U.S. Geological Survey
Fact Sheet 094-01
1Nevada Department of Agriculture, Reno, Nevada
About 1 billion pounds of pesticides are used per year in agricultural and urban areas throughout the United States to control weed encroachment, plant disease, and insect predation (U.S. Geological Survey, 1999). Frequency of pesticide detections in ground water has increased over the last 20 years (U.S. Environmental Protection Agency, 1992). In 1985, the U.S. Environmental Protection Agency (USEPA) estimated the detection of at least 17 agricultural pesticides in the ground water of 23 states. By 2000, the U.S. Geological Survey (USGS) reported at least one pesticide was found in almost every water and fish sample collected in streams and in more than one-half of shallow wells sample in agricultural and urban areas (USGS, 2000). To protect ground water from pesticide contamination, USEPA, through the Federal Insecticide Fungicide and Rodenticide Act (FIFRA), requires all states to institute a ground water protection program. This fact sheet describes current (2001) pesticide monitoring of ground water in Nevada by the Nevada Department of Agriculture (NDOA) and supersedes Adams and others (1997).
Pesticides enter ground water directly and indirectly (fig. 1). Direct entry may result from pesticide spills near poorly sealed wells and from pesticide application through improperly designed or malfunctioning chemigation (chemical and irrigation delivery) systems, typically those systems without backflow protection. Indirect entry may result from percolation of lawn and agricultural irrigation water, urban runoff, and municipal wastewater effluent containing pesticides through soil, drainage ditches, and streambeds.
The NDOA, in cooperation with USEPA, currently (2001) is developing a management plan to protect Nevada's ground-water resources from pesticide contamination. An essential element of the NDOA plan is the network of ground-water sampling sites (fig. 2) that will help detect contamination in its early stages. Ground-water is monitored in areas where pesticides potentially may cause adverse effects to human health or the environment. NDOA uses this information to develop programs for managing pesticide use and for minimizing pesticide contamination.
The NDOA began monitoring ground water in 1993 in Mason Valley. This site is 1 of 20 geographic areas in the monitoring network (fig. 2; table 1). Initially, water from generally deep, irrigation, domestic and municipal wells was sampled. No pesticides were detected in water samples from the NDOA network of supply wells, which were not sampled by NDOA after 1997. Recently, however, the USGS National Water-Quality Assessment (NAWQA) Program reported the detection of pesticides in shallow ground water (less than 100 feet below land surface) from 1993 to 1995 within the urban areas of Reno-Sparks and Las Vegas, and in the agricultural areas of Carson Valley and Carson Desert (Bevans and others, 1998; Lico, 1998). This information led NDOA and USGS, in a cooperative effort, to modify the design of the pesticide monitoring network.
In most geographic areas, about 20 wells in the upper 10 to 20 feet of the water table are sampled in a designated year (table 1). The water from these wells is sampled semi-annually, in spring before irrigation and pesticide application and in the fall after the growing season. The objectives of sampling water are to assess the occurrence of pesticides within recharge areas of shallow ground water that underlie residential, commercial and agricultural settings and to protect the deep, potable ground water. Each ground-water sample is analyzed for 47 pesticides (table 2).
To date (2001), 10 pesticides have been detected from the monitoring network (table 2). A summary of pesticide detections in seven of the geographic areas sampled since 1997 is listed in table 3. Monitoring results show (1) that the use of more sensitive analytical methods and sampling of shallow ground water after 1997 resulted in the detection of more pesticides, (2) that only the concentration of atrazine exceeded the USEPA Maximum Contaminant Level (MCL) of 3.0 µg/L for public drinking water at only one shallow monitoring site in the Orovada area, (3) concentrations of 28 pesticide detections generally are <1 µg/L, but 8 of the 10 pesticides detected do not have MCL's and may be of concern, and (4) pesticides are more likely to be detected in the fall after the summer growing season. Monitoring for pesticides in shallow ground water, using more sensitive analytical methods, can provide early warning of potential contamination of deeper water supplies. Monitoring also can permit identification of potential sources of pesticides and possible routes for their transport (fig. 1). This information can be used to establish effective programs for protecting Nevada's ground-water resources.
Adams, P.A., Moses, C.W., and Bevans, H.E., 1997, Monitoring for pesticides in ground water in Nevada: U.S. Geological Survey Fact Sheet FS 139-97, 2 p.
Bevans, H.E., Lico, M.S., and Lawrence, S.J., 1998, Water quality in the Las Vegas Valley area and the Carson and Truckee River Basins, Nevada-California, 1992-96: U.S. Geological Survey Circular 1170, 47 p.
Cardinalli, J.L., Roach, L.M., Rush, F.E., and Vasey, B.J., 1968, State of Nevada hydrographic areas: Nevada Division of Water Resources map, scale 1:500,000.
Lico, M.S., 1998, Quality of ground water beneath urban and agricultural lands in Las Vegas Valley, and the Carson and Truckee River Basins, Nevada -- implications for water supply: U.S. Geological Survey Water-Resources Investigations Report 97-4259, 24 p.
Rush, F.E., 1968, Index of hydrographic areas in Nevada: Nevada Division of Water Resources, Information Report 56, 38 p.
U.S. Environmental Protection Agency, 1992, Pesticides in drinking-water wells: U.S. Environmental Protection Agency EPA 20T-1004, 15 p.
------ 2000, Drinking water standards and health advisories table: U.S. Environmental Protection Agency, EPA 822-B-00-001 Summer 2000, 12 p.
U.S. Geological Survey, 1996, Pesticides in ground water -- current understanding of distribution and major influences: U.S. Geological Survey Fact Sheet FS-244-95, 4 p.
------ 1999, Pesticides in stream sediment and aquatic biota -- current understanding of distribution and major influences: U.S. Geological Survey Fact Sheet FS 092-00, 4 p.
For more information on pesticide monitoring programs in Nevada:
Charles W. Moses
Nevada Department of Agriculture
350 Capital Hill Avenue
Reno, NV 89502
Telephone: (775) 887-1182
Fax: (775) 688-1178
URL: http://agri.state.nv.us
For more information on water resources in Nevada:
Public Information Assistant
U.S. Geological Survey
333 W. Nye Lane, Room 203
Carson City, NV 89706-0866
Telephone: (775) 887-7649
Fax: (775) 887-7629
E-mail: GS-W-NVpublic-info@usgs.gov
URL: nevada.usgs.gov