Abstract

Across the nation many hundreds of springs are used as public drinking-water sources, and many of these springs will be included in state wellhead protection programs. Two springs in Utah were selected to develop and field-test an applicable method to delineate protection areas around springs in bedrock settings. Sheep Spring, in southwestern Utah near the city of Santa Clara, was selected to be representative of springs in clastic-bedrock aquifers. Sheep Spring is located near the top of the lower member of the Jurassic Kayenta Formation, which consists of interbedded siltstone, sandstone, and shale. Closely-spaced north-striking joints appear to influence ground-water flow to this spring.

Hydrogeologic mapping is the focus of this project; chemical analyses of spring discharge, drilling, aquifer testing, and dye tracing will be used to support the mapping. Water samples taken quarterly were analyzed for major chemical and radiological constituents, pH, conductivity, and dissolved solids to document seasonal chemical variations and characterize the water. Significant chemical variations for the one-year period were noted for sulfate content, gross alpha, and gross beta. Water from Sheep Spring was tested monthly in the field for temperature, pH, and conductivity. Water temperature varied by 4.5°C (8.1°F). Tritium analyses yielded 2.4 (±2.8) and 1.9 (±2.6) tritium units, indicating recharge before 1953. Future investigations will include the installation of monitoring wells upgradient from the spring to provide data on the local hydraulic gradient, ground-water level changes, aquifer characteristics, stratigraphy, and geologic structure.