORE

VALLEY

121° 120°

37°

36°

0 5 10 20 MILES

0 5 10 20 KILOMETERS

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014 KINGS CO FRESNO CO

SAN BENITO CO

MADERA CO

MARIPOSA CO

TUOLUMNE CO

MERCED CO

STANISLAUS CO

SAN

JOAQUIN

CO

SANTA CLARA CO

ALAMEDA CO

CONTRA COSTA 

CO

MONTEREY CO

SAN LUIS OBISPO CO KERN CO

District 3

District 4

District 5

District 6

302

204

432

434

790

826

802

456

616

392 390254

786

816

818

404

314

787

149

413

346

210

344

578

296

792

831

794

366

326

288

558

150 152

292

800 112

113

656

134

100

248

086

084

809

614

300

584

654

266

470

144

467

058

806

513

350

436

448

474

580

644

676

534 348

051

457

459

E

Kettleman

Plain

SAN JOAQUIN VALLEY

LIVERMORE

VALLEY

SANTA

CLARA

VALLEY

GILROYHOLLISTER

VALLEY

SALINAS

VALLEY

PANOCHE

VALLEY

LOS BANOS

CREEK

VALLEY

CHOLAME

VALLEY

LOCKWOOD

VALLEY

VALLECITOS CREEK

VALLEY

CORRALITOS

VALLEY

CARMEL

VALLEY

QUIEN

SABE

VALLEY

SANTA

ANA

VALLEY

TRES PINOS

VALLEY

SAN BENITO RIVER 

VALLEY

DRY LAKE VALLEY

BITTER WATER VALLEY

HERNANDEZ

VALLEY

PEACH TREE

VALLEY

UPPER SANTA

ANA VALLEY

SUNOL

VALLEY

Base modified from U.S. Geological Survey and other Federal and 

State digital data, various scales; Albers Equal-Area Conic projection, 

standard parallels are 29°30’ N. and 45°30’ N.; North American 

Datum of 1983

Redding

Sacramento

San

Francisco

San Diego

Los Angeles

Map area

CALIFORNIA

Figure 16. —Continued
Results of the Prioritization Analysis 97

sac17-0645_fig 16eContinued

Numbers in water-well density indicate the field codes

EXPLANATION

Water-well density

High Moderate Low DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Ash Slough Gas

Bitterwater

Burrel

Burrel, Southeast

Camden

Cantua Creek

Cantua Nueva

Cheney Ranch Gas

Chowchilla Gas

Collegeville, East

Coalinga

Coalinga, East Extension

Devils Den

Dudley Ridge Gas

Five Points

French Camp Gas 

Gill Ranch Gas

051

058

084

086

100

112

113

134

144

149

150

152

204

210

248

254

266

Field

name

Field

code

Guijarral Hills

Hanford

Harvester Gas

Helm

Hollister

Hospital Nose Gas

Jacalitos

Kettleman North Dome

Kettleman Middle Dome

Deer Creek

King City

Kreyenhagen

Lathrop Gas

Lathrop Southeast Gas

Livermore

Lone Tree Creek Gas

Lost Hills

288

292

296

300

302

314

326

344

346

348

350

366

390

392

404

413

432

Lost Hills, Northwest

Lynch Canyon

McCool Ranch

McMullin Ranch Gas

Merrill Avenue Gas

Merrill Avenue, Southeast, Gas

Mint Road Gas

Moffat Ranch Gas

Monroe Swell

Oakdale Gas

Paris Valley

Pleasant Valley

Pyramid Hills

Quinado Canyon

Raisin City

Riverdale

Roberts Island Gas

434

436

448

456

457

459

467

470

474

513

534

558

578

580

584

614

616

644

654

656

676

786

787

790

792

794

800

802

806

809

816

818

826

831

Field

name

Field

code

Field

code

San Ardo

San Joaquin

San Joaquin Gas, Northwest

Sargent

Tracy Gas

Tracy, West, Gas

Trico Gas

Trico Gas, Northwest

Tulare Lake

Turk Anticline

Union Island Gas

Vallecitos

Van Ness Slough

Vernalis Gas

Vernalis, Southwest Gas

Welcome Valley

Westhaven

Field

name

Figure 16. —Continued
98 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 17a

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 10 20 40 MILES

0 10 20 30 40 KILOMETERS

30

Sacramento

San Francisco

Los Angeles

San Diego

Redding Lassen

Peak

Klamath Mountains

Map

area

A

B

CALIFORNIA

District 6

District 5

District 3

B

Sacramento

San Francisco

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

A

Coast

Ranges

Sierra

Nevada

802

456

452

616

392 390 254

719

786

816

818

294

072717510 659

073

359

610

404

314

706 218

398

094

400 229

709

276

612

772

442

402

606

460

351

225

770

408

264

411

409

082

202 200

354

722 352

634

026 356

074

090

088 828

730

030

713

380

164

535 162

403

686

715

574

062 004

016

002

846

406

536

216

138 526

306

430 842

492

810

093

778

576

636

604

172

638

278

850

148

252 718 564

458

192 249

556

214 212 721

552

852

862

864

317

293

207

854

736

788

227

335 821

253

615

506

541

243

776

732 734

482

840

444

287

540

780

738

358 596

528 590

597

176

174

281

538

177

844

183

787

592

847

518

370

290

149

413

542

455

603

513

284

209

206

244

361

466

684

282

415

841

059

MENDOCINO CO

NAPA CO

SOLANO CO

SONOMA CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS

CO

STANISLAUS CO

SACRAMENTO CO

SAN JOAQUIN CO

MERCED CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

Figure 17. Oil and gas fields in district 6, Sacramento Valley, showing classifications for A, priority; B, petroleum-well density;

C, volume of injection; D, vertical proximity; and E, water-well density.
Results of the Prioritization Analysis 99

