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. . at a trading disadvantage, the San Juan Basin will not likely become a higWy industrialized or densely populated area. No mitigation would be required with the adoption and implementation of the flood control operations as described in the water control manual because there are no significant impacts to socioeconomics. . 4.7 Water Quality. The chemical, physical, and biological properties of surface water at any given point are the product of a multitude of factors, including geography; geology; climatic conditions; discharge; floral and faunal communities; ground water supply; and, of major significance, the effect of humans, their activities, and their domestic animals. Both the chemical and biological qualities of the Uncompahgre River are fair in the upper reaches, but gradually degrade in a downstream direction. This is typical for most San Juan Basin streams and consistent with the general rule that the amount of solids and bacterial and algal growth increases from material and man- made sources as water flows downstream. Pollution by mine drainage, alkaline runoff, agricultural wastes, and occasional construction activities in the basin has caused water quality in Ridgway Reservoir and the Uncompahgre River to deteriorate, Mining activities and natural runoff contribute copper, iron, aluminum, zinc, manganese, arsenic, selenium, silver, lead, chromium, and cyanide to the reservoir. A primary source of these pollutants is Red Mountain Creek, which flows through an area of historically intense mining activities and enters the river 15 miles upstream from the reservoir. The diluting effects from cleaner tributaries entering the Uncompahgre at and below the town of Ouray tend to decrease overall heavy metal concentrations. Except for Red Mountain Creek, waterways associated with the project have an alkaline pH. This alkaline characteristic decreases the overall heavy metal threat to biological activity throughout the aquatic ecosystem. With this alkalinity, the heavy metals and other toxic substances tend to precipitate into fonns unavailable for biological uptake. As long as the water remains alkaline, the threat of heavy metal contamination to the food chain is decreased. . Data obtained from the Colorado Department of Health for the Uncompahgre River at Ridgway show that concentrations of sulfates, ammonia nitrogen, iron, and manganese occasionally equal or exceed the limits recommended for drinking water by the U.S. Public Health Service. For aquatic life, such as fish, these data indicate that. zinc and ammonia nitrogen conCentrations have exceeded recognized limits. At Ridgway, water quality testing in the past has shown a concentration of aluminum as high as 5.2 mg!1 on one occasion prior to 1968, arsenic as high as 0.03 mg/l, selenium as high as 0.01 mgfl, and lead as high as 0.03 mg!I. These data indicate that periodically the concentrations of arsenic, cyanide, and selenium have exceeded or equaled the U.S. Public Health Standards for drinking water; and concentrations of aluminum, cyanide, and selenium have exceeded the generally recognized standards for aquatic life. Because the high concentrations of heavy metals and toxic elements recorded by all sampling agencies are short term, sporadic, and deviate from the norm,. 13 .