Publication Summary

The Washington State Pesticide Monitoring Program, initiated in 1988, has sampled ground water at 243 sites in 11 study areas. Sites ranged from a field drain at a depth of 5 feet to a 200 foot well.

The Washington State Pesticide Monitoring Program, initiated in 1988, has sampled ground water at 243 sites in 11 study areas. Sites ranged from a field drain at a depth of 5 feet to a 200 foot well.

A total of 145 different pesticides have been tested, although not all were tested at each site. Twenty-one of the 145 pesticides were detected in ground water. Of the 23,370 individual pesticide analyses, 168 were positive detections. One or more of these detections occurred at 102 of the 243 sites (42%). The average depth of wells with detected pesticides was 38 feet. The five pesticides detected most often were dacthal (DCPA) detected at 16% of sites; 1,2-dichloropropane (DCP) detected at 13% of sites; ethylene dibromide (EDB) detected at 11% of sites; atrazine detected at 7% of sites; and simazine detected at 2% of sites. Three pesticides -- DCP, EDB, and 1,2-dibromo-3-chloropropane (DBCP - one detection) -- were detected at concentrations exceeding human health criteria. Agricultural use of DCP and DBCP was canceled in 1977, and use of EDB was canceled in 1984.

The data do not suggest that pesticides in ground water pose a significant environmental or public health threat in Washington. At the same time, the limited sampling does not prove that pesticides do not pose a threat, or that problems will not develop in the future. To ensure that pesticides do not become a problem, Ecology should implement a systematic ground-water monitoring program including pesticide sampling.