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CWM 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 />volumetric water content at a soil matric potential pressure of 30 kPa. Benson (2006) recommends <br />soil matric potential pressures of 1500 kPa and 33 kPa for estimation of wilting point and field <br />capacity, respectively. <br />b) The moisture holding capacity of the development rock is assumed equal to the difference <br />between the field capacity and the wilting point, which is based on Guyman (1994). If the amount <br />of water stored in the development rock pile during any given water year exceeds the moisture <br />holding capacity, the excess water will percolate through the pile. At this point, the field capacity <br />of the development rock has been exceeded and water will drain from the rock by gravity. <br />c) The moisture holding capacity calculated for the Topaz Mine sample (presented in Section 5 <br />below) was lower than for the West Sunday Mine sample. Therefore, the lower moisture holding <br />capacity from the Topaz Mine sample was selected to complete the water balance calculation in <br />order to provide the most conservative estimate of potential percolation. Calculation using the <br />Topaz Mine sample data is assumed to represent all of the mines in the Sunday Mines Group. <br />d) To account for uncertainties between actual field conditions and laboratory test conditions, the <br />moisture holding capacity as calculated from SWCC testing data is multiplied by a factor of 0.75, <br />as recommended by Benson (2006). <br />e) The water content of the development rock is assumed to be at the wilting point (10.64% water <br />by volume based on SWCC testing for sample DM-TP-SMCC from the Topaz Mine) at the <br />beginning of the water year (defined as the beginning of October through the end of September <br />of the following year). This assumption is supported by site specific moisture content data for the <br />rock of 1.4 % by weight (3.8 % by volume), collected in August 2008, which indicate actual rock <br />percent moisture is less than the wilting point. <br />f) There is no zone of saturation within the development rock piles (i.e., groundwater). This <br />assumption is supported by the fact that there are no observed springs or seeps emanating from <br />the development rock piles. <br />g) Evaporation is assumed to occur from development rock in the pile at depths ranging from the <br />surface to 1 meter. Development rock piles within the Sunday Mines Group do not currently have <br />significant development of vegetation. Therefore, transpiration by plants is assumed to be zero <br />for the water balance model. <br />h) Any percolation below a depth of 1 meter would continue to the base of the pile and discharge <br />from the pile. This is a conservative assumption because additional water holding capacity is <br />likely present in the development rock pile at a depth of greater than 1 meter. <br />i) For the water balance calculation, stormwater runoff from the development rock piles is <br />assumed to be 10% of the precipitation, as recommended by Guyman (1994). <br />5.0 Calculations <br />A. Basic Equations and Model Input Calculations <br />E <br /> <br /> <br />MathCAD V14 Saved 2/17/20095:15 PM Page 2 <br />N:\64986-Denison Mines\Task Order 3 - DMO