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Ie . . i . ....- ...,..,.;' l ! . bacteria. Aquatic life inhabiting the river is limited by temperature and suspended solids. Ground Water Ground water quality in the project area varies considerably depending on the local geology. Sandstone Aquifers produce water hign in calcium carbonate, whereas water from shale aquifers is predominantly sodium bicarbonate. Formations containing coal and/or carbonaceous shale usually produce either calcium or sodium sulfate-type waters. These and other bedrock aquifers also contain concentrations of chloride, iron, manganese, nitrate, selenium, and sulfate. Concentrations of total dissolved solids range from 220 to 7,130 mg/L. Alluvial aquifers are the most variable and produce calcium bicarbonate, sodium bicarbonate, and calcium sulfate-type water at concentrations of 150 to 1000 mg/L total dissolved solids. Concentrations of total dissolved solids along with iron, manganese, sulfate, and selenium have exceeded the Public Health Drinking Water Standards in several wells tested. Selenium has been found in two wells within the area, at concentrations just slightly over the .01 mg/L recommended standard for drinking water. Selenium is usually not found in excessive quantities in the geological formations in the project area. It is usually associated with the Animas and San Jose Formations east of the project area. Sulfate, iron, and manganese are associated with the saline and carbonaceous material found in the area. Pro;ect Impacts Animas River Water quality of the Animas River would not significantly change under the proposed project. During construction of project features, some suspended solids would enter the river and increase turbidity temporarily. During project operation small increases in salinity, nutrients, trace elements, and water temperatures are predicted. The water quality changes should not alter downstream water uses. During construction of the Durango Pumping Plant, increases in turbidity and suspended solids and a slight decrease in light transmission in the Animas River are anticipated. Placing of the concrete pad and bottom vanes of the intake structure into the river would not cause any other changes in water quality. Because it is an off-stream site, major construction activity on Ridges Basin Dam would not have a significant impact on the Animas River. The effects of project operation on water quality in the Animas River consist of changes in nutrients, coliform organisms, trