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<br />. <br /> <br />GUNNISON RIVER BASIN (I,AU 140200) <br /> <br />N <br />N <br />C <br />~ <br /> <br />Little is known about the ground water resources of the Gun- <br />. nison River Basin (Fig. D.J). Some general statements can be IDBde, <br />however. The geology of the upper Gunnison and Uncompahgre rivers <br />is extremely complex and tapping successful wells into this region <br />would be difficult. Near ~ontrose, Colorado, shallow wells in the <br />Dakota Sandstone yield fresh to moderately saline water (TDS from <br />288 to 4,200 mg/liter); alluvial sources produce water with even <br />lower IDS levels (Meeks, 1950). <br /> <br />Much of the region encompassing the lower Gunnison and Uncom- <br />pahgre rivers is believed to have meager supplies of ground water <br />since much of this area is surrounded by impermeable Mancos Shale. <br />To the southwest, however, large areas of potential grcund water <br />supplies exist in the Dakota Sandstone. Well yields from this rock <br />unit are generally less than 50 gpm (Boettcher, 1972). <br /> <br />DOLORES RIVER BASIN (Study Subunit 140300B) <br /> <br />. <br /> <br />Only one ground water study has been completed for the Dolores <br />River Basin (-i3. D.3) (Garrels, 1956). That study, by D. A. <br />Phoenix, was concerned only with the Salt Wash Member of the Morrison <br />Formation, which is a common geologic unit along the San Miguel and <br />Dolores rivers. Water fro!!! the Selt \,esh Member "as found to be <br />largely unconfined. The few confined sources yielded only about <br />30 gprn to wells for a few months. Dissolved solids were found to <br />be mostly in the range of 400 to 900 mg/liter but some wells were as <br />high as 3,700 mg/liter. <br /> <br />UPPER SAN JUfu~ RIVER BASIN (Studv Subunits 140801A, 14080LB <br /> <br />Interest in power production and coal gasification in the Upper <br />San Juan River Eosin (Figs. D.3 and D.S) has led to a n~mber of <br />recent ground water studies in the basin. With few exceptions, <br />ground water yields are meager, though it is estimated that water <br />storage is 257 maf in the entire San Juan River Basin (at least 10 <br />times that in the Piceance Greek Basin). Yields are low (generally <br />less than 20 gpm) primarily because rocks in the basin are relatively <br />impermeable (U.S. Bureau of Reclamation, 1976; U.S. Bureau of Land <br /> <br />Mgmt., 1977). <br /> <br />Another factor contributing to small well yields is the snaIl <br />quantity of recharge in much of the San Juan River Basin. The only <br />area where there is significant recharge is along the San Juan <br /> <br />. <br /> <br />D-19 <br />