HYDROLOGIC AND HYDROGEOLOGIC ASSESSMENT OF THE SURFACE WATER AND GROUNDWATER RESOURCES AFFECTING THE CASTLE VALLEY SPRINGS AND WELLS, CASTLE VALLEY, UTAH: THE ROLE OF DIAPIR FRACTURE AND FAULT ZONES IN DETERMINING GROUNDWATER FLOWPATHS, STORAGE CAPACITY, RECHARGE, WATER QUALITY AND WATER BALANCES IN MOUNTAIN/PLATEAU HYDROLOGIC SYSTEMS

The purpose of this study was to perform a Hydrologic and Environmental System Analysis (HESA) of Castle Valley, Utah, supported by GIS databases and maps, to develop an updated Conceptual Model of hydrogeologic and hydrologic characteristics of the groundwater and surface water systems; and develop a current water budget to be used for the water rights defense of closing the aquifer for development, and urbanization- and climate-change driven planning affecting the groundwater sustainability of the region.

The results of this study are a broader conceptual model on how mountain/plateau hydrologic systems in southeast Utah are structured and function with respect to subregional and local fracture and fault zones caused by Diapiric processes. These hydrostructures, acting as French drains, as opposed to matrix flow, dominate the surface water and groundwater flowpaths, storage capacity, and recharge, and partially account for the sustainability of these complex hydrologic systems. The water balance guided by this conceptualization more accurately represents the properties of the complex hydrologic systems for water rights, management, and modeling purposes. Specific hydrogeological results show that two hydrologic subsystems were identified in the Castle Valley study area: 1) La Sal Mountain Subsystem; and 2) Castle Creek and Placer Creek Hillslope and Valley Bottom Shallow Aquifer Subsystems. The shallow groundwater in the La Sal Mountain Subsystem is dominated by the Quaternary deposits, which receive natural recharge by infiltration of precipitation (snow and rain); input from hillside (slope) deposits located upgradient from a given location; and input from the two bedrock aquifers: the Geyser Creek Fanglomerate, and the Tertiary Intrusive units. Within the Castle Valley proper, the shallow Castle Creek and Placer Creek colluvium and alluvium aquifer subsystem has matrix flow characteristics and storage, aquifer thicknesses controlled by subsurface paleovalley location, and low TDS (less than 1000 mg/l) water quality, underlain by the fractured arkose and White Rim members of the Permian Cutler formation bedrock hydrogeologic unit subsystems with associated high K fracture zone hydrostructures and high TDS (greater that 1000 mg/l) water quality.