## Wyoming Department of **Agriculture Wyoming Department of**  **Environmental Quality** 

Alcova Reservoir 

### High Medium high Medium Medium low Low **Mapped ground-water vulnerability to**  **pesticide contamination**

**Sampled well Rank of county’s**  **ground-water vulnera- bility to pesticide con-**  **tamination (Wyoming Ground-water and**  **Pesticides Strategy Committee, 1999)** 
0 0 60 MILES 60 KILOMETERS 

### EXPLANATION **MONTANA WYOMING** 

Lusk Cody Basin

Casper Lander

Laramie Rawlins Douglas Jackson Worland Buffalo

**Cheyenne** Evanston Kemmerer Pinedale Gillette Sundance Sheridan

Wheatland Newcastle

Torrington

Green River Thermopolis **YELLOWSTONE**
**NATIONAL PARK**  110° 109° 108° 107° 106° 105°

41° 42° 43° 44° 45°

River S w e e t w a t e r Pathfinder Reservoir

Seminoe Reservoir Boysen Reservoir Keyhole Res

Glendo Reservoir

Guernsey Reservoir Fontenelle Reservoir
Wheatland Reservoir River River Platte North

L a r a m i e Cheyenne River River
Belle F o u r c h e River Tongue

P o w d e r R

Lake DeSmet Bighorn Lake Bighorn

R Shoshone Buffalo Bill Reservoir River South Fork G

re

y b u l

l River

River Wind River Snake River Greys River Fork New

Green River Fork Hams

R i v e r

H

e n r

y s F k River

River B i g S a n d y River

River M

e d

i c i

n e Fork Blacks B e a r R S m i t h s F k R Salt

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 Afton

Saratoga Glenrock Riverton

Rock Springs Lovell Powell

Yellowstone

Lake

Jackson

Lake

Flaming Gorge Reservoir G r o s V

e n t r e R i v e r **PARK (2)**  **BIG HORN** 

**(7) SHERIDAN**  **(8)**

**WASHAKIE (1)**  **JOHNSON (10)**  **CAMPBELL (21)**  **CROOK (11)** 

**WESTON**

**(13) TETON** 

**(15) HOT**  **SPRINGS**

**(19)**

**LINCOLN**

**(5)**

**UINTA (16)**  **SWEETWATER (14)**  **NATRONA (12)**  **CONVERSE (18)** 

**ALBANY**

**(17) CARBON** 

**(20)**
**LARAMIE (6)** 

**GOSHEN**

**(3) PLATTE** 

**(9) NIOBRARA**  **(23) FREMONT**  **(4) SUBLETTE** 

**(22)** River Powder Little

Bow North Platte Popo Agie **(23)** 111°

**IDAHO UTAH** 

**UTAH COLORADO SOUTH DAKOTA NEBRASKA** 

**U.S. Department of the Interior U.S. Geological Survey**  **Fact Sheet 2009–3006 February 2009**  

## Prepared in cooperation with the Wyoming Department of Agriculture and the Wyoming Department of Environmental Quality, on behalf of the **Wyoming Ground-water and Pesticides Strategy Committee** 

# Pesticides in Ground Water of Wyoming, 1995–2006

Printed on recycled paper 

## Figure 1. Aquifer vulnerability mapped across the State of Wyoming was based on hydrogeologic features and land use (Hamerlinck and Arneson, 1998). Two hundred and ninety-six wells were sampled to evaluate the presence of pesticides in Wyoming’s most vulnerable aquifers. **In 1991, members of local, State, and Federal governments, as well as industry and interest groups, formed the Ground-water and Pesticides Strategy Committee (GPSC) to prepare the State of Wyoming Generic Management Plan for Pesticides in Ground**  **Water. Little existing information was available describing pesticide occurrence in ground water; therefore, statewide baseline ground-water sampling was considered a high priority by the GPSC.**  **The GPSC identified 20 pesticides and degradates for baseline ground-water sampling (referred to herein as focal pesticides). Sampling focused on the State’s most vulnerable ground water (Wyoming Ground-water and Pesticides Strategy Committee, 1999)**  **as determined by Hamerlinck and Arneson (1998; fig. 1). Ground-water vulnerability is based on inherent sensitivity of the hydro**   ** geology (such as a shallow water table or highly permeable aquifer materials) and overlying land use.** 

