U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5064

Prepared in cooperation with the Wyoming Department of Agriculture on behalf 

of the Wyoming Ground-water and Pesticides Strategy Committee

Pesticides in Wyoming Groundwater, 2008–10
Cover. Bighorn Basin geographic area. Photograph by Cheryl Eddy-Miller, U.S. Geological Survey.
Pesticides in Wyoming Groundwater, 

2008–10

By Cheryl A. Eddy-Miller, Timothy T. Bartos, and Michelle L. Taylor

Prepared in cooperation with the Wyoming Department of Agriculture on behalf 

of the Wyoming Ground-water and Pesticides Strategy Committee

Scientific Investigations Report 2013–5064

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Eddy-Miller, C.A., Bartos, T.T., and Taylor, M.L., 2013, Pesticides in Wyoming Groundwater, 2008–10: U.S. Geological 

Survey Scientific Investigations Report 2013–5064, 45 p.

ISBN 978-1-4113-3579-0
iii

Acknowledgments

The authors gratefully acknowledge the generous assistance of landowners throughout 

Wyoming who provided access to their property and wells for the sampling. The authors 

also acknowledge assistance with site selection from the many Conservation Districts 

and County Weed and Pest Districts in Wyoming. 
iv

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Methods of Investigation..............................................................................................................................2

Selection of Sampling Locations........................................................................................................2

Sample Collection and Chemical Analyses......................................................................................5

Data Reporting and Treatment............................................................................................................5

Laboratory Reporting Levels......................................................................................................5

Recensoring and Assessment Levels ....................................................................................14

Quality-Control Samples and Quality Assurance ..........................................................................14

Field-Blank Samples..................................................................................................................14

Replicate Samples.....................................................................................................................14

Field-Matrix Spike Samples .....................................................................................................17

Pesticide Occurrence during 2008–10 Resampling Study ....................................................................17

Pesticides Detected during 2008–10 Resampling Study ..............................................................17

Pesticide Detection Frequency by Well During the 2008–10 Resampling Study......................19

Pesticide Detections by Action During the 2008–10 Resampling Study....................................19

Differences in Pesticide Occurrence between 1995–2006 Baseline and 2008–10 Resampling 

Studies..............................................................................................................................................19

Differences in Pesticides Detected.................................................................................................19

Differences in Pesticide Detections................................................................................................19

Differences in Pesticide Concentrations........................................................................................19

Differences in Pesticide Detections and Detection Frequency Relative to Land Use and 

Geographic Area ...................................................................................................................25

Summary........................................................................................................................................................32

References Cited..........................................................................................................................................33

Appendixes ...................................................................................................................................................35

Figures

1. Map showing wells sampled from the eight geographic areas of Wyoming during

the 1995–2006 baseline study .....................................................................................................3

2. Map showing location of, and land use near, the 52 wells sampled during the

2008–10 resampling study, Wyoming.........................................................................................4

3. Graph showing pesticide detections and concentrations (using no assessment

level) in groundwater samples collected from 52 wells during the 2008–10

resampling study, Wyoming......................................................................................................18

4. Graph showing number of pesticides detected in groundwater samples collected

from 52 wells sampled during the 2008–10 resampling study (using no assessment

level), compound-specific assessment level, and common assessment level, 

Wyoming.......................................................................................................................................22
v

5. Graph showing pesticide detections relative to pesticide action in groundwater

samples collected from 52 wells sampled during the 2008–10 resampling study,

Wyoming.......................................................................................................................................22

6. Graph showing pesticide detections and concentrations (using no assessment

level) in groundwater samples collected from 52 wells during the 1995–2006

baseline study .............................................................................................................................24

7. Pie diagram showing difference in number of pesticides detected in the same well

between the 1995–2006 baseline and 2008–10 resampling studies ...................................25

8. Graphs showing pesticide detections and concentrations in groundwater samples

collected from 52 wells during 1995–2006 baseline study and 2008–10 resampling 

study, Wyoming...........................................................................................................................28

9. Graphs showing percentage of wells with at least one pesticide detected in

groundwater samples collected from 52 wells relative to land use and geographic

area during the 1995–2006 baseline study and the 2008–10 resampling study, 

Wyoming.......................................................................................................................................30

10. Pie diagrams showing difference in number of pesticides detected in the same

well between 1995–2006 baseline and 2008–10 resampling studies..................................31

Tables

1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with

trade names, pesticide actions, pesticide classes, laboratory reporting levels, and

U.S. Environmental Protection Agency drinking-water standards ......................................6

2. Pesticides detected in groundwater samples collected from 52 wells sampled

during both 1995–2006 baseline study and 2008–10 resampling study..............................15

3. Summary of pesticide detections and concentrations in groundwater sampled

during the 2008–10 resampling study, Wyoming ..................................................................20

4. Pesticides detected in the 52 wells sampled during 1995–2006 baseline study and

(or) 2008–10 resampling study, Wyoming ...............................................................................23

5. Differences in pesticide detections between the 1995–2006 baseline study and the

2008–10 resampling study, Wyoming.......................................................................................26

Appendix 1. Blank data for sample collected at site 410817104470201, November 2009 .............36

Appendix 2. Replicate sample data for detected pesticides from samples collected at sites

4108108104223501 (September 2009) and 444603108383401 (September 2010)................36

Appendix 3. Spike recovery data from sample collected from site 41101910405130 (Lr7),

September 2008...........................................................................................................................37

Appendix 4. Name, number, and ancillary information for 52 wells sampled during

1995–2006 baseline study and 2008–10 resampling study, Wyoming.................................39

Appendix 5. Summary of pesticides distributed within Wyoming, 2007..........................................41
vi

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Concentrations of chemical constituents in water are given in micrograms per liter (μg/L).

Abbreviations

CAL common assessment level

CSAL compound-specific assessment level

E estimated

GPSC Ground-water and Pesticides Strategy Committee

KSOCRL U.S. Geological Survey Organic Chemistry Research Laboratory in 

Lawrence, Kansas 

LHA Lifetime Health Advisory

LRL laboratory reporting level

LT-MDL long-term method detection level

MCL Maximum Contaminant Level

MDL method detection limit

MRL minimum reporting level

NAL no assessment level 

NLCD National Land Cover Data

NWQL National Water Quality Laboratory of U.S. Geological Survey

QA quality assurance

QC quality control

RPD relative percentage difference

SMP State of Wyoming Generic Management Plan for Pesticides in Ground Water

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

WDA Wyoming Department of Agriculture

WDEQ Wyoming Department of Environmental Quality
Pesticides in Wyoming Groundwater, 2008–10 

By Cheryl A. Eddy-Miller, Timothy T. Bartos, and Michelle L. Taylor

Abstract

Groundwater samples were collected from 296 wells 

during 1995–2006 as part of a baseline study of pesticides in 

Wyoming groundwater. In 2009, a previous report summarized 

the results of the baseline sampling and the statistical evaluation of the occurrence of pesticides in relation to selected 

natural and anthropogenic (human-related) characteristics. 

During 2008–10, the U.S. Geological Survey, in cooperation with the Wyoming Department of Agriculture, resampled 

a subset (52) of the 296 wells sampled during 1995–2006 

baseline study in order to compare detected compounds 

and respective concentrations between the two sampling 

periods and to evaluate the detections of new compounds. 

The 52 wells were distributed similarly to sites used in the 

1995–2006 baseline study with respect to geographic area and 

land use within the geographic area of interest. 

Because of the use of different types of reporting levels and variability in reporting-level values during both 

the 1995–2006 baseline study and the 2008–10 resampling 

study, analytical results received from the laboratory were 

recensored. Two levels of recensoring were used to compare 

pesticides—a compound-specific assessment level (CSAL) 

that differed by compound and a common assessment level 

(CAL) of 0.07 microgram per liter. The recensoring techniques 

and values used for both studies, with the exception of the 

pesticide 2,4–D methyl ester, were the same. Twenty-eight 

different pesticides were detected in samples from the 52 wells 

during the 2008–10 resampling study. Pesticide concentrations 

were compared with several U.S. Environmental Protection 

Agency drinking-water standards or health advisories for 

finished (treated) water established under the Safe Drinking 

Water Act. All detected pesticides were measured at concentrations smaller than U.S. Environmental Protection Agency 

drinking-water standards or health advisories where applicable 

(many pesticides did not have standards or advisories). 

One or more pesticides were detected at concentrations 

greater than the CAL in water from 16 of 52 wells sampled 

(about 31 percent) during the resampling study. Detected 

pesticides were classified into one of six types: herbicides, 

herbicide degradates, insecticides, insecticide degradates, 

fungicides, or fungicide degradates. At least 95 percent of 

detected pesticides were classified as herbicides or herbicide 

degradates. 

The number of different pesticides detected in samples 

from the 52 wells was similar between the 1995–2006 baseline 

study (30 different pesticides) and 2008–2010 resampling 

study (28 different pesticides). Thirteen pesticides were 

detected during both studies. The change in the number of 

pesticides detected (without regard to which pesticide was 

detected) in groundwater samples from each of the 52 wells 

was evaluated and the number of pesticides detected in 

groundwater did not change for most of the wells (32). Of 

those that did have a difference between the two studies, 

17 wells had more pesticide detections in groundwater during 

the 1995–2006 baseline study, whereas only 3 wells had more 

detections during the 2008-2010 resampling study.

The difference in pesticide concentrations in groundwater samples from each of the 52 wells was determined. Few 

changes in concentration between the 1995–2006 baseline 

study and the 2008–2010 resampling study were seen for most 

detected pesticides. Seven pesticides had a greater concentration detected in the groundwater from the same well during 

the baseline sampling compared to the resampling study. 

Concentrations of prometon, which was detected in 17 wells, 

were greater in the baseline study sample compared to the 

resampling study sample from the same well 100 percent of 

the time. 

The change in the number of pesticides detected (without regard to which pesticide was detected) in groundwater 

samples from each of the 52 wells with respect to land use 

and geographic area was calculated. All wells with land use 

classified as agricultural had the same or a smaller number of 

pesticides detected in the resampling study compared to the 

baseline study. All wells in the Bighorn Basin geographic area 

also had the same or a smaller number of pesticides detected 

in the resampling study compared to the baseline study.

Introduction

In October 1991, the U.S. Environmental Protection 

Agency (USEPA) completed the “Pesticides and GroundWater Strategy” that describes, in part, a Federal-State partnership approach to address potential risks posed to groundwater 

by the use of pesticides (Wyoming Ground-water and Pesticides Strategy Committee, 1999). In response, the State of 

Wyoming created the Ground-water and Pesticide Strategy 
2 Pesticides in Wyoming Groundwater, 2008–10

Committee (GPSC) consisting of members of local, State, and 

Federal government, as well as industry and interest groups, to 

prepare the State of Wyoming Generic Management Plan for 

Pesticides in Ground Water (known as the “State Management 

Plan” (SMP) (Wyoming Ground-water and Pesticides Strategy 

Committee, 1999). The SMP includes information describing 

individuals and organizations involved with implementation of 

the SMP, groundwater contamination prevention, groundwater 

monitoring, and required responses if pesticides are detected 

in groundwater.

 In Wyoming, little existing information was available 

describing pesticide occurrence in groundwater. In accordance 

with the SMP, the GPSC began a program to conduct baseline 

groundwater sampling to characterize pesticide occurrence 

in Wyoming’s groundwater. In addition, the GPSC identified 

20 pesticides (18 parent pesticides and 2 degradates, defined 

as “focal compounds” and referred to in the present report as 

“focal pesticides”) as being of greatest interest during baseline 

groundwater sampling). 

The U.S. Geological Survey (USGS), in cooperation with 

the Wyoming Department of Agriculture (WDA), acting on 

behalf of the GPSC, later with assistance from the Wyoming 

Department of Environmental Quality (WDEQ), began statewide implementation of this baseline groundwater sampling 

in 1995. Water samples were collected during fall and spring 

from 296 wells in Wyoming during 1995–2006 and analyzed 

for pesticides. Bartos and others (2009) published a report 

summarizing the occurrence of pesticides in the State of Wyoming, and statistically evaluated the occurrence of pesticides 

in relation to selected natural and anthropogenic (humanrelated) characteristics such as geography, soils, hydrogeology, 

selected water-quality constituents and characteristics, and 

land use.

During 2008–10, the USGS, in cooperation with the 

WDA, resampled a subset of 52 of the 296 wells that had been 

sampled during the 1995–2006 baseline study. The purpose of 

the 2008–10 resampling was to compare detected compounds 

and their respective concentrations between the two sampling 

periods, and evaluate the occurrence of new compounds. The 

52 resampled wells were distributed similarly to wells used 

in the 1995–2006 baseline study with respect to geographic 

area and land use within the geographic area of interest. In 

order to help evaluate changes in pesticide occurrence, wells 

with pesticide detections during the baseline study were given 

resampling priority. 

Purpose and Scope

The purpose of this report is to (1) summarize the occurrence of pesticides in Wyoming groundwater during 2008–10 

resampling study, (2) compare the pesticides detections and 

concentrations during the 2008–10 resampling study with the 

detections and concentrations found during the 1995–2006 

baseline study, and (3) compare relations between pesticide 

occurrence in groundwater in 2008–10 resampling study and 

selected natural and anthropogenic factors. The summary of 

pesticide occurrence includes detection frequencies; detections 

by action, class, and individual pesticides; concentrations and 

comparisons to USEPA standards and health advisories; and 

detections in relation to pesticide use. Natural and anthropogenic factors were evaluated for relations with pesticide 

occurrence including geographic area and land use, as defined 

in Bartos and others (2009). 

Methods of Investigation

Published methods for the selection of sampling locations, collection of groundwater samples and analysis for 

pesticides using USGS laboratory analytical methods and 

reporting conventions, and the collection and analysis of 

quality-control samples as part of a quality-assurance program 

were used in this study. The approach used to censor data and 

assemble final datasets was the same as the 1995–2006 baseline study (Bartos and others, 2009).

Selection of Sampling Locations

Fifty-one of the 52 wells sampled during the 2008–10 

resampling study are a subset of the 296 wells sampled during the 1995–2006 baseline study (figs. 1 and 2; appendix 1). 

Because access to one well located in the Bighorn Basin 

geographic area was denied, a neighbor’s well with similar depth and the same land use was used for the 2008–10 

resampling study. Bartos and others (2009) described the site 

selection process for the 1995–2006 baseline study, including determination of geographic areas and land use. Land use 

within a 500-m (1,640-ft) radius surrounding each sampled 

well was classified using an enhanced version of the USGS 

1992 National Land Cover Data (NLCD) set (Nakagaki and 

Wolock, 2005). The NLCD classified land use for each 30-by30-m area of the United States. Individual land uses classified 

within the 500-m radius then were used to classify land use 

into one of four predominant land-use categories using the 

following criteria: (1) agricultural [greater than (>) 50 percent 

agricultural land and less than or equal to (≤) 5 percent urban 

land]; (2) urban (> 25 percent urban land use and ≤ 25 percent 

agricultural land); (3) rangeland/undeveloped (≤ 5 percent 

urban land and ≤ 25 percent agricultural land); and (4) mixed 

(all other combinations of urban, agricultural, and rangeland/

undeveloped land). Each sampled well then was assigned to 

one of these four land-use categories to relate pesticide detections to overlying land use.

Analysis of sample data from the 1995–2006 baseline 

study indicated that the frequency of pesticide detections in a 

well was related to the geographic area in which the well was 

located, and to the land use surrounding the well (Bartos and 
Methods of Investigation 3

Figure 1. Wells sampled from the eight geographic areas of Wyoming during the 1995–2006 baseline study (from Bartos and others, 

2009).

