The distribution of radon-222 in the ground water of the north-central Tucson basin and its relationship to the hydrogeology

Abstract

A reconnaissance study of ²²²Rn concentrations in the ground water of the North-Central Tucson basin revealed a range of concentrations from 80 to 1400 pCi/L in wells, and 60 to 1260 pCi/L in domestic waters. Estimated degradation of Rn in water from wells to homes ranges from 8 to 50%. The interior well field of mid-Tucson, may represent background concentrations of Rn with a mean value of 250 pCi/L. The limited data define an anomalous trend (500 to 1400 pCVL) of ²²²Rn paralleling the Santa Cruz River area. 222Rn concentrations above 500 pCVL correlate positively with temperature, and no low temperature water contains high ²²²Rn levels. Weak inverse correlations of ²²²Rn with pumping bowl depth, pumping water level and average upper perforation intervals are evident. It is concluded that the source of ²²²Rn is close to the well bore. Considered are several possible hypothesis and mechanisms responsible for the anomalous Santa Cruz ²²²Rn trend, including mechanisms related to water circulation along the Santa Cruz fault, lithology, and aquifer compaction.