U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2014–3031

July 2014 Printed on recycled paper

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

Groundwater Quality in the Klamath Mountains, 

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 

Klamath Mountains constitute one of the study units being evaluated. 

The Klamath Mountains Study Unit Overview of Water Quality

The Klamath Mountains study unit covers more than 8,800 square miles and consists primarily of hard rock terranes characterized by high peaks and deep river gorges 

with relatively few groundwater basins (Bennett and others, 2014). Most of the study 

unit consists of metamorphic, ultramafic, and granitic rocks. The primary aquifer system 

sampled in the study unit, in contrast to most other study units evaluated by the GAMA 

Priority Basin Project, consisted of localized areas of fractured bedrock. The fracture 

systems may be interconnected or isolated, resulting in variability in water levels, well 

yields, and water quality on local and regional scales (California Department of Water 

Resources, 2003). The primary aquifer system in the study unit is defined as those parts 

of the aquifer corresponding to the open or perforated intervals of wells listed in the 

California Department of Public Health (CDPH) database. 

Drinking water in the Klamath Mountains comes mainly from springs (approximately 18 percent [%] of sampled sites) and wells (approximately 82% of sites) 

screened in sediment from glacial, alluvial, or fluvial sources. Most wells that were 

sampled are drilled to depths of 25 to 400 feet, consist of solid casing or seal from the 

land surface to a depth of about 24 to 300 feet, and are open or perforated below the 

solid casing or seal. Water quality in the primary aquifer system may differ from that in 

the shallow and deep water-bearing zones. 

Land use in the study unit is approximately 97% natural (forest, grasslands, and 

bare rock), 2% urban, and 1% agricultural.

The study unit has warm, 

dry summers and cool, moist 

winters. Average annual rainfall ranges from 69 inches on 

the western edge of the study 

unit to 40 inches in the central 

and eastern parts of the study 

unit. The study unit is primarily 

drained by the Klamath-Trinity, 

Sacramento, and Smith River 

drainage systems.

Groundwater recharge in 

the study unit occurs from the 

ambient recharge of runoff and 

snowmelt that penetrates the 

bedrock through faults and fractures at higher elevations. The 

primary sources of groundwater 

discharge are water pumped for 

municipal supply, evaporation, 

and discharge to streams.

GAMA’s Priority Basin Project evaluates the quality of untreated groundwater. 

However, for context, benchmarks established for drinking-water quality are used 

for comparison. Benchmarks and definitions of high, moderate, and low concentrations are discussed in the inset box, 

“Benchmarks for Evaluating Groundwater 

Quality,” on page 3.

Many inorganic constituents occur 

naturally in groundwater, but their concentrations can be affected by natural 

processes as well as by human activities. 

In the Klamath Mountains study unit, 

one or more inorganic constituents were 

present at high concentrations in about 

3% of the primary aquifer system and at 

moderate concentrations in about 10%.

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, organic 

constituents were not present at high 

concentrations in the primary aquifer 

system, but were present at moderate 

concentrations in about 2%.

Oregon

§ ̈5

§ ̈5

§ ̈5

§ ̈5

SISKIYOU CO

TRINITY CO SHASTA CO

HUMBOLDT CO

TEHAMA CO

DEL NORTE CO

Etna

Yreka

Redding

Gasquet

Dunsmuir

Weaverville

Willow Creek

Mount Shasta

Smith River Smith River

Klamath RiverKlamath River

South Fork Trinity River South Fork Trinity River

Pit River Pit River

Trinity RiverTrinity River

Trinity RiverTrinity River

Willow CreekWillow Creek

Sacramento River Sacramento River

124° 123°30' 123° 122°30' 122°

42°

41°

41°30'

40°30'

0 10 20 40 Miles

0 10 20 5 Kilometers

High Moderate

CONSTITUENT CONCENTRATIONS

Low or not detected 

Pie charts illustrate the percentage of the primary 

aquifer system, on an areal basis, with concentrations in the 

three specified categories.

