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JD-9 Mine Report Geoscience Services 4.0 Model Description A two-dimensional computer model was developed for the SM-18 that overlies similaz geology as the JD-9 mine. However, there is approximately 200 feet of Brushy Basin shales and mudstones at the JD-9 mine that are absent at the SM-18 mine. Consequently, the extent if contaminant transport at JD-9 should be less than predicted for SM-18. The model used 132 by 89 variable-size grids to define the problem domain which is a vertical slice running from the mining operations to the nearby San Miguel River. The base of the Entrada Sandstone forms the base of the model where it is assumed that horizontal groundwater flow dominates flow conditions. Mixed flow conditions were assigned to the end boundaries of the model. No flow conditions were assigned to the unsaturated portion of these boundaries (flow in the unsaturated zone is assumed to be vertical) and constant head boundaries were assigned in the Entrada Sandstone aquifer based on river elevation and an assumed hydraulic gradient of 0.007 (constant head boundaries assume horizontal saturated groundwater flow) Constant flux conditions were maintain at the top of the model to simulation rechazge by precipitation at a rate equal to 1/10°i of the yearly precipitation rate of 12 inches for the area. This is considered a conservative assumption since potential evapotranspiration rates for the area far exceed yeazly precipitation. Nodes within the problem domain were assigned hydraulic properties to delineate the various sandstone and shale/mudstone Layers that underlie the mine site. There is only limited information available for the hydraulic properties of the geologic formations that underlie the mine and control the transport of water and constituents of concern. Consequently, these properties were estimated based on available data sources of tests conducted in the specific geologic formation, regardless of the locations, or hydraulic properties were estimated based on lithology. Table 2 provides a list of hydraulic properties available for the geologic formations underlying the mine site. There is a limited amount of information that requires estimates for these properties in the groundwater flow and transport model.