The U.S. Environmental Protection Agencies (USEPA) STORET data base for atrazine was analyzed using a Geographic Information System (GIS) to determine: 1) How the publicly available data base (STORET) for atrazine in ground-water related to the results from other studies including the USEPA's National Pesticide Survey; 2) If there existed any geographical trends in the data; and, 3) The general quality of data in STORET.

The STORET data base confirms that in general atrazine was detected in less than 10-percent (6.6%) of the 4,224 wells sampled in 34 states and usually detected in trace quantities (less than 0.5 parts per billion (ppb)). The occurrence of atrazine in ground-water above the Health Advisory was limited to less than 1-percent (0.7%) of detections. Over 50-percent of the data was generated by the U.S. Geological Survey and can be considered of good quality complying in general with Good Laboratory Practices for sample collection, preservation, and analysis.

There appears to be two geographic regions where the bulk of detections, including those exceeding the 3.0 ppb Health Advisory, are common. Thematic maps for atrazine in ground-water showed that the Northern Corn Belt, defined by Minnesota, Iowa, and Nebraska, contains the most detections; the Mid-Atlantic states of Maryland, Delaware, New Jersey, and Pennsylvania also show considerable detections of atrazine.

Overall, the STORET data base for atrazine in ground-water is of good quality. Few wells were poorly located and those with inaccurate locations generally had no detections of atrazine.

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