U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3011

April 2012

U.S. Geological Survey and the California State Water Resources Control Board

Groundwater Quality in the Southern Sierra 

Nevada, California 

Groundwater provides more than 40 percent of California’s drinking water. To protect this vital resource, the State of 

California created the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The Priority Basin Project of the GAMA Program provides a comprehensive assessment of the State’s groundwater quality and increases 

public access to groundwater-quality information. The Tehachapi-Cummings Valley and Kern River Valley basins 

and surrounding watersheds in the Southern Sierra Nevada constitute one of the study units being evaluated.

Organic 

Constituents

Inorganic 

Constituents

High Moderate

CONSTITUENT CONCENTRATIONS

Low or not detected 

Values are a percentage of the area of the primary aquifers

with concentrations in the three specified categories. Values

on pie chart may not equal 100 due to rounding of percentages.

34 32

97

3

34

Printed on recycled paper

Tehachapi Tehachapi Creek

Kern River Kern River

Kern River Kern River

South Fork South Fork

Los Angeles Aqueduct Los Angeles Aqueduct

Caliente Caliente Creek

Lake Isabella

State Water State Water ProjectAqueduct ProjectAqueduct

Walker Creek Valley

Kern River

Valley

Kern

County

Tulare

County Inyo

Co

Walker Creek Valley

Kern River

Valley

Kern

County

Tulare

County Inyo

Co

Study unit

CDWR groundwater basins

Watershed boundary

Tehachapi

West Valley

Tehachapi

East Valley

Tehachapi

Brite

Valley

Cummings

Valley 0 105 Miles

0 105 Kilometers

The Southern Sierra Nevada Study Unit

The Southern Sierra Nevada study unit is approximately 1,800 square miles; it 

includes six groundwater basins (California Department of Water Resources, 2003) and 

parts of the hard-rock watersheds surrounding the basins (Fram and Belitz, 2007). The 

primary aquifers in the Tehachapi-Cummings Valley basins in the southern part of the 

study unit consist of alluvial fan and floodplain sediments (mixtures of sand, silt, clay, 

gravel, cobbles, and boulders). The primary aquifers in the Kern River Valley basin in the 

northern part of the study unit are composed of fluvial sediments from the Kern River. 

Outside of and beneath the basins, the primary aquifers are fractured granitic and metamorphic rocks.

The primary aquifers in the study unit are defined as those parts of the aquifers corresponding to the screened or open intervals of wells listed in the California Department 

of Public Health database. In the Tehachapi-Cummings basins, these wells typically are 

drilled to depths between 300 and 500 feet, consist of solid casing from land surface to 

a depth of about 100 to 225 feet, and are screened or open below the solid casing. In the 

Kern River Valley basin, these wells typically are 50 to 175 feet deep, and are screened or 

open below 25 to 100 feet. Water quality in the shallower and deeper parts of the aquifer 

system may differ from that in the primary aquifers.The areas outside of the basins have 

both wells and developed springs.

The Southern Sierra Nevada study unit has warm, dry summers and cold, wet winters. Average annual precipitation ranges 

from about 11 inches in the basins to over 

50 inches in the surrounding mountains, 

and the majority of precipitation falls as 

snow. Land use in the Southern Sierra 

Nevada study unit is approximately 90 

percent (%) undeveloped (grasslands and 

scrublands), 8% cultivated agriculture, 

and 2% urban. The undeveloped lands 

are used mostly for recreation and openrange grazing. The largest urban areas are 

the city of Tehachapi and the small towns 

surrounding Lake Isabella.

Recharge to the groundwater 

flow system is mainly from mountainfront recharge at the margins of the 

basins, stream-channel infiltration, 

and direct infiltration of precipitation. 

Groundwater leaves the aquifer system 

mainly as pumpage for irrigation and 

drinking-water supply, flow into streams 

and lakes, and evaporation from areas 

with a shallow depth to groundwater.

Overview of Water Quality

GAMA’s Priority Basin Project evaluates the quality of untreated 

groundwater. However, for context 

benchmarks established for drinkingwater quality are used for comparison. 

Benchmarks and definitions of high, 

moderate, and low concentrations are 

discussed in the inset box on page 3.

