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inputs being made relative to the fluoride mass input to the ground water aquifer and the <br />absorptive and advective conditions related to the movement of this solute along the <br />ground water gradient. Once these models were conceptualized, the models were then <br />built, tested, and run for the expected scenario under which Battle Mountain Resources, <br />Inc. expects to operate the irrigation pivots at the Salazar Ranch with West Pit water. The <br />following sections describe these processes and, ultimately, the results of expected <br />downgradient concentrations of fluoride in the valley fill aquifer. <br />Conceptual Model <br />Prior to developing a model that estimates movement of fluoride in the subsurface, an <br />understanding of the dynamics of ground water flow in the area was necessary. The <br />initial step in the development of the ground water flow model was to characterize the <br />ground water system. The model area, which includes the Salazar Ranch and the Town <br />of San Luis (San Luis), is characterized by two layers, with both of these layers having <br />parameters that are homogeneous and isotropic. The top layer is modeled as an <br />unconfined aquifer. The bottom layer is modeled as a confined aquifer. The top layer <br />thickness was chosen such that the entire top layer would encompass the full depth of the <br />deepest San Luis well (300 feet (ft)). <br />Aquifer parameters used for this model were extracted from Colorado's Rio Grande <br />Decision Support System (RGDSS) model and from topographic parameters of the area: <br />• The bottom elevations of the lower layer of the model were taken from the bottom <br />of layer 5 in the RGDSS model. <br />• The hydraulic conductivity is 14 ft per day (ft/d) and the porosity is 0.2. <br />• According to the RGDSS model, the specific yield for this area is 0.2. <br />• Ground surface elevation was taken from US Geological Survey 7.5-minute <br />quadrangle mapping. <br />• The distance between the source location and the SLM-2 well is about 3,200 ft. <br />Dispersivity was estimated to be approximately 10 percent of this distance, or <br />-2-