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<br />Computer simulations by Thomas (1989) indi-
<br />cate that both upward and downward movement of
<br />water between aquifers is likely, but that downward
<br />movement probably accounts for a substantial part of
<br />eN the recharge to deeper formations that do not crop out
<br />Ul in areas where abundant precipitation is available for
<br />m recharge. In parts of the study area, the potential for
<br />--l vertical ground-water movement as a result of differ-
<br />ences in hydraulic head between the aquifers is down-
<br />ward from upper Paleozoic to middle Paleozoic rocks
<br />(Weiss, 1991, p. 28)(fig. 3). Natural movement of
<br />water from middle Paleozoic aquifers (Leadville Lime-
<br />stone) and upper Paleozoic aquifers and confining lay-
<br />ers (Hermosa Group) to the middle Mesozoic aquifers
<br />(Navajo Sandstone) is therefore not likely in these parts
<br />of rhe area.
<br />On the basis of differences in potentiometric con-
<br />tours, however, Freethey andCordy(l991, fig. 58, p. C
<br />83) showed that an upward gradient from the upper
<br />Paleozoic aquifer (Cutler Formation) to the middle
<br />Mesozoic aquifers (Navajo aquifer) was present in an
<br />area north and south of the San Juan River near Aneth
<br />(fig. 8). This interpretation was made by superimpos-
<br />ing water-level contour maps of the.middle Mesozoic
<br />and upper Paleozoic aquifers. Comparison of water-
<br />k'vel altitudes for selected wclls in the upper Paleozoic
<br />aquifer (determined from drill-stem test data) and in the
<br />middle Mesozoic aquifers (determined from measure-
<br />ment of water levels or pressure heads) in this area indi-
<br />cates that water levels in the upper Paleozoic aquifer
<br />were higher than water levels in the middle Mesozoic
<br />aquifers. This area of upward potential may be smaller
<br />or larger than that indicated by Freethey and Cordy
<br />(1991). Data from "Report of Water Encountered Dur-
<br />ing Drilling" (Utah Division of Water Rights, unpub.
<br />dara) also indicate that water levels (hydraulic head) in
<br />the upper Paleozoic aquifer are high enough to enable
<br />water to discharge at land surface in the vicinity of the
<br />Greater Aneth Oil Field. Barnes (unpub. data, 1959, p.
<br />15) estimated that yields of as much as 100 gaJlmin
<br />were possible from the DeChelly Sandsrone near the
<br />San Juan River.
<br />
<br />Hydraulic-head values determined from drill-
<br />stem data from the upper Paleozoic aquifer were com-
<br />pared with water-level dara from the Navajo aquifer to
<br />determine the potential for upward movement of water
<br />between these units. Density differences and osmotic-
<br />pressure gradients also affect movement of water
<br />through and between aquifers (Weiss, 1991, p. 25), but
<br />these effects were not evaluated and are probably rela-
<br />tively minor when compared with the driving forces
<br />
<br />28
<br />
<br />that result from differences in hydraulic head. Head
<br />differences determined from drill-stem test data and
<br />measured water levels substantiate that upward move-
<br />ment of water from the upper Paleozoic aquifer (Cutler
<br />Fonnation or DeChelly Sandstone Member) into the
<br />Navajo aquifer is possible in part of the study area (fig.
<br />8). In an evaluation of the DeChelly Sandstone as a
<br />potential water source for Texaco water-flood opera-
<br />tions (Barnes, unpub. data, 1959, p. 14), the shut-in
<br />pressure from a drill-stem test from a well in T. 40 S.,
<br />R. 24 E., Sec. 25 showed that the hydraulic head in the
<br />DeChelly Sandstone was about 60 ft higher than the
<br />hydraulic head in the Navajo Sandstone, indicating that
<br />potential upward movement of water between these
<br />formations was possible in this area. Formation pres-
<br />sure from a wireline test of the DeChelly Sandstone in
<br />theMobil18-43B injection well (T 4\ S., R. 24 E., Sec.
<br />] 8) was used to calculate shut-in pressure of the forma-
<br />tion at a depth of 2,663 ft (James Vanderhill, Mobil
<br />Exploration and Producing, U.S., Inc., written com-
<br />mun., 1995). By using the Weigel (1987, p. 9) formula
<br />
<br />H = A - D + 2.33 x Pf (I)
<br />
<br />where:
<br />H is shut-in head, in ft above sea level,
<br />A is altitude of land surface at the well,
<br />D is depth of drill-stem test interval,
<br />Pf is formation pressure, in pounds per square
<br />inch, and
<br />2.33 is a constant to convert formation pressure
<br />to equivalent freshwater head, in ft,
<br />a head of 5,117 ft was obtained, compared with a head
<br />(water-level altitude) of about 4,660 ft in (he Navajo
<br />aquifer in this area (fig. 8). Similar calculations using
<br />pump-test data from Mobil's Ratherford Unit 14-33
<br />well in T. 41 S., R. 23 E., Sec. 14 also indicate that
<br />hydraulic head in rhe DeChelly Sandstone at a depth of
<br />about 2,500 ft exceeded that in the Navajo aquifer by
<br />about 300 ft, thus confirming a potential for upward
<br />vertical movement in this area.
<br />Drill-srem test data from seJected wells in the
<br />DeChelly Sandstone in the Boundary Butte Oil Field in
<br />the southwestern part of the study area (fig. I) indicate
<br />that hydraulic head in the Navajo aquifer exceeds that
<br />in the DeChelly Sandstone by less than 100 ft (Whit-
<br />field and others, 1983, table 14, p. 75) and indicate that
<br />(he potential for vertical movement of water is down-
<br />ward from the Navajo aquifer to the upper Paleozoic
<br />aquifer in this area. These wells are located outside and
<br />southwest of the area of upward potential (fig. 8) as out-
<br />lined by Freethey and Cordy (1991). Relative differ-
<br />
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