80

25

80

80

25

90

90

85

85

20

16

14 16

16

89

310

287 20

191

30

30

189

0

0

50

50

100 MILES

100 KILOMETERS

Alcova

Reservoir

River

Pathfinder

Reservoir

Seminoe

 Reservoir

Boysen

Reservoir

Keyhole

Reservoir

Glendo

Reservoir

Fontenelle

 Reservoir

Wheatland

Reservoir

River

Platte

River

North

Laramie

Cheyenne

River

River

Belle

Fourche

River

Tongue R

Lake DeSmet

Bighorn 

 Lake

Bighorn

Shoshone

R

Buffalo Bill

Reservoir

River

South

Fork

Greybull River

River

Wind

River

Snake

River

Greys

River

Fork

New

Green

Fork

River

Hams

River

Henrys Fk

River

River

Big Sandy

River

River

Medicine

Fork

B

Blacks

ear R

Smiths Fk

R

Salt

Yellowstone

Lake

Jackson

Lake

Flaming Gorge

Reservoir

Gros Ventre River

River

Powder Little

Bow

North

Platte

PopoAgie

Ocean

Lake

Guernsey

 Reservoir

Sweetwater

Powder

Bighorn Basin (11)

Central Basins (10)

Green River Basin (6)

High Plains/Casper Arch (13)

Northwest Basins (1)

Overthrust Belt (2)

Powder River Basin (6)

Wind River Basin (4)

 EXPLANATION

Geographic area and number of different 

pesticides detected using the common 

assessment level (CAL) in parentheses ()

Well sampled for pesticides

No pesticide detected

One or more pesticides detected at concentration 

greater than the CAL (0.07 micrograms per liter)

Lusk

Cody

Basin

Casper

Lander

Laramie

Rawlins

Douglas

Jackson

Worland

Buffalo

Cheyenne

Evanston

Kemmerer

Pinedale

Gillette

Sundance

Sheridan

Wheatland

Newcastle

Torrington

Green

River

Thermopolis

110°

109° 108° 107° 106° 105°

41°

42°

43°

44°

45°

Afton

Saratoga

Glenrock

Riverton

Rock Springs

Lovell Powell

111°

CROOK

PARK

BIG

HORN

SHERIDAN

WASHAKIE

JOHNSON

CAMPBELL

TETON HOT

SPRINGS

FREMONT

LINCOLN

UINTA

SWEETWATER

NATRONA

CONVERSE

NIOBRARA

WESTON

GOSHEN

PLATTE

ALBANY

CARBON

LARAMIE

SUBLETTE

Base from U.S. Geological Survey digital data, 2003, 1:2,000,000

Albers Equal-area Conic projection

Standard parallels 29°30’N and 45°30’N, central meridian 107°30’W

North American Datum of 1983 (NAD 83)

YELLOWSTONE

NATIONAL

PARK
4 Pesticides in Wyoming Groundwater, 2008–10

Figure 2. Location of, and land use near, the 52 wells sampled during the 2008–10 resampling study, Wyoming.

80

25

80

80

25

90

90

85

85

20

16

14 16

16

89

310

287 20

191

30

30

189

0

0

50

50

100 MILES

100 KILOMETERS

Alcova

Reservoir

River

Pathfinder

Reservoir

Seminoe

 Reservoir

Boysen

Reservoir

Keyhole

Reservoir

Glendo

Reservoir

Fontenelle

 Reservoir

Wheatland

Reservoir

River

Platte

River

North

Laramie

Cheyenne

River

River

Belle

Fourche

River

Tongue R

Lake DeSmet

Bighorn 

 Lake

Bighorn

Shoshone

R

Buffalo Bill

Reservoir

River

South

Fork

Greybull River

River

Wind

River

Snake

River

Greys

River

Fork

New

Green

Fork

River

Hams

River

Henrys Fk

River

River

Big Sandy

River

River

Medicine

Fork

B

Blacks

ear R

Smiths Fk

R

Salt

Yellowstone

Lake

Jackson

Lake

Flaming Gorge

Reservoir

Gros Ventre River

River

Powder Little

Bow

North

Platte

PopoAgie

Ocean

Lake

Guernsey

 Reservoir

Sweetwater

Powder

Lr12

Lr11

Lr4

Lr7

Lr2

A7

G21

G25

G7

G4

G24

Nb7

Pt12

Pt5

Pt4

Cv7

Cv4

Nt3

Nt2

Nt8

Cp6

Cb1

Sh15

Sh3 Sh5

B17 B12

B1

B6

B5

Pk1 Pk10

Pk14

Pk19

Pk5

Pk7 Pk25

Wk7

Wk10

Wk3

Wk13 H9

H11

F12

F19

F3

Sw9

Sw3

J14

Sb3

Bighorn Basin (11)

Central Basins (10)

Green River Basin (6)

High Plains/Casper Arch (13)

Northwest Basins (1)

Overthrust Belt (2)

Powder River Basin (6)

Wind River Basin (4)

 EXPLANATION

Geographic area and number of different 

pesticides detected using the common 

assessment level (CAL) in parentheses ()

Pesticide sampling location

Site sampled during 2008–10 

resampling study with 

site name and land use

near well

Land use

Cb1

Agricultural

Urban

Undeveloped

U2

U10

Lusk

Cody

Basin

Casper

Lander

Laramie

Rawlins

Douglas

Jackson

Worland

Buffalo

Cheyenne

Evanston

Kemmerer

Pinedale

Gillette

Sundance

Sheridan

Wheatland

Newcastle

Torrington

Green

River

Thermopolis

110°

109° 108° 107° 106° 105°

41°

42°

43°

44°

45°

Afton

Saratoga

Glenrock

Riverton

Rock Springs

Lovell Powell

111°

CROOK

PARK

BIG

HORN

SHERIDAN

WASHAKIE

JOHNSON

CAMPBELL

TETON HOT

SPRINGS

FREMONT

LINCOLN

UINTA

SWEETWATER

NATRONA

CONVERSE

NIOBRARA

WESTON

GOSHEN

PLATTE

ALBANY

CARBON

LARAMIE

SUBLETTE

Base from U.S. Geological Survey digital data, 2003, 1:2,000,000

Albers Equal-area Conic projection

Standard parallels 29°30’N and 45°30’N, central meridian 107°30’W

North American Datum of 1983 (NAD 83)

YELLOWSTONE

NATIONAL

PARK
Methods of Investigation 5

others, 2009; Eddy-Miller and others, 2009; fig. 2). Therefore, preference for the 2008–10 resampling was given to the 

two geographic areas in the baseline study having the highest 

detection frequencies; the High Plains/Casper Arch and Bighorn Basin, which were resampled in 2008 (19 wells sampled) 

and 2009 (18 wells sampled), respectively. Samples from 

the rest of the State (15 wells) were collected during 2010. 

Because land use also affected the frequency of pesticide 

detections in a well, 2008–10 resampling sites within each of 

the eight geographic areas were selected to represent a similar 

distribution of land use; that is, a similar percentage of wells in 

each of the four land-use categories was selected for 2008–10 

resampling compared to the 1995–2006 baseline sampling.

Because the 1995–2006 baseline study also showed that a 

larger number of different pesticides were detected in the fall 

(August–October) than in the spring (March–May), samples 

were collected in the fall for all three years of the 2008–10 

resampling study. 

Sample Collection and Chemical Analyses

During the 2008–10 resampling study, groundwater 

samples were collected and processed in a mobile waterquality laboratory using procedures specified by the USGS 

National Water-Quality Assessment Program (Koterba and 

others, 1995; Koterba, 1998) and by the USGS National 

Field Manual for the Collection of Water-Quality Data (U.S. 

Geological Survey, variously dated). Samples were sent to the 

USGS National Water Quality Laboratory (NWQL) in Denver, 

Colo., for analysis using analytical methods selected to detect 

the 19 pesticides (17 parent pesticides and 2 pesticide degradates) identified in the SMP as focal pesticides of greatest concern (table 1). (Analysis of one focal pesticide, difenzoquat, 

was not made, as analytical methods were not available.) The 

USGS NWQL analytical methods selected to detect focal pesticides in groundwater samples also could detect many additional nonfocal (as many as 136) pesticides (table 1) (Furlong 

and others, 2001; Madsen and others, 2003; Sandstrom and 

others, 2001; Zaugg and others, 1995). Additionally during the 

2008–10 resampling study, samples were collected and sent 

to the U.S. Geological Survey Organic Chemistry Research 

Laboratory in Lawrence, Kansas (KSOCRL) for analysis of 

glyphosate and its degradates using methods described in 

Meyer and others (2009).

Data Reporting and Treatment

Groundwater samples were analyzed using USGS analytical methods with laboratory reporting levels much smaller 

than typically used in routine pesticide monitoring of public 

drinking-water supplies. Consequently, it is likely that much 

more frequent rates of detection were obtained than would 

have been possible with less sensitive analytical methods. 

Reporting levels during the 1995–2006 baseline study varied 

by pesticide, and many reporting levels changed during the 

12 years of the baseline study. Therefore, Bartos and others 

(2009) recensored pesticide detections to two different assessment levels to account for (1) variations in reporting levels 

for the same compound and (2) variations in reporting levels 

among the different compounds. The assessment levels were 

determined for all analytical results before data were summarized and analyzed.

Laboratory Reporting Levels

During the 1995–2006 baseline study (Bartos and others, 

2009) and the 2008–10 resampling study, the USGS NWQL 

reported analytical results for pesticides relative to three types 

of reporting levels, referred to as “original NWQL censoring.” 

Very small concentrations are censored and reported as “less 

than” values by the NWQL to avoid false-positive detections (reporting detections when the analytes are not actually 

present in the sample). Censoring levels, generally known as 

“reporting levels,” are specific to analytical methods and can 

change over time as methods change. During analysis of the 

1995–2006 baseline data, extensive evaluation of the three 

types of reporting levels was performed and documented 

(Bartos and others, 2009). The three types of reporting levels 

used by the NWQL during 1995–2006 included (1) the oldest 

and most basic of the three types, the minimum reporting level 

(MRL), which is defined as the minimum concentration of a 

constituent that can be reliably measured using a given analytical method (Timme, 1995); (2) the method detection limit 

(MDL), which is defined as the minimum concentration of a 

constituent that can be identified, measured, and reported with 

99-percent confidence to be significantly greater than zero 

(Childress and others, 1999); and (3) the laboratory reporting 

level (LRL), a reporting level used to minimize both falsepositive and false-negative detections (reporting a nondetection when the actual concentration in the sample is greater 

than the MDL; Childress and others, 1999). The reporting 

level during the 2008–10 resampling study was the LRL.

NWQL also calculates a long-term method detection 

level (LT-MDL), which is determined from the standard 

deviation of long-term laboratory spike samples (Bartos and 

others, 2009). NWQL qualifies detections less than the LRL, 

but greater than the LT-MDL as an estimated or “E” value. For 

this study, detections qualified with an “E” remark code were 

treated as quantified values. This approach preserves all of the 

information provided by the laboratory and acknowledges that 

values with an “E” remark code have concentrations greater 

than true nondetections.
Table 1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with trade names, pesticide actions, pesticide classes, land U.S. Environmental Protection Agency drinking-water standards. [Pesticides detected during 2008–10 resampling study are in bold type. Focal pesticides, as determined by the Ground-water and Pesticides Strategy Committee, are shown with U.S. Geological Survey; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; --, not applicable; USGS analytical method: 1 = USGS laboratory schedulschedule 2050, 3 = USGS laboratory schedule 1379, 4 = USGS laboratory schedule 2060, 5 = USGS laboratory schedule 2033, 6 = USGS Organic Chemistry Research Laboratoule LCGY; USEPA standard or health advisory: LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), MCL = USEPA Maximum Contmental Protection Agency, 2012), RSD4 = USEPA Risk-Specific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); DCPA, dimethyl tetrachloroterephthalane; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-Chloro-2-methylphenoxy)acetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid; U, chemical was analyzed for

Pesticide Trade name Pesticide action Pesticide class (or parent compound class) USGS laboratory parameter code USGS analytical method (see headnote) Laboratory repo

(μg/L) 

Minimum 

1-Naphthol Fourrine Insecticide Carbamate 49295 2, 5 0.036 2,4,5–T1 Dacamine, Emulsavert, Line Rider Herbicide Chlorophenoxy 39742 2, 4 0.01 2,4–D methyl ester -- Herbicide Chlorophenoxy 50470 4 0.009 2,4–D Dacamine, Weed-B-Gon Herbicide Chlorophenoxy 39732 2, 4 0.01 2,4–DB Butoxone, Butyrac Selective herbicide Chlorophenoxy 38746 2, 4 0.01 2,6-Diethylaniline Alachlor degradate -- Amide/acetanilide 82660 1, 5 0.002 2-Chloro-2’,6’-diethylacetanilide Butenachlor degradate -- Amide 61618 5 0.005 2-Chloro-4-isopropylamino-6-amino-striazine (CIAT) Atrazine degradate -- Triazine 04040 1, 3, 4, 5 0.002 2-Chloro-6-ethylamino4-amino-s-triazine 

(CEAT)

Atrazine/cyanazine/Simazine degradate -- Triazine 04038 3, 4 0.01 

2-Ethyl-6-methylaniline Metolachlor degradate -- Amide 61620 5 0.004 2-Hydroxy-4-isopropylamino-6-ethylamino-striazine (OIET) Atrazine degradate -- Triazine 50355 4 0.008 2-Methyl-4,6-dinitrophenol 

(DNOC)1

Dinitro-o-cresol, Elgetol Herbicide Miscellaneous 49299 2 0.01 

3,4-Dichloroaniline Propanil degradate -- Urea 61625 5 0.004 3,5-Dichloroaniline Iprodione degradate -- Miscellaneous 61627 5 0.004 3-Hydroxycarbofuran Carbofuran degradate -- Carbamate 49308 2, 4 0.006 3-keto-Carbofuran1 Carbofuran degradate -- Carbamate 50295 4 0.01 4-Chloro-2-methylphenol MCPA degradate -- Urea 61633 5 0.005 
Pesticide Trade name Pesticide action

Pesticide class 

(or parent compound 

class)

USGS 

laboratory parameter 

code

USGS 

analytical 

method (see 

headnote)

Laboratory repo

(μg/L)

Minimum 

Acetochlor Guardian, Harness, Relay Preplant herbicide Amide/ chloroacetamide 49260 1, 3, 5 0.002 Acifluorfen Blazer, Tackle 2S, Astic Herbicide Miscellaneous acid 49315 2, 4 0.007 Alachlor Alanex, Lasso, Shroud Herbicide Amide/ acetanilide 46342 1, 3, 5 0.002 Aldicarb Temik Insecticide, nematicide, acaricide Carbamate 49312 2, 4 0.02 Aldicarb sulfone Standak, aldoxycarb, 

aldicarb metabolite

Insecticide Carbamate 49313 2, 4 0.02 

Aldicarb sulfoxide Aldicarb degradate -- Carbamate 49314 2, 4 0.008 alpha-Endosulfan Endosulfan degradate -- Organochlorine 34362 5 0.005 alpha-HCH1 Insecticide Organochlorine 34253 1, 3, 5 0.002 Ametryn1 Evik Herbicide Triazine 38401 3 0.05 Aminomethylphosphonic 

acid3

Glyphosate degradate -- 62649 6 0.02 

Atrazine Aatrex, Atranex Herbicide Triazine 39632 1, 3, 4, 5 0.001 Azinphos-methyl Guthion, Crysthyon Insecticide Organophosphate 82686 1, 5 0.001 Azinphos-methyl-oxon 61635 0.12 Bendiocarb Ficam, Garrox, Turcam Insecticide Carbamate 50299 4 0.02 Benfluralin Balan, Benefin Herbicide Dinitroaniline 82673 1, 5 0.002 Benomyl Benlate, Benex Fungicide Carbamate 50300 4 0.004 Bensulfuron, methyl Escuri, Londax Herbicide Urea/sulfonyurea 61693 4 0.02 Bentazon Basagram, Bentzone Herbicide Miscellaneous 38711 2, 4 0.01 Bromacil Hyvar X Herbicide Miscellaneous 04029 2, 3, 4 0.01 Bromoxynil Buctril, Brominal, Agristar Herbicide Miscellaneous 49311 2, 4 0.01 

Table 1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with trade names, pesticide actions, pesticide classes, land U.S. Environmental Protection Agency drinking-water standards.—Continued[Pesticides detected during 2008–10 resampling study are in bold type. Focal pesticides, as determined by the Ground-water and Pesticides Strategy Committee, are shown with U.S. Geological Survey; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; --, not applicable; USGS analytical method: 1 = USGS laboratory schedulschedule 2050, 3 = USGS laboratory schedule 1379, 4 = USGS laboratory schedule 2060, 5 = USGS laboratory schedule 2033, 6 = USGS Organic Chemistry Research Laboratoule LCGY; USEPA standard or health advisory: LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), MCL = USEPA Maximum Contmental Protection Agency, 2012), RSD4 = USEPA Risk-Specific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); DCPA, dimethyl tetrachloroterephthalane; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-Chloro-2-methylphenoxy)acetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid; U, chemical was analyzed for
Pesticide Trade name Pesticide action Pesticide class (or parent compound class) USGS laboratory parameter code USGS analytical method (see headnote) Laboratory repo

(μg/L) 

