Synthetic organic pesticides

are used to control weeds, insects,

and other organisms in a wide

variety of agricultural and nonagricultural settings. The use of

pesticides has helped to make the

United States the largest producer

of food in the world and has

provided other benefits, but the

use has also been accompanied by

concerns about their potential

adverse effects on the environment

and human health. A potential

pathway for the transport of

pesticides is through hydrologic

systems, which supply water for

both humans and natural ecosystems. Water is one of the primary

ways pesticides are transported

from an application area to other

locations in the environment

(fig. 1).

Pesticide contamination of

ground water is a national issue

because ground water is used for

drinking water by about 50 percent

of the Nation's population.

Concern about pesticides in

ground water is especially acute in

rural agricultural areas where over

95 percent of the population relies

upon ground water for drinking

water.

In 1991, the Ground-water and

Pesticide Strategy Committee

(GPSC) began developing the

generic State Management Plan

for Pesticides in Ground Water for

the State of Wyoming. The SMP

will be required by the U.S.

Environmental Protection Agency

(EPA) in order for individuals to

continue using certain pesticides in

Wyoming. The SMP includes

information relating to agencies

and individuals involved with the

implementation of the SMP,

ground-water monitoring, methods

of preventing ground-water

contamination, and what the

responses will be to detections of

pesticides in ground water.

In 1991, members of local, State, and Federal governments, as well as industry and interest groups,

formed the Ground-water and Pesticide Strategy Committee to prepare the State of Wyoming's generic

Management Plan for Pesticides in Ground Water (SMP). Part of this management plan is to sample

and analyze Wyoming's ground water for pesticides. In 1995, the U.S. Geological Survey, in cooperation

with the Ground-water and Pesticide Strategy Committee, began implementation of the SMP by sampling wells in Goshen County, Wyoming. In 1997, baseline monitoring began in Washakie County.

PESTICIDES IN GROUND WATER

WYOMING'S PESTICIDE

MANAGEMENT PLAN

Pesticides in Ground Water - Washakie County, Wyoming, 1997-98

In cooperation with the Wyoming Department of Agriculture (WDA)

and the Wyoming Department of Environmental Quality (WDEQ)

Wyoming Department of

Agriculture (WDA)

Wyoming Department of

Environmental Quality (WDEQ),

Water Quality Division

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 098-98

September 1998

RUNOFF

EVAPORATION

SPRAY DRIFT

WIND EROSION

SEEPAGE GROUND-WATER

DISCHARGE

TO STREAMS

RECHARGE

FROM

STREAMS

PRECIPITATION

PESTICIDE

APPLICATION

SEEPAGE

ENTRY

THROUGH

WELLS

WITHDRAWAL

FROM

WELLS

REGIONAL TRANSPORT

Figure 1. Pathways of pesticide movement in the hydrologic cycle (modified from

U.S. Geological Survey Fact Sheet FS-244-95).

RUNOFF
One critical part of the SMP is

ground-water monitoring. The

ground-water sampling program

has two phases. The first phase

involves baseline monitoring,

which is an initial survey of the

pesticides detected in a county's

ground water. The second phase is

problem identification monitoring,

which is used to gather more

information about the ground

water near wells with significant

pesticide detections.

Baseline monitoring is directed

by a county rank and the vulnerability of the ground water to

pesticides. During the development of the SMP, the GPSC

evaluated each county in Wyoming

to determine the potential vulnerability of the county's ground water

to pesticides. Each county was

ranked based on the extent of

cropland and urban areas in the

county, as well as the amount of

pesticides sold within the county in

1991.

A ground-water vulnerability

map is prepared for the uppermost

or shallowest aquifer. The map, a

summation of seven maps describing the hydrogeology and land use,

is used to assist in the selection of

monitoring sites in each county.

The monitoring focuses on areas

where the ground water is most

vulnerable.

The GPSC selected 18

pesticides of focus and 2 degradation products to be sampled as part

of the SMP (table 1). An

additional 66 pesticides and

degradation products are included

in USGS pesticide analyses,

leading to possible detections of

non-focal pesticides. Ground water

from all wells in the baseline

monitoring program was analyzed

for the pesticides listed in table 1,

with the exception of Difenzoquat

and Metsulfuron.

The ground-water sampling

part of the SMP began in Goshen

County in 1995. The goal of the

sampling program is to collect

ground-water samples for pesticide

analyses in all 23 Wyoming

counties.

