Groundwater extraction and radon anomalies in the Picacho area, south-central Arizona

Abstract

Radon is a noble gas which decays by alpha radiation. Previous studies have shown land surface concentrations to be related to tectonic stress and rock deformation. A radon survey was conducted in the Picacho Basin area in south central Arizona. The basin is presently subsiding due to groundwater withdrawal. The radon survey was performed to determine relationships, if any, between stresses involved with subsidence and radon concentrations in groundwater and soil gas. Analyses of radon concentrations were made on three different levels. A regional analysis compared radon levels in the Picacho Basin to levels in a similar basin which was not known to be subsiding. The results show a definite contrast between the basins. Generally higher levels occurred within the Picacho Basin. Basic trends in radon levels were also observed within local areas in the basin. A local analysis studied radon in an area of land fissuring caused by subsidence. The observations suggest that radon is closely related to the state of stress across fissures. Soil gas measurements were made near operating water wells. The stresses placed on the aquifer system by water being pumped were found to increase radon concentrations.