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basin. This quantity of ground water cannot be pumped annually, however, without long-term continued depletion of the quantity in storage and without eventual effects on streamflow and bottomland vegetation. Well yields greater than 1,000 gallons per minute can be developed in most of the basin, provided wells are drilled sufficiently deep--several thousand feet in some areas--to tap all available aquifers. Yields of more than 1,000 gpm can be developed from the deep sandstone aquifers in the southern part of the basin and from the Green River Formation in the Piceance Creek Basin. The alluvium along major streams in the northern part of the Upper Colorado River Basin yields as much as 1,500 gpm to individual wells. In much of the basin, however, such quantities may be developed on a time- limited basis only, owing to the effects of large-scale pumping on streamflow and to depletion (mining) of ground water in storage. Chemical quality of ground water is an additional constraint on its use for public supply and some energy conversion processes, although some uses such as cooling and slurry transport of coal or spent shale are not constrained by quality. Patterns of ground water quality are not well defined in the basin; however, a general rule is that salinity increases with depth. Dissolved solids concentration ranges from a few hundred to more than 40,000 milligrams per litre and, depending on the particular use for ground water, consideration of a desalination process or blending of saline ground water with better quality surface water may be required. The potential for energy related ground water development in the Upper Colorado River Basin is best illustrated by current activities in the Piceance Creek Basin, where detailed hydrologic studies provide sufficient information to evaluate the ground water supply and to define the effects of pumping. Recent and current studies indicate that the amount of ground water in storage in the Green River and Uinta Formations alone is on the order of 25 million acre- feet, plus an undetermined amount in the stream valley alluvium. Computer model studies are under way to predict the amount that can be pumped within existing hydrologic constraints and to evaluate the hydrologic effects of pumping. The annual recharge to ground water in the Piceance Creek Basin is abOut 29,000 acre-feet, which is discharged by evapotranspiration and by subsurface flow into streams. Pumping of ground water in excess of the amount annual recharged would have an ultimate, if not immediate, effect on streamflow and bottomland vegetation in the developed area. A beneficial effect of pumping, however, would be to create additional storage space 35