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<br />distinct water level, but only a single water level exists in the weil. As water level in the <br />. weil fails through the sequence of layers, the contribution from the various layers can be <br />expected to change, decreasing in the upper zones as the upper layers are dewatered <br />and increasing in the lower zones to maintain discharge from the well. Calculation of <br />the water level in the weil through time is a difficuil problem which few available <br />simulation models can solve. <br /> <br />. <br /> <br />. <br /> <br />We would expect the different layers in the aquijers to have different aquifer <br />properties. In some of the aquifers, particularly the Arapahoe, geophysical logs suggest <br />that the lower sandstone layers may be more productive than the upper layers. It is not <br />clear how this wiil affect weil production and pumping water levels. <br /> <br />Plan view models with fairly large ceils such as those used by Robson and Banta <br />give good estimates of regional changes in water level but do not provide pumping <br />water levels in the individual weils located in those ceils. If we consider a weillocated in <br />the center of a model ceil, we can see the difference between the water level in the ceil <br />and the water level in the well. Figure 4.1 shows a cross sectional representation of a <br />typicai ceil containing a pumping weil. In this figure, the model ceil is 1.5 miles wide <br />(7920 feet, r1 in the figure), and extends from .3960 feet to the left of the weil to 3960 <br />feet to the right of the weil, The ground water fiow model calculates a single water level <br />in the ceil based on flow conditions and the withdrawal rate from the well. Water level <br />in the aquifer varies both above and below this calculated water level within the ceil, <br />with pumping water level in the weil being significantly below the level in the cell. In this <br />figure, water level in the weil is between the top and bottom of the screen and the weil <br />is able to produce at the desired pumping rate. <br /> <br />Previous work in the Denver Basin has indicated that it should be possible to meet <br />the projected demand under Banta's SIMGRO scenario for 100 years without many <br />model ceils going dry. This means that it should be possible to meet demand without <br />water level in the ceils dropping below the bottom of the aquijer in the ceils. In Figure <br />4.2, we see the same weil discussed above with a slightly lower water level in the ceil <br /> <br />11 <br />