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Calculation Brief <br />Evaluation of the Sensitivity of Percolation Estimates through <br />Mine Rock Stockpiles on the Simulated Precipitation Rate <br />• Seki, K., 2007, SWRC Fit- A Nonlinear Fitting Program with a Water Retention Curve for <br />Soils Having Unimodal and Bimodal Pore Structure, Hydrology and Earth System <br />Sciences Discussions, Vol 4. <br />Swanson, D.A., Savci, G., Danziger, G., Williamson, A., Barnes, C., 2000, Unsaturated <br />Hydrologic Assessment of Waste Rock Stockpiles in Semi-Arid Climates, in Semi-Arid Mine <br />Waste Issues, ICARD 2000-Proceedings from the 5th International Conference on Acid <br />Mine Drainage. <br />Weir, James E.; Maxfield, E. Blair; Zimmerman; Everett A. 1983. Regional Hydrology of <br />the Dolores River Basin, Eastern Paradox Basin, Colorado and Utah. USGS Water- <br />Resources Investigations Report 83-4217. <br />4.0 Assumptions <br />¦ This sensitivity analysis used development rock geotechnical data from a samples <br />collected at the Topaz Mine, which is located in the Uravan Mineral district near <br />the Van 4 mine. The rock mined at both the Topaz and Van 4 mines is very similar <br />and is extracted from the same geological unit, the Salt Wash Member of the <br />Morrison Formation. This analysis assumes that that the Topaz sample is <br />representative of the development rock present at the nearby Van 4 mine. <br />¦ This estimate also assumes that the Topaz sample and associated laboratory data <br />are representative of the pile. An inherent uncertainty in this assumption relates to <br />the presence of cobbles and boulders in the piles, which will not fit in the <br />laboratory capillary moisture test apparatus. However, infiltration and percolation <br />under unsaturated conditions occurs preferentially through the fine-grained <br />materials (Swanson et al 2000). Therefore, this assumption is considered adequate <br />for the purposes of this estimate. <br />¦ This estimate includes development rock extending to a depth of 3 meters. Any <br />water flux passing through the 3 meter depth is assumed to percolate to the base of <br />the pile. <br />¦ The estimate assumes that there is no zone of saturation within the development <br />rock piles (i.e., no groundwater is present within the pile). This assumption is <br />supported by the fact that there are no observed springs or seeps emanating from <br />the development rock piles. <br />¦ UNSAT-H does not simulate the effects of snow pack moisture or freezing ground <br />conditions. This simulation assumes that effects of snow pack moisture and <br />freezing ground conditions on percolation are negligible at the Van 4 Mine. <br />• <br /> <br />C:\Nelson_work\Denison\UNSAT_H\HPR sensbAty\Van 4 HPR Sensitivity talc brie(.doc