Many inorganic constituents occur 

naturally in groundwater. The concentrations of the inorganic constituents can 

be affected by natural processes as well 

as by human activities. In the Southern 

Sierra Nevada study unit, one or more 

inorganic constituents were present at 

high concentrations in about 32% of the 

primary aquifers and at moderate concentrations in about 34%.

Human-made organic constituents 

are found in products used in the home, 

business, industry, and agriculture. 

Organic constituents can enter the environment through normal usage, spills, or 

improper disposal. In this study unit, one 

or more organic constituents were present at moderate concentrations in about 

3% of the primary aquifers, and none 

were detected at high concentrations.
 

 

RESULTS: Groundwater Quality in the Southern Sierra Nevada Study Unit

Inorganic Constituents with Human-Health Benchmarks

Trace and minor elements are naturally present in the minerals in rocks and soils, 

and in the water that comes into contact with those materials. In the Southern Sierra 

Nevada study unit, trace and minor elements were present at high concentrations in 

about 28% of the primary aquifers, and at moderate concentrations in about 16%. 

Arsenic, fluoride, and boron were the trace and minor elements that most frequently 

occurred at high and moderate concentrations. Aluminum and antimony also were 

detected at high concentrations, but in less than (<) 1% of the primary aquifers.

Radioactivity is the emission of energy or particles during spontaneous decay of 

unstable atoms. Humans are exposed to small amounts of natural radioactivity every 

day. Most of the radioactivity in groundwater comes from decay of naturally occurring 

uranium and thorium in the rocks or sediments of the aquifers. Radioactive constituents 

occured at high levels in about 21% of the primary aquifers, and at moderate levels in 

about 17%. Gross alpha particle, uranium, and radon-222 activities were the radioactive 

constituents that most frequently occurred at high and moderate levels. 

Nutrients, such as nitrogen, are naturally present at low concentrations in groundwater. High and moderate concentrations generally occur as a result of human activities. 

Common sources of nutrients include fertilizer applied to crops and landscaping, seepage from septic systems, and human and animal waste. The nutrient nitrate was present 

at high concentrations in about 3% of the primary aquifers, and at moderate concentrations in about 24%.

Inorganic Constituents with Non-Health Benchmarks

(Not included in water-quality overview charts shown on the front page)

 Some constituents affect the aesthetic properties of water, such as taste, color, 

and odor, or may create nuisance problems, such as staining and scaling. The State of 

California has a recommended and an upper limit for total dissolved solids (TDS). All 

water naturally contains TDS as a result of the weathering and dissolution of minerals 

in soils. Iron and manganese are naturally occurring constituents that commonly are 

present together in groundwater. Anoxic conditions in groundwater (very low amounts 

of dissolved oxygen) may result in release of manganese and iron from minerals into 

groundwater. 

In the Southern Sierra Nevada study unit, TDS was present at high concentrations 

(greater than the upper limit) in about 3% of the primary aquifers, and at moderate concentrations (between the recommended and upper limits) in about 15% of the primary 

aquifers. Manganese and (or) iron, were present at high concentrations in about 23% of 

the primary aquifers, and at moderate concentrations in about 20%. 

Perchlorate

(Not included in water-quality overview charts shown on the front page)

Perchlorate is an inorganic constituent that has been regulated in California drinking water since 2007. It is an ingredient in rocket fuel, fireworks, safety flares and other 

products, may be present in some fertilizers, and also occurs naturally at low concentrations in groundwater. Perchlorate was detected at moderate concentrations in about 9% 

of the primary aquifers.

Trace 

elements

Total 

Dissolved 

Solids

Radioactive

constituents

Nutrients

Manganese

or iron

Perchlorate

INORGANIC CONSTITUENTS

INORGANIC CONSTITUENTS SPECIAL-INTEREST CONSTITUENTS

56

28

16

24

15

17

21

73

82

20

91

57

23

3

3

9

62
Solvents

Pesticides

Other volatile 

organic 

compounds

ORGANIC CONSTITUENTS

3

97

100

100

RESULTS: Groundwater Quality in the Southern Sierra Nevada Study Unit

Organic Constituents

The Priority Basin Project uses laboratory methods that can detect the presence 

of low concentrations of volatile organic compounds (VOC) and pesticides, far below 

human-health benchmarks. VOCs and pesticides detected at these very low concentrations can be used to help trace water from the landscape into the aquifer system.

