2009-05-19_REVISION - M1981021 (36)

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Section 13 Geochemical Data and Analysis the pile by ET in later months. Monthly estimated ET exceeds monthly precipitation during all months of the year. Exhibit 13-2 presents a similar estimate using precipitation conditions the occurred during the wettest year on record, 1997. Exhibit 13-2. Estimated percolation through development rock areas for zvettest year on record. Month Potential ET (in.) Precipitation (in.) Actual ET in.) Runoff in. Infiltration (in.) Percolation (in.) October 3.36 2.36 2.12 0.24 2.12 0.00 November 2.19 2.16 1.94 0.22 1.94 0.00 December 0.48 1.80 0.48 0.18 1.62 0.00 January 0.47 1.09 0.47 0.11 0.98 0.00 February 1.94 0.48 1.94 0.05 0.43 0.00 March 2.93 0.17 0.30 0.02 0.15 0.00 April 3.70 2.41 2.17 0.24 2.17 0.00 May 4.93 1.78 1.60 0.18 1.60 0.00 June 5.72 0.62 0.56 0.06 0.56 0.00 Jul 6.34 1.20 1.08 0.12 1.08 0.00 August 5.74 1.10 0.99 0.11 0.99 0.00 September 4.43 4.70 4.23 0.47 4.23 0.00 Annual Total 42.23 19.87 17.88 1.99 17.88 0.00 The estimate summarized in Exhibit 13-2 for the wettest year on record indicates that potential ET exceeds precipitation by a ratio of approximately 2.1:1, and suggests that water infiltrating the pile also evaporates during the year. During the months of December and January, the monthly precipitation exceeds the estimated monthly ET. Therefore, stored moisture within the rock pile would be expected to increase during December and January. However, excess ET occurring in latter months is estimated to be adequate to remove this moisture through evapotranspiration, preventing percolation through the pile. The primary ET mechanism contributing to this water balance assessment is evaporation. Unsaturated Flow Modeling: Unsaturated flow modeling was used to estimate percolation through the rock piles in a more rigorous manner. UNSAT-H (Fayer 2000) is a Fortran-based model that is used to simulate the one-dimensional flow of water, vapor, and heat in soils. The code addresses the processes of precipitation, evaporation, plant transpiration, storage, and deep drainage. The procedure for this estimation included: ¦ Estimate physical and hydrological characteristics of development rock using site specific sampling and laboratory analyses. ¦ Compile climate data from locations as close as possible to the site. ¦ Estimate percolation through development rock areas using UNSAT-H. 13-7 T:\64986-Denison Mines\Task Order 4 - EPP Sunday Mines GroupTiNAL EPPWINAL - Environmental Protection Plan Sunday Mines.doc