Minimum 

Butachlor1 Butanex, Lambast, Machete Herbicide Amide 04026 3 0.05 Butylate1 Sutan+, Genate Plus Herbicide Carbamate 04028 1, 3 0.002 Carbaryl Carbatox, Sevin Insecticide Carbamate 49310 2, 4 0.008 Carbaryl Carbatox, Sevin Insecticide Carbamate 82680 1, 5 0.003 Carbofuran Furadan, Futura Insecticide Carbamate 49309 2, 4 0.006 Carbofuran Furadan, Futura Insecticide Carbamate 82674 1, 5 0.003 Carboxin1 Kisvax, Oxatin, Vitavax Fungicide Miscellaneous 04027 3 0.05 Chloramben, methyl ester Chloramben Herbicide Miscellaneous acid 61188 2, 4 0.01 Chlorimuron Classic, Darban, Lory Herbicide Urea/sulfonyurea 50306 4 0.01 Chlorodiamino-s-triazine 

(CAAT)1

Atrazine degradate -- Triazine 04039 4 0.04 

Chlorothalonil1 Bravo Fungicide Organochlorine 49306 2, 4 0.01 Chlorpyrifos Dursban, Lorsban Insecticide Organophosphate 38933 1, 5 0.0036 cis–Permethrin Ambush, Pounce Insecticide Pyrethroid 82687 1, 5 0.005 cis-Propiconazole -- Miscellaneous 79846 5 0.008 Clopyralid Stinger, Lontrel Herbicide Pyridinecarboxylic 

acid

49305 2, 4 0.01 

Cyanazine Bladex Selective herbicide Triazine 04041 1, 3, 5 0.004 Cycloate Ro-Neet Selective herbicide Carbamate/ thiocarbamate 04031 3, 4 0.01 Cyfluthrin Aztec, Bug-b-gon, Laser, 

Raid, Tempo

Insecticide Pyrethroid 61585 5 0.016 

Cypermethrin Barricade, Cymbush Insecticide Pyrethroid 61586 5 0.009 Dacthal mono-acid Dacthal degradate -- Organochlorine 49304 2, 4 0.01 DCPA Dacthal Herbicide Organochlorine 82682 1, 5 0.002 

Table 1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with trade names, pesticide actions, pesticide classes, land U.S. Environmental Protection Agency drinking-water standards.—Continued[Pesticides detected during 2008–10 resampling study are in bold type. Focal pesticides, as determined by the Ground-water and Pesticides Strategy Committee, are shown with U.S. Geological Survey; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; --, not applicable; USGS analytical method: 1 = USGS laboratory schedulschedule 2050, 3 = USGS laboratory schedule 1379, 4 = USGS laboratory schedule 2060, 5 = USGS laboratory schedule 2033, 6 = USGS Organic Chemistry Research Laboratoule LCGY; USEPA standard or health advisory: LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), MCL = USEPA Maximum Contmental Protection Agency, 2012), RSD4 = USEPA Risk-Specific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); DCPA, dimethyl tetrachloroterephthalane; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-Chloro-2-methylphenoxy)acetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid; U, chemical was analyzed for
Pesticide Trade name Pesticide action

Pesticide class 

(or parent compound 

class)

USGS 

laboratory parameter 

code

USGS 

analytical 

method (see 

headnote)

Laboratory repo

(μg/L)

Minimum 

Desulfinylfipronil amide Fipronil degradate -- Pyrazole 62169 1, 5 0.009 Desulfinylfipronil Fipronil degradate -- Pyrazole 62170 1, 5 0.004 Diazinon Basudin, Spectracide, 

Knoxout

Insecticide, nematicide Organophosphate 39572 1, 5 0.002 

Dicamba Banvel, Banex Herbicide Miscellaneous acid 38442 2, 4 0.01 Dichlobenil1 Barrier, Casoron, Rootx Herbicide Organochlorine 49303 2 0.02 Dichloroprop Weedone, Polymone Herbicide Chlorophenoxy 49302 2, 4 0.01 Dichlorvos DDVP, Vapona Insecticide Organophosphate 38775 5 0.04 Dicrotophos Bidrin, Penetrex Insecticide Organophosphate 38454 5 0.08 Dieldrin Panoram D-31, Octalox Insecticide Organochlorine 39381 1, 5 0.001 Dimethoate Cygon, Defend, Rogor Insecticide Organophosphate 82662 1, 5 0.006 Dinoseb Premerge Herbicide Miscellaneous 49301 2, 4 0.01 Diphenamid Dymid, Enide Selective herbicide Amide 04033 3, 4 0.01 Disulfoton sulfone Disyston sulfone Insecticide Organophosphate 61640 5 0.01 Disulfoton Di-Syston Insecticide, acaricide Organophosphate 82677 1, 5 0.02 Diuron Durashield, Karmex Herbicide Urea 49300 2, 4 0.01 Endosulfan Sulfate Endosulfan degradate -- Organochlorine 61590 5 0.014 EPTC Eptam, Eradicane Herbicide Carbamate 82668 1, 5 0.002 Ethalfluralin1 Eptam, Eradicane Herbicide Dinitroaniline 82663 1 0.004 Ethion monoxon Ethion degradate -- Organophosphate 61644 5 0.002 Ethion Klear-all, Rhodocide Insecticide Organophosphate 82346 5 0.004 Ethoprop (Ethoprophos) Mocap, Prophos Insecticide, nematicide Organophosphate 82672 1, 5 0.003 Fenamiphos sulfone Fenamiphos degradate -- Organophosphate 61645 5 0.049 Fenamiphos sulfoxide Fenamiphos degradate -- Organophosphate 61646 5 0.04 Fenamiphos Nemacur Insecticide Organophosphate 61591 5 0.03 

Table 1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with trade names, pesticide actions, pesticide classes, land U.S. Environmental Protection Agency drinking-water standards.—Continued[Pesticides detected during 2008–10 resampling study are in bold type. Focal pesticides, as determined by the Ground-water and Pesticides Strategy Committee, are shown with U.S. Geological Survey; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; --, not applicable; USGS analytical method: 1 = USGS laboratory schedulschedule 2050, 3 = USGS laboratory schedule 1379, 4 = USGS laboratory schedule 2060, 5 = USGS laboratory schedule 2033, 6 = USGS Organic Chemistry Research Laboratoule LCGY; USEPA standard or health advisory: LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), MCL = USEPA Maximum Contmental Protection Agency, 2012), RSD4 = USEPA Risk-Specific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); DCPA, dimethyl tetrachloroterephthalane; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-Chloro-2-methylphenoxy)acetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid; U, chemical was analyzed for
Pesticide Trade name Pesticide action Pesticide class (or parent compound class) USGS laboratory parameter code USGS analytical method (see headnote) Laboratory repo

(μg/L) 

Minimum 

Fenuron Fenuron Herbicide Urea 49297 2, 4 0.01 Fipronil sulfide Fipronil degradate -- Pyrazole 62167 1, 5 0.005 Fipronil sulfone Fipronil degradate -- Pyrazole 62168 1, 5 0.005 Fipronil Combat, Frontline, Max- force, Regent Insecticide Pyrazole 62166 1, 5 0.007 Flumetsulam Broadstrike, Python Herbicide Miscellaneous 61694 4 0.01 Fluometuron Cotoran Herbicide Urea 38811 2, 4 0.01 Fonofos Dyfonate Insecticide Organophosphate 04095 1, 5 0.003 Glufosinate3 Glyphosate degradate -- 62721 6 0.02 Glyphosate3 Roundup Herbicide Organophosphate 62722 6 0.02 Hexazinone Buckshot, Pronone, 

Velpar

Herbicide Triazine 04025 3, 5 0.012 

Imazaquin Scepter Herbicide Miscellaneous 50356 4 0.02 Imazethapyr New Path, Pursuit Herbicide Miscellaneous 50407 4 0.02 Imidacloprid Admire, Provado Insecticide Miscellaneous 61695 4 0.007 Iprodione Chipco, Rovral Fungicide Dicarboximide 61593 5 0.014 Isofenphos Amaze, Pryfon Insecticide Organophosphate 61594 5 0.003 lambda-Cyhalothrin Commodore, Icon Insecticide Pyrethroid 61595 5 0.009 Lindane (gamma-HCH)1 Lindane, Isotoz Insecticide Organochlorine 39341 1 0.004 Linuron Linurex, Lorox Herbicide Urea 38478 2, 4 0.01 Linuron1 Linurex, Lorox Herbicide Urea 82666 1 0.002 Malaoxon Malathion degradate -- Organophosphate 61652 5 0.022 Malathion Cythion, Malaspray Insecticide Organophosphate 39532 1, 5 0.005 MCPA Solve, MCP Herbicide Chlorophenoxy 38482 2, 4 0.01 MCPB Butoxone M40, Thistrol Herbicide Chlorophenoxy 38487 2, 4 0.01 

Table 1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with trade names, pesticide actions, pesticide classes, land U.S. Environmental Protection Agency drinking-water standards.—Continued[Pesticides detected during 2008–10 resampling study are in bold type. Focal pesticides, as determined by the Ground-water and Pesticides Strategy Committee, are shown with U.S. Geological Survey; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; --, not applicable; USGS analytical method: 1 = USGS laboratory schedulschedule 2050, 3 = USGS laboratory schedule 1379, 4 = USGS laboratory schedule 2060, 5 = USGS laboratory schedule 2033, 6 = USGS Organic Chemistry Research Laboratoule LCGY; USEPA standard or health advisory: LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), MCL = USEPA Maximum Contmental Protection Agency, 2012), RSD4 = USEPA Risk-Specific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); DCPA, dimethyl tetrachloroterephthalane; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-Chloro-2-methylphenoxy)acetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid; U, chemical was analyzed for
Pesticide Trade name Pesticide action

Pesticide class 

(or parent compound 

class)

USGS 

laboratory parameter 

code

USGS 

analytical 

method (see 

headnote)

Laboratory repo

(μg/L)

Minimum 

Metalaxyl Apron, Ridamil, Subdue Fungicide Miscellaneous 50359 4 0.01 Metalaxyl Apron, Ridamil, Subdue Fungicide Miscellaneous 61596 5 0.005 Methidathion Somanil, Supracide Insecticide Organophosphate 61598 5 0.006 Methiocarb Mesurol Insecticide Carbamate 38501 2, 4 0.008 Methomyl Lannate, Nudrin Insecticide Carbamate 49296 2, 4 0.004 Methyl paraoxon Methyl parathion degradate -- Organophosphate 61664 5 0.014 Methyl parathion Penncap-M, Paratox Insecticide Organophosphate 82667 1, 5 0.006 Metolachlor Bicep, Dual Herbicide Amide 39415 1, 3, 5 0.002 Metribuzin Lexone, Sencor Herbicide Triazine 82630 1, 3, 5 0.004 Metsulfuron-methyl Ally, Escort Herbicide Urea/sulfonyurea 61697 4 0.03 Molinate Hydram, Ordram Herbicide Carbamate 82671 1, 5 0.002 Myclobutanil Rally, Systhane Fungicide Miscellaneous 61599 5 0.008 N-(4-Chlorophenyl)-N’-

methylurea

Diuron degradate -- Urea 61692 4 0.02 

Napropamide1 Devrinol Herbicide Amide 82684 1 0.003 Neburon Granurex, Propuron Herbicide Urea 49294 2, 4 0.01 Nicosulfuron Accent, OneHope Herbicide Urea/sulfonyurea 50364 4 0.01 Norflurazon Zorial, Solicam Herbicide Miscellaneous 49293 2, 4 0.02 Oryzalin Surflan Herbicide Dinitroaniline 49292 2, 4 0.01 Oxamyl Vydate Insecticide, acaricide, 

nematicide

Carbamate 38866 2, 4 0.01 

Oxyfluorfen Goal Herbicide Miscellaneous 61600 3 0.007 Parathion1 Alkron, Bladan, Fighter Insecticide Organophosphate 39542 1 0.004 Pebulate1 Tillam Herbicide Carbamate 82669 1 0.002 Pendimethalin Prowl, Stomp Herbicide Dinitroaniline 82683 1, 5 0.004 

Table 1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with trade names, pesticide actions, pesticide classes, land U.S. Environmental Protection Agency drinking-water standards.—Continued[Pesticides detected during 2008–10 resampling study are in bold type. Focal pesticides, as determined by the Ground-water and Pesticides Strategy Committee, are shown with U.S. Geological Survey; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; --, not applicable; USGS analytical method: 1 = USGS laboratory schedulschedule 2050, 3 = USGS laboratory schedule 1379, 4 = USGS laboratory schedule 2060, 5 = USGS laboratory schedule 2033, 6 = USGS Organic Chemistry Research Laboratoule LCGY; USEPA standard or health advisory: LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), MCL = USEPA Maximum Contmental Protection Agency, 2012), RSD4 = USEPA Risk-Specific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); DCPA, dimethyl tetrachloroterephthalane; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-Chloro-2-methylphenoxy)acetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid; U, chemical was analyzed for
Pesticide Trade name Pesticide action Pesticide class (or parent compound class) USGS laboratory parameter code USGS analytical method (see headnote) Laboratory repo

(μg/L) 

Minimum 

Phorate oxon Phorate degradate -- Organophosphate 61666 5 0.027 Phorate Thimet, Rampart Insecticide Organophosphate 82664 1, 5 0.02 Phosmet oxon3 Phosmet degradate -- Organophosphate 61668 5 0.05 Phosmet3 Imidan, Percolate, Prolate Insecticide Organophosphate 61601 5 0.008 Picloram Tordon Herbicide Pyridinecarboxylic 

acid

49291 2, 4 0.02 

Prometon Pramitol, Gesafram Herbicide Triazine 04037 1, 3, 5 0.01 Prometryn Caparol, Selectin Herbicide Triazine 04036 3, 5 0.005 Propachlor1 Ramrod, Prolex Herbicide Amide 04024 1, 3 0.007 Propanil Stamp Herbicide Amide 82679 1, 5 0.004 Propargite Comite, Omite Insecticide, acaricide Miscellaneous 82685 1, 5 0.01 Propazine1 Milogard, Tritol Herbicide Triazine 38535 3 0.05 Propham Chem Hoe Herbicide Carbamate 49236 2, 4 0.01 Propiconazole Banner Fungicide Miscellaneous 50471 4 0.01 Propoxur Baygone, Suncide Fungicide Carbamate 38538 2, 4 0.008 Propyzamide (Pronamide) Kerb Herbicide Amide 82676 1, 5 0.003 Siduron Tupersan Herbicide Urea 38548 4 0.02 Silvex1 (2,4,5–TP) Silvex, Weed-B-Gon Herbicide Chlorophenoxy 39762 2 0.02 Simazine Aquazine, Princep Herbicide Triazine 04035 1, 3, 5 0.005 Simetryn1 Cymetrin, Gy-bon Herbicide Triazine 04030 3 0.05 Sulfometruron-methyl Oust Herbicide Urea/sulfonyurea 50337 4 0.009 Tebuconazole Elite, Folicur, Raxil Fungicide Azole 62852 5 0.02 Tebuthiuron Graslan, Spike Herbicide Urea 82670 1, 4, 5 0.01 Tefluthrin Demand, Force, Karate Insecticide Pyrethroid 61606 5 0.003 Terbacil1 Sinbar, Herbicide 732 Herbicide Miscellaneous 82665 1 0.007 

Table 1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with trade names, pesticide actions, pesticide classes, land U.S. Environmental Protection Agency drinking-water standards.—Continued[Pesticides detected during 2008–10 resampling study are in bold type. Focal pesticides, as determined by the Ground-water and Pesticides Strategy Committee, are shown with U.S. Geological Survey; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; --, not applicable; USGS analytical method: 1 = USGS laboratory schedulschedule 2050, 3 = USGS laboratory schedule 1379, 4 = USGS laboratory schedule 2060, 5 = USGS laboratory schedule 2033, 6 = USGS Organic Chemistry Research Laboratoule LCGY; USEPA standard or health advisory: LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), MCL = USEPA Maximum Contmental Protection Agency, 2012), RSD4 = USEPA Risk-Specific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); DCPA, dimethyl tetrachloroterephthalane; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-Chloro-2-methylphenoxy)acetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid; U, chemical was analyzed for
Pesticide Trade name Pesticide action

Pesticide class 

(or parent compound 

class)

USGS 

laboratory parameter 

code

USGS 

analytical 

method (see 

headnote)

Laboratory repo

(μg/L)

Minimum 

Terbacil Sinbar, Herbicide 732 Herbicide Miscellaneous 04032 3, 4 0.01 Terbufos Counter, Contraven Insecticide Organophosphate 82675 1, 5 0.01 Terbuthylazine Gardoprim Herbicide Triazine 04022 1, 3, 5 U Thiobencarb Bolero, Saturn Herbicide Carbamate 82681 1, 5 0.002 trans-Propiconazole -- -- Miscellaneous 79847 5 0.01 Triallate1 Far-Go, Avadex BW Herbicide Carbamate 82678 1 0.001 Tribenuron1 Express, Urgent Herbicide Urea/sulfonyurea 61159 4 0.009 Tribuphos Def, Easy off-D, Folex Herbicide Organophosphate 61591 5 0.004 Triclopyr Garlon Herbicide Chlorophenoxy 49235 2, 4 0.02 Trifluralin Treflan, Trim Herbicide Dinitroaniline 82661 1, 5 0.002 Trifluralin1 Treflan, Trim Herbicide Dinitroaniline 04023 3 0.05 Vernolate1 Surpass, Vernam Herbicide Carbamate 04034 2 0.05 

1Pesticide was not on analytical schedules 2008–10.2The MCL for any combination of two or more of these three chemicals (aldicarb, aldicarb sulfoxide, and aldicarb sulfone) is 7 μg/L.3Pesticide was not on analytical schedules 1995–2008.

