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<br />s. Metn5:400del Requirements Memo <br /> <br />January 8. 2001 <br />Page 5 <br /> <br />performing a subregional comparative modeling analysis that will investigate the feasibility, and <br />value-added, of considering annual or seasonal pumping schedule. <br /> <br />3. CRITICAL MODELING ISSUES <br /> <br />Based on written materials and verbal feedback provided Study Board members, Hydrosphere <br />has identified three critical modeling issues which may significantly impact the model <br />development process. Those issues are: I) types of mode! output needed, 2) incorporating new <br />hydrologic input data that will drive the model, and 3) representation of wells and well-fields, <br />and treatment of fine-grained interbeds and three-dimensional flow components within the <br />aquifer units. <br /> <br />3.1 Types of Model Output <br /> <br />Given the Study Board's stated modeling objectives, /he model should be capable of reporting <br />on: <br /> <br />i. regional drawdowns across the en/ire basin, <br />ii. volume/ric pumping withdrawals for any desired loea/ioll in /he basin, and <br />Ill. localized drawdowns a/ a selected representative set of well and well-field locations. <br /> <br />) <br /> <br />The first two output criteria are easily met using the SB-74 model, whereas the last (well and <br />well-field drawdowns) will require a significant extension to SB-74. Providing defensible local <br />drawdowns requires careful consideration of aquifer heterogeneity (e.g., fine-grained interbeds) <br />at the local scale; these issues are discussed in section 3.3. <br /> <br />3.2 Incorporating New Hydrologic Input Data That Will Drive The Model <br /> <br />To obtain better predictions for the South Metro area, the South Metro regional groundwater <br />model will incorporate hydrologic property (e.g., transmissivities and storativities derived from <br />pumping tests of South Metro supply wells) and observation (South Metro well hydrographs) <br />data that was not employed in developing the calibrated SB-74 model. It is possible that some of <br />the new data may exhibit significant deviations for SB-74 input parameters or calibration data. If <br />significant deviations arc found, it may be necessary to re-calibrate the model. <br /> <br />As part of/he Sou/h Melro regional groundwa/er modeling projec/, a procedure will need /0 be <br />developed /ha/ screens new da/a and compares it to data and information used in developing the <br />SED SB-74 Denver Basin Model. <br /> <br />3.3 Treatment Of Fine-Grained Interbeds at Well-Field Scale <br /> <br />As discussed in section 2. I, interbedded fme-grained materials within the aquifers are less areally <br />) extensive that the aquitards that separate the aquifers, and exert less impedence to pressure <br /> <br />Hydrosphere Resource Consultants <br />1002 Walnut Suite 200, Boulder, CO 80302 <br />PO Box 445, Socorro. NM 87801 <br />