USING TEMPERATURE TO TEST MODELS OF FLOW NEAR YUCCA MOUNTAIN, NEVADA

Groundwater temperatures in the fractured volcanic aquifer near Yucca Mountain, Nevada have previously been shown to have significant spatial variability with regions of elevated temperatures coinciding roughly with near-vertical north-south trending faults. Using insights gained from one-dimensional models, previous investigators have suggested upwelling along faults from an underlying aquifer as a likely explanation for this groundwater temperature pattern. Using a three-dimensional coupled flow and heat transport model, we show that the thermal high coinciding with the Paintbrush fault zone can be explained without significant upwelling from the underlying aquifer. Instead, the thermal anomaly is consistent with thermal conduction enhanced slightly by vertical groundwater movement within the volcanic aquifer sequence. If more than ~400 m3/day of water enters the volcanic aquifer from below along a 10 km fault zone, then the calculated temperatures at the water table are significantly greater than the measured temperatures. These results illustrate the potential limitations in using one-dimensional models to interpret groundwater temperature data, and underscore the value in combining temperature data with fully coupled three-dimensional simulations. (This abstract documents work performed by the CNWRA for the NRC under contract. It is an independent product of the CNWRA and does not necessarily reflect the views or regulatory position of the NRC.)