# Ground-Water Sampling The U.S. Geological Survey (USGS), in cooperation with the Wyoming Departments of Agriculture and Environmental Quality, on behalf of the GPSC, conducted baseline sampling in Wyoming to characterize the large-scale occurrence of pesticides in ground water. During 1995–2006, sampling was conducted in each county, during which generally two water samples were collected (once in the fall and spring) from each of 296 wells. Five to 28 wells were selected for sampling in each county with site selection focused on areas where the ground water is most vulnerable, shown as areas of high or medium high vulnerability in figure 1. The order of counties sampled was based on a ranking from the GPSC (fig. 1; Ground-water and Pesticides Strategy Committee, 1999). Most wells selected for this study were either a domestic, monitoring, or stock well. The depths of all wells were between 7 and 200 feet below land surface, with most well depths less than 100 feet. Most (78 percent) wells were completed in unconsolidated aquifers, and 22 percent of wells were completed in consolidated (bedrock) aquifers (Bartos and others, 2009). Ground-water samples were analyzed for the 20 focal pesti

cides (table 1), plus as many as 136 additional pesticides (Bartos and others, 2009) using USGS laboratory methods. These highly

## Table 1. Focal pesticides and nonfocal pesticides, as determined by the Wyoming Ground-water Pesticides Strategy Committee (1999), detected in Wyoming ground water, 1995–2006 (compiled from Bartos and others, 2009). [Compounds in **bold type** were detected at concentrations greater than the CSAL. CSAL, compound-specific assessment level; μg/L, micrograms per liter; --, not applicable; NA, not assigned; USEPA, U.S. Environmental Protection Agency]



### Common name **Trade name Type of**  **pesticide (Meister, 2002)**  **Number of detections (using CSAL)/number of**  **samples (CSAL noted in**  **parentheses, in μg/L) Median concentration of**  **two or more detections, or value if only one detection,** 

**greater than CSAL (μg/L) USEPA standard or**  **health advisory (μg/L)**  Focal pesticides 1 

### from Wyoming Ground-water and Pesticides Strategy Committee (1999) Alachlor Lasso, Alanex, Shroad Herbicide 0/589 (0.05)

-- 2 

### 2 Aldicarb Temik Insecticide 0/577 (NA)

-- 2,3 

### 3 **Aldicarb sulfone** Aldicarb degradate, Standek, Aldoxycarb Insecticide 6/569 (0.11) 0.24 2,3 

### 2 **Aldicarb sulfoxide** Aldicarb degradate

-- 6/571 (0.14) .47 2,3 

### 4 **Atrazine** Aatrex, Atranex Herbicide 160/578 (0.004) .010 2 

### 3 **Bromacil** Hyvar X Herbicide 18/574 (0.06) .52 4 

### 70 **Clopyralid** Stinger, Lontrel Herbicide 3/567 (0.26) 22 ( 7 

### ) **Cyanazine** Bladex Herbicide 2/535 (0.013) .074 4 

### 1 **2,4–D** Dacamine, Weed-B-Gon Herbicide 5 

### 1/580 (0.15) 13.8 2 

### 70 **DCPA** Dacthal Herbicide 5 

### 1/587 (0.004) .004 4 

### 70 **Dicamba** Banvel, Banex Herbicide 5 

### 1/575 (0.13) 1.1 4 

### 4,000 cis - and trans -1,3-

Dichloropropene Telone Nematicide 0/570 (NA)

