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 2004–2005, baseline monitoring was conducted in Sublette County. This 

fact sheet describes and summarizes results of the baseline monitoring in Sublette 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, also has 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 one-half 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 Ground-water and Pesticides Strategy Committee, 1999). Wyoming 

was required by the U.S. Environmental 

Protection Agency to have 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 entered 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.

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 

Pesticides in Ground Water - Sublette County, Wyoming, 2004–2005

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006-3121

November 2006

Wyoming Department 

of Environmental 

Quality
Table 1. Summary of baseline monitoring for pesticides in Sublette County, September 2004 and April 2005.

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

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 Sublette County ground water

Atrazine Aatrex Selective herbicide 1/20 0.007 0.007 -- 3

Bromacil Hyvar XL Herbicide 2/20 .03 E2 C1 590

Clopyralid Stinger, Curtail Herbicide 2/20 .02 E.1 C.08 51,000

Picloram Tordon Systemic herbicide 1/20 .02 E.4 -- 500

Simazine Princep Selective herbicide 1/20 .005 .01 -- 4

Tebuthiuron Spike Herbicide 3/20 .02 .4 .2 5500

Non-focal pesticides detected in Sublette County ground water

p,p’-DDE DDT degradation product-- 1/20 0.003 0.02 -- --

Dieldrin Panoram D 31 Insecticide 1/20 .005 E.007 -- 62

Diuron Durashield Herbicide 2/20 .01 .08 0.08 510

cis-Permethrin Ambush, Pounce Herbicide 1/20 .006 .01 -- --

Prometon Pramitol Non-selective herbicide 3/20 .01 .02 .01 5100

Sulfometuron Oust Herbicide 1/20 .009 E.02 -- --

Focal pesticides not detected in Sublette County ground water

Alachlor, Aldicarb, Aldicarb Sulfone7, Aldicarb Sulfoxide7, Cyanazine, 2,4-D, 

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

Focal pesticide not included in analysis of Sublette County ground water (no method of analysis available)

Difenzoquat

1

Meister (2002)

2

Each of the 10 wells was sampled twice.

3

The laboratory minimum 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, 2004).

5

U.S. Environmental Protection Agency Lifetime Health Advisory Level 

(U.S. Environmental Protection Agency, 2004).

6

U.S. Environmental Protection Agency Drinking Water Equivalent Level 

(U.S. Environmental Protection Agency, 2004).

7

Degradation product of aldicarb.

(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 vulnerable because of either 

inherent sensitivity of the hydrogeology or 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 and 

2 degradation products as the focal pesticides 

for analysis as part of the SMP (table 1). The 

analytical methods used to detect the focal 

pesticides also detect 115 other pesticides and 

degradation products. Any additional pesticides 

that were detected are listed in table 1 as nonfocal 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 an analytical 

method was not available.

The goal of the ground-water monitoring 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 (1995–1996), Park (1997), Washakie 

(1997–1998), Fremont (1998–1999), Laramie 

(1998–1999), Lincoln (1998–1999), Big Horn 

(1999–2000), Sheridan (1999–2000), Crook 

(2000–2001), Platte (2000–2001), Johnson 

(2000–2001), Natrona (2001–2002), Sweetwater (2001–2002), Teton (2001–2002), Uinta 

(2002–2003), Albany (2003–2004), Converse 

(2003–2004), Hot Springs (2003–2004), Campbell (2004–2005), Carbon (2004–2005), and

Niobrara and Weston (2005–2006) Counties.

Ground-Water Monitoring in 

Sublette County

Ground water in Sublette County was ranked 

twenty-second most vulnerable to pesticide 

contamination in Wyoming (Wyoming Groundwater and Pesticide Strategy Committee, 1999). 

The vulnerability map created by the Spatial Data 

and Visualization Center (Hamerlinck and Arneson, 1998), identifies unconsolidated Quaternaryage deposits in the county (primarily alluvial and 

terrace deposits) that underlie 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 Green River, New Fork River, Piney Creek, 

Horse Creek, and North Piney Creek (fig. 3). 

Some mountainous areas in Sublette County also

were considered highly vulnerable (fig. 2). These 

areas were not sampled because, although the 

hydrogeology makes the ground water susceptible 

to contamination, the land use does not create a 

large potential for contamination.

Ten wells were selected in Sublette County 

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

located in the red areas shown on figure 2; however, in some areas, the alluvial and terrace deposits were not thick enough to provide water for 

wells, and the wells in the area were completed 

in the Tertiary-age Wasatch Formation. All wells 

were sampled twice, once in September 2004 and 

once in April 2005.
Figure 2. Vulnerability of Sublette County, Wyoming ground water to pesticide contamination (from Hamerlinck and Arneson, 1998).

