Water Quality on the Island of Oahu 

Hawaii, 1999–2001

U.S. Department of the Interior

U.S. Geological Survey

Circular 1239
Points of Contact and Additional Information

The companion Web site for NAWQA summary reports:

http://water.usgs.gov/nawqa/nawqa_sumr.html/

Other NAWQA summary reports

River Basin Assessments

Acadian-Pontchartrain Drainages (Circular 1232)

Albemarle-Pamlico Drainage Basin (Circular 1157)

Allegheny and Monongahela River Basins (Circular 1202)

Apalachicola-Chattahoochee-Flint River Basin (Circular 1164)

Central Arizona Basins (Circular 1213)

Central Columbia Plateau (Circular 1144)

Central Nebraska Basins (Circular 1163)

Connecticut, Housatonic and Thames River Basins (Circular 1155)

Cook Inlet Basin (Circular 1240)

Delaware River Basin (Circular 1227)

Delmarva Peninsula (Circular 1228)

Eastern Iowa Basins (Circular 1210)

Georgia-Florida Coastal Plain (Circular 1151)

Great and Little Miami River Basins (Circular 1229) 

Great Salt Lake Basins (Circular 1236)

Hudson River Basin (Circular 1165)

Kanawha - New River Basins (Circular 1204)

Lake Erie - Lake Saint Clair Drainages (Circular 1203)

Long Island - New Jersey Coastal Drainages (Circular 1201)

Lower Illinois River Basin (Circular 1209)

Lower Susquehanna River Basin (Circular 1168)

Lower Tennessee River Basin (Circular 1233)

Las Vegas Valley Area and the Carson and Truckee River Basins (Circular 1170)

Mississippi Embayment (Circular 1208)

Mobile River Basin (Circular 1231)

New England Coastal Basins (Circular 1226)

Northern Rockies Intermontane Basins (Circular 1235)

Ozark Plateaus (Circular 1158)

Potomac River Basin (Circular 1166)

Puget Sound Basin (Circular 1216)

Red River of the North Basin (Circular 1169)

Rio Grande Valley (Circular 1162)

Sacramento River Basin (Circular 1215)

San Joaquin-Tulare Basins (Circular 1159)

Santa Ana Basin (Circular 1238)

Santee River Basin and Coastal Drainages (Circular 1206)

South-Central Texas (Circular 1212)

South Platte River Basin (Circular 1167)

Southern Florida (Circular 1207)

Trinity River Basin (Circular 1171)

Upper Colorado River Basin (Circular 1214)

Upper Illinois River Basin (Circular 1230)

Upper Mississippi River Basin (Circular 1211)

Upper Snake River Basin (Circular 1160)

Upper Tennessee River Basin (Circular 1205)

Western Lake Michigan Drainages (Circular 1156)

White River Basin (Circular 1150)

Willamette Basin (Circular 1161)

Yakima River Basin (Circular 1237)

Yellowstone River Basin (Circular 1234)

National Assessments

The Quality of Our Nation‘s Waters—Nutrients and Pesticides (Circular 1225)

Oahu Study Unit contact and Web site:

USGS State Representative

U.S. Geological Survey

677 Ala Moana Blvd. Suite 415

Honolulu, HI 96813

email: dc_hi@usgs.gov

http://hi.water.usgs.gov/

National NAWQA Program:

Chief, NAWQA Program

U.S. Geological Survey

12201 Sunrise Valley Drive, M.S. 413

Reston, VA 20192

http://water.usgs.gov/nawqa/

Front cover: Island of Oahu as seen by Landsat satellite (cloud-free mosaic by the Pacific Disaster Center).

Back cover: Left, the city of Honolulu looking north (photograph by Douglas Peebles); right, shaded relief map 

of Oahu. 
Water Quality on the Island of Oahu, 

Hawaii, 1999–2001

By Stephen S. Anthony, Charles D. Hunt, Jr., Anne M.D. Brasher, Lisa D. Miller, 

and Michael S. Tomlinson

Circular 1239

U.S. Department of the Interior

U.S. Geological Survey
For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Anthony, Stephen S., Hunt, Jr., Charles D., Brasher, Anne M., Miller, Lisa D., and Tomlinson, Michael S., 2004, Water 

quality on the island of Oahu, Hawaii: Reston, Va., U.S. Geological Survey Circular 1239, 37 p.

Library of Congress Cataloging-in-Publication Data

Water quality on the island of Oahu, Hawaii, 1999–2001 / Stephen S. Anthony ... [et al.].

 p. cm. -- (Circular ; 1239)

 Includes bibliographical references.

 ISBN 0-607-92618-X

 1. Water quality -- Hawaii -- Oahu. I. Anthony, Stephen S. II. Geological Survey (U.S.)

 III. U.S. Geological Survey circular ; 1239.

 TD224.H3.W38 2003

 363.739’4’099693--dc22 2003063065
iii

Contents

National Water-Quality Assessment Program ......................................................... iv

What kind of water-quality information does the NAWQA Program provide? ............... v

Introduction to this Report .............................................................................. vi

Summary of Major Findings ........................................................................... 1

Stream Highlights ................................................................................. 1

Ground-Water Highlights ........................................................................ 2

Introduction to the Oahu Study Unit .................................................................. 3

Land use is changing from agriculture to urban ................................................ 4

Ground water provides public supplies, streams provide aquatic habitat and

irrigation water ........................................................................... 4

Drinking-water aquifer is vulnerable to contamination ....................................... 4

Below-normal rainfall may have affected water quality ....................................... 5

Major Findings .......................................................................................... 6

Ground Water ....................................................................................... 6

Organic compounds were detected in most wells, but few concentrations

exceeded drinking-water standards ............................................. 6

Nutrient concentrations were elevated in agricultural areas but did not exceed

drinking-water standards ......................................................... 7

Land use and aquifer vulnerability influence ground-water contamination ......... 8

Mixtures of organic compounds were common in ground water ..................... 9

Ground-water contamination in central Oahu reflects decades-old releases and

former land use ..................................................................... 10

Surface Water ....................................................................................... 10

Contaminants in stream water varied with land use, storms, and ground-water

inflow ................................................................................. 10

Excess nutrients may adversely affect stream and coastal ecosystems ............ 13

Streambed Sediment and Fish Tissue ............................................................ 14

Aquatic habitat is degraded by nonpoint-source pollution .............................. 14

Discontinued organochlorine pesticides persist in the environment .................. 14

Human activities elevate trace elements in stream sediments ........................ 16

Stream Ecology .................................................................................... 16

Urban alteration of stream habitat has adversely affected native aquatic species 16

Benthic invertebrates reflect degraded stream quality ................................. 19

Most identified invertebrates were nonnative .......................................... 19

Study Unit Design ....................................................................................... 20

Ground-Water Chemistry ........................................................................ 20

Stream Chemistry ................................................................................. 20

Stream Ecology .................................................................................... 20

References Cited .......................................................................................... 22

Glossary ................................................................................................... 24

Appendix. Water Quality Data from the Island of Oahu, Hawaii, in a National Context ......... 26
iv

National Water-Quality Assessment Program

The quality of the Nation’s water resources is integrally linked to the long-term availability of 

water that is clean and safe for drinking and recreation and also suitable for industry, irrigation, 

and habitat for fish and wildlife. Recognizing the need for long-term, nationwide assessments 

of water resources, the U.S. Congress has appropriated funds since 1991 for the USGS to conduct the National Water-Quality Assessment (NAWQA) Program. Scientists in the NAWQA 

Program work with partners in government, research, and public interest groups to assess the 

spatial extent of water-quality conditions, how water quality changes with time, and how human 

activities and natural factors affect water quality. This information is useful for guiding watermanagement and protection strategies, research, and monitoring in different hydrologic and 

land-use settings across the Nation.

The island of Oahu is one of 51 water-quality assessments initiated since 1991. Together, the 

51 major river basins and aquifer systems, referred to as “Study Units,” include water resources 

used by more than 60 percent of the population in watersheds that cover about one-half of the 

land areas of the conterminous United States. Timing of the assessments varies because of the 

program’s rotational design in which one-third of all Study Units are intensively investigated 

for 3 to 4 years, with trends assessed every 10 years. As indicated on the map, the island of 

Oahu is part of the third set of intensive investigations, which began in 1997.

1991–95 

1994–98

1997–2001

Not yet scheduled

High Plains Regional

Ground Water Study, 

1999–2004

NAWQA Study Units— 

Assessment schedule

Oahu Study Unit
What kind of water-quality information does the NAWQA 

Program provide?

Water-quality assessments by a single program cannot possibly address all of the Nation’s 

water-resources needs and issues. Therefore, it is necessary to define the context within which 

NAWQA information is most useful. 

• Total resource assessment—NAWQA assessments are long-term and interdisciplinary, 

and include information on water chemistry, hydrology, land use, stream habitat, and 

aquatic life. Assessments are not limited to a specific geographic area or water-resource 

problem at a specific time. Therefore, the findings describe the general health of the total 

water resource, as well as emerging water issues, thereby helping managers and decision 

makers to set priorities.

• Source-water characterization—Assessments focus on the quality of the available, 

untreated resource and thereby complement (rather than duplicate) Federal, State, and 

local programs that monitor drinking water. Findings are compared to drinking-water 

standards and health advisories as a way to characterize the resource.

• Compounds studied—Assessments focus on chemical compounds that have well-established methods of investigation. It is not financially or technically feasible to assess all 

the contaminants in our Nation’s waters. In general, the NAWQA Program investigates 

those pesticides, nutrients, volatile organic compounds, and metals that have been or are 

currently used commonly in agricultural and urban areas across the Nation. A complete 

list of compounds studied is on the NAWQA Web site at http://water.usgs.gov/nawqa.

• Detection relative to risk—Compounds are measured at very low concentrations, often 

10 to 100 times lower than Federal or State standards and health advisories. Detection of 

compounds, therefore, does not necessarily translate to risks to human health or aquatic 

life. However, these analyses are useful for identifying and evaluating emerging issues, 

as well as for tracking contaminant levels over time.

• Multiple scales—Assessments are guided by a nationally consistent study design and 

uniform methods of sampling and analysis. Findings thereby pertain not only to water 

quality of a particular stream or aquifer, but also contribute to the larger picture of how 

and why water quality varies regionally and nationally. This consistent, multiscale 

approach helps to determine if a water-quality issue is isolated or pervasive. It also 

allows direct comparisons of how human activities and natural processes affect water 

quality in the Nation’s diverse environmental settings. 

v
vi

Introduction to this Report

This report contains the major findings of a 1999–2001 assessment of water quality on the 

island of Oahu, Hawaii. It is one of a series of reports by the National Water-Quality Assessment (NAWQA) Program that present major findings in 51 major river basins and aquifer 

systems across the Nation. 

In these reports, water quality is discussed in terms of local, State, and regional issues. Conditions in a particular basin or aquifer system are compared to conditions found elsewhere and 

to selected national benchmarks, such as those for drinking-water quality and the protection of 

aquatic organisms. 

This report is intended for individuals working with water-resource issues in Federal, State, or 

local agencies, universities, public interest groups, or in the private sector. The information will 

be useful in addressing a number of current issues, such as the effects of agricultural and urban 

land use on water quality, human health, drinking water, source-water protection, and excessive 

growth of algae and plants, pesticide registration, and monitoring and sampling strategies. This 

report is also for individuals who wish to know more about the quality of streams and ground 

water in areas near where they live, and how that water quality compares to the quality of water 

in other areas across the Nation.

The water-quality conditions on Oahu summarized in this report are discussed in detail in other 

reports that can be accessed from (http://hi.water.usgs.gov/nawqa). Detailed technical information, data and analyses, collection and analytical methodology, models, graphs, and maps 

that support the findings presented in this report in addition to reports in this series from other 

basins can be accessed from the national NAWQA Web site (http://water.usgs.gov/nawqa). 

“The NAWQA study results 

provide Hawaii with an 

important database describing the status of water quality 

in aquifers, and the status 

of water quality, habitat, 

and aquatic communities in 

selected streams on Oahu. 

Many of Oahu’s surface and 

ground waters have been 

subject to only limited monitoring in the past, so these 

data will represent a baseline 

to which results from future 

studies can be compared. 

Reports on chemical contaminants in aquifers, stream 

sediments and fish tissues are 

particularly useful because 

these data are expensive to 

obtain and thus rarely collected. Similar data sets from 

the other Hawaiian islands are 

sorely needed.”

Dr. June Harrigan, 

Hawaii Department of Health,

Environmental Planning Office

“The data on benthic invertebrates is a major contribution of this study, because 

such data have seldom been 

collected for Hawaiian 

streams and never before 

in conjunction with such a 

wealth of other water-quality 

parameters. This information 

could provide the basis for 

an important new component 

in water-quality monitoring 

in Hawaii, which would be 

especially useful for volunteer monitors and educational 

groups.”

Dr. Carl Evenson, 

University of Hawaii at Manoa, 

College of Tropical Agriculture and 

Human Resources

Electrofishing in an Oahu stream. (Photograph by Anne Brasher, U.S. Geological 

Survey.)
Honolulu

Kaneohe

Waianae

Wahiawa

Waipahu

Manoa

Kailua

Haleiwa

Waihee

Kahana

Lake Wilson

Punaluu

EXPLANATION

LAND USE

Agriculture

Urban

Other (mostly forest)

158 ̊

158 ̊10'

21 ̊40'

21 ̊30'

21 ̊20'

157 ̊50'

157 ̊40'

0 5 10 MILES

0 5 10 KILOMETERS

C E N

T R A L P L A

T E A

U

K

O

O L A U R A

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W A I A N A E

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• Excessive nutrients in streams and ground water could 

have adverse effects on coastal ecosystems such as estuaries and coral reefs (p. 13–14).

• Trace elements were elevated above background levels 

in streambed sediments in urban and agricultural basins. 

Arsenic exceeded aquatic-life guidelines at 67 percent of 

agricultural sites, and lead and zinc exceeded guidelines at 

50 and 75 percent of urban sites, respectively. Chromium 

and copper exceeded guidelines in all land uses as a result 

of high natural abundance in Hawaii rocks and soil (p. 16).

• Urban streams had fewer numbers of invertebrates but a 

greater number of invertebrate taxa than forested streams, 

reflecting ecosystem degradation and dominance by 

nonnative species (p. 19).

1

Stream Highlights

Urban and agricultural land use greatly 

influence the water quality and ecology of 

Oahu streams. Although streams do not supply 

drinking water, they do provide irrigation water 

and habitat1 for aquatic life. Guidelines established to protect freshwater aquatic life and 

fish-eating wildlife were exceeded for

several organic compounds, nutrients, and 

trace elements; however, guidelines have not 

been established for all detected chemicals.

• Urban alteration of stream habitat has 

adversely affected native aquatic species, 

interfering with migration cycles of native 

fish, shrimp, and snails. Introduced species 

are more tolerant of altered habitat and

proliferate where native species cannot. 

Few native fish were collected (p. 18).

