KW

Occurrence of Pesticides in Streams and Ground 

Water in the Puget Sound Basin, Washington, 

and British Columbia, 1996-98

<D

By G. C. Bortleson and J. C. Ebbert

X

BRITISH COLUMBIA

CANADA_ 

UNITED STATES

5 uget Sound Basin

National Water-Quality Assessment Study Unit

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 00-4118

Occurrence of Pesticides in Streams and Ground 

Water in the Puget Sound Basin, Washington, 

and British Columbia, 1996-98

By G. C. Bortleson and J. C. Ebbert

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 00-4118

Tacoma, Washington 

2000
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Geological Survey.

For additional information write to:

District Chief

U.S. Geological Survey

1201 Pacific Avenue, Suite 600

Tacoma, Washington 98402

Copies of this report can be purchased 

from:

U.S. Geological Survey 

Information Services 

Box 25286 

Federal Center 

Denver, CO 80225
FOREWORD

The mission of the U.S. Geological Survey 

(USGS) is to assess the quantity and quality of the earth 

resources of the Nation and to provide information that 

will assist resource managers and policymakers at 

Federal, State, and local levels in making sound 

decisions. Assessment of water-quality conditions and 

trends is an important part of this overall mission.

One of the greatest challenges faced by waterresources scientists is acquiring reliable information that 

will guide the use and protection of the Nation's water 

resources. That challenge is being addressed by Federal, 

State, interstate, and local water-resource agencies and 

by many academic institutions. These organizations are 

collecting water-quality data for a host of purposes that 

include: compliance with permits and water-supply 

standards; development of remediation plans for a 

specific contamination problem; operational decisions 

on industrial, wastewater, or water-supply facilities; and 

research on factors that affect water quality. An 

additional need for water-quality information is to 

provide a basis on which regional and national-level 

policy decisions can be based. Wise decisions must be 

based on sound information. As a society we need to 

know whether certain types of water-quality problems 

are isolated or ubiquitous, whether there are significant 

differences in conditions among regions, whether the 

conditions are changing over time, and why these 

conditions change from place to place and over time. 

The information can be used to help determine the 

efficacy of existing water-quality policies and to help 

analysts determine the need for and likely consequences 

of new policies.

To address these needs, the Congress appropriated funds in 1986 for the USGS to begin a pilot 

program in seven project areas to develop and refine the 

National Water-Quality Assessment (NAWQA) 

Program. In 1991, the USGS began full implementation 

of the program. The NAWQA Program builds upon an 

existing base of water-quality studies of the USGS, as 

well as those of other Federal, State, and local agencies. 

The objectives of the NAWQA Program are to:

 Describe current water-quality conditions for a 

large part of the Nation's freshwater streams, 

rivers, and aquifers.

 Describe how water quality is changing over time.

 Improve understanding of the primary natural and 

human factors that affect water-quality conditions.

This information will help support the development and evaluation of management, regulatory, and 

monitoring decisions by other Federal, State, and local 

agencies to protect, use, and enhance water resources.

The goals of the NAWQA Program are being 

achieved through ongoing and proposed investigations 

of more than 50 of the Nation's most important river 

basins and aquifer systems, which are referred to as 

study units. These study units are distributed throughout 

the Nation and cover a diversity of hydrogeologic 

settings. More than two-thirds of the Nation's freshwater use occurs within these study units and more than 

two-thirds of the people served by public water-supply 

systems live within their boundaries.

National synthesis of data analysis, based on 

aggregation of comparable information obtained from 

the study units, is a major component of the program. 

This effort focuses on selected water-quality topics 

using nationally consistent information. Comparative 

studies will explain differences and similarities in 

observed water-quality conditions among study areas 

and will identify changes and trends and their causes. 

The first topics addressed by the national synthesis are 

pesticides, nutrients, volatile organic compounds, and 

aquatic biology. Discussions on these and other waterquality topics will be published in periodic summaries 

of the quality of the Nation's ground and surface water 

as the information becomes available.

This report is an element of the comprehensive 

body of information developed as part of the NAWQA 

Program. The program depends heavily on the advice, 

cooperation, and information from many Federal, State, 

interstate, Tribal, and local agencies and the public. The 

assistance and suggestions of all are greatly appreciated.

Robert M. Hirsch 

Chief Hydrologist
CONTENTS

Abstract.........................................................................................................................................................^ 1

Introduction .....................................................................................................................................^ 1

Study design and methods..................................................................................................................................................... 3

Surface-water sampling............................................................................................................................................... 3

Ground-water sampling............................................................................................................................................... 3

Sampling and analytical methods................................................................................................................................ 3

Pesticide occurrence in surface and ground water................................................................................................................. 6

Agricultural land use ................................................................................................................................................... 8

Urban land use............................................................................................................................................................. 8

Mixed land use.........................................................................._ 8

Comparison of shallow and deep ground water .......................................................................................................... 9

Extent of pesticide contamination and possible concerns..................................................................................................... 9

Summary....................................................................................................................................................^ 13

References cited......................................................................_ 13

FIGURES

1. Map showing surface-water sites sampled by the U.S. Geological Survey's National Water-Quality

Assessment Program in the Puget Sound Basin ......................................................................................................... 2

