Wyoming Department of

Agriculture (WDA)

Wyoming Department of

Environmental Quality (WDEQ),

Water Quality Division

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.

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

PESTICIDES IN GROUND WATER

WYOMING'S PESTICIDE

MANAGEMENT PLAN

Pesticides in Ground Water - Park County, Wyoming, 1997

In cooperation with the Wyoming Department of Agriculture (WDA)

and the Wyoming Department of Environmental Quality (WDEQ)

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 097-98

September 1998

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 Park County.
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.

Pesticide

Focal pesticides detected in Park County ground water

Non-focal pesticides detected in Park County ground water

Focal pesticides not detected in Park 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 42/54

8/54

8/54

0.001

0.021

0.016

0.18

2.5E

0.36

0.02

0.5

0.2

3

354

354

7/54 0.05 0.062 0.009 2005 Hexazinone

Simazine 6/54

3/54

1/54

1/54

0.05

0.01

0.05

0.05

trace

0.24

0.46

trace

trace

0.16

0.46E

trace

4

500

5005

705

Prometon 18/54 0.05 0.49 0.08 1005

Alachlor

1

2

3

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

Degradation product of Aldicarb.

Action of parent product, Aldicarb.

4

5

6

EPA Drinking Water Equivalent Level (EPA, 1996).

EPA Lifetime Health Advisory Level (EPA, 1996).

No method of analysis available.

Aldicarb

Aldicarb Sulfone2

Insecticide, nematicide3

Insecticide, nematicide3

Selective herbicide

Selective herbicide

Selective herbicide

Selective herbicide

Herbicide

Non-selective herbicide

Systemic herbicide

Aldicarb Sulfoxide2

Bromacil Clopyralid DCPA

Tebuthiuron

Dicamba

Metolachlor

Cyanazine

Picloram

Metsulfuron6 Metribuzin

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

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

Difenzoquat6 Telone

2,4-D
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.

The vulnerability of ground

water in Park County was ranked

second in Wyoming and sampling

began in April 1997. The vulnerability map for Park County (fig. 2)

was created by the University of

Wyoming Spatial Data and

Visualization Center. The alluvial

and terrace aquifers, usually

located in stream valleys and on

benches, were identified as the

most vulnerable to pesticides in

Park County.

Twenty-seven sites were

selected for baseline monitoring in

Park 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

three Park County Conservation

Districts. All sites were sampled

twice, either during the spring and

late summer of 1997, or the late

summer of 1997 and spring of

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 Park County

(table 1). All levels of pesticides

detected were less than two-thirds

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.

GROUND-WATER MONITORING

IN PARK COUNTY

110° 109° 45°

44°

R. 98 W.

T. 45 N.

T. 46 N.

T. 47 N.

T. 48 N.

T. 49 N.

T. 50 N.

T. 51 N.

T. 52 N.

T. 58 N.

T. 57 N.

T. 56 N.

T. 55 N.

T. 54 N.

T. 53 N.

R. 99 W.

R. 100 W.

R. 101 W.

R. 109 W.

104

105

106

107

108

103 R. 102 W.

120

120

296

291

295

114

16

16

14

14 20

212

Buffalo Bill

Reservoir

Clarks

North

South

Greybull

R

Shoshone

Fork

Fork

Fork

River

River

Greybull

River Wood

Yellowstone

River

WYOMING

Map area

Park County

EXPLANATION

VULNERABILITY TO

PESTICIDE

CONTAMINATION

High

Medium high

Medium

Medium low

Low

Figure 2. Vulnerability of Park County ground water to pesticide contamination

(University of Wyoming Spatial Data and Visualization Center, written commun., 1998).

10 15 MILES

10

5

5

0

0 15 KILOMETERS

Clark

Cody

Meeteetse

Powell

Ralston
At least one pesticide was

detected in 21 of the 27 wells

sampled in the county (fig. 3). The

pesticide with the highest concentration was Aldicarb sulfoxide, a

degradation product of Aldicarb.

More than 75 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 42 samples from 21 of

the 27 wells.

The sampling results have been

given to local Conservation

Districts interested in pesticides in

ground water in Park County. The

information can be used by citizens

and local governments to help

understand current conditions.

Baseline sampling in Washakie

County was also started in 1997.

Fremont, Lincoln, and Laramie

County sampling will begin in

August 1998. Results of all analyses are available from the U.S.

Geological Survey in Cheyenne

(Mason and Green, 1998).

The use of trade, product, industry,

or firm names is for descriptive

purposes only and does not imply

endorsement by the U.S. Government.

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 Groundwater and Pesticide Strategy Committee.

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:

FOR MORE INFORMATION,

CONTACT:

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.

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.

REFERENCES:

Layout and final illustrations

by Suzanne C. Roberts

Prepared by Cheryl A. Eddy-Miller

110° 109° 45°

44°

R. 98 W.

T. 45 N.

T. 46 N.

T. 47 N.

T. 48 N.

T. 49 N.

T. 50 N.

T. 51 N.

T. 52 N.

T. 58 N.

T. 57 N.

T. 56 N.

T. 55 N.

T. 54 N.

T. 53 N.

R. 99 W.

R. 100 W.

R. 101 W.

R. 109 W.

104

105

106

107

108

103 R. 102 W.

Clarks

North

South

Greybull

River

Shoshone

Fork

Fork

Fork

River

River

Greybull

River

Wood

Yellowstone

River

120

120

296

291

295

114

16

16

14

14 20

212

10 15 MILES

10

5

5

0

0 15 KILOMETERS

Figure 3. Location of wells sampled in Park County, and notation of pesticide detection

in each well.

NO PESTICIDE DETECTED IN WELL

EXPLANATION

PESTICIDE DETECTED IN WELL

WYOMING

Map area

Park County

Clark

Cody

Meeteetse

Powell

Ralston

Buffalo Bill

Reservoir