Volatile Organic Compounds with Human-Health Benchmarks

VOCs are in many household, commercial, industrial, and agricultural products, 

and are characterized by their tendency to volatilize (evaporate) into the air. 

Solvents are used for a number of purposes, including manufacturing and cleaning. 

In the Southern Sierra Nevada study unit, solvents were not present at high concentrations in the primary aquifers. Solvents were present at moderate concentrations in about 

3% of the primary aquifers, and at low concentrations (or not detected) in about 97%. 

Other VOCs include trihalomethanes, gasoline additives, refrigerants, and organic 

synthesis reagents. Trihalomethanes form during disinfection of water supplies, and 

may enter groundwater by the infiltration of landscape irrigation water or leakage of 

distribution lines. Gasoline additives increase the efficiency of fuel combustion. Other 

VOCs were not detected at high or moderate concentrations in the primary aquifers. Trihalomethanes, gasoline additives, and refrigerants were detected at low concentrations 

in the primary aquifers. Organic synthesis reagents were not detected.

Pesticides with Human-Health Benchmarks

Pesticides, including herbicides, insecticides, fungicides, and fumigants, are 

applied to crops, gardens, lawns, around buildings, and along roads to help control 

unwanted vegetation (weeds), insects, fungi, and other pests. In the Southern Sierra 

Nevada study unit, pesticides were not detected at high or moderate concentrations in 

the primary aquifers. Herbicides were detected at low concentrations. Organic synthesis 

reagents were not detected.

BENCHMARKS FOR EVALUATING GROUNDWATER QUALITY

 GAMA’s Priority Basin Project uses benchmarks established for drinking water to 

provide context for evaluating the quality of untreated groundwater. After withdrawal, 

groundwater may be disinfected, filtered, mixed, and exposed to the atmosphere before 

being delivered to consumers. Federal and California regulatory benchmarks for protecting human health (Maximum Contaminant Level, MCL) were used when available. 

Nonregulatory benchmarks for protecting aesthetic properties, such as taste and odor 

(Secondary Maximum Contaminant Level, SMCL), and nonregulatory benchmarks for 

protecting human health (Notification Level, NL, and Lifetime Health Advisory, HAL) 

were used when Federal or California regulatory benchmarks were not available.

High concentrations

Moderate concentrations

EX

Low concentrations

AMPLE Values are a percentage of the area of the primary aquifers

with concentrations in the three specified categories. Values

on pie chart may not equal 100 due to rounding of percentages.

CONSTITUENT CONCENTRATIONS

High, moderate, and low concentrations are defined relative to benchmarks

Concentrations are considered high if they are greater than a benchmark. For inorganic constituents, concentrations are moderate if they are greater than one-half of a benchmark. For organic constituents and perchlorate, concentrations are moderate if they are 

greater than one-tenth of a benchmark; this lower threshold was used because organic constituents generally are less prevalent and 

have smaller concentrations relative to benchmarks than inorganic constituents. Low values include non-detections and values less 

than moderate concentrations. Methods for evaluating water quality are discussed in Fram and Belitz (2012).
Caliente Creek

Caliente Creek

TehachapiTehachapi CreekTehachapiTehachapi Creek

Los Angeles AqueductLos Angeles Aqueduct

Kern

River KernRiver

Kern RiverKern RiverKern RiverKern River

Kern

River KernRiver

South Fork South ForkSouth Fork South Fork

Los Angeles AqueductLos Angeles Aqueduct

Caliente CreekCaliente Creek

Lake Isebella Lake Isebella

Constituent concentration

USGS well

High

Moderate

Low

CDPH well

Aquifer rock type

Arsenic Uranium

Granitic

Metamorphic

Volcanic

Sedimentary

 deposits

0 105 Miles

0 105 Kilometers

72

22

6 63

21

16

Factors that Affect Groundwater Quality

In the Southern Sierra Nevada study unit, arsenic and uranium were two of the constituents most frequently present at high and moderate concentrations. The USEPA MCL 

for arsenic is 10 micrograms per liter and the California MCL for uranium is 20 picocuries 

per liter. Groundwater with high or moderate concentrations of arsenic or uranium was 

found more frequently in the Kern River Valley basin and surrounding watershed than in 

the Tehachapi-Cummings Valley basins and surrounding watershed. Dissolution of arsenic 

and uranium from minerals in the aquifer sediments or rocks requires appropriate groundwater geochemical conditions (such as pH and dissolved oxygen concentration), enough 

time for dissolution, and presence of minerals containing arsenic and uranium.

