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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 />• <br />CLIMATEDATA, 2008, Climate data from Uravan, Montrose, and Grand Junction Colorado <br />Weather stations, Volume 19.0, NCDC Summary of the Day-West 1, Hydrosphere Data <br />Products, 2008 <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 estimate assumes that the Topaz sample and associated laboratory data are <br />representative of the development rock pile. An inherent uncertainty in this <br />assumption relates to the presence of cobbles and boulders in the piles, which will • <br />not fit in the laboratory capillary moisture test apparatus. However, infiltration and <br />percolation under unsaturated conditions occurs preferentially through the fine- <br />grained materials (Swanson et al 2000). Therefore, this assumption is considered <br />adequate 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 Sunday Mines <br />Group. <br />5.0 Calculations <br />The UNSAT-H model was chosen for this evaluation because it simulates both <br />downward movement of water into the development rock piles during infiltration <br />and upward movement of water from the rock piles caused by evaporation. <br /> <br />C:\Nelson work\Denison\UNSAT_H\HPR sensitivity\Sundav HPR Sensitivity talc brief noc