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o N 1'\:. --J levels in USBR no. 11 indicates a strong hydraulic connection to the Colorado River and no detect- able hydraulic connec-tion to the Redstone 21-9 well. This is consistent with USBR no. 11's being the closest monitored well to the river and the farthest from the production well. This study clearly demonstrated that hydraulic connection exists between alluvium, the Leadville Limestone, and the Colorado River at the Glenwood Springs test site. Within a radius determined by the rate and duration of discharge, alluvial wells near a well discharging from the Leadville Limestone will have lowered water levels; springs near the discharging well will discharge water at decreased rates. The magnitudes of these declines generally can be expected to decrease with distance from the discharging bedrock well. However, near the Colorado River, fluctuations in stage also affect water levels in alluvial wells. Rises in river stage may prevent or diminish water-level decreases in alluvial wells near discharging bedrock wells. Declines in river stage can prevent recov- ery of water levels in alluvial wells after flow from a bedrock well has ceased. Thus, the water leveUn an alluvial well near a discharging bedrock well and the Colorado River should be intermediate between the levels expected because of proximity to either the bedrock well or the river. S. Conclusions Drawn By Eisenhauer u Glenwood Springs Aquifer -- A salty aquifer located about 21.3 m (70 ft) below the ground elevation of 1748 m (5735 ft) emerges as 14 identified springs in and near the Colorado River in the vicinity of the town of Glenwood Springs. Here the Colorado River has a surface elevation of 1739 m (5705 ft). The aquifer has a salt content of 22200 mg/L, or 2.2 percent, a temperature of 50 C (122 F), and a pH of 6.3. When brought to the surface, the aquifer water effervesces from the escaping carbon dioxide. Major salt constituents. - IDS includes 88 percent sodium salt and 10 percent calcium salt. Potassium and magnesium account for the other 2 percent salt. Anion composition includes 78 percent chloride, 13 percent sulfate, and 9 percent bicarbonate salts. About 60 percent of the calcium is bicarbonate, or temporary hardness, and 40 percent is chloride, or permanent hardness. Minor dissotved constituents. - Significant amounts of minor chemicals dissolved in aquifer water include 1030 mg/L of carbon dioxide, 3 mg/L of fluoride, 40 mg/L of silica, 13 mg/L of stron- tium, 0.7 mg/L of sulfide, and 4 mg/L of iron. About 7 mg/L of dissolved organic nitrogen compound and 3 mg/L of total organic compounds were found. Radioactivity. - Dissolved radioactive salts in aquifer water are well below hazardous levels. However, exposure to gross beta levels that could be retained in recovered anhydrous salts might exceed Federal Occupational Guide Limits of 5000 mrem/a. By Geldon u 1. Twenty-seven geologic units of Paleozoic age in northwestern Colorado can be grouped into eleven hydro stratigraphic units on the basis of lithologic and hydrologic properties. Regional aquifers include the Devonian and Mississippian carbonate rocks hydrostratigraphic unit and the Pennsylvanian and Permian sandstone hydrostratigraphic unit. Local aquifers in the study area include the C1mbrian sandstone, Cambrian and Ordovician carbonate rocks, Mississippian carbonate and clastic rocks, and Pennsylvanian and Permian red beds and carbonate rocks hydrostratigraphic units. Confining layers in the study area include the Cambrian shale, Devonian carbonate and clastic rocks, Mississippian and Pennsylvanian shale and carbonate rocks, Pennsylvanian carbonate rocks and evaporites, and Permian shale and carbonate rocks hydrostratigraphic units. A-IS .L ..;;i