Organic

constituents

Inorganic

constituents

87 98

3 10 2
RESULTS: Groundwater Quality in the Klamath Mountains 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 Klamath Mountains 

study unit, trace elements were present at high concentrations in about 3% of the primary aquifer system and at moderate concentrations in about 5%. Arsenic, antimony, 

and boron were the trace elements that occurred at high concentrations.

Radioactivity is the release of energy or energetic particles during spontaneous 

decay of unstable atoms. Most of the radioactivity in groundwater comes from the 

decay of naturally occurring isotopes of uranium and thorium in minerals present in 

fractures or sediments of the aquifer. Activities of radioactive constituents were not 

detected at high levels, but were present at moderate levels in about 5% of the primary 

aquifer system.

Nutrients, such as nitrogen, are naturally present at low concentrations in 

groundwater. High and moderate concentrations generally occur as a result of human 

activities, such as applying fertilizer to crops and landscaping, seepage from septic systems, and from human and animal waste. In the Klamath Mountains study unit, nutrients were not detected at high concentrations, but were present at moderate concentrations in about 1% of the primary aquifer system.

Total dissolved

solids

Iron or manganese

92

95

99

3

96

3

5

5

Trace 

elements

Radioactive

constituents 

Nutrients

INORGANIC CONSTITUENTS

1

1

13

10

77

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) in 

drinking water. All groundwater naturally contains TDS as a result of the weathering 

and dissolution of minerals in soils. Iron and manganese occur naturally in minerals 

in rocks and soils. Anoxic conditions in groundwater (very low amounts of dissolved 

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

(Hem, 1985).

In the Klamath Mountains study unit, TDS was present at high concentrations 

(greater than the upper limit) in about 1% of the primary aquifer system and at moderate concentrations (between the recommended and upper limit) in about 3%. Iron and 

(or) manganese were present at high concentrations in about 13% of the primary aquifer 

system and at moderate concentrations in about 10%.
RESULTS: Groundwater Quality in the Klamath Mountains Study Unit

Organic Constituents

The GAMA Priority Basin Project uses laboratory methods that can detect low 

concentrations of volatile organic compounds (VOCs) and pesticides, far below humanhealth benchmarks. VOCs and pesticides detected at these 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 used in many household, commercial, industrial, and agricultural products and are characterized by their tendency to volatilize (evaporate) into the air. In the 

Klamath Mountains study unit, VOCs were not present at high concentrations in the 

primary aquifer system.

One component of gasoline, the gasoline oxygenate methyl tert-butyl ether 

(MTBE), was present at moderate concentrations in about 2% of the primary aquifer 

system. Gasoline components (additives and oxygenates) increase the efficiency of fuel 

combustion.

Other VOCs include solvents, trihalomethanes, refrigerants, and organic synthesis reagents. Solvents are used for a number of purposes, including manufacturing and 

cleaning. Trihalomethanes can form during disinfection of water supplies and may enter 

groundwater by the infiltration of landscape irrigation water or leakage from distribution lines. Other VOCs were not detected at high or moderate concentrations in the 

primary aquifer system. Solvents, trihalomethanes, and refrigerants were infrequently 

detected at low concentrations in the primary aquifer system.

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 Klamath Mountains study unit, pesticides were not detected at high or moderate concentrations in the 

primary aquifer system, although herbicides were infrequently detected at low concentrations.

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. Otherwise, non-regulatory benchmarks for protecting aesthetic properties, such as 

taste and odor (Secondary Maximum Contaminant Level, SMCL), and non-regulatory 

benchmarks for protecting human health (Notification Level, NL, and Lifetime Health 

Advisory, HAL) were used. 

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, concentrations are moderate if they are greater than 

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

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

moderate concentrations. Methods for evaluating water quality are discussed by Bennett and others (2014).

ORGANIC CONSTITUENTS

Gasoline

components

Other volatile

organic

compounds

Pesticides

2

98

100

100

High

Moderate

EX

Low or not detected

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

system with concentrations in the three specified categories.

