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<br />South ~lf~oundU'ater Model Development Report <br /> <br />Oct. 11.2001 <br />Page 13 <br /> <br />') differences between the single- and IS-layer models, again with the deviations increasing <br />as the value of YCONT decreases. Hydrographs from the MW-2 location exhibit similar <br />differences. <br /> <br />4.2.3 Vertical Head Distributions <br /> <br />To assess the vertical head distributions for the IS-layer eases, we prepared plots showing <br />this for an intensively pumped region (Figure 4.8) and an unpumped region (Figure 4.9). <br />These two plots clearly illustrate again that the magnitude ofVcont makes a significant <br />difference). Tables 4.2 and 4.3 provide the data used to generate Figures 4.8 and 4.9 <br />respectively. <br /> <br />I. In the pumped region (Figure 4.8) all models indicate the top seven layers are <br />completely de-watered, but the head values in the remaining saturated layers are <br />significantly different. <br /> <br />) <br /> <br />2. The unpumped area (Figure 4.9) exhibits a different degree of de-watering depending <br />on VCONT: the highest VCONT values (derived from the SB-153 report for Castle <br />Pines well A-3) show the top two layers de-watered and a fairly uniform head value <br />beneath the water table on the order of 4,608 ft above mean sea level. The <br />YCONT=O.O case, however, shows the entire aquifer remains wetted, and the head <br />profile is highly non-uniform. This is consistent with expectations: very low VCONT <br />values a1]ow the development oflarge vertical head gradients. <br /> <br />) <br />, <br /> <br />]n general, these results stand the test of hydrogeologic common sense. In the heavily <br />pumped area, there are wells in almost every gridblock and these wells allow for a <br />vertical equilibration of heads between layers no matter what VCONT value is used. As <br />was correctly noted by Banta (personal communication, Ned Banta to Peter Binney, <br />8/24/0]), this is particularly true for MODFLOW-SURF ACT, where a ] -D element <br />representing a well is superimposed on the 3-D mesh representing the porous medium <br />(Sudicky et aI., 1995). The effect of this superposition is that the hydraulic conductance <br />due to the well is added to the vertical conductance term representing the porous medium <br />(in MODFLOW, the vertical conductance term is defined by VCONT.) The conductance <br /> <br />Hydrosphere Resource Consultants <br />1002 Walnut Suite 200, Boulder, CO 80302 <br />PO Box 441, Socorro, NM 87801 <br />