Although agriculture and urban activities have substantially affected water quality in several areas of the South Platte River Basin, concentrations of pesticides and volatile organic chemicals (VOCs), such as MTBE, are generally below levels of concern for human health, according to the results of a 5-year investigation of water quality by the U.S. Geological Survey.

This study was among the first 20 studies conducted by the USGS as part of the National Water-Quality Assessment (NAWQA) Program to determine the status and trends, and understand the natural and human factors that affect water-quality conditions across the nation.

"From the standpoint of human health in agricultural areas, we were most concerned about nitrate and pesticides in local drinking water," said Kevin Dennehy, USGS hydrologist in charge of the study. "While we found pesticides in 29 out of the 30 wells sampled, the concentrations were low throughout the agricultural land use area, and concentrations generally were below the regulatory criteria for each of the individual pesticides."

Surface- and ground-water resources in the Denver metropolitan area are susceptible to contamination from pesticides and VOCs. All surface-water samples collected at two urban sites contained at least one pesticide, and water from 90 percent of the wells in the shallow alluvial aquifer contained at least one pesticide. VOCs were detected in 86 percent of the wells sampled from the shallow alluvial aquifer. Sixty-two percent of the samples had more than one VOC present.

The most frequently detected VOC was methyl tert-butyl ether (MTBE), a gasoline additive used to reduce carbon monoxide emissions from vehicles during winter. Although pesticide and VOC concentrations generally were small, their widespread occurrence is a concern. Currently, neither surface nor ground water from t
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Contact: Kevin F. Dennehy
kdennehy@usgs.gov
(303)236-4882 X312
United States Geological Survey
16-Apr-1998