CONSTITUENT CONCENTRATIONS
Iron and Manganese in the Klamath Mountains 

Study Unit

No constituents having health-based benchmarks were present at high 

concentrations in more than 3% of the Klamath Mountains study unit primary aquifer 

system. In contrast, iron was present at concentrations above the aesthetic-based 

secondary maximum contaminant level (SMCL) benchmark of 300 micrograms per 

liter (μg/L) in about 8% of the primary aquifer system, and manganese was present at 

concentrations above the SMCL of 50 μg/L in about 11%. Iron and manganese were 

present at high concentrations in 7 to 31% of the primary aquifer systems in most 

USGS-GAMA study units statewide. Although harmless at concentrations typically 

found in natural waters, high concentrations of iron and manganese in groundwater 

may cause metallic-tasting and (or) foul-smelling water that produces black, brown, or 

reddish staining of surfaces that come in contact with the water.

In the Klamath Mountains study unit, high concentrations of iron and manganese 

were associated with low dissolved oxygen concentrations and groundwater having 

longer residence times in the aquifer (Bennett and others, 2014). Concentrations of 

iron and manganese in groundwater are strongly controlled by the oxidation-reduction 

conditions. Minerals containing iron and manganese commonly dissolve more easily 

in groundwater with low amounts of dissolved oxygen (called reducing conditions). 

In addition to reducing conditions, production of high concentrations of iron and 

manganese in groundwater also requires sufficient amounts of minerals containing iron 

and manganese in the aquifer rocks and sufficient time for the minerals to dissolve. 

The conditions that are the most conducive to manganese and high iron concentrations 

in groundwater were relatively rare in the Klamath study unit, with well-oxygenated 

modern-age groundwater occurring most frequently.

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 shallower and deeper parts may 

differ from that in the primary aquifer 

system. GAMA’s Domestic Well Project 

assesses water quality in the shallower 

parts of the aquifer system. Ongoing 

assessments are being conducted in more 

than 120 basins throughout California. 

The GAMA-PBP assessments are 

based on comparisons of constituent 

concentrations in untreated groundwater 

with benchmarks established for the protection of human health and for aesthetic 

concerns. The GAMA-PBP does not 

evaluate the quality of drinking water 

delivered to consumers. 

The GAMA-PBP uses two scientific approaches for assessing groundwater quality. The first approach uses a 

network of wells to statistically assess 

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 Klamath Mountains study 

unit, data were collected by the GAMAPBP in 2010 and from the CDPH database for 2007–2010. The PBP includes 

chemical analyses not generally available as part of regulatory compliance 

monitoring, including measurements at 

concentrations much lower than humanhealth benchmarks, and measurement of 

constituents that can be used to trace the 

sources and movement of groundwater.

By George L. Bennett V and Miranda S. Fram

SELECTED REFERENCES

Bennett, G.L., V, Fram, M.S., and Belitz, Kenneth, 2014, Status and understanding of 

groundwater quality in the Klamath Mountains study unit, 2010—California GAMA 

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

2014-5065, 58 p.

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

Department of Water Resources Bulletin 118, 246 p. Available at http://www.water.

ca.gov/pubs/groundwater/bulletin118/bulletin118update2003.cfm

Hem, J.D., 1985, Study and interpretation of the chemical characteristics of natural 

waters (3d ed.): U.S. Geological Survey Water-Supply Paper 2254, 213 p.

For more information

Technical reports and hydrologic 

data collected for the GAMA Program 

may be obtained from:

GAMA Project Chief

U.S. Geological Survey

California Water Science Center

6000 J Street, Placer Hall

Sacramento, CA 95819-6129

Telephone number: (916) 278-3000

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

GAMA Program Unit Chief

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/

Modern age

category

Pre-modern

or mixed age

category

0.01

0.1

1

10

Relative-concentration, dimensionless

Oxic

conditions

Anoxic or mixed

conditions

Low

Moderate

High

Maximum relative-concentration of iron or manganese

26 13 32 7

22

EXPLANATION

Number of sites

90th percentile

75th percentile

50th percentile Interquartile

(median) range

25th percentile

10th percentile

ISSN 2327-6916 (print)

ISSN 2327-6932 (online)

http://dx.doi.org/10.3133/fs20143031