sac17-0645_fig 17aContinued

Field

name

Field

code

Afton Gas

Afton Gas, South

Angel Slough Gas

Arbuckle Gas

Artois Gas

Bixler Gas

Bounde Creek Gas

Brentwood

Brentwood, East Gas

Buckeye Gas

Bullock Bend Gas

Bunker Gas

Butte Sink Gas

Butte Slough Gas

Cache Creek Gas

Cache Slough Gas

Chico Gas

Clarksburg Gas

Collegeville, East

Compton Landing Gas

Compton Landing, South Gas

Concord Gas

Conway Ranch Gas

Corning Gas

Corning Gas, South

Cotati Gas

Crossroads Gas

Davis Southeast Gas

Denverton Gas

Denverton Creek Gas

Dixon Gas

Dixon Gas, East

Dry Slough Gas

Dufour Gas

Dunnigan Hills Gas

Durham Gas

Dutch Slough Gas

East Islands Gas

El Dorado Bend Gas

Elkhorn Slough Gas

Everglade Gas

002

004

016

026

030

059

062

072

073

074

079

082

088

090

093

094

138

148

149

162

164

168

172

174

176

177

183

192

200

202

206

207

209

212

214

216

218

225

227

229

243

Field

name

Field

code

Fairfield Knolls Gas

Florin Gas

Freeport Gas

Fremont Landing Gas

French Camp Gas

Galt Gas

Grand Island Gas

Greens Lake Gas

Greenwood Gas

Grimes Gas

Grimes, West Gas

Half Moon Bay

Hanford

Harlan Ranch Gas

Harte Gas

Honker Gas

Hospital Nose Gas

Howells Point Gas

Karnak Gas

King Island Gas

Kirby Hill Gas

Kirby Hill Gas, North

Kirk Gas

Kirkwood Gas

Knightsen Gas

Knights Landing Gas

La Honda

Larkin, West Gas

Lathrop Gas

Lathrop Southeast Gas

Liberty Cut Gas

Liberty Island Gas

Lindsey Slough Gas

Little Butte Creek Gas

Livermore

Llano Seco Gas

Lodi Gas

Lodi Airport Gas

Lodi, Southeast Gas

Lone Tree Creek Gas

Lone Star Gas

244

249

252

253

254

264

276

278

281

282

284

290

292

293

294

306

314

317

335

351

352

354

356

358

359

361

370

380

390

392

398

400

402

403

404

406

408

409

411

413

415

Los Medanos Gas

Maine Prairie Gas

Malton-Black Butte Gas

McDonald Island Gas

Medora Lake Gas

McMullin Ranch Gas

Merritt Gas

Merritt Island Gas

Millar Gas

Moon Bend Gas

Mulligan Hill Gas

Nicolas Gas

Oakley Gas

Oakdale Gas

Oil Creek

Ord Bend Gas

Orland Gas

Peace Valley Gas

Perkins Lake Gas

Petaluma Gas

Pierce Road Gas

Pinole Point

Madison Gas

Pleasant Creek Gas

Poppy Ridge Gas

Princeton Gas

Putah Sink Gas

Rancho Capay Gas

Red Bank Creek Gas

Rice Creek Gas

Rice Creek, East Gas

Rindge Tract Gas

Rio Jesus Gas

Rio Vista Gas

River Break Gas

River Island Gas

Robbins Gas

Roberts Island Gas

Ryer Island Gas

Sacramento Airport Gas

Sacramento By-Pass Gas

430

442

444

452

455

456

458

460

466

482

492

506

510

513

518

526

528

535

536

538

541

542

552

556

564

574

576

590

592

596

597

603

604

606

610

612

615

616

634

636

638

659

684

686

706

709

713

715

717

718

719

721

722

730

732

734

736

770

772

776

778

786

787

788

802

810

816

818

821

828

840

841

842

844

846

847

850

852

854

862

864

Field

name

Field

code

Field

code

Sand Mound Slough Gas

Saxon Gas

Schohr Ranch Gas

Sherman Island Gas

Snodgrass Slough Gas

Greenwood Gas, South

Stegeman Gas

Oakley Gas, South

Stone Lake Gas

Stockton Gas

Sugarfield Gas

Suisun Bay Gas

Sutter Buttes Gas

Sutter City Gas

Sycamore Gas

Sycamore Slough Gas

Thornton Gas

Thornton, West-Walnut Grove Gas

Tisdale Gas

Todhunters Lake Gas

Tracy Gas

Tracy, West, Gas

Tremont Gas

Union Island Gas

Van Sickle Island Gas

Vernalis Gas

Vernalis, Southwest Gas

Verona Gas

West Butte Gas

Wild Goose Gas

Williams Gas

Willow Pass Gas

Willow Slough Gas

Willows-Beehive Bend Gas

Wilson Creek Gas

Winchester Lake Gas

Winters Gas

Woodland Gas

Zamora Gas

Zamora Gas, North

Field

name

Numbers in priority classifications indicate the field codes

Priority classifications

High Low

Moderate 

EXPLANATION

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Figure 17. —Continued
100 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 17b

