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R. 68 W. R. 67 W. R. 66 W. R. 65 W. R. 64 W. R. 63 W. R. 62 W. R.61W. R.60W.

Base modified from U.S. Geological Survey

‘Wyoming State base map, 1:500,000, 1980

Lambert Conformal Conic projection

Standard parallels 33° and 45°, central meridian -90°00'

Modified from Case, J.C., Ameson, C.S., and Hallberg, L.L.,
Wyoming Surficial Geology, 1998, scale 1:500,000

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

Mason, J.P., Swanson, R.B., and Roberts,
S.C., 2001, Water resources data,
Wyoming, water year 2000, Volume 2.
Ground Water: U.S. Geological Survey
Water-Data Report WY-00-2, 117 p.

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, Water-resources data, Wyoming,
water year 2001, Volume 2, Ground
Water: U.S. Geological Survey Water-
Data Report WY-01-2, 127 p.

U.S. Environmental Protection Agency, 1996,
Drinking water regulations and health
advisories: EPA 822-B-96-002.

® Printed on recycled paper

Wyoming Department of Environmental
Quality, 1993, Procedures for establishing
environmental restoration standards for
leaking underground storage tank
remediation actions, WDEQ/WQD Rules
and Regulations, Chapter XVII.

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:
Jim Bigelow

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
Laura Gianakos
Layout prepared by Suzanne C. Roberts


aUSGS

science for a changing world

Md Wyoming Department of
R Agriculture

Wyoming Department of
Environmental Quality,
Water Quality Division

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

Environmental Quality (WDEQ)

Pesticides in Ground Water - Crook County, Wyoming, 2000-01

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. In 2000, baseline monitoring began in Crook County.

PESTICIDES IN GROUND WATER

Synthetic organic pesticides are used
to control weeds, insects, and other
organisms in a wide variety of agricul-
tural 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.

WITH-
DRAWAL.

FO
WELLS:
7
SEEPAGE
FROM

REGIONAL TRANSPORT

GROUND-WATE!
CenOM DISCHARGE
STREAMS TO STREAMS

Water is one of the primary ways pesti-
cides 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 per-
cent of the Nation's population. Concern
about pesticides in ground water is espe-
cially acute in rural agricultural areas
where over 95 percent of the population
relies upon ground water for their drink-

PESTICIDE
‘APPLICATION.

RUNOFF

R SEEPAGE

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

Barbash and Resek, 1996).

ing water (Solley and others, 1998),
although application rates and the variety
of pesticides used may be greater in
urban areas.

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). The SMP is required
by the U.S. Environmental Protection
Agency in order for individuals and
organizations to continue using certain
pesticides in Wyoming. The SMP
includes information relating to individu-
als and organizations involved with the
implementation of the SMP, methods of
preventing ground-water contamination,
ground-water monitoring, and what the
responses will be if pesticides are
detected in ground water.

One critical part of the SMP is
ground-water monitoring. The ground-
water monitoring program has two
phases. The first phase involves baseline
monitoring, which is designed to
determine what pesticides, if any, have
leached into the county's ground water.
The second phase is problem identifica-
tion monitoring, which is used to gather
more information about the ground water
near wells with 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

U.S. Department of the Interior
USS. Geological Survey

USGS Fact Sheet 070-02
July 2002


Table 1. Baseline monitoring for pesticides in Crook County, late summer 2000 and spring 2001.

[ug/L, micrograms per liter; NA, not applicable; E, estimated]

Number of Laboratory Average Safe drinking
detections/ minimum Maximum __ concentration water
Pesticide number of reporting limit? concentration of detections’ —standard®
Pesticide trade name Pesticide action’ samples? (ug/L) (ug/L) (ug/L) (ug/L)
Crook County ground water
Atrazine Aatrex Selective herbicide 3/19 0.007 0.02 £0.01 3
DCPA Banvel Herbicide Ag 0.003 E0.004 NA 16
Picloram Tordon Systemic herbicide 4g 0.09 2 0.7 500
Tebuthiuron Spike Herbicide 19 0.02 0.3 NA 6500
Non-focal pesticides detected in Crook County ground water
Prometon Pramitol Non-selective herbicide 6/19 0.02 O41 £0.03 6100
Focal pesticides not detected in Crook County ground water
Alachlor Aldicarb Sulfone” Bromacil Clopyralid Dicamba Metolachlor Simazine
Aldicarb Aldicarb Sulfoxide” 2,4-D Cyanazine Hexazinone Metribuzin Telone
Focal pesticides not analyzed in Crook County ground water (no method of analysis available)
Difenzoquat Metsulfuron

‘Meister (1996)

*Each of 9 wells was sampled twice. One well was only sampled in the

summer of 2000.

