A hydrogeochemical evaluation of the lower Cienega Creek sub-basin, Pima County, Arizona

Abstract

Mass transport modeling of ground and surface waters upstream of perennial Cienega Creek, Arizona, delineate processes which control ground water chemistry in this arid alluvial basin. NETPATH modeling shows that the aquifer is open to CO2 flux, and that dissolution of gypsum, redistribution of carbonate minerals, and cation exchange of Ca2+ for Na+, control the evolution of ground and surface water chemistry. Calcium bicarbonate waters which recharge the basin margin, evolve to calcium-sulfate waters during passage through the alluvial aquifer, and produce a quantifiable chemical evolution of ground water within the aquifer. Evaluation of a 10-year data base, plus the clarification of controlling chemical processes, allow a reinterpretation of the source of Cienega Creek waters, which is shown in this study to be the upstream alluvial basin. These findings are partially corroborated by an associated geophysical study which confirms a basin flow pattern parallel to the flow path assumed by this investigation.