Table 1. Pesticides analyzed in 1995–2006 baseline and 2008–10 resampling studies, with trade names, pesticide actions, pesticide classes, land U.S. Environmental Protection Agency drinking-water standards.—Continued[Pesticides detected during 2008–10 resampling study are in bold type. Focal pesticides, as determined by the Ground-water and Pesticides Strategy Committee, are shown with U.S. Geological Survey; μg/L, micrograms per liter; USEPA, U.S. Environmental Protection Agency; --, not applicable; USGS analytical method: 1 = USGS laboratory schedulschedule 2050, 3 = USGS laboratory schedule 1379, 4 = USGS laboratory schedule 2060, 5 = USGS laboratory schedule 2033, 6 = USGS Organic Chemistry Research Laboratoule LCGY; USEPA standard or health advisory: LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), MCL = USEPA Maximum Contmental Protection Agency, 2012), RSD4 = USEPA Risk-Specific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); DCPA, dimethyl tetrachloroterephthalane; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-Chloro-2-methylphenoxy)acetic acid; MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid; U, chemical was analyzed for
14 Pesticides in Wyoming Groundwater, 2008–10

Recensoring and Assessment Levels

Because of the use of three different types of reporting 

levels and variability in reporting-level values during the 

1995–2006 baseline study, analytical results received from 

the NWQL with original censoring were recensored. The 

recensoring techniques and all but one value used for the data 

during the 1995–2006 baseline study (Bartos and others, 2009) 

were also used to recensor the 2008–10 resampling study 

data. During the 1995–2006 baseline study, recensoring was 

necessary to account for different types of reporting levels 

(MRL, MDL, or LRL) and (or) variable laboratory reporting 

levels either for a specific pesticide or between individual 

pesticides. The reporting levels typically vary over time due 

to changes in analytical methods, differences in laboratory 

equipment, equipment sensitivity, experience and skill of 

equipment operators, and laboratory conditions. Recensoring 

to a common value (referred to herein as the assessment level) 

allows for accurate calculation and comparison of detection 

frequencies and concentrations between individual pesticides 

or groups of pesticides with different types and values of 

reporting levels, as well as the use of quantitative statistical 

methods to examine pesticide occurrence. 

Typically, recensoring is conducted by comparing 

concentrations of reported detections to all LRLs; all detections less than the largest LRL are recoded as nondetections, 

and all detections greater than the largest LRL are retained as 

detections at the originally reported laboratory concentrations. 

Unfortunately, pesticide reporting levels varied widely during 

the baseline study (table 1), and selection of the largest LRL 

for recensoring would result in many, if not most, detections 

being recoded as nondetections. Consequently, an approach 

was used to recensor the data in an attempt to retain as many 

pesticide detections as possible while still adhering to a rigorous and defensible procedure for assembly of the final dataset. 

In order to be able to compare data from the 1995–2006 

baseline study to the 2008–10 resampling study, the laboratory reported pesticide concentrations from the 2008–10 

resampling study were recensored in the same manner as the 

1995–2006 baseline study data.

During the 1995–2006 baseline study data analyses, two 

levels of recensoring were developed to compare pesticides—

a compound-specific assessment level (CSAL) that differed 

by compound, and a common assessment level (CAL) of 

0.07 microgram per liter (μg/L) (Bartos and others, 2009).

During the analysis of the 2008–10 resampling study data, 

the CSAL for all pesticides and the CAL were evaluated to 

determine if adjustments were needed based on the LRL 

reported by the NWQL during 2008–10. All pesticide CSALs 

remained the same as the level determined during the baseline 

study, with the exception of 2,4–D methyl ester, for which the 

CSAL increased from 0.009 to 0.02 μg/L (table 2). The CAL 

(0.07 μg/L) remained the same for the 2008–2010 resampling 

data as the value used during the 1995–2006 baseline study. In 

addition to the two levels of recensoring, no assessment level 

(NAL) also was used to compare pesticide results. The NAL is 

the value the NWQL or the KSOCRL determined and reported 

for the sample.

Quality-Control Samples and Quality Assurance

In addition to collection of environmental groundwaterquality samples, three types of quality-control (QC) samples 

were collected as part of the overall quality-assurance (QA) 

program—field-blank samples, replicate samples, and fieldmatrix spike samples. The QC samples were collected, preserved, and analyzed using the same methods and equipment 

as for environmental samples. Collection and evaluation of 

QC samples, in addition to strict sample collection, processing, and analysis procedures, composed the field QA program. 

Results for the QC samples can be found in appendix 1.

Field-Blank Samples

Field-blank samples were collected to evaluate bias from 

the potential introduction of contamination to environmental 

samples during sample collection, sampling equipment cleaning, and laboratory analytical procedures. Specially prepared 

water that is certified to be free of organic constituents was 

used as the source-water for blank samples. No detections of 

pesticides were found in the one field-blank sample (site number 410817104470201) that was collected in conjunction 

with another project, using the same sampling equipment and 

procedures as the 2008–10 resampling study. This result indicated that decontamination procedures were adequate and that 

field and laboratory contamination of environmental samples 

by pesticides was minimal, and was consistent with results 

of field-blank samples collected during 1995–2006 baseline 

sampling.

Replicate Samples

A replicate sample (duplicate) is a sample collected 

immediately after the primary environmental sample to assess 

combined effects of sample-collection and laboratory procedures on measurement variability (precision). Two replicate 

samples were collected for analysis at sites 410108104223501 

(Lr4) and 444603108383401 (Pk1) (appendix 2). The replicate and environmental samples had a total of 274 pairs of 

individual analyses, of which six pairs had detections of a 

pesticide in both the replicate and the environmental samples. 

Two sample pairs had detections in only one set of samples 

(either the replicate or the environmental sample); however, it 

should be noted that the detections in the one sample for both 

pesticides were estimated (“E”) values at 6 and 25 percent of 

the LRL. All reported detections were used in analysis of the 

replicate data, including the values assigned an “E” remark 

code (85 percent of reported detections). All replicate data 

were used without recensoring.
Methods of Investigation 15

Table 2. Pesticides detected in groundwater samples collected from 52 wells sampled during both 1995–2006 baseline study1

and 2008–10 resampling study.

[Pesticides in bold were not included on the analytical schedules used during the 1995–2006 baseline study. NAL, no assessment level; CSAL, compoundspecific assessment level; CAL, common assessment level; μg/L, micrograms per liter; I, insecticide; H, herbicide; HD, herbicide degradate; FD, fungicide 

degradate; ID, insecticide degradate; F, fungicide; BF, detected during 1995–2006 baseline study fall sampling; BS, detected during 1995–2006 baseline study 

spring sampling; RF, detected during 2008–10 resampling study fall sampling; NS, not on analytical schedule]

Pesticide Pesticide 

action

Detection with original laboratory 

censoring (NAL)

Laboratory reporting level 

range (μg/L)

Assigned assessment 

level (μg/L)

Baseline 

spring Baseline fall Resampling fall 1995–2006 2008–10 CSAL CAL 

1-Napthol I -- -- RF 0.09 0.036–0.04 0.02 0.07

2,4-D methyl ester H -- BF -- 0.009–0.016 0.02 20.02 0.07

2,4-D H -- BF -- 0.01–0.73 0.03 0.15 0.07

2-Chloro-4-isopropylamino-6-amino-striazine (CIAT)HD BS BF RF 0.002–0.05 0.006–.014 0.05 0.07

2-Chloro-6-ethylamino4-amino-s-triazine 

(CEAT)

HD BS -- RF 0.01–0.08 0.06–0.08 0.04 0.07

2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine 

(OIET)

HD -- -- RF 0.008–0.032 0.003 0.016 0.07

3,4-Dichloroanaline HD -- -- RF 0.004 0.02–0.03 0.004 0.07

3,5-Dichloroaniline FD -- -- RF 0.004–0.012 0.003–0.003 0.003 0.07

Aldicarb sulfone ID BS BF 0.02–1.31 0.04 0.11 0.07

Aldicarb sulfoxide ID BS BF RF 0.008–0.27 0.03 0.14 0.07

Aminomethylphosphonic acid

HD -- -- RF NS 0.02 0.02 0.07

Atrazine H BS BF RF 0.001–0.05 0.004 0.004 0.07

Benfluralin H -- BF -- 0.002–0.013 0.007 0.013 0.07

Bentazon H -- -- RF 0.01–0.06 0.03 0.06 0.07

Bromacil H BS BF RF 0.01–1.1 0.01–0.03 0.06 0.07

Bromoxynil H -- BF -- 0.01–1.6 0.06 0.07 0.07

Carbaryl I -- BF -- 0.003–0.046 0.01–0.02 0.05 0.07

Carbofuran I -- BF -- 0.003–0.02 0.02 0.02 0.07

Chlorimuron H -- -- -- 0.01–0.046 0.04 0.046 0.07

cis-Permethrin I -- BF -- 0.005–0.016 0.005–0.007 0.016 0.07

Clopyralid H BS BF -- 0.01–1.82 0.03 0.26 0.07

Cyanazine H BS BF -- 0.004–0.2 0.011 0.013 0.07

Cypermethrin I -- -- RF 0.009–0.046 0.014–0.020 0.01 0.07

DCPA H -- -- -- 0.002–0.004 0.004 0.004 0.07

Diazinon I BS -- -- 0.002–0.008 0.003 0.008 0.07

Dicamba H -- -- -- 0.01–0.35 0.02–0.03 0.13 0.07

Dichloroprop H -- -- -- 0.01–0.13 0.02 0.06 0.07

Dieldrin I -- BF -- 0.001–0.009 0.004 0.008 0.07

Diuron H BS BF RF 0.01–0.42 0.02 0.06 0.07

Fipronil I -- -- RF 0.004–0.012 0.018–0.040 0.02 0.07

Fipronil sulfide ID -- BF -- 0.005–0.013 0.006 0.006 0.07
16 Pesticides in Wyoming Groundwater, 2008–10

Detected pesticide Pesticide 

action

Detection with original laboratory 

censoring (NAL)

Laboratory reporting level 

range (μg/L)

Assigned assessment 

level (μg/L)

Baseline 

spring Baseline fall Resampling fall 1995–2006 2008–10 CSAL CAL 

Fipronil sulfone ID -- BF -- 0.005–0.024 0.012 0.012 0.07

Flumetsulam H -- -- -- 0.01–0.06 0.03 0.06 0.07

Fluometuron H -- -- RF 0.01–0.36 0.04 0.02 0.07

Glyphosate H -- -- RF NS 0.02 0.02 0.07

Hexazinone H -- -- RF 0.013–0.05 0.005–0.007 0.05 0.07

Imidacloprid I -- -- RF 0.007–0.241 0.03–0.1 0.02 0.07

Metalaxyl F -- -- RF 0.01–0.02 0.007–0.018 0.02 0.07

Metolachlor H BS BF RF 0.002–0.05 0.01 0.009 0.07

Metribuzin H BS BF RF 0.004–0.05 0.006 0.05 0.07

Metsulfuron-methyl H -- -- RF 0.03–0.07 0.07 0.07 0.07

Norfllurazon H BS BF RF 0.02–0.32 0.02 0.06 0.07

Oryzalin H -- BF -- 0.01–1.25 0.02 0.31 0.07

Picloram H BS BF RF 0.02–0.26 0.06 0.06 0.07

Prometon H BS BF RF 0.01–0.05 0.006 0.05 0.07

Simazine H BS BF RF 0.005–0.05 0.005 0.05 0.07

Suflometuron-methyl H -- BF RF 0.009–0.091 0.03 0.09 0.07

Tebuthiuron H BS BF RF 0.01–0.026 0.01–0.14 0.01 0.07

Triallate H BS BF -- 0.001–0.008 NS 0.003 0.07

Triclopyr H BS BF -- 0.02–0.36 0.04 0.36 0.07

Trifluralin H -- BF -- 0.002–0.012 0.006–0.009 0.012 0.07

1

Bartos and others (2009).

2

The CSAL for 2,4–D methyl ester for the 2008–10 resampling study was modified from the assigned CSAL for the 1995–2006 baseline study because of a 

statistical change in the long-term method detection level.

Table 2. Pesticides detected in groundwater samples collected from 52 wells sampled during both 1995–2006 baseline study1

and 2008–10 resampling study.—Continued

[Pesticides in bold were not included on the analytical schedules used during the 1995–2006 baseline study. NAL, no assessment level; CSAL, compoundspecific assessment level; CAL, common assessment level; μg/L, micrograms per liter; I, insecticide; H, herbicide; HD, herbicide degradate; FD, fungicide 

degradate; ID, insecticide degradate; F, fungicide; BF, detected during 1995–2006 baseline study fall sampling; BS, detected during 1995–2006 baseline study 

spring sampling; RF, detected during 2008–10 resampling study fall sampling; NS, not on analytical schedule]

The relative percentage difference (RPD) was calculated 

to compare the pesticide concentrations measured in both the 

environmental (sample1) and replicate (sample2) samples 

using the following equation:

RPD sample sample

sample sample = −

 +



 









absolute value 1 2

1 2

2





















×100 (1)

RPDs were not calculated for pairs where one value was 

reported as less than the LRL and not as an estimated value.

Evaluation of the two pairs of individual results with 

detections (six pesticides detected in both environmental and 

replicate samples) indicated five pesticide pairs had an RPD of 

less than 13 percent, and the remaining pesticide pair had an 

RPD of 29 percent. The differences generally were attributable 

to small concentration differences that resulted in relatively 

large RPDs because both environmental and replicate sample 

concentrations were estimated and small. These results were 

considered acceptable for this resampling study, generally 

were similar to the in-depth replicate sampling conducted 

during the 1995–2006 baseline study, and consequently, no 

detections were qualified or deleted on the basis of calculated 

RPDs.
Pesticide Occurrence during 2008–10 Resampling Study 17

Pesticides Detected during 2008–10 Resampling 

Study

Twenty-eight different pesticides were detected using 

NAL from the 52 wells resampled in 2008–10 (fig. 3; table 2). 

Concentrations of detected pesticides generally were small 

(less than 1 μg/L). Three different pesticides (bromacil, 

glyphosate, and picloram) were detected at concentrations 

greater than 1 μg/L one time each (table 3; fig. 3), and in 

groundwater from three different wells. Bromacil was detected 

at 1.87 μg/L (table 3) in water from well Nt8 (fig. 2) in the 

High Plains/Casper Arch geographic area. Glyphosate was 

detected at 1.6 μg/L (table 3) in water from well Sh3 (fig. 2) 

in the Powder River Basin geographic area. Picloram was 

detected at 9.88 μg/L (table 3) in water from well Sh5 (fig. 2), 

also in the Powder River Basin geographic area. 

The USEPA has established standards for physical 

properties and chemical constituents in drinking water that 

may have adverse effects on human health or that may cause 

cosmetic effects (for example, skin or tooth discoloration) 

or aesthetic effects (for example, color, taste, or odor). The 

Maximum Contaminant Level (MCL) is a legally enforceable 

and health-based standard and is the maximum permissible 

level for a constituent in drinking water that is delivered to 

a user of a public-water system (U.S. Environmental Protection Agency, 2012). A health advisory is a nonenforceable 

level that establishes acceptable constituent concentrations for 

different exposure periods (1 day, 10 days, long-term, and lifetime). A Lifetime Health Advisory Level is the concentration 

of a chemical that would not result in any known or anticipated adverse noncarcinogenic health effects over a lifetime of 

exposure (70 years) (U.S. Environmental Protection Agency, 

2012). The Risk-Specific Dose is a concentration of a chemical with a specific risk level under certain exposure conditions 

over a lifetime (70 years) (U.S. Environmental Protection 

Agency, 2012). The USEPA drinking-water standards and 

health advisory levels serve as technical guidance to evaluate 

the suitability of water collected from private wells for human 

consumption.

