Pesticides in ground water - Campbell County, Wyoming, 2004-2005

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

In 1991, members of local, State, and Federal governments, as well as industry and interest groups, formed the Ground-water and Pesticide Strategy Committee to prepare the State of Wyoming’s generic Management Plan for Pesticides in Ground Water. Part of this management plan is to sample and analyze Wyoming’s ground water for pesticides. In 1995, the U.S. Geological Survey, in cooperation with the Ground-water and Pesticide Strategy Committee, began statewide implementation of the sampling component of the State of Wyoming’s generic Management Plan for Pesticides in Ground Water. During 2004–2005, baseline monitoring was conducted in Campbell County. This fact sheet describes and summarizes results of the baseline monitoring in Campbell County.

Synthetic organic pesticides are used to control weeds, insects, and other organisms in a wide variety of agricultural and nonagricultural settings. The use of pesticides has helped to make the United States the world’s largest producer of food (Barbash and Resek, 1996). Pesticide use, however, also has been accompanied by concerns about potential adverse effects

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

Wyoming Department of Agriculture

on the environment and human health. A potential pathway for the transport of pesticides is through hydrologic systems, which supply water for both humans and natural ecosystems. Water is one of the primary ways pesticides are transported from an application area to other locations in the environment (fig. 1) (Barbash and Resek, 1996).

Pesticide contamination of ground water is a national issue because of the widespread use of pesticides, the expense and difficulty of remediating ground water, and the fact that ground water is used for drinking water by about one-half the Nation’s population. Although application rates and the variety of pesticides used may be greater in urban areas, concern over their presence in ground water is especially acute in rural agricultural areas where more than 95 percent of the population rely upon this resource for drinking water (Hutson and others, 2004).

Wyoming’s Pesticide Management Plan

The Ground-water and Pesticide Strategy Committee (GPSC) has developed the generic State Management Plan for Pesticides in Ground Water for the State of Wyoming (SMP) (Wyoming Ground-water and Pesticides Strategy Committee, 1999). Wyoming was required by the U.S. Environmental Protection Agency to have an SMP in order for individuals and organizations to continue using certain pesticides in the State. The SMP includes information relating to individuals and organizations involved with implementation of the SMP, methods of preventing ground-water contamination, ground-water monitoring, and the responses required if pesticides are detected in ground water.

One critical part of the SMP is ground-water monitoring. This ground-water monitoring program has two phases. The first phase, baseline monitoring, is designed

Wyoming Department of Environmental Quality

to determine what pesticides, if any, have entered into the county’s ground water. The second phase, problem identification monitoring, is used to gather additional information about the ground water near wells with samples having significant pesticide detections.

Baseline monitoring is prioritized by a county rank and the vulnerability of the county’s ground water to pesticides. During the development of the SMP, the GPSC evaluated each county in Wyoming to determine the potential vulnerability of the county’s ground water to pesticides. Each county was ranked according to the extent of cropland and urban areas in the county, as well as the amount of pesticides sold within the county in 1991 (Wyoming Ground-water and Pesticides Strategy Committee, 1999).

A ground-water vulnerability map was prepared for the uppermost or shallowest aquifer (Hamerlinck and Arneson, 1998). A Geographic Information System was used to overlay seven layers describing hydrogeology and land use. Ground water is vulnerable because of either inherent sensitivity of the hydrogeology or the combination of the sensitivity and associated land use. The map was used to assist in the selection of monitoring sites in each county. The monitoring focuses on areas where the ground water is most vulnerable.

The GPSC selected 18 pesticides and 2 degradation products as the focal pesticides for analysis as part of the SMP (table 1). The analytical methods used to detect the focal pesticides also detect 115 other pesticides and degradation products. Any additional pesticides that were detected are listed in table 1 as nonfocal pesticides. Ground water from all wells in the baseline-monitoring program was analyzed for the pesticides listed in table 1, with the exception of difenzoquat, for which an analytical method was not available.

The goal of the ground-water monitoring part of the SMP is to analyze ground-water samples for pesticides in all 23 Wyoming counties. To date, sampling has been completed in Goshen (1995–1996), Park (1997), Washakie (1997–1998), Fremont (1998–1999), Laramie (1998–1999), Lincoln (1998– 1999), Big Horn (1999–2000), Sheridan (1999–2000), Crook (2000–2001), Johnson (2000–2001), Platte (2000–2001), Natrona (2001–2002), Sweetwater (2001–2002), Teton (2001–2002), Uinta (2002–2003), Albany (2003–2004), Converse (2003–2004), Hot Springs (2003–2004), Carbon (2004–2005), Sublette (2004–2005), and Niobrara and Weston (2005–2006) Counties.

Ground-Water Monitoring in Campbell County

Ground water in Campbell County was ranked twenty-first most vulnerable to pesticide contamination in Wyoming (Wyoming Ground-water and Pesticide Strategy Committee, 1999). The vulnerability map created by the Spatial Data and Visualization Center (Hamerlinck and Arneson, 1998), identifies unconsolidated Quaternary-age alluvial deposits in the county and Tertiary formations that underlie urban land use as the most vulnerable to pesticides (shown as red or yellow on fig. 2).

Eight wells were selected in Campbell County (fig. 3) for baseline monitoring. All wells were located in the red or yellow areas shown on figure 2. The Quaternary-age alluvial deposits in these areas were not thick enough to provide water for wells, and all wells sampled were completed in either the Tertiary-age Wasatch Formation or Fort Union Formation. All wells were sampled twice, once in August 2004 and once in April 2005.

Figure 2. Vulnerability of Campbell County, Wyoming ground water to pesticide contamination (from Hamerlinck and Arneson, 1998).

Two of the 19 focal pesticides and 3 nonfocal pesticides were detected in Campbell County (table 1). Pesticides were detected in three of the eight wells sampled in Campbell County; concentrations of each detected pesticide were less than 1/50 of the applicable drinking-water standard (U.S. Environmental Protection Agency, 2004) (table 1).

The most commonly detected pesticide (6 of 16 samples) in Campbell County was prometon, which is the active ingredient in the generaluse pesticide Pramitol. Prometon typically is detected in areas with urban land use (Barbash and others, 1999). Prometon was the most commonly detected pesticide in Albany, Carbon, Converse, Crook, Johnson, Natrona, Sheridan, Sublette, Teton, and Uinta Counties.

Data Distribution and Availability

Sampling results have been provided to local groups interested in pesticides in ground water in Campbell County. The information can be used by citizens and local governments to help understand current conditions. Analytical results of the Campbell County sampling can be found in Blajszczak and others (2005), and Blajszczak and others (2006) or on the Internet at http://waterdata.usgs.gov/wy/nwis/qwdata. Analytical results and fact sheets for all counties sampled to date are available from the U.S. Geological Survey in Cheyenne by phone, email, or on the Internet at http://wy.water.usgs.gov/projects/pesticide/.

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