• Streams in different land-use settings 

contain different pesticides. Herbicides

were detected more frequently than insecticides in Waikele 

Stream (which drains agricultural and urban land), whereas 

insecticides were detected more frequently in urban Manoa 

Stream (p. 10).

• Contamination also depends on rainfall and ground-water 

inflow. At Waikele Stream, for example, insecticides were 

detected more frequently in storm runoff, whereas herbicides and nutrients were detected more frequently and at 

highest concentrations in fair-weather base flow supplied 

by ground water (p. 11).

• The insecticides carbaryl, diazinon, dieldrin, and malathion 

exceeded aquatic-life guidelines in water. Dieldrin, used to 

control termites, was detected in almost all water samples 

from urban Manoa Stream and exceeded the aquatic-life 

guideline in 26 percent of the samples (p. 12). 

• Organochlorine pesticides, polychlorinated biphenyls 

(PCBs), and semivolatile organic compounds (SVOCs) 

were pervasive in urban and agricultural-urban streams. 

Concentrations exceeded aquatic-life guidelines in bed 

sediment and wildlife guidelines in fish. Chlordane and 

dieldrin concentrations were among the highest in the 

Nation (p. 14–17).

• Νitrogen and phosphorus concentrations frequently 

exceeded State stream-water standards and were highest in 

agricultural-urban Waikele Stream Basin, where fertilizers 

were applied intensively for decades (p. 13–14). 

1

 Terms defined in the Glossary (p. 24) are shown in boldface type where 

they first appear.

Oahu is the most urbanized island in Hawaii and home to the State 

capital and largest city, Honolulu. The resident and visitor population is about 1 million people. The island is a fully enclosed hydrologic system that encompasses 586 square miles and includes 

two mountain ranges. Public water supplies are provided entirely 

by ground water, whereas streams provide irrigation water and 

aquatic habitat.

Summary of Major Findings

Major Influences on Streams

• Contaminants in runoff from urban and agricultural land

• Pesticides and nutrients in ground-water-fed base flow

• Degraded stream habitat in urban and agricultural areas
2 Water Quality on the Island of Oahu, Hawaii, 1999–2001

• Current contamination reflects historical use of chemicals 

more than present use; for example, there were numerous 

detections of fumigants, herbicides, and fertilizers formerly 

used on agricultural land. Ground-water movement is slow 

(about 5 feet per day), and chemicals take decades to be 

flushed through the aquifer system. Single detections of 

three turfgrass herbicides used only since 1990 suggest 

that chemicals used in urban areas converted from cropland 

have begun to reach the water table (p. 10).

• Detection frequencies in Oahu public-supply wells were 

highest in the Nation for fumigants and third highest for 

solvents out of more than 80 NAWQA assessments of 

VOCs in major aquifers. Fumigants are applied for pineapple cultivation, and solvent use is widespread in military 

and civilian sectors of the urban environment (p. 9).

• Nitrate concentrations were elevated in agricultural areas 

but did not exceed the USEPA drinking-water standard. 

Phosphorus concentrations were high enough to potentially 

promote nuisance plant growth (eutrophication) where 

ground water discharges to streams (p. 7).

• Trace-element concentrations were within drinking-water 

standards. Arsenic, which is a concern in the Northeastern 

and Western United States, was not detected in publicsupply wells on Oahu (p. 6).

Ground-Water Highlights

Ground water provides virtually all drinking water on 

Oahu, and much of the Study Unit is a U.S. Environmental 

Protection Agency (USEPA) designated sole-source aquifer. 

The most common chemicals detected in untreated water from 

public-supply and monitor wells were fumigants, solvents, 

herbicides, and elevated concentrations of nutrients. The 

chemical quality of the untreated water does not necessarily 

reflect that of treated drinking water delivered to the public.

• Few chemicals exceeded drinking-water standards in 

ground water. USEPA standards were exceeded by the 

solvent trichloroethene and the radioactive gas radon in 

one public-supply well each. Fumigants exceeded more 

stringent State standards in four supply wells (p. 6–8).

• Ground-water contamination is determined largely by 

chemical use, land use, and aquifer vulnerability. Contamination is greatest in central Oahu, where solvents, herbicides, and fertilizers are used over vulnerable unconfined

aquifers. In contrast, minimal contamination was detected 

in urban Honolulu, where chemicals are used and stored 

mostly over less vulnerable confined aquifers (p. 8–9).

Selected Indicators of Ground-Water Quality

Public-Supply

Wells

Nitrate

Arsenic

Herbicides

Insecticides

Radon

Volatile

organics1

—

—

Proportion of samples with detected concentrations

greater than or equal to health-related national

guidelines for drinking water

Proportion of samples with detected concentrations less than health-related national guidelines for drinking water

Proportion of samples with no detections

Not assessed

1 Solvents, refrigerants, fumigants, gasoline compounds, and

trihalomethanes.

Monitor Wells

Small Streams

Undeveloped/

Forest Urban

Selected Indicators of Stream-Water Quality

Agricul- tural

—

Nitrate

Total

phosphorus

Herbicides

Insecticides

Volatile organics3

Semivolatile

organics4

Organochlorines

in fish tissue2

Organochlorines

in sediment

2

Proportion of samples with detected concentrations

greater than or equal to health-related national

guidelines for drinking water, protection of aquatic life, or

the desired goal for preventing nuisance plant growth

Proportion of samples with detected concentrations less

than health-related national guidelines for drinking

water, protection of aquatic life, or below the desired

goal for preventing nuisance plant growth

Proportion of samples with no detections

Not assessed or insufficient data

Mixed

Land Uses

—

—

—

—

—

—

—

—

—

1 Metals. 2 Organochlorine pesticides and PCBs.

3 Solvents, refrigerants, fumigants, gasoline compounds, and

trihalomethanes in water.

4 Byproducts of fossil-fuel combustion; components of coal and crude

oil in sediment.

Trace

elements

in sediment

1

Major Influences on Ground Water

• Solvents from military and civilian urban sources and 

from pesticide formulations

• Fumigants applied to pineapple fields

• Agricultural herbicides and fertilizers from agriculture 

and from urban lands, including parks and golf courses
Introduction 3

Introduction to the Oahu Study Unit

Oahu is the center of population 

and commerce in Hawaii and home 

to the State capital and largest city, 

Honolulu. The 586-mi2 landscape is 

dominated by two volcanic mountain 

ranges dissected by deep valleys 

(fig. 1). A gently sloping central plateau separates the mountain ranges, 

and a coastal plain extends around 

the island margin. The island is a 

fully enclosed hydrologic system, 

encompassing entire streams from 

their headwaters to their mouths and 

entire ground-water flow systems 

from inland recharge areas to 

coastal discharge zones. Waikele 

Stream has the largest drainage 

basin, which occupies much of 

south-central Oahu. Manoa Stream is 

a prominent urban stream that drains 

a broad valley in urban Honolulu and 

empties into a large drainage canal 

that borders the tourist enclave of 

Waikiki. Streams are short and steep, 

and streamflow is flashy (stormflows 

peak and recede within hours). Most 

streams are intermittent through 

their mid-reach; flow is perennial at 

high altitudes where rainfall is persistent and along low-altitude gaining reaches where streams intersect 

the water table near their mouths. 

Streams in northeastern Oahu 

intercept high-level, dike-impounded 

ground water and are perennial over 

most of their lengths.

Climate is subtropical, with mild 

temperatures, moderate humidity, 

and prevailing northeasterly trade 

winds. Rainfall variation is extreme 

over short distances, ranging from 

280 inches per year near the crest of 

the Koolau Range to 20 inches per 

year in the rain-shadowed lowlands 

of western Oahu (fig. 2; Giambelluca and others, 1986). As a result, 

microenvironments range from rain 

forest to dry grassland with cactus and 

kiawe (similar to mesquite). Rainfall is 

seasonal: November through April are 

relatively wet months, and May through 

October are drier. Storms can occur at 

any time of the year.

Figure 1. Urban and agricultural development are concentrated along the coast and throughout the gently sloping plateau of central Oahu. Forests blanket the more rugged, mountainous 

terrain. (All photographs by Douglas Peebles.)

Honolulu

Kaneohe

Waianae

Wahiawa

Waipahu

Haleiwa

Manoa

Kailua

Waihee

Kahana

Waikele

Lake

Wilson

Punaluu

EXPLANATION

LAND USE

Agriculture

Urban

Other (mostly unde- 

 veloped forest)

Urban, converted from

 agricultural use 

 from 1950 to 1998

158 ̊

158 ̊10'

21 ̊40'

21 ̊30'

21 ̊20'

157 ̊50'

157 ̊40'

0 5 10 MILES

0 5 10 KILOMETERS

Urban Honolulu houses a dense population of 

residents and visitors. Shown here is the Waikiki area 

with the extinct volcanic crater of Diamond Head in 

the background.

Forests cover 60 percent of the Study Unit.

Shown here is Kahana Stream Valley in eastern 

Oahu, which is typical of forested basins.

Urban residential developments now occupy 

former sugarcane land in south-central Oahu. 

Sugarcane cultivation was discontinued in 

the 1990s.

Agriculture in central Oahu includes 

pineapple (shown) and diversified 

crops.

C E N T R A L P L A T E A U

K

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4 Water Quality on the Island of Oahu, Hawaii, 1999–2001

Land use is changing from 

agriculture to urban

The dominant land cover on Oahu 

(fig. 1) is undeveloped forest (about 60 

percent); about 25 percent is urbanized, 

and the remaining 15 percent is used 

for agriculture (Klasner and Mikami, 

2003). The principal industry is tourism, followed by military activity and 

agriculture. The resident population was 

876,000 in 2000, which is more than 

double the population in 1950. Some 

80,000 additional people visit the island 

at any time, on average. Because much 

of the island is covered by protected 

forest reserves, developed areas on Oahu 

are some of the most densely populated 

areas in the United States.

Major land-use changes are underway in central Oahu (fig. 1) following a 

period of about 100 years in which plantation agriculture dominated the landscape. Before 1950, urban and industrial development was concentrated in 

Honolulu, on the coastal plain near Pearl 

Harbor, and at several military bases 

and a nearby town (Wahiawa) in central 

Oahu. In recent decades, large tracts of 

land used for sugarcane and pineapples 

in central Oahu have been converted to 

suburban use (in the south) and 

diversified-crop agriculture (in both 

north and south) (Oki and Brasher, 

2003). These conversions may result in 

hydrologic changes such as increased 

runoff and reduced ground-water 

recharge and water-quality changes 

related to new types and amounts of 

chemicals.

Ground water provides public 

supplies, streams provide aquatic 

habitat and irrigation water

Ground water provides all public 

drinking-water supply on Oahu (fig. 3), 

while streams provide irrigation water 

and riparian and instream habitat for 

native species and other aquatic life. 

Stream habitat has been degraded by 

poor water quality, channel alteration, 

and flow diversion. The same factors 

responsible for degrading aquatic habitat 

also cause large sediment and chemical 

loads in streams, which can adversely 

affect the ecology and esthetics of 

receiving waters. The bays, estuaries, 

Figure 2. Oahu’s mountainous landscape and moist trade winds cause steep rainfall gradients. (Modified from Giambelluca and others, 1986). 

200

120

80

60

32

24

60

80

40

160

275 235

40

40

158°

158°10'

21°40'

21°30'

21°20'

157°50'

157°40'

200 160

275 235

120

80

60

32 40

40

40

32

24

32

60

80

C E N

T R A L P L A

T E A

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C O A S T A L P L A I N

K

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W A I A N A E

R A N G E

EXPLANATION

LINE OF EQUAL MEAN ANNUAL

RAINFALL, IN INCHES. INTERVAL

IS VARIABLE

0 5 10 MILES

0 5 10 KILOMETERS

PREVAILING TRADE WINDS

and nearshore marine waters of Oahu are 

critical to the tourism-based economy.

Drinking-water aquifer is vulnerable to contamination

The deep volcanic-rock aquifer in 

central Oahu and Honolulu supplies 

more than 90 percent of the island’s public water supply and is designated as a 

Sole Source Drinking-Water Aquifer by 

the USEPA. The aquifer is highly permeable and unconfined except near the 

coast (see map, p. 20), making it vulnerable to contamination despite depths to 

water of hundreds of feet in most places. 

Although overlying rock is weathered 

to depths of 50–200 feet (Hunt, 1996), 

this soil and clay-rich overburden does 

not prevent downward migration of 

chemicals applied or spilled at land 

surface (fig. 4). Contaminants reach 

the deep water table within a few years 

and persist in the aquifer and unsaturated zone for several decades (Hunt, 

2004; Oki and Brasher, 2003). Agricultural and industrial chemicals have 

been detected in many wells, and some 

ground water requires treatment to meet 

drinking-water standards. Unresolved 

ground-water issues include flushing 

times of chemicals through the aquifer 

and effects of ongoing land-use changes 

on chemical use and migration.

Figure 3. Ground water is the sole source of 

public drinking-water supplies on Oahu and 

accounts for most other withdrawals as well. 

Surface water is used only for irrigation and 

provides habitat for aquatic life. 

0

50

100

150

200

250

TOTAL

WITHDRAWALS

PUBLIC SUPPLY AND

DOMESTIC

IRRIGATION

INDUSTRIAL

SURFACE WATER

GROUND WATER

WATER WITHDRAWALS,

IN MILLIONS OF GALLONS PER DAY
Introduction 5

Figure 4. In central Oahu, recharge containing agricultural and urban chemicals infiltrates from land surface 

to the drinking-water aquifer in a matter of years. That 

same water discharges to streams and coastal sediments 

decades later. Soil and contaminants are washed into 

streams within hours of the start of a rainstorm. (Modified 

from block diagram provided by Scot Izuka, U.S. Geological 

Survey.) 

10

100

1,000

O N D J F M

1998 1999 2000 2001

A M J J A S O N D J F M A M J J A S O N D J F M A M J J A 1

75th percentile flow

for 1951–2001

25th percentile flow

for 1951–2001

Daily streamflow

Waikele Stream at Waipahu, station 16213000

STREAMFLOW, IN CUBIC

FEET PER SECOND

SAMPLING TIMELINES

GROUND-WATER CHEMISTRY

STREAM CHEMISTRY (WATER)

STREAM ECOLOGY STREAM ECOLOGY

STREAM CHEMISTRY (BED SEDIMENT AND FISH TISSUE)

Oahu

GROUND-WATER DISCHARGE FROM

SEDIMENTS TO STREA

GROUND-WATER DISCHARGE FROM

SEDIMENTS TO STREA

VOLCANIC-ROCK

DRINKING-WATER

AQUIFER

VOLCANIC-ROCK

DRINKING-WATER

AQUIFER

SEDIMENTARY AQUIFERS AND

CONFINING UNITS

SEDIMENTARY AQUIFERS AND

CONFINING UNITS

WATER TABLEWATER TABLE

GROUND-WATER DISCHARGE FROM

VOLCANIC-ROCK AQUIFER TO

SEDIMENT

G

S

ROUND-WATER DISCHARGE FROM

VOLCANIC-ROCK AQUIFER TO

SEDIMENTS

AQUIFER FLOWPATH

(decades)

AQUIFER FLOWPATH

(decades)

N

COASTAL PLA

VO

IN

LCANIC-ROCK

DRINKING-WATER

AQUIFER

SEDIMENTARY AQUIFERS AND

CONFINING UNITS

WATER TABLE

RESIDENTIAL

RESIDENTIAL

FALLOW

(formerly sugarcane)

PINEAPPLE

SPRING

GROUND-WATER DISCHARGE FROM

VOLCANIC-ROCK AQUIFER TO

SEDIMENTS

GROUND-WATER DISCHARGE FROM

SEDIMENTS TO STREAM

CENTRAL

PLATEAU

UPPER

WAIKELE

SITE

LOWER

WAIKELE

SITE

OCEAN

RUNOFF

RUNOFF

RECHARGE

(1-10 years)

AQUIFER FLOW PATH

(decades)

RECHARGE

r

r

r

a

RUNOFF

(hours to

days)

Waikele Stream

Figure 5. Annual streamflow at Waikele Stream was less than long-term average flow 

in all 3 years of this study (21, 23, and 40 percent below normal).

