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R.70W. R6OW. R6BW. RE7W. R.EOW. R.6SW.

Base modified from US. Geological
Survey Wyorning State base map,
1500,000, 1980

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

Lambert Conformal Conic projection o 5 10 15 MILES.
‘Standard parallels 33° and 45°,
central meridian -90°00" 0 5 10 15 KILOMETERS.
EXPLANATION “4 TI
QUATERNARY ALLUVIAL AND Pr _ ia
TERRACE DEPOSITS | an

@ NO PESTICIDE DETECTED IN WELL
@ PESTICIDE DETECTED IN WELL

ms ne

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

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.

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., Blajszezak, E.J., Roberts, $.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.

Wyoming Department of Environmental Quality,
1993, Procedures for establishing environ-
mental 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.

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

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

® Printed on recycled paper


aUSGS

Science for a changing world

37 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 - Platte 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 Platte 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.
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

REGIONAL TRANSPORT

Figure 1. Pathways of pesticide movement in the hydrologic cycle (modified from
Barbash and Resek, 1996).

where over 95 percent of the population
relies upon ground water for their drink-
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.

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

USGS Fact Sheet 068-02
July 2002


Table 1. Baseline monitoring for pesticides in Platte County, late summer/fall 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)
Focal pesticides detected in Platte County ground water
Atrazine Aatrex Selective herbicide 6/24 0.01 0.1 £0.03 3
Bromacil Hyvar XL Herbicide 2/24 0.09 1 1 ®90
2,4-D 2,4-D Selective herbicide 1/24 0.1 £0.04 NA 70
Picloram Tordon Systemic herbicide 4/24 0.09 3 —1 500
Tebuthiuron Spike Herbicide 2/24 0.02 0.07 0.05 ®500
Non-focal pesticides detected in Platte County ground water
Prometon Pramitol Non-selective herbicide 4/24 0.02 0.04 £0.01 *100
Focal pesticides not detected in Platte County ground water
Alachlor Aldicarb Sulfone” Clopyralid DCPA Hexazinone Metribuzin Telone
Aldicarb Aldicarb Sulfoxide” Cyanazine Dicamba Metolachlor Simazine
Focal pesticides not analyzed in Platte County ground water (no method of analysis available)
Difenzoquat Metsulfuron

‘Meister (1996)
Each of the 12 wells was sampled twice.

The laboratory minimum reporting limit is the lowest concentration at
which a pesticide concentration can be quantified without estimation.
“The average concentration is noted as E, estimated, if one or more

SEPA Maximum Contaminant Level unless otherwise noted

(U.S. Environ

values used in the calculation was an estimated value.

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
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.

mental Protection Agency, 1996).

°EPA Lifetime Health Advisory Level (U.S. Environmental
Protection Agency, 1996).
Degradation product of Aldicarb.

GROUND-WATER MONITORING
IN PLATTE COUNTY

The ground water in Platte County
was ranked ninth most vulnerable to
pesticide contamination in Wyoming
(Wyoming Ground-water and Pesticide
Strategy Committee, 1999). The
vulnerability map for Platte County
(fig. 2) (Hammerlink and Arneson, 1998)
identifies shallow alluvial and terrace
deposits, as well as Quaternary sand and
loess deposits as the most vulnerable in
the county.

Twelve wells were selected in Platte
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 Platte County
Conservation District. All wells were
sampled twice, in late summer or fall
2000 and spring 2001.

Five of the 18 focal pesticides and
1 non-focal pesticide were detected in
Platte County (table 1). Pesticides were
detected in 6 of the 12 wells sampled in


105°15" 104°45"

105°00"

T.30 N.

T.29N.

T. 28 N.

T. 24N.

T. 23 N.

T.22N.

R69W. R68W. RE7W. R.EOW. R.65W.
Base modified from U.S. Geological Survey 0 5 10 15 MILES
\Wyorning State base map, 1:500,000, 1980
Lambert Conformal Conic projection 0 5 10 15 KILOMETERS

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

EXPLANATION
VULNERABILITY TO PESTICIDE CONTAMINATION hy

|| High
[| Medium high
Wi Medium

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

PAS

Medium low

| A
. ! + Platte:

Platte County; however the concentrations of
each pesticide detected were less than 1/30 of
the applicable drinking-water standard

(U.S. Environmental Protection Agency,
1996; Wyoming Department of
Environmental Quality, 1993) (table 1).
Several of the detections were less than the
minimum reporting level, at trace concentra-
tions. A trace concentration indicates that the
pesticide was detected, but at a concentration
too small to quantify without estimation.
Trace concentrations are qualified with an
“E” (table 1).

The most commonly detected pesticide in
Platte County was atrazine (detected in 6 out
of 24 samples). Atrazine was also the most
commonly detected pesticide in Goshen,
Park, Washakie, Fremont, and Laramie
Counties. Atrazine is an agricultural
chemical typically used for weed control in
corn and other crops (Meister, 1996).

Picloram and prometon were the second
most commonly detected pesticides in Platte
County (both were detected in 4 out of
24 samples). Picloram is the active ingredi-
ent in the agricultural pesticide, Tordon, and
is one of the most commonly used pesticides
in Wyoming. Prometon in the active
ingredient in Pramitol. Prometon is a
general-use pesticide and its detection is
typically associated with urban land use
(Barbash and others, 1999).

DATA DISTRIBUTION AND
AVAILABILITY

The sampling results have been provided
to local groups interested in pesticides in
ground water in Platte County. The informa-
tion can be used by citizens and local
governments to help understand current
conditions. Analytical results of the Platte
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, RJ, 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 vulnerability