Wyoming Water Resources Center
Katta J. Reddy and Chris M. Goertler, Wyoming Water Resources Center; Jack T. Cecil and Charlene Stephenson, Torrington Research and Extension Center; and Joe G. Hiller, Wyoming Cooperative Extension Service, University of Wyoming.
Approximately 75% percent of Wyoming's population uses groundwater as their primary drinking source. This water resource is also frequently used for livestock watering throughout Wyoming and the semi-arid West. Groundwater, however, can become quickly contaminated through the application of fertilizers and pesticides. Therefore, a cooperative study involving local citizens, the Wyoming Cooperative Extension Service, and the Wyoming Water Resources Center was begun in 1993 to assess the concentrations of nitrate, atrazine, and aldicarb in the groundwaters of Goshen County, Wyoming; one of the more concentrated agricultural areas in the state.
Wells chosen for sample collection were located throughout the study area along the North Platte River Valley upstream and downstream of the town of Torrington, Wyoming (Figure 1). Wells were selected with the assistance of local University of Wyoming Cooperative Extension Service personnel. Thirteen landowners were chosen as cooperators.
The rapid enzyme immunoassay technique was utilized to determine the concentrations of atrazine and aldicarb in groundwater samples collected during March, May, and July before, during, and after the growing season. Sample analysis was conducted within 24-hours of collection at the Torrington Research and Extension Center. Nitrate samples were collected concurrently and analysis was performed at the Wyoming Water Resources Center's Environmental and Water Quality Lab located on the University of Wyoming campus using the ion chromatography technique. All samples were maintained at a cooler temperature (approximately 2° C) prior to analysis.
Project results are presented in Table 1. The pH of all groundwater samples was recorded within the Environmental Protection Agency (EPA) suggested ranges of 6.5-8.5. Atrazine was detected in 85% of the groundwater wells samples, but in only 31% of the wells during all three sampling periods. Aldicarb was recorded in all groundwater wells during the May and July sampling periods, but was recorded in only one well, at 0.01 micrograms per liter (µL -1), during March prior to planting.
Nitrate-N concentrations ranged from non-detectable levels to a high of 53.6 milligrams per liter (mg L-1), well above the EPA's recognized safe drinking water limit of 10 mg L-1. In most instances, nitrate concentrations did decline after the growing season.
Both atrazine and aldicarb have been used as pesticides in Goshen County, Wyoming, though atrazine has been classified by the EPA as a restricted-use pesticide. This research suggests that pesticides levels are well below the EPA's recognized safe drinking water limits although concentration of both pesticides tended to increase as the crop growing season progressed.
Nitrate, however, continues to be a problem in the Goshen County, Wyoming area. Groundwater wells located just outside of the North Platte River floodplain had the highest nitrate concentrations reaching approximately five times the EPA recommended limit during the crop growing season.
Landowner cooperators were informed of the research results and at least one has since altered the type and application of fertilizer to his fields in an effort to reduce nitrate levels in the area. Landowners making changes on their own, without coercion from outside sources is an indication that this educational and outreach effort was successful.
Table 1. Groundwater data for pH, nitrate, and pesticides; A=before planting, B=during crop growth, C=after the harvest, #=not detected and below 0.01 micrograms per liter (µL-1), *=not detected and below 1 milligram per liter (mg L-1of nitrate. Wells are numbered 1-13, and their relative locations are identified on Figure 1.
|pH||Atrazine||Aldicarb||Nitrate as Nitrogen|
|EPA Limit||6.5-8.5||3 (µL-1)||10 (µL-1)||10 (mgL-1)|
Monitoring for pesticides in the Torrington area has recently been completed by the U.S. Geological Survey and more detailed pesticide data should soon be available. Nitrate concentrations are still being monitored by several groups in Goshen County area groundwaters and educational efforts are underway to promote nitrate reductions. In addition, research is underway at the University of Wyoming and the Wyoming Water Resources Center to develop inexpensive and practical methodologies to remove nitrate from Wyoming's groundwater resources.
Goertler, C.M., K.J. Reddy, J.G. Hiller, J.T. Cecil, and C. Stephenson. 1997. Citizen's Network for monitoring groundwater quality in Goshen County, Wyoming: An educational and outreach project. In: Wyoming Water 1997: What's New in the Toolbox? Applied Research for Management of Wyoming's Water Resources Conference Proceedings, April 21-23, 1997, pp. 204-205.
Goertler, C.M., K.J. Reddy, J.G. Hiller, J.T. Cecil, and C. Stephenson. 1996. Citizen monitoring network for nitrate and pesticides in groundwaters of Goshen County, Wyoming. 1996 Agronomy Abstracts, Extension Education Division, p 22.
Wyoming Water Resources Center
P.O. Box 3067, University Station
Laramie, WY 82071-3067
Fax: (307) 766-3718
RESEARCH BRIEFS are published by the Wyoming Water Resources Center with funds provided in part by the US Geological Survey, Department of Interior, as authorized by the Water Resources Research Act of 1984. The research on which this report is based was financed in part by the US Geological Survey, Department of Interior, and Wyoming Water Resources Center. The views expressed do not necessarily represent those of the Department of Interior or the WWRC. Persons seeking admission, employment, or access to programs at the University of Wyoming shall be considered without regard to race, color, national origin, sex, age, religion, political belief, handicap, or veteran status.
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