U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2020–1116

October 2020

ISSN 2331-1258

https://doi.org/10.3133/ofr20201116

Prepared in cooperation with the California State Water Resources Control Board

Multiple-Well Monitoring Site Adjacent to the North and 

South Belridge Oil Fields, Kern County, California

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

The U.S. Geological Survey (USGS), in cooperation 

with the California State Water Resources Control Board, is 

evaluating several questions about oil and gas development and 

groundwater resources in California, including (1) the location 

of groundwater resources; (2) the proximity of oil and gas 

operations to groundwater and the geologic materials between 

them; (3) evidence (or no evidence) of fluids from oil and gas 

sources in groundwater; and (4) the pathways or processes 

responsible when fluids from oil and gas sources are present 

in groundwater (U.S. Geological Survey, 2017). As part of this 

evaluation, the USGS installed a multiple-well monitoring site in 

the southern San Joaquin Valley groundwater basin adjacent to 

the North and South Belridge oil fields, about 7 miles southwest 

of Lost Hills, California (fig. 1). Data collected at the Belridge 

multiple-well monitoring site (BWSD) provide information 

about the geology, hydrology, geophysical properties, 

and geochemistry of the aquifer system, thus enhancing 

understanding of relations between adjacent groundwater and 

the North and South Belridge oil fields in an area where there 

are few groundwater data. This report presents construction 

information for the BWSD and initial hydrogeologic data 

collected from the site. A similar site installed to the east of the 

Lost Hills oil field, 11.5 miles to the north of the BWSD site, 

was described by Everett and others (2020a).

Study Area

The Belridge multiple-well monitoring site (BWSD) 

is in the Kern County subbasin of the San Joaquin Valley 

groundwater basin situated on the southern end of the Tulare 

Lake Hydrologic Region (California Department of Water 

Resources, 2016; fig. 1). The BWSD is located due east of the 

administrative boundary between the North and South Belridge 

oil and gas fields; approximately 7,000 feet (ft; 1.3 miles [mi]) 

east and downgradient (Williamson and others, 1989) from the 

northeast corner of the South Belridge field.

119°55' 119°50' 119°45' 119°40' 119°35'

35°25'

35°30'

0 1 2 3 4 MILES

0 2 3 4 KILOMETERS 1

Base modified from U.S. Geological Survey, historic produced water storage area data from California State Water Resources

Control Board (2018), oil and gas well data from the California Department of Conservation (2018) and other Federal digital data, 

various scales; Albers Equal-Area Conic projection, standard parallels are 29°30’ N. and 45°30’ N.; North American Datum of 1983

sBWSD

KERN COUNTY

SAN LUIS OBISPO COUNTY

5

33 North

Belridge

oil field

South

Belridge

oil field

EXPLANATION

s

Area of historical produced water storage

Oil and gas field administrative boundary

Kern County subbasin boundary

Tulare Lake hydrologic region

Belridge multiple-well monitoring

 site (BWSD)

Disposal well

Injection well (steam flood,

 water flood)

Oil and gas production well

Plugged or buried well

CALIFORNIA

Sacramento

San

Diego

Kern

County

subbasin

Tulare Lake

Hydrologic

Region

San Joaquin

Valley

groundwater

basin

Modesto

Corcoran

Lost Hills North and

South

Belridge

oil fields

Bakersfield

Figure 1. Belridge multiple-well monitoring site (BWSD) and selected other wells in relation to the North and South Belridge oil 

fields, Kern County, California.
The primary water-bearing units 

on the west side of the Tulare Lake 

Hydrologic Region lie within the 

Pliocene- to Pleistocene-age Tulare 

Formation, the overlying Holocene-age 

older alluvium and terrace deposits, 

and recent alluvial and river sediments 

(California Department of Water 

Resources, 2015). The Tulare aquifer 

system comprises the water-bearing 

units within the Tulare Formation that 

are separated locally and regionally by 

confining units. The alluvial aquifer 

system, comprised of the sediments 

overlying the Tulare Formation, is a 

complex set of interbedded aquifers 

and aquitards that function regionally 

as a single water-yielding unit (Sneed, 

2001). Numerous lenses of fine-grained 

sediments are distributed throughout 

the San Joaquin Valley; these generally 

constitute more than 50 percent of the 

total thickness of the valley fill (Faunt, 

2009). Faunt (2009) also noted that 

sediments in the western part of the San 

Joaquin Valley generally are finer-grained 

than sediments located to the east.

