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<br />Job #: 68838.64986.03.3.14 Calc By: N. Anton; M. Nelson <br />Client: Denison Mines CHK By: G. Hazen Date: 1/27/2009 <br />Project: Hydrogeology Report Date: 2/312009 Calc #: 1 <br />Detail: Water Balance Estimation of Percolation <br />A:= 1 V = area of water balance block model (mz) <br />Sa := SAf • 39.3696 Sa = moisture holding capacity (in), using 39.3696 in/m conversion <br />Sa = 2.0669 <br />The same calculation was performed for the second laboratory sample (DM-WS-SWCC from the <br />West Sunday Mine development rock pile) to yield Sa = 2.54 in. The lower Sa value from the <br />Topaz Mine sample was selected for the water balance model. <br />A.2 Potential Evapotranspiration Calculation <br />Evapotranspiration (ET) defined in Equation 2 is associated with two terms, the potential <br />evapotranspiration (PET) and the actual evapotranspiration (AET) (Guyman 1994). PET is the <br />maximum possible amount of evapotranspiration that could occur at the site based on climatic <br />conditions. AET is the actual evapotranspiration based on the changed stored soil moisture. <br />• <br />Monthly PET was calculated using the Blaney-Criddle Formula (Subramanya 1994). An <br />example of this calculation for the month of January is illustrated below: <br />K:= 0.8 Empirical coefficient for crop type, assumed for light density natural <br />(non-crop) vegetation (Table 3.7, Subramanya 1994) <br />Ph := 6.76 Ph = percent of annual day-time hours for January, dependent on the <br />site latitude of approximately 380 (Table 3.6, Subramanya 1994) <br />Tf 28.97 Tf = mean monthly temperature (°F) for January, averaged from <br />temperature data at the Uravan, CO NOAA weather station <br />F Ph' Tf F = monthly consumptive use factor <br />100 <br />PET := K • F PET = Potential evapotranspiration (in) <br />PET = 1.5667 <br />This calculation was repeated for each month of the year. For the months of December and <br />January, the mean monthly temperature is below freezing (32°F). For these months, Benson <br />(2006) recommends reducing the PET to account for freezing of the soil surface. Based on this <br />recommendation, a factor of 0.3 was selected for a no-snow and frozen-ground condition, as <br />shown in the following calculation: <br />PETc := PET • 0.3 PETC = Corrected potential evapotranspiration for winter months with <br />mean temperature below freezing (in) <br />PETc = 0.47 <br />J <br />MathCAD V14 <br />N:\64986-Denison Mines\Task Order 3 - DMO <br />Saved 2/17/20095:15 PM <br />Page 4