Below-normal rainfall may have 

affected water quality

Lower than normal rainfall and 

streamflow throughout this 3-year study 

(fig. 5) may have reduced the amount of 

sediment being washed into streams, as 

well as contaminants that attach to sediment particles, such as phosphorus and 

some trace elements. In contrast, concentrations of dissolved constituents, 

particularly those contributed by ground 

water and wastewater effluent, may have 

been higher than normal during this 

relatively dry period.

Ground-water quality probably was 

less affected by the dry conditions than 

were streams. Ground water tends to 

integrate and “smooth” year-to-year climatic effects more than streams do and 

tends to more closely reflect recharge 

and chemical-use patterns that persist for 

a decade or longer.

Additional Information

Oahu NAWQA study:

http://hi.water.usgs.gov/nawqa/

USGS water programs in Hawaii: 

http://hi.water.usgs.gov/

Ground water and aquifers in

Hawaii: http://capp.water.usgs.

gov/gwa/ch_n
6 Water Quality on the Island of Oahu, Hawaii, 1999–2001

These findings are supported by the Study-Unit 

Design presented on pages 20 and 21 of this 

report.

Ground Water

Organic compounds were 

detected in most wells, but 

few concentrations exceeded 

drinking-water standards

Organic compounds were detected 

in 73 percent of 30 public-supply wells 

and in all 15 monitor wells (Hunt, 2004; 

see map, p. 20, for well locations). 

Forty-two different organic compounds 

were detected at least once: 25 volatile 

organic compounds (VOCs), 16 pesticides, and caffeine. Sixty-three percent 

of public-supply wells contained at least 

one VOC or pesticide (fig. 6). Types of 

compounds detected most commonly 

were solvents (cleaning and degreasing 

agents), fumigants (used locally to combat rootworms in pineapple), trihalomethanes (generally thought to originate 

from chlorinated water), and herbicides. 

Gasoline components and insecticides 

were detected in only a few wells.

Chemicals and concentrations 

were similar in public-supply 

and monitor wells

Many of the same compounds were 

detected in public-supply wells and 

monitor wells, and at roughly similar 

concentrations (figs. 7 and 8). This is not 

surprising because both groups of wells 

tap the same deep aquifer, although 

most monitor wells are open at the 

water table, whereas most supply wells 

are protectively solid-cased for some 

distance below it (median depth below 

water table to top of open interval is 

60 feet).

The solvent trichloroethene had 

the highest VOC concentration at 

20.4 micrograms per liter (fig. 8). The 

most common VOC was chloroform 

(trichloromethane), which was detected 

in 47 percent of supply wells (fig. 7). 

Chloroform is used as a solvent and is 

a breakdown product 

of carbon tetrachloride 

(tetrachloromethane). 

On Oahu, solvents 

appear to be the main 

source of chloroform 

because it was at highest concentration where 

other solvents (including carbon tetrachloride) were highest. But 

chloroform also can 

form as a disinfection 

byproduct where chlorine contacts organic 

material (the reaction can take place in 

wastewater disinfected 

with chlorine, or in soils 

where chlorinated drinking water is used 

to water lawns). A disinfection origin 

cannot be ruled out for Oahu because 

chlorinated water is used for landscape 

irrigation, and wastewater discharged 

to a central Oahu stream and lake was 

chlorinated for decades, although it is no 

longer.

The most common pesticide in 

ground water was the herbicide bromacil, which was detected in 41 percent 

of public-supply wells (fig. 7) and had 

the highest concentration among pesticides, 1.08 micrograms per liter (fig. 8). 

Bromacil has been applied in pineapple 

cultivation in central Oahu. Three other 

commonly detected herbicides—atrazine, diuron, and hexazinone—have 

been used on both sugarcane and 

pineapple. Breakdown products of atrazine and diuron were detected in more 

public-supply wells than were their 

parent compounds (fig. 7). Only two 

insecticides were detected: dieldrin (a 

termiticide) and p,p'-DDE (a breakdown 

product of DDT). Three turfgrass herbicides that were first used in the 1990s 

(bentazon, imazaquin, and metsulfuron 

methyl) were detected in monitor wells 

that tap shallow ground water beneath a 

golf course and a cemetery.

Monitoring programs that only 

test for primary chemicals would not 

reveal the pesticide breakdown products 

detected in this study, some of which 

persist longer in the environment and 

have similar or greater toxicity than parent compounds. 

Federal drinking-water 

standards were exceeded in 

two public-supply wells

Although organic compounds commonly were detected, most concentrations were low (less than 1 microgram 

per liter) and only a few concentrations 

exceeded drinking-water standards 

(table 1 and Appendix, p. 26–28). [Note: 

all supply wells exceeding standards 

are either out of service or have watertreatment equipment installed to reduce 

contaminants to acceptable levels.] 

Federal drinking-water standards 

(U.S. Environmental Protection Agency, 

2002a) were exceeded in two publicsupply wells: one central Oahu well in 

which trichloroethene (TCE) concentration was 20.4 micrograms per liter (the 

USEPA standard is 5) and one Honolulu 

well in which radon concentration was 

397 picocuries per liter (the proposed 

USEPA standard is 300). Trichloroethene is a common solvent, and radon 

is a radioactive gas formed naturally 

by decay of uranium, which is present 

in volcanic rock. Trichloroethene also 

exceeded the USEPA standard in one 

monitor well (fig. 8). Concentrations of 

Figure 6. Solvents, fumigants, and herbicides were detected 

in many public-supply wells. The high detection rate for trihalomethanes was due to a single compound, chloroform. 

Detected in

63 percent

of wells

Organic Compound Classes in Public-Supply Wells

0 10 20 30 40 50 60 70 80

Organic compounds

VOCs

PESTICIDES

VOC and pesticide mixtures

Solvents

Fumigants

Trihalomethanes

Gasoline components

Refrigerants

Herbicides

Insecticides

PERCENTAGE OF WELLS

Major Findings
Major Findings 7

Figure 7. Organic compounds detected in public-supply wells included 22 VOCs and 

12 pesticides. Only three compound concentrations exceeded drinking-water standards.

Figure 8. Detected compounds and concentrations were similar in public-supply and 

monitor wells. Trichloroethene and bromacil were the highest-concentration VOC and 

pesticide.

Volatile Organic Compounds (VOCs) Pesticides

MAINLY URBAN USE

MAINLY AGRICULTURAL USE

Detected at or

above Federal

or State drinking

water standard

in 13 percent of wells

Detected in

33 percent

of wells

Compound

ORGANIC COMPOUNDS IN PUBLIC-SUPPLY WELLS

0 5 10 15 20 25 30 35 40 45 50

Trichloromethane (chloroform)

1,2-Dichloropropane (DCP)

1,2,3-Trichloropropane (TCP)

Trichloroethene (TCE)

Tetrachloromethane (carbon tetrachloride)

Tetrachloroethene (PCE)

1,2-Dibromo-3-chloropropane (DBCP)

1,2-Dibromoethane (EDB)

cis-1,2-Dichloroethene

trans-1,2-Dichloroethene

1,1,2-Trichloroethane

1,1,1,2-Tetrachloroethane

1,2,4-Trimethylbenzene

Bromodichloromethane

Dichloromethane

1,1-Dichloroethene

Chlorobenzene

1,1-Dichloropropene

Tribromomethane (bromoform)

Dibromochloromethane

Ethyl tert-butyl ether (ETBE)

Methylbenzene (toluene)

Bromacil 3(4-Chlorophenyl)-1-methyl urea

3,4-Dichloroaniline

Deethylatrazine

Diuron

Atrazine

Dieldrin

Hexazinone

2-Hydroxyatrazine

Deethyldeisopropylatrazine

Deisopropylatrazine

p,p'-DDE

Compound class

Trihalomethane; solvent

Fumigant

Fumigant

Solvent

Solvent

Solvent

Fumigant

Fumigant

Solvent

Solvent

Solvent

Solvent

Gasoline component

Trihalomethane

Solvent

Solvent

Solvent

Fumigant

Trihalomethane

Trihalomethane

Gasoline component

Gasoline component

Herbicide Herbicide (diuron breakdown product)

Herbicide (diuron breakdown product)

Herbicide (atrazine breakdown product)

Herbicide

Herbicide

Insecticide

Herbicide

Herbicide (atrazine breakdown product)

Herbicide (atrazine breakdown product)

Herbicide (atrazine breakdown product)

Insecticide (DDT breakdown product)

PERCENTAGE OF WELLS

PUBLIC-SUPPLY WELLS (30)

CONCENTRATION, IN MICROGRAMS PER LITER

0.001 0.01 0.1 1 10 100

MONITOR WELLS (15)

0.001 0.01 0.1 1 10 100

Volatile Organic Compounds (VOCs) Pesticides

MAINLY URBAN USE

MAINLY AGRICULTURAL USE

SOLVENTS

FUMIGANTS

REFRIGERANTS

TRIHALOMETHANES

GASOLINE

COMPOUNDS

HERBICIDES

INSECTICIDES

CAFFEINE

USEPA

MCL=5

MCL Maximum Contaminant Level

USEPA U.S. Environmental Protection Agency

Hawaii

MCL=0.04

Hawaii

MCL=0.8

Hawaii

MCL=0.04

Hawaii

MCL=0.8

USEPA

MCL=5

Tetrachloromethane (carbon tetrachloride)

Dichloromethane

Tetrachloroethene (PCE)

Trichloroethene (TCE)

cis-1,2-Dichloroethene

trans-1,2-Dichloroethene

1,1,2-Trichloroethane

1,1,1,2-Tetrachloroethane

1,1-Dichloroethene

1,2-Dichloroethane

Chlorobenzene

1,2-Dibromoethane (EDB)

1,2-Dibromo-3-chloropropane (DBCP)

1,2,3-Trichloropropane (TCP)

1,2-Dichloropropane (DCP)

1,1-Dichloropropene

Trichlorofluoromethane (CFC-11)

1,1,2-Trichloro-1,2,2-trifluoroethane (CFC-113)

Tribromomethane (bromoform)

Dibromochloromethane

Trichloromethane (chloroform)

Bromodichloromethane

1,2,4-Trimethylbenzene

Ethyl tert-butyl ether (ETBE)

Methylbenzene (toluene)

Atrazine

Deethylatrazine

Deethyldeisopropylatrazine

Deisopropylatrazine

2-Hydroxyatrazine

Diuron

3,4-Dichloroaniline

3(4-Chlorophenyl)-1-methyl urea

Bromacil

Hexazinone

2-Chloro-2,6-diethylacetanilide

Bentazon

Imazaquin

Metsulfuron methyl

Dieldrin

p,p'-DDE

Caffeine

trace elements did not exceed standards, 

and arsenic was not detected in publicsupply wells.

State drinking-water standards 

(State of Hawaii, 1999) were exceeded 

in four central Oahu public-supply wells 

by fumigants: 1,2-dibromo-3-chloropropane (DBCP) and 1,2,3-trichloropropane 

(TCP) in one well each, and by both 

compounds in two wells (table 1). State 

standards are more stringent (substantially lower) than USEPA standards or 

guidelines for these fumigants. Two 

central Oahu monitor wells also had 

fumigant concentrations that exceeded 

State standards (fig. 8).

Nutrient concentrations were 

elevated in agricultural areas 

but did not exceed drinkingwater standards

Nutrient concentrations in central 

Oahu ground water were greater than 

background concentrations, most likely 

as a result of decades of agricultural 

fertilizer application. Background concentrations of nitrate in forested areas 

were 1 milligram per liter or less as 

nitrogen, whereas the median concentration in agricultural areas was 2.5 and 

the maximum was 5.2 (about one-half 

the USEPA drinking-water standard of 

10 milligrams per liter). Phosphorus 

background concentrations were

0.1 milligram per liter or less, as compared to a median of 0.2 and maximum 

of 0.4 in agricultural areas. There is no 

drinking-water standard for phosphorus, 

but two-thirds of ground-water samples 

had phosphorus concentrations that 

exceeded the USEPA recommended goal 

of 0.1 milligram per liter for preventing nuisance plant growth in streams. 

Excessive nutrients in ground-water 

discharge may foster excessive plant 

or algal growth (eutrophication) that 

can interfere with stream or coral-reef 

ecology. Oahu NAWQA surface-water 

studies (Tomlinson and Miller, in press) 

have attributed high nitrate and phosphorus concentrations in stream base flow 

to nutrient-rich ground water (see p. 13, 

“Ground water contributes nutrients to 

gaining streams”).
8 Water Quality on the Island of Oahu, Hawaii, 1999–2001

Table 1. Four chemicals in untreated water from public-supply wells exceeded drinking-water standards.

[All concentrations in micrograms per liter except 222-Radon in picocuries per liter; USEPA, U.S. Environmental Protection Agency; MCL, Maximum 

Contaminant Level standard; HAL, Lifetime Health Advisory Level guideline; --, not applicable; 222-Radon MCL is a proposed standard]

Chemical

Type of 

chemical

Maximum concentration in 

public-supply 

wells

Drinking-water standards 

or guidelines

Number of wells with concentrations exceeding standards

USEPA

MCL

Hawaii

MCL

USEPA

HAL

USEPA

MCL

Hawaii

MCL

Trichloroethene (TCE) Solvent 20.4 5 5 -- 1 1

222-Radon Radionuclide 397 300 300 -- 1 1

1,2-Dibromo-3-chloropropane (DBCP) Fumigant 0.146 0.2 0.04 -- 0 3

1,2,3-Trichloropropane (TCP) Fumigant 2.7 -- 0.8 40 0 3

Figure 9. Solvents were detected in central Oahu ground water 

near urban areas and military installations.

Figure 10. Fumigants were detected in central Oahu ground 

water, in and near present and former pineapple fields.

