Wyoming Department 

of Agriculture

Printed on recycled paper

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

and Resek, 1996).

In cooperation with the Wyoming Department of Agriculture (WDA) and the Wyoming Department of 

Environmental Quality (WDEQ)

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. 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 statewide implementation of the sampling component of the State of Wyoming’s generic Management 

Plan for Pesticides in Ground Water. During 2003-04, baseline monitoring was conducted in Converse County.

PESTICIDES IN GROUND WATER

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 world’s largest producer of food 

(Barbash and Resek, 1996). Pesticide use, 

however, has also been accompanied by 

concerns about 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) (Barbash and 

Resek, 1996).

Pesticide contamination of ground 

water is a national issue because of the 

widespread use of pesticides, the expense 

and difficulty of remediating ground 

water, and the fact that ground water is 

used for drinking water by about half of 

the Nation’s population. Although application rates and the variety of pesticides 

used may be greater in urban areas, concern over their presence in ground water is 

especially acute in rural agricultural areas 

where more than 95 percent of the population rely upon this resource for drinking 

water (Hutson and others, 2004).

WYOMING’S PESTICIDE 

MANAGEMENT PLAN

The Ground-water and Pesticide Strategy Committee (GPSC) has developed 

the generic State Management Plan for 

Pesticides in Ground Water for the State 

of Wyoming (SMP) (Wyoming Groundwater and Pesticides Strategy Committee, 

1999). Wyoming was required by the U.S. 

Environmental Protection Agency to have 

a SMP in order for individuals and organizations to continue using certain pesticides 

in the State. The SMP includes information relating to individuals and organizations involved with implementation of the 

SMP, methods of preventing ground-water 

contamination, ground-water monitoring, 

and the responses required if pesticides are 

detected in ground water.

One critical part of the SMP is groundwater monitoring. This ground-water monitoring program has two phases. The first 

phase, baseline monitoring, is designed 

to determine what pesticides, if any, have 

leached into the county’s ground water. 

Pesticides in Ground Water - Converse County, Wyoming, 2003-04

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2005-3089

July 2005

Wyoming Department of 

Environmental Quality, 

Water Quality Division
Table 1. Summary of baseline monitoring for pesticides in Converse County, September–October 2003 and April 2004.

[μg/L, micrograms per liter; NA, not applicable; T, trace concentration, value is estimated; E, value is estimated; C, estimated value used in calculation]

Pesticide

Pesticide

trade name Pesticide action1

Number of

detections/

number of

samples2

Laboratory 

minimum

reporting level3

(μg/L)

Maximum

concentration

(μg/L)

Average

concentration

of detections

(μg/L)

Safe drinking

water

standard4

(μg/L)

Focal pesticides detected in Converse County ground water

Atrazine Aatrex Selective herbicide 2/20 0.007 0.005T 0.004C 3

Clopyralid Stinger, Curtail Herbicide 2/19 0.01 22E 22C 1,000

2,4-D 2,4-D Selective herbicide 1/19 0.02 14E NA 70

Simazine Princep Selective herbicide 2/20 0.005 0.01 0.008 4

Tebuthiuron Spike Herbicide 2/20 0.02 0.4E 0.3C 5

500

Non-focal pesticides detected in Converse County ground water

Prometon Pramitol Non-selective herbicide 4/20 0.02 0.2 0.1 5100

Triclopyr Garlon Systemic herbicide 2/20 0.02 19E 12C 400

Focal pesticides not detected in Converse County ground water

Alachlor, Aldicarb, Aldicarb Sulfone6

, Aldicarb Sulfoxide6, Bromacil, Cyanazine,

DCPA, Dicamba, Hexazinone, Metalachlor, Metribuzin, Metsulfuron, Picloram, Telone

Focal pesticides not analyzed in Converse County ground water (no method of analysis available)

Difenzoquat

1

Meister (2002)

2

Each of the 10 wells was sampled twice. One well had only one analysis of 

clopyralid and 2,4-D.

3

The laboratory minimun reporting level is the lowest concentration at which a 

pesticide concentration can be quantified without estimation.

4

U.S. Environmental Protection Agency Maximum Contaminant Level unless 

otherwise noted (U.S. Environmental Protection Agency, 2002).

