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G.3.3.2 Amount of Fluoride in Pit Discharge Water <br />For purposes of this evaluation, the assumption is made that the West Pit wells will be <br />pumped continuously at an average annual rate of 225 gpm without significant <br />seasonal variation. Over the period of available record, the average fluoride <br />concentration in the pit water is 4.5 mg/L. Therefore, the average chemical mass flux <br />of fluoride to the irrigation system is equal to the product of the flow rate and <br />concentration, or 2,016 kg of fluoride per year. <br />G.3.3.3 Modeling Ground Water Fluoride Concentration <br />Fluoride concentration in ground water at the Salazar Ranch is affected by the rate <br />and direction of ground water flow, along with the location and amount of fluoride <br />entering the aquifer. To predict the effect of water containing fluoride from the West <br />Pit that is applied onto the North and South pivots, a ground water flow model and a <br />solute transport model were developed. <br />A three-dimensional ground water flow model was constructed using the public <br />domain computer model MODFLOW. MODFLOW uses a numerical finite <br />differencing scheme to solve the governing equation for ground water flow based on <br />mass balance. The model was based on parameters developed from the Colorado <br />Department of Natural Resources Rio Grande Decision Support System (RGDSS) <br />model and parameters given in this report. Appendix F provides a detailed <br />description of the MODFLOW model. <br />Initially, a steady-state model was constructed to calculate ground water levels that <br />reflect equilibrium conditions in the ground water system, i.e. inputs and outputs of <br />ground water are consistent so that ground water levels do not change further with <br />time. The general layout and resulting steady-state ground water levels are shown in <br />G.3-2. <br />Battle Mountain Resources, Inc. 36 <br />P:1Pmjects5212-Newmont(SenL,is)\S"LuisWetmit Amendment- West Pit Memgem AVS Repod&PDFATe tT-itAmeudme?_v5c.doc December 2007