2. Map showing ground-water sites sampled by the U.S. Geological Survey's National Water-Quality

Assessment Program in the Puget Sound Basin ......................................................................................................... 5

3. Box plots showing depths of sampled wells............................................................................................................... 6

4. Histogram showing the number of pesticide detections per stream ........................................................................... 9

5. Graph showing pesticide detections in surface and ground water.............................................................................. 10

6. Graph showing frequency of one or more pesticide detections in surface and ground water.................................... 11

7. Histogram showing the number of pesticide detections per well............................................................................... 12

8. Graph showing pesticide detections in ground water by well depth .......................................................................... 12

TABLES

1. Pesticide detections in surface and ground water in the Puget Sound Basin.............................................................. 4

2. Pesticide detections in surface and ground water by land use.................................................................................... 7

3. Pesticide detections in shallow and deep water.......................................................................................................... 9

4. Minimum and maximum concentrations of pesticides in surface water, and chronic criteria for the

protection of freshwater aquatic life........................................................................................................................... 11

IV
Occurrence of Pesticides in Streams and Ground 

Water in the Puget Sound Basin, Washington, 

and British Columbia, 1996-98

By G. C. Bortleson and J. C. Ebbert

ABSTRACT

This report discusses the occurrence of pesticide 

compounds in surface and ground water in the Puget 

Sound Basin. The findings are based on data collected 

in 1996-1998 by the U.S. Geological Survey National 

Water-Quality Assessment Program, and by a separate 

U.S. Geological Survey study in 1994 of pesticide 

occurrence in public water-supply wells.

A widespread detection of pesticide compounds 

was observed in surface waters of the Puget Sound 

Basin. Fifty-five percent of the 47 pesticide compounds analyzed were detected in surface water, and 17 

percent were detected in ground water. The herbicides 

atrazine, prometon, simazine, and tebuthiuron were 

among the most frequently detected in both surface and 

ground water. The number of pesticide compounds 

found in ground water influenced by agricultural, 

urban, and mixed land uses was far fewer than surface 

water influenced by the same land uses.

Herbicides were the most common type of 

pesticide found in a small agricultural stream, and 

herbicides were the only type of pesticide found in 

shallow ground water underlying agricultural land. 

Compared with small urban streams and large rivers, 

the highest number of individual pesticide compounds 

were detected in the agricultural stream. Insecticides, 

in addition to herbicides, were detected frequently in 

urban streams. Sampled urban streams showed the 

highest detection frequencies for the insecticides 

carbaryl, Diazinon, and malathion. Concentrations of 

Diazinon, the most common of the insecticides 

detected, exceeded chronic criteria for protection of 

aquatic life in streams influenced by agricultural, 

urban, and mixed land uses. On the other hand, 

insecticides were not detected in shallow ground water 

underlying urban residential areas. A relatively few 

herbicides, atrazine, prometon, and simazine, and the

transformation product of atrazine, desethylatrazine, 

were detected at frequencies of 7 percent or less in 

shallow ground water in urban residential areas.

Seven pesticide compounds were detected at 

relatively high frequencies of 20 percent or more in 

large rivers draining mixed land use. In contrast, seven 

pesticide compounds in ground water from mixed land 

use were detected at lower frequencies of 15 percent or 

less. Most ground water, including shallow ground 

water, had no detections of pesticide compounds. In 

basin-wide sampling of ground water representing 

mixed land use, only two herbicides, atrazine and 

simazine, were detected in deep ground water from a 

single well. The concentrations of all pesticides 

detected in shallow and deep ground water did not 

exceed drinking water standards or guidelines.

INTRODUCTION

From 1996 to 1998, the U.S. Geological Survey 

(USGS) conducted studies to assess the occurrence of 

pesticides in surface and ground water in the Puget 

Sound Basin (fig. 1). Herbicides are used to control 

weeds in areas such as agricultural fields, lawns, and 

roadsides. Insecticides are used to control insects, 

mostly in agricultural and urban settings. Previous 

studies have indicated that the detection of pesticides in 

small urban streams in the heavily populated Puget 

Sound Basin is widespread, and pesticides found in 

waters are generally those that are most commonly 

used (Bortleson and Davis, 1997; Voss and others, 

1999). This report provides a discussion of pesticide 

occurrence in streams and ground water in the Puget 

Sound Basin. For more information about the environmental setting and the factors that affect water quality 

in the Puget Sound Basin, see Staubitz and others 

(1997).
123° 121°

49'

47<

EXPLANATION

Urban land 

Agricultural land 

Forested and other land 

Water bodies

 Study area boundary

 International boundary

 Rivers

 Intensively sampled site

 Storm sampling site

10 20 30 40 50 MILES 

0 10 20 30 40 50 KILOMETERS

Figure 1. Surface-water sites sampled by the U.S. Geological Survey's National Water-Quality Assessment Program 

in the Puget Sound Basin.
STUDY DESIGN AND METHODS

This study was designed to obtain data on the 

spatial distribution and occurrence of pesticides in 

streams and ground water at different sampling scales 

in the Puget Sound Basin. Surface- and ground-water 

samples were analyzed for 43 pesticides and 4 transformation products (table 1). This suite of 47 pesticide 

compounds, which was analyzed for in all samples, 

allows for a comparison of pesticides detected among 

small streams, large rivers, and shallow and deep 

ground water within different land uses.

