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<br />South 5'lt5<3'oundwater Model Development Report <br /> <br />Oct. 11, 2001 <br />Page 9 <br /> <br />'1 <br /> <br />that gridblock, depending on the intensity of urban development in the grid block <br />(as qualitatively detennined from the map). The stored groundwater volume in <br />the grid block was calculated as: <br />V = ASyb <br />where Sy is the specific yield, A is the plan view area of the grid block, and b is <br />the thickness of the layer in the grid block - all values were based on original <br />SEa model parameters. No pumping was specified in grid blocks that do not <br />contain development (e.g., areas of designated open space). For all simulations <br />using this constant Tate pumping scenario, we examined output after 60 and 120 <br />years. <br />~ Pumping Case 2: Pumping well locations are the same as in simulation Pumping <br />Case I. The seasonal fluctuations were represented by taking the V values as <br />calculated above and setting Q equal to 2/3 V for the months of April through <br />October and 1/3 V for November through March. Again, we examined output after <br />60 and 120 years of seasonably variable pumping. <br /> <br />) <br /> <br />4.1.3 Base Case (Single Layer) Model Set-up <br /> <br />The Base Case (single layer) model utilized the Upper Arapahoe distributions of <br />transmissivity and primary and secondary storage values as prescribed in the original SB- <br />74 regional model for the subregion, together with the boundary I pumping conditions as <br />described above. <br /> <br />4.1.4 Layered Models <br /> <br />As described above, the purpose of the regional model comparative analysis was to <br />contrast the vertically homogeneous (single layer) aquifer modeling approach as <br />implemented in the SB-74 model with layered approaches that explicitly account for fine- <br />grained (low permeability) interbeds within the aquifer units. To accomplish this, we <br />developed a IS-layer model based on vertical heterogeneity observed in the field. <br /> <br />The SB-IS3 investigation of Denver Basin aquifer economic life (HRS, 1997) provides a <br />useful description of aquifer interbed heterogeneity. For our layered model, we adapted <br />) the interbed interpretation of Castle Pines Arapahoe Well A3 (HRS, 1997; Robson and <br /> <br />Hydrosphere Resource Consultants <br />1002 Walnut Suite 200, Boulder, CO 80302 <br />PO Box 44S, SocolTo. NM 87801 <br />