124° 123° 122° 121°

40°

39°

38°

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 10 20 40 MILES

0 10 20 30 40 KILOMETERS

30

District 6

District 5

District 3

Sacramento

San Francisco

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

MENDOCINO CO

NAPA CO

SOLANO CO

SONOMA CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS

CO

STANISLAUS CO

SACRAMENTO CO

SAN JOAQUIN CO

MERCED CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

802

456

452

616

392 390

254

719

786

816

818

294

072 059

510 659 610 218

073

717 359

404

314

290

370

518

706

400

398

094

229

709

276

612

772

442

402

606

460

351

225

770

408 264

411

409

082

202 200

354

352 722

634

026 074 356

090828

730

030

713

380

164 535 162

403

686

715

574

062 004

002

846 406

536 216

526 138

016

306

430 168 842

492

810

093

778

576

636

253

604

172

638

278

850

148

252

718

458

192 249

564

556

214 212

552

852

862

864

317

293

206

207

854

736

788

227

721

335 821

615

506

541

243

776

732 734

088

482

840

444

358 596

528 590

597

176

174

281

538

177

079

844

183

787

592

847

149

513

413

542

455

603

284

209

244

361

466

684

282

415

841

B

CALIFORNIA

Lassen

Peak

Klamath Mountains

Map

area Sacramento

San Francisco

San Diego

Redding

Los Angeles

Figure 17. —Continued
Results of the Prioritization Analysis 101

sac17-0645_fig 17bContinued

Numbers in petroleum-well density indicate the field codes

EXPLANATION

Petroleum-well density

High Low

Moderate 

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Afton Gas

Afton Gas, South

Angel Slough Gas

Arbuckle Gas

Artois Gas

Bixler Gas

Bounde Creek Gas

Brentwood

Brentwood, East Gas

Buckeye Gas

Bullock Bend Gas

Bunker Gas

Butte Sink Gas

Butte Slough Gas

Cache Creek Gas

Cache Slough Gas

Chico Gas

Clarksburg Gas

Collegeville, East

Compton Landing Gas

Compton Landing, South Gas

Concord Gas

Conway Ranch Gas

Corning Gas

Corning Gas, South

Cotati Gas

Crossroads Gas

Davis Southeast Gas

Denverton Gas

Denverton Creek Gas

Dixon Gas

Dixon Gas, East

Dry Slough Gas

Dufour Gas

Dunnigan Hills Gas

Durham Gas

Dutch Slough Gas

East Islands Gas

El Dorado Bend Gas

Elkhorn Slough Gas

Everglade Gas

002

004

016

026

030

059

062

072

073

074

079

082

088

090

093

094

138

148

149

162

164

168

172

174

176

177

183

192

200

202

206

207

209

212

214

216

218

225

227

229

243

Field

name

Field

code

Fairfield Knolls Gas

Florin Gas

Freeport Gas

Fremont Landing Gas

French Camp Gas

Galt Gas

Grand Island Gas

Greens Lake Gas

Greenwood Gas

Grimes Gas

Grimes, West Gas

Half Moon Bay

Hanford

Harlan Ranch Gas

Harte Gas

Honker Gas

Hospital Nose Gas

Howells Point Gas

Karnak Gas

King Island Gas

Kirby Hill Gas

Kirby Hill Gas, North

Kirk Gas

Kirkwood Gas

Knightsen Gas

Knights Landing Gas

La Honda

Larkin, West Gas

Lathrop Gas

Lathrop Southeast Gas

Liberty Cut Gas

Liberty Island Gas

Lindsey Slough Gas

Little Butte Creek Gas

Livermore

Llano Seco Gas

Lodi Gas

Lodi Airport Gas

Lodi, Southeast Gas

Lone Tree Creek Gas

Lone Star Gas

244

249

252

253

254

264

276

278

281

282

284

290

292

293

294

306

314

317

335

351

352

354

356

358

359

361

370

380

390

392

398

400

402

403

404

406

408

409

411

413

415

Los Medanos Gas

Maine Prairie Gas

Malton-Black Butte Gas

McDonald Island Gas

Medora Lake Gas

McMullin Ranch Gas

Merritt Gas

Merritt Island Gas

Millar Gas

Moon Bend Gas

Mulligan Hill Gas

Nicolas Gas

Oakley Gas

Oakdale Gas

Oil Creek

Ord Bend Gas

Orland Gas

Peace Valley Gas

Perkins Lake Gas

Petaluma Gas

Pierce Road Gas

Pinole Point

Madison Gas

Pleasant Creek Gas

Poppy Ridge Gas

Princeton Gas

Putah Sink Gas

Rancho Capay Gas

Red Bank Creek Gas

Rice Creek Gas

Rice Creek, East Gas

Rindge Tract Gas

Rio Jesus Gas

Rio Vista Gas

River Break Gas

River Island Gas

Robbins Gas

Roberts Island Gas

Ryer Island Gas

Sacramento Airport Gas

Sacramento By-Pass Gas

430

442

444

452

455

456

458

460

466

482

492

506

510

513

518

526

528

535

536

538

541

542

552

556

564

574

576

590

592

596

597

603

604

606

610

612

615

616

634

636

638

659

684

686

706

709

713

715

717

718

719

721

722

730

732

734

736

770

772

776

778

786

787

788

802

810

816

818

821

828

840

841

842

844

846

847

850

852

854

862

864

Field

name

Field

code

Field

code

Sand Mound Slough Gas

Saxon Gas

Schohr Ranch Gas

Sherman Island Gas

Snodgrass Slough Gas

Greenwood Gas, South

Stegeman Gas

Oakley Gas, South

Stone Lake Gas

Stockton Gas

Sugarfield Gas

Suisun Bay Gas

Sutter Buttes Gas

Sutter City Gas

Sycamore Gas

Sycamore Slough Gas

Thornton Gas

Thornton, West-Walnut Grove Gas

Tisdale Gas

Todhunters Lake Gas

Tracy Gas

Tracy, West, Gas

Tremont Gas

Union Island Gas

Van Sickle Island Gas

Vernalis Gas

Vernalis, Southwest Gas

Verona Gas

West Butte Gas

Wild Goose Gas

Williams Gas

Willow Pass Gas

Willow Slough Gas

Willows-Beehive Bend Gas

Wilson Creek Gas

Winchester Lake Gas

Winters Gas

Woodland Gas

Zamora Gas

Zamora Gas, North

Field

name

Figure 17. —Continued
102 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 17c

124° 123° 122° 121°

40°

39°

38°

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 10 20 40 MILES

0 10 20 30 40 KILOMETERS

30

District 6

District 5

District 3

Sacramento

San Francisco

MENDOCINO CO

NAPA CO

SOLANO CO

SONOMA CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS

CO

STANISLAUS CO

SACRAMENTO CO

SAN JOAQUIN CO

MERCED CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

802

456

452

616

392 390 254

719

786

816

818

294

072

510

218

659

073 717 359

610

404

314

706

400

398

094

229

709

612

772

442

402

606

460

351

225

770

408

264

411

409

082

202 200

354

722 352

634

026 356

074

090

828

730

030

713

380

164 535 162

403

686

715

574

062 004

002

846

406

536

216

526 138

016

306

430

168 492

810

093 721

778

576

636

253 604

172

638

278

850

148 252 718

458

192 249

564

556

214 212

552

852

862

864

317

293

206

207

854

736

788

227 335821

615

506

541

243

776

734 732

088

482

840

444

358 596

528 590

597

176

174

281

538

177

079

844

183

787

592

847

518

370

290

149

413

542

455

603

513

284

209

244

361

466

684

282

415

841

059

C

CALIFORNIA

Lassen

Peak

Klamath Mountains

Map

area Sacramento

San Francisco

San Diego

Redding

Los Angeles

Figure 17. —Continued
Results of the Prioritization Analysis 103

sac17-0645_fig 17cContinued

Numbers in volume of injection indicate the field codes

EXPLANATION

Volume of injection

High Low

Moderate 

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Afton Gas

Afton Gas, South

Angel Slough Gas

Arbuckle Gas

Artois Gas

Bixler Gas

Bounde Creek Gas

Brentwood

Brentwood, East Gas

Buckeye Gas

Bullock Bend Gas

Bunker Gas

Butte Sink Gas

Butte Slough Gas

Cache Creek Gas

Cache Slough Gas

Chico Gas

Clarksburg Gas

Collegeville, East

Compton Landing Gas

Compton Landing, South Gas

Concord Gas

Conway Ranch Gas

Corning Gas

Corning Gas, South

Cotati Gas

Crossroads Gas

Davis Southeast Gas

Denverton Gas

Denverton Creek Gas

Dixon Gas

Dixon Gas, East

Dry Slough Gas

Dufour Gas

Dunnigan Hills Gas

Durham Gas

Dutch Slough Gas

East Islands Gas

El Dorado Bend Gas

Elkhorn Slough Gas

Everglade Gas

002

004

016

026

030

059

062

072

073

074

079

082

088

090

093

094

138

148

149

162

164

168

172

174

176

177

183

192

200

202

206

207

209

212

214

216

218

225

227

229

243

Field

name

Field

code

Fairfield Knolls Gas

Florin Gas

Freeport Gas

Fremont Landing Gas

French Camp Gas

Galt Gas

Grand Island Gas

Greens Lake Gas

Greenwood Gas

Grimes Gas

Grimes, West Gas

Half Moon Bay

Hanford

Harlan Ranch Gas

Harte Gas

Honker Gas

Hospital Nose Gas

Howells Point Gas

Karnak Gas

King Island Gas

Kirby Hill Gas

Kirby Hill Gas, North

Kirk Gas

Kirkwood Gas

Knightsen Gas

Knights Landing Gas

La Honda

Larkin, West Gas

Lathrop Gas

Lathrop Southeast Gas

Liberty Cut Gas

Liberty Island Gas

Lindsey Slough Gas

Little Butte Creek Gas

Livermore

Llano Seco Gas

Lodi Gas

Lodi Airport Gas

Lodi, Southeast Gas

Lone Tree Creek Gas

Lone Star Gas

244

249

252

253

254

264

276

278

281

282

284

290

292

293

294

306

314

317

335

351

352

354

356

358

359

361

370

380

390

392

398

400

402

403

404

406

408

409

411

413

415

Los Medanos Gas

Maine Prairie Gas

Malton-Black Butte Gas

McDonald Island Gas

Medora Lake Gas

McMullin Ranch Gas

Merritt Gas

Merritt Island Gas

Millar Gas

Moon Bend Gas

Mulligan Hill Gas

Nicolas Gas

Oakley Gas

Oakdale Gas

Oil Creek

Ord Bend Gas

Orland Gas

Peace Valley Gas

Perkins Lake Gas

Petaluma Gas

Pierce Road Gas

Pinole Point

Madison Gas

Pleasant Creek Gas

Poppy Ridge Gas

Princeton Gas

Putah Sink Gas

Rancho Capay Gas

Red Bank Creek Gas

Rice Creek Gas

Rice Creek, East Gas

Rindge Tract Gas

Rio Jesus Gas

Rio Vista Gas

River Break Gas

River Island Gas

Robbins Gas

Roberts Island Gas

Ryer Island Gas

Sacramento Airport Gas

Sacramento By-Pass Gas

430

442

444

452

455

456

458

460

466

482

492

506

510

513

518

526

528

535

536

538

541

542

552

556

564

574

576

590

592

596

597

603

604

606

610

612

615

616

634

636

638

659

684

686

706

709

713

715

717

718

719

721

722

730

732

734

736

770

772

776

778

786

787

788

802

810

816

818

821

828

840

841

842

844

846

847

850

852

854

862

864

Field

name

Field

code

Field

code

Sand Mound Slough Gas

Saxon Gas

Schohr Ranch Gas

Sherman Island Gas

Snodgrass Slough Gas

Greenwood Gas, South

Stegeman Gas

Oakley Gas, South

Stone Lake Gas

Stockton Gas

Sugarfield Gas

Suisun Bay Gas

Sutter Buttes Gas

Sutter City Gas

Sycamore Gas

Sycamore Slough Gas

Thornton Gas

Thornton, West-Walnut Grove Gas

Tisdale Gas

Todhunters Lake Gas

Tracy Gas

Tracy, West, Gas

Tremont Gas

Union Island Gas

Van Sickle Island Gas

Vernalis Gas

Vernalis, Southwest Gas

Verona Gas

West Butte Gas

Wild Goose Gas

Williams Gas

Willow Pass Gas

Willow Slough Gas

Willows-Beehive Bend Gas

Wilson Creek Gas

Winchester Lake Gas

Winters Gas

Woodland Gas

Zamora Gas

Zamora Gas, North

Field

name

Figure 17. —Continued
104 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 17d