It should be noted that for most of the groundwater samples, an additional suite of pesticide 

compounds was collected and analyzed as part of .the 

National Water-Quality Assessment (NAWQA) study, 

but for purposes of consistency of comparison in this 

study, only the single suite of 47 pesticide compounds 

is discussed in this report. All the pesticides measured 

during the NAWQA study are presented in other 

reports (see http://wa.water.usgs.gov/ps.pub.html).

Surface-Water Sampling

Two sampling approaches were used to determine the occurrence of pesticides in streams of the 

Puget Sound Basin. One approach was to sample four 

streams intensively over a period ranging from 1 to 

2 years; they included two small streams and two large 

rivers (fig. 1). The small streams were Thornton Creek, 

an urban stream draining to Lake Washington, and 

Fishtrap Creek, an agricultural stream draining to the 

Nooksack River. The two large rivers were sampled at 

downstream sites draining mixed land uses. The 

Nooksack River at Brennan drains mostly forest in the 

uplands and mostly agricultural land in the lowlands. 

The Duwamish River near Tukwila, which was sampled in an urban setting, drains mostly forest in the 

uplands and mixed land uses in the lowlands (fig. 1). 

The two small streams and two large rivers were 

sampled monthly and during storms for a total of about 

18 samples per site per year. Except for Thornton 

Creek, samples at the other three sites were collected 

from March 1996 through April 1997. Thornton Creek 

was sampled from March 1996 through May 1998.

In addition to the 4 streams sampled intensively, 

10 small urban streams (fig. 1) were sampled for pesticides from 2 to 4 times each during periods of spring 

storm runoff in 1998. Thornton Creek shown in figure 

1 was sampled at three locations, one of which was an

intensively sampled site. The streams were all sampled 

over a short time period during spring storms when the 

largest number of pesticides are likely to be transported 

in surface runoff and detected in streams (Voss and 

others, 1999).

Ground-Water Sampling

Ground water was sampled at local and basinwide scales (fig. 2). Locally, ground water was 

sampled from 27 wells in urban residential areas near 

Tacoma and Olympia and 22 wells in an agricultural 

area of the Nooksack River Basin (fig. 2). These wells 

were installed at depths ranging from 20 to 137 feet 

deep in coarse-grained glacial deposits, where pesticide infiltration to the water table is more likely than 

fine-grained deposits (fig. 3).

In a basin-wide survey of ground-water quality, 

30 existing domestic wells (fig. 2), with well screens 

finished in coarse-grained glacial deposits, were randomly selected for sampling with the aid of a computer 

model (Scott, 1990). These wells were deeper than the 

urban residential and agricultural wells but still relatively shallow, often between 40 and 80 feet deep 

(fig. 3). Although not part of the NAWQA study, data 

from 78 public water-supply wells sampled for pesticides in 1994 are included in this report. These wells 

were sampled by the USGS as part of a cooperative 

project with the State of Washington Department of 

Health (Ryker and Williamson, 1996). Most of the 

sampled wells were deeper than 100 feet (fig. 3), and 

they are generally less vulnerable to contamination 

from pesticides than shallow wells. It should be noted 

that some of the public water-supply wells and domestic wells are within the areas where wells were installed 

to sample ground water in urban and agricultural 

areas (fig. 2).

Sampling and Analytical Methods

Methods of collecting surface- and ground-water 

samples are described by Wagner and Roberts (1998). 

After collection, about 1 liter of sample water was 

filtered through a 0.7-micrometer glass-fiber filter, and 

pesticides were extracted from the filtrate by pumping 

it through a solid-phase extraction cartridge as 

described by Shelton (1994). Filtration and extraction 

of most samples were done in the field immediately 

after collection; however, some of the samples
Table 1. Pesticide detections in surface and ground water in the Puget Sound Basin

[}lg/L, micrograms per liter; H, herbicide; I, insecticide; T, transformation product; D, detected; --, not detected]

Pesticide

Acetochlor

Alachlor

Atrazine

Azinphos-methyl

Benfluralin

Butylate

Carbaryl

Carbofuran

Chlorpyrifos

Cyanazine

DCPA

p,p'-DDE

Desethylatrazine (DEA)

Diazinon

Dieldrin

2,6-Diethylanaline

Disulfoton

EPIC

Ethalfluralin

Ethoprop

Fonofos

alpha-HCH

gamma-HCH

Linuron

Malathion

Methyl parathion

Metolachlor

Metribuzin

Molinate

Napropamide

Parathion

Pebulate

Pendimethalin

cw-Permethrin

Phorate

Prometon

Pronamide

Propachlor

Propanil

Propargite

Simazine

Tebuthiuron

Terbacil

Terbufos

Thiobencarb

Triallate

Trifluralin

Trade 

or 

common 

name(s)

