An Interpretation of the Water Chemistry and Hydrogeology of Skull Valley, Tooele County, Utah

Abstract Skull Valley is an arid, fault-bounded closed basin located in Tooele County, Utah, southwest of the Great Salt Lake. Hydrostratigraphy, structure, topography, and evaporation are the controlling factors on the water chemistry, recharge, movement, and discharge of ground water. The hydrogeology of Skull Valley can be used as a model for other areas of western Utah. Water chemistry data from 27 springs and wells were analyzed using geochemical techniques to determine possible ground-water flow paths and the types of valley aquifers. Four major types of ground-water flow systems were identified: (1) a deep, confined, regional-valley aquifer system, (2) a shallow, unconfined, intermediate- to regional-valley aquifer system, (3) unconfined, intermediate to local alluvial-fan aquifer systems, and (4) local, unconfined mountain aquifer systems. Water quality varies greatly among these systems. Ground water is brackish where evapotranspiration and dissolution of bedded salt have occurred in shallow valley aquifers and along major faults in the northern part of the valley. The ground water is likely brackish in deep, confined system due to longer residence time and a larger variety of rock types with which to react. Mountain and alluvial aquifer systems typically contain fresh water. Ground water recharge occurs from direct infiltration of precipitation, seepage from surface streams, and ground-water flow from the nearby mountains. Ground water flows along bedrock joints and fractures in the mountains and/or through interfingering sands and gravels of valley-fill deposits. The storage capacities of Skull Valley aquifers varies with the largest probably in alluvial-fan systems. Ground water discharges by evapotranspiration and through water wells and springs. Similar conditions probably characterize other valleys in western Utah.