Wyoming Department 

of Agriculture

Wyoming Department of 

Environmental Quality, 

Water Quality Division

Printed on recycled paper

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 2001-02, baseline monitoring was conducted in Sweetwater 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 50 percent 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 (Solley and others, 1998).

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 

developed an 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 

Pesticides in Ground Water - Sweetwater County, Wyoming, 2001-02

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2004-3078

August 2004

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

Barbash and Resek, 1996).
Table 1. Baseline monitoring for pesticides in Sweetwater County, late summer/fall 2001 and spring 2002.

[μg/L, micrograms per liter; NA, not applicable; E, trace concentration too small to quantify without estimation; C, estimated value used in calculation]

Pesticide

Pesticide

trade name Pesticide action1

Number of

detections/

number of

samples2

Maximum

concentration

(μg/L)

Average

concentration

of detections

(μg/L)

Safe drinking

water

standard3

(μg/L)

Focal pesticides detected in Sweetwater County ground water

Atrazine Aatrex Selective herbicide 2/22 0.02 0.02 3

Bromacil Hyvar XL Herbicide 1/21 0.1 NA 490

Picloram Tordon Systemic herbicide 1/15 0.04E NA 500

Tebuthiuron Spike Herbicide 5/22 0.05 0.03C 4500

Non-focal pesticides detected in Sweetwater County ground water

Prometon Pramitol Non-selective herbicide 3/22 0.09 0.05C 4100

Focal pesticides not detected in Sweetwater County ground water

2,4-D Aldicarb Aldicarb Sulfoxide5 Cyanazine Dicamba Metalachlor Simazine

Alachlor Aldicarb Sulfone5 Clopyralid DCPA Hexazinone Metribuzin Telone

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

Difenzoquat Metsulfuron

1

Meister (1996)

2

Each of the 11 wells was sampled twice. One well had only one analysis for 

bromacil. Seven wells had only one analysis for picloram. 3

U.S. Environmental Protection Agency Maximum Contaminant Level unless 

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

4

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

Environmental Protection Agency, 2002). 5

Degradation product of aldicarb.

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. 

The second phase, problem identification 

monitoring, is used to gather additional 

information about the ground water near 

wells having significant pesticide detections.

Baseline monitoring is prioritized by 

a county rank and the vulnerability of the 

county’s ground water to pesticides. During 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 (Hammerlink 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 

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 pesticides listed in table 1, with the exception 

of difenzoquat and metsulfuron, for which 

analytical methods were 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), Teton 

(2001-02), and Uinta (2002-03) Counties. 

Sampling began in 2003 in Albany, Converse, and Hot Springs Counties.

GROUND-WATER MONITORING IN 

SWEETWATER COUNTY

Ground water in Sweetwater County 

was ranked fourteenth most vulnerable 

to pesticide contamination in Wyoming 

(Wyoming Ground-water and Pesticide 

Strategy Committee, 1999). In general, the 

vulnerability map created by the Spatial 

Data and Visualization Center (Hammerlink and Arneson, 1998), identifies ground 

water found in unconsolidated Quaternary 

deposits including alluvial and terrace 

deposits, and sand and loess deposits, as 

the most vulnerable in the county (shown 

as red or yellow on fig. 2). All ground 

water found in rocks and deposits, consisting primarily of Cretaceous and Tertiary 

rocks and Quaternary alluvial deposits, 

that underlie Rock Springs and Green 

River also were considered highly vulnerable (fig. 3). The large sand deposits in 

the northern and the southeastern parts of 

the county were not sampled. Although 

the hydrogeology makes ground water in 

these areas susceptible to contamination, 

land use there does not create a potential 
for contamination, nor were sampling 

locations available.

Eleven wells were selected in Sweetwater County (fig. 3) for baseline monitoring. All wells were sampled in late 

summer/fall 2001 and spring 2002. Four 

of the 18 focal pesticides and 1 non-focal 

pesticide were detected in Sweetwater 

County (table 1). Pesticides were detected 

in 5 of 11 wells sampled; however, the 

concentrations of each pesticide detected 

were less than 1/150 of the applicable 

drinking-water standard (U.S. Environmental Protection Agency, 2002) (table 1). 

Many detections were at trace concentrations too small to quantify without estimation. Trace concentrations are denoted 

with an “E” in table 1.

The most commonly detected pesticide 

in Sweetwater County was tebuthiuron 

(detected in 5 out of 22 samples). Tebuthiuron is an herbicide used in noncropland 

areas, rangeland, and right-of-ways 

Figure 2. Vulnerability of Sweetwater County ground water to pesticide contamination (from Hammerlink and Arneson, 1998).

(Meister, 1996). No other county sampled 

to date had tebuthiuron as the most commonly detected pesticide.

The second most commonly detected 

pesticide in Sweetwater County was 

prometon, the active ingredient in Pramitol, which is a general-use pesticide. 

Prometon’s detection is typically associated with urban land use (Barbash and 

others, 1999).

DATA DISTRIBUTION AND 

AVAILABILITY

Sampling results have been provided 

to local groups interested in pesticides 

in ground water in Sweetwater County. 

The information can be used by citizens 

and local governments to help understand 

current conditions. Analytical results of 

the Sweetwater County sampling can be 

found in Swanson and others (2002) and 

Swanson and others (2003), 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 by phone, email, and 

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

Hammerlink, J.D., and Arneson, C.S., editors, 

1998, Wyoming ground water vulnerability 

assessment 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.

Meister, R.T., 1996, Farm Chemicals Handbook: Willoughby, Ohio, Meister Publishing 

Co., variable pagination.

Solley, W.B., Pierce, R.R., and Perlman, H.A., 

1998, Estimated use of water in the United 

States in 1995: U.S. Geological Survey 

Circular 1200, 71 p.

Swanson, R.B., Blajszczak, E.J., Roberts, S.C., 

Watson, K.R., and Mason, J.P., 2002, Waterresources data, Wyoming, water year 2001, 

Volume 2. Ground Water: U.S. Geological 

Survey Water-Data Report WY-01-2, 127 p.

Swanson, R.B., Blajszczak, E.J., Roberts, S.C., 

Watson, K.R., and Mason, J.P., 2003, Waterresources data, Wyoming, water year 2002, 

Volume 2. Ground Water: U.S. Geological 

Survey Water-Data Report WY-02-2, 140 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.

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 Non-Point 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:

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

Cheryl Eddy Miller

U.S. Geological Survey, WRD

2617 E. Lincolnway, Suite B

Cheyenne, Wyoming 82001

(307) 778-2931

Email: cemiller@usgs.gov

• Prepared by Cheryl A. Eddy-Miller and 

Kendra J. Remley

• Layout prepared by Suzanne C. Roberts