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(United Kingdom), Exxon Production Research, Failure Analysis Associates Inc., Fluor <br />Daniels Inc., Gaz de France (France), SAIC, Shell Oil, SOHIO, and Westinghouse <br />Hanford Company. Over 100 publications and project reports on the benchmarking, <br />verification, and applications of PORFLOW are currently available. <br />In summary, PORFLOW is a robust simulation code that has a direct application <br />to the multi -phase contaminant transport problem at the mine site. The code has been <br />extensively validated by independent researchers and has been used to model similar <br />hydrogeologic systems at other facilities. <br />4.0 Model Description <br />8 <br />SM -18 Mine Report <br />GeoScience Services <br />A two - dimensional computer model was developed using 132 by 89 variable -size <br />grids to define the problem domain which is a vertical slice running from the mining <br />operations to the nearby San Miguel River. The base of the Entrada Sandstone forms the <br />base of the model where it is assumed that horizontal groundwater flow dominates flow <br />conditions. Mixed flow conditions were assigned to the end boundaries of the model. No <br />flow conditions were assigned to the unsaturated portion of these boundaries (assumes <br />vertical movement of water in the unsaturated zone) and constant head boundaries were <br />assigned in the Entrada Sandstone aquifer based on river elevation and an assumed <br />hydraulic gradient of 0.007 (assumes horizontal groundwater flow in the Entrada <br />Aquifer). Constant flux conditions were maintain at the top of the model to simulation <br />recharge by precipitation at a rate equal to 1 /10` of the yearly precipitation rate of 12 <br />inches for the area. This is considered a conservative assumption since potential <br />evapotranspiration rates for the area far exceed yearly precipitation. <br />Nodes within the problem domain were assigned hydraulic properties to delineate <br />the various sandstone and shale /mudstone layers that underlie the mine site. There is <br />only limited information available for the hydraulic properties of the geologic formations <br />that underlie the mine and control the transport of water and constituents of concern. <br />Consequently, these properties were estimated based on available data sources of tests <br />