158 ̊

158 ̊10'

21 ̊40'

21 ̊30'

21 ̊20'

157 ̊50'

157 ̊40'

CENTRAL OAHU

HONOLULU

0 5 10 MILES

0 5 10 KILOMETERS

EXPLANATION

PUBLIC-SUPPLY WELL

MONITOR WELL

SOLVENTS IN GROUND WATER

Not detected

Low (less than 1 microgram per liter)

Medium (greater than 1 microgram per liter)

High (exceeded Federal USEPA drinking-water standard of

5 micrograms per liter)

LAND USE

Agriculture

Urban

Other (mostly forest)

MILITARY INSTALLATION

BOUNDARY BETWEEN

HONOLULU AND CENTRAL OAHU AREAS

STUDY AREA BOUNDARY

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How NAWQA findings relate to drinking-water standards

NAWQA studies are designed to characterize ambient ground water within aquifers. Although aquifers provide source

water for drinking supplies, NAWQA collects samples at the wellhead before any water treatment or blending of sources 

prior to consumption. NAWQA analyses differ from tests performed to check whether drinking water complies with 

Federal or State drinking-water standards and do not reflect the quality of finished (treated) drinking water delivered to 

the public. Nevertheless, this report discusses chemical concentrations in relation to existing USEPA and State drinkingwater standards, which are set to ensure that drinking water does not pose health risks. Drinking-water standards have not 

been established for all chemicals, however. Out of 25 VOCs and 16 pesticides detected in Oahu NAWQA ground-water 

samples, 4 VOCs and 10 pesticide compounds do not have USEPA drinking-water standards or health advisory guidelines.

Land use and aquifer vulnerability influence ground-water 

contamination

Characteristic suites of chemicals 

in ground water were associated with 

particular land uses and locales. Specifically:

1. Solvents were prevalent throughout 

central Oahu (fig. 9), with highest concentrations beneath urban 

areas and military installations and 

mostly trace concentrations beneath 

agricultural lands.

2. Fumigants (fig. 10), herbicides, 

and elevated nutrient concentrations were prevalent beneath central 

Oahu agricultural lands.

3. Minimal contamination was 

detected in urban Honolulu, including 2–3 detections each of gasoline 

components, herbicides, and the 

insecticide dieldrin.

Widespread ground-water contamination in central Oahu is a consequence 

of intensive chemical use in recharge 

areas over unconfined aquifers. Large 

tracts of agricultural land have received 

repeated applications of fumigants, herbicides, and fertilizers for decades
Major Findings 9

Detection rates in ground water were highest in the Nation for 

fumigants and among the highest for solvents, VOCs, and insecticides

Out of more than 80 NAWQA studies 

of VOCs in major aquifers nationwide, 

Oahu ranked first in the percentage of 

wells in which fumigants were detected, 

third in solvent detections, and fourth 

in overall VOC detections using data 

screened at 0.2 microgram per liter (see 

“NAWQA measures compounds at trace 

concentrations” below). The high fumigant ranking reflects a combination of 

factors, including extensive pineapple 

acreage in central Oahu, high fumigant 

application rates (for example, 1.8 million 

pounds in 1970 at a rate of 115 pounds 

per acre; Takahashi, 1982), and high 

rainfall (40–80 inches per year) that 

promotes leaching from soil to ground 

water. The high solvent ranking is believed 

to reflect past military use of solvents in 

central Oahu dating back to the 1940s 

at aircraft and automotive maintenance 

shops (Harding Lawson Associates, 1995; 

U.S. Environmental Protection Agency, 

2000). The high VOC ranking simply 

reflects the high rankings for the fumigant 

and solvent VOC subclasses.

For pesticides, Oahu ranked 12th in 

insecticide detections and 51st in herbicide 

detections out of more than 90 NAWQA 

studies of pesticides in major aquifers. 

The insecticide ranking resulted from four 

detections in public-supply wells: dieldrin 

in three wells and p,p'-DDE (a DDT breakdown product) in one well. Notably, the 

herbicide ranking does not tell the entire 

herbicide story for Oahu. More than 75 

percent of Oahu herbicide detections were 

from two supplemental lists of pesticides 

(Hunt, 2004) that were not factored into 

the national rankings because they were 

not analyzed in all Study Units. The 

supplemental lists contain several of the 

most widely used and detected herbicides 

on Oahu, namely bromacil, diuron, and 

hexazinone. 

NAWQA measures compounds at trace concentrations

NAWQA measures compounds at trace levels, commonly 10 to 1,000 times lower than drinking-water standards and 

aquatic-life guidelines. Trace concentrations are useful in assessing contaminant occurrence, distribution, and variation 

over time. Detection rates and concentrations contained in this report include all chemical detections, including trace-level 

detections. Higher reporting levels are sometimes used to screen data when making comparisons among NAWQA Study 

Units nationwide. This is done to include early NAWQA studies that had higher laboratory reporting levels than later 

studies (in the case of VOCs) or to include results of several different laboratory methods, each having different reporting 

levels (such as multiple pesticide methods). Of the 25 VOCs and 16 pesticides detected in ground water on Oahu, only 

9 VOCs and 5 pesticides were detected at concentrations at or above screening levels commonly used in NAWQA StudyUnit comparisons (0.2 microgram per liter for VOCs and 0.05 microgram per liter for pesticides).

Figure 11. Most public-supply wells contained 2 or more organic compounds, and 

as many as 13 were detected in one well.

MULTIPLE ORGANIC COMPOUNDS IN PUBLIC-SUPPLY WELLS

0 5 10 15 20 25 30

13

12

11

10

9

8

7

6

5

4

3

2

1

0 NUMBER OF ORGANIC COMPOUNDS

PERCENTAGE OF WELLS

(Yim and Dugan, 1975; Oki and 

Brasher, 2003). Solvents and petroleum 

products have been used and stored at 

several military installations since the 

1940s (Harding Lawson Associates, 

1995; U.S. Environmental Protection 

Agency, 2000), and potential civilian 

sources of these contaminants include 

gasoline stations and automotive repair 

shops in suburban residential areas.

In contrast to central Oahu, few 

organic compounds were detected in 

Honolulu wells despite the high urban 

density there. Much of Honolulu is 

underlain by sedimentary confining 

units or lies in the zone of aquifer 

discharge near the coast. Lands that do 

overlie unconfined recharge zones are 

mainly residential, with little industrial 

or military use. This reflects nearly 

a century of sound urban planning 

and watershed protection by State and 

county agencies that directed intensive 

chemical use and storage away from 

inland recharge areas of urban Honolulu.

Mixtures of organic 

compounds were common in 

ground water

Organic compounds seldom 

occurred alone in ground water on Oahu 

(fig. 11). Multiple organic compounds 

were detected in 63 percent of publicsupply wells, and combinations of VOCs 

and pesticides were detected in 53 percent (fig. 6). Many wells in central Oahu 

contained several types of compounds, 

such as solvents, fumigants, and herbicides. Sampled wells contained as many 

as 10 solvent compounds, and samples 

with the highest fumigant concentrations contained 3 to 4 fumigants, as well 

as trace concentrations of herbicides 

and solvents. Herbicides also occurred 

together, with as many as 10 herbicide 

compounds detected in one sample.
10 Water Quality on the Island of Oahu, Hawaii, 1999–2001

chemicals were detected in monitor 

wells: the post-1990 turfgrass herbicides 

bentazon, imazaquin, and metsulfuron 

methyl beneath a golf course and cemetery. The prevalence of several older 

agricultural chemicals in ground-water 

samples suggests that there has not yet 

been a wholesale changeover to a newer 

“urban” ground-water quality. This 

likely reflects a combination of factors: 

(1) older water and chemicals have not 

yet been fully flushed out of the aquifer 

and unsaturated zone by younger water, 

(2) some newer chemicals may break 

down more rapidly or leach less than 

older chemicals, and (3) wells selected 

for this study inadequately sampled 

younger water. Short-screened monitor wells (such as the 15 monitor wells 

sampled in this study) are useful for 

early detection of new contaminants 

arriving at the water table. Sampling of 

shallower unsaturated-zone water would 

provide even earlier warning of future 

contamination.

Surface Water

Contaminants in stream water 

varied with land use, storms, 

and ground-water inflow

Some chemicals are used primarily 

for agriculture and others primarily in 

urban environments, so land use largely 

determines which chemicals are present in a particular stream. The linkage 

between chemical use and contamination is important because managing 

chemical use and improving application 

efficiency can help reduce contaminant 

levels in both urban and agricultural 

settings. Also important are the properties of the chemicals themselves: some 

chemicals break down rapidly and others 

persist in the environment for decades; 

some chemicals dissolve readily in water 

and infiltrate to ground water, whereas 

other chemicals bind strongly to soil 

particles and are washed into streams by 

storm runoff. 

Of the 47 pesticides detected in 

stream water, insecticides were detected 

more frequently than herbicides in urban 

Manoa Stream, whereas herbicides were 

detected more frequently in Waikele 

Stream, which drains mixed agricultural 

and urban land (Tomlinson and Miller, 

in press). Both streams contained more 

herbicides than insecticides. Different 

pesticides were present at low and high 

flow, with herbicides generally detected 

more frequently in base flow and insecticides generally detected more frequently 

in storm runoff. Many of the pesticides 

detected frequently in base flow also were 

present in ground water. 

Volatile organic compounds (VOCs)

also showed a distinct pattern: VOCs 

detected in urban Manoa Stream included 

gasoline components (benzene, toluene, 

m- and p-xylene, 1-isopropyl4-ethylbenzene, styrene) and solvents 

(acetone, chloromethane), whereas VOCs 

detected in agricultural-urban Waikele 

Stream were the fumigants 1,2,3-trichloropropane (TCP), 1,2-dichloropropane 

(DCP), and 1,2-dibromoethane (EDB); 

the solvent trichloroethene (TCE); the 

trihalomethane chloroform; and a gasoline hydrocarbon, toluene. The fumigants 

were highest in concentration at base 

flow and also were detected in central 

Oahu wells. Ground water is the main 

source of elevated concentrations of 

chemicals in stream base flow at Waikele 

Stream (fig. 12).

Figure 12. Ground-water inflow elevates 

herbicide, fumigant, and nutrient concentrations in Waikele Stream base flow.

Additional Information

Oahu NAWQA ground water: http://

hi.water.usgs.gov/nawqa/gw.html

USEPA drinking-water regulations: 

http://epa.gov/safewater/mcl.html

Hawaii drinking-water regulations: 

http://state.hi.us/doh/rules/11-20.pdf

Toxicological evaluations of risks 

to human health have been used to 

establish drinking-water standards for 

many individual compounds. Risks 

associated with compound mixtures, 

however, are not as well understood but 

have been reported to be greater than 

those of the individual compounds in 

some cases (Bartsch and others, 1998; 

Carpenter and others, 1998). 

Ground-water contamination 

in central Oahu reflects 

decades-old releases and

former land use

Ground-water ages estimated from 

analyses of chlorofluorocarbons (CFCs) 

and sulfur hexafluoride (SF6) spanned 

the last 60 years or so, coinciding with 

increasingly widespread and intensive 

chemical use in the second half of the 

20th century. Only 1 of 45 groundwater samples had a pre-1940 apparent 

recharge date (no CFCs present), and 6 

samples (13 percent) consisted of water 

that was recharged as recently as the 

1990s (Hunt, 2004). The young ages and 

the prevalence of organic compounds in 

central Oahu highlight the vulnerability 

of Hawaii’s unconfined volcanic-rock 

aquifers to contamination from human 

activities: water can travel from land 

surface to the deep water table within a 

decade or so, carrying spilled or applied 

chemicals with it. 

From a land-use perspective, however, it is notable that most water samples had apparent ages from the 1950s to 

1980s. Therefore, much of the observed 

organic and nutrient contamination on 

Oahu corresponds to historical chemical 

releases and applications and, in some 

cases, to discontinued chemicals and 

outmoded practices. Several detected 

compounds such as EDB, DBCP, and 

DDT (whose breakdown product p,p'-

DDE was detected) were discontinued 

from use in the 1970s and 1980s.

One objective of the Oahu 

NAWQA study was to detect changes 

in water quality that might accompany 

the recent conversion of former plantation lands to residential use and diversified-crop agriculture in central Oahu. 

Only a few unambiguously “new” urban 

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

Bromacil

(herbicide)

TCP

1,2,3-Trichloropropane

(fumigant)

BROMACIL AND 1,2,3-TCP CONCENTRATION,

IN MICROGRAMS PER LITER

not detected in runoff

Base flow

Storm runoff

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Nitrate

(nutrient)

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER
Major Findings 11

Land use largely determined 

which pesticides were 

detected in streams

Herbicides detected most frequently in agricultural-urban Waikele 

Stream were bromacil, atrazine, diuron, 

breakdown products of atrazine and 

diuron, and imazaquin (fig. 13). Herbicides detected most frequently in urban 

Manoa Stream were prometon and 

bentazon. The insecticides diazinon, carbaryl, and malathion were detected frequently in both settings, but dieldrin was 

detected only in urban Manoa Stream, 

and chlorpyrifos was detected only in 

agricultural-urban Waikele Stream.

Ground water supplies older 

herbicides to streams

Different pesticides were present in base flow than in storm runoff in 

agricultural-urban Waikele Stream, and 

many of the pesticides detected frequently in base flow also were present in 

ground water. The herbicides bromacil, 

atrazine, and diuron were detected more 

frequently and at higher concentrations 

in base flow than during storms (fig. 13). 

These herbicides have been used extensively since the 1950s and 1960s to control weeds in sugarcane and pineapple 

and were detected widely in wells in 

central Oahu (see p. 6, “Chemicals and 

concentrations were similar in publicsupply and monitor wells”). Because it 

takes decades for water to move through 

the ground-water system, the deep 

volcanic aquifer serves as a long-term 

reservoir that contributes herbicides and 

other constituents to stream base flow. 

The older herbicides were detected less 

frequently and at lower concentrations 

in runoff than in base flow because of 

increased dilution by rainfall. 

In contrast to the older herbicides, 

bentazon and imazaquin (herbicides 

introduced on Oahu since 1990 and 

used on turfgrass) were detected more 

frequently or at higher concentrations 

in storm runoff than in base flow at 

Waikele Stream. Bentazon and imazaquin were detected in only one central 

Oahu monitor well. These newer herbicides appear to be washed off or flushed 

from soil during storms, and they either 

do not reach ground water in detectable 

concentrations or have not had sufficient 

time to accumulate in deep ground water 

like the older agricultural herbicides 

bromacil, atrazine, and diuron.

In urban Manoa Stream, prometon 

was detected more frequently in base 

flow than during storms, whereas diuron, 

3,4-dichloroaniline (a diuron breakdown 

product), and the three post-1990 turfgrass herbicides bentazon, imazaquin, 

and metsulfuron methyl (not shown) 

were either detected more frequently 

or at highest concentrations in storm 

runoff. The causes of these associations 

are unclear but may have to do with 

compound mobility, relative affinity for 

water or sediment, date of introduction, 

and compound buildup in the valley-fill 

aquifer system that supplies base flow 

to Manoa Stream. Notably, the frequent 

detection of diuron and diuron breakdown products in storm runoff at urban 

Manoa Stream is opposite the pattern 

at agricultural-urban Waikele Stream. 

