Solute and isotopic geochemistry and ground water flow in the central Wasatch Range, Utah

Abstract

Ground water flow systems in the rugged central Wasatch Range, Utah, were investigated by solute and isotopic methods. Six types of ground water systems were identified on the basis of rock type and structure. The systems are broadly grouped into four categories: (1) granitic systems; (2) non-granitic systems: (a) unconsolidated alluvial systems, (b) consolidated sedimentary rock systems, and (c) fault controlled systems; (3) thermal systems; (4) mine drainage systems. These ground water systems have distinctive solute and isotopic chemistries. Based on an analysis of 3H and 14C data, all of the ground waters have a component of post-1952 recharge water, and most of the ground waters are composed almost entirely of post-1952 recharge water. A few of the ground water systems contain some water which is hundreds to perhaps thousands of years old. The δ 18O and δ 2H data plot on a local meteoric water line, and none of the data exhibit a positive δ 18O shift. The absence of a positive δ 18O shift suggests maximum aquifer temperatures are approximately 100°C. Granitic terrains are dominated by fracture controlled, local ground water flow systems which respond rapidly to recharge events. The granitic ground water systems have estimated maximum circulation depths of about 160 m below land surface. All the alluvial, most of the consolidated sedimentary bedrock, and some of the fault controlled ground water systems are shallow circulating, local flow systems with short travel times. Ground water circulation of most of the local flow systems is within 200 m of land surface and is bedding plane controlled. Some of the consolidated bedrock and many of the fault controlled ground water systems are of the intermediate type and have circulation depths to 500 m. Four thermal ground water systems have been identified. The thermal systems are heated by the geothermal gradient and have not circulated deeper than 2–2.5 km. The thermal systems are of the intermediate and regional type. The solute chemistry of most of the non-granitic ground waters may be attributed to the dissolution of carbonate minerals and minor amounts of gypsum. Contributions of external CO 2(g) to some of the thermal systems from either metamorphic or silicate hydrolysis processes is suspected.