Guardian

Lasso

AAtrex

Guthion

Balan, Benefin

Sutan +, Genate Plus

Sevin, Savit

Furadan

Lorsban, Dursban

Bladex

Dacthal

none

none

Diazinon

PanoramD-31

none

Di-Syston

Eptam, Eradicane

Sonalan, Curbit EC

Mocap

Dyfonate

none

Lindane

Lorox, Linex

malathion

Penncap-M

Dual, Pennant

Lexone, Sencor

Ordram

Devrinol

several

Tillam

Prowl, Stomp

Ambush, Pounce

Thimet, Rampart

Pramitol

Kerb

Ramrod

Stampede

Comite, Omite

Aquazine, Princep

Spike

Sinbar

Counter

Bolero

Far-Go

Treflan, Trilin

Type 

of 

pesticide

H

H

H

I

H

H

I

I

I

H

H

T

T

I

I

T

I

H

H

I

I

T

I

H

I

I

H

H

H

H

I

H

H

I

I

H

H

H

H

I

H

H

H

I

H

H

H

Chemical 

Abstract 

Services 

registry 

number

15972-60-8

15972-60-8

1912-24-9

86-50-0

1861-40-1

2008-41-5

63-25-2

1563-66-2

2921-88-2

21725-46-2

1861-32-1

72-55-9

6190-65-4

333-41-5

60-57-1

579-66-8

298-04-4

759-94-4

55283-68-6

13194-48-4

944-22-9

319-84-6

58-89-9

330-55-2

121-75-5

298-00-0

51218-45-2

21087-64-9

2212-67-1

15299-99-7

56-38-2

1114-71-2

40487-42-1

57608-04-5

298-02-2

1610-18-0

23950-58-5

1918-16-7

709-98-8

2312-35-8

122-34-9

34014-18-1

5902-51-2

13071-79-9

28249-77-6

2303-17-5

1582-09-8

Method 

detection 

limit 

(|lg/L)

0.002

0.002

0.001

0.001

0.002

0.002

0.003

0.003

0.004

0.004

0.002

0.006

0.002

0.002

0.001

0.003

0.017

0.002

0.004

0.003

0.003

0.002

0.004

0.002

0.005

0.006

0.002

0.004

0.004

0.003

0.004

0.004

0.004

0.005

0.002

0.018

0.003

0.007

0.004

0.013

0.005

0.01

0.007

0.013

0.002

0.001

0.002

Sample type

Surface 

water

D

D

D

~

--

-

D

D

D

-

D

--

D

D

-

-

-

D

~

D

-

-

D

D

D

~

D

D

D

D

-

D

-

-

~

D

D

~

-

D

D

D

D

~

--

~

D

Ground 

water

D

--

-

-

~

-

~

D

D

D

~

-

-

-

-

~

~

~

~

-

--

-

~

-

-

D

-

-

-

«

~

D

~

-

~

~

D

D

-

~

--

-

-
123" 121°

49C

47'

Wells in agricultural area

Seattle A

O Lake Washington

Wells in urban residential areas

0 10 20 30 40 50 MILES

i r

0 10 20 30 40 50 KILOMETERS

EXPLANATION

Urban land 

Agricultural land 

Forested and other land 

Water bodies

Study area boundary 

 International boundary 

Rivers

Public water-supply well 

 NAWQA well

I___________

Figure 2. Ground-water sites sampled by the U.S. Geological Survey's National Water-Quality Assessment 

Program in the Puget Sound Basin.
500

400

w 300

Qj 200

100

(78) (30)

(30)

EXPLANATION

Number of observations

Outlier data value more than 1.5 times the 

interquartile range outside the quartile

Data value less than or equal to 1.5 times 

the interquartile range outside the quartile

75th percentile

Median

25th percentile

(27)

(22)

Public watersupply wells

Basin-wide 

wells

Wells in urban 

residential areas

Wells in 

agricultural areas

MIXED LAND USE

Figure 3. Depths of sampled wells. Two values for public supply wells (612 feet and 

1,240 feet) not shown.

collected from public water-supply wells were shipped 

on ice to the USGS National Water Quality Laboratory 

(NWQL) for filtration and extraction.

Samples were analyzed for 47 pesticide compounds at the NWQL using gas chromatography and 

mass spectrometry (Zaugg and others, 1995). The 

compounds and method detection limits in micrograms 

per liter are shown in table 1. Quality assurance 

included the analysis of blank, spiked, and replicate 

samples. Results indicated good laboratory performance and no sample contamination.

PESTICIDE OCCURRENCE IN SURFACE 

AND GROUND WATER

Slightly more than one half of the pesticide compounds (26 of 47 analyzed) were detected in surface

water, indicating a widespread presence of pesticides in 

waters of the Puget Sound Basin. As expected, more 

pesticide compounds were detected in streams than in 

ground water, due in large part to adsorption and 

degradation of pesticides in soil and sediment as water 

infiltrates to ground water. Of the 47 pesticide compounds of interest, 55 percent were detected in streams 

and 17 percent were detected in ground water. Atrazine, prometon, simazine, and tebuthiuron are commonly used herbicides in the Puget Sound Basin (Tetra 

Tech Incorporated, 1988; Bortleson and Davis, 1997; 

and Majewski, 1997), and these four herbicides were 

the most frequently detected in both streams and 

ground water (table 2). Furthermore, atrazine, prometon, simazine, and tebuthiuron also are among the most 

frequently detected herbicides in streams and ground 

water nationwide (Gilliom and others, 1999).
Table 2. Pesticide detections in surface and ground water by land use