-- 6 

### 40 Difenzoquat Avenge Herbicide No analytical method available

-- ( 7 

### ) **Hexazinone** Buckshot, Pronone, Velpar Herbicide 5 

### 1/46 (0.05) .06 4 

### 400 **Metolachlor** Bicep, Dual Herbicide 5/534 (0.009) .024 4 

### 700 Metribuzin Lexone, Sencor Herbicide 0/589 (0.05)

-- 4 

### 70 Metsulfuron Ally, Escort Herbicide 0/142 (0.07)

-- ( 7 

### ) **Picloram** Tordon Herbicide 36/569 (0.06) .35 2 

### 500 **Simazine** Princep, Primatol, Aquazine Herbicide 4/589 (0.05) .08 2 

### 4 **Tebuthiuron** Graslan, Spike Herbicide 65/589 (0.01) .05 4 

### 500 Nonfocal pesticides detected above applicable CSAL 1 

### Bentazon Basagram, Bentazone Herbicide 2/578 (0.06) 0.36 4 

### 200 **Bromoxynil** Agristar, Brominal, Buctril Herbicide 5 

### 1/580 (0.07) .22 ( 7 

### ) **Carbofuran** Furadan, Futura Insecticide 2/587 (0.02) .032 2 

### 40 **2,4–D methyl ester**

-- Herbicide 5 

### 1/140 (0.009) .74 ( 7 

### ) **Deethylatrazine** Atrazine degradate

-- 25/591 (0.05) .21 ( 7 

### ) **Deisopropylatrazine** Atrazine/cyanazine/simazine degradate -- 2/217 (0.05) .12 ( 7 

### ) **Diazinon** Basudin, Spectracide, Knoxout Insecticide, nematicide 5 

### 1/587 (0.008) .016 4 

### 1 **3,4-Dichloroaniline** Propanil degradate

-- 5 

### 1/21 (0.004) .007 ( 7 

### ) **Dichlorprop** Weedone, Polymone Herbicide 5 

### 1/583 (0.06) .07 ( 7 

### ) **Diuron** Durashield, Karmex Herbicide 5/585 (0.06) .11 6 

### 200 **Fipronil sulfide** Fipronil degradate

-- 2/154 (0.006) .007 ( 7 

### ) **Flumetsulam** Broadstrike, Python Herbicide 2/142 (0.06) .07 ( 7 

### ) **Hydroxyatrazine** Atrazine degradate

-- 5 

### 1/141 (0.016) .02 ( 7 

### ) **Imidacloprid** Admire, Provado Insecticide 2/141 (0.02) .03 ( 7 

### ) **Oryzalin** Surflan Herbicide 5 

### 1/520 (0.31) .63 ( 7 

### ) **Prometon** Pramitol, Gesafram Herbicide 74/549 (0.05) .11 4 

### 100 **Triallate** Far-Go, Avadex BW Herbicide 5 

### 1/541 (0.003) .005 ( 7 

### ) **Triclopyr** Garlon Herbicide 2/584 (0.36) 10.1 ( 7 

### )

1 

### For a list of all pesticides analyzed for during the study, see Bartos and others, 2009, table 1. 2 

### MCL, USEPA Maximum Contaminant Level (U.S. Environmental Protection Agency, 2006). 3 

### The MCL for any combination of two or more of these three chemicals (aldicarb, aldicarb sulfoxide, and aldicarb sulfone) should not exceed 7 μg/L because of similar mode of action.

4 

### LHA, USEPA Lifetime Health Advisory Level (U.S. Environmental Protection Agency, 2006). 5 

### If a compound was only detected once, that value rather than a median is presented. 6 

### RSD4, USEPA Risk-Specific Dose at 10 -4 

### Cancer Risk (U.S. Environmental Protection Agency, 2006). 7 

### At the time of publication, a standard or health advisory had not been established by the USEPA.Alcova Reservoir 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°

River S w e e t w a t e r Pathfinder Reservoir

Seminoe Reservoir Boysen Reservoir Keyhole Reservoir

Glendo Reservoir

Guernsey Reservoir Fontenelle Reservoir
Wheatland Reservoir River River Platte North

L a r a m i e Cheyenne River River
Belle F o u r c h e River Tongue

P o w d e r R

Lake DeSmet Bighorn Lake Bighorn

R Shoshone Buffalo Bill Reservoir River South Fork G

re

y b u l

l River

River Wind River Snake River Greys River Fork New

Green River Fork Hams

R i v e r

H

e n r

y s F k River

River B i g S a n d y River

River M

e d

i c i

n e Fork Blacks B e a r R S m i t h s F k R Salt

0 0 60 MILES 60 KILOMETERS Afton

Saratoga Glenrock Riverton

Rock Springs Lovell Powell

Yellowstone

Lake

Jackson

Lake

Flaming Gorge Reservoir G r o s V

e n t r e R i v e r River Powder Little

Bow North Platte Popo Agie 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 **YELLOWSTONE**
**NATIONAL PARK**  