The primary confining unit of 

the Tulare Lake Hydrologic Region is 

the Corcoran Clay (Frink and Kues, 

1954) and its equivalent, the E-clay of 

Croft (1972). For the purposes of this 

discussion, the Corcoran Clay and the 

E-Clay are simply referred to as the 

Corcoran Clay. The Corcoran Clay 

underlies approximately the western 

two thirds of the San Joaquin Valley 

extending from the southern edge of the 

valley, near Kern Lake (not shown), to 

north of Modesto (Faunt, 2009). The 

Corcoran Clay is thicker in an area 

between Lost Hills and Corcoran, located 

about 35 mi to the north, and may be as 

thick as 200 ft approximately 14 mi north 

of Lost Hills (Faunt, 2009). Petroleum 

companies operating in the area refer to a 

basal alluvial clay at the contact between 

the Tulare Formation and overlying 

alluvium as the Corcoran Clay equivalent 

(Gilespie and others, 2019a). The exact 

relation between the Corcoran Clay 

equivalent and the Corcoran Clay is not 

defined; therefore, for the purposes of this 

report the clay at the BWSD site will be 

termed the Corcoran Clay equivalent and 

is presumed to be the lateral equivalent 

of the Corcoran Clay. At the BWSD, the 

top of the Corcoran Clay equivalent is 

determined to be 284 feet below land 

surface (ft bls), and the clay is 42-ft thick. 

Locally, Faunt (2009) showed the western 

edge of the clay generally is coincident 

with the eastern edge of the South 

Belridge oil field administrative boundary 

whereas Gillespie and others (2019a) 

mapped the Corcoran Clay equivalent 

farther west into the field and suggested 

the extent is closer to the western edge of 

the South Belridge oil field administrative 

boundary. The confining clay layers and 

land surface slope downward gradually 

from the North and South Belridge 

oil fields toward the BWSD borehole 

(Gillespie and others, 2019a).

The BWSD location was 

selected to provide better information 

regarding vertical and lateral changes 

in groundwater gradients and water 

quality of the alluvial and Tulare 

aquifer system. The site is situated 

east of the North and South Belridge 

oil fields and downgradient from 

these intensively developed oil fields 

where the detection of oil-field fluids 

in overlying and adjacent groundwater 

zones, when present, could exist from 

(1) naturally existing oil and gas in 

aquifers in proximity to oil fields or 

(2) a range of historical and current oil 

and gas development activities. There 

are a number of activities in developed 

oil fields that could affect groundwater 

including surface spills, leakage of 

produced water from disposal ponds, 

injection of fluids into the subsurface for 

enhanced recovery and produced-water 

disposal, and potential introduction of 

preferential pathways such as leaky or 

improperly abandoned oil and gas wells 

or test holes (Davis and others, 2018a; 

Gillespie and others, 2019a).

There is a high concentration of 

oil-production activities near the BWSD. 

The BWSD is approximately 1,400 ft 

from the nearest idle well, 7,100 ft from 

the nearest water disposal well, 7,300 ft 

from the nearest active oil well, 8,200 ft 

from the nearest active steam flood well 

(injection of steam for enhanced recovery 

of oil), and 10,000 ft from the nearest 

water flood well. Activities within 2 

mi to the south and west of the BWSD 

include 512 wells that are plugged or 

buried; 194 steam-flood wells, 108 oilor gas-production wells that are active, 

inactive, or new; 16 water-flood wells 

that are active, inactive, or new; 13 

water-disposal wells, and 1 area where 

produced water-storage ponds have 

been or are currently located (California 

Department of Conservation, 2018).

