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Environmental Setting and Implications on Water Quality, <br />Upper Colorado River Basin, Colorado and Utah <br />By Lori E. Apodaca, Nancy E. Driver, Verlin C. Stephens, and Norman E. Spahr <br />Abstract <br />The Upper Colorado River Basin in <br />Colorado and Utah is 1 of 60 study units selected <br />for water-quality assessment as part of the <br />U.S. Geological Survey's National Water-Quality <br />Assessment program, which began full implemen- <br />tation in 1991. Understanding the environmental <br />setting of the Upper Colorado River Basin study <br />unit is important in evaluating water-quality issues <br />in the basin. Natural and human factors that affect <br />water quality in the basin are presented, including <br />an overview of the physiography, climatic condi- <br />tions, general geology and soils, ecoregions, <br />population, land use, water management and use, <br />hydrologic characteristics, and to the extent <br />possible aquatic biology. These factors have sub- <br />stantial implications on water-quality conditions <br />in the basin. For example, high concentrations of <br />dissolved solids and selenium are present in the <br />natural background water conditions of surface <br />and ground water in parts of the basin. In addition, <br />mining, urban, and agricultural land and water <br />uses result in the presence of certain constituents <br />in the surface and ground water of the basin that <br />can detrimentally affect water quality. The envi- <br />ronmental setting of the study unit provides a <br />framework of the basin characteristics, which is <br />important in the design of integrated studies of <br />surface water, ground water, and biology. <br />60 study units representing the Nation's most important <br />river basins and aquifers are being investigated. <br />Information obtained from the different study units will <br />help in the management, regulatory, and monitoring <br />decisions by other Federal, State, and local agencies to <br />better protect, use, and enhance water resources. To <br />effectively design and conduct a multidisciplinary <br />water-quality assessment of a large basin, the current <br />environmental setting and implications on water <br />quality need to be determined. <br />The Upper Colorado River Basin study unit <br />(fig. 1) in Colorado and Utah has a drainage area of <br />about 17,800 miz; all except 100 mil of this area is in <br />Colorado (Driver, 1994). The Colorado River and its <br />tributaries originate in the mountains of central <br />Colorado and flow about 230 mi southwest into Utah. <br />These mountains form the Continental Divide, which is <br />the eastern and southern boundary of the study unit. <br />The major tributaries to the Colorado River in the study <br />unit are the Blue, Eagle, Roaring Fork, and Gunnison <br />Rivers. <br />The study unit is predominantly rural and has a <br />population of about 234,000 people (Bureau of Census, <br />1990), with more than 99 percent of the people residing <br />in Colorado. The largest population center in the basin <br />is the area around Grand Junction, Colo. Tourism is a <br />major year-round activity and accounts for substantial <br />increases in population primarily during the winter and <br />summer (Driver, 1994). <br />Purpose and Scope <br />INTRODUCTION <br />In 1991, the U.S. Geological Survey, <br />U.S. Department of the Interior, began full implemen- <br />tation of the National Water-Quality Assessment <br />(NAWQA) program. The long-term goals of the <br />NAWQA program are to: (1) Describe current water- <br />quality conditions for a large part of the Nation's <br />freshwater streams, rivers, and aquifers; (2) describe <br />how water quality is changing over time; and <br />(3) improve understanding of the primary natural and <br />human factors that affect water-quality conditions <br />(Leahy and others, 1990). In meeting these goals, <br />This report describes environmental characteris- <br />tics of the Upper Colorado River Basin study unit and <br />the natural and human factors that are considered to <br />affect current (1995) water-quality conditions in the <br />basin. The description of the environmental setting is <br />based on a review of data and reports from Federal, <br />State, and local agencies and industries. For more <br />information on environmental characteristics and <br />water-quality conditions and issues in the study unit, <br />the reader can refer to a bibliography ofwater-related <br />studies within the Upper Colorado River Basin (Bauch <br />and Apodaca, 1995) or to specific literature cited in this <br />report. <br />Abstract <br />