Pesticide concentrations detected during the 2008–10 

resampling study were evaluated by comparing the levels 

of these concentrations with several USEPA standards for 

drinking water or health advisories for finished (treated) water 

established under the Safe Drinking Water Act. In addition, 

pesticide detections were evaluated by the GPSC and compared to Wyoming groundwater-quality standards in accordance with the SMP (Wyoming Ground-water and Pesticides 

Strategy Committee, 1999).

All detected concentrations of pesticides during 2008–10 

resampling study were lower than USEPA drinking-water standards or health advisories, where applicable (many pesticides 

did not have standards or advisories) (table 3). Most pesticide 

concentrations were at least an order of magnitude smaller 

Field-Matrix Spike Samples

Field-matrix spike samples were analyzed to evaluate bias and variability from the environmental groundwater 

matrix or potential degradation of the constituent during 

sample processing, storage, and analysis. Field-matrix spike 

samples were collected in the same manner as the environmental samples, immediately following collection of the 

environmental samples. The samples then were injected with 

a known concentration of selected pesticides. Forty-five spike 

samples were collected during the 1995–2006 baseline study, 

and laboratory recoveries of most field-matrix spike samples 

ranged from 60 to 120 percent of the pesticide or degradate 

known to be in the sample during that time (Bartos and others, 

2009). Because the same analytical methods were used during 

the 2008–10 resampling study, spike samples were collected at only one well, site number 41101910405130 (Lr 7) 

(appendix 3).

Overall recoveries of pesticides and degradates during the 

2008-2010 resampling study averaged about 90 percent, which 

indicates a possible slight low bias in reported concentrations. 

Analysis of a subset of field-matrix spike data that included 

only pesticides and degradates detected in environmental 

samples showed about the same average recovery (93 percent). Two pesticides and degradates detected in environmental samples (1-napthol and bentazon), however, had low fieldmatrix spike recoveries indicating a general low bias (average 

recoveries less than 60 percent). Concentrations of aldicarb 

sulfoxide, fipronil, and sulfometuron-methyl may have been 

biased slightly high, as the calculated recoveries were 123, 

127, and 158 percent, respectively. These results were considered acceptable for this study, and consequently, no detections 

were qualified or deleted on the basis of poor recoveries.

Pesticide Occurrence during 2008–10 

Resampling Study

The occurrences of pesticides in the samples collected 

from 52 wells during the 2008–10 resampling study are summarized and described in relation to pesticide action. Waterquality analyses for each well can be accessed at http://nwis.

waterdata.usgs.gov/wy/nwis/qwdata (U.S. Geological Survey, 

2012), by using the site number shown in appendix 4. In general, the NAL is used when describing any indication that the 

pesticide was detected. The CSAL is the level of assessment 

used when comparing detections of the same pesticide over 

time or between wells. The CAL is the level of assessment 

used when comparing detections that include different pesticides. In selected tables and figures, results for all assessment 

levels are shown for interpretive purposes.
Figure 3. Pesticide detections and concentrations (using no assessment level) in groundwater samples collected from 52 wells during the 2008–10 Wyoming.

0.0001

0.001

0.01

0.1

1

10

100

1-Naphthol

2,4-Dmethylester

2,4-D

2-Chloro-4-isopropylamino-6-amino-striazine

2-Chloro-6-ethylamino-4-amino-striazine

2-Hydroxy-4-isopropylamino-6-ethylamino-striazine

3,4-Dichloroaniline

3,5-Dichloroaniline

Aldicarbsulfone

Aldicarbsulfoxide

Aminomethylphosphonicacid

Atrazine

Benfluralin

Bentazon

Bromacil

Bromoxynil

Carbaryl

Carbofuran

cisPermethrin

Clopyralid

Cyanazine

Cypermethrin

Die

ldrin

Diuron

Fipronil

Fipronilsulfide

Fipronilsulfone

Fluometuron

Glyphosate

Hexazinone

Imidacloprid

Metalaxyl

Metolachlor

Metribuzin

Metsulfuron-methyl

Norflurazon

Oryzalin

Picloram

Prometon

Concentration,inmicrogramsperliter

Pesticide

Pesticide detected durin

Bartos and others, 2

Compound-specific assCommon assessment leConcentration of detect

2008–10 resampling 

EXPLANA
Differences in Pesticide Occurrence between 1995–2006 Baseline and 2008–10 Resampling Studies 19

than USEPA drinking-water standards or health advisories. 

The largest pesticide or degradate concentration relative to 

a drinking-water standard was bromacil, at a concentration 

slightly less than 3 percent of the Lifetime Health Advisory 

Level (table 3).

Pesticide Detection Frequency by Well During 

the 2008–10 Resampling Study

The number of pesticides detected (pesticide detection frequencies) in groundwater from each of the 52 wells 

sampled during the 2008–10 resampling study was examined 

using the NAL, CSAL, and CAL. Pesticide detection frequencies varied, as expected, based on the assessment level used. 

One or more pesticides were detected at concentrations greater 

than the CAL in water from 16 of 52 wells sampled (about 

31 percent) during the resampling study (fig. 4). As many as 

nine pesticides per well were detected using the NAL.

Pesticide Detections by Action During the 

2008–10 Resampling Study

Detected pesticides were classified into one of six 

actions: herbicides, herbicide degradates, insecticides, 

insecticide degradates, fungicides, or fungicide degradates 

(fig. 5, table 2). At least 95 percent of detected pesticides were 

classified as herbicides or herbicide degradates regardless of 

whether data were examined with original censoring (NAL), 

or with assessment levels CSAL or CAL. Pesticides classified as insecticides, insecticide degradates, fungicides, or 

fungicide degradates were detected much less frequently. The 

prevalence of pesticides classified as herbicides was expected 

because herbicide use is more common than insecticide use in 

Wyoming, and the eight most distributed pesticides in Wyoming are herbicides (Hank Uhden, Wyoming Department of 

Agriculture, written commun., 2010; appendix 5). 

Differences in Pesticide Occurrence 

between 1995–2006 Baseline and 

2008–10 Resampling Studies

One purpose of the 2008–10 resampling study was to 

determine whether the pesticides detected in groundwater 

differed over time, and whether the concentrations of pesticides detected during the baseline study differed. Because the 

2008–10 resampling study collected its samples only during 

the fall, the data from the samples collected from 52 wells 

were compared only to fall samples collected during the 

1995–2006 baseline study. Observed changes are described in 

terms of pesticides (or their degradates) detected, the concentrations of detected pesticides, and the detections in relation to 

surrounding land use and geographic area. 

Differences in Pesticides Detected

The number of different pesticides detected in samples 

from the 52 wells was similar between 2008–10 resampling 

study (28 different pesticides) (fig. 3) and the 1995–2006 baseline study (30 pesticides) (table 4; fig. 6). Thirteen pesticide 

detections were common to both sampling periods. Fifteen 

pesticides were detected during the 2008–10 resampling study 

that had not been detected in fall samples collected during 

the baseline study from the 52 wells; three of these pesticides 

were not on the analytical schedules used during the baseline 

study. Sixteen pesticides were not detected during the 2008–10 

resampling study that had been detected previously during the 

1995–2006 baseline study. Most of the pesticides detected in 

only one study, but not the other, were only detected one or 

two times, with the exception of hexazinone that was detected 

three times during the resampling study.

Differences in Pesticide Detections

The change in the number of pesticides detected (without regard to which pesticide was detected) in groundwater 

samples between the 1995–2006 baseline study and 2008–10 

resampling study from each of the 52 sampled wells is shown 

in figure 7. Most of the wells (32) had no changes in the 

number of pesticides detected in groundwater samples. Of 

the wells that did have a difference between the two sampling 

studies, 17 wells had more pesticide detections during the 

1995–2006 baseline study, whereas only 3 wells had more pesticide detections during the 2008–10 resampling study.

Differences in Pesticide Concentrations

Pesticide concentration changes in groundwater samples 

collected from the 52 wells was determined by evaluating pesticides with at least 50 analyses during both studies, and with 

at least one concentration greater than the CSAL (table 5). 

Most pesticides (11 of the 19 evaluated) with detections had 

little change in concentration between the 1995–2006 baseline 

study and 2008–10 resampling study. Seven pesticides generally had greater concentrations in the groundwater from the 

same well during the 1995–2006 baseline study than during 

the 2008-2010 resampling study. Concentrations of atrazine, 

which was detected in 33 wells, and concentrations of the 

atrazine degradate 2-chloro-4-isopropylamino-6-amino-straizine, were greater in the 1995–2006 baseline study sample 

than in the 2008–10 resampling study sample about 80 percent 

of the time. Concentrations of prometon, detected in 17 wells, 

were greater in the 1995–2006 baseline study sample than 

in the 2008–10 resampling study sample 100 percent of the 

time. Only one pesticide, diuron, detected in only four wells 

at concentrations greater than the CSAL, generally had greater 

concentrations in the 2008–10 resampling study sample than 

in the 1995–2006 baseline study sample.
20 Pesticides in Wyoming Groundwater, 2008–10

Pesticide CSAL 

(μg/L)

Number of wells with detections Number of 

analyses 

Percent of wells with detections 

NAL CSAL CAL NAL CSAL CAL 

1-Naphthol 0.02 1 0 0 52 1.9 0.0 0.0 

2-Chloro-4-isopropylamino6-amino-s-triazine 0.05 26 1 0 52 50.0 1.9 0.0 

2-Chloro-6-ethylamino4-amino-s-triazine 0.04 2 0 0 52 3.8 0.0 0.0 

2-Hydroxy-4-isopropylamino6-ethylamino-s-triazine 0.016 8 2 0 52 15.4 3.8 0.0 

3,4-Dichloroaniline 0.004 6 4 1 52 11.5 7.7 1.9 

3,5-Dichloroaniline 0.003 1 1 0 52 1.9 1.9 0.0 

Aldicarb sulfoxide 0.11 1 0 0 52 1.9 0.0 0.0 

Aminomethylphosphonic acid 0.02 7 7 1 52 13.5 13.5 1.9 

Atrazine 0.004 24 24 1 52 46.2 46.2 1.9 

Bentazon 0.06 1 1 0 52 1.9 1.9 0.0 

Bromacil 0.06 7 5 4 52 13.5 9.6 7.7 

Cypermethrin 0.01 1 1 1 52 1.9 1.9 1.9 

Diuron 0.06 6 1 1 52 11.5 1.9 1.9 

Fipronil 0.02 1 0 0 52 1.9 0.0 0.0 

Fluometuron 0.02 2 0 0 52 3.8 0.0 0.0 

Glyphosate 0.02 2 2 2 52 3.8 3.8 3.8 

Hexazinone 0.05 4 2 0 52 7.7 3.8 0.0 

Imidacloprid 0.02 1 0 0 52 1.9 0.0 0.0 

Metalaxyl 0.02 2 0 0 52 3.8 0.0 0.0 

Metolachlor 0.009 1 0 0 52 1.9 0.0 0.0 

Metribuzin 0.05 1 0 0 52 1.9 0.0 0.0 

Metsulfuron-methyl 0.07 1 0 0 52 1.9 0.0 0.0 

Norflurazon 0.06 1 0 0 52 1.9 0.0 0.0 

Picloram 0.06 5 4 4 52 9.6 7.7 7.7 

Prometon 0.05 35 10 7 52 67.3 19.2 13.5 

Simazine 0.05 12 0 0 52 23.1 0.0 0.0 

Sulfometuron-methyl 0.09 3 0 0 52 5.8 0.0 0.0 

Tebuthiuron 0.01 14 14 7 52 26.9 26.9 13.5 

1

Bartos and others (2009).

Table 3. Summary of pesticide detections and concentrations in groundwater sampled during the 2008–10 resampling study, 

Wyoming.

[Pesticides highlighted in yellow were analyzed for, but not detected during the 1995–2006 baseline study;1 pesticides highlighted in orange were not analyzed 

for during the 1995–2006 baseline study.1 NAL, no assessment level; CSAL, compound-specific assessment level; CAL, common assessment level; μg/L, 

micrograms per liter; USEPA, U.S. Environmental Protection Agency; USEPA standard or health advisory: MCL = USEPA Maximum Contaminant Level (U.S. 

Environmental Protection Agency, 2012), LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), RSD4 = USEPA RiskSpecific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); --, not applicable]
Differences in Pesticide Occurrence between 1995–2006 Baseline and 2008–10 Resampling Studies 21

Detected concentration range (μg/L) Median of detected concentrations 

(μg/L)

USEPA standard or health 

advisory 

(μg/L)

NAL CSAL CAL

minimum maximum minimum maximum minimum maximum NAL CSAL CAL

0.004 0.004 -- -- -- -- -- -- -- --

0.003 0.05 0.05 0.05 -- -- 0.009 -- -- --

0.02 0.03 -- -- -- -- 0.025 -- -- --

0.006 0.025 0.019 0.025 -- -- 0.012 0.022 -- --

0.002 0.078 0.004 0.078 0.078 0.078 0.004 0.0095 -- --

0.017 0.017 0.017 0.017 -- -- -- -- --

0.006 0.006 -- -- -- -- -- -- 4 (MCL)

0.02 0.49 0.02 0.49 0.49 0.49 0.03 0.03 -- --

0.005 0.071 0.005 0.071 0.071 0.071 0.0075 0.0075 -- 3 (MCL)

0.06 0.06 0.06 0.06 -- -- -- -- 200 (LHA)

0.01 1.87 0.06 1.87 0.18 1.87 0.18 0.31 0.35 70 (LHA)

0.335 0.335 0.335 0.335 0.335 0.335 -- -- -- --

0.0026 0.39 0.39 0.39 0.39 0.39 0.035 -- -- 200 (RSD4)

0.001 0.001 -- -- -- -- -- -- -- --

0.01 0.01 -- -- -- -- 0.01 -- -- 90 (LHA)

0.07 1.6 0.07 1.6 0.07 1.6 0.835 0.835 0.835 70 (MCL)

0.021 0.68 0.068 0.068 -- -- 0.045 0.068 -- 400 (LHA)

0.007 0.007 -- -- -- -- -- -- -- --

0.007 0.009 -- -- -- -- 0.008 -- -- --

0.005 0.005 -- -- -- -- -- -- -- 700 (LHA)

0.013 0.013 -- -- -- -- -- -- -- 70 (LHA)

0.01 0.01 -- -- -- -- -- -- -- --

0.0017 0.0017 -- -- -- -- -- -- -- --

0.04 9.88 0.15 9.88 0.15 9.88 0.66 0.78 0.78 500 (MCL)

0.005 0.484 0.05 0.484 0.09 0.484 0.024 0.09 0.105 100 (LHA)

0.006 0.02 -- -- -- -- 0.0075 -- -- 4 (MCL)

0.004 0.018 -- -- -- -- 0.013 -- -- --

0.01 0.38 0.01 0.38 0.07 0.38 0.065 0.065 0.24 500 (LHA)

Table 3. Summary of pesticide detections and concentrations in groundwater sampled during the 2008–10 resampling study, 

Wyoming.—Continued

[Pesticides highlighted in yellow were analyzed for, but not detected during the 1995–2006 baseline study;1 pesticides highlighted in orange were not analyzed 

for during the 1995–2006 baseline study.1 NAL, no assessment level; CSAL, compound-specific assessment level; CAL, common assessment level; μg/L, 

micrograms per liter; USEPA, U.S. Environmental Protection Agency; USEPA standard or health advisory: MCL = USEPA Maximum Contaminant Level (U.S. 

Environmental Protection Agency, 2012), LHA = USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2012), RSD4 = USEPA RiskSpecific Dose at 10-4 Cancer Risk (U.S. Environmental Protection Agency, 2012); --, not applicable]
22 Pesticides in Wyoming Groundwater, 2008–10

Figure 4. Number of pesticides detected in groundwater samples collected from 52 wells sampled during the 2008–10 resampling 

study using no assessment level, compound-specific assessment level, and common assessment level, Wyoming.