This may reflect a lesser ground-water 

Figure 13. In general, herbicides were detected more frequently in stream base 

flow (supplied by ground water) and insecticides were detected more frequently in 

storm runoff. Dieldrin was detected at both high and low flow in Manoa Stream.

reservoir of diuron at Manoa Stream in 

comparison to Waikele Stream.

Insecticides exceeded aquaticlife guidelines in water and are 

carried mainly by runoff

The insecticides carbaryl, diazinon, malathion, and chlorpyrifos were 

detected more frequently and at higher 

concentrations in storm runoff than in 

base flow (fig. 13). This indicates that 

they mainly are washed off or flushed 

from soil by rainstorms. Dieldrin was 

present in nearly all samples from urban 

Manoa Stream and was detected with 

nearly equal frequency at both high 

and low flow. Carbaryl, diazinon, and 

malathion have been used for vegetable 

crops and to control insects around 

the home. These insecticides were not 

detected in wells, probably because they 

break down relatively quickly or are not 

particularly soluble in water. 

Dieldrin, carbaryl, diazinon, and 

malathion exceeded aquatic-life guideManoa Stream – Urban Land-Use Site

0

20

40

60

80

100

Not detected

Not detectedNot detected in runoffNot detected in runoff

Not detected in runoff

Not detected in base flowNot detected in base flow

Not detected in base flowNot detected in base flow

Not detected

Not detected

BASE FLOW

STORM RUNOFF

Waikele Stream – Mixed Agricultural and Urban Land-Use Site

0

20

40

60

80

100

PERCENT DETECTIONS HERBICIDES MAINLY AGRICULTURAL USE

HERBICIDES MAINLY URBAN USE INSECTICIDES

Bromacil

Atrazine

Diuron

3,4-Dichloroaniline

Imazaquin

Bentazon

Prometon

Dieldrin

Diazinon

Carbaryl

Malathion

Chlorpyrifos
12 Water Quality on the Island of Oahu, Hawaii, 1999–2001

WATER TABLE

VALLEY-FILL AQUIFERS AND CONFINING UNITS

(not used for public drinking water supply)

VALLEY-FILL AQUIFERS AND CONFINING UNITS

(not used for public drinking water supply)

VOLCANIC-ROCK DRINKING-WATER

AQUIFER

VOLCANIC-ROCK DRINKING-WATER

AQUIFER

VOLCANIC-ROCK DRINKING-WATER

AQUIFER

VOLCANIC-ROCK DRINKING-WATER

AQUIFER

GROUND-WATER DISCHARGE TO

STREAM

GROUND-WATER DISCHARGE TO

STREAM

GROUND-WATER FLOW TO UNDERLYING

VOLCANIC-ROCK AQUIFER

GROUND-WATER FLOW TO UNDERLYING

VOLCANIC-ROCK AQUIFER

VALLEY-FILL AQUIFERS AND CONFINING UNITS

(not used for public drinking- water supply)

VOLCANIC-ROCK DRINKING-WATER

AQUIFER

WATER TABLE

VOLCANIC-ROCK DRINKING-WATER

AQUIFER

RECHARGE TO VOLCANIC-ROCK

AQUIFER

MANOA SAMPLING

SITE

RECHARGE TO VALLEY-FILL AQUIFERS

GROUND-WATER DISCHARGE TO

STREAM

RECHARGE TO VOLCANIC-ROCK

AQUIFER

GROUND-WATER FLOW TO UNDERLYING

VOLCANIC-ROCK AQUIFER

RUNOFF TO STREAM

SPRING

SPRING

�

�

�

M anoa St ream

Oahu

lines in Manoa and Waikele Streams 

(table 2). Dieldrin exceeded its USEPA 

aquatic-life guideline in 26 percent of 

samples from Manoa Stream, and by 

extrapolating from continuous flow data 

it is estimated that dieldrin might exceed 

the guideline about 47 percent of the 

time. Aquatic-life guidelines have been 

established for only 13 of the 47 pesticides detected in Oahu streamwater.

Dieldrin persists in urban 

streams

The organochlorine insecticides 

dieldrin, aldrin (which breaks down to 

dieldrin), chlordane, and heptachlor 

were used for decades in Hawaii to 

control termites but were phased out 

by about 1988 in favor of less persistent compounds (Brasher and Anthony, 

2000; Brasher and Wolff, 2004). 

Dieldrin was detected more often in 

urban Manoa Stream water than any 

other insecticide. Concentrations of 

dieldrin in Manoa Stream were highest in base flow (reaching a maximum 

of 0.077 microgram per liter) but also 

remained elevated during storms. In 

fact, concentrations of dieldrin during 

storms were still one-half to one-third 

the concentration in base flow, despite 

as much as a hundredfold dilution of 

base flow by storm runoff. This suggests that dieldrin originates from several 

sources in the Manoa Stream drainage 

(fig. 14): it may be flushed from soil and 

carried to the stream by rainfall runoff, it 

may be supplied by ground-water inflow, 

and it may dissolve into the water column from stream sediments (Larson and 

others, 1997).

More frequent detection of dieldrin 

than other insecticides probably is due 

to its being one of the more long-lived 

compounds within the historically used 

organochlorine group, resulting in great 

persistence in soils (Fuhrer and others, 

1999). Soils and stream sediments in 

urban Honolulu likely serve as long-term 

reservoirs of dieldrin. The valley-fill 

aquifer system immediately beneath the 

stream may also act as a persistent reservoir of dieldrin. The valley-fill aquifer 

system is not used for drinking-water 

supply, but it does contribute base flow 

to Manoa Stream. Although dieldrin was 

detected in the deep volcanic aquifer in 

Honolulu (the drinking-water aquifer), 

this probably is not a source of dieldrin 

to Manoa Stream. Concentrations of 

dieldrin in water from the deep aquifer 

were 2 to 10 times lower than concentrations in stream base flow (0.003–0.015 

compared to 0.032–0.077 microgram 

per liter), and ground-water levels are 

not high enough to force seepage from 

the deep aquifer into the stream at the 

sampling site.

Table 2. Concentrations of four insecticides sometimes exceeded aquaticlife guidelines in urban Manoa Stream and agricultural-urban Waikele 

Stream.

[E, estimated]

Pesticide

Aquatic life 

guideline 

(micrograms

per liter)

Percentage of 

samples that 

exceeded guideline 

(in parentheses)

Range of concentrations 

detected at the site 

(micrograms per liter)

Dieldrin 10.056 Manoa (26) 0.015 – 0.077

Malathion 10.1 Waikele (5) E0.004 – 0.184

Diazinon 20.08 Manoa (4)

Waikele (14)

 0.003 – 0.083

 0.004 – 0.293

Carbaryl 30.2 Manoa (11)

Waikele (10)

 E0.007 – E0.37

 E0.01 – E0.294

1

 USEPA chronic water-quality criteria for protection of aquatic organisms (U.S. Environmental

Protection Agency, 2002b). 2

 Great Lakes water-quality objectives (International Joint Commission United States and Canada, 

1989). 3

 Canadian water-quality guidelines (Canadian Council of Ministers of the Environment, 1999).

Figure 14. Possible sources of dieldrin in 

Manoa Stream include surface runoff of 

water and soil, transfer from stream sediments to the water column, and groundwater inflow from the valley-fill aquifer 

system. The volcanic-rock aquifer probably is not a source because water levels 

in that aquifer are lower than the stream. 

(Modified from block diagram provided by 

Scot Izuka, U.S. Geological Survey.)
Major Findings 13

Excess nutrients may adversely 

affect stream and coastal 

ecosystems

 Concentrations of nutrients in 

Oahu streams were moderate to high 

in comparison to streams studied by 

NAWQA across the Nation. Flowweighted mean concentrations of total 

nitrogen in Manoa and Waikele Streams 

ranked in the middle 50 percent of 

497 streams sampled nationwide, and 

mean concentrations of total phosphorus ranked in the highest 25 percent 

of streams. Nutrient concentrations 

consistently exceeded State water-quality guidelines (State of Hawaii, 2002) 

and may be of concern locally because 

of nutrient-sensitive coral reefs along the 

coast.

Agricultural fertilizers are a 

source of nutrients

Agricultural-urban Waikele Stream 

had dissolved nitrate concentrations 

more than 10 times greater (median 

value 1.2 milligrams per liter as N) 

than those in urban Manoa Stream or 

forested Waihee Stream (fig. 15). Dissolved phosphorus at Waikele (median 

concentration 0.14 milligram per liter as 

P) was about 4 to 6 times higher than at 

Manoa or Waihee. High concentrations 

of nutrients in Waikele Stream likely 

result from large amounts of fertilizers applied to agricultural land in the 

Waikele basin.

Ground water contributes 

nutrients to gaining streams

Nutrient contamination in streams 

is commonly attributed to agricultural 

runoff or to effluent discharged from 

wastewater-treatment plants. However, 

ground water largely controls nutrient 

concentrations in Waikele Stream, which 

more closely resemble ground-water 

concentrations than concentrations in 

Manoa or Waihee Streams (fig. 15).

The influence of ground water was 

studied by sampling two sites along 

Waikele Stream (fig. 4). Nitrate and 

phosphorus concentrations were much 

lower at the upper Waikele site than at 

the lower Waikele site a short distance 

downstream (fig. 16). The increased 

concentrations are directly attributable 

to ground-water inflow to the stream. 

The regional water table lies beneath the 

streambed at the upper site but intersects 

it at the lower site, causing a gaining 

reach of stream where streamflow is 

augmented by ground-water discharge. 

Despite the ground-water contribution, 

nutrient concentrations at the lower 

Waikele site were not as high as in 

nearby ground water (median concentration from five nearest wells). Possible 

reasons include spatial variability of 

nutrients in ground water (concentrations right at the streambed may differ 

from concentrations at nearby wells), 

natural removal processes such as plant 

uptake or denitrification that could 

reduce nutrient concentrations, and 

dilution by the upstream component of 

streamflow arriving at the lower Waikele 

site. Dilution alone cannot explain the 

differences between ground-water and 

stream concentrations, however. Flow 

at lower Waikele in figure 16 was about 

88 percent ground-water-derived, yet 

median stream concentrations were less 

than one-half the median ground-water 

concentrations instead of the approximately nine-tenths proportion that would 

be expected from simple dilution by 

upper Waikele streamwater.

Dilution is most distinct during 

storms, as can be seen by segregating the 

lower Waikele data into base-flow and 

storm events (fig. 17). Lower nutrient 

concentrations during storms reflect 

dilution of ground-water-fed base flow at 

the lower Waikele site by large amounts 

of storm runoff from upstream.

Ground-water contributions of 

nutrients and other contaminants are 

significant to water-resource programs 

such as those that establish Total 

Maximum Daily Loads (TMDLs) in 

streams. If ground-water contributions 

are not adequately defined, this would 

prevent a full accounting of all contributing sources and limit the effectiveness 

that TMDLs would have in future stream 

restoration and protection.

Nutrients and suspended sediments exceeded state standards for 

streamwater quality and may affect 

coastal ecosystems

More than 30 streams on Oahu 

have been identified by the State as 

water-quality impaired, primarily for 

exceeding standards for nutrients and 

suspended sediment (Henderson and 

Harrigan, 2002). As a consequence, the 

State is coordinating with stakeholders 

and government agencies to reduce nonpoint-source pollution and is studying 

Figure 15. Agricultural fertilizers cause 

elevated nutrient concentrations in 

Waikele Stream and in ground water.

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

MANOA (URBAN)

MEDIAN CONCENTRATION,

IN MILLIGRAMS PER LITER

WAIKELE (MIXED) WAIHEE (FOREST)GROUND WATER (45 wells)

DISSOLVED NITRATE

DISSOLVED PHOSPHORUS

Figure 16. Nutrient concentrations at 

Waikele increase downstream because 

of nutrient-laden ground-water inflow.

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

UPPER WAIKELE LOWER WAIKELE GROUND WATER (nearest 5 wells)

DISSOLVED NITRATE

DISSOLVED PHOSPHORUS

MEDIAN CONCENTRATION,

IN MILLIGRAMS PER LITER

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

BASE

FLOW

LOWER WAIKELE

STORM

RUNOFF

MEDIAN CONCENTRATION,

IN MILLIGRAMS PER LITER

GROUND

WATER

(nearest

5 wells)

DISSOLVED NITRATE

DISSOLVED PHOSPHORUS

Figure 17. Ground-water inflow (base 

flow) containing substantial nutrients is 

diluted by runoff during storms. 
14 Water Quality on the Island of Oahu, Hawaii, 1999–2001

concern for Hawaiian coastal waters 

because of potential effects on nearshore 

coral reefs, which are an important biological resource and an integral part of 

Hawaii’s economically important tourist 

industry. Reefs and associated estuaries 

are susceptible to nutrient and sediment 

loading above natural background levels 

(U.S. Coral Reef Task Force, 1999; 

Clark, 1995). Nutrient concentrations 

in streams and ground water are 100 to 

1,000 times the nutrient guidelines for 

coral reefs. 

Streambed Sediment and 

Fish Tissue

Aquatic habitat is degraded by 

nonpoint-source pollution

Traditionally, water-quality 

monitoring has focused on surfacewater sampling. There are compelling 

reasons why contaminants in streambed sediment and fish tissue also were 

analyzed in the Oahu NAWQA study. 

Different types of compounds are more 

readily detected in sediment and tissue (hydrophobic compounds) than in 

water (hydrophilic, or water-soluble, 

compounds). Furthermore, analyses of 

sediment and fish provided measures of 

these contaminants that are integrated 

over time. A joint approach of sampling 

water, sediment, and fish provides the 

best means of detecting chemicals in the 

hydrologic system and the most information for management decisions.

Nonpoint-source pollution is an 

urban as well as an agricultural problem. 

Some of the greatest nonpoint-source 

effects on stream quality on Oahu are in 

urban watersheds, where contaminants 

such as organochlorine compounds 

and semivolatile organic compounds 

(SVOCs) were detected at greater 

frequencies and concentrations than in 

other land-use settings. Improvements in 

water quality will therefore depend not 

only on managing point sources of

pollution, but also on managing various 

diffuse, nonpoint contributions from 

lawns, gardens, cars, and developed 

land.

Discontinued organochlorine 

pesticides persist in the 

environment

The organic compounds of greatest concern in Oahu streams are 

organochlorine insecticides used for 

termite control: dieldrin and chlordane. 

Chlordane and aldrin (which breaks 

down to dieldrin) were used heavily in 

urban settings until discontinued in the 

mid-1980s (Takahashi, 1982) and persist 

today in streambed sediment and fish at 

concentrations well above aquatic-life 

and wildlife guidelines (Appendix, 

p. 29). DDT, another organochlorine 

insecticide, was used in both agricultural 

and urban settings on Oahu (Honolulu 

Star Bulletin, 1944) before being discontinued from use in the United States in 

1972. Although environmental concentrations have decreased substantially 

since the 1970s, DDT and its breakdown 

products still are present at elevated levels in Oahu streams (Appendix, p. 29).