[H, herbicide; I, insecticide; T, transformation product; NAWQA, USGS National Water-Quality Assessment Program]

Pesticide detections, as a percentage of total number of samples 

(Number of detections in parentheses)

Pesticide

Acetochlor

Alachlor

Atrazine

Carbaryl

Carbofuran

Chlorpyrifos

DCPA

p,p'-DDE

Desethylatrazine (DBA)

Diazinon

EPTC

Ethoprop

gamma-HCH (Lindane)

Linuron

Malathion

Metolachlor

Metribuzin

Molinate

Napropamide

Pebulate

Prometon

Pronamide

Propargite

Simazine

Tebuthiuron

Terbacil

Trifluralin

Total number of sites

Number pf sites with

compounds detected

Total number of samples

Type

of 

pesticide

H

H

H

I

I

I

H

T

T

I

H

I

I

H

I

H

H

H

H

H

H

H

I

H

H

H

H

Number of compounds detected

Agricultural land use

Small stream Shallow 

(Fishtrap ground

Creek)

12

6

97

9

3

0

6

0

97

44

19

6

0

9

3

44

6

3

22

6

69

3

0

97

66

6

3

1

1

32

24

(4)

(2)

(31)

(3)

(1)

(2)

(31)

(14)

(6)

(2)

(3)

(1)

(14)

(2)

0)

(7)

(2)

(22)

(1)

(3D

(21)

(2)

(1)

water

0

0

41 (9)

0

0

0

0

0

45 (10)

0

0

0

0

0

0

0

0

0

4 (1)

0

0

0

,/ °

/"36 (8)

''. 14 (3)

/ 0

0

22

12

22

5

Urban land use

Small

streams

1

0

45

20

0

6

1

0

5

84

4

0

10

0

21

9

0

0

9

0

91

1

0

45

5

0

11

12

12

80

17

(1)

(36)

(16)

(5)

(1)

(4)

(67)

(3)

(8)

(17)

(7)

(7)

(73)

(1)

(36)

(4)

(9)

Shallow 

ground

water

0

0

7 (2)

0

0

0

0

0

4 (1)

0

0

0

0

0

0

0

0

0

0

0

4 (1)

0

0

4 (1)

0

0

0

27

3

27

4

Mixed land use

Public water-supply 

Large and NAWQA

rivers basin-wide wells

2

0

63

0

0

0

0

0

24

20

0

2

0

0

4

41

0

0

2

2

35

4

2

59

33

2

0

2

2

46

15

(1)

(29)

(H)

(9)

(0

(2)

(19)

(1)

(1)

(16)

(2)

(1)

(27)

(15)

(1)

0

0

15

0

0

0

1

3

11

0

0

0

0

0

0

0

0

0

0

0

4

0

0

7

2

0

0

108

22

108

7

(17)

(1)

(3)

(13)

(5)

(8)

(2)
The transformation product of atrazine, desethylatrazine (DEA), was detected in ground water and 

streams influenced by all land uses. Both atrazine and 

DEA are relatively soluble and often coexist if water is 

contaminated with the parent herbicide compound, 

atrazine (Larson and others, 1997). On the other hand, 

a transformation product of DDT, p,p'-DDE, was 

detected in ground water but not in streams. The parent 

compound DDT is not readily soluble in water, and if 

detected in the aquatic environment, it is usually found 

attached to bed sediment or in fish (U.S. Geological 

Survey, 1999a). Although DDT has been banned for 

use in the United States, it is not unusual for the 

relatively soluble ;?,/?'-DDE to be detected in ground 

water (Barbash and Resek, 1996).

Agricultural Land Use

Herbicides were the most common type of pesticide found in Fishtrap Creek (an agricultural stream, 

fig. 1) and were the only type of pesticide found in shallow ground water beneath agricultural areas (table 2). 

The five herbicides, atrazine, metolachlor, prometon, 

simazine, tebuthiuron, and the transformation product 

DEA were detected in more than 40 percent of the samples from Fishtrap Creek (table 2). Atrazine, simazine, 

and DEA were found at lower detection rates (36-45 

percent) in shallow ground water underlying agricultural land. The insecticide Diazinon was found in 44 

percent of the samples from Fishtrap Creek, but it was 

not found in shallow ground water.

Overall, about one half of the 47 pesticide compounds analyzed were detected in Fishtrap Creek (table 

2). The high frequency of pesticide detections in 

Fishtrap Creek is related to agricultural as well as urban 

influences. An urban influence exists from nearby 

towns in the basin, even though Fishtrap Creek is 

located primarily in an agricultural setting. For 

example, simazine, prometon, and tebuthiuron are 

considered primarily urban herbicides (U.S. Geological Survey, 1999a), but they were detected at high 

frequencies in Fishtrap Creek. In particular, prometon 

is not applied to cropland, so its presence in streams is 

due to nonagricultural applications. Also, the insecticide Diazinon was detected at a high frequency in 

Fishtrap Creek, but it is not detected at a high frequency 

in most agricultural settings, compared to urban 

settings nationwide (Gilliom and others, 1999; 

U.S. Geological Survey, 1999a).

