Atrazine in a Stream-Aquifer System: Transport of Atrazine and Its Environmental Impact Near Ashland, Nebraska

The municipal wellfield for Lincoln, Nebraska, consists of 44 wells located adjacent to the Platte River near Ashland, Nebraska. The herbicide atrazine was monitored in the river and two transects of monitoring wells. The amount of atrazine transported down the Platte River in 1989, 1990, and 1991 was shown to increase each year. Induced recharge from the Platte River results in movement of atrazine from the river into the aquifer. A 21-day lag time was determined for the movement of atrazine from the river to a transect of monitoring wells 10 feet west of the bank. The role that colloids play on the transport of atrazine was determined to be insignificant. A small percentage of atrazine found in the river was determined to come from rain water. The infiltration of agrichemical-contaminated river water was shown to significantly reduce the quality of raw water and finished water being produced by the adjacent aquifer. Introduction This study was designed to use the agricultural chemical atrazine as a means to trace the path of water moving along a zone of induced recharge within a river-aquifer system and to study the impact of agrichemicals on the surrounding environment. Atrazine (2-chloro-4isopropylamino6-e thylamino-striazine CAS# 1912-24-9) is a widely used triazine herbicide in the Platte Valley region and has been found to be transported into the Platte River with precipitation runoff (Snow and Spalding 1988; Duncan et al. 1991). It degrades in soil and water. The half-life has been estimated in soil to be between four and 57 weeks, depending on the temperature and soil type. The half-life in ground water has been approximated to be between 10 weeks and two years (Cohen et al. 1984; Dao et al. 1979). Therefore, atrazine can be used as a tracer of ground water movement because the half-life would extend beyond the time period of the study. Atrazine is typically applied by soil incorporation of a powder associated with clay particles, so very little would be sprayed directly into the air. Atrazine’s solubility in water is 70 ppm at 25 °C. The system chosen was within the Lincoln municipal wellfield near Ashland, Nebraska. The wellfield consists of 44 wells in an alluvial aquifer adjacent to the Platte River. The Platte River acts as a line source of induced recharge, thus allowing contaminants already contained in the river to be used as a tracer of induced recharge (Duncan et al. 1991). As atrazine moved into the wellfield, concentrations were monitored in two transects of monitoring wells. These tranPublished in Ground Water Monitoring and Remediation 11 (Spring 1993), pp. 125–133. Copyright © 1993 National Groundwater Association; published by Wiley-Blackwell. Used by permission. Atrazine in a Stream-Aquifer System: Transport of Atrazine and Its Environmental Impact Near Ashland, Nebraska