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<br />South Met[y4itY~dwaler Model Developmenl Repor/ <br /> <br />Gel. 11, 200 I <br />Page 8 <br /> <br />aquifer transmissivity distribution was equivalent for both cases. The future pumping <br />demand was developed based on the Douglas County Master Plan and state-allowed <br />groundwater extraction schedules (i.e., 1% of stored resource per year). <br /> <br />) <br /> <br />4.1.1 Scenarios Considered <br />More than 40 different model runs were performed for this subregional model, with <br />varying pumping scenarios, layering schemes, and hydrologic property specifications. <br />Following a presentation of model set-up aspects that were common to all runs, we <br />describe the inputs for representative model runs selected to illustrate the range of results <br />for the model configurations investigated. Table 4.1 provides a summary description of <br />several key model scenarios, and the following sections provide the detailed backup <br />descriptions to supplement Table 4.1. <br /> <br />4.1.2 Model Sel-up (Boundary and Pumping Condilions) <br />Common 10 All Scenarios Invesligaled <br /> <br />The foundations for all models were directly extracted from the existing SEO model, <br />including grid size and grid block properties. From this foundation, the subregional <br />model was built as follows: <br /> <br />) <br /> <br />. No-flow boundary conditions were placed around the outside of the subregional <br />model domain; this boundary specification is representative ofa development pattern <br />in the regions surrounding the simulation domain that is similar to that within the <br />simulation domain. <br />. Recharge was set to zero in all grid blocks; recharge is unlikely to affect the issues <br />that we were focussed on in this comparative modeling study. <br />. Initial heads were obtained by running subregional models with SB-74 initial heads to <br />steady state under an unstressed (no pumping) condition. Heads resulting from the <br />steady-state run were then used as initial heads for the models. <br />. Two pumping scenarios were considered, one with a constant rate throughout the <br />simulation (pumping Case I) and the other with a seasonal fluctuation (Pumping Case <br />2): <br />}> Pumping Case 1: Pumping wells were placed in 108 grid blocks that contain areas <br />of urban and suburban development based on the Douglas County Master Plan <br />Map (Douglas County, 2000). The annual pumping rate (Q) for each well was <br />specified to be either 1%, 0.75%, or 0.5% of groundwater volume (JI) stored in ~ <br /> <br />Hydrosphere Resource Consultants <br />1002 Walnut Suite 200, Boulder, CO 80302 <br />PO Box 445. Socorro, NM 87801 <br />