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• <br /> Job#: 68838-64986.09.5 Calc by: M. Nelson <br />Client: Denison Mines <br />USA Corp. Checked by: S. <br />Fundin stand Date: December 18, 2009 <br />Project: Van 4 Mine <br />Rock Report Date: December 22, 2009 Calc No. <br />Detail: Evaluation of Reviewed: Revision: <br />HPR sensitivity in <br />UNSAT-H model Date: Date: <br />Calculation Brief Title: <br />Evaluation of the Sensitivity of Percolation <br />Estimates through Mine Rock Stockpiles on <br />the Simulated Precipitation Rate <br />1.0 Purpose/Objective <br />UNSAT-H was used to estimate the percolation of water through development rock <br />piles at the Van 4 Mine, Uravan Mining District, Colorado. UNSAT-H is a fortran- <br />based model that is used to simulate the one-dimensional flow of water, vapor, and <br />heat in soils. The code addresses the processes of precipitation, evaporation, plant <br />• transpiration, storage, and deep drainage (Fayer 2000). <br />In a review of the initial modeling results presented in Environmental Geochemistnj <br />Investigation of Soil and Rock Materials, Van 4 Mine (CDM 2009), the Colorado Division <br />of Reclamation, Mining and Safety (DRMS 2009) provided the following comment: <br />Unsaturated (UNSAT-H) model and percolation estimation. <br />Denison has provided information showing the limited mobility <br />and reduced threat from various minerals in the mined and <br />unmined rock material, based on the geologic characteristics as <br />well as the and climate at the mine. The wettest months are <br />August through October, which suggests that precipitation <br />during those months is delivered via thunderstorms - <br />potentially high intensity events. It is known that plumes can <br />form beneath waste rock facilities in and climates in response to <br />seasonal patterns of such high intensity events. Please address <br />the following: Does the model account for high-intensity, short- <br />duration precipitation events such as thunderstorms? If not, <br />what effect would these have on percolation estimates? <br />Additional UNSAT-H simulations were completed to address this DRMS comment by <br />• evaluating the sensitivity of the UNSAT-H model to various rates of precipitation. <br />The simulated rate of precipitation in the UNSAT-h model is governed by a variable <br />called HPR, which is the simulated hourly rate of precipitation. This calculation sheet <br />1-1 <br />C:\Nelson_work0enison\UNSAT_H\HPR sensdivityWan 4 HPR Sensitivity calc brief.doc