CHARACTERIZING THE STEAMBOAT SPRINGS, COLORADO, HOT-SPRINGS GEOTHERMAL RESOURCE

The low-temperature (20-40°C) hot-springs geothermal resource in Steamboat Springs, Colorado, has drawn humans to the area for more than 150 years. Discharge from one of the geothermal springs supports a unique biologic environment in Sulphur Cave, a cavern that the National Park Service designated as a National Natural Landmark in 2021. Relatively little is known about the subsurface flow patterns, geochemistry, and sustainability of the geothermal resource despite its importance to local ecosystems, culture, and tourism. This study aims to better characterize the stability, groundwater flux, and origins of this geothermal system to aid resource protection and management. Longer-term stability is assessed through comparison of historical spring discharge, geochemistry, and temperature data to new measurements. Periodic geochemical sampling and continuous temperature monitoring of the springs was performed to evaluate seasonal variations in the geothermal system. In addition to direct spring discharge measurements, geothermal groundwater flux was estimated by using mass balance streamgaging techniques within the adjacent Yampa River. These data, along with groundwater age tracers, stable isotopes, and geothermometry, are used to support hydrothermal modeling to further explore the system’s origins and subsurface flow patterns. Results show that the system has likely been generally stable over the last 50 years, though the springs are sensitive to physical anthropogenic activities like road and rail maintenance. Flux estimates indicate that more than 950 gpm (5.2 million L/day) of moderately saline (about 5,900 mg/L TDS) geothermal water discharges into the Yampa River. Subsurface temperature estimates ranging from 101 to 130°C indicate groundwater circulation depths greater than 2 to 3 km prior to the waters ascending to the surface along faults. The sampled geothermal waters are estimated to be thousands of years old with notable temperature and geochemical differences among the various flow-supporting faults. Ongoing exploratory modeling aims to further refine the conceptualization of the resource. Overall, this study provides a greater understanding of the vulnerability of this resource and its dependent ecosystems, allowing for more robust protection and sustainable management.