124° 123° 122° 121°

40°

39°

38°

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 10 20 40 MILES

0 10 20 30 40 KILOMETERS

30

District 6

District 5

District 3

Sacramento

San Francisco

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

SACRAMENTO CO

MENDOCINO CO

NAPA CO

SOLANO CO

SONOMA CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS

CO

STANISLAUS CO

SACRAMENTO CO

SAN JOAQUIN CO

MERCED CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

802

456

452

616

392 390 254

719

786

816

818

294

072 359 717

218

073

610 659 510

404

314

706

398

094

400

229

709

276

612

772

442

402

606

460

351

225

770

408

264

411

409

082

202 200

354

352 722

634

026 356

074

828

730

030

713

380

164

535

162

403

686

715

574

062 004

016

002

846

406

536 216

138 526

306

430 842

492

810

093 721

778

576

636

604

253

172

278

850

148

252 718 564

458

192 249

556

214 212

552

852

862

864

317 079

293

207

206

854

736

788

227 335

821

615

506

541

243

776

732 734

088

090 482

840

444

358 596

528590

597

176

174

281

538

177

844

183

787

592

847

518

370

290

149

413

542

455

603

513

284

209

244

361

466

684

282

415

841

059

D

CALIFORNIA

Lassen

Peak

Klamath Mountains

Map

area Sacramento

San Francisco

San Diego

Redding

Los Angeles

Figure 17. —Continued
Results of the Prioritization Analysis 105

sac17-0645_fig 17dContinued

Numbers in vertical proximity indicate the field codes

EXPLANATION

Vertical proximity

Close Far

Moderate Unknown

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Field

name

Field

code

Afton Gas

Afton Gas, South

Angel Slough Gas

Arbuckle Gas

Artois Gas

Bixler Gas

Bounde Creek Gas

Brentwood

Brentwood, East Gas

Buckeye Gas

Bullock Bend Gas

Bunker Gas

Butte Sink Gas

Butte Slough Gas

Cache Creek Gas

Cache Slough Gas

Chico Gas

Clarksburg Gas

Collegeville, East

Compton Landing Gas

Compton Landing, South Gas

Concord Gas

Conway Ranch Gas

Corning Gas

Corning Gas, South

Cotati Gas

Crossroads Gas

Davis Southeast Gas

Denverton Gas

Denverton Creek Gas

Dixon Gas

Dixon Gas, East

Dry Slough Gas

Dufour Gas

Dunnigan Hills Gas

Durham Gas

Dutch Slough Gas

East Islands Gas

El Dorado Bend Gas

Elkhorn Slough Gas

Everglade Gas

002

004

016

026

030

059

062

072

073

074

079

082

088

090

093

094

138

148

149

162

164

168

172

174

176

177

183

192

200

202

206

207

209

212

214

216

218

225

227

229

243

Field

name

Field

code

Fairfield Knolls Gas

Florin Gas

Freeport Gas

Fremont Landing Gas

French Camp Gas

Galt Gas

Grand Island Gas

Greens Lake Gas

Greenwood Gas

Grimes Gas

Grimes, West Gas

Half Moon Bay

Hanford

Harlan Ranch Gas

Harte Gas

Honker Gas

Hospital Nose Gas

Howells Point Gas

Karnak Gas

King Island Gas

Kirby Hill Gas

Kirby Hill Gas, North

Kirk Gas

Kirkwood Gas

Knightsen Gas

Knights Landing Gas

La Honda

Larkin, West Gas

Lathrop Gas

Lathrop Southeast Gas

Liberty Cut Gas

Liberty Island Gas

Lindsey Slough Gas

Little Butte Creek Gas

Livermore

Llano Seco Gas

Lodi Gas

Lodi Airport Gas

Lodi, Southeast Gas

Lone Tree Creek Gas

Lone Star Gas

244

249

252

253

254

264

276

278

281

282

284

290

292

293

294

306

314

317

335

351

352

354

356

358

359

361

370

380

390

392

398

400

402

403

404

406

408

409

411

413

415

Los Medanos Gas

Maine Prairie Gas

Malton-Black Butte Gas

McDonald Island Gas

Medora Lake Gas

McMullin Ranch Gas

Merritt Gas

Merritt Island Gas

Millar Gas

Moon Bend Gas

Mulligan Hill Gas

Nicolas Gas

Oakley Gas

Oakdale Gas

Oil Creek

Ord Bend Gas

Orland Gas

Peace Valley Gas

Perkins Lake Gas

Petaluma Gas

Pierce Road Gas

Pinole Point

Madison Gas

Pleasant Creek Gas

Poppy Ridge Gas

Princeton Gas

Putah Sink Gas

Rancho Capay Gas

Red Bank Creek Gas

Rice Creek Gas

Rice Creek, East Gas

Rindge Tract Gas

Rio Jesus Gas

Rio Vista Gas

River Break Gas

River Island Gas

Robbins Gas

Roberts Island Gas

Ryer Island Gas

Sacramento Airport Gas

Sacramento By-Pass Gas

430

442

444

452

455

456

458

460

466

482

492

506

510

513

518

526

528

535

536

538

541

542

552

556

564

574

576

590

592

596

597

603

604

606

610

612

615

616

634

636

638

659

684

686

706

709

713

715

717

718

719

721

722

730

732

734

736

770

772

776

778

786

787

788

802

810

816

818

821

828

840

841

842

844

846

847

850

852

854

862

864

Field

name

Field

code

Field

code

Sand Mound Slough Gas

Saxon Gas

Schohr Ranch Gas

Sherman Island Gas

Snodgrass Slough Gas

Greenwood Gas, South

Stegeman Gas

Oakley Gas, South

Stone Lake Gas

Stockton Gas

Sugarfield Gas

Suisun Bay Gas

Sutter Buttes Gas

Sutter City Gas

Sycamore Gas

Sycamore Slough Gas

Thornton Gas

Thornton, West-Walnut Grove Gas

Tisdale Gas

Todhunters Lake Gas

Tracy Gas

Tracy, West, Gas

Tremont Gas

Union Island Gas

Van Sickle Island Gas

Vernalis Gas

Vernalis, Southwest Gas

Verona Gas

West Butte Gas

Wild Goose Gas

Williams Gas

Willow Pass Gas

Willow Slough Gas

Willows-Beehive Bend Gas

Wilson Creek Gas

Winchester Lake Gas

Winters Gas

Woodland Gas

Zamora Gas

Zamora Gas, North

Field

name

Figure 17. —Continued
106 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Sac17-0645_fig 17e

124° 123° 122° 121°

40°

39°

38°

Base modified from U.S. Geological Survey and other Federal and State digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 

29°30’ N. and 45°30’ N.; North American Datum of 1983

0 10 20 40 MILES

0 10 20 30 40 KILOMETERS

30

District 6

District 5

District 3

Sacramento

San Francisco

Data sources: California Department of Water Resources (DWR), 2003, 2016;