Drilling and Well 

Installation

The BWSD pilot borehole, 

with a diameter ranging from 8 1/

2

to 7 5/

8

 inches, was drilled to a depth 

of 1,800 ft bls during July 2018 by 

using direct mud-rotary drilling. Drill 

cuttings were collected throughout the 

drilling process and analyzed (along 

with notes from the on-site geologist) 

to summarize the lithology (fig. 2) 

following the procedures described by 

Everett and others (2013). To assist 

in the identification of lithologic and 

stratigraphic units, geophysical logging 

of the borehole was completed using 

standard methods (Keys and MacCary, 

1971; Shuter and Teasdale, 1989; 

Keys, 1990; Kenyon and others, 1995). 

Geophysical logs completed at the site 

include caliper, natural gamma, resistivity 

(16- and 64-inch normal), spontaneous 

potential (SP), electromagnetic 

induction, temperature, full wave 

sonic (sonic porosity), and nuclear 

magnetic resonance (NMR) porosity 

(fig. 2). Logging in the small-diameter 

pilot hole was advantageous because 

it allowed for higher-quality logs to 

be collected compared to logs from 

larger diameter holes. Well-screen and 

filter-pack intervals were selected based 

on the geophysical and lithologic data. 

After these intervals were selected, the 

pilot hole was then reamed to increase 

the borehole diameter to allow for the 

construction of the five-well monitoring 

site. The deepest well (BWSD #1) was 

constructed with 2.5-inch-diameter 

polyvinyl chloride (PVC) casing to allow 

for future geophysical logging, and the 

four shallow wells were constructed with 

2-inch-diameter PVC casing. The wells 

were installed with screened intervals 

from 260 to 280 (BWSD #5); 510 to 530 

(BWSD #4); 870 to 890 (BWSD #3); 

1,170 to 1,190 (BWSD #2); and 1,495 

to 1,515 (BWSD #1) ft bls (table 1). 

A filter pack of #3 sand (granules) was 

installed around each well screen, and 

a low-permeability bentonite grout was 

placed in the depth intervals between 

the filter packs to seal/isolate each of the 

wells (fig. 2).
Alluvial deposits Tulare Formation San Joaquin

 Formation

246’

297’

489’

538’

843’

919’

1,155’

1,211’

1,460’

1,560’

o

o

oo

oo

o

o

o

oo

ooooo

o

oo

ooo

ooo

Filter

pack

Grout

Silty clay, minor sand

Sand

Silty clay, minor sand

Sandy silty clay

Sand, trace gravel

Silty clayey sand

Sandy silt, minor clay

Sandy silty clay

Clayey silty sand

Sandy silty clay

Clayey silty sand

Sandy silty clay

Clayey silty sand

Sandy silty clay

Clay, minor silt and

 sand

Clayey silty sand

Sand

Sandy silty clay

Sandy clayey silt

Silty clay

Silty sand, minor clay

Sandy clayey silt

Silty sand, trace clay

Clayey silt

Silty sand, trace clay

Clayey silt

Silt, minor sand and

 clay

Clay, minor silt and

 sand

Silty clay with shell

 fragments

BWSD #1

Fluid volume, Well construction Lithologic summary

in percent

64N

16N

 0

100

200

300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,400

1,500

1,600

1,700

1,800

Depth, in feet below land surface

90 100 0 100

0 100

Porosity,

in percent

Sonic

NMR

–80 20–30 95 50

0 10050 50

0 200100 0 2010

Spontaneous

 potential,

in millivolts

Electromagnetic

induction, in

millimhos per

meter

Caliper (pilot

borehole), in

inches

–20 0 20

Clay-bound

Capillary-

 bound

Mobile

Corcoran Clay

 equivalent

Middle Tulare

 clay

Amnicola clay

Potential oil show

Depth to water on

 03/27/2019

o

–20 0 20 BWSD #5

BWSD #3 BWSD #2

BWSD #4

Resistivity, in

ohm-meters

Caliper, in

inches

Natural gamma,

in API units

Temperature,

in Deg F

Well screen

Figure 2. Well construction, summary lithology, and geophysical log data from the Belridge multiple-well monitoring site (BWSD), Kern 

County, California. (Abbreviations: API, American Petroleum Institute units; 16N, 16-inch normal; 64N, 64-inch normal; Deg, degrees; 

F, Fahrenheit; NMR, nuclear magnetic resonance).
Table 1. Identification and construction information from the Belridge multiple-well 

monitoring site (BWSD), Kern County, California.

