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<br />~ mountains generally are thin and poorly developed and <br />o primarily are a product of physical weathering of rocks , <br />W Soils in the Colorado Plateau are thicker and are <br />fonned on deposits of recent geologic age, Suspended <br />sediment in the basin predominantly is a result of <br />channel erosion and soil erosion from overland flow, <br />Generally, suspended-sediment concentrations <br />increase from the eastern edge of the Colorado Plateau <br />physiographic province to the outflow of the basin at <br />the Colorado-Utah State line, Suspended-sediment <br />concentrations are smallest during base-flow condi- <br />tions and largest during spring runoff when streamflow <br />discharges are large and sediment is available, Soils in <br />the agricultural areas of the basin contain soluble salts <br />that could greatly affect the concentrations of sodium <br />and calcium in the surface and ground water, <br /> <br />Human Factors <br /> <br />Human factors can adversely affect water quality <br />a~ a result of point and nonpoint sources of chemical <br />constituents, Because the economy of the mountainous <br />region depends on outdoor recreation and water-based <br />activities, such as fishing, white-water boating, flat- <br />water boating, camping, and hiking, this area is a prior- <br />ity to the State's water-quality program, For example, <br />State water-quality standards for aquatic life have nol <br />been met for cadmium, copper, lead, and zinc in <br />streams downstream from active and abandoned mines <br />in the headwaters, In addition, many of the shallow, <br />unconfined aquifers in Colorado have become contam- <br />inated with nitrates and salinity resulting from agricul- <br />tural activities (Colorado Depanment of Health, 1992), <br />Human factors also can improve water quality; for <br />example, reselVoirs can trap sediments and metals, <br />resulting in downstream reaches having better water <br />quality than the upstream reaches, <br />Human factors can be described according to the <br />water and land uses discussed earlier in this report, <br />Interbasin water transfers, mining, urbanization, and <br />agriculture are the principal activities that affect water <br />quality in the basin, In the Upper Colorado River <br />Basin, these activities occur approximately in a down- <br />stream order, Interbasin water transfers are in the head- <br />waters, mining is located in the mountainous areas, <br />urbanization is in the Southern Rocky Mountains and <br />Colorado Plateau, and agriculture predominantly is in <br />the valleys of the Colorado Plateau, <br />Because interbasin water transfers generally are <br />made near the stream headwaters, the amount of <br />streamflow diverted can be a substantial part of the <br />streamflow near these sources; however, the effect <br />decreases farther downstream as the volume of flow <br /> <br />increa~es, Diversions from the ba~in account for about <br />12 percent of the mean annual streamflow at the <br />Colorado River near the Colorado-Utah State line, <br />The Alva B, Adanls Tunnel, which diverts the largest <br />anlOunt of water in the entire study unit, may be the <br />cause of increases in dissolved-solids concentrations <br />in the Colorado River near Glenwood Springs <br />(Liebennann and others, 1989), Although 9,000 tons <br />of dissolved solids are removed annually from the <br />Upper Colorado River Basin through the Alva B, <br />Adams Tunnel, the principal effect of this diversion is <br />the removal of relatively pure water from the Colorado <br />River system, <br />Mining practices have affected water quality in <br />several parts of the basin, The headwaters of several <br />tributaries to the Colorado River such as the Blue, <br />Eagle, Roaring Fork, and Gunnison Rivers drain one of <br />the primary metal-mining regions in Colorado, A large <br />number of active and abandoned metal mines exist in <br />this region, which is referred to as the Colorado <br />Mineral Belt. Metal-mining activities usually arc in <br />areas ofhigh precipitation, resulting in a greater risk of <br />perennial or ephemeral mine drainage as well a~ stonn- <br />induced mine drainage from mine dumps and tailings, <br />Streams have been affected by point-source mine <br />discharge and nonpoint-source runoff from mined <br />area~ (Wentz, 1974), Concentrations of cadmium, <br />copper, iron, lead, manganese, mercury, molybdenum, <br />and zinc exceed State water-quality standards for local- <br />ized reaches of these streams (Colorado Water Quality <br />Control Division, 1989), Some reaches in the basin, <br />such as Red Mountain Creek near Ouray, are affected <br />by acid mine drainage, Although local reaches of these <br />streams have been affected, little is known about the <br />transport of these metals downstream into the larger <br />tributaries and the Colorado River, <br />Coal mining in the area can affect water quality <br />by increases in dissolved solids, particularly sulfate, <br />and increases in trace-element concentrations, There <br />are a number of active oil and gas fields and large <br />deposits of oil shale, primarily in Garfield County, <br />Although the effects from oil and gas drilling on the <br />surface and ground water can be considerable locally, <br />little is known as to the areal extent of the effects from <br />this activity, Uranium mining was once active in the <br />basin, and mining and milling wastes pose serious <br />threat~ to ground water from radionuclide contamina- <br />tion, High radium concentrations occur in shallow <br />aquifers in Montrose County in association with <br />uranium mining and milling operations (Colorado <br />Deparunent of Health, 1992), <br />Urbanization has an important effect on the <br />water quality of the study unit. Population is increas- <br />ing at a rate of about 10 percent annually in some of the <br /> <br />IMPUCATIONS OF ENVIRONMENTAL SETTING ON WATER QUAUTV 29 <br />