0 10 20 30 40 50 60 70 80 90

0

1 or more

2 or more

3 or more

4 or more

5 or more

6 or more

7 or more

8 or more

9 or more

Percentage of wells

Number of pesticides detected per well

No assessment level (NAL)

Compound-specific assessment level (CSAL)

Common assessment level (CAL)

EXPLANATION

Figure 5. Pesticide detections relative to pesticide action in groundwater samples collected from 52 wells sampled during the 

2008–10 resampling study, Wyoming.

0 10 20 30 40 50 60 70 80 90 100

Common

assessment 

level

(CAL)

Compound-specific

assessment 

level 

(CSAL)

No 

assessment

level 

(NAL)

Percentage of detections by pesticide action and assessment level

EXPLANATION

Herbicide

Herbicide degradate

Insecticide

Insecticide degradate

Fungicide

Fungicide degradate

Pesticide action
Differences in Pesticide Occurrence between 1995–2006 Baseline and 2008–10 Resampling Studies 23

Table 4. Pesticides detected in the 52 wells sampled during 1995–2006 baseline study1 and (or) 2008–10 resampling study, Wyoming.

[CSALs and CALs shown in bold indicate pesticide detected at concentration equal to or greater than the assessment level in at least one well in resampling 

study. NAL, no assessment level; CSAL, compound-specific assessment level; CAL, common assessment level; μg/L, micrograms per liter; ND, not detected; 

D, detected; NA, not analyzed]

Pesticide Number of analyses Detection of pesticide 

during study (NAL)

Pesticide assessment 

level1 (μg/L)

1995–2006 2008–10 1995–2006 2008–10 CSAL CAL

1-Naphthol 1 52 ND D 0.02 0.07

2,4–D methyl ester 9 52 D ND 0.02 0.07

2,4–D 51 52 D ND 0.15 0.07

2-Chloro-4-isopropylamino-6-amino-s-triazine 52 52 D D 0.05 0.07

2-Chloro-6-ethylamino-4-amino-s-triazine 0 52 NA D 0.04 0.07

2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine 8 52 ND D 0.016 0.07

3,4-Dichloroaniline 1 52 ND D 0.004 0.07

3,5-Dichloroaniline 1 52 ND D 0.003 0.07

Aldicarb sulfone 52 52 D ND 0.11 0.07

Aldicarb sulfoxide 51 52 D D 0.14 0.07

Aminomethylphosphonic acid 0 52 NA D 0.02 0.07

Atrazine 52 52 D D 0.004 0.07

Benfluralin 52 52 D ND 0.013 0.07

Bentazon 50 52 ND D 0.06 0.07

Bromacil 51 52 D D 0.06 0.07

Bromoxynil 51 52 D ND 0.07 0.07

Carbaryl 52 52 D ND 0.05 0.07

Carbofuran 52 52 D ND 0.02 0.07

cis-Permethrin 52 52 D ND 0.016 0.07

Clopyralid 51 52 D ND 0.26 0.07

Cyanazine 52 52 D ND 0.013 0.07

Cypermethrin 1 52 ND D 0.01 0.07

Dieldrin 52 52 D ND 0.008 0.07

Diuron 51 52 D D 0.06 0.07

Fipronil 9 52 ND D 0.02 0.07

Fipronil sulfide 9 52 D ND 0.006 0.07

Fipronil sulfone 9 52 D ND 0.012 0.07

Fluometuron 9 52 ND D 0.02 0.07

Glyphosate 0 52 NA D 0.02 0.07

Hexazinone 1 52 ND D 0.05 0.07

Imidacloprid 9 52 ND D 0.02 0.07

Metalaxyl 9 52 ND D 0.02 0.07

Metolachlor 52 52 D D 0.009 0.07

Metribuzin 52 52 D D 0.05 0.07

Metsulfuron-methyl 9 52 ND D 0.07 0.07

Norflurazon 51 52 D D 0.06 0.07

Oryzalin 51 52 D ND 0.31 0.07

Picloram 51 52 D D 0.06 0.07

Prometon 52 52 D D 0.05 0.07

Simazine 52 52 D D 0.05 0.07

Sulfometuron-methyl 9 52 D D 0.09 0.07

Tebuthiuron 52 52 D D 0.01 0.07

Triallate 52 0 D NA 0.003 0.07

Triclopyr 51 52 D ND 0.36 0.07

Trifluralin 52 52 D ND 0.012 0.07

1

Bartos and others (2009), fall samples only.
Figure 6. Pesticide detections and concentrations (using no assessment level) in groundwater samples collected from 52 wells during the 1995samples only; Bartos and others, 2009).

Notanalyzed

Notanalyzed

Notanalyzed

0.0001

0.001

0.01

0.1

1

10

100

1-Naphthol

2,4-Dmethylester

2,4-D

2-Chloro-4-isopropylamino-6-amino-striazine

2-Chloro-6-ethylamino-4-amino-striazine

2-Hydroxy-4-isopropylamino-6-ethylamino-striazine

3,4-Dichloroaniline

3,5-Dichloroaniline

Aldicarbsulfone

Aldicarbsulfoxide

Aminomethylphosphonicacid

Atrazine

Benfluralin

Bentazon

Bromacil

Bromoxynil

Carbaryl

Carbofuran

cisPermethrin

Clopyralid

Cyanazine

Cypermethrin

Die

ldrin

Diuron

Fipronil

Fipronilsulfide

Fipronilsulfone

Fluometuron

Glyphosate

Hexazinone

Imidacloprid

Metalaxyl

Metolachlor

Metribuzin

Metsulfuron-methyl

Norflurazon

Oryzalin

Picloram

Concentration,inmicrogramsperliter

Pesticide

Pesticide detected 

Bartos and othe

Compound-specific Common assessmeConcentration of d

1995–2006 base

EX
Differences in Pesticide Occurrence between 1995–2006 Baseline and 2008–10 Resampling Studies 25

Figure 7. Difference in number of pesticides detected in 

the same well between the 1995–2006 baseline (fall samples 

only; Bartos and others, 2009) and 2008–10 resampling studies. 

Pesticide detection is based on the common assessment level.

Differences in Pesticide Detections and 

Detection Frequency Relative to Land Use and 

Geographic Area

The change in the number of pesticides detected and the 

detection frequency relative to land use and geographic area 

between the baseline and resampling studies was determined. 

Concentrations of pesticides detected during the baseline and 

resampling studies by assessment levels, including land use, 

are shown in figure 8. 

The overall frequency of pesticide detections in groundwater from the 52 wells was examined by calculating the 

percentage of wells with at least one pesticide detected at concentrations greater than the CAL with respect to land use near 

the well and geographic area (fig. 9). The detection frequency 

of at least one pesticide in groundwater from a well decreased 

or remained unchanged, regardless of land use or geographic 

area, between the 1995–2006 baseline and 2008–10 resampling studies. The detection frequency within the agricultural 

land-use category had the largest change from the 1995–2006 

baseline study to the 2008–10 resampling study, changing 

from 38 percent detection frequency to zero. The detection frequency within the Bighorn Basin geographic area had the largest change from the 1995–2006 baseline study to the 2008–10 

resampling study, changing from 56 percent to 17 percent.

The change in the number of pesticides detected (without regard to which pesticide was detected) between the 

1995–2006 baseline study and the 2008–10 resampling study 

in groundwater samples from each of the 52 wells with respect 

to land use and geographic area was calculated and is shown 

in figure 10. Results shown in figure 10 are a refinement of 

figure 7, and indicate as expected, that most wells had no 

change in the number of pesticides detected, regardless of land 

use or geographic area. This refinement shows that all wells 

with nearby land use classified as agricultural had the same 

or a smaller number of pesticides in the 2008–10 resampling 

study compared to the 1995–2006 baseline study. Figure 10 

also shows that all wells in the Bighorn Basin geographic area 

had the same or a smaller number of pesticides detected in 

the 2008–10 resampling study compared to the 1995–2006 

baseline study. 

Number of wells in category

Changes in number of pesticides

One more resampling

Two more resampling

No difference between baseline and resampling

One more baseline 

Two more baseline

Three more baseline

Four more baseline 

EXPLANATION

Greater number in 1995–2006 baseline study

Greater number in 2008–10

 resampling study

8

7

1 1 1 2

32

No change between 1995–2006 baseline and 2008–10 resampl ni g stud ei s

2

USGS hydrologist measuring the water level in a well in the Bighorn Basin 

geographic area. Photograph by Seth L. Davidson, September 2009.
Table 5. Differences in pesticide detections between the 1995–2006 baseline study1 and the 2008–10 resampling study, Wyoming. Differences were cbasis for pesticides with at least 50 analyses during both sampling studies and with at least one concentration greater than the compound-specific as[Pesticides highlighted in green indicate minimal change between baseline study and resampling study (one well or fewer with a concentration difference); pesticides highlighted greater concentrations detected in baseline study than in resampling study from same well; pesticides highlighted in tan indicate generally greater concentrations detected in resastudy from same well] Pesticide Number of analyses Pesticide not detected above CSAL in either sample Concentration greater than CSAL in at least one sam

Concentrations greater in baseline study Concentrations equal in baseline and resampling studies C

1995–2006 baseline study2 2008–10 resampling study Number of wells Percentage Number of wells Percentage Num

2,4-D 51 52 50 1 100 0 0 

2-Chloro-4-isopropylamino6-amino-s-triazine 52 52 47 4 80 0 0 

Aldicarb sulfone 51 52 48 3 100 0 0 

Aldicarb sulfoxide 51 52 47 4 100 0 0 

Atrazine 52 52 19 25 76 1 3 

Bentazon 50 52 49 0 0 0 0 

Bromacil 51 52 44 4 57 0 0 

Bromoxynil 51 52 50 1 100 0 0 

Carbaryl 52 52 51 1 100 0 0 

Carbofuran 52 52 51 1 100 0 0 

Clopyralid 51 52 50 1 100 0 0 

Cyanazine 52 52 51 1 100 0 0 

Diuron 51 52 47 1 25 0 0 

Metolachlor 52 52 50 2 100 0 0 

Oryzalin 51 52 50 1 100 0 0 

Picloram 51 52 44 4 57 0 0 

Prometon 52 52 35 17 100 0 0 

Tebuthiuron 52 52 36 9 56 1 6 

Triclopyr 51 52 50 1 100 0 0 

1Bartos and others (2009), fall samples only.2Number of samples used for comparison.
Differences in Pesticide Occurrence between 1995–2006 Baseline and 2008–10 Resampling Studies 27

Well with primarily urban land use nearby, in the High 

Plains/Casper Arch geographic area. Photograph by 

Cheryl A. Eddy-Miller, September 2008.

Sugar beet field in the Bighorn Basin geographic area. The pesticide detection frequency within the Bighorn Basin geographic area had the largest change from 

the 1995–2006 baseline study to the 2008–10 resampling study, changing from 56 percent to 17 percent. Photograph by Cheryl A. Eddy-Miller, September 2009.
28 Pesticides in Wyoming Groundwater, 2008–10

Figure 8. Pesticide detections and concentrations in groundwater samples collected from 52 wells during 1995–2006 baseline study 

(fall samples only; Bartos and others, 2009) and 2008–10 resampling study, Wyoming.

Agricultural

Urban

Mixed

Undeveloped

Pesticide concentration and land use

EXPLANATION

1-Naphthol

2,4-D methyl ester

2,4-D

2-Chloro-4-isopropylamino-6-amino-s-triazine

2-Chloro-6-ethylamino-4-amino-s-triazine

2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine

3,4-Dichloroaniline3,5-Dichloroaniline

Aldicarb sulfone

Aldicarb sulfoxide

Aminomethylphosphonic acid

Atrazine

Benfluralin

Bentazon

Bromacil

Bromoxynil Carbaryl

Carbofuran

cis-Permethrin

Clopyralid

Cyanazine

Cypermethrin

Dieldrin

Diuron

Fipronil

Fipronil sulfide

Fipronil sulfone

Fluometuron

Glyphosate

Hexazinone

Imidacloprid

Metalaxyl

Metolachlor

Metribuzin

Metsulfuron-methyl

Norflurazon

Oryzalin

Picloram

Prometon

Simazine

Sulfometuron-methyl Tebuthiuron

Triallate

Triclopyr

Trifluralin

Concentration, in micrograms per liter

0.0001

0.001

0.01

100

0.1

1

10

0.0001

0.001

0.01

100

0.1

1

10

Pesticide

0.0001

0.001

0.01

100

0.1

1

10

Not analyzed

Not analyzed Not analyzed

Not analyzed

Not analyzed Not analyzed

A. No assessment level in baseline study

B. Compound-specific assessment level in baseline study

C. Common assessment level in baseline study

Not analyzed

Not analyzed Not analyzed
Differences in Pesticide Occurrence between 1995–2006 Baseline and 2008–10 Resampling Studies 29

Figure 8. Pesticide detections and concentrations in groundwater samples collected from 52 wells during 1995–2006 baseline study 

(fall samples only; Bartos and others, 2009) and 2008–10 resampling study, Wyoming.—Continued

1-Naphthol

2,4-D methyl ester

2,4-D

2-Chloro-4-isopropylamino-6-amino-s-triazine

2-Chloro-6-ethylamino-4-amino-s-triazine

2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine

3,4-Dichloroaniline3,5-Dichloroaniline

Aldicarb sulfone

Aldicarb sulfoxide

Aminomethylphosphonic acid

Atrazine

Benfluralin

Bentazon

Bromacil

Bromoxynil Carbaryl

Carbofuran

cis-Permethrin

Clopyralid

Cyanazine

Cypermethrin

Dieldrin

Diuron

Fipronil

Fipronil sulfide

Fipronil sulfone

Fluometuron

Glyphosate

Hexazinone

Imidacloprid

Metalaxyl

Metolachlor

Metribuzin

Metsulfuron-methyl

Norflurazon

Oryzalin

Picloram

Prometon

Simazine

Sulfometuron-methyl Tebuthiuron

Triallate

Triclopyr

Trifluralin

Concentration, in micrograms per liter

0.0001

0.001

0.01

100

0.1

1

10

0.0001

0.001

0.01

100

0.1

1

10

Pesticide

Not analyzed Not analyzed Not analyzed

0.0001

0.001

0.01

100

0.1

1

10

Agricultural

Urban

Mixed

Undeveloped

Pesticide concentration and land use

EXPLANATION

D. No assessment level in resampling study

E. Compound-specific assessment level in resampling study

F. Common assessment level in resampling study
30 Pesticides in Wyoming Groundwater, 2008–10

Figure 9. Percentage of wells with at least one pesticide detected in groundwater samples collected from 52 wells relative to land use 

and geographic area during the 1995–2006 baseline study (fall samples only; Bartos and others, 2009) and the 2008–10 resampling study, 

Wyoming. A, Detections relative to land use, 1995–2006 baseline study. B, Detections relative to geographic area, 1995–2006 baseline 

study. C, Detections relative to land use, 2008–10 resampling study. D, Detections relative to geographic area, 2008–10 resampling study.

EXPLANATION EXPLANATION

A B

0 20 40 60 80 100

Percentage of wells within a land-use category with at least one

pesticide detected at a concentration greater than the

common assessment level (CAL)

C

0 20 40 60 80

Percentage of wells within a geographic area with at least one pesticide

detected at a concentration greater than the

common assessment level (CAL) 

D

Land use

Agricultural

Urban

Undeveloped

Mixed

Geographic area

High Plains/Casper Arch

Bighorn Basin

Rest of Wyoming
Differences in Pesticide Occurrence between 1995–2006 Baseline and 2008–10 Resampling Studies 31

Figure 10. Difference in number of pesticides detected in the same well between 1995–2006 baseline (fall samples only; Bartos and 

others, 2009) and 2008–10 resampling studies. A, Land use near wells. B, Geographic area of well in each category. Pesticide detection 

is based on the common assessment level (CAL).

One more resampling

Two more resampling

No difference between baseline 

and resampling

One more baseline 

Two more baseline

Three more baseline

Four more baseline 

EXPLANATION

Land use

Agricultural

Urban

Undeveloped

Mixed

Geographic area

North Platte/Casper Arch

Bighorn Basin

Rest of Wyoming

B

A

Number of wells in category

Changes in number of pesticides

1

One more resampling

Two more resampling

No difference between baseline 

and resampling

One more baseline 

Two more baseline

Three more baseline

Four more baseline 

EXPLANATION

Number of wells in category

Changes in number of pesticides

2

1 1

1 1 1

1

1

5

2

3

3

7

2

13

10

1

2

1 1

1

5

2

4

3

11

12

9
32 Pesticides in Wyoming Groundwater, 2008–10

Summary

The Ground-water and Pesticide Strategy Committee 

(GPSC) consisting of members of local, State, and Federal 

government, as well as industry and interest groups, prepared 

the State of Wyoming Generic Management Plan for Pesticides in Ground Water. A key component of this plan was to 

conduct baseline groundwater sampling to characterize pesticide occurrence in Wyoming’s groundwater. 