Urban Land Use

In addition to herbicides, insecticides were 

detected frequently in urban streams. Sampled urban 

streams showed the highest detection rates for the three 

insecticides carbaryl, Diazinon, and malathion (table 

2). Diazinon and malathion are among the most 

frequently used insecticides in the Puget Sound Basin 

(Tetra Tech Incorporated, 1988; Majewski, 1997). 

Other insecticides detected less often were chlorpyrifos 

and lindane. Insecticides are commonly used for 

home, garden, and commercial purposes in urban 

areas. The more frequent occurrence of insecticides in 

urban streams, compared with agricultural streams, is 

common throughout the United States (Gilliom and 

others, 1999). The herbicides atrazine, prometon, and 

simazine also were detected at high frequencies in 

small urban streams (table 2).

A relatively few pesticide compounds were 

detected at frequencies of 7 percent or less in shallow 

ground water of urban residential areas. DEA and the 

herbicides atrazine, prometon, and simazine, were the 

same as those most frequently detected in urban 

streams. Insecticides were not detected in shallow 

ground water below urban residential land.

Mixed Land Use

Seven pesticide compounds, atrazine, Diazinon, 

metolachlor, prometon, simazine, tebuthiuron, and 

DEA, were detected in large rivers at frequencies of 20 

percent or greater. Large rivers integrate the effects of 

urban and agricultural influences, as well as those of 

upland forests. The integration of influences is shown 

by the fact that 14 of the 15 pesticides detected in large 

rivers were the same group of pesticides detected in 

either urban or agricultural streams (table 2).

Ground water from domestic and public watersupply wells sampled basin-wide represent water from 

mixed land-use sources. With two exceptions, the 

pesticides detected in domestic and public watersupply wells were the same as those in shallow ground 

water underlying agricultural or urban land; however, 

all the pesticides in ground water sampled basin-wide 

were detected at frequencies of 15 percent or less (table 

2). One reason detection rates of pesticides in samples 

from domestic and public water-supply wells sampled 

basin-wide were low is because many of these wells are 

deeper than wells sampled in agricultural and urban 

areas (fig. 3).
Comparison of Shallow and 

Deep Ground Water

The domestic and public water-supply wells 

sampled basin-wide were divided into shallow and 

deep wells. Fifty-one wells over 100 feet deep were 

designated as deep wells, and 106 wells less than or 

equal to 100 feet deep were designated as shallow wells 

(table 3).

Only two herbicides, atrazine and simazine, 

were detected in a single deep well. However, a total 

of eight pesticide compounds were detected in shallow 

wells (table 3). In the shallow wells, atrazine and DEA 

were the only pesticide compounds detected at 

relatively high frequencies. Simazine was detected at 

the third highest frequency in shallow ground water.

EXTENT OF PESTICIDE CONTAMINATION 

AND POSSIBLE CONCERNS

The data indicate that, in all the streams and 

rivers sampled, multiple pesticides occur. The number 

of pesticides detected in streams and rivers ranged from 

3 to 23, and the most common number detected was 6

(fig. 4). Of most concern, especially in small streams, 

are the effects on aquatic life, as none of the small 

streams sampled is a source of drinking water for 

humans.

HI DC 

tob- 2

DC 

LU 

CD

3 4 5 6 7 9 10 13 15 

NUMBER OF PESTICIDES DETECTED

Figure 4. Number of pesticide detections per stream. 

Numbers not shown were zero detections.

Table 3. Pesticide detections in shallow and deep water

[<, less than or equal to; >, greater than; H, herbicide; T, transformation product]

Pesticide detections, as a percentage of total

number of samples 

(Number of detections in parentheses)

1>pe of

Pesticide pesticide

Atrazine

DCPA

Desethylatrazine (DEA)

p,p'-DDE

Napropamide

Prometon

Simazine

Tebuthiuron

Total number of samples

Number of compounds detected

H

H

T

T

H

H

H

H

Shallow ground

water (<100 feet)

25

1

23

3

1

6

15

5

106

8

(27)

(1)

(24)

(3)

(1)

(6)

(16)

(5)

Deep ground

water (> 100 feet)

2

0

0

0

0

0

2

0

51

2

(1)

(1)
-UJ 100 W-l 

ZCL

02

LUU.

DOT

il

DC_i

Ou_

to

o<

^UJ o"

LLjDL 

LL 0-

z

80

60

40

20

Agricultural 

land use

-

-

-

Mixed 

land use

 

1

L 

la

rba 

id u

EXPLANATION 

-, Samples with detections at or above 

se ' ' USGS laboratory method detection limit ~~

i i Samples with detections equal to or 

1 1 greater than 0.01 microgram per liter

i i Samples with detections equal to or ~ 

i I greater than 0.05 microgram per liter

 

Mixed 

land use

Ag

la

icultura! 

nd use

 I

-

Urban

residential ~~ 

land use

Large rivers Small streams Deep and shallow Shallow ground Shallow ground 

ground water, basin-wide water water

Small agricultural

stream 

(Fishtrap Creek)

Figure 5. Pesticide detections in surface and ground water.