Hoback R e iv r

Cliff Creek

River

River

Green

Creek

East

Fork

River

River

Sandy

Creek

Creek

Sandy

Sandy

Little

Dry

Big

La Barge

Creek

Muddy

Creek

Pole

River

River

Creek

Creek

Creek

Creek

Creek

Creek

Horse

Creek

North

Creek

Creek

Fish

Piney

Piney

Muddy

Cottonwood

C o o tt onw od

Piney

Piney

South

North

Middle

Fork

Fork

New

New

Green

Green

 River

 Lakes

New Fork

Lakes

Willow

Lake

Fremont

 Lake

 Boarder

Lake

Big Sandy

Reservoir

Pine

Creek

WYOMING

Sublette

County

110°30'

110°00'

109°30'

43°00'

Big Piney

Big Sandy

Pinedale

Merna

42°30'

15 MILES

0 5 10 15 KILOMETERS

0 5 10

T. 27 N.

T. 28 N.

T. 29 N.

T. 30 N.

T. 31 N.

T. 32 N.

T. 33 N.

T. 35 N.

T. 36 N.

T. 37 N.

T. 38 N.

T. 39 N.

T. 40 N.

R. 112 W. R. 111 W. R. 110 W. R. 109 W. R. 108 W. R. 107 W. R. 106 W. R. 105 W. R. 104 W. R. 103 W. R. 115 W. R. 114 W. R. 113 W.

Base modified from U.S. Bureau of the Census digital data, 2001

Public land survey system from Wyoming Water Resources Center digital data, 1994

Albers Equal-Area Conic projection, Standard parallels 29°30' and 45°30', central meridian 110°00'

353

351

352

191

191

189

189

EXPLANATION

Vulnerability to pesticide

 contamination

High

Medium high

Medium

Medium low

Low T. 34 N.

Six of the 19 focal pesticides with available analyses and 6 non-focal pesticides 

were detected in Sublette County (table 1). 

Pesticides were detected in 3 of the 10 wells 

sampled in Sublette County; concentrations of 

each detected pesticide were less than or equal 

to 1/45 of the applicable drinking-water standard (U.S. Environmental Protection Agency, 

2004) (table 1).

The most commonly detected pesticides 

(3 of 20 samples) in Sublette County were 

tebuthiuron and prometon. Tebuthiuron is an 

herbicide used in non-cropland areas, rangeland, and rights-of-ways (Meister, 2002). 

Tebuthiuron also was the most commonly 

detected pesticide in Sweetwater and Hot 

Springs Counties. Prometon, the active ingredient in the general-use pesticide Pramitol, typically is detected in areas with urban land use 

(Barbash and others, 1999). Prometon was the 

most commonly detected pesticide in Albany, 

Campbell, Carbon, Converse, Crook, Johnson, 

Natrona, Sheridan, Teton, and Uinta Counties.

Data Distribution and Availability

Sampling results have been provided to 

local groups interested in pesticides in ground 

water in Sublette County. The information can 

be used by citizens and local governments to 

help understand current conditions. Analytical 

results of the Sublette County sampling can 

be found in Blajszczak and others (2005), and 

Blajszczak and others (2006) 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, or 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: Chelsea, Mich., Ann 

Arbor Press, Pesticides in the Hydrologic 

System series, v. 2, 588 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, 181 p.
Figure 3. Location of wells sampled in Sublette County, Wyoming, and notation of pesticide detection in samples from each well.

Hoback R e iv r

Cliff Creek

River

River

Green

Creek

East

Fork

River

River

Sandy

Creek

Creek

Sandy

Sandy

Little

Dry

Big

La Barge

Creek

Muddy

Creek

Pole

River

River

Creek

Creek

Creek

Creek

Creek

Creek

Horse

Creek

North

Creek

Creek

Fish

Piney

Piney

Muddy

Cottonwood

C o o tt onw od

Piney

Piney

South

North

Middle

Fork

Fork

New

New

Green

Green

 River

 Lakes

New Fork

Lakes

Willow

Lake

Fremont

 Lake

 Boarder

Lake

Big Sandy

Reservoir

Pine

Creek

WYOMING

Sublette

County

Big Piney

Big Sandy

Pinedale

Merna

15 MILES

0 5 10 15 KILOMETERS

0 5 10

T. 27 N.

T. 28 N.

T. 29 N.

T. 30 N.

T. 31 N.

T. 32 N.

T. 33 N.

T. 34 N.

T. 35 N.

T. 36 N.

T. 37 N.

T. 38 N.

T. 39 N.

T. 40 N.

R. 112 W. R. 111 W. R. 110 W. R. 109 W. R. 108 W. R. 107 W. R. 106 W. R. 105 W. R. 104 W. R. 103 W. R. 115 W. R. 114 W. R. 113 W.

353

351

352

191

191

189

189

110°30'

110°00'

109°30'

43°00'

42°30'

Base modified from U.S. Bureau of the Census digital data, 2001

Public land survey system from Wyoming Water Resources Center digital data, 1994

Albers Equal-Area Conic projection, Standard parallels 29°30' and 45°30', central meridian 110°00'

Quaternary alluvial and

 terrace deposits

EXPLANATION

No pesticide detected

 in samples

Pesticide detected in at

 least one sample

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

Roberts, S.C., and Miller, K.A., 2006, 

Water-resources data, Wyoming, water 

year 2005, Volume 2. Ground Water: U.S. 

Geological Survey Water-Data Report 

WY–05–2, 173 p.

Hamerlinck, 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.

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.

U.S. Environmental Protection Agency, 2004, 

Drinking water regulations and health advisories: EPA 822–R–04–005, 12 p.

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 fact sheet 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

Cheryl Eddy Miller

U.S. Geological Survey

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