5

U.S. Environmental Protection Agency Lifetime Health Advisory Level (U.S. 

Environmental Protection Agency, 2002).

6

Degradation product of aldicarb.

The second phase, problem identification 

monitoring, is used to gather additional 

information about the ground water near 

wells with samples having significant 

pesticide detections.

Baseline monitoring is prioritized by 

a county rank and the vulnerability of 

the county’s 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 according to the 

extent of cropland and urban areas in the 

county, as well as the amount of pesticides 

sold within the county in 1991 (Wyoming 

Ground-water and Pesticides Strategy 

Committee, 1999).

A ground-water vulnerability map was 

prepared for the uppermost or shallowest 

aquifer (Hamerlinck and Arneson, 1998). 

A Geographic Information System was 

used to overlay seven layers describing 

hydrogeology and land use. Ground water 

is more vulnerable because of either inherent sensitivity of the hydrogeology, or 

because of the combination of the sensitivity and associated land use. The map was 

Teton (2001-02), Uinta (2002-03), Albany 

(2003-04), Converse (2003-04), and Hot 

Springs (2003-04) Counties. Sampling 

began in 2004 in Carbon, Campbell, and 

Sublette Counties.

GROUND-WATER MONITORING IN 

CONVERSE COUNTY

The ground water in Converse County 

was ranked eighteenth most vulnerable 

to pesticide contamination in Wyoming 

(Wyoming Ground-water and Pesticide 

Strategy Committee, 1999). The vulnerability map created by the Spatial Data 

and Visualization Center (Hamerlinck and 

Arneson, 1998), identifies ground water 

in unconsolidated quaternary deposits in 

the county (primarily alluvial and terrace 

deposits) with urban and agricultural land 

use as the most vulnerable to pesticides 

(shown as red on fig. 2). The focus of the 

sampling was in the alluvial and terrace 

deposits of the North Platte River, Deer 

Creek, and La Bonte Creek (fig. 3).

Ten wells were selected in Converse 

County (fig. 3) for baseline monitoring. 

All wells were located in the Quaternary 

alluvial or terrace deposits. All wells were 

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 (focal 

pesticides) and 2 degradation products to 

be sampled as part of the SMP (table 1). 

The analytical method used to detect the 

focal pesticides can also detect 66 other 

pesticides and degradation products. Any 

additional pesticides detected are listed 

in table 1 as 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, for which analytical 

methods are not available.

The goal of the ground-water sampling 

part of the SMP is to collect ground-water 

samples for pesticide analyses in all 23 

Wyoming counties. To date, sampling has 

been completed in Goshen (1995-96), Park 

(1997), Washakie (1997-98), Fremont 

(1998-99), Lincoln (1998-99), Laramie (1998-99), Big Horn (1999-2000), 

Sheridan (1999-2000), Platte (2000-01), 

Johnson (2000-01), Crook (2000-01), 

Natrona (2001-02), Sweetwater (2001-02), 
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Figure 2. Vulnerability of Converse County, Wyoming ground water to pesticide 

contamination (from Hamerlinck and Arneson, 1998).

sampled in September or October 2003 

and April 2004.

Five of the 19 focal pesticides or degradation products and 2 non-focal pesticide were detected in Converse County 

(table 1). Pesticides were detected in 3 of 

the 10 wells sampled in Converse County. 

Pesticide detections in two of the three 

wells were at low or trace concentrations. 

A trace concentration indicates that the 

pesticide was detected, but at a concentra-

(Barbash and others, 1999). Prometon 

was also the most commonly detected 

pesticide in Sheridan, Crook, Johnson, 

Natrona, Teton, Uinta, and Albany 

Counties.

Clopyralid and triclopyr were 

detected in one well in the county. 

The detections are the first for these 

two pesticides during the sampling 

program.

DATA DISTRIBUTION AND 

AVAILABILITY

Sampling results have been provided to local groups interested in 

pesticides in ground water in Converse 

County. The information can be used 

by citizens and local governments to 

help understand current conditions. 

