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<br />S Melro G~~equirements Memo <br /> <br />January 8, 200 I <br />Page 4 <br /> <br />In the lower portions of the basin, the bedrock aquifers discharge to streams and the shallow ') <br />alluvial aquifer. In addition to these natural discharge modes, in relatively recent times (starting <br />in 1883) wells advanced into the bedrock aquifers have affected anthropogenic discharge from <br />the aquifer. In recent decades, the bedrock aquifers have been developed as the primary water <br />supply source for several communities in the South Metro area. The model needs 10 adequately <br />accouni for all natural and anthropogenic discharges from the basin, both historic and <br />projected. <br /> <br />To adequately capture the long-term behavior of each of the aquifers with respect to modeling <br />objectives, the model must be capable of mimicking historic observed drawdown trends, as well <br />as appropriately representing aquifer hydraulics to project future drawdowns. This means Ihat an <br />adequate record of historic pumping must be available as model input, as well as long term <br />water level hydrographs in wells throughout the basin that can be used as a basis for model <br />calibration. In addition, defensible projections of future groundwater demands must be <br />provided. <br /> <br />Each of the model requirements italicized in the above discussion ofthe conceptual model is <br />addressed to a large degree in the SED SB-74 Denver Basin groundwater model. The only <br />possible exception to this statement is the very last sentence in the immediate preceding <br />paragraph: SB-74 future demand projections for the South Metro region likely need refining <br />based on direct feedback that can be provided by S. Metro water suppliers. This point is <br />elaborated on in section 2.2. <br /> <br />) <br /> <br />2.2 Water Demands and System Operating Procedures <br /> <br />As stated above, water demands specifications are one of the key input parameters for the <br />groundwater model. For publicly supplied water users, the groundwater-pumping demands will <br />be provided by the water suppliers in the region. If no projections are provided by some of the <br />suppliers, Hydrosphere will work with the Study Board to select a defensible assumed demand <br />schedule from the non-respondents. <br /> <br />In addition to the publicly supplied water users, there are hundreds (if not thousands) of <br />individual domestic wells in the study area. If the SED database does not list permitted water <br />rights for those wells, Hydrosphere will need to work with the Study Board to develop assumed <br />pumping rates. <br /> <br />To project long-term rates of drawdown as listed under study objectives, the model is most <br />efficiently run by considering annual pumping rates from the aquifer. Even though it is <br />recognized that system experiences wide swings in demand on a seasonal basis, it may be <br />difficult (with the project budget and time constraints) for us to incorporate in the model seasonal <br />or perhaps even annual pumping data. In other words, the model must be capable of looking at <br />"ending points" consistent with defensible water demand projections, which may well be in <br />decade long slices. For instance, in the SED 8B-74 Denver basin model, stress periods (periods <br />of constant boundary conditions) range from 3 to 61 years. At this time, Hydrosphere is <br /> <br />J I <br /> <br />Hydrosphere Resource Consultants <br />1002 Walnut Suite 200, Boulder, CO 80302 <br />PO Box 445, Socorro, NM 87801 <br />