The U.S. Geological Survey (USGS), in cooperation 

with the Wyoming Department of Agriculture (WDA), acting on behalf of the GPSC, later with assistance from the 

Wyoming Department of Environmental Quality (WDEQ), 

began statewide implementation of this baseline groundwater 

sampling in 1995. During 1995–2006, samples were collected 

from 296 wells in Wyoming. Results of this study were previously summarized to describe the occurrence of pesticides 

in the State of Wyoming, and were statistically evaluated 

to determine occurrence of pesticides in relation to selected 

natural and anthropogenic characteristics. During 2008–10, 

the USGS, in cooperation with the WDA, resampled a subset 

of 52 wells that were sampled during the 1995–2006 baseline 

study in order to compare detected compounds and respective concentrations between the two sampling periods, and to 

evaluate the occurrence of new pesticides. The 52 wells were 

distributed similarly to sites used in the 1995–2006 baseline 

study with respect to geographic area and land use within the 

geographic area of interest. In order to help evaluate changes 

in pesticide occurrence, wells with previous detections of 

pesticides were given priority for resampling.

Because of the use of different types of “reporting levels” 

and variability in reporting-level values during the 1995–2006 

baseline study and the 2008–10 resampling study, analytical 

results received from the laboratory were recensored. The 

recensoring techniques and values used for the resampling 

study were the same as used during the baseline study. In 

addition to using no assessment level, two levels of recensoring were used to compare pesticides—a compound-specific 

assessment level (CSAL) that differed by compound and a 

common assessment level (CAL) of 0.07 microgram per liter.

Twenty eight different pesticides were detected using 

no assessment level in samples from the 52 wells during 

the 2008–10 resampling study. Concentrations of detected 

pesticides generally were small (less than 1 microgram per 

liter), although three pesticides—bromacil, glyphosate, and 

picloram—were measured at concentrations greater than 

1 microgram per liter one time each in groundwater from three 

different wells. 

Pesticide concentrations were compared with several 

U.S. Environmental Protection Agency (USEPA) drinkingwater standards or health advisories for finished (treated) 

water established under the Safe Drinking Water Act. All 

detected pesticide concentrations were smaller than USEPA 

drinking-water standards or health advisories where applicable 

(many pesticides did not have standards or advisories). Most 

pesticide concentrations were at least an order of magnitude 

smaller than USEPA standards or health advisories. 

The overall detection frequency of pesticides in groundwater from the 52 wells was examined by calculating the 

percentage of wells with at least one pesticide detected at 

concentrations greater than the CAL. One or more pesticides 

were detected at concentrations greater than the CAL in water 

from 16 of 52 wells sampled (about 31 percent) during the 

resampling study. 

Detected pesticides were classified into one of six 

actions: herbicides, herbicide degradates, insecticides, insecticide degradate, fungicides, or fungicide degradates. At least 

95 percent of detected pesticides were classified as herbicides 

or herbicide degradates. 

The purpose of the 2008–10 resampling study was to 

determine if the specific pesticides detected in groundwater changed over time, and if the concentrations of previously detected pesticides changed as well. The data from the 

52 wells sampled during the 2008–10 resampling study were 

compared to fall samples collected during the 1995–2006 

baseline study.

The number of different pesticides detected in samples 

from the 52 wells was similar between the baseline study 

(30 different pesticides) and the resampling study (28 different pesticides). Thirteen pesticides were common to both 

sampling periods. During the baseline study, 16 additional 

pesticides were detected that were not detected during the 

resampling study. Fifteen pesticides were detected during the 

resampling study that had not been detected in the fall samples 

from the 52 wells sampled in the baseline study; however, 

three of these pesticides were not on the analytical schedules 

used during the baseline study. Most pesticides detected in one 

of the studies, but not the other, were only detected in one or 

two samples.

The change in the number of pesticides detected (without regard to which pesticide was detected) in groundwater 

samples from each of the 52 wells was calculated, and most 

of the wells (32) had no changes in the number of pesticides 

detected. Of those wells that did have a difference between the 

two studies, 17 wells had more pesticide detections in groundwater during the baseline study, whereas only 3 wells had 

more detections during the resampling study.

The change in concentration over time in groundwater 

samples from the 52 wells was determined by evaluating 

pesticides with at least 50 analyses during both sampling 

studies, and with at least one concentration greater than the 

CSAL. Most pesticides with detections had little change in 

concentration between the baseline study and resampling 

study. Seven pesticides had a greater concentration detected 

in groundwater from the same well during the baseline study 

than during the resampling study. Concentrations of atrazine, 
References Cited 33

which was detected in 33 wells, and the atrazine degradate 

2-chloro-4-isopropylamino-6-amino-s-triazine were greater in 

the baseline study sample than in the resampling study sample 

about 80 percent of the time. Concentrations of prometon, 

detected in 17 wells, were greater in the baseline study sample 

than in the resampling study sample 100 percent of the time. 

The overall detection frequency of pesticides in groundwater from the 52 wells was examined by calculating the 

percentage of wells with at least one pesticide detected at 

concentrations greater than the CAL with respect to land use 

near the well and geographic area. The detection frequency of 

at least one pesticide in groundwater from a well decreased 

or remained unchanged, regardless of land use or geographic 

area, between the 1995–2006 baseline and 2008–10 resampling study. The detection frequency within the agricultural land-use category had the largest change between the 

1995–2006 baseline and 2008–10 resampling studies, decreasing from 38 percent to zero. The detection frequency within 

the Bighorn Basin geographic area had the largest change 

between the 1995–2006 baseline and 2008–10 resampling 

studies, decreasing from 56 percent to 17 percent.

The change in the number of pesticides detected (without regard to which pesticide was detected) between the 

1995–2006 baseline study and the 2008–10 resampling study 

in groundwater samples from each of the 52 wells with respect 

to land use and geographic area was calculated. All wells with 

land use classified as agricultural had the same or a smaller 

number of pesticides detected in the resampling study compared to the baseline study. All wells in the Bighorn Basin 

geographic area also had the same or a smaller number of 

pesticides detected in the resampling study compared to the 

baseline study. 

References Cited

Bartos, T.T., Eddy-Miller, C.A., and Hallberg, L.L., 2009, 

Occurrence of pesticides in ground water of Wyoming, 

1995–2006: U.S. Geological Survey Scientific Investigations Report 2009–5024, 72 p. (Also available at http://

pubs.usgs.gov/sir/2009/5024/.) 

Childress, C.J. Oblinger, Foreman, W.T., Connor, B.F., and 

Maloney, T.J., 1999, New reporting procedures based on 

long-term method detection levels and some considerations 

for interpretations of water-quality data provided by the 

U.S. Geological Survey National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 99–193, 20 p.

Eddy-Miller, C.A., Bartos, T.T., Hallberg, L.L., 2009, Pesticides in ground water of Wyoming, 1995–2006: U.S. Geological Survey Fact Sheet 2009–3006, 4 p. (Also available 

at http://pubs.usgs.gov/fs/2009/3006/.) 

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., 

Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of pesticides in water 

by graphitized carbon-based solid-phase extraction and 

high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations 

Report 01–4134, 73 p. 

Koterba, M.T., 1998, Ground-water data-collection protocols 

and procedures for the National Water-Quality Assessment 

Program—Collection, documentation, and compilation of 

required site, well, subsurface, and landscape data for wells: 

U.S. Geological Survey Water-Resources Investigations 

Report 98–4107, 91 p.

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, 

Ground-water data-collection protocols and procedures for 

the National Water-Quality Assessment Program—Collection and documentation of water-quality samples and related 

data: U.S. Geological Survey Open-File Report 95–399, 

113 p.

Madsen, J.E., Sandstrom, M.W., and Zaugg, S.D., 2003, Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—A method supplement for the 

determination of fipronil and degradates in water by gas 

chromatography/mass spectrometry: U.S. Geological Survey Open-File Report 02–462, 11 p.

Meyer, M.T., Loftin, K.A., Lee, E.A., Hinshaw, G.H., Dietze, 

J.E., Scribner, E.A., 2009, Determination of glyphosate, its 

degradation product aminomethylphosphonic acid, and glufosinate, in water by isotope dilution and online solid-phase 

extraction and liquid chromatography/tandem mass spectrometry: U.S. Geological Survey Techniques and Methods, 

book 5, chap. A10, 32 p.

Nakagaki, Naomi, and Wolock, D.M., 2005, Estimation of 

agricultural pesticide use in drainage basins using land 

cover maps and county pesticide data: U.S. Geological 

Survey Open-File Report 2005–1188, 46 p.

Sandstrom, M.W., Stroppel, M.E., Foreman, W.T., and Schroeder, M.P., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—Determination of moderate-use pesticides and selected degradates in 

water by C–18 solid-phase extraction and gas chromatography/mass spectrometry: U.S. Geological Survey WaterResources Investigations Report 01–4098, 70 p.

Timme, P.J., 1995, National Water Quality Laboratory 1995 

services catalog: U.S. Geological Survey Open–File 

Report 95–352, 92 p.
34 Pesticides in Wyoming Groundwater, 2008–10

U.S. Environmental Protection Agency, 2012, 2012 Edition of 

the drinking water standards and health advisories: Washington, D.C., U.S. Environmental Protection Agency, Office 

of Water, EPA 822–S–12–001, spring 2012, 20 p., accessed 

August 24, 2012, at http://www.epa.gov/waterscience/

criteria/drinking/dwstandards.pdf.

U.S. Geological Survey, variously dated, National field 

manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chaps. A1–A9, 2 v., variously paged, accessed 

August 26, 2012, at http://pubs.water.usgs.gov/twri9A. 

U.S. Geological Survey, 2012, National Water Information 

System, accessed August 26, 2012, at http://nwis.waterdata.

usgs.gov/wy/nwis/qwdata.

Wyoming Ground-water and Pesticides Strategy Committee, 1999, Wyoming generic State management plan for 

pesticides and ground water: Cheyenne, Wyo., prepared for 

Wyoming Department of Agriculture, 103 p.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory—Determination of pesticides in water by C–18 solid-phase extraction 

and capillary-column gas chromatography/mass spectrometry with selected-ion monitoring: U.S. Geological Survey 

Open–File Report 95–181, 49 p.
Appendixes
36 Pesticides in Wyoming Groundwater, 2008–10

Appendix 1. Blank data for sample collected at site 

410817104470201, November 2009.

[μg/L, micrograms per liter; <, less than]

Pesticide Concentration 

(μg/L)

Acrylonitrile <0.80

Bromacil <0.36

Bromomethane <0.2

Carbaryl <0.38

Carbazole <0.030

Carbon disulfide <0.04

Chlorpyrifos <0.16

cis-1,3-Dichloropropene <0.10

DEET <0.06

Diazinon <0.16

Iodomethane <0.26

Metalaxyl <0.12

Metolachlor <0.080

Prometon <0.12

trans-1,3-Dichloropropene <0.14

Appendix 2. Replicate sample data for detected pesticides from samples collected at sites 4108108104223501 (September 2009) and 

444603108383401 (September 2010). All other pesticides analyzed for had no detection in either the environmental or replicate sample.

[RPD, relative percent difference; μg/L, micrograms per liter; E, estimated value; <, less than; NC, not calculated]

Pesticide

Samples for site 410108104223501 (Lr4) Samples for site 444603108383401 (Pk1)

Environmental 

(μg/L)

Replicate 

(μg/L)

RPD 

percent

Environmental 

(μg/L)

Replicate 

(μg/L)

RPD 

percent

2-Chloro-4-isopropylamino6-amino-s-triazineE0.025 E0.022 13 <0.014 <0.014 NC

3,4-Dichloroaniline E0.004 E0.0035 13 <0.004 <0.004 NC

Atrazine 0.015 0.014 7 <0.007 <0.007 NC

Diuron E0.0026 <0.04 NC <0.04 <0.04 NC

Fluometuron E0.01 <0.04 NC E0.01 E0.01 0

Picloram E0.04 E0.04 0 <0.12 <0.12 NC

Sulfometuron-methyl E0.004 E0.003 29 <0.060 <0.060 NC
Appendixes 37

Appendix 3. Spike recovery data from sample collected from site 41101910405130 (Lr7), September 2008.

Pesticide Spike recovery 

percent

1-Naphthol 35

2,4-D 58

2,4-DB 44

2,6-Diethylaniline 94

2-Chloro-2’,6’-diethylacetanilide 110

2-Chloro-4-isopropylamino-6-amino-s-triazine 61

2-Chloro-6-ethylamino-4-amino-s-triazine 99

2-Ethyl-6-methylaniline 94

2-Hydroxy-4-isopropylamino-6-ethylamino-striazine

88

3,4-Dichloroaniline 78

3,5-Dichloroaniline 84

3-Hydroxy carbofuran 105

4-Chloro-2-methylphenol 60

Acetochlor 119

Acifluorfen 38

Alachlor 118

Aldicarb sulfone 99

Aldicarb sulfoxide 123

alpha-Endosulfan 82

Atrazine 109

Azinphos-methyl 81

Azinphos-methyl oxygen analog 28

Bendiocarb 34

Benfluralin 83

Benomyl 158

Bensulfuron-methyl 143

Bentazon 41

Bromacil 92

Bromoxynil 20

Carbaryl 78

Carbaryl 109

Carbofuran 106

Carbofuran 116

Chloramben methyl ester 82

Chlorimuron-ethyl 179

Chlorpyrifos 93

cis-Permethrin 62

cis-Propiconazole 119

Clopyralid 51

Cyanazine 100

Cycloate 54

Cyfluthrin 64

Pesticide Spike recovery 

percent

Cypermethrin 61

DCPA 115

DCPA monoacid 51

Desulfinylfipronil 122

Desulfinylfipronil amide 110

Diazinon 107

Dicamba 51

Dichlorprop 68

Dichlorvos 8

Dicrotophos 40

Dieldrin 104

Dimethoate 43

Dinoseb 24

Diphenamid 116

Disulfoton 66

Disulfoton sulfone 94

Diuron 105

Endosulfan sulfate 88

EPTC 90

Ethion 90

Ethion monoxon 89

Ethoprop 103

Fenamiphos 111

Fenamiphos sulfone 102

Fenamiphos sulfoxide 16

Fenuron 116

Fipronil 128

Fipronil sulfide 119

Fipronil sulfone 88

Flumetsulam 143

Fluometuron 99

Fonofos 98

Hexazinone 70

Imazaquin 204

Imazethapyr 187

Imidacloprid 106

Iprodione 51

Isofenphos 107

lambda-Cyhalothrin 28

Linuron 85

Malaoxon 59

Malathion 94
38 Pesticides in Wyoming Groundwater, 2008–10

Pesticide Spike recovery 

percent

MCPA 61

MCPB 41

Metalaxyl 99

Metalaxyl 129

Methidathion 100

Methiocarb 68

Methomyl 108

Methyl paraoxon 53

Methyl parathion 101

Metolachlor 113

Metribuzin 108

Metsulfuron-methyl 61

Molinate 98

Myclobutanil 97

N-(4-Chlorophenyl)-N’-methylurea 119

Neburon 92

Nicosulfuron 337

Norflurazon 112

Oryzalin 78

Oxamyl 68

Oxyfluorfen 76

Pendimethalin 101

Phorate 76

Phorate oxygen analog 113

Appendix 3. Spike recovery data from sample collected from site 41101910405130 (Lr7), September 2008.—Continued

Pesticide Spike recovery 

percent

Picloram 61

Prometon 104

Prometryn 119

Propanil 111

Propargite 59

Propham 74

Propiconazole 85

Propoxur 109

Propyzamide 115

Siduron 136

Simazine 99

Sulfometuron-methyl 158

Tebuthiuron 119

Tefluthrin 57

Terbacil 96

Terbufos 88

Terbufos oxygen analog sulfone 65

Terbuthylazine 114

Thiobencarb 106

trans-Propiconazole 114

Tribuphos 62

Triclopyr 58

Trifluralin 94
Appendixes 39

Appendix 4. Name, number, and ancillary information for 52 wells sampled during 1995–2006 baseline study1 and 2008–10 resampling 

study, Wyoming.