Analytical results of the Converse 

County sampling can be found in 

Swanson and others (2004), and 

Blajszczak and others (2005), or on the 

internet at http://waterdata.usgs.gov/wy/

nwis/qwdata. Analytical results and fact 

sheets for all counties sampled to date 

are available from the U.S. Geological 

Survey in Cheyenne either by phone, 

email, or on the internet at 

http://wy.water.usgs.gov/projects/

pesticide/.

REFERENCES

Barbash, J.E., and Resek, E.A., 1996, 

Pesticides in ground water: Distribution, trends, and governing factors: 

in Gilliom, R.J., ed., Pesticides in 

the hydrologic system (v. 2): Lewis 

Publishers, 590 p.

Barbash, J.E., Thelin, G.P., Kolpin, 

D.W., and Gilliom, R.J., 1999, 

Distribution of major herbicides in 

ground water of the United States: 

U.S. Geological Survey WaterResources Investigations Report 

98-4245, 64 p.

Blajszczak, E.J., Mason, J.P., Watson, 

K.R., Roberts, S.C., and Miller, 

K.A., 2005, Water-resources data, 

Wyoming, water year 2004, Volume 2. Ground Water: U.S. Geological Survey Water-Data Report 

WY-04-2.

Hamerlinck, J.D., and Arneson, 

C.S., eds., 1998, Wyoming ground 

water vulnerability assessment 

tion too small to quantify without estimation. 

Trace concentrations are qualified with a “T” 

in table 1. All concentrations of the pesticides 

detected were less than 1/5 of the applicable 

drinking-water standard (U.S. Environmental 

Protection Agency, 2002) (table 1).

The most commonly detected pesticide 

(4 of 20 samples) in Converse County was 

prometon, the active ingredient in Pramitol, 

a general-use pesticide. Prometon’s detection 

is typically associated with urban land use 
Figure 3. Location of wells sampled in Converse County, Wyoming, and notation of pesticide 

detection in each well.

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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.

This project has been funded in part with a Section 319 

grant from the U.S. Environmental Protection Agency to 

Wyoming Department of Environmental Quality’s NonPoint Source Program.

The use of trade, product, industry, or firm names is for 

descriptive purposes only and does not imply endorsement by the U.S. Government.

FOR MORE INFORMATION, CONTACT:

Roy Reichenbach

Wyoming Department of Agriculture

2219 Carey Avenue

Cheyenne, Wyoming 82002

(307) 777-6590

Kevin Frederick

Wyoming Department of Environmental 

Quality, Water Quality Division

Herschler Building West, 4th Floor

Cheyenne, Wyoming 82002

(307) 777-5985

handbook: Volume 2. Assessing 

ground water vulnerability to 

pesticides: University of Wyoming, Laramie, Spatial Data and 

Visualization Center Publication 

SDVC 98-01-2, variable pagination.

Hutson, S.S., Barber, N.L., Kenny, 

J.F., Linsey, K.S., Lumia, D.S., 

and Maupin, M.A., 2004, Estimated use of water in the United 

States in 2000: U.S. Geological 

Survey Circular 1268, 46 p.

Meister, R.T., 2002, Farm Chemicals 

Handbook: Willoughby, Ohio, 

Meister Publishing Co., variable 

pagination.

Swanson, R.B., Blajszczak, E.J., 

Roberts, S.C., Watson, K.R., 

and Mason, J.P., 2004, Waterresources data, Wyoming, water 

year 2003, Volume 2. Ground 

Water: U.S. Geological Survey 

Water-Data Report WY-03-2, 

141 p.

U.S. Environmental Protection 

Agency, 2002, Drinking water 

regulations and health advisories: 

EPA 822-R-02-038.

Wyoming Ground-water and Pesticides Strategy Committee, 1999, 

Wyoming generic state management plan for pesticides and 

ground water: prepared for Wyoming Department of Agriculture, 

Cheyenne, Wyoming, 103 p.

• Prepared by Cheryl A. Eddy-Miller and 

Kendra J. Remley

• Layout prepared by Suzanne C. Roberts

Cheryl Eddy Miller

U.S. Geological Survey

2617 E. Lincolnway, Suite B

Cheyenne, Wyoming 82001

(307) 778-2931

Email: cemiller@usgs.gov