USING SHALLOW SEISMIC REFRACTION AND GROUND TEMPERATURES TO EXAMINE SUBSURFACE FLOWPATHS AT BURGDORF HOT SPRINGS, IDAHO

Burgdorf Hot Springs is a recreational bathing resort located in the Payette National Forest, north of McCall, Idaho. Anecdotal evidence from melting snow indicates the presence of near-surface flowpaths feeding spring boxes located 30–50 m away from the observed melting. We employed high-resolution (1.5x1.5 m resolution) ground temperature measurements, in combination with a geostatistical analysis, to develop an image of heat loss from the shallow subsurface. The ground temperature analysis identified three to four areas of upwelling hydrothermal fluids, apparently from fractures in the local granite bedrock; flow then migrates laterally at the bedrock/alluvium contact to the spring boxes that feed the recreational bathing pools. The seismic data allow us to estimate the thickness of alluvial cover, and provide the information necessary to calculate heat loss along the fluid flowpath. Taken together, the shallow ground temperature and seismic data offer the potential to model fluid temperatures along the lateral flowpath, allowing calculation of the temperature of upwelling fluids at the granite/alluvium interface. The detailed understanding of the near-surface flowpaths proceeding from this study is an important step toward the development of sustainable plans for direct use of the hydrothermal fluids.