California Division of Oil, Gas, and Geothermal Resources (DOGGR), 2014

MENDOCINO CO

NAPA CO

SOLANO CO

SONOMA CO

MARIN CO

HUMBOLDT CO

TRINITY CO

TEHAMA CO

GLENN CO

COLUSA CO

YOLO CO

SANTA CLARA CO

SAN MATEO CO

ALAMEDA CO

CONTRA COSTA CO

LAKECO

SIERRA CO

NEVADA CO

PLACER CO

EL DORADO

CO

AMADOR

CO

CALAVERAS

CO

STANISLAUS CO

SACRAMENTO CO

SAN JOAQUIN CO

MERCED CO

YUBA CO

SUTTER CO

BUTTE CO

PLUMAS CO

802

456

452

616

392 390

254

719

786

816

818

294

404

314

706

400

398

094

229

709

612

772

442

402

606

460

351

225

770

408

264

411

409

082

202 200

354

722 352

634

026 356 074

090 828

730

030

713

380

164 535 162

403

686

715

574

062 004

002

846

406

536 216

526 138

016

306

430

842

492

810

093

721

778

576

636

253

604

172

638

278

850

148

252

718

458

192 249

564

556

214 212

552

852

862

864

317

293

206

207

854

736

788

227 335

615

506

541

243

776

732 734

088

482

840

444

358596

528 590

597

176

174

281

538

177

079

844

183

787

592

847

518

370

290

149

413

542

455

603

513

284

209

244

361

466

684

282

415

841

072

510

218

659

073 717 359

610

059

E

CALIFORNIA

Lassen

Peak

Klamath Mountains

Map

area Sacramento

San Francisco

San Diego

Redding

Los Angeles

Figure 17. —Continued
Results of the Prioritization Analysis 107

sac17-0645_fig 17eContinued

Field

name

Field

code

Afton Gas

Afton Gas, South

Angel Slough Gas

Arbuckle Gas

Artois Gas

Bounde Creek Gas

Brentwood

Brentwood, East Gas

Buckeye Gas

Bullock Bend Gas

Bunker Gas

Butte Sink Gas

Butte Slough Gas

Cache Creek Gas

Cache Slough Gas

Chico Gas

Clarksburg Gas

Collegeville, East

Compton Landing Gas

Compton Landing, South Gas

Concord Gas

Conway Ranch Gas

Corning Gas

Corning Gas, South

Cotati Gas

Crossroads Gas

Davis Southeast Gas

Denverton Gas

Denverton Creek Gas

Dixon Gas

Dixon Gas, East

Dry Slough Gas

Dufour Gas

Dunnigan Hills Gas

Durham Gas

Dutch Slough Gas

East Islands Gas

El Dorado Bend Gas

Elkhorn Slough Gas

Everglade Gas

002

004

016

026

030

062

072

073

074

079

082

088

090

093

094

138

148

149

162

164

168

172

174

176

177

183

192

200

202

206

207

209

212

214

216

218

225

227

229

243

Field

name

Field

code

Fairfield Knolls Gas

Florin Gas

Freeport Gas

Fremont Landing Gas

French Camp Gas

Galt Gas

Greens Lake Gas

Greenwood Gas

Grimes Gas

Grimes, West Gas

Half Moon Bay

Hanford

Harlan Ranch Gas

Harte Gas

Honker Gas

Hospital Nose Gas

Howells Point Gas

Karnak Gas

King Island Gas

Kirby Hill Gas

Kirby Hill Gas, North

Kirk Gas

Kirkwood Gas

Knightsen Gas

Knights Landing Gas

La Honda

Larkin, West Gas

Lathrop Gas

Lathrop Southeast Gas

Liberty Cut Gas

Liberty Island Gas

Lindsey Slough Gas

Little Butte Creek Gas

Livermore

Llano Seco Gas

Lodi Gas

Lodi Airport Gas

Lodi, Southeast Gas

Lone Tree Creek Gas

Lone Star Gas

Los Medanos Gas

244

249

252

253

254

264

278

281

282

284

290

292

293

294

306

314

317

335

351

352

354

356

358

359

361

370

380

390

392

398

400

402

403

404

406

408

409

411

413

415

430

Maine Prairie Gas

Malton-Black Butte Gas

McDonald Island Gas

Medora Lake Gas

McMullin Ranch Gas

Merritt Gas

Merritt Island Gas

Millar Gas

Moon Bend Gas

Mulligan Hill Gas

Nicolas Gas

Oakley Gas

Oakdale Gas

Oil Creek

Ord Bend Gas

Orland Gas

Peace Valley Gas

Perkins Lake Gas

Petaluma Gas

Pierce Road Gas

Pinole Point

Madison Gas

Pleasant Creek Gas

Poppy Ridge Gas

Princeton Gas

Putah Sink Gas

Rancho Capay Gas

Red Bank Creek Gas

Rice Creek Gas

Rice Creek, East Gas

Rindge Tract Gas

Rio Jesus Gas

Rio Vista Gas

River Break Gas

River Island Gas

Robbins Gas

Roberts Island Gas

Ryer Island Gas

442

444

452

455

456

458

460

466

482

492

506

510

513

518

526

528

535

536

538

541

542

552

556

564

574

576

590

592

596

597

603

604

606

610

612

615

616

634

636

638

659

684

686

706

709

713

715

717

718

719

721

722

730

732

734

736

770

772

776

778

786

787

788

802

810

816

818

828

840

841

842

844

846

847

850

852

854

862

864

Field

name

Field

code

Field

code

Sacramento Airport Gas

Sacramento By-Pass Gas

Sand Mound Slough Gas

Saxon Gas

Schohr Ranch Gas

Sherman Island Gas

Snodgrass Slough Gas

Greenwood Gas, South

Stegeman Gas

Oakley Gas, South

Stone Lake Gas

Stockton Gas

Sugarfield Gas

Suisun Bay Gas

Sutter Buttes Gas

Sutter City Gas

Sycamore Gas

Sycamore Slough Gas

Thornton Gas

Thornton, West-Walnut Grove Gas

Tisdale Gas

Todhunters Lake Gas

Tracy Gas

Tracy, West, Gas

Tremont Gas

Union Island Gas

Van Sickle Island Gas

Vernalis Gas

Vernalis, Southwest Gas

West Butte Gas

Wild Goose Gas

Williams Gas

Willow Pass Gas

Willow Slough Gas

Willows-Beehive Bend Gas

Wilson Creek Gas

Winchester Lake Gas

Winters Gas

Woodland Gas

Zamora Gas

Zamora Gas, North

Field

name

Numbers in vertical proximity indicate the field codes

EXPLANATION

Water-well density

High Low

Moderate 

DOGGR district boundary

DWR groundwater basins County

DWR groundwater subbasins

Figure 17. —Continued
108 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Summary

The California State Water Resources Control Board 

(SWRCB) initiated a Regional Groundwater Monitoring 

Program (RGMP) to protect waters designated for any 

beneficial use in the vicinity of oil and gas fields in California, 

while prioritizing the monitoring of groundwater that is or 

has the potential to be a source of drinking water. The pace of 

implementation of the RGMP across the 487 onshore oil and 

gas fields has been limited in that detailed characterization 

work can only be done in a few fields each year. For 

program planning purposes, a prioritization of oil and gas 

fields is needed for consideration in implementing regional 

groundwater monitoring. In cooperation with the SWRCB, the 

USGS characterized, assessed, and classified oil and gas fields 

(1) individually with respect to key factors contributing to the 

potential risk to California’s groundwater resources from oil 

and gas resources in the subsurface, and (2) comparatively 

assigning overall prioritization rankings to California oil and 

gas fields for regional groundwater monitoring.

California’s 487 onshore oil and gas fields, covering an 

aggregated field area of 3,392 square miles, were prioritized 

for regional groundwater monitoring using a statewide 

systematic analysis of the relative intensity of petroleum 

development and proximity to groundwater resources. High 

priority was assigned to fields with the greatest intensity of 

oil and gas development measured by petroleum-well density 

and volume of injection, often coupled with proximity to 

groundwater resources as measured by vertical proximity 

of petroleum resources to groundwater resources and by 

water-well density overlying and adjacent to the field. The 

prioritization of fields for regional groundwater monitoring 

resulted in 107 fields (22 percent) classified as high overall 

priority, 114 fields (23 percent) as moderate priority, and 

266 fields (55 percent) as low priority (table 5; fig. 10). On 

an area-weighted basis, 41 percent of the aggregated field 

area ranked high priority, indicating that the largest fields 

tend to have the most oil and gas development activities. 

