GROUNDWATER RESIDENCE TIMES IN THE BRYCE CANYON AREA, GARFIELD COUNTY, UTAH

Abstract

Groundwater in the Bryce Canyon area provides domestic water to Bryce Canyon National Park (BCNP), as well as domestic and stock water to Bryce Canyon City and southwestern Johns Valley. A potential increase in development could affect existing groundwater usage, so the Utah Division of Water Rights and National Park Service funded the Utah Geological Survey to conduct a hydrogeologic study of the Bryce Canyon area, with emphasis on characterizing groundwater chemistry, flow paths, and connection to surface water. Water samples from ten wells and four springs were analyzed for carbon isotopes, tritium, deuterium and oxygen isotopes, and general solute chemistry. Our results indicate that groundwater in the Bryce Canyon area aquifers is a mixture of modern (recharged since 1950) and old (recharged several thousand years ago) components. The region has three primary aquifers: a shallow valley-fill aquifer, the limestone of the Eocene Claron Formation, and a Cretaceous sandstone aquifer. Water from the valley-fill aquifer, including the BCNP well field, as well as water from the four springs sampled, which all discharge from the Claron, consists of modern groundwater recharged since or just prior to 1950. By contrast, water from wells completed in the Cretaceous aquifer consists of old groundwater, recharged at least several thousand years ago. Groundwater from the valley fill and Claron Formation generally has lower total-dissolved-solids concentrations than groundwater from the Cretaceous aquifer. The presence of modern groundwater in most wells and springs suggests these aquifers are actively recharged and thus sensitive to climate change, as well as susceptible to surface-based contamination sources. Careful land-use planning and resource management is warranted to preserve groundwater resources in the Bryce Canyon area.