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The city of Lincoln draws water from a well field along the banks of the Platte River in east-central Nebraska. We have been able to follow the infusion of atrazine into this well field under induced recharge. Samples of water from the river, several monitoring wells and a production well were analyzed by GC/MS and solid phase extraction and found to change in concentration over the range 0.1 and 5.0 ppb of atrazine through the spring, summer, and fall 1989. Increases in the concentration of atrazine relating to precipitation events in the Platte River Basin were observable in the well water samples and ultimately in Lincoln municipal tap water. Atrazine from the river was seen to move via induced recharge and into well field ground water and away from the river at an observable rate. The concentration of atrazine in the river is dependent upon time of year and precipitation in the river basin.

A method was developed to detect atrazine at a 0.05 ppb detection limit with a 10 ml_ sample volume. The herbicide Is extracted from 10 mL water with C18 solid-phase extraction and eluted into a reduction vessel with ethyl acetate. The sample is then evaporated to dryness under a stream of nitrogen and redlssolved for Injection Into a gas chromatograph/ mass spectrometer. Terbuthylazlne is used as Internal standard to compensate for extraction process variables. Standard curves have consistently shown correlation coefficients of 0.99 or better. Duplicate samples show a variance of 5% or less. Twelve samples can be extracted In about 1.5 h with

An economical ground-water sampling system was constructed using readily available parts. The design is durable and easy to use in the field. Problems with cross contamination between wells are minimized; however, this sampling system is limited to shallow depths and is not appropriate when change in sample pressure would significantly affect the water chemistry.