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Movement of three herbicides in a fine sand aquifer

Schneider, A.D., Wiese, A.F., Jones, O.R.
Agronomy journal 1977 v.69 no.3 pp. 432
herbicide residues, picloram, atrazine, trifluralin, groundwater contamination, aquifers, sand, groundwater flow, wells, remediation, Texas
In order to determine movement of farm chemicals that might accidentally contaminate underground water supplies, low concentrations of three herbicides and NaNO3 as a tracer were injected into a sand aquifer through a dual-purpose well. Herbicides used were picloram, atrazine, and trifluralin. Recharge by injection continued for 10 days at an average rate of 81.8 m3/hour. After a 10-day pause, the well was pumped for 12 days to determine if the herbicides and tracer could be recovered. Water samples were pumped from observation wells located 9, 20, and 45 m from the dual-purpose well. Herbicides were detected in the 9- and 20-m distant wells, but none of the herbicides or the tracer was detected in the 45-m distant well. Picloram and atrazine moved freely through the aquifer, but some trifluralin adsorbed to aquifer particles around the well. Although, two herbicides moved freely from the point of injection, all of the chemicals were removed from the aquifer by pumping the contaminated water. Ninety-three percent of the NO3 tracer and more than 90% of each herbicide were recovered with the pumped water. This study indicates that herbicides accidentally injected into a well in a relatively static aquifer can be recovered by pumping. Water could be utilized for irrigation of tolerant crops.