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Job #: 68838.64986.03.3.14 Cale By: N. Anton; M. Nelson <br />Client: Denison Mines CHK By: G. Hazen Date: 1/27/2009 <br />Project: Hydrogeology Report Date: 2/3/2009 Cale #: 1 <br />Detail: Water Balance Estimation of Percolation <br />A:= 1 V = area of water balance block model (m2) <br />Sa := Af • 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 />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 e 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 (320F). 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 PETS = Corrected potential evapotranspiration for winter months with <br />mean temperature below freezing (in) <br />PETe = 0.47 <br />• <br /> <br />LI <br />MathCAD V14 Saved 2/17/20095:15 PM Page 4 <br />N:164986-Denison Mines\Task Order 3 - DMO