[See figure 1 for well locations. Wells ordered from shallowest to deepest. The 15-digit U.S. Geological 

Survey (USGS) site identification number is used to uniquely identify the well. The common name is used 

throughout the report for quick reference. Land-surface datum (LSD) is a datum plane that is approximately 

at land surface at each well. The elevation of the LSD is described in feet above the North American Vertical 

Datum of 1988 (NAVD88). Abbreviations: NWISWeb, National Water Information System web interface; 

ft bls, feet below land surface]

Common 

well 

name

USGS site 

identification 

number (hyperlinked 

to NWISWeb)

Elevation 

of LSD 

(ft above 

NAVD88)

Well 

diameter 

(inside, 

inches)

Depth to 

bottom of 

well 

(ft bls)

Depth to 

top of well 

screen 

(ft bls)

Depth to 

bottom of 

well screen 

(ft bls)

BWSD #5 353049119434105 492.03 1.94 280 260 280

BWSD #4 353049119434104 492.03 1.94 530 510 530

BWSD #3 353049119434103 492.03 1.94 890 870 890

BWSD #2 353049119434102 492.03 1.94 1,190 1,170 1,190

BWSD #1 353049119434101 492.03 2.32 1,515 1,495 1,515

After construction was completed, 

the wells were developed by airlifting 

and using a surging technique with 

compressed air to remove drilling fluid 

and develop the filter pack surrounding 

each monitoring well. The field 

parameters that were recorded during the 

process include specific conductance, pH, 

water temperature, apparent color, and 

turbidity. Well development continued 

until drilling mud was not evident and 

field parameters were stabilized. The 

average flow rate and development time 

was used to estimate the total discharge 

and total purge volumes of the casing 

and filter pack (table 2). After well 

development, the turbidity of all wells 

was equal to or below 10 nephelometric 

turbidity units (NTU; table 2).

Sediment Analysis

The lithology at the site consists 

of gravel, sand, silt, and clay (fig. 2) in 

overlying alluvial deposits and the Tulare 

Formation and marine silts and clays of 

the underlying San Joaquin Formation. 

The lithology at this location primarily 

is fine-grained and is consistent with 

observations by Page (1983) that the 

Tulare Formation along the western edge 

of the southern San Joaquin Valley is 

fine grained, particularly at depth. The 

contact between the alluvial deposits and 

the Tulare Formation is estimated to be 

at 273 ft bls based on changes in color of 

the sediment from light yellowish brown 

to olive gray and an abrupt change in the 

SP log; however, as noted by Wood and 

Davis (1959), it is difficult to distinguish 

the alluvial deposits from the upper 

Tulare Formation in this region. The 

depths to the top and bottom contacts of 

several prominent clay layers within the 

Tulare Formation observed at BWSD are 

more apparent based on characteristic 

shifts in borehole geophysical logs 

observed across the area (Gillespie 

and others, 2019a) and are identified 

as Corcoran Clay equivalent, 284–326 

ft bls; middle Tulare clay, 764–820 ft 

bls; and Amnicola clay, 1,269–1,290 ft 

bls. The base of the Tulare Formation 

is estimated at 1,671 ft bls based on 

borehole log interpretation (Gillespie and 

others, 2019a).

Shell fragments were observed 

at several depths below 1,700 ft bls 

(fig. 2). Shell fragments observed at 

about 1,715 ft bls were identified simply 

as “molluscan.” Trace amounts of shell 

fragments less than 2 millimeters in size 

observed below 1,760 ft bls were not 

identified.

Hydrocarbon fluorescence under 

ultraviolet light can indicate the 

presence of oil in small amounts. The 

most reliable test for hydrocarbons in 

drill cuttings is the cut fluorescence, or 

wet cut test, which utilizes an organic 

solvent to dissolve the oil and observing 

the fluorescence of the resulting cut 

(Swanson, 1981). Samples collected 

every 10 feet were lightly rinsed in 

acetone and then inspected under a 

black light for fluorescence (Wyman and 

Castano, 1974; Swanson, 1981). The 

presence of any fluorescence was noted 

as a potential oil show (fig. 2).