The persistence of organochlorine compounds in Oahu streams 

likely reflects slow breakdown of the 

compounds, persistent reservoirs of 

the compounds in soils, and continual 

delivery to streams. Organochlorine 

compounds are hydrophobic: they do 

not dissolve well in water but instead 

bind strongly to soil particles and are 

carried with eroded soils to streams by 

runoff. Once in streams, the soil-bound 

compounds dissolve in water to a slight 

degree but mostly remain suspended or 

settle to the streambed. From the water 

column or sediment, the compounds 

Figure 18. Tons of nutrients and suspended sediment are delivered to coastal 

waters by a single Oahu stream. Dissolved 

nitrogen and phosphorus account for the 

bulk of the nutrient load, much of it originating from ground-water inflow to the stream.

Additional Information

Oahu NAWQA surface water: http:

//hi.water.usgs.gov/nawqa/sw.html

USEPA surface-water standards: 

http://epa.gov/waterscience/standards

Hawaii water quality standards: 

http://www.state.hi.us/doh/

rules/11-54.pdf

selected streams under the USEPA Total 

Maximum Daily Load (TMDL) program 

of the Clean Water Act.

NAWQA sampling showed that 

concentrations of nutrients in urban 

Manoa Stream and agricultural-urban 

Waikele Stream consistently exceeded 

State water-quality standards by a factor 

of 3 or 4 (State of Hawaii, 2002). Even 

undeveloped, forested Waihee Stream 

consistently exceeded State standards 

for total nitrogen, total phosphorus, 

and dissolved nitrogen. Standards for 

suspended solids were consistently 

exceeded at urban Manoa Stream and 

sometimes exceeded at agriculturalurban Waikele Stream and forested 

Waihee Stream.

Annual amounts (or loads) of 

nutrients and suspended sediment carried from the Waikele Stream basin to 

coastal waters were estimated at about 

28 tons of dissolved nitrogen, 3.5 tons 

of dissolved phosphorus, and 4,300 tons 

of suspended sediment, respectively 

(fig. 18; Tomlinson and Miller, in press). 

Nutrients also enter Hawaiian coastal 

waters from numerous other streams, as 

well as from ground-water discharge. 

In fact, submarine discharge of nutrients 

to the ocean may far exceed nutrients 

delivered by stream runoff, as indicated 

by elevated concentrations of nutrients 

in Oahu ground water. Nutrients and 

suspended sediment are a management 

1

10

100

1,000

10,000

Dissolved nitrogen

Total nitrogen

Dissolved phosphorus

Total phosphorus

Suspended sediment

ANNUAL LOAD, IN TONS

Waikele Stream

(mixed agricultural

and urban land use)
Major Findings 15

may be absorbed by plants or ingested 

by invertebrates and fish. Streams can 

transport significant amounts of dissolved or sediment-bound chemicals 

to nearshore coastal waters, a major 

concern in island ecosystems. Although 

little can be done about present-day 

concentrations in soils, controlling soil 

erosion could reduce the quantities of 

contaminated sediment entering streams 

and, ultimately, estuaries and nearshore 

marine waters. 

Organochlorine compounds 

and SVOCs in sediment were 

strongly associated with urban 

land use

Land use largely determines what 

compounds are used in a given area, as 

well as the concentrations at which they 

are detected in the environment. For 

example, more organochlorine compounds (as many as 15) were detected 

in streambed sediments and fish tissue 

at urban and mixed land-use sites than 

at agricultural or forested sites (fig. 19). 

This is because organochlorine pesticides and polychlorinated biphenyls 

(PCBs) are primarily urban-use chemicals. Chlordane compounds were the 

most frequently detected organochlorine compounds at urban sites (present 

in 100 percent of sediment and fish 

samples), followed by dieldrin, DDT 

compounds, and total PCBs (Appendix, 

p. 29–30). Chlordane and dieldrin were 

not detected at agricultural or forested 

sites, again because they are used in 

Hawaii as urban termiticides. DDT compounds were detected in fish tissue and 

streambed sediments at agricultural sites 

(Brasher and Wolff, 2004).

Semivolatile organic compounds 

(SVOCs) were detected in streambed 

sediment at nearly every urban and 

mixed land-use site (Appendix, p. 30). 

SVOCs are used for a wide variety of 

functions, and some are nearly ubiquitous in the environment (Lopes and 

Furlong, 2001; Van Metre and others, 

2000). Urban and agricultural-urban 

sites had the highest number of SVOCs 

detected, as many as 30 of the 65 compounds analyzed (Brasher and Wolff, 

2004). Only one SVOC was detected at 

an agricultural site, and between zero 

and four at forested sites. Of the SVOC 

subclasses, phthalates were most commonly found in areas of residential land 

use. Phthalates have been used in paint, 

construction materials, wood preservatives, disinfectants, and as plasticizers 

in a variety of household items including appliances, furnishings, and food 

containers and wrappings (Smith and 

others, 1988). Polyaromatic hydrocarbons (PAHs) mainly occurred in areas 

of industrial and commercial land use. 

PAHs are associated with incomplete 

combustion, such as from vehicle 

exhaust, waste incinerators, and—notably in Hawaii—burning sugarcane. 

PAHs also are present in mothballs, pesticides, dyes, synthetic resins, solvents, 

and lubricants.

Organochlorine compounds 

accumulate in fish and may be 

transferred to fish-eating birds 

and wildlife

Chemicals in water and sediment 

can be taken up and accumulate in tissues of invertebrates 

and fish. Chemical concentrations tended to be higher in 

fish tissue than in sediment on 

Oahu. For example, certain 

organochlorine contaminants—DDT, chlordane, and 

dieldrin—were as much as 

ten- or a hundredfold more 

concentrated in fish than in 

sediment (Appendix, p. 29). 

Contaminated fish can pose 

Figure 19. Streambed sediment and fish tissue from 

urban streams contained the greatest numbers of 

organochlorine compounds (including PCBs).

0

2

4

6

8

10

12

14

16

AGRICULTURAL LAND

URBAN

LAND

MIXED

AGRICULTURAL

AND URBAN LAND

FORESTED LAND

NUMBER OF COMPOUNDS DETECTED

MAXIMUM AVERAGE

MINIMUM

SEDIMENT

FISH

risks to fish-eating birds and wildlife and 

ordinarily might present a human-health 

risk. However, stream fish generally 

are not consumed on Oahu, and warnings against consumption are posted at 

contaminated streams. 

Organochlorine compounds 

and SVOCs exceeded aquaticlife and wildlife guidelines in 

streambed sediment and fish

Chemical concentrations in many 

sediment and fish samples exceeded 

guidelines designed to protect aquatic 

life (Canadian Council of Ministers of 

the Environment, 1999) and fish-eating 

wildlife (Newell and others, 1987). Of 

the organochlorine compounds, chlordane, dieldrin, and heptachlor epoxide 

consistently exceeded guidelines in 

urban streams (appendix, p. 29–30; 

Brasher and Wolff, 2004). Total DDT 

(o,p'- and p,p'-DDT, and breakdown 

products DDD and DDE) exceeded 

wildlife guidelines in fish at 33 percent 

of agricultural sites and 10 percent of 

agricultural-urban sites. DDE exceeded 

the aquatic-life guideline in sediment 

at the only agricultural site sampled for 

sediment, at 43 percent of agriculturalurban sites, and at 17 percent of urban 

sites. Total PCBs exceeded the wildlife 

guideline in fish at 12 percent of urban 

sites and 20 percent of agriculturalurban sites and exceeded the aquatic-life 

guideline in sediment at 17 percent of 

urban sites. Very few SVOCs have established aquatic-life guidelines. The PAHs 

benzo(a)anthracene, phenanthrene, and 

pyrene exceeded aquatic-life guidelines in sediment at one urban and one 

agricultural-urban site, and anthracene 

and chrysene exceeded guidelines at one 

urban site (Appendix, p. 30).

It is difficult to assess what effects 

the observed chemical concentrations 

in sediment and fish might have on 

local aquatic life. One might attribute a 

paucity of certain types of fish or invertebrates to chemical contamination, but 

other factors such as temperature, flow 

volume and depth, or predation could 

have equal or greater importance. Investigation of physical abnormalities and 
16 Water Quality on the Island of Oahu, Hawaii, 1999–2001

reproductive-cycle disturbances would 

be needed to define chemical influences 

on aquatic life, whereas ecological 

surveys would be needed to better define 

effects of physical habitat disturbances 

and interspecies competition.

Human activities elevate trace 

elements in stream sediments

Concentrations of some trace 

elements in streambed sediments were 

higher in developed basins than in 

undeveloped forested basins, suggesting human sources of those elements. 

Contamination was greatest at urban 

sites for barium, cadmium, lead, tin, and 

zinc; arsenic contamination was greatest 

at agricultural sites (fig. 20). The mean 

concentration of lead in urban sediment 

samples was 35 times higher than the 

mean concentration at forested sites. 

Possible urban sources of trace elements 

include vehicular traffic (lead from 

leaded gasoline; barium, cadmium, and 

zinc from tire wear), batteries and paint 

(lead), and galvanized metal (zinc). A 

possible source of arsenic is fertilizer, 

in which arsenic is a common impurity. 

Probable Effect Level (PEL) aquatic-life 

guidelines for sediment were exceeded 

by lead and zinc at urban sites and 

arsenic at agricultural sites (fig. 21). 

Leaded gasoline and lead-based paint 

were phased out in the 1970s, but lead 

persists in soils and will continue to 

enter Oahu’s streams with sediment in 

runoff (DeCarlo and Anthony, 2002). 

Chromium, cobalt, copper, nickel, 

and vanadium varied little by land use; 

their presence in sediments is due to 

natural abundance in volcanic rocks and 

soil and not to human contamination. 

Concentrations of chromium, copper, 

and nickel in all Oahu sediment samples 

were in the upper 25 percent of concentrations from 1,297 NAWQA samples 

nationwide. Chromium concentrations 

exceeded aquatic-life guidelines for 

sediments in all Oahu samples, ranging 

from 3 to 7 times the PEL guideline. 

Copper concentrations exceeded the 

PEL guideline in more than two-thirds 

of Oahu samples.

Stream Ecology

Urban alteration of stream 

habitat has adversely affected 

native aquatic species

Evidence of degradation in biological communities—aquatic invertebrates 

and fish—includes the elevated abundance of nonnative and pollution-tolerant taxa. Physical habitat disturbance 

has affected Oahu watersheds as much 

as, or more than, chemical degradation. 

Improvements to stream quality will 

require management of physical alterations to landscapes and stream habitats, 

in addition to management of nonpointsource pollution runoff. 

Stream ecology differed substantially among Oahu streams, judging 

from assessments of instream and 

riparian habitat conditions, and species 

composition and abundance of invertebrates, fish, and algae (see map, p. 20). 

Guidelines for Protection of Aquatic Life and Wildlife

Contaminant concentrations in streambed sediment were compared with the 

Canadian Sediment Quality Guidelines (CSQG) for the protection of aquatic 

life (Canadian Council of Ministers of the Environment, 1999). The Probable 

Effect Level (PEL) defines the level above which adverse effects to biota are 

expected to occur frequently. The guidelines are based on chronic (long-term) 

effects of individual contaminants on aquatic invertebrates. Contaminants in 

fish were compared with the New York State Department of Environmental 

Conservation (NYSDEC) guidelines for the protection of birds and wildlife 

such as mammals that consume fish (Newell and others, 1987). The NYSDEC 

guidelines are based on analyses of whole fish, not fillets. 

Although similar standards have not been established nationally or in Hawaii, 

the Canadian and New York guidelines have been adopted in the NAWQA 

Program to flag cautionary concentrations of trace elements, organochlorine 

pesticides, and SVOCs that may adversely affect aquatic organisms or wildlife. 

Limitations of these guidelines are that they have been established only for a 

small number of constituents, the toxicities of compound mixtures and breakdown products generally are not considered, and effects such as endocrine disruption and unique responses of sensitive individuals have not been assessed.

Figure 20. Concentrations of several 

trace elements in streambed sediment 

were elevated in comparison to forested 

sites (where the enrichment factor equals 

1). Cadmium and lead were highest at 

urban sites, arsenic at agricultural sites.

1

10

100

Arsenic

Barium

Cadmium

Lead

Tin

Zinc

ELEMENT

ENRICHMENT FACTOR

URBAN

MIXED AGRICULTURAL - URBAN

AGRICULTURE

0.1

1

10

100

1,000

Chromium

Copper ArsenicCadmium Lead Zinc

ELEMENT

MEAN CONCENTRATION, IN

MILLIGRAMS PER KILOGRAM

(DRY WEIGHT)

URBAN MIXED AGRICULTURAL - URBAN

AGRICULTURE FORESTED

Aquatic-life guideline

EXPLANATION

Figure 21. Arsenic, lead, and zinc exceed 

aquatic-life guidelines in streambed sediments because of agricultural and urban 

contamination. Chromium and copper 

exceed guidelines because of high natural 

abundance in rocks and soil.

Additional Information

Oahu NAWQA bed sediment and 

fish tissue: http://hi.water.usgs.

gov/nawqa/bst.html
Major Findings 17

Concentrations of organic compounds in sediment and 

fish were among the highest in the nation

Concentrations of organic compounds 

in streambed sediment and fish tissue on 

Oahu were mostly in the upper one-half of 

the national range for more than a thousand 

NAWQA stream sites sampled nationwide. Total organochlorine compounds in 

sediment and fish from urban and mixed 

land-use sites typically were in the highest 

25 percent of the national range. Total PCBs 

in sediment were in the highest 15 percent 

at five sites (three urban and two agricultural-urban), but were not detected at any 

other sites. Total PAH concentrations in 

sediment were in the highest 25 percent of 

the national range at eight sites and in the 

middle half at six other sites. At undeveloped forested sites, organochlorine pesticides, PCBs, and PAHs were not detected 

in most samples, placing Oahu in the lowest 

part of the national concentration range for 

undeveloped stream basins.

Of the organochlorine pesticides, 

concentrations of the termiticides dieldrin 

and chlordane were in the highest 5 percent 

nationally in sediment at urban Oahu sites 

and were highest in the Nation at one site 

(dieldrin in sediment and total chlordane 

in sediment and fish at Nuuanu Stream). 

Total DDT concentrations in sediment also 

were in the highest 5 percent of the national 

range at two agricultural-urban sites and 

an agricultural site, where it was the only 

organochlorine pesticide detected.

