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The hydraulic conductivity(K) of the alluvial aquifer used in the model was input as 500 feet per <br />day(fpd). This value is based on the Hydrogeologic Evaluation performed by Blue Earth <br />Solutions (2013). We assumed an anisotropy ratio of 0.1 (Kv/Kr), meaning that the value in the <br />vertical direction(Kv) is one order of magnitude lower than the value in the radial direction(Kr). <br />A groundwater elevation contour map for the alluvial aquifer provides the starting heads for the <br />finite difference solution and defines constant head boundary values. This surface was <br />developed using the alluvial water level contours from 1966 data compiled by Nelson et.al. <br />1989) and field measurements taken in September 2017. The 1966 contours were roughly <br />adjusted for the shift in vertical datums between the North American Vertical Datum(NAVD) of <br />1929 to NAVD88. The altitude of the groundwater surface from Nelson et al. (1989)is shown <br />on Figure E-1. <br />Boundary Conditions <br />The boundary conditions used for the model include four(4) constant head boundaries and one <br />1)no-flow boundary. Specified groundwater head values(elevations) from the input <br />groundwater surface are assigned to the constant head boundaries and do not vary during the <br />simulations. Two constant head boundaries are present at the western and eastern ends of the <br />model domain, one on the northern edge of the Arkansas River and one as the pond west of the <br />site (elevation 4530 feet). <br />These boundary conditions define the sources and sinks for the water budget of the model. The <br />sink in the model is the eastern boundary where alluvial underflow leaves the model. Well <br />pumping compared to irrigation recharge is likely a net sink,but this magnitude is likely small, <br />and was therefore not included in the model. The sources include the Arkansas River, alluvial <br />underflow under the western boundary, and recharge from the pond west of the site. No other <br />recharge sources are included in the model, as precipitation is considered a negligible source <br />within the domain. The system is assumed to be in equilibrium under pre-mining conditions. <br />The model domain is inactive outside of the defined boundary conditions. The resulting model <br />conforms to the conceptual model as presented in Section 2. <br />Calibration Targets and Goals <br />The calibration targets for the model include the measured groundwater elevations observed in <br />seven monitoring wells measured in September 2017. The calibration goal is to adjust model <br />inputs such that the steady state groundwater heads for the pre-mining conditions are similar to <br />measured heads in the field. Of these wells,two have been installed upgradient of the <br />reclamation activity(Wells 262268 and 279124). Therefore, these two wells are the best targets <br />for the predictive mounding simulations. The goals of the predictive simulation targets are: 1) <br />to show how field measured groundwater heads differ from those in the predictive simulations, <br />2)to show how pre-mining groundwater heads differ from those in the predictive simulations, <br />and 3)to compare post-mitigation heads to pre-mitigation mounded heads. <br />E-4