Pesticide

Focal pesticides detected in Washakie County ground water

Non-focal pesticides detected in Washakie County ground water

Focal pesticides not detected in Washakie County ground water

Number

detected/

Number

sampled

Pesticide action

(Farm Chemicals

Handbook and

Dictionary, 1996)

Minimum

reporting

limit

( g/L) m

Maximum

concentration

( g/L) m

Average

concentration

of detections

( g/L) m

Safe drinking

water standard

( g/L)

1

m

Atrazine

1/23 0.1 0.17E 0.17 354

Cyanazine

Simazine

Prometon 13/23 0.018 0.13 0.04 1005

Alachlor

1

2

3

4

EPA Maximum Contaminant Level unless otherwise noted (EPA, 1996).

Degradation product of Aldicarb.

Action of parent product, Aldicarb.

EPA Drinking Water Equivalent Level (EPA, 1996)

5

6

7

EPA Lifetime Health Advisory Level (EPA, 1996).

WDEQ Drinking Water Equivalent Level, (WDEQ, 1993)

No method of analysis available.

Aldicarb

Aldicarb Sulfone2

Insecticide, nematicide3

Insecticide, nematicide3

Selective herbicide

Selective herbicide

Selective herbicide

Selective herbicide

Herbicide

Non-selective herbicide

Selective herbicide

Aldicarb Sulfoxide2

Bromacil Clopyralid Difenzoquat7

Dicamba

Tebuthiuron

Hexazinone

DCPA

Metolachlor

Metsulfuron7 Metribuzin Picloram

Table 1. Baseline monitoring for pesticides in Washakie County, 1997-98.

[ g/L, micrograms per liter; E, estimated; trace, pesticide detected, but at a concentration too small to quantify] m

Telone

2,4-D

18/23

2/23

0.001

0.02

0.02

0.52E

0.006

0.33

3

354

2/23 0.004 0.008 0.007 15

5/23

1/23

5/23

1/23

0.005

0.01

0.002

0.002

0.007

trace

0.02

trace

0.004

trace

0.009

trace

4

5005

705

166
The vulnerability of ground

water in Washakie County was

ranked first in Wyoming and

sampling began in August 1997.

The vulnerability map for

Washakie County (fig. 2) was

created by the University of

Wyoming Spatial Data and

Visualization Center. The shallow

alluvial aquifers, usually located in

stream valleys, were identified as

the most vulnerable to pesticides in

Washakie County.

Thirteen sites were selected for

baseline monitoring in Washakie

County. All wells were selected in

the two most vulnerable rankings

(areas in red and yellow). The

wells were inspected and selected

with the assistance of the Washakie

County Conservation District. All

sites were sampled twice, late

summer 1997 and spring 1998.

These time periods were selected

to correspond with deepest and

shallowest water-table conditions.

Six of the 18 pesticides of focus

and the two degradation products

were detected in Washakie County

(table 1). All levels of pesticides

detected were less than one-fifth of

the drinking water standard or its

equivalent established by the EPA

for domestic supplies (U.S.

Environmental Protection Agency,

1996). Although these standards

do not apply to private domestic

wells, they do provide a reference

to the acceptable amount of

chemicals in drinking water.

At least one pesticide was

detected in 10 of the 13 wells

sampled in the county (fig. 3). The

pesticide with the highest concentration was Aldicarb sulfoxide, a

degradation product of Aldicarb.

More than 90 percent of the detections were trace quantities. A trace

quantity indicates the pesticide was

detected, but at a level too small to

quantify. Atrazine was the most

commonly detected pesticide,

detected in 18 samples from 10 of

the 13 wells.

The sampling results have been

given to local Conservation

Districts interested in pesticides in

ground water in Washakie County.

The information can be used by

citizens and local governments to

help understand current conditions.

Baseline sampling in Park

County was conducted in 1997.

Fremont, Lincoln, and Laramie

County sampling will begin in

August 1998. Results of the 1997

sampling program can be found in

Mason and Green, 1998. Results of

all analyses are available from the

U.S. Geological Survey in

Cheyenne.

GROUND-WATER MONITORING

IN WASHAKIE COUNTY

10 15 MILES

10

5

5

0

0 15 KILOMETERS

WYOMING

Washakie

County

Figure 2. Vulnerability of Washakie County ground water to pesticide contamination (University of Wyoming

Spatial Data and Visualization Center, written commun., 1998).

