Introduction Groundwater has played a significant role in the development of Wyoming. A large number of public water supplies in the state of Wyoming utilize groundwater resources. Wells provide drinking water for approximately 75% of the state's population and are a principal source of water for livestock (U.S. Geological Survey, 1985). It is in the public and state interest to protect these groundwater resources from contamination by various pollutants which can be harmful to the health and welfare of humans and livestock.
The impacts of intensive agricultural practices (non-point source pollution) on the quality of groundwater are well documented throughout the United States. Nitrate (NO3-) and pesticides are most frequently detected in groundwater associated with the intensive agricultural areas. High nitrate concentration in drinking water can cause blue baby syndrome (oxygen deficiency) in infants (Fletcher, 1991). Therefore, the Environmental Protection Agency (EPA) drinking water standard for NO3- is 10 milligrams per liter (nitrate as nitrogen).
During the mid 1980's, the EPA reported 17 pesticides in groundwaters of 27 states at concentrations ranging from a trace to several milligrams per liter (Sun, 1986). A later survey conducted by Parsons and Witt in 1988 on "Pesticides in Groundwater in the United States of America" indicated 67 pesticides in 33 states. Seventeen of these pesticides from this latter study were detected at levels greater than the U.S. EPA's Health Advisory limit (HAL).
Two pesticides most frequently detected in groundwaters are atrazine and aldicarb. Atrazine has been reported to be the second most widely used pesticide in the U.S at 79 million pounds of active ingredient applied yearly as a pre- or post-emergent treatment to control weeds. An estimated 12,000 acres, or 13% of Wyoming's corn acreage is treated with atrazine (Legg et alĄ 1992). Because of its possible carcinogen (cancer causing agent) nature, the EPA has set the HAL for atrazine at 3 micrograms per liter in drinking water (U.S. EPA, 1989).
Aldicarb is extensively used to control mites, nematodes, and aphids by direct application to soils and plants. In Wyoming, aldicarb is applied to approximately 22,000 acres, or 30% of the total acreage of sugarbeets (Legg et al., 1992). Aldicarb has been detected in groundwaters of several states with 175 wells exceeding the HAL of 10 micrograms per liter (Parsons and Witt, 1988). Although Wyoming has a lower application rate of fertilizers and pesticides than many high production areas in the United States (i.e., Corn Belt, Atlantic Seaboard, Southwestern and Pacific Regions), their extensive use in several Wyoming counties (e.g., Goshen, Park) may present a potential problem. For example, the Torrington area of the North Platte River valley located in Goshen County is one of four major irrigated agricultural areas in Wyoming. High levels of nitrate (> 10 milligrams per liter nitrate as nitrogen) have been detected in several wells throughout the Torrington area (Parks, 1991). The presence of high nitrates in Torrington area groundwaters may be an indication of a potential for leaching of other pollutants such as pesticides. In another case, leaching of aldicarb from the soils of the Powell area was reported (Barkan and Nelson, 1991).
Since the detection of isolated groundwater quality problems in Goshen County, different Wyoming state agencies, in cooperation with the EPA, are developing strategies to help citizens and landowners protect groundwater quality. These agencies include: the Wyoming Department of Environmental Quality (WDEQ), Wyoming Department of Agriculture (WDA), U.S. Geological Survey (USGS), and Wyoming Water Resources Center (WWRC). Additionally, other groups such as the Wyoming Association for Rural Water Users (WARWU), the Midwest Assistance Program (MAP), and various consulting firms are also offering assistance to citizens and landowners throughout the state to develop wellhead protection methods to improve groundwater quality.
The protection of groundwater quality from non-point source pollution is a complex issue and requires an interdisciplinary team approach. Thus, the purpose of this report is to review the efforts of WWRC in Goshen County, Wyoming in protecting groundwater resources from non-point source pollution. The WWRC with the cooperation of the WDEQ, EPA, Torrington Research and Extension Center, and Wyoming Cooperative Extension Service is working with local citizens and landowners for protecting groundwater resources from non-point source pollution.
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