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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: 2/3/2009 Calc #: 1 <br />Detail: Water Balance Estimation of Percolation <br />Percolation through development rock piles can be estimated through a water balance approach. <br />The following is the basic hydrologic equation used for the water balance: <br />ASm/OT = Pi- Ro - ET - Po+ AW Equation 1 <br />Where: <br />Sm = Soil Moisture Storage (cm/month) <br />T = Time (month) <br />Pi = Precipitation (cm/month) <br />AW = Applied Water (cm/ month) <br />ET = Evapotranspiration (cm/month) <br />Po = Percolation (cm/ month) <br />Ro = Runoff (cm/month) <br />Equation 1 is a rate-based equation where each of the input/output terms are expressed as a <br />time rate. Equation 1 may be simplified by analyzing the balance in time increments, in which <br />case the AT variable can be removed from the equation. In addition, for the development rock <br />pile analysis, there is no applied water term for the equation (i.e., irrigation water). Therefore, <br />Equation 1 can be simplified to: <br />• <br />Sm=Pi- Ro - ET - Po <br />A monthly stepwise water balance calculation can be completed using Equation 2 to determine <br />if stored soil moisture (Sm) will exceed the moisture holding capacity (Sa) of the rock pile. If Srn <br />exceeds Sa for a given month, then stored water will percolate through the pile. <br />Equation 2 <br />A.1 Moisture Holding Capacity Calculation <br />Moisture holding capacity was estimated from laboratory SWCC testing using the following <br />calculation (for sample DM-TP-SMCC from the Topaz Mine development rock pile): <br />Oc := .1764 Oc = field capacity water content (volume fraction), assumed to be <br />equal to the volumetric water content at 33 KPa suction <br />Omin •1064 Omin = wilting point water content (volume fraction), assumed to be <br />equal to the volumetric water content at 1500 KPa suction <br />Saf (Oc - Omin) • 0.75 Saf = moisture holding capacity (volume <br />fraction), and 0.75 correction factor is applied to <br />Saf - 0.0525 account for differences between field and <br />laboratory conditions. <br />In order to use this moisture holding capacity for the water balance calculation, a volume <br />must be assumed for the model. In this case, a volume 1 cubic meter is assumed and the <br />volume fraction Sa can then be converted to a distance measurement: <br />V:= 1 V = volume of water balance block model (m3) <br /> <br />MathCAD V14 <br />N:\64986-Denison Mines\Task Order 3 - DMO <br />Saved 2117/20095:15 PM <br />Page 3