The ranges of groundwater geochemical conditions and ages were similar in the 

northern and southern parts of the study unit, suggesting that the chemical and mineralogical compositions of the aquifer materials in the north and south were different (Fram 

and Belitz, 2012). The granitic and metamorphic rocks in the north contain many more 

historical prospects and mines (primarily gold, tungsten, and uranium) than do the rocks 

in the south (U.S. Geological Survey, 2005). This suggests the rocks in the north naturally 

have greater abundances of these metals. Many metals, including gold, commonly occur 

with sulfide minerals that may contain arsenic. In addition to natural dissolution of metals 

from rocks into groundwater, disturbances caused by mining activities may increase the 

rate at which metals are dissolved.

By Miranda S. Fram and Kenneth Belitz

SELECTED REFERENCES

California Department of Water Resources, 2003, California’s groundwater: California Department of 

Water Resources Bulletin 118, 246 p. http://www.water.ca.gov/groundwater/bulletin118/update2003.

cfm.

Fram, M.S., and Belitz, Kenneth, 2007, Groundwater quality data in the Southern Sierra study unit, 

2006: Results from the California GAMA Program: U.S. Geological Survey Data Series 301, 78 p. 

(Also available at http://pubs.usgs.gov/ds/301/.)

Fram, M.S., and Belitz, Kenneth, 2012, Status and understanding of groundwater quality in the 

Tahoe-Martis, Central Sierra, and Southern Sierra study units, 2006–2007—California GAMA 

Program Priority Basin Project: U.S. Geological Survey Scientific Investigations Report 2011-

5216, 222 p. (Also available at http://pubs.usgs.gov/sir/2011/5216.)

U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey. http://tin.

er.usgs.gov/mrds/

Priority Basin Assessments 

GAMA’s Priority Basin Project 

(PBP) assesses water quality in that part 

of the aquifer system used for drinking 

water, primarily public supply. Water 

quality in the primary aquifers, assessed 

by the PBP, may differ from that in 

the deeper parts of the aquifer, or from 

the shallower parts, which are being 

assessed by GAMA’s Domestic Well 

Project. Ongoing assessments are being 

conducted in more than 120 basins 

throughout California.

The PBP assessments are based on 

a comparison of constituent concentrations in untreated groundwater with 

benchmarks established for protection of 

human health and for aesthetic concerns. 

The PBP does not evaluate the quality of 

drinking water delivered to consumers.

The PBP uses two scientific 

approaches for assessing groundwater quality. The first approach uses a 

network of wells to assess statistically 

the status of groundwater quality. The 

second approach combines water-quality, hydrologic, geographic, and other 

data to help assess the factors that affect 

water quality. In the Southern Sierra 

Nevada study unit, data were collected 

by the PBP in 2006, and from the CDPH 

database for 2003 – 2006. The PBP 

includes chemical analyses not generally 

available as part of regulatory compliance monitoring, including measurements at concentrations much lower 

than human-health benchmarks, and 

measurement of constituents that can be 

used to trace the sources and movement 

of groundwater.

For more information

Technical reports and hydrologic 

data collected for the GAMA PBP 

Program may be obtained from:

GAMA Project Chief

U.S. Geological Survey

California Water Science Center

4165 Spruance Road, Suite 200

San Diego, CA 92101

Telephone number: (619) 225-6100

WEB: http://ca.water.usgs.gov/gama

GAMA Program Unit

State Water Resources Control Board

Division of Water Quality

PO Box 2231, Sacramento, CA 95812

Telephone number: (916) 341-5779

WEB: http://www.waterboards.ca.gov/gama