More than half of the high priority fields were in the southern 

San Joaquin Valley and the Los Angeles Basin. Moderatepriority fields (30 percent of aggregated field area) generally 

had intermediate characteristics and further analysis of each 

of these fields is needed to determine if they would be better 

classified as low or high priority for regional groundwater 

monitoring. The 266 low-priority fields accounted for 

29 percent of the aggregated field area, indicating the smallest 

fields generally did not have high intensity of petroleum 

resources. About half of the low priority fields (131 of 

266 fields) were located in district 6, which is the largest of 

the districts and contains mostly gas fields. Low priority is 

based on low to moderate intensity of oil and gas activities, 

and low to moderate horizontal or vertical proximity to 

groundwater resources.

The prioritization does not represent an assessment 

of groundwater risk from oil and gas development, which 

needs to be based on detailed analysis of data from regional 

groundwater monitoring near the oil fields selected for study 

in the future. Rather, this analysis identifies between 100 

and 200 oil fields that are principal candidates for the next 

steps in the regional groundwater monitoring program. The 

next steps can include compiling, analyzing, and developing 

three-dimensional visualizations of existing data, including 

geological frameworks, salinity mapping, identification of 

surface features that could potentially affect groundwater 

quality, locations and depths of petroleum and water wells, 

cataloging well-construction integrity issues, and evaluating 

groundwater-flow directions. These analyses and data 

are required to determine where existing wells should be 

monitored and where new monitoring wells may need to 

be drilled. The U.S. Geological Survey, in collaboration 

with the State Water Resources Control Board and other 

agencies, has begun the next steps of the regional groundwater 

monitoring through the California Oil, Gas, and Groundwater 

cooperative program.

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in Gautier, D.L., Dolton, G.L., Takahashi, K.I., and 

Varnes, K.L., eds., 1995 National assessment of United 

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Appendix 1. Statistical Summaries of Data used to Calculate Factors 111

In the preliminary assessment of petroleum resource 

development and proximity to groundwater resources, 

data and supporting information related to the variables 

measuring petroleum-well density, volume of injection, 

and vertical proximity were compiled for reference and to 

evaluate results of the assessment. Data were compiled from 

databases available during 2014–15 from the California 

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

Raw data (with the exception of injection volumes) are 

available in the U.S. Geological Survey data release at 

https://doi.org/10.5066/F7FJ2DV3.

Petroleum-Well Density 

Data related to petroleum-well density that were 

summarized for each oil and gas field were the total number 

of petroleum wells by well type, number of abandoned wells, 

and age of wells as reported in the 2014 DOGGR All Wells 

dataset (appendix table 1–1). The minimum and maximum 

well spud dates (marking the beginning of well drilling) or 

completion dates and well abandonment dates were calculated 

for petroleum wells for each oil and gas field. Dates were 

not available for every well; therefore, the dates represent 

estimates of well ages. 

Petroleum wells outside field boundaries were assigned 

to the nearest oil and gas field. Total wells nearby each oil 

and gas field and the maximum distance of the wells from the 

nearest field’s boundary are listed in appendix table 1–1. Wells 

outside field boundaries were not included in calculations of 

petroleum-well density.

Generally, the well type listed in the “GISSymbol” 

column of the 2014 DOGGR All Wells dataset were used to 

classify each well (see table 1 for well types). Wells that did 

not have a specified well type were classified as unknown; 

well types may be found on the DOGGR Well Finder website 

at http://maps.conservation.ca.gov/doggr/. Wells can have 

more than one well type or the well type changes over time. 

For example, a cyclic steam (SC) well is a type of oil and gas 

extraction well that uses cycles of steam injection followed 

by production to increase productivity and may be coded as 

SC or oil and gas production (OG). Production wells that have 

been converted to injection wells were coded as OG wells or 

as an injection well, such as water flood or waste disposal. 

Therefore, injection in a field may not be evident in current 

well counts and densities, but would likely be evident in the 

volumes of injection. 

Volume of Injection

Volumes of water and steam injection for each oil and gas 

field were compiled, along with the years of injection for each 

field, and information on injection for petroleum wells outside 

field boundaries (appendix tables 1–1 and 1–2). Injection and 

production volumes were compiled from DOGGR’s online 

injection and production databases (California Division of Oil, 

Gas, and Geothermal Resources, 2015). Although volume of 

water produced in each field was not part of the prioritization 

analysis, total water production volumes were presented in 

the ancillary dataset and include water production volumes 

for wells outside field boundaries. The years of recorded 

production and injection correspond to the minimum and 

maximum year of any recorded volume for that field. 

Water production and injection records are not 

released to the public for wells with confidential status and 

consequently were not available for inclusion in the production 

and injection volume calculations. Petroleum wells that meet 

the criteria for confidentiality are exploratory wells or wells 

for which there are extenuating circumstances preventing 

the well operator from having the competitive advantage of 

using information obtained from the well. At the time of this 

study, there were 180 confidential wells located throughout 

the State, and they were primarily active and new production 

wells drilled for exploratory purposes or using new technology 

(confidential well list accessed December 16, 2015, at 

ftp://ftp.consrv.ca.gov/pub/oil/new_database_format/).

Some wells outside field boundaries had production 

and injection records for 1977–2015; maximum distance 

of production and injection from nearest field boundary 

was 8 miles and 12 miles, respectively. Wells outside field 

boundaries were included in calculations for total injection 

volumes for the nearest field (appendix tables 1–1 and 1–2).

About 57 injection wells had recorded water injection 

outside oil and gas fields, and they plotted near the boundaries 

of 14 fields (appendix table 1–2). Total water injected outside 

field boundaries during 1977–2015 is 583 million barrels 

(MMB), which is less than 1 percent of the total water and 

steam injected in the State (about 85 billion barrels). Recorded 

injection was primarily for waste-water disposal wells, yet 

enhanced oil recovery wells near five fields (Arroyo Grande, 

Casmalia, Edison, Raisin City, and San Ardo) had recorded 

injection. Of the total waste-water disposal outside field 

boundaries, 345 MMB were injected within 2 miles of the 

Lost Hills field, and 172 MMB were injected within 8 miles of 

the San Ardo field. 

Appendix 1. Statistical Summaries of Data used to Calculate Factors
112 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

There was reported water production from about 

75 production wells that plotted nearby 98 fields. Total water 

produced outside field boundaries during 1977–2015 was 

95 MMB, which was less than 0.1 percent of the total water 

produced in the State (about 96 billion barrels). Of the total 

water production outside fields, about 91 MMB were produced 

within 2 miles of the Lost Hills field, and 3 MMB were 

produced within 2 miles of the Raisin City field. 

Vertical Proximity

Variables included in the calculations of vertical 

proximity were depth to top of perforated intervals (TOP) 

for petroleum wells, depth to base of freshwater (BFW) for 

petroleum wells, and total well depth (TD) for water wells. 

The availability of depth data varied between fields and 

between categories of wells (production versus injection, for 

petroleum wells), and required combining depth data and 

calculation methods to estimate vertical proximity for oil and 

gas fields. The depth of oil and gas development may vary 

within a field, in which case compilation and averaging of 

depths on a field scale may not represent vertical proximity for 

the entire field. Perforation depths depend on several factors, 

including the use of each well and regional geology. Samples 

of depth data for wells were tested for statistical differences 

based on well categories for oil and gas fields with sufficient 

data (5 or more data points for each group compared). 