### EXPLANATION **Geographic area and number of different**  **pesticides detected using the common**  **assessment level (CAL) in parentheses ()**  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) **Well sampled for pesticide**  No pesticide detected Pesticide detected at concentration greater than the CAL (0.07 μg/L)



## Figure 2. One or more pesticides were detected at concentrations greater than the CAL (0.07 μg/L) in water from 23 percent of the wells s ampled during 1995–2006. The largest percentage of pesticide detections was in ground water from the High Plains/Casper Ar ch geographic area. sensitive methods often have analytical reporting limits 100 to 1,000 times lower than State and Federal drinking-water standards and guidelines for protecting water quality or routine pesticide monitoring of public drinking-water supplies. All concentrations of pesticides detected during the study were less than State and Federal standards and guidelines. Detections, therefore, do not nec

essarily indicate a concern to human health but rather help identify the environmental presence of pesticides and track their occurrence over time. Maximum Contaminant Levels (MCLs). Concentrations of some unregulated compounds were compared to USEPA Lifetime Health Advisory Levels (LHAs) or toxicity information, if available. Sixteen of the detected compounds listed in table 1 do not have human-health benchmarks or adequate toxicity information for evaluating results in a human-health context. 

## Pesticide Detections—Statewide Descriptions of pesticide detections are useful for understand

ing the nature of pesticides in ground water throughout the State and are as follows: • No pesticide concentrations exceeded USEPA drinkingwater standards or health-advisory levels (available for 18 of 32 detected pesticides; table 1). • One or more pesticides were detected at concentrations greater

than the CAL (0.07 μg/L) in water from about 23 percent of wells sampled in the State. • Most detected pesticides (81 percent) were classified as herbi

cides or herbicide degradates. • Thirty-two different pesticides were detected at concentrations

greater than applicable CSALs. • A greater number of pesticides were detected at concentrations

greater than the CSAL during the fall (28 different compounds) compared to the spring (21 different compounds). 

## Pesticide Detections—Geographic Area The State was divided into eight different regional geographic areas by Bartos and others (2009), on the basis of regional areas having similar natural characteristics (geography, physical features, 

# Data Analysis Results of baseline ground-water sampling were analyzed to describe pesticide occurrence (Bartos and others, 2009). Although the data were collected over a 12-year period, the data were not conducive to trend analyses, because most sites were only sampled during a 1-year period. Most pesticide detections were at low levels—concentrations that approach laboratory analytical capabilities. When comparing detections of the same pesticide over time, all sample detections were recensored to a single reporting level (noted as the CSAL, compound-specific assessment level). In order to compare different compounds to each other, pesticide detections were again recen

sored to a common assessment level (CAL) of 0.07 microgram per liter (μg/L). A screening-level assessment of the possible significance of detected compounds to human health was done and was basedon a comparison of measured concentrations to available humanhealth benchmarks. Concentrations of regulated compounds were compared to U.S. Environmental Protection Agency (USEPA)

## Figure 4. Urban land use has the highest percentage of wells with at least one pesticide detected. Agricultural, mixed, and rangeland/ undeveloped land uses had fewer wells with at least one pesticide detection. 0 10 20 30 40 50 60 R A N G E L A N D / U N D E V E L O P E D M I X E D U R B A N A G R I C U L T U R AL

P E R C E N T A G E O F W E L L S W I T H IN A L A N D
- U S E C A T E G O R Y, WITH AT L E A S T O N E P E S T I C I D E D E T E C T E D AT CONCENTRATIONS GREATER THAN THE COMPOUND-SPECIFIC ASSESSMENT LEVELLAND-USECATEGORY



### 16.5 percent 36.1 percent 59.6 percent 38.9 percent 0 5 10 15 20 25 30 35 40 45 W I N D R I V E R BASIN P O W D E R RIVER BASIN O V E R T H R U S T BELT N O R T H W E S T BASINS H I G H P L A I N S / C A S P E R ARCH G R E E N R I V E R BASIN C E N T R A L

