Estimation of percolation flux from borehole temperature data at Yucca Mountain, Nevada.

Temperature data from the unsaturated zone (UZ) at Yucca Mountain are analyzed to estimate percolation-flux rates and overall heat flux. A multilayer, one-dimensional analytical solution is presented for determining percolation flux from temperature data. Case studies have shown that the analytical solution agrees very well with results from the numerical code, TOUGH2. The results of the analysis yield percolation fluxes in the range from 0 to 20 mm/year for most of the deep boreholes. This range is in good agreement with the results of infiltration studies at Yucca Mountain. Percolation flux for the shallower boreholes, however, cannot be accurately determined from temperature data alone because large gas flow in the shallow system alters the temperature profiles. Percolation-flux estimates for boreholes located near or intersecting major faults are significantly higher than those for other boreholes. These estimates may be affected by gas flow in the faults.