EXPLANATION

VULNERABILITY TO PESTICIDE

CONTAMINATION

High

Medium high

Medium

Medium low

Low

108 30 ° ¢

44 00 ° ¢

43 45 ° ¢

R. 89 W.

R. 90 W.

R. 92 W.

R. 94 W.

R. 95 W.

R. 96 W.

R. 97 W.

R. 93 W.

R. 91 W.

R. 88 W. R. 87 W. R. 86 W.

T. 41 N.

T. 42 N.

T. 43 N.

T. 44 N.

T. 45 N.

T. 46 N.

T. 47 N.

T. 48 N.

108 15 ° ¢ 108 00 ° ¢ 107 45 ° ¢ 107 30 ° ¢ 107 15 ° ¢

Nowood

River

Tensleep

Creek

Leigh

Cr

Canyon

Creek

Spring Creek

Otter

Creek

Little

Canyon

Cr

Nowood

River

Box

Elder

Creek

Deep

Creek

Fork

Middle

Powder

River

Bighorn

Cottonwood

Cr

Gooseberry

Creek

River

Tensleep

Worland

20

16

20

16
The use of trade, product, industry, or firm

names is for descriptive purposes only and

does not imply endorsement by the

U.S. Government.

Farm Chemicals Handbook and

Dictionary, 1996: Willoughby,

Ohio, Meister Publishing Co.,

variable pagination.

Mason, J.P., and Green, S.L., 1998,

Water resources data, Wyoming,

water year 1997: U.S. Geological

Survey Water-data Report,

WY-97-2, 147 p.

Wyoming Department of Environmental Quality, 1993, Procedures

for establishing environmental

restoration standards for

leaking underground storage

tank remediation actions,

WDEQ/WQD Rules and

Regulations, Chapter XVII.

U.S. Environmental Protection

Agency, 1996, Drinking water

regulations and health

advisories: EPA 822-B-96-002.

U.S. Geological Survey, 1995,

Pesticides in ground water: U.S.

Geological Survey Fact Sheet

FS-244-95, 4 p.

Jim Bigelow

Wyoming Department of Agriculture

2219 Carey Avenue

Cheyenne, Wyoming 82002

(307) 777-7324

Kevin Frederick

Wyoming Department of

Environmental Quality,

Water Quality Division

4th Floor, Herschler Building

Cheyenne, Wyoming 82002

(307) 777-7781

District Chief

U.S. Geological Survey, WRD

2617 E. Lincolnway, Suite B

Cheyenne, Wyoming 82001

(307) 778-2931

staterep_wy@mailcheyenne.cr.usgs.gov

http://wyoming.usgs.gov/welcome.html

Email:

Internet:

Prepared by Cheryl A. Eddy-Miller

REFERENCES:

FOR MORE INFORMATION, CONTACT:

This document was prepared by the

U.S. Geological Survey (USGS), the

Wyoming Department of Agriculture

(WDA), and the Wyoming Department of Environmental Quality,

Water Quality Division (WDEQ).

All agencies are members of the

Ground-water and Pesticide Strategy

Committee.

Layout and final illustrations by Suzanne C. Roberts

108 30 ° ¢

44 00 ° ¢

43 45 ° ¢

R. 89 W.

R. 90 W.

R. 92 W.

R. 94 W.

R. 95 W.

R. 96 W.

R. 97 W.

R. 93 W.

R. 91 W.

R. 88 W. R. 87 W. R. 86 W.

T. 41 N.

T. 42 N.

T. 43 N.

T. 44 N.

T. 45 N.

T. 46 N.

T. 47 N.

T. 48 N.

108 15 ° ¢ 108 00 ° ¢ 107 45 ° ¢ 107 30 ° ¢ 107 15 ° ¢

Nowood

River

Tensleep

Creek

Leigh

Cr

Canyon

Creek

Spring

Creek

Otter

Creek

Little

Canyon

Creek

Nowood

River

Box

Elder

Creek

Deep

Creek

Fork

Middle

Powder

River

Bighorn

Cottonwood

Cr

Gooseberry

Creek

River

Tensleep

Worland

20

16

20

16

Figure 3. Location of wells sampled in Washakie County, and notation of pesticide detection in each well.

NO PESTICIDE DETECTED IN WELL

EXPLANATION

PESTICIDE DETECTED IN WELL

10 15 MILES

10

5

5

0

0 15 KILOMETERS

WYOMING

Washakie

County