Aquifer dispersivity by recharge-discharge of a fluorescent dye tracer through a single well.

Abstract

Various techniques have been proposed and employed for field determinations of aquifer dispersivity. This paper is the result of an attempt to evaluate one of these techniques, the "Single Well Technique," in an alluvial basin aquifer as a field method for investigating aquifer dispersivity. The "Single Well Technique" was employed at the University of Arizona Water Resources Research Center's artificial recharge facilities by imposing on the aquifer a systematic series of injection and pumping regimes through a 150 foot recharge well. Cooling tower blowdown water from a power plant was injected into the pump column. Rhodamine WT fluorescent dye was used as a tracer, as well as the relative difference in dissolved solids between the native ground water and the recharge water. The concentration of the dye was measured continuously by a C. K. Turner Model 111 Fluorometer during the injection and subsequent pumping phases. Temperature and specific conductances were also taken throughout the tests. The relation between the relative concentration of the pumped water during the discharge phase and the ratio between the pumped to the injected volume yielded values of aquifer dispersivity that ranged from 0.25 feet to 0.82 feet.