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 2002-03, baseline monitoring was conducted in Uinta 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 Ground-water 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 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 with samples having significant pesticide detections.

Pesticides in Ground Water - Uinta County, Wyoming, 2002-03

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2004-3093

August 2004

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

and Resek, 1996).
Table 1. Summary of baseline monitoring for pesticides in Uinta County, September 2002 and April 2003

[μg/L, micrograms per liter; NA, not applicable; E, trace concentration, 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 Uinta County ground water

Atrazine Aatrex Selective herbicide 5/24 0.001 0.01 0.008C 3

Bromacil Hyvar XL Herbicide 1/24 0.04 0.1 NA 590

Simazine Princep Selective herbicide 3/24 0.005 0.06 0.03C 4

Tebuthiuron Spike Herbicide 1/24 0.01 0.01E NA 5500

Non-focal pesticides detected in Uinta County ground water

Prometon Pramitol Non-selective herbicide 11/24 0.02 1 0.2C 5100

Focal pesticides not detected in Uinta County ground water

2,4-D, Alachlor, Aldicarb, Aldicarb Sulfone6, Aldicarb Sulfoxide6, Clopyralid, Cyanazine, DCPA, Dicamba, Hexazinone,

Metalachlor, Metribuzin, Picloram, Telone

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

Difenzoquat, Metsulfuron

1

Meister (1996)

2

Each of the 12 wells was sampled twice.

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.

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 (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 

the 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), 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 

UINTA COUNTY

Ground water in Uinta County was ranked 

sixteenth 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 (Hammerlink and 

Arneson, 1998), identifies ground water found 

in unconsolidated Quaternary deposits in the 

county (primarily alluvial and terrace deposits) 

with urban and agricultural land use as the 

most vulnerable to pesticide contamination 

(shown as red in fig. 2). The focus of the sampling was in the alluvial and terrace deposits 

of the Bear and Blacks Fork Rivers and their 

tributaries (fig. 3).

Twelve wells were selected in Uinta County 

(fig. 3) for baseline monitoring. All wells were 

completed in the Quaternary or terrace deposits. All wells were sampled in September 2002 

and April 2003.

Four of the 18 focal pesticides and 1 nonfocal pesticide were detected in Uinta County 

(table 1). Pesticides were detected in 6 of the 

12 wells sampled; however, the concentrations 

of each pesticide detected were generally less 

than 1/66 of the applicable drinking-water standard (U.S. Environmental Protection Agency, 

2002) (table 1). About one-third of the 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 (11 

of 24 samples) in Uinta County was prometon, 

the active ingredient in Pramitol, a general-use 

pesticide. Prometon’s detection is typically 

associated with urban land use (Barbash and 

others, 1999). Prometon also was the most 

commonly detected pesticide in Sheridan, 

Crook, Johnson, Natrona, and Teton Counties.

The second most commonly detected pesticide in Uinta County was atrazine (detected in 

5 out of 24 samples). Atrazine is an agricultural 

chemical typically used for weed control in 

corn and other crops (Meister, 1996).
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DATA DISTRIBUTION AND 

AVAILABILITY

The sampling results have been provided to 

local groups interested in pesticides in ground 

water in Uinta County. The information can 

be used by citizens and local governments to 

help understand current conditions. Analytical results of the Uinta County sampling can 

be found in Swanson and others (2003), and 

Swanson and others (2004), 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/.

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

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.

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

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., 2003, Waterresources data, Wyoming, water year 2002, 

Volume 2. Ground Water: U.S. Geological 

Survey Water-Data Report WY-02-2, 140 p.
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Figure 3. Location of wells sampled in Uinta County, Wyoming, and notation of pesticide detection in each well.

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 Prepared by Cheryl A. Eddy-Miller and Cheryl A. Eddy-Miller and

Kendra J. Remley

• Layout prepared by Layout prepared by Suzanne C. Roberts Suzanne C. Roberts

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.

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:

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

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