GEOPHYSICAL IMAGING AND MONITORING OF THE GROUNDWATER AQUIFER AT THE OKLAHOMA STATE UNIVERSITY GEOLOGY FIELD CAMP FACILITY NEAR CAÑON CITY, COLORADO

The Boone Pickens School of Geology of Oklahoma State University holds an annual summer geology field camp at the Les Huston camp facility near Cañon City, Colorado. The geophysics section of the field camp curriculum focuses on training students on the acquisition, processing and interpretation of near surface geophysical data, in particular, electrical resistivity tomography (ERT), seismic refraction, and ground penetrating radar (GPR) methods. The field camp acquired twenty 2D ERT profiles of 50 to 170m in length over five years that characterized the upper 30 m of the subsurface within the camp and adjacent properties. The seismic refraction and GPR data were acquired only for one year. The ERT profiles showed a low-resistivity layer of a variable thickness (3-15m) at varying depths below the ground surface, interpreted as the Quaternary aquifer. The top of the interpreted aquifer correlates well with the top of a relatively high seismic velocity layer along the seismic refraction profiles and with the water level in the water well at the site. The acquired GPR data did not image the top of the aquifer and exhibited gradual signal attenuation with depth. The variation in the depth of the aquifer correlates to the variation in vegetation density at the surface. Comparing the resistivity profiles acquired over the years showed a fluctuation in depth to the top of the interpreted aquifer layer of about 3.6 m. The bedrock surface shows along the ERT profiles as a high-resistivity layer at a relatively variable depth ranging from 12 to 26 m, and includes a feature identified as a potential fault. We recommend acquiring additional collocated ERT, seismic and deep GPR profiles at the site to better monitor the aquifer and trace the potential fault.