Concentrations of organochlorine pesticides in fish over time

Following a trend that has been observed across the country (Schmitt and others, 1990; Nowell and others, 1999; Wong 

and others, 2000), concentrations of organochlorine compounds in stream fish on Oahu declined substantially from maximum values in the 1970s to 1998–2000 values observed by NAWQA sampling (Brasher and Anthony, 2000; Brasher and 

Wolff, 2004). Although early studies used different analytical methods and slightly different fish species than the NAWQA 

study, the data are useful for looking at trends over time. At urban Manoa Stream, total DDT in fish declined 62-fold 

from 1,870 to 30 μg/kg (micrograms per kilogram), total chlordane declined sevenfold (6,360 to 885 μg/kg), and dieldrin 

declined eightfold (9,100 to 885 μg/kg). Despite an initial decline, dieldrin concentrations in fish from Manoa Stream 

are still similar to those measured in the 1980s. At agricultural-urban Waikele Stream, total DDT in fish declined almost 

200-fold (2,510 to 43 μg/kg), total chlordane declined 67-fold (470 to 7 μg/kg), and dieldrin declined 77-fold (770 to 

10 μg/kg). Although total PCBs were present in fish from Manoa and Waikele Streams in the 1970s (1,700 and 1,200 μg/

kg, respectively) and 1980s, no PCBs were detected in 1998–2000. However, PCBs were detected in fish from other freshwater bodies on Oahu: Nuuanu Stream, South Fork Kaukonahua Stream, Ala Wai Canal, and Wahiawa Reservoir (Lake 

Wilson).

Concentrations of organochlorine compounds in streambed sediment were high on Oahu and in other urban areas. 

Organic compounds in streambed sediment at urban Oahu stream 

sites were in the highest 25 percent of the national range.

Sum of organochlorine pesticide concentrations

Urban Streams

Aquatic-life guidelines

Bold outline indicates exceedance by

one or more organochlorine pesticides

Highest 25 percent nationwide

Second highest 25 percent

Lowest 50 percent (all with no detections)

Urban areas

(shown only for conterminous United States)

EXPLANATION

158°

158°10'

21°40'

21°30'

21°20'

157°50'

157°40'

EXPLANATION

LAND USE

Agriculture

Urban

Other (mostly forest)

Highest 25 percent 25 percent 15 percent nationwide

Second highest 25 percent 55 percent -- nationwide

Lowest 50 percent 20 percent 85 percent nationwide

0 5 10 MILES

0 5 10 KILOMETERS

Range

PAHs PCBs

OCs

Total organochlorine pesticides (OCs) Total polyaromatic hydrocarbons (PAHs)Total polychlorinated biphenyls (PCBs)
18 Water Quality on the Island of Oahu, Hawaii, 1999–2001

Compared to forested streams (fig. 22), 

urban and mixed agricultural-urban sites 

typically were channelized (fig. 23) and 

had less riparian vegetation, less largeboulder habitat, and siltier substrates). 

High proportions of impervious surfaces 

in urban areas can increase runoff, 

and land clearing for construction can 

promote soil erosion and siltation. Lack 

of overhanging trees reduces shade, 

warming streamwater and causing large 

temperature fluctuations. At urban 

Kaneohe Stream, the average water 

temperature was about 9 degrees Celsius 

higher than at forested Punaluu Stream, 

and the seasonal temperature range was 

about 10 degrees as compared to only 

4 degrees at Punaluu (fig. 24). 

Few native fish were collected

Only two of five stream fishes 

native to Hawaii were found in considerable numbers on Oahu: oopu akupa 

(Hawaiian name), or Eleotris sandwicensis (latin name); and oopu naniha 

(Stenogobius hawaiiensis) (fig. 25). 

These species are relatively tolerant to 

large variations in environmental conditions such as temperature, turbidity, 

and siltation. Native fishes least tolerant 

of habitat degradation—oopu alamoo

(Lentipes concolor) and oopu nopili

(Sicyopterus stimpsoni)—were not 

found in the streams sampled, and the 

fifth native species, oopu nakea (Awaous 

guamensis), was occasionally found. 

Two native and four introduced species 

of crustaceans were found. Two species 

were present primarily at forested sites: 

the native atyid shrimp opae kalaole

(Atyoida bisulcata) and the introduced 

Tahitian prawn (Macrobrachium lar). 

The other native crustacean, Macrobrachium grandimanus, is an estuarine 

species and was found only near stream 

mouths.

Introduced fishes are more 

tolerant of altered, degraded 

habitat than native fishes

Surveys on the islands of Oahu, 

Kauai, and Hawaii show that urban 

land use is associated with the highest 

Figure 24. Urban streams are shallower 

and less shaded than forested streams, 

causing higher water temperatures and 

larger temperature fluctuations.

Figure 23. A channelized urban stream. 

(Photograph by Anne Brasher, U.S. Geological Survey.)

Figure 25. Native fish were rarely found 

in streams on Oahu. Those found tended 

to be of the more tolerant species such as 

oopu naniha (Stenogobius hawaiiensis). 

(Photograph by Eric Nishibayashi.) 

1999

MAXIMUM DAILY STREAM

TEMPERATURE, IN

DEGREES CELSIUS

2000

19

21

23

25

27

29

31

33

35

A M J J A S O N D J F M A M J J A S

URBAN (Kaneohe Stream)

missing

data

FOREST (Punaluu Stream)

abundances of nonnative species, such 

as green swordtails, mollies, and jewel 

cichlids, which have been introduced for 

mosquito control or have been released 

from home aquariums (Devick, 1991). 

Habitat characteristics associated with 

urbanization favor nonnative species that 

tend to be tolerant generalists (Brown 

and others, 1999). Forested stream 

basins on Kauai had the greatest relative 

abundance of native fishes, whereas 

heavily urbanized stream basins on 

Oahu had the least.

Habitat alteration inhibits 

upstream migration and downstream dispersal of native fish, 

shrimp, and snails

Native fish, shrimp, and snails in 

Hawaii are primarily amphidromous 

(they have a marine larval life-stage). 

Adults lay eggs in streams, the eggs 

hatch, and the larvae drift to the ocean 

where they mature for 4 to 7 months 

before returning to a stream. Distribution 

of these animals in streams is affected 

by spatial and year-to-year variability in 

recruitment (their ability to return from 

ocean to stream mouth) and by their 

ability to migrate upstream unimpeded 

(Kinzie, 1988, 1990).

The more urbanized streams, such 

as Manoa, produced the fewest drifting 

fish and shrimp larvae, whereas forested 

streams, such as Punaluu, produced the 

most larvae (Luton and Brasher, 2001). 

The most frequently collected native 

larval species, oopu akupa (Eleotris 

sandwicensis) and the crustaceans Macrobrachium sp., are tolerant of a wide 

range of environmental conditions.

Stream channels have been altered 

most near their mouths for flood control. 

Lower stream reaches are essential pathways for native amphidromous species 

requiring downstream dispersal of larvae 

and upstream migration of post-larval 

juveniles or adults. Diversions and channelization may block these pathways and 

inhibit migrations required for completion of the life cycle. Native species 

also are subject to substantial predation 

(commonly by introduced species) as 

they attempt to settle in altered habitat or 

Figure 22. Measuring habitat characteristics in a forested stream. (Photograph by 

Anne Brasher, U.S. Geological Survey.) 
Major Findings 19

migrate through to upstream reaches of 

streams (Brown and others, 1999).

Benthic invertebrates reflect 

degraded stream quality

Urban and agricultural activities 

can degrade habitat quality, alter natural 

streamflows, and increase contaminants and temperatures, all of which 

are reflected in invertebrate community 

structure. Smaller numbers of invertebrates but greater numbers of invertebrate species were found at urban and 

mixed agricultural-urban stream sites on 

Oahu than at undeveloped forested sites 

(Brasher and others, in press). This pattern reflects the naturally low diversity 

of native invertebrate species that would 

be expected in unaltered Hawaiian 

streams and the proliferation of nonnative species that are more tolerant 

of physically and chemically degraded 

environments in the more heavily developed and urbanized basins.

Distinct assemblages of invertebrates were found in streams with 

different amounts of habitat degradation 

and consequently can be used to indicate 

stream quality (by equating assemblages 

at undeveloped forested sites with good 

quality). At forested sites, insects typically made up more than 80 percent of 

the invertebrates present, and molluscs 

(clams and snails) were few (fig. 26). At 

urban and agricultural-urban sites with 

degraded environmental quality, invertebrate communities typically contained 

about 50 percent insects and 30 percent 

molluscs. True flies (Diptera) and caddisflies (Trichoptera; fig. 27) were the 

most common insects at all sites, with 

forested sites dominated by caddisflies 

and urban and agricultural-urban sites 

dominated by true flies.

Most identified invertebrates 

were nonnative

Hawaiian streams have far fewer 

native species than continental streams, 

even under undisturbed conditions. A 

total of 75 invertebrate species were 

identified at 10 sites on Oahu. Of 

these, 5 percent were native, 48 percent 

were introduced, and the remaining 

47 percent were undetermined (for a 

species list see Brasher and others, in 

press). Common, widespread orders 

of insects such as mayflies (Ephemeroptera), stoneflies (Plecoptera), and 

caddisflies (Trichoptera) are absent 

from native biota in Hawaii (Howarth 

and Polhemus, 1991). Historically, 

the geographic isolation of Hawaii 

prevented large-scale colonization by 

aquatic invertebrates, and most native 

stream species probably originated from 

marine ancestors.

Figure 27. Many invertebrates, such as 

caddisflies (Trichoptera), live in the stream 

as larvae, but the adults are terrestrial 

(flying insects in this case). (Photograph by 

Mark Vinson.)

Figure 26. Stream-habitat quality can 

be inferred from ratios of less-tolerant to 

more-tolerant invertebrates, for example 

insect-to-mollusc and caddisfly-to-truefly (Trichoptera-to-Diptera) ratios. Higher 

proportions of insects or caddisflies were 

associated with less-degraded streams, 

whereas lower proportions reflect degradation of the stream environment.

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Mollusc abundance was strongly 

associated with urban land use. 

Although a number of native freshwater 

molluscs are known in Hawaii (including neritid limpets and lymnaeid snails), 

they tend to inhabit the less disturbed 

streams, and none were found during 

this study. The most abundant molluscs 

collected were the pan-tropical thiarid 

snails, the introduced clam Corbicula 

fluminea, and the limpet Ferrissia 

sharpi, whose status as native or nonnative is uncertain.

Three nonnative crustaceans were 

collected primarily at urban and agricultural-urban sites: a recently introduced 

shrimp Neocaridina denticulata, an 

amphipod Hyalella azteca, and a crayfish Procambarus clarkii. The native 

shrimp Atyoida bisulcata was found 

only at undeveloped forested sites.

Additional Information

Oahu NAWQA aquatic ecology: 

http://hi.water.usgs.gov/nawqa/eco.

html
20 Water Quality on the Island of Oahu, Hawaii, 1999–2001

Study Unit Design

The Oahu NAWQA study was designed to assess physical, chemical, and biological characteristics of surface and 

ground water by means of nationally consistent protocols and 

methods (Gilliom and others, 1995). Thus, findings from the 

Oahu Study Unit can be compared to findings in other Study 

Units and placed in a national context.

Ground-Water Chemistry

Randomly selected public-supply wells were sampled to 

characterize water quality in major drinking-water aquifers 

(volcanic-rock aquifers) in central Oahu and Honolulu. Monitor wells also were sampled to assess effects of human activities on recently recharged ground water; for example, effects 

from recent conversion of sugarcane plantations to diversified 

crops and residential areas.

Waihee). At most other sites, one water sample was collected 

to coincide with sediment samples, fish samples, or ecologic 

assessments.

Stream Chemistry

Sampling was concentrated in three representative areas: 

central Oahu with varied land uses (agricultural, residential 

urban, military, and forested), windward Oahu (mostly forested, with some residential urban and agricultural use), and 

Honolulu (high-density urban).

Assessments focused on how water quality varies in 

relation to land use and the natural setting. Contaminants were 

analyzed in samples from the water column, bed sediment, 

and whole fish collected at 3 agricultural sites, 8 urban sites, 

12 mixed land-use (agricultural-urban) sites, and 11 forested 

sites. Frequent water samples were collected (monthly and 

during storms) at three stream sites (Manoa, Waikele, and 

Stream Ecology

Ecologic assessments focused on describing how land 

use affects biological communities. Assessments measured 

instream and riparian habitat conditions and species composition and abundance of invertebrates, fish, and algae. Watercolumn samples also were collected at each stream ecology 

site, and bed-sediment and fish-tissue samples were collected 

at six of the sites.

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Kaukonahu a Str

Kipapa

Wa

Str

ikele Str

Waiawa Str

Kalihi Str

Nuuanu Str

Manoa

Maunawili Str

Waihee Str

Pu naluu Str

Kaluanui Str

Op aeula Str

Waimano Str

Poamoho Str

Luluku Str

Ala Wai Canal

Wahiwa Res

Koloa Gl

Waimanalo Str

Kaneohe S t

Keaah r

ala S tr

North Fork

Sou th Fork

Kalauao Str

Waiahole Str

Kawainui Can Waiake akua Str

Waikakalaua Str

Stream Chemistry

158°

158°10'

21°40'

21°30'

21°20'

157°50'

157°40'

EXPLANATION

LAND USE

Agriculture

Urban

Other (mostly forest)

DATA COLLECTION SITES

Water column

Basic and intensive sampling

Sampled runoff component only

Bed sediment and/or fish tissue

0 5 10 MILES

0 5 10 KILOMETERS

Stream Ecology

158°

158°10'

21°40'

21°30'

21°20'

157°50'

157°40'

EXPLANATION

LAND USE

Agriculture

Urban

Other (mostly forest)

ECOLOGIC ASSESSMENT SITE

0 5 10 MILES

0 5 10 KILOMETERS
Study Unit Design 21

Summary of data collection on the island of Oahu

Study

component What data are collected and why Types of sites sampled Number of sites sampled

Sampling frequency 

and period

Ground-Water Chemistry

Major aquifer 

study

Nutrients, major ions, pesticides, volatile 

organic compounds, trace elements, and 

radon in deep, unconfined, volcanic-rock 

aquifer to assess the quality of Oahu’s 

main drinking-water aquifer.

Existing public-supply wells 

widely distributed throughout the 

central Oahu ground-water flow 

system.

30 Once; 2000

Special study Nutrients, major ions, pesticides, volatile 

organic compounds, and trace elements 

in deep, unconfined, volcanic-rock aquifer to assess anthropogenic effects on 

central Oahu ground water.

Existing monitor wells that sample 

young, newly recharged ground 

water in central Oahu.

15 Once; 2001

Stream Chemistry

Water column 

sites, basic

Streamflow and general water-quality 

properties and constituents (dissolved 

oxygen, pH, alkalinity, specific conductance, temperature, nutrients, major ions, 

organic carbon, and suspended sediment) 

to assess occurrence and concentration.

Forested site in windward Oahu 

(Waihee Stream).

1 Monthly plus storms 

March 1999 – June 

2001

Water column 

sites, intensive

Streamflow and general waterquality properties and constituents as 

above plus trace elements and pesticides 

at Waikele and Manoa, and volatile 

organic compounds at Manoa only to 

assess occurrence and concentration.

Urban land-use site in Honolulu 

(Manoa Stream), and a mixed 

agricultural-urban land-use site in 

central Oahu (Waikele Stream).

2 Monthly plus storms 

March 1999 – June 

2001

Water column 

site, runoff 

component 

only

Streamflow and general water-quality 

properties and constituents plus pesticides and VOCs to characterize stream 

water before it enters the downstream 

gaining reach at Waikele Stream site.

