Investigations of the Steamboat Hills geothermal reservoir beneath the University of Nevada, Reno's Redfield Campus using shallow geophysical techniques

The University of Nevada, Reno's Redfield Campus lies on the northwest boundary of the Steamboat Hills Geothermal Complex. Steamboat Hills, which has been studied for the past 70 plus years, is the largest geothermal reservoir in the state of Nevada. The Steamboat Hills produce in excess of 90 MW, and is currently operated by Ormat technology. The structure of the northwestern reservoir boundary has not previously been defined, however geophysical and thermal anomalies from previous large scale studies suggest the boundary is linear and spatially abrupt. There is no surface geologic expression of structure, or borehole data on the campus to confirm this. This study used gravity, ground magnetics, vertical electrical soundings (VES) and shallow temperature probes, to define the structure beneath the campus, and to determine if hot waters exist at shallow depths. Gravity measurements defined an east-northeast striking fault system, with down-dropped blocks to the northwest, that left-steps across north striking normal faults with down-to-the-west displacements. The ground magnetic survey revealed magnetic lows correlated with areas of shallow geothermal activity, as marked by fumaroles or silicified sediments. Several of the magnetic lows become strongly expressed along segments of the gravity defined east-northeast fault system, suggesting the fault has acted as a local conduit for geothermal waters. The VES showed a very low resistivity layer at depths between 8 and 18 meters on the northern part of the campus indicative of a clay layer or geothermal fluids. The shallow temperature probes showed a strong thermal anomaly on the northeastern part of the campus near the previously mapped fumaroles (Coolbaugh, unpublished). Six possible well targets were chosen on the Redfield Campus for waters to heat the buildings on the campus.