Table 2. Well development and water-level data from the Belridge multiple-well monitoring site (BWSD), Kern County, California.

[Wells ordered from shallowest to deepest. Abbreviations: ft bls, feet below land surface; gal/min, gallons per minute; gal, gallon; v/v, volume per volume; NTU, 

nephelometric turbidity units]

Common 

well name

Pre-development 

depth to water 

(ft bls)

Post-development 

depth to water 

(ft bls) 

(Nov. 20, 2018)

Depth to water 

(ft bls) 

(Mar. 27, 2019)

Average 

flow 

(gal/min)

Hours of 

development

Estimated 

total 

discharge 

(gal)

Purge per 

casing 

volume 

(v/v)

Purge per 

sand pack 

volume 

(v/v)

Postdevelopment 

turbidity 

(NTU)

BWSD #5 158.46* 158.36 157.88 5.0 24 6,700 345 31 7

BWSD #4 193.79* 192.14 191.15 5.0 16 4,600 86 21 7

BWSD #3 513.87* 513.68* 513.89 3.2 33.5 4,600 76 24 4

BWSD #2 514.59* 514.91 514.88 3.3 14 2,900 27 16 3

BWSD #1 659.40* 662.41 663.13 8.0 48 16,900 79 94 10

*Value from Everett and others, 2020b.
Hydrology

Aquifer Tests

The hydraulic conductivity (K) 

of the aquifer material adjacent to the 

screened interval was estimated from 

pneumatic slug tests completed on each 

of the wells. Compressed nitrogen gas 

was used to depress the water level in the 

well by using a pressure regulator and 

well-head apparatus following procedures 

similar to Leap (1984) and Greene and 

Shapiro (1995). Induced declines in 

water levels were hundreds of feet above 

the perforations so that no nitrogen 

gas entered the formation through the 

well screen. Multiple slug tests were 

completed in each well except for well 

#3, and average values are shown in 

table 3. Aquifer properties analysis was 

completed using AQTESOLV software 

(Duffield, 2007). Data from BWSD 

#1, #2, and #5 were analyzed using the 

Kansas Geological Survey (KGS) Model 

package for overdamped slug tests in 

partially penetrating wells in a confined 

aquifer (Hyder and others, 1994). Data 

from BWSD #4 were analyzed using the 

Butler-Zhan solution which allows for 

the analysis of an underdamped response 

(Butler and Zhan, 2004). Data from 

BWSD #3 were not analyzed because the 

well may not have been fully developed 

at the time of testing. Slug test data are 

available in Everett and others (2020b).

Hydraulic conductivity estimates 

ranged from 1 foot per day (ft/day) in 

BWSD #5 to 17 ft/day in BWSD #4 

(table 3; Everett and others, 2020b). 

These values were in the range of values 

expected for sand with gravel, silt, 

and clay, although the value at BWSD 

#5 of 1 ft/day was at the low end of 

typical values (Heath, 1983). Belridge 

multiple-well monitoring site BWSD 

#5 is completed in a thin sand layer 

below a silty clay and is just above the 

Corcoran Clay equivalent. The presence 

of fine-grained sediments in the sand 

layer that were not observed in the 

drill cuttings could account for the low 

hydraulic conductivity.

Water Levels

Water-level data collected included 

periodic discrete manual measurements 

and hourly data recorded by downhole 

pressure transducers. Methods described 

by Cunningham and Schalk (2011) 

were used to collect and quality-assure 

the water-level records. The data were 

analyzed to identify vertical water-level 

gradients, which indicate direction and 

variability of potential groundwater flow 

between aquifer layers and responses 

to factors such as recharge and local 

groundwater withdrawal.

Before installation of the BWSD, 

there were no available data on vertical 

profiles of groundwater flow across the 

full thickness of the alluvial and Tulare 

aquifer systems near the North and 

South Belridge oil fields. The vertical 

water-level 

gradients at the 

site calculated 

from multiple 

discrete water-level 

measurements 

collected on 

March 27, 2019 

(fig. 3; table 2), 

indicated that 

groundwater should flow downward 

through the Tulare aquifer system. The 

groundwater gradient was highest, –0.897 

foot per foot (ft/ft), between BWSD #4 

and BWSD #3 and lowest, –0.003 ft/

ft, between BWSD #3 and BWSD #2. 

