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HAHN WATER RESOURCES, LLC <br /> Model Domain <br /> The model domain is square, measuring 7,000 feet x 7,000 feet. Model cells measure 100 feet x <br /> feet. The model grid is aligned in a north-south direction. <br /> Aquifer Properties <br /> The principal aquifer properties of interest in this investigation are: <br /> • Saturated thickness (b) — the thickness of the saturated porous medium measured as the <br /> difference between the static water level and the base of the aquifer, measured in feet. <br /> The model was based on an average saturated thickness of 18 feet. <br /> • Hydraulic conductivity (K)—a measure of the capacity of a porous medium to transmit a <br /> volume of water through a unit cross-sectional area, typically expressed in units of feet <br /> per day. The aquifer was assigned a uniform hydraulic conductivity of 1,000 feet per day. <br /> • Storage coefficient or specific yield (Sy) — the volume of water released from a unit <br /> volume of saturated aquifer per unit decline in head, expressed as a fraction. The aquifer <br /> was assigned a uniform value of 0.2 for specific yield. <br /> • Transmissivity (T) — a measure of the capacity of a porous medium to transmit a volume <br /> of water through the entire saturated thickness, expressed in units of feee per day. <br /> Transmissivity is obtained by multiplying the hydraulic conductivity by the saturated <br /> thickness (T=K x b). Transmissivity was therefore set equal to 18,000 feet2 per day. <br /> Boundary Conditions <br /> The northern edge of the model coincides with the Colorado River. The river is modeled using <br /> the "river package" of MODFLOW. The southern edge of the model terminates at the first <br /> apparent river terrace above the floodplain. This feature is mapped as a no-flow boundary (no <br /> water can enter or leave the model through this boundary). The eastern and western boundaries <br /> of the model are modeled using the "general-head boundary package" of MODFLOW. This type <br /> of boundary condition allows for movement into and out of the model, based on the difference <br /> between groundwater levels that are predicted to occur within the model domain and <br /> groundwater levels that are specified for locations outside of the model's domain. <br /> Recharge <br /> It is understood that any surface water runoff, tail water from ditches and laterals, irrigation <br /> return flows, and other sources of surface water entering the site will be re-routed in advance of <br /> the mining. The Last Chance Ditch lateral (mapped as entering the site along the eastern <br /> boundary) will likely be routed into the dewatering trench. In light of these plans, there are no <br /> sources of surface water that were modeled as entering the groundwater system on site. Rainfall <br /> recharge was set at approximately 10 percent of total rainfall, and represents the net recharge to <br /> the groundwater system. <br /> The Last Chance Ditch (running approximately east-west through the southern portion of the <br /> model was assumed to leak water, with leakage ultimately recharging the groundwater system. <br /> Leakage from this ditch was modeled as a constant value of approximately 20,000 cubic feet per <br /> day over the portion of the canal lying within the model domain. <br /> 2 <br /> 6589 Elaine Road -Evergreen,Colorado 80439 - office 720.242.8639 -cell: 303.870.5757 <br /> hahnwaterresources@gmail.com -www.hahnwaterresources.com <br />