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<br />. <br /> <br />N <br />N <br />o <br />::J1 <br /> <br />Dissolved solid levels from the carbonate rocks are high and <br />are above 1962 drinking ~ater standards (500 mg/1iter of TDS). <br />Water samples range from 755 to 4,670 mg/1iter of TDS, ~ith an <br />average of about 2,000 mg/1iter (Hampton, 1974). <br /> <br />Near Glenwood Springs, Colorado, basalt, colluvial (landslide <br />deposits, slope taluses, or mud flows) and alluvial aquifers are <br />the predominate sources of ground water (Brogden and Giles, 1976a). <br />Basalt aquifers in the Cattle Creek Basin yield 25 to 50 gpm or as <br />much as 100 gPffi in collapsed portions of this rock structure. Alluvia <br />and co11uvia along the Roaring Fork and Crystal rivers produce 2S to <br />75 gpm. Some ground water is obtained from minor occurrences of Lead- <br />ville Limestone aquifers and Pennsylvanian.carbonates. Ty?ica1 yields <br />from these aquifers range from 5 to 25 gpm, though some wells produce <br />as much as 50 gpm (Brogden and Giles, 1976a). <br /> <br />. <br /> <br />Water obtained from basalts in the G1enwood Springs area has <br />excellent quality--TDS are as low as 111 mg/1iterand only as high <br />as 475 mg/liter. Alluvial aquifers generate fresh to slightly saline <br />water. Dissolved solids range from 245 to 1,460 mg/liter, except <br />that water from the Eagle Valley Evaporite along the valley edges of <br />the Roaring Fork and Crystal rivers and Cattle Creek contributes TDS <br />loads of about 2,000 mg/liter. All bedrock and unconsolidated aqui- <br />fers are alkaline (calcium bicarbonate) (Brogden and Giles, 1976a). <br /> <br />The Grand Valley is largely underlain by Henco; Shale and is <br />nearly void of ground water; the most important aquifers appear on <br />either side of the valley. Southwest of Grand Junction, Colorado, <br />Wingate Sandstone and Entrada Sandstone yield 2 to 13 gpm of artesian <br />water at a depth of 350 to 1,500 feet. The only unconfined ground <br />water aquifers in this region are low-yielding alluvia along the Colo- <br />rado and Gunnison rivers (Lohman, 1965). Two other,more minor aquifers, <br />the Salt Wash Member of the Morrison Fo~ation and the Dakota Sand- <br />stone, lie southeast of Crand Junction. The recharge rate for bedrock <br />aquifers in the Grand Junction area is extremely low; it takes several <br />thousand years for water to reach wells from recharge points (Lohman, <br />1965). <br /> <br />Ground water quality is quite variable. Water from alluvia is <br />too hard (as measured by calcium carbonate ions) for domestic use. <br />Since a significant quantity of the ground water is from saline stream <br />recharge, shallow wells, especially, will have enhanced mineral levels. <br />This is particularly true of shallow (less than 100 feet) wells from <br />Dakota Sandstone (Lohman, 1965). Wells drilled into the Wingate and <br />Entrada formations produce very good quality water (300 to 400 mg/liter <br />of TDS) at less than 1,000 feet but very saline water (over 10,000 <br />mg/liter of TDS) below 2,000 feet deep. Water from the Wingate and <br />Entrada formations also has a low content of calcium and magnesium <br />ions (Lohman, 1965; Boettcher, 1972). <br /> <br />. <br /> <br />D-18 <br />