The frequency of detecting one or more pesticides in individual samples was highest for Fishtrap 

Creek, an agricultural stream with some urban influence, followed by urban streams, and then large rivers 

draining mixed land use (fig. 5). By showing detection 

frequencies at the method detection limit (see table 1) 

and at two arbitrary reporting limits, 0.01 and 

0.05 micrograms per liter, information about relative 

concentrations can be obtained from figure 5. For 

example, concentrations of pesticides equal to or 

greater than 0.05 micrograms per liter were found in 

only about 10 percent of the samples from large rivers, 

compared with 50 percent for urban and agricultural 

streams, indicating the relatively lower concentrations 

in large rivers. At least three pesticide compounds 

were found in each sample collected from Fishtrap 

Creek, while about 5 percent of samples from urban 

streams and 20 percent of samples from large rivers 

contained no pesticides (fig. 6). Pesticides transported 

to the large rivers are diluted by the volume of water in 

the rivers and by high-quality water from forested 

headwaters.

Thirteen of the 26 pesticide compounds detected 

in surface water have aquatic-life criteria established 

by the U.S. Environmental Protection Agency or other 

agencies. Minimum and maximum concentrations of 

pesticides found in small streams and large rivers are 

shown in table 4 if the chronic criteria for the protection 

of aquatic life have been established for the compound. 

Three insecticides, chlorpyrifos, Diazinon, and 

lindane, exceeded aquatic-life criteria in a total of six 

occurrences (table 4). Concentrations of Diazinon, the 

most common insecticide detected, exceeded aquaticlife criteria in streams influenced by agricultural, 

urban, and mixed land use. The maximum concentrations for chlorpyrifos, Diazinon, and lindane were 

0.074, 0.501, and 0.095 micrograms per liter, 

respectively.

In contrast to streams, most ground water, 

including shallow ground water, contained no pesticides (fig. 7). Additionally, the frequency of detecting 

one or more pesticides in individual ground-water 

samples was lower than that for streams and rivers 

(fig. 5), and fewer pesticide compounds were found in 

ground-water samples (fig. 6). Ground water sampled

10
I 100 

H W 

H Q

£^80

60

^ LJJ 

< DO 40

fei

ai D 

o LU 

££li 20

EXPLANATION 

Agricultural land use -

small stream (Fishtrap Creek) 

Urban land use -

small streams 

Mixed land use -

large rivers

Agricultural land use -

shallow ground water 

Mixed land use -

deep and shallow ground water,

basin-wide 

Urban residential land use -

shallow ground water

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

NUMBER OF PESTICIDE COMPOUNDS DETECTED 

Figure 6. Frequency of one or more pesticide detections in surface and ground water.

Table 4. Minimum and maximum concentrations of pesticides in surface water, and chronic criteria for the protection 

of freshwater aquatic life

[Chronic criteria are from U.S. Geological Survey (1999b); concentrations are in micrograms per liter; bold type indicates value 

above criterion; H, herbicide; I, insecticide; e, estimated value; nd, not detected]

Pesticide

Atrazine

Carbaryl

Carbofuran

Chlorpyrifos

Diazinon

Lindane

Linuron

Malathion

Metolachlor

Metribuzin

Simazine

Tebuthiuron

Trifluralin

Type of 

pesticide

H

I

I

I

I

I

H

I

H

H

H

H

H

Chronic 

criteria

1.8

0.2

1.8

0.041

0.08

0.01

7

0.1

7.8

1

10

1.6

0.2

Agricultural stream 

Minimum Maximum

0.012

e 0.074

e 0.005

nd

e 0.004

nd

0.03

0.025

e 0.002

0.012

e 0.004

e 0.003

0.005

1.4

e 0.133

e 0.005

nd

0.113

nd

0.32

0.025

0.037

0.025

1

0.095

0.005

Concentration range 

for urban streams 

Minimum Maximum

e 0.002

e 0.003

nd

0.006

e 0.003

0.019

nd

0.01

0.004

nd

e 0.002

0.025

e 0.002

0.021

e 0.046

nd

0.074

0.501

0.095

nd

0.087

0.141

nd

5

0.03

0.007

Large 

Minimum

e 0.003

nd

nd

nd

e 0.004

nd

nd

e 0.003

e 0.002

nd

e 0.003

e 0.003

nd

rivers 

Maximum

0.042

nd

nd

nd

0.083

nd

nd

e 0.005

0.013

nd

0.194

0.087

nd

11
125

1234 

NUMBER OF PESTICIDES DETECTED 

Figure 7. Number of pesticide detections per well.

45

Q 

£ 40

I m 

5 n 35

12co

30

25

;o 20

rn w CD LU

Z LU

LU OC 

00

15

10

LU

O

EXPLANATION

Samples with detections at or above 

USGS laboratory method detection limit

Samples with detections equal to or 

greater than 0.01 microgram per liter

Samples with detections equal to or 

greater than 0.05 microgram per liter

Less than 50 feet deep 

(66 wells)

50 to 100 feet deep 

(40 wells)

Greater than 100 feet 

(51 wells)

WELL DEPTH, IN FEET 

Figure 8. Pesticide detections in ground water by well depth.

12
from below urban residential land had the fewest pesticides per sample, but for surface water, large rivers had 

the fewest pesticides per sample (fig. 6).