Mixed land-use site upstream from 

the Waikele intensive site, which 

gains from ground-water inflow.

1 Three times during 

fair-weather base 

flow and one storm 

in 2001

Contaminants 

in bed sediment

Trace elements and (or) organic compounds to determine occurrence and 

distribution related to land use.

Depositional zones of all three 

water-column basic and intensive 

sites and 22 additional sites.

25 Once; 1998 and 2000

Contaminants 

in whole fish

Trace elements and (or) organic compounds to assess occurrence and distribution related to land use.All but one of the bed-sediment 

sites and three additional sites.

27 Once; 1998, and 

2000–2001

Stream Ecology

Ecologic 

assessments

Invertebrate, algae, and fish communities, streamflow, water chemistry, and 

instream and riparian habitat conditions 

to assess land-use effects on aquatic communities. Algae data were not available 

for inclusion in this report.

All three water-column basic and 

intensive sites, three of the bedsediment sites, and four additional 

forested sites.

10 One reach at each 

site in 1999; and, at 

Waihee Stream, three 

reaches in 2000 and 

one reach in 2001.
22 Water Quality on the Island of Oahu, Hawaii, 1999–2001

References Cited

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Griem, H., 1998, Maximum workplace concentration values 

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p. 1291–1293. 

Brasher, A.M.D., and Anthony, S.S., 2000, Occurrence of 

organochlorine pesticides in streambed sediment and fish 

from selected streams on the island of Oahu, Hawaii, 1998: 

U.S. Geological Survey Fact Sheet 140–00, 6 p.

Brasher, A.M.D., and Wolff, R.H., 2004, Relations between 

land use and organochlorine pesticides, PCBs, and semivolatile organic compounds in streambed sediment and fish 

tissue on the island of Oahu, Hawaii: Archives of Environmental Contamination and Toxicology, v. 46, p. 385–398.

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of Oahu, Hawaii: U.S. Geological Survey Water-Resources 

Investigations Report 03–4256.

Brown, L.R., Brasher, A.M., Harvey, B.C., and Matthews, M., 

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Hawaii, in Claudi, R., and Leach, J.H., eds., Nonindigenous 

freshwater organisms—Vectors, biology, and impacts: Boca 

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guidelines, 1999, accessed July 10, 2003, at 

http://www.ec.gc.ca/ceqg-rcqe

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S., and Vakharia, D.D., 1998, Human health and chemical 

mixtures—An overview: Environmental Health Perspectives, v. 106, supplement 6, p. 1263–1270.

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Raton, Fla., CRC Lewis Publishers, 694 p.

DeCarlo, E.H., and Anthony, S.S., 2002, Spatial and temporal 

variability of trace element concentrations in an urban subtropical watershed, Honolulu, Hawaii: Applied Geochemistry, v. 17, p. 475–492.

Devick, W.S., 1991, Patterns of introductions of aquatic 

organisms to Hawaiian fresh waters, in New directions in 

research, management and conservation of Hawaiian freshwater stream ecosystems: Proceedings of the 1990 Symposium on Freshwater Stream Biology and Fisheries Management, State of Hawaii, Department of Land and Natural 

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Fuhrer, G.J., Gilliom, R.J., Hamilton, P.A., Morace, J.L., 

Nowell, L.H., Rinella, J.F., Stoner, J.D., and Wentz, D.A, 

1999, The quality of our Nation’s waters—Nutrients and 

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References Cited 23

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24 Water Quality on the Island of Oahu, Hawaii, 1999-2001

Glossary

Anthropogenic–A condition that is the result of, or is influenced by, human activity. 

Aquatic-life guidelines–Specific levels of water or sediment 

quality which, if reached, may adversely affect aquatic life. 

These are nonenforceable guidelines issued by a governmental 

agency or other institution. 

Aquifer–A water-bearing layer of soil, sand, gravel, or rock 

that will yield usable quantities of water to a well. 

Background concentration–A concentration of a substance 

in a particular environment that is indicative of minimal influence by human (anthropogenic) sources. 

Base flow–Sustained, low flow in a stream; ground-water 

discharge is the source of base flow in most places. 

Bed sediment–The material that temporarily is stationary in 

the bottom of a stream or other watercourse. 

Benthic–Refers to plants or animals that live on the bottom of 

lakes, streams, or oceans. 

Concentration–The amount or mass of a substance present in a given volume or mass of sample. Usually expressed 

as micrograms/liter (water sample) or micrograms/kilogram 

(sediment or tissue sample). 

Confined aquifer (artesian aquifer)–An aquifer that is completely filled with water under pressure and that is overlain by 

material that restricts the movement of water. 

Contamination–Degradation of water quality, caused by 

human activity, compared to original or natural conditions. 

Denitrification–A process by which oxidized forms of nitrogen such as nitrate (NO3

–

) are reduced to form nitrites, nitrogen oxides, ammonia, or free nitrogen: commonly brought 

about by the action of denitrifying bacteria and resulting in the 

escape of nitrogen to the air. 

DDT–Dichloro-diphenyl-trichloroethane. An organochlorine 

insecticide no longer registered for use in the United States. 

Dissolved constituent–Operationally defined as a constituent 

that passes through a 0.45-micrometer filter. 

Drainage basin–The part of the surface of the Earth that contributes water to a stream through overland runoff, including 

tributaries and impoundments. 

Drinking-water standard or guideline–A threshold concentration in a public drinking-water supply, designed to protect 

human health. Standards are enforceable maximum contaminant levels (MCLs) for public water systems designed to protect the public welfare. Guidelines have no regulatory status 

and are issued in an unenforceable advisory capacity only. 

Ecosystem–The interacting populations of plants, animals, 

and microorganisms occupying an area, plus their physical 

environment. 

Eutrophication–The process by which water becomes 

enriched with plant nutrients, most commonly phosphorus and 

nitrogen. 

Fumigant–A substance or mixture of substances that produces 

gas, vapor, fume, or smoke intended to destroy insects, bacteria, or rodents. 

Habitat–The part of the physical environment where plants 

and animals live. 

Herbicide–A chemical or other agent applied for the purpose 

of killing undesirable plants. See also Pesticide. 

Insecticide–A substance or mixture of substances intended to 

destroy or repel insects. See also Pesticide.

Intermittent stream–A stream that flows only when it 

receives water from rainfall runoff or springs, or from some 

surface source such as melting snow. 

Invertebrate–An animal having no backbone or spinal 

column.

Load–General term that refers to a material or constituent in 

solution, in suspension, or in transport; usually expressed in 

terms of mass or volume. 

Nitrate–An ion consisting of nitrogen and oxygen (NO3

–

). 

Nitrate is a plant nutrient and is very mobile in soils. 

Nonpoint source–A pollution source that cannot be defined as 

originating from discrete points such as pipe discharge. Areas 

of fertilizer and pesticide applications, atmospheric deposition, 

manure, and natural inputs from plants and trees are types of 

nonpoint source pollution. 

Nutrient–Element or compound essential for animal and plant 

growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium. 

Organochlorine compound–Synthetic organic compounds 

containing chlorine. Examples include organochlorine insecticides, polychlorinated biphenyls, and some solvents containing chlorine. 

Perennial stream–A stream that normally has water in its 

channel at all times. 

Pesticide–A chemical applied to crops, rights-of-way, lawns, 

or residences to control weeds, insects, fungi, nematodes, 

rodents, or other pests. 

Phosphorus–A nutrient essential for growth that can play a 

key role in stimulating aquatic growth in lakes and streams. 

Reach–A continuous part of a stream between two specified 

points along its length. 

Recharge–Water that infiltrates the ground and reaches the 

saturated zone. 
Glossary 25

Relative abundance–The number of organisms of a particular 

kind present in a sample relative to the total number of organ-

isms in the sample. 

Riparian–Areas adjacent to rivers and streams with a high 

density, diversity, and productivity of plant and animal species 

relative to nearby uplands. 

Runoff–Excess rainwater or snowmelt that is transported to 

streams by overland flow, tile drains, or ground water. 

Semivolatile organic compound (SVOC)–Operation-

ally defined as a group of synthetic organic compounds 

that are solvent-extractable and can be measured by gas 

chromatography/mass spectrometry. SVOCs include phenols, 

phthalates, and polycyclic aromatic hydrocarbons (PAHs). 

Sole-source aquifer–A ground-water system that supplies at 

least 50 percent of the drinking water to a particular human 

population; the term is used to denote special protection 

requirements under the Safe Drinking Water Act and may be 

used only by approval of the U.S. Environmental Protection 

Agency. 

Suspended (as used in tables of chemical analyses)–The 

amount (concentration) of undissolved material in a watersediment mixture. It is associated with the material retained on 

a 0.45-micrometer filter. 

Total Maximum Daily Load (TMDL) –The maximum 

amount of a pollutant that a water body can receive and still 

meet water-quality standards, and an allocation of that amount 

to the pollutant’s sources.

Trace element–An element found in only minor amounts 

(concentrations less than 1.0 milligram per liter) in water or 

sediment; includes arsenic, cadmium, chromium, copper, lead, 

mercury, nickel, and zinc. 

Unconfined aquifer–An aquifer whose upper surface is a 

water table; an aquifer containing unconfined ground water. 

Volatile organic compounds (VOCs)–Organic chemicals 

that have a high vapor pressure relative to their water solu-

bility. VOCs include components of gasoline, fuel oils, and 

lubricants, as well as organic solvents, fumigants, some inert 

ingredients in pesticides, and some byproducts of chlorine 

disinfection. 
26 Water Quality on the Island of Oahu Hawaii, 1999–2001

Appendix—Water-Quality Data from the Island of Oahu, Hawaii, 

in a National Context

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Coordination with agencies and organizations in the Oahu Study Unit was integral to the success of 

this water-quality assessment. We thank those who served as members of our liaison committee. 

Federal agencies

U.S. Air Force, Hickam AFB 

U.S. Army Garrison Hawaii

U.S. Navy, Pearl Harbor 

USDA Forest Service

Natural Resources Conservation Service

U.S. Environmental Protection Agency 

U.S. Geological Survey, Pacific Island 

Ecosystem Research Center

State agencies

Hawaii Department of Agriculture

Hawaii Department of Business, 

 Economic Development, and Tourism

Hawaii Department of Health

Hawaii Department of Land and Natural

 Resources 

Office of Hawaiian Affairs

Local agencies

Honolulu Board of Water Supply 

Honolulu Department of Environmental

 Services 

Honolulu Department of Planning and

 Permitting

Universities

University of Hawaii 

Other public and private organizations

Ala Wai Canal Watershed Improvement

 Project

Hawaii Agriculture Research Center

Land Use Research Foundation

We thank the following organizations and individuals for contributing to this effort. 

For permission to sample and for logistical assistance: Honolulu Board of Water Supply; Honolulu Wastewater Treatment and 

Disposal Division; Hawaii Department of Transportation; Hawaii Department of Land and Natural Resources; U.S. Army Garrison 

Hawaii, Directorate of Public Works; U.S. Navy Public Works Center (Pearl Harbor); U.S. Air Force Environmental Flight (Hickam 

AFB); Del Monte Fresh Produce (Hawaii) Inc.; Dole Food Company Hawaii; Ewa Plains Water Development Corporation; Hawaii 

Country Club; JAC Hawaii, Inc.; Kamehameha Schools; Kyoya Company, Ltd.; The Queen’s Medical Center; Waiahole Irrigation Co.; 

Hoomaluhia Botanical Garden, Punaluu Community Association.

For assistance to ground-water studies: Daniel Masuno, Erwin Kawata, Charlie Roquero, and well operators, Honolulu Board of 

Water Supply. Bill Wong and Dan Chang, Hawaii Department of Health. Robert Boesch, Hawaii Department of Agriculture. Scott 

Myhre, Ron Tollison, and Greg Zabinski, The Queen’s Medical Center. Robert Stender, Eddie Wassman, Whitney Cobb, and Kenneth 

Tsuji, Kamehameha Schools. Calvin Oda and well operators, Del Monte Fresh Produce Hawaii. Jim Crittenden, Dole Food Company 

Hawaii. Dan Collins, Doonwood Engineering. Marty Heede, Sheraton Princess Kaiulani Hotel. Karen Maddox, Hawaii Country Club. 

Leighton Wong, Royal Kunia Golf Course. Rick McComb, U.S. Air Force. Tony Dilullo, Paul Eyre, Ron Soares, and well operators, 

U.S. Navy. Jon Fukuda and Monty Martin, U.S. Army. Nathan Punahele and Ron Soroos, Harding ESE, Inc. Mike Knight, Jack Kronen, and environmental technicians, URS Corporation. Steve Dollar, Marine Research Consultants.

For assistance to surface-water and ecology studies: Robert Boesch, Hawaii Department of Agriculture. Don Heacock, Glenn 

Higashi, and Mike Yamamoto, Hawaii Division of Aquatic Resources. June Harrigan, Susan Burr, Katina Henderson, and Dave 

Penn, Hawaii Department of Health. Phil Anderson, Tim Jones, Hal Richmond, Alison Sherwood, Sonia Stephens, and Milt Stetson, University of Hawaii. Adam Asquith, Sea Grant Hawaii. Arlene Pangelinan, Gordon Smith, and Chris Swenson, U.S. Fish and 

Wildlife Service. Sally Beavers, National Park Service. Terrell Kelley, Natural Resources Conservation Service. Charlie McDonald, 

National Tropical Botanical Gardens. Volunteers Donna Ashizawa, Jason Bazzano, Mehmet Boysal, Phil Dendel, Jake Douglas, 

Monica Furness, David Johnson, Morten Karnuth, Wendy Kunimitsu, Matt Monte, Jen O’Neill, Ramsay Taum, Anne Williams, and 

Ann Yokoyama.

U.S. Geological Survey employees and contractors aided in sampling and data analysis: Nate Adams, Marcael Ball, Greg Berman, Larry Brown, Wade Bryant, Jamie Carter, Eric DeCarlo, Chad Durkin, Brian Farm, Ron Fay, Steve Goodbred, Dan Hoover, 

Fritz Klasner, Allyson Kriney, Dennis LaPointe, Paige Little, Corene Luton, Dale Mikami, Cathy Munday, Craig Oberst, Todd Presley, 

Austin Seid, Wayne Shibata, Terry Short, Toby Vana, Julian Wayland, Chris Wellise, and Reuben Wolff. Karen Fields-Poasa and Luis 

Menoyo prepared the page layout and illustrations for this report, and Twyla Thomas, Martha Erwin, and Pixie Hamilton served as 

editors.

For providing outside technical reviews of this report, we thank Carl Evenson, University of Hawaii; John McHugh, Hawaii Farm 

Bureau Federation; and June Harrigan, State of Hawaii Department of Health.
Anthony and others— Water Quality on the Island of Oahu 

U.S. Geological Survey Circular 1239

National Water-Quality Assessment (NAWQA) Program

Island of Oahu

NAWQA

Honolulu

Kaneohe

Waianae

Wahiawa

Waipahu

Haleiwa