$The laboratory minimum reporting limit is the lowest concentration at
which a pesticide concentration can be quantified without estimation

SEPA Maximum Contaminant Level unless otherwise noted

(U.S. Environmental Protection Agency, 1996)

SEPA Lifetime Health Advisory Level (U.S. Environmental

“The average concentration is noted as E, estimated, if one or more
values used in the calculation was an estimated value.

Wyoming to determine the potential
vulnerability of the county's ground water
to pesticides. Each county was ranked
based on 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. 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 chemical analysis
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), and Crook (2000-01) Counties.
Sampling is currently being conducted in
Natrona, Sweetwater, and Teton
Counties.

GROUND-WATER MONITORING
IN CROOK COUNTY

The ground water in Crook County
was ranked eleventh most vulnerable to
pesticide contamination in Wyoming
(Wyoming Ground-water and Pesticide
Strategy Committee, 1999). The
vulnerability map for Crook County
(fig. 2) (Hammerlink and Arneson, 1998)
identifies shallow alluvial and terrace

Protection Agency, 1996)
Degradation product of Aldicarb.

deposits as the most vulnerable in the
county.

Ten wells were selected in Crook
County (fig. 3) for baseline monitoring.
All wells were located in the Quaternary
deposits deemed most vulnerable (shown
as red in fig. 2). The wells were selected
with the assistance of the Crook County
Conservation District. Nine of the ten
wells were sampled twice, in late summer
2000 and spring 2001. One well was
only sampled in the late summer 2000, as
the well had been taken out of service by
spring 2001.

Four of the 18 focal pesticides and
1 non-focal pesticide were detected in
Crook County (table 1). Pesticides were
detected in 7 of the 10 wells sampled in
Crook County; however, the concentra-
tions of each pesticide detected were less
than 1/150 of the applicable drinking-
water standard (U.S. Environmental
Protection Agency, 1996; Wyoming
Department of Environmental Quality,
1993) (table 1). Some of the detections
were less than the minimum reporting
level, at trace concentrations. A trace
concentration indicates that the pesticide
was detected, but at a concentration too


105°00’ MONTANA

104°45'
45°00" .

T. 56/2 N

4a°a5'

44°30"

44°15"

R.68W. R.67W.  R.66W.

Base modified from U.S. Geological Survey
‘Wyoming State base map, 1:500,000, 1980
Lambert Conformal Conic projection

Standard parallels 33° and 45°, central meridian -90°00

R.65 W.

104°30"

R.64W, R. 62 W.

R. 63 W.
0 5
0 5

ce
Nowy MING

| - meh |
cL or ty

T.56N.
EXPLANATION
VULNERABILITY TO PESTICIDE
T.55 N. CONTAMINATION

|| High

LL] Medium high
HE vedium
HE Medium iow
Ho

T.54N,

T.53N.

T.52N.

SIN.

= SOUTH DAKOTA =
A
8
Z

s
é
Zz

R.61W. R.60W.

10 MILES

10 KILOMETERS.

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

small to quantify without estimation.
Trace concentrations are qualified with
an “E” (table 1).

The most commonly detected
pesticide in Crook County was prometon
(detected in 6 out of 19 samples), the
active ingredient in Pramitol. Prometon
is a general-use pesticide and its detec-
tion is typically associated with urban
land use (Barbash and others, 1999).
This is different than most counties
sampled for baseline monitoring, where
atrazine was the most commonly detected
pesticide (Goshen, Park, Washakie,
Fremont, Laramie, Big Horn, and Platte
Counties).

Picloram was the second most
commonly detected pesticide in Crook
County (detected in 4 out of 19 samples).
Picloram is the active ingredient in the

agricultural pesticide, Tordon, and is one
of the most commonly used pesticides in
Wyoming.

DATA DISTRIBUTION AND
AVAILABILITY

The sampling results have been
provided to local groups interested in
pesticides in ground water in Crook
County. The information can be used by
citizens and local governments to help
understand current conditions. Analytical
results of the Crook County sampling can
be found in Mason and others (2001), and
Swanson and others (2002). 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
(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): Chelsea, Mich., Ann Arbor
Press, 588 p.

Barbash, J.E., Thelin, GP., Kolpin, D.W., and
Gillom, R.J., 1999, Distribution of major
herbicides in ground water of the United
States: U.S. Geological Survey Water-
Resources Investigations Report 98-4245,
64 p.

Hammerlink, J.D., and Arneson, C.S., editors,
1998, Wyoming ground water vulnerabil-
ity 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.