BASINS B IGHORN

BASINGEOGRAPHIC AREA

PERCENTAGE OF TOTAL PESTICIDE DETECTIONS (GREATER THAN THE COMMON ASSESSMENT LEVEL) IN GEOGRAPHIC AREA 

### 2
. 3 percent 8
. 6 percent 2
. 3 percent 0
. 5 percent 4 0 .0 percent 6
. 8 percent 1 3
. 2 percent 26
. 4 percent



## Figure 3. Forty percent of all pesticide detections in Wyoming were in the High Plains/Casper Arch geographic area. hydrology, and geology) and land use (fig. 2). Evaluation of pesti

cide occurrence in relation to geographic areas showed that: • The largest percentages of pesticide detections were in water

from the High Plains/Casper Arch and Bighorn Basin geographic areas, where 40 and 26 percent, respectively, of all detections occurred at concentrations greater than the CAL (fig. 3). • The number of different pesticides detected at concentrations

greater than the CAL was largest in water from the High Plains/ Casper Arch, Bighorn Basin, and Central Basins geographic areas (fig. 2). • Prometon (a nonagricultural pesticide) was the only pesticide

detected in all eight geographic areas. 

## Pesticide Detections—Hydrogeology The frequency of pesticide detection was examined in relation to hydrogeology. This involved assessing the aquifer type, water level and well depth, well type, and soil characteristics. A notable outcome of this analysis was: • The percentage of wells with at least one pesticide detected was

larger for wells completed in unconsolidated aquifers than in bedrock aquifers regardless of assessment level. 

## Pesticide Detections—Land Use Land use was mapped within a 500-meter radius of each sampled well and classified into one of four predominant land-use categories (agricultural, urban, rangeland/undeveloped, and mixed) so that pesticide detections in ground water could be examined in relation to overlying land use. The following information was noted in regard to land use: • Pesticides were detected most frequently in water from wells

located in areas classified as predominantly urban (59.6 percent) and agricultural (38.9 percent; fig. 4). • Pesticides were detected least frequently in water from wells

located in areas classified as predominantly rangeland/undevel

oped, as only 16.5 percent of the water samples from these wells had a pesticide detection. 

# Future of Ground-Water Monitoring Program The completion of baseline ground-water quality sampling and the analysis of that data have provided the State with an oppor

tunity to move forward with monitoring Wyoming’s ground water. Information gained from this effort is helping to refine and guide a new, more focused ground-water monitoring program, with the ulti

mate goal of protecting Wyoming’s ground water while allowing responsible use of pesticides to continue (Wyoming Ground-water and Pesticides Strategy Committee, oral commun., 2008).



## By Cheryl A. Eddy-Miller, Timothy T. Bartos, and Laura L. Hallberg Layout and design by Suzanne C. Roberts Publishing support provided by the USGS Helena Publishing Service Center This study has been supported in part with a Section 319 grant from the U.S. Environmental Protection Agency to the Wyoming Department of Environmental Quality’s Non-Point Source Program. The use of trade, product, industry, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 

## U.S. Environmental Protection Agency, 2006, 2006 Edition of the drinking-water standards and health advisories: Washington, D.C., U.S. Environmental Protection Agency, Office of Water, EPA 822– R–06–013, summer 2006, 11 p., accessed January 22, 2008, at http://www.epa.gov/waterscience/criteria/drinking/dwstandards.pdf Wyoming Ground-water and Pesticides Strategy Committee, 1999, Wyoming generic State management plan for pesticides and ground water: prepared for Wyoming Department of Agriculture, Cheyenne, Wyo., 103 p. 

# Selected References Bartos, T.T., Eddy-Miller, C.A., and Hallberg, L.L., 2009, Occurrence of pesticides in ground water of Wyoming, 1995–2006: U.S. Geo

logical Survey Scientific Investigations Report 2009–5024, 72 p. Hamerlinck, J.D., and Arneson, C.S., eds., 1998, Wyoming ground water vulnerability assessment handbook, volume 2. Assessing ground-water vulnerability to pesticides: Laramie, University of Wyoming, Spatial Data and Visualization Center Publication SDVC 98–01–2 [variously paged]. Meister, R.T., 2002, Farm chemicals handbook: Willoughby, Ohio, Meister Publishing Co. [variously paged].