The steep gradient between BWSD #4 

and BWSD #3 indicated that the middle 

Tulare clay, which separates these two 

wells, is an effective aquitard separating 

overlying and underlying aquifer layers at 

this location.

Water-level changes that happened 

over time were used to help determine 

the degree of hydraulic interaction 

between aquifer layers that are restricted 

by confining clay layers. The change 

in water level for each well relative to 

November 20, 2018, at 4:00 p.m. Pacific 

daylight time (PDT) was calculated 

(fig. 4; BWSD #3 had no data for that 

date and time but was estimated to 

be 513.83 ft bls based on the average 

difference in water level from BWSD 

#2). During the period between 

November 20, 2018, and September 6, 

2019, a water-level rise of 2.5 feet was 

observed in BWSD #4, and a decline of 

about 3.75 feet was observed in BWSD 

#1, the deepest well. A slight rise, less 

than 0.5 ft, was observed in BWSD #2, 

#3, and #5. The water level in BWSD 

#4 rose by about 2 ft during a 3-week 

period beginning in late May 2019 and 

Table 3. Summary results of slug tests from the Belridge 

multiple-well monitoring site (BWSD), Kern County, 

California.

[Wells ordered from shallowest to deepest. Abbreviations: ft bls, feet 

below land surface; ft/day, feet per day; KGS, Kansas Geological 

Survey; NA, not analyzed]

Common 

well name

Screened interval 

(ft bls)

Method of 

analysis

Hydraulic 

conductivity 

(ft/day)

BWSD #5 260–280 KGS model 1

BWSD #4 510–530 Butler-Zhan 17

BWSD #3 870–890 NA NA

BWSD #2 1,170–1,190 KGS model 2

BWSD #1 1,495–1,515 KGS model 3

Water level versus well depth 

Depth to water, in feet below land surface, March 27, 2019

Depth to top of well screen interval, in feet below land surface

1,800

0

200

400

600

800

1,000

1,200

1,400

1,600

0 200 400 600 800

Corcoran Clay equivalent

BWSD #1

BWSD #2

BWSD# 3

BWSD #4

BWSD #5

Middle Tulare clay

Amnicola clay

Base of Tulare Formation

Figure 3. Vertical flow gradient at the Belridge multiple-well 

monitoring site (BWSD), Kern County, California.
Increase in water level Decrease in water level

2018 2019

7 14 21 28 7 14 21 28 7 14 21 28 7 14 2128 7 14 21 28 7 14 21 28 7 14 21 28 7 14 21 28 7 14 21 28 7 14 21 28 7 14 21 28 7 14 21

Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct.

–5

–4

–3

–2

–1

0

1

2

3

4

 Change in water level (feet) relative to November 20, 2018,

at 4:00 p.m. Pacific daylight time 

BWSD #4

BWSD #5

BWSD #3

BWSD #2

BWSD #1

EXPLANATION

BWSD #5, 260’ to 280’

BWSD #4, 510’ to 530’

BWSD #3, 870’ to 890’

BWSD #2, 1,170’ to 1,190’

BWSD #1, 1,495’ to 1,515’

Well identifier and screen interval (in feet below land surface)

Figure 4. Change in water level relative to November 20, 2018, observed in wells at the Belridge multiple-well monitoring site 

(BWSD), Kern County, California.

then declined by about 2 ft during the 

next 2 weeks. The exact cause of this 

short-term fluctuation in water level 

is not known. Water levels typically 

recover in the winter in correlation with 

decreased withdrawal and increased 

recharge from precipitation, and they 

decline in the summer due to increased 

water use and groundwater withdrawal. 

No corresponding rise in water level was 

observed in the overlying BSWD #5; 

therefore, recharge from precipitation 

does not seem to be the likely cause 

for the rise in water level observed in 

BWSD #4. The fluctuations in water 

level in BWSD #4 over the short term 

(less than 7 days) were greater than those 

observed in the other wells, indicating 

that the layer in the upper part of the 

Tulare Formation is more strongly 

affected by groundwater pumping than 

the middle part of the Tulare Formation. 

