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' CashMineWaterMonitoring AdrianBrown <br />GROUNDWATER MODEL <br />A groundwater model has been constructed to evaluate the groundwater flow regime, the inflow to the <br />Cash Mine, and the groundwater flow conditions following closure of the mine. <br />' COMPUTATIONAL METHOD <br />The computational method used in the analysis is the Finite Element Method. The code used is <br />' ABCFEM, a code developed by Adrian Brown for analysis of mine-related groundwater flows and <br />impacts. This code is available through the International Groundwater Modeling Center, at the Colorado <br />' School of Mines, Golden, CO. <br />CONSTRUCTION <br />' The groundwater model is atwo-dimensional model of the flow in a slice of the hillside, running from <br />the crest of the hill at the Gold Hill Mill, through the Cash Mine, and to Gold Run, approximately at <br />Summerville. The location of the section is indicated in Plate 1. <br />The model domain has been subdivided into triangulaz elements, bounded by nodes at the corners of the <br />elements (Plate 7). The nodes near the surface pass parallel to the surface, through the #1, #3, #5, #7, and <br />#9 levels of the Cash Mine. <br />' PARAMETERS <br />Hydraulic Conductivity <br />' The model is divided into two hydraulic conductivity zones: <br />1. A shallow rockmass, with 1 ft/yr hydraulic conductivity, representing stress-relieved rock in the <br />' uppermost 50 feet below the surface; and <br />2. The deeper rockmass, with 0.3 fl/yr hydraulic conductivity, representing the low permeability <br />' countryrock. <br />The hydraulic conductivity zones are shown in Plate 7. <br />' Infiltration <br />The model infiltration occurs at the ground surface. Infiltration is applied at a rate of 2" per yeaz (10% of <br />the total precipitation). <br />' Boundary Conditions <br />Swamping Boundary Nodes <br />' The boundaries of the model aze no-flow, except for the nodes along the upper surface of the domain. <br />These nodes are set so as to allow outflow to Gold Run Creek from the groundwater domain when the <br />' heads at the nodes exceed the elevation of the groundwater surface at the nodes. <br />Fixed Head Mine Nodes <br />' In the analysis of conditions during mining, the head at the mine nodes is set at 350 feet below ground <br />surface. This simulates the groundwater level in the mine at present, which is approximately at the <br />historic median. <br />1 <br />' 1601A-20067106 11 <br />