Concentrations of triazine herbicides in the unsaturated zone in western Harvey County, Kansas, spring and fall 1992-93

To assess the potential transport of triazine herbicides into the Equus Beds aquifer, soil samples were collected from the unsaturated zone at 27 dryland and 30 irrigated sites in western Harvey County, Kansas. All sites were sampled at a depth of 4 to 6 feet (that is, immediately below the root zone) during March and October-November 1992 and March and October-November 1993. During the October-November 1992 and March 1993 sampling periods, five sites also were sampled at depths of 0 to 4 and 6 to 10 feet. All samples were analyzed for total triazine concentrations using a 20-gram extraction, immunoassay technique with a 0.02 microgram per kilogram detection level. Additionally, 20 samples from each sampling period were analyzed specifically for atrazine and two atrazine metabolites (deethylatrazine and deisopropylatrazine) using a 20-gram extraction, gas chromatography/mass spectrometry procedure with a 0.5 microgram per kilogram detection level. Total triazine concentrations at the 4- to 6-foot depth, with one exception, were less than 1.0 microgram per kilogram, with the majority of the concen- trations less than 0.10 microgram per kilogram. Triazine concentrations at the O- to 4-foot depth ranged from 0.51 to 12.20 micrograms per kilogram. Triazine concentrations at the 6- to 10-foot depth ranged from less than 0.02 to 0.33 microgram per kilogram. The atrazine metabolite deethylatrazine was detected in three samples, with concentrations of 0.63, 1.44, and 1.48 micrograms per kilogram. The atrazine metabolite deisopropylatrazine was not detected in any of the soil samples analyzed. Because the 1992 and 1993 growing seasons included periods of above-normal rainfall, the concentrations of triazine herbicides and metabolites measured during this study may not be indicative of average conditions.