Stable Oxygen and Sulfur Isotopes as Indicators of Recharge Processes and Groundwater Flow Paths in Tucson Basin, Arizona

Groundwater in the Tucson Basin recharges from surface water in the major drainages entering the basin, as well as from fractures in crystalline rocks beneath the alluvial basin fill. Although varying transmissivities and pumping-induced upwelling complicate the groundwater flow paths, stable isotope characteristics enable us to infer groundwater sources and flow paths. Oxygen and hydrogen stable isotopes in groundwater can indicate elevation of recharge water, and sulfur stable isotopes in dissolved sulfate help distinguish the sulfur source-rock type. In many cases the ranges of d-values of possible sources of groundwater do not overlap, enabling unequivocal inference of groundwater sources and pathways. The stable isotopes indicate at least one previously unrecognized groundwater source plume and several groundwater mixing zones in the basin.