Pesticides were detected in ground water underlying urban, agricultural, and mixed land-use settings. 

Of concern is that pesticides that are most heavily used 

and applied to the land are detected not only in streams 

but also in ground water. Water infiltrating through soil 

and sediment to ground water reduces considerably the 

detection rate of pesticides, compared with streams. 

However, shallow ground water is much more likely to 

contain pesticides than deep ground water (fig. 8). For 

example, about 40 percent of the samples from wells 

less than 50 feet contained one or more pesticides, 

whereas only 1 of 51 wells more than 100 feet deep 

contained pesticides (fig. 8).

The presence of pesticides in ground water raises 

a question about health concerns because ground water 

in the basin is often used for drinking water. In the 

Puget Sound Basin, concentrations of pesticides in 

ground water did not exceed drinking water standards, 

and only two herbicides, atrazine and simazine, were 

detected in 1 of the 51 wells (mostly public watersupply wells) deeper than 100 feet.

SUMMARY

A widespread detection of pesticide compounds 

was observed in surface waters of the Puget Sound 

Basin. As expected, more pesticide compounds were 

detected in surface water than ground water, due in 

large part to adsorption and degradation of pesticides 

infiltrating through soil and sediment. Water sampled 

from large rivers had the fewest pesticides per sample, 

compared with streams in urban and agricultural landuse settings. In contrast to surface water, most ground 

water, including shallow ground water, had no detections of pesticides. Fifty-five percent of the 47 pesticide compounds of interest were detected in streams, 

and 17 percent were detected in ground water. The 

herbicides atrazine, prometon, simazine, and tebuthiuron were the most frequently detected herbicides in 

surface and ground water. The number of pesticide 

compounds found in ground water was far fewer than 

those found in streams. Ground water sampled from 

the urban residential areas had the fewest pesticides per 

sample, compared with agricultural and mixed 

land-use areas.

Herbicides were the most common type of pesticide found in Fishtrap Creek (an agricultural stream) 

and the only type of pesticide found in shallow ground 

water underlying agricultural land. The herbicide compounds, atrazine, metolachlor, prometon, simazine, 

tebuthiuron, and desethylatrazine (a transformation 

product of atrazine) were detected in more than 40 

percent of the samples from Fishtrap Creek. In shallow 

ground water below agricultural land, the herbicide 

compounds atrazine, simazine, and desethylatrazine 

were detected at lower frequencies (36-45 percent). 

Insecticides, in addition to herbicides, were detected 

frequently in urban streams. Sampled urban streams 

showed the highest detection rate for the three insecticides carbaryl, Diazinon, and malathion. Concentrations of the insecticide Diazinon, the most common, 

exceeded chronic criteria for aquatic life in streams 

influenced by agricultural, urban, and mixed land uses. 

On the other hand, no insecticides were found in 

shallow ground water below urban residential land. 

The herbicide compounds atrazine, prometon, 

simazine, and desethylatrazine were found in less than 

7 percent of the samples from shallow ground water in 

urban areas.

Seven pesticide compounds were found at relatively high frequencies of 20 percent or more in large 

rivers. Most ground water, including shallow ground 

water, had no detections of pesticide compounds. In 

basin-wide sampling of deep ground water representing mixed land use, only two herbicides, atrazine and 

simazine, were detected in water from a single well. 

No pesticides in ground water were found to exceed 

drinking water standards or guidelines.

REFERENCES CITED

Barbash, I.E., and Resek, E.A., 1996, Pesticides in ground 

water Distribution, trends, and governing factors: 

Chelsea, Mien., Ann Arbor Press, Pesticides in the 

Hydrologic System series, v. 2, 588 p.

Bortleson, G.C., and Davis, D.A., 1997, Pesticides in

selected small streams in the Puget Sound Basin, 1987- 

1995: U.S. Geological Survey Fact Sheet 067-97, 4 p.

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Majewski, Mike, 1997, National and study-unit pesticide 

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supply wells in Washington State: U.S. Geological 

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Scott, J.C., 1990, Computerized stratified random siteselection approaches for design of ground-waterquality sampling network: U.S. Geological Survey 

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Staubitz, W.W., Bortleson, G.C., Semans, S.D., Tesoriero, 

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___1999b, Pesticides analyzed in NAWQA samples Use, 

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Geological Survey, accessed April 12, 2000, at URL 

http://water.wr.usgs.gov/pnsp/anstrat/

Voss, Frank D., Embrey, Sandra S., Ebbert, James C., Davis, 

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County, Washington: U.S. Geological Survey Fact 

Sheet 097-99,4 p.

Wagner, R.J., and Roberts, L.M., 1998, Pesticides and 

volatile organic compounds in surface and ground 

water of the Palouse subunit, central Columbia Plateau, 

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K.M., 1995, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-- 

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14

£ U.S. GOVERNMENT PRINTING OFFICE: 2000 589-121 / 03021 Region No. 10
Bortleson, G.C. and Ebbert, J.C. OCCURRENCE OF PESTICIDES IN STREAMS AND GROUND WATER 

IN THE PUGET SOUND BASIN, WASHINGTON, AND BRITISH COLUMBIA, 199