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 Natrona 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 (fi g. 1) 

(Barbash and Resek, 1996).

 Pesticide contamination of ground water 

is a national issue because of the widespread 

use of pesticides, the expense and diffi culty 

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 

fi rst phase, baseline monitoring, is designed 

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

 U.S. Department of the Interior

 U.S. Geological Survey 

 USGS Fact Sheet 2004-3079

 August 2004 

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

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

 [μg/L, micrograms per liter; 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 Natrona County ground water

Atrazine Aatrex Selective herbicide 7/22 0.2 0.06C 3

Bromacil Hyvar XL Herbicide 3/22 8 5 490

Picloram Tordon Systemic herbicide 3/22 0.3 0.1C 4500

Simazine Princep Selective herbicide 2/22 0.04 0.04 4

Tebuthiuron Spike Herbicide 5/22 0.6E 0.3C 4500

Non-focal pesticides detected in Natrona County ground water

Prometon Pramitol Non-selective herbicide 9/22 1 0.3C 4100

Focal pesticides not detected in Natrona County ground water

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

Alachlor Aldicarb Sulfone5 Clopyralid DCPA Hexazinone Metribuzin

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

Difenzoquat Metsulfuron

 1

Meister (1996)

 2

Each of the 11 wells was sampled twice.

 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. 

to determine what pesticides, if any, have 

leached into the county’s ground water. The 

second phase, problem identifi cation monitoring, is used to gather additional information about the ground water near wells 

having signifi cant 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, 

and 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), 

and Unita (2002-03) Counties. Sampling 

began in 2003 in Albany, Converse, and Hot 

Springs Counties.

 GROUND-WATER MONITORING IN 

NATRONA COUNTY

 Ground water in Natrona County was 

ranked twelfth 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) identifi es 

three types of ground-water settings as the 

most vulnerable to pesticide contamination 

in the county (shown as red or yellow on 

fi g. 2). Unconsolidated Quaternary deposits, 

including alluvial and terrace deposits, and 

sand and loess deposits make up the largest 

vulnerable area in the county. Ground water 

found in all rocks and deposits, consisting 

primarily of Cretaceous Cody Shale and 

Quaternary alluvial deposits, that underlie 

Casper were considered highly vulnerable. Also considered vulnerable were the 

mountainous areas in the northwestern part 

of the county and due south of Casper. The 

focus of the sampling was in the Casper area 

and along the North Platte River (fi g. 3). 

Although the surfi cial geology makes the 

ground water susceptible to contamination, the large sand deposits north of Casper 

(trending eastward from near Waltman) and 

the mountainous areas were not sampled 

because land use does not create a large 

potential for contamination, and because 

sampling locations were not available in 

these areas.

 Eleven wells were selected in Natrona 

County (fi g. 3) for baseline monitoring. All 

wells were located in Quaternary deposits 

or Cody Shale in locations deemed most 

vulnerable to contamination (shown as red 

on fi g. 2). All wells were sampled in late 

summer 2001 and spring 2002. 
 Five of the 18 focal pesticides and 1 nonfocal pesticide were detected in Natrona 

County (table 1). Pesticides were detected in 

6 of 11 wells sampled; however concentrations of each pesticide were less than 1/10 

of the applicable drinking-water standard 

(U.S. Environmental Protection Agency, 

2002) (table 1). Many 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 

in Natrona County was prometon (detected 

in 9 out of 22 samples). Prometon is the 

active ingredient in Pramitol, a generaluse pesticide, and its detection is typically 

associated with urban land use (Barbash and 

others, 1999). Prometon was also the most 

commonly detected pesticide in Sheridan, 

Crook, Johnson, and Teton Counties.

 The second most commonly detected 

pesticide was atrazine. Atrazine is an agricultural chemical typically used for weed 

control in corn and other crops (Meister, 

1996).

 Bromacil was detected in 3 of 22 

samples. A detection of 8 μg/L (parts per billion) of bromacil (drinking-water standard, 

90 μg/L) is the highest level of the pesticide 

detected in the 14 counties sampled to date 

as part of this project.

 DATA DISTRIBUTION AND 

AVAILABILITY

 The sampling results have been provided to local groups interested in pesticides 

in ground water in Natrona County. The 

information can be used by citizens and 

local governments to help understand current 

conditions. Analytical results of the Natrona 

County sampling can be found in Swanson 

and others (2002) and Swanson and others 

(2003), or on the internet at 

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

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 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 Publishing, 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 Natrona 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 fi rm 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