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Several picks are plotted just outside the aquifer extent in Township 5S and Range 68W, <br />which may indicate that the confining unit between the Upper and Lower Arapahoe <br />Aquifers extends beyond the outline shown. A comparison of the top and bottom <br />elevations of the confining unit indicates that its thickness extends up to 150 feet. A <br />comparison of the top of the Lower Arapahoe and bottom elevations of the Arapahoe <br />Aquifer indicates that the Lower Arapahoe's thickness extends to 300 feet. <br />Figure 17 presents the bottom elevation of the Arapahoe Aquifer. A total of 1,762 <br />database picks with additional control picks were used to develop the contours for the <br />bottom of the Arapahoe Aquifer (Table 1). Picks are distributed over the entire extent of <br />the aquifer, but the majority of the picks are in the northern half of the aquifer. Bottom <br />elevations range from approximately 6,100 feet along the southern margins to 4,100 feet <br />in Townships 5S and 6S and Range 66W. The geometry of the contours reveals a surface <br />that is steeply sloping along the western margin of the aquifer and more gently sloping <br />to the northwest along the eastern margin, also showing the asymmetric synclinal shape <br />of the Denver Basin. A comparison of the top and bottom elevations of the Arapahoe <br />Aquifer indicates that its thickness extends up to 550 feet in many areas. <br />Figure 18 presents the net or cumulative sand thickness of the Upper Arapahoe Aquifer <br />in the divided region. A total of 558 database picks with additional control picks were <br />used to contour the sand thickness of the Upper Arapahoe Aquifer (Table 1). Net sand <br />thickness extends up to 200 feet along the western, southern, and eastern boundaries. <br />From the western margin, two channel-shaped areas of thicker sands can be observed <br />which branch apart and extend to the east; these are interpreted as being paleochannel <br />features that formed when this formation was being deposited. <br />Figure 19 presents the net or cumulative sand thickness of the Lower Arapahoe Aquifer <br />in the divided region. A total of 565 database picks with no additional control picks were <br />used to contour the sand thickness of the Lower Arapahoe Aquifer (Table 1). Net sand <br />thickness extends up to 200 feet in Township 3S and Range 69W but the majority of the <br />aquifer possesses a sand thickness of less than a 100 feet. <br />Figure 20 presents the net or cumulative sand thickness of the Arapahoe Aquifer in the <br />divided and undivided regions. In the divided region, the net sand thickness represents <br />the sum of the Upper and Lower Arapahoe sands. A total of 1,440 database picks with <br />no additional control picks were used to contour this surface Table 1). The majority of <br />the sand picks are located in the northern half of the aquifer. Net sand thickness extends <br />up to 400 feet with an area of relatively large net sand thickness near the western edge of <br />the basin from Townships 6S to 12S. This paloechannel of thick sands begins along the <br />western margin, trends north, and then begins to lessen in thickness to the east. In <br />Township 6S and 7S and Ranges 68W and 67W is an area of lesser sand thickness to the <br />west of an area of relatively greater sand thickness. This is inconsistent with the model <br />of depositional sources coming from the mountains located to the west of this area. It is <br />recommended that the net sand thickness picks from logs in this area be reevaluated. <br />3.4 Laramie-Fox Hills Aquifer Configuration <br />SPDSS Phase 2 Task 42.2 TM -Final 17 <br />2/13/06 <br />