Differences in the availability of data for variables, perforation 

depths based on well category, and land surface elevations 

were evaluated for potential biases when assessing vertical 

proximity for fields. Percentiles and number of available 

depth data for petroleum and water wells are presented in 

appendix table 1–3. Summary statistics were presented for all 

water wells and petroleum wells with depth data, and depth 

to TOP data for petroleum wells were divided into categories: 

production, injection, and the sub-categories of injection 

(waste-disposal wells versus all other injection types “nonwaste-disposal wells”). 

The Wilcoxon rank-sum test (equivalent to the MannWhitney test) was used to evaluate the differences between 

two groups of data (Helsel and Hirsch, 2002). Nonparametric 

rank-based methods were used for statistical analysis because 

these techniques are generally not affected by outliers and 

do not require that the data follow a normal distribution 

(Helsel and Hirsch, 2002). The significance level (p) used 

for hypothesis testing was compared to a threshold value 

(α) of 5 percent (α=0.05) to evaluate whether the relation 

was statistically significant (p≤α). All statistical analyses 

were done using R, version 3.1.2 (The R Foundation for 

Statistical Computing). For fields that had p≤0.05, the relative 

percent difference (RPD) of the median values for the two 

groups was calculated. The RPD is defined as the difference 

between the two values divided by the mean of the values 

and expressed as a percentage. RPD was used to identify the 

fields with greatest differences between the two groups of 

data compared. A positive RPD between the two groups of 

data compared indicates the median value for the first group 

was greater than the median value for the second group, 

and a negative RPD indicates the first group had a smaller 

median value. Variability in TOP-depth values within a field 

was estimated using the interquartile range (IQR), defined 

as the 75th percentile minus the 25th percentile (Helsel and 

Hirsch, 2002).

Land surface elevations (LSEs) were attributed for all 

petroleum and water wells in each field using the California 

National Elevation Dataset and ESRI ArcGIS software, 

and summary statistics are presented in appendix table 1–4. 

Differences in well elevations within a field and between well 

categories can indicate differences in regional geology, which 

were considered in the evaluation of grouping depth data by 

field to calculate vertical separation distance. For instance, 

vertical separation may be inaccurate as calculated when 

comparing the depth to TOP for a petroleum well located in 

the mountains with depth to BFW for a petroleum well or total 

well depth for a water well located in a valley. Water wells did 

not have exact well locations and were plotted at the center 

of the section in which they were located as indicated by the 

location information in well completion reports. Multiple 

water wells within a field often had the same elevation 

attributed. Initial results of Wilcoxon rank-sum tests were 

significant for even the slightest differences in land surface 

elevation between the water wells and petroleum wells, and 

therefore are not presented in this report. Results of statistical 

tests comparing LSE for petroleum wells with depth to TOP 

versus petroleum wells with depth to BFW are also not 

presented. Most fields for which vertical separation distance 

was calculated by pooling TOP-depth and BFW-depth data 

(method 3) did not have sufficient data to run statistical tests. 

Variability in LSEs, as measured by the IQR, between wells 

in a field for categories of wells (water wells and petroleum 

wells) are included in appendix table 1–4. The measured 

variability in LSEs for water wells in a field may be less than 

if LSE was attributed to water wells using more precise well 

locations.
Appendix 1. Statistical Summaries of Data used to Calculate Factors 113

Comparison of Depths to Top of Perforations for 

Production versus Injection Petroleum Wells

For the assessment of vertical proximity in each field, the 

depth at which petroleum resource development is prevalent 

in each field was estimated using depths to TOP for both 

production wells and injection wells. Whereas the injection 

well depths are almost a complete record of injection depths in 

each field, the production well depths are a randomly-selected 

and spatially-distributed sample of depths for all production 

wells. As a result, 84 percent of the 174 fields with sufficient 

data to assess vertical proximity had at least one injection 

well with depth to TOP, compared to only 47 percent of the 

total 487 oil and gas fields having contained injection wells. 

Because there were more injection well TOP-depths readily 

available for the assessment of vertical proximity, vertical 

proximity of injection activities to groundwater resources 

was predominate in the calculation of median vertical 

separation distance. 

Statewide, the total number of TOP-depths for injection 

wells greatly exceeded the number for production wells; 

however, more fields had a greater number of TOP-depths for 

production wells than for injection wells. Of the 174 fields 

assessed for vertical proximity, 96 fields had more production 

well TOP-depths, 74 fields had more injection well TOPdepths, and 4 fields were equal (appendix table 1–3). The 

fields with more TOP-depth data for injection wells than for 

production wells had a total of about 16,800 depths and the 

majority of these data are concentrated in a few fields. Fields 

that accounted for about 67 percent of the injection well data 

in the state are South Belridge (4,002 TOP-depths), MidwaySunset (2,611 TOP-depths), Lost Hills (1,559 TOP-depths), 

Kern River (1,275 TOP-depths), Coalinga (1,162 TOPdepths), and Wilmington (1,044 TOP-depths).

For a field-scale estimate of vertical proximity based 

on median separation distance, vertical proximity is largely 

dependent on well perforation depths for the well category 

with more data. Statistical tests comparing well perforation 

depths for injection and production wells for fields with 

sufficient data indicated that well perforation depths were 

statistically different (p≤0.05) between the two well categories 

for about half (37 fields) of the 71 fields tested (appendix 

table 1–5). Of the 37 fields, TOP-depths were deeper for 

production wells than for injection wells (RPD>0) in 26 fields, 

and TOP-depths were shallower for production wells than 

for injection wells (RPD<0) in 11 fields. Examples of fields 

that had the greatest absolute RPD between median depths 

are Asphalto (RPD=164 percent), Kettleman North Dome 

(RPD=153 percent), Ojai (RPD=−110 percent), Helm 

(RPD=108 percent), Oxnard (RPD=107 percent), Edison 

(RPD=101 percent), and Rose (RPD=100 percent) fields. 

On average, these fields had deeper perforation depths for 

production wells than for injection wells except for the Ojai 

field; median depth to TOP at Ojai was 948 feet (ft) for 

production wells and 3,285 ft for injection wells. 

For a few fields that had statistically different depths to 

TOP for production and injection wells, the depth of petroleum 

resource development as characterized by median depth to 

TOP for injection and production wells may be biased towards 

the well category with more depth data. For 33 of the 37 fields 

with statistically different samples of data (p≤0.05), median 

TOP-depth for petroleum wells was closer to median TOPdepth for the well category with more depth data (appendix 

table 1–5). As an example, the Asphalto field has median 

depth to TOP of 720 ft for injection wells, median depth to 

TOP of 7,354 ft for production wells, and median depth to 

TOP of 750 ft for the combination of well categories. There 

were more depths to TOP values available for injection wells 

(19 values) in this field than for production wells (6 values), 

and consequently vertical proximity of injection activities to 

groundwater resources was predominate in the calculation of 

median vertical separation distance (−750 ft). In contrast, the 

Ten Section field had more depth data available for injection 

wells than production wells, yet median TOP-depth of all 

petroleum wells (7,790 ft) was closer to median TOP-depth 

of production wells (8,076 ft) than to median TOP-depth of 

injection wells (3,087 ft). The interquartile range of TOPdepths for injection wells showed relatively large variability 

in the data (IQR=5,262 ft; appendix table 1–3). Variability in 

well perforation depths for injection wells suggests multiple 

injection zones at different depths within the field. Variability 

in depths may also indicate differences in land surface 

elevations, but in the Ten Section field, LSE only varied by 

about 20 ft for injection wells (appendix table 1–4). 