Site name 

(shown on 

fig. 2)

Site number County Geographic area Land use Well depth 

(feet)

Years fall sample 

was collected

A7 411842105362901 Albany Central Basins Urban 12 2003, 2010

B1 444914108214101 Big Horn Bighorn Basin Agricultural 22 1999, 2009

B5 442912108240601 Big Horn Bighorn Basin Agricultural 27 1999, 2009

B6 442650108251501 Big Horn Bighorn Basin Mixed 23 1999, 2009

B12 445324108310601 Big Horn Bighorn Basin Agricultural 7 1999, 2009

B17 445014108224301 Big Horn Bighorn Basin Mixed 22 1999, 2009

Cb1 411303106464201 Carbon Central Basins Mixed 13 2004, 2010

Cp6 442055105315801 Campbell Powder River Basin Urban 20 2004, 2010

Cv4 425154105513101 Converse High Plains/Casper Arch Urban 20 2003, 2008

Cv7 424536105231801 Converse High Plains/Casper Arch Urban 20 2003, 2008

F3 425242108465301 Fremont Wind River Basin Agricultural 40 1998, 2010

F12 431202108254401 Fremont Wind River Basin Agricultural 50 1998, 2010

F19 430119108225701 Fremont Wind River Basin Urban 60 1998, 2010

G4 420029104170601 Goshen High Plains/Casper Arch Agricultural 142 1995, 2008

G7 420836104223501 Goshen High Plains/Casper Arch Agricultural 42 1995, 2008

G21 420531104100201 Goshen High Plains/Casper Arch Agricultural 23 1995, 2008

G24 421219104310401 Goshen High Plains/Casper Arch Agricultural 25 1995, 2008

G25 420241104105301 Goshen High Plains/Casper Arch Mixed 36 1995, 2008

H9 434358108102901 Hot Springs Bighorn Basin Mixed 45 2003, 2009

H11 433843108122001 Hot Springs Bighorn Basin Urban 20 2003, 2009

J14 434143106250901 Johnson Powder River Basin Mixed 27 2000, 2010

Lr2 410327104232301 Laramie High Plains/Casper Arch Agricultural 100 1998, 2008

Lr4 410108104223501 Laramie High Plains/Casper Arch Undeveloped 80 1998, 2008

Lr7 411019104051301 Laramie High Plains/Casper Arch Mixed 243 1998, 2008

Lr11 410834104491601 Laramie High Plains/Casper Arch Urban 20 1998, 2008

Lr12 410906104515101 Laramie High Plains/Casper Arch Urban 20 1998, 2008

Nb7 424526104271101 Niobrara High Plains/Casper Arch Urban 17.5 2005, 2008

Nt2 425137106180401 Natrona High Plains/Casper Arch Urban 15 2001, 2008

Nt3 425101106185701 Natrona High Plains/Casper Arch Urban 14 2001, 2008

Nt8 425400106272101 Natrona High Plains/Casper Arch Urban 24 2001, 2008

Pk1 444603108383401 Park Bighorn Basin Agricultural 35 1997, 2009

Pk5 444147108472802 Park Bighorn Basin Agricultural 40 1997, 2009

Pk7 444453108452301 Park Bighorn Basin Urban 18 1997, 2009

Pk10 444212108390801 Park Bighorn Basin Agricultural 94 1997, 2009

Pk14 443254109000601 Park Bighorn Basin Mixed 80 1997, 2009

Pk19 444514108545401 Park Bighorn Basin Agricultural 90 1997, 2009

Pk25 444633108450401 Park Bighorn Basin Agricultural 20 1997, 2009

Pt4 415733105030901 Platte High Plains/Casper Arch Agricultural 68 2000, 2008

Pt5 420151105011401 Platte High Plains/Casper Arch Agricultural 100 2000, 2008

Pt12 421532104441001 Platte High Plains/Casper Arch Urban 25 2000, 2008
40 Pesticides in Wyoming Groundwater, 2008–10

Site name 

(shown on 

fig. 2)

Site number County Geographic area Land use Well depth 

(feet)

Years fall sample 

was collected

Sb3 425633110142401 Sublette Green River Basin Mixed 90 2004, 2010

Sh3 444338106161001 Sheridan Powder River Basin Undeveloped 30 1999, 2010

Sh5 444645106574001 Sheridan Powder River Basin Urban 24 1999, 2010

Sh15 445014106490701 Sheridan Powder River Basin Agricultural 50 1999, 2010

Sw3 413454109133501 Sweetwater Green River Basin Urban 19 2001, 2010

Sw9 420635109270101 Sweetwater Green River Basin Undeveloped 80 2001, 2010

U2 411643110583401 Uinta Overthrust Belt Mixed 35 2002, 2010

U10 411937110172801 Uinta Green River Basin Urban 13 2002, 2010

Wk3 440031107573701 Washakie Bighorn Basin Urban 30 1997, 2009

Wk7 440232107561201 Washakie Bighorn Basin Agricultural 125 1997, 2009

Wk10 435402108052101 Washakie Bighorn Basin Agricultural 27 1997, 2009

Wk13 435819107580601 Washakie Bighorn Basin Agricultural 30 1997, 2009

1

Bartos and others (2009).

Appendix 4. Name, number, and ancillary information for 52 wells sampled during 1995–2006 baseline study1 and 2008–10 resampling 

study, Wyoming.—Continued
Appendixes 41

Appendix 5. Summary of pesticides distributed within Wyoming, 2007.1

[NAL, no assessment level; H, Herbicide; F, Fungicide; I, Insecticide; R, Rodenticide; L, Larvicide; S, Soil fumigant; ST, Seed treatment; CP, Crop protectant; 

GR, Growth regulator; B, Bactericide, Algaecide; MCPA, (4-chloro-2-methylphenoxy)acetic acid; EPTC, S-ethyl dipropylthiocarbamate; DCPA, dimethyl tetrachloroterephthalate; MSMA, monosodium methyl arsenate; PCNB, pentachloronitrobenzene; --, not on analytical schedule]

Pesticide Pesticide 

action

Distribution 

rank2

Number of detections (NAL)

1995–2006 baseline study 

(598 samples)3

2008–10 resampling study 

(52 samples)

Dicamba H 1 1 0

2,4–D amine H 2 3 --

Glyphosate H 3 -- 2

Diuron H 4 17 6

Mecoprop-p H 5 -- --

2,4–D methyl ester H 6 1 0

Clopyralid H 7 9 0

Triclopyr H 8 2 0

Copper compounds F 9 -- --

Piperonyl butoxide I 10 -- --

Permethrin I 11 1 --

Malathion I 12 2 0

MCPA H 12 0 0

Fluroxypyr H 14 -- --

Bromacil H 15 21 6

Metsulfuron-methyl H 15 1 1

Imazapyr H 17 -- --

Chlorpyrifos I 18 0 0

Bacillus thuringiensis I 19 -- --

Carbaryl I 19 2 0

Pendimethalin H 19 0 0

Prometon H 22 177 35

Diflufenzopyr H 23 -- --

Bromoxynil H 24 1 0

Mancozeb F 24 -- --

Bentazon H 26 4 1

Chlorsulfuron H 27 -- --

Diquat dibromide H 27 -- --

2,4–D H 29 3 0

B-Cyfluthrin I 29 0 --

Tebuthiuron H 29 67 14

Chlorophacinone R 32 -- --

Hexazinone H 32 1 4

EPTC H 34 0 0

Metolachlor H 34 16 1

Clethodim H 36 -- --

Metribuzin H 36 3 1

Simazine H 36 48 12

Sodium chlorate H 36 -- --

Sodium metaborate H 36 -- --
42 Pesticides in Wyoming Groundwater, 2008–10

Pesticide Pesticide 

action

Distribution 

rank2

Number of detections (NAL)

1995–2006 baseline study 

(598 samples)3

2008–10 resampling study 

(52 samples)

Imidacloprid I 41 2 1

Picloram H 41 43 5

Atrazine H 43 190 24

Bromadiolone R 43 -- --

Desmedipham H 43 -- --

Ethofumesate H 43 -- --

Flumioxazin H 43 -- --

S-Methoprene I 43 -- --

Dichlobenil H 49 0 0

Terbufos I 49 0 0

Acetochlor H 51 0 0

Sulfometuron-methyl H 51 3 3

Dimethoate I 53 0 0

Paraquat dichloride H 53 -- --

2,4–DB H 56 0 0

Bifenthrin I 56 -- --

Carfentrazone-ethyl H 56 -- --

Dimethenamid-P H 56 -- --

Aldicarb I 60 0 --

Dithiopyr H 60 -- --

Mineral oil I, F 60 -- --

Prodiamine H 60 -- --

Pyrethrins I 60 -- --

Trifluralin H 60 2 0

Benefin H 66 -- --

Hydramethylnon I 66 -- --

Tefluthrin I 66 0 0

Triallate H 66 2 --

Trichlorfon I 66 -- --

Chlorothalonil F 71 0 0

Cypermethrin I 71 0 1

Imazamox H 71 -- --

Imazapic H 71 -- --

Metalaxyl F 71 0 2

Thifensulfuron H 71 -- --

Tribenuron H 71 0 0

Bacillus sphaericus L 78 -- --

Dinotefuran I 78 -- --

d-Phenothrin I 80 -- --

Ethalfluralin H 81 0 0

Appendix 5. Summary of pesticides distributed within Wyoming, 2007.1—Continued

[NAL, no assessment level; H, Herbicide; F, Fungicide; I, Insecticide; R, Rodenticide; L, Larvicide; S, Soil fumigant; ST, Seed treatment; CP, Crop protectant; 

GR, Growth regulator; B, Bactericide, Algaecide; MCPA, (4-chloro-2-methylphenoxy)acetic acid; EPTC, S-ethyl dipropylthiocarbamate; DCPA, dimethyl tetrachloroterephthalate; MSMA, monosodium methyl arsenate; PCNB, pentachloronitrobenzene; --, not on analytical schedule]
Appendixes 43

Pesticide Pesticide 

action

Distribution 

rank2

Number of detections (NAL)

1995–2006 baseline study 

(598 samples)3

2008–10 resampling study 

(52 samples)

Fludioxonil F 82 -- --

Hydrotreated paraffinic oil I 82 -- --

Rimsulfuron H 82 -- --

Strychnine R 82 -- --

Thiophanate-methyl F 82 -- --

Triflusulfuron methyl H 82 -- --

Azoxystrobin F 88 -- --

Esfenvalerate I 88 -- --

Quinclorac H 88 -- --

Resmethrin I 88 -- --

Sulfentrazone H 88 -- --

Tebuconazole F 88 -- --

1,3-Dichloropropene S 94 0 --

Aluminum phosphide I 94 -- --

Captan I 94 -- --

Carbofuran I 94 2 0

Carboxin ST 94 0 0

Isoxaben H 94 -- --

Kaolin CP 94 -- --

Methidathion I 94 0 0

Naled I 94 -- --

Oxydemeton-methyl I 94 -- --

Phenmedipham H 94 -- --

Phorate I 94 0 0

Phosmet H 94 0 0

Pronamide H 94 -- --

Propionic acid F 94 -- --

Sodium methyldithiocarbamate S 94 -- --

Sulfur F 94 -- --

Tebupirimfos I 94 -- --

Zinc phosphide R 94 -- --

Acephate I 113 -- --

Boscalid F 113 -- --

Carbon R 113 -- --

Clodinafop-propargyl H 113 -- --

Cycloate H 113 0 0

Diphacinone R 113 -- --

Endothall H 113 -- --

Fenoxaprop-p-ethyl H 113 -- --

Fluazifop-P-butyl H 113 -- --

Appendix 5. Summary of pesticides distributed within Wyoming, 2007.1—Continued

[NAL, no assessment level; H, Herbicide; F, Fungicide; I, Insecticide; R, Rodenticide; L, Larvicide; S, Soil fumigant; ST, Seed treatment; CP, Crop protectant; 

GR, Growth regulator; B, Bactericide, Algaecide; MCPA, (4-chloro-2-methylphenoxy)acetic acid; EPTC, S-ethyl dipropylthiocarbamate; DCPA, dimethyl tetrachloroterephthalate; MSMA, monosodium methyl arsenate; PCNB, pentachloronitrobenzene; --, not on analytical schedule]
44 Pesticides in Wyoming Groundwater, 2008–10

Pesticide Pesticide 

action

Distribution 

rank2

Number of detections (NAL)

1995–2006 baseline study 

(598 samples)3

2008–10 resampling study 

(52 samples)

Fluridone H 113 -- --

Flurprimidol GR 113 -- --

Flutolanil F 113 -- --

Foramsulfuron H 113 -- --

lambda-Cyhalothrin I 113 0 0

Lindane I 113 0 0

Mesotrione H 113 -- --

MSMA H 113 -- --

Myclobutanil F 113 0 0

Nicosulfuron H 113 0 0

Novaluron I 113 -- --

Oryzalin H 113 1 0

Pinoxaden H 113 -- --

Poly(oxy-1,2-ethanediyl), 

α-isoctadecyl-ω-hydroxyl

I 113 -- --

Prallethrin I 113 -- --

Propargite I 113 0 0

Pyraclostrobin F 113 -- --

Pyrazon H 113 -- --

Sethoxydim H 113 -- --

Siduron H 113 0 0

Sodium nitrate R 113 -- --

Streptomycin B 113 -- --

Sulfosulfuron H 113 -- --

Sulfur R 113 -- --

Temephos I 113 -- --

Terbacil H 113 0 0

Tetraconazole F 113 -- --

Tralkoxydim H 113 -- --

Triphenyltin hydroxide F 113 -- --

Abamectin I 151 -- --

Aminopyralid H 151 -- --

Bifenazate I 151 -- --

Butoxypolypropylene glycol I 151 -- --

DCPA H 151 5 0

Diazinon I 151 1 0

Difenoconazole I 151 -- --

Ethephon GR 151 -- --

Fipronil H 151 0 1

Appendix 5. Summary of pesticides distributed within Wyoming, 2007.1—Continued

[NAL, no assessment level; H, Herbicide; F, Fungicide; I, Insecticide; R, Rodenticide; L, Larvicide; S, Soil fumigant; ST, Seed treatment; CP, Crop protectant; 

GR, Growth regulator; B, Bactericide, Algaecide; MCPA, (4-chloro-2-methylphenoxy)acetic acid; EPTC, S-ethyl dipropylthiocarbamate; DCPA, dimethyl tetrachloroterephthalate; MSMA, monosodium methyl arsenate; PCNB, pentachloronitrobenzene; --, not on analytical schedule]
Appendixes 45

Pesticide Pesticide 

action

Distribution 

rank2

Number of detections (NAL)

1995–2006 baseline study 

(598 samples)3

2008–10 resampling study 

(52 samples)

Imazethapyr H 151 0 0

Iprodione F 151 0 0

Oxyfluorfen H 151 1 0

Paclobutrazol GR 151 -- --

PCNB F 151 -- --

Propiconazole F 151 0 0

Pyraflufen ethyl H 151 -- --

Quizalofop-P-ethyl H 151 -- --

Spiromesifen I 151 -- --

Triadimefon F 151 -- --

1

Data from Wyoming Department of Agriculture (Hank Uhden, Wyoming Department of Agriculture, written commun., 2010). Summary includes pesticides 

that were distributed in Wyoming in 2007. This does not necessarily mean the pesticide was sold or used during 2007.

2

A ranking of 1 represents the active ingredient distributed most frequently. Progressively higher ranking numbers represent progressively lower distribution.

3

Bartos and others (2009).

Appendix 5. Summary of pesticides distributed within Wyoming, 2007.1—Continued

[NAL, no assessment level; H, Herbicide; F, Fungicide; I, Insecticide; R, Rodenticide; L, Larvicide; S, Soil fumigant; ST, Seed treatment; CP, Crop protectant; 

GR, Growth regulator; B, Bactericide, Algaecide; MCPA, (4-chloro-2-methylphenoxy)acetic acid; EPTC, S-ethyl dipropylthiocarbamate; DCPA, dimethyl tetrachloroterephthalate; MSMA, monosodium methyl arsenate; PCNB, pentachloronitrobenzene; --, not on analytical schedule]
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For more information concerning this publication, contact:

Director, Wyoming Water Science Center

U.S. Geological Survey

521 Progress Circle, Suite 6

Cheyenne, Wyoming 82007

(307) 778-2931

Or visit the Wyoming Water Science Center Web site at:

http://wy.water.usgs.gov/

Eddy-Miller and others—Pesticides in Wyoming Groundwater, 2008–10—Scientific Investigations Report 2013–5064

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