The pattern of decreased water levels 

observed in well BWSD #1 over time 

differed from the observations of the 

other wells (BWSD #2–5), indicating that 

water levels at the bottom of the Tulare 

Formation are responding to different 

hydrologic stresses than the overlying 

layers. These stresses may include 

upgradient oil-field activities (injection, 

steam or water flooding, or pumping) 

to the southwest or other unknown 

deep aquifer stresses. The short-term 

fluctuations of less than 0.25 foot in 

water level, primarily observed between 

November 2018 and March 2019, could 

be indicative of upgradient pumping or 

injection activity or that the well is in a 

relatively low permeability layer that is 

highly responsive to changes in aquifer 

conditions. Further analysis of water 

levels over time in comparison with 

oil-field activities, such as pumping and 

injection, could be used to help determine 

the hydrologic stresses affecting 

water levels at the base of the Tulare 

aquifer system.

Geochemistry

To delineate the chemical 

characteristics and source of the 

groundwater, samples were collected 

from each well in accordance with the 

protocols established by the USGS 

National Field Manual (U.S. Geological 

Survey, 2012) and analyzed for 

major-ion chemistry; minor and trace 

elements; nutrients; radium isotopes; 

dissolved organic carbon and organic 

carbon characteristics; volatile organic 

compounds; low molecular weight 

organic acids; concentrations and isotopic 

values of light hydrocarbon gases; the 

stable isotopes of hydrogen (deuterium) 

and oxygen (oxygen-18) in water; boron, 

strontium, and lithium isotopes; carbon 

(carbon-13) in dissolved inorganic carbon 

and carbon-14 activities, noble gases, 

atmospheric gases, and groundwater-age 

tracers tritium and sulfur hexafluoride. 

The collection and analysis procedures 

are further described by Dillon and 

others (2016), Davis and others 

(2018b), and Wright and others (2019). 

Sampling of the five monitoring wells 

occurred between late November 2018 

and mid-March 2019, with delays 

related to weather, site access, and 

equipment. Results for many analytes 

were not available at the time this 

report was prepared (September 2019). 

Consequently, results of water-quality 

samples are not discussed in this report 

other than the distribution of total 

dissolved solids (TDS).
The permeable zones above 1,190 ft 

bls (BWSD #2), slightly above the 

Amnicola clay, had TDS concentrations 

of less than 10,000 milligrams per liter 

(mg/L). The water samples from the 

BWSD wells had TDS concentrations 

ranging from 2,340 (BWSD #4) to 

21,100 (BWSD #1) mg/L residue on 

evaporation at 180 degrees Celsius 

(table 4). Total dissolved solids were 

calculated at multiple depths from the 

geophysical logs using the algorithm 

developed by Bateman and Konen (1977; 

fig. 5) and following procedures outlined 

by Gillespie and others (2019a, b). Total 

dissolved solids were not calculated 

between 700 and 1,200 ft bls because of 

the absence of clean sands throughout 

this interval. Total dissolved solids 

measured from groundwater samples 

collected from the wells confirmed 

that the calculated estimates from the 

geophysical logs are reasonable. Total 

dissolved solids calculations at selected 

depths shown on figure 5 indicate that 

TDS values were around 3,000 mg/L near 

the surface and exceeded 10,000 mg/L 

below 1,200 ft. A best-fit line for the TDS 

estimates between 1,200 and 1,420 ft 

suggested the depth to 10,000 mg/L was 

around 1,190 ft bls.

Accessing Data

The data presented in this report 

can be accessed using the USGS 

National Water Information System 

(NWIS) web interface (NWISWeb) at 

https://waterdata.usgs.gov/nwis/ (U.S. 

Geological Survey, 2019a). All discrete 

water-level measurements and the 

daily maximum, minimum, and median 

values for all time-series water-level 

data for sites presented in this report are 

available through the USGS NWISWeb. 