Comparison of Depths to Top of Perforations for 

Waste-Disposal versus Non-Waste-Disposal 

Wells

Additional comparisons of TOP-depths for wastedisposal wells and all other types of injection wells (nonwaste-disposal), indicated that for fields with production, 

injection for enhanced oil recovery, and injection for waste 

disposal, the calculated median separation distance for a field 

may not characterize the proximity of groundwater resources 

to each of these activities. Well perforation depths for wastedisposal wells (including waste-water disposal, WD, and gas 

disposal, GD, well types) and non-waste-disposal injection 

wells (including WF, SF, SC, GS, and LG well types) were 

statistically different (p≤0.05) for most of the fields tested 

(25 of the 29 fields; appendix table 1–6). Of the 25 fields 

with different depths, median TOP-depth was deeper for 

waste-disposal wells than for non-waste-disposal wells 

(RPD>0) in 14 fields, and median TOP-depth was shallower 

for waste-disposal wells than for non-waste-disposal wells 

(RPD<0) in 11 fields. In general, there more depths to TOP 

for non-waste-disposal wells than for waste-disposal wells 

(23 of the 29 fields compared; appendix table 1–6), and 

were predominate in calculation of median depth to TOP for 

injection wells in each field. 
114 Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring

Examples of fields that had the greatest absolute RPD 

between median depths for waste-disposal wells and nonwaste-disposal wells are Elk Hills (RPD=−165 percent), 

Edison (RPD=115 percent), North Belridge 

(RPD=−113 percent), South Mountain (RPD=103 percent), 

and Ten Section (RPD=−102 percent) fields. In the example 

of the Ten Section field in which there was variability in 

TOP-depths for wells in the injection well category, grouping 

wells into the sub-categories resulted in greater precision of 

average well depths. There was a large spread of perforations 

depths for injection wells at Ten Section (IQR=5,262 ft), 

yet variability for TOP-depths in each of the sub-categories 

was comparatively small: median depth to TOP was 2,540 ft 

for waste-disposal wells (IQR=197 ft) and 7,796 ft for other 

injection wells (IQR=51 ft; appendix table 1–3). Even though 

there were more depths to TOP for waste-disposal wells than 

non-waste-disposal injection wells and more depths to TOP for 

injection wells than production wells at this field, the depths 

of waste-disposal wells were outweighed in the combination 

of depths for injection wells and production wells (median 

TOP-depth for production wells was 8,076 ft). Median 

vertical separation distance for the Ten Section field (6,072 ft 

separation, appendix table 1–5) was biased to non-wastedisposal injection activities and production activities in zones 

deeper than average TOP-depths for waste-disposal wells.

Comparisons of Vertical Proximity Classifications 

using Separation-Distance Calculation 

Methods 1 and 2

Separation distance values and vertical proximity 

classifications were compared between calculation methods 1 

and 2, which were considered the most robust of the methods 

and provided median separation distance values for the most 

fields (see “Methods” section “Calculation of Variables” for 

a description of the five methods used to calculate vertical 

proximity). Of the 81 fields that had separation distance values 

calculated from both method 1 and method 2 and for which 

a comparison could be made, 25 fields were classified into 

different categories (close, moderate, and far) for vertical 

proximity depending on the calculation method. A comparison 

of the separation distance values between methods 1 and 

2 showed that more fields would be classified as “far” for 

vertical proximity of petroleum and groundwater resources 

based on method 2 calculations, and fewer fields would be 

classified as “moderate” and “close.” The vertical separation 

distance determined from calculation method 1 was used 

in the prioritization analysis in most cases. For fields that 

had different vertical proximity classifications based on 

varying values between the two methods, the classification 

representing greater potential risk to groundwater resources 

was used in the overall prioritization analysis. The overall 

priority classification for fields rarely changed by differing 

vertical proximity classifications between the two methods.

Generally, median separation distance calculated from 

method 1 for each field was less than the median distance 

calculated from method 2 (72 out of 81 fields compared; 

appendix table 1–7). Of the 25 fields with differing vertical 

proximity classifications between the two methods, 22 fields 

had a higher ranking (less distance between resources) using 

vertical separation values determined from method 1 than 

from method 2. Most often the higher ranking for method 1 

was moderate (16 fields), and the other 6 fields were ranked 

high using method 1. The vertical separation distance between 

petroleum and groundwater resources would be expected to 

be smaller as calculated from method 1 than from method 2, 

because method 1 uses depths to BFW to characterize the 

depth of groundwater resources, and depths to BFW are 

typically deeper than the TD of groundwater wells used in 

method 2 (fig. 5). Variations in separation distance values 

between the two methods can also be attributed to differences 

in the depths to TOP that were included in each calculation 

method. More depths to BFW were available for injection 

wells than for production wells, and in effect, greater weight 

was given to injection wells in method 1 calculations than in 

method 2 calculations. 

Only the three fields Coalinga, Livermore, and Orcutt 

had a lower ranking for vertical proximity (greater distance 

between resources) using separation distance values 

determined from method 1 than from method 2 (appendix 

table 1–7). In the example of the Coalinga field, median 

TD of water wells overlying the field was 600 ft (calculated 

from data for 47 water wells), whereas the median depth to 

BFW was 270 ft (calculated from data for 586 petroleum 

wells; appendix table 1–3). One explanation for the depth to 

BFW being shallower than water well depths is that depths 

to BFW reported in well records were sometimes a single 

value applied to petroleum wells throughout the field rather 

than values determined from each well’s geophysical logs. 

For these three fields, the vertical proximity classification for 

method 2 was used in the prioritization analysis so that values 

that are most protective of groundwater quality are used in the 

prioritization of oil fields.
Appendix 1. Statistical Summaries of Data used to Calculate Factors 115

The overall priority classification of a field was only 

affected by the vertical proximity ranking for fields with 

petroleum resource development closest to groundwater 

resources (fig. 8). The variability in results from each 

calculation method mostly affected the overall priority 

classification of fields that had separation distance values 

near the boundary between close and moderate classifications 

(1,000 ft median separation distance; table 2). Vertical 

proximity classifications varied between close and moderate 

between the two methods for eight fields: Coalinga, Fruitvale, 

Jasmin, Livermore, Malton-Black Butte Gas, Poso Creek, 

Rosedale Ranch, Round Mountain (appendix table 1–7). 

Several of the fields that had median separation distance near 

the classification boundary were ranked high for petroleumwell density and volume of water injection and would be 

classified as high overall priority based on rankings for factors 

other than vertical proximity. Only the Jasmin, Livermore, 

and Malton-Black Butte Gas fields would have a different 

overall priority classification based on differing vertical 

proximity classifications for method 1 and method 2; these 

fields would be classified as moderate priority if the lower 

ranking classification for vertical proximity had been used in 

the prioritization analysis. These three fields had moderate 

petroleum-well density, low to moderate volume of injection, 

and moderate to high water-well density (table 6). Of the 

81 fields compared, 31 percent had differing vertical proximity 

classifications between method 1 and method 2, and using the 

higher ranking of the two classifications in the prioritization 

analysis resulted in high overall priority classifications than 

would have been assigned based on the other factors assessed 

for less than 4 percent of the compared fields. 

References Cited

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page, accessed November 30, 2015, at 

ftp://ftp.consrv.ca.gov/pub/oil/new_database_format/.

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Johnson, J., Johnson, T., Brilmyer, C., and Dillon, D.B., 

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Publishing support provided by the U.S. Geological Survey

 Science Publishing Network, Sacramento Publishing Service Center

For more information concerning the research of this report, contact the

 Director, California Water Science Center

 U.S. Geological Survey

 6000 J Street, Placer Hall

 Sacramento, California 95819

 http://ca.water.usgs.gov
Davis and others—Prioritization of Oil and Gas Fields for Regional Groundwater Monitoring Based on a Preliminary Assessment of Petroleum Resource 

Development and Proximity to California’s Groundwater Resources—Scientific Investigations Report 2018–5065

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20185065