In digital copies of this report, the 

site identification numbers (table 1) 

presented in the tables are hyperlinked 

directly to the data on NWISWeb. Any 

updates applied to data presented in this 

report after publication will be available 

on NWISWeb.

Geophysical logs can be accessed 

through the USGS GeoLog Locator 

portal (https://webapps.usgs.gov/

GeoLogLocator; U.S. Geological Survey, 

2019b) under the site identification 

number for the deepest monitoring well 

BWSD #1 (353049119434101). Sites 

with available geophysical logs can be 

searched by the USGS site identification 

number (table 1) or can be located using 

the interactive map. Lithologic samples 

collected using different methods 

(termed shaker and sieve, Everett and 

others, 2013) during the drilling of the 

multiple-completion monitoring wells 

are archived at the USGS office in San 

Diego, California. Photos of the shaker 

and sieve samples (along with the full 

descriptions and notes recorded by the 

site hydrologist) can be accessed through 

the USGS GeoLog Locator. Formal 

requests for access to samples, field 

notes, or bench notes can be directed to 

the U.S. Geological Survey California 

Water Science Center.

Table 4. Water-quality indicators (field parameters) and total dissolved solids in samples collected from 

the Belridge multiple-well monitoring site (BWSD), Kern County, California.

[Wells ordered from shallowest to deepest. The five-digit U.S. Geological Survey (USGS) parameter code below the 

constituent name is used to uniquely identify a specific constituent or property. Threshold type: SMCL-CA, California 

Department of Public Health secondary maximum contaminant level; SMCL-US, U.S. Environmental Protection Agency 

secondary maximum contaminant level. Abbreviations: mm/dd/yyyy, month/day/year; mg/L, milligrams per liter; °C, degrees 

Celsius; μS/cm, microsiemens per centimeter; CaCO3, calcium carbonate; na, not available; *, value above threshold level]

Common well 

name

Sample date 

(mm/dd/yyyy)

pH, field 

(standard 

units) 

(00400)

Water 

temperture, 

field

(°C)

(00010)

Specific 

conductance, 

field 

(μS/cm at 25 °C) 

(00095)

Alkalinity, lab 

(mg/L as CaCO3

) 

(29801)

Total 

dissolved 

solids 

(mg/L) 

(70300)

Threshold type na SMCL-US na SMCL-CA na SMCL-US

Threshold level na 6.5–8.5 na 1

900 (1,600) na 500

BWSD #5 02/11/2019 7.3 26.5 *3,650 184 *3,120

BWSD #4 11/28/2018 7.3 23.5 *3,460 318 *2,340

BWSD #3 03/19/2019 7.2 27.0 *7,270 208 *4,950

BWSD #2 02/11/2019 7.5 25.4 *15,500 323 *9,420

BWSD #1 02/13/2019 6.9 24.6 *33,000 397 *21,100

1

The SMCL-CA for specific conductance has recommended lower and upper threshold values. The upper value is shown 

in parentheses.
0

100

200

300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,400

1,500

1,600

1,700

Depth, in feet below land surface

Total dissolved solids, in milligrams per liter

0 5,000 10,000 15,000 20,000 25,000

EXPLANATION

Measured and calculated1 total dissolved solids (TDS) 1

Calculated values determined using the Bateman

and Konen equation (1977) 

Measured TDS

Calculated TDS

Polynomial trendline of calculated

 TDS for selected depths between

 1,220 and 1,440 feet below land 

 surface

Middle Tulare clay

Amnicola clay

Base of Tulare Formation

3,000 TDS 10,000 TDS

Corcoran Clay equivalent

Figure 5. Measured and calculated total dissolved solids 

(TDS) for selected depths at the Belridge multiple-well 

monitoring site (BWSD), Kern County, California.

By Rhett R. Everett, Anthony A. Brown, 

Janice M. Gillespie, Adam Kjos, and 

Nicole C. Fenton

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For more information concerning the research in this report, contact the

Director, California Water Science Center

U.S. Geological Survey

6000 J Street, Placer Hall

Sacramento, California 95819

https://ca.water.usgs.gov

Publishing support provided by the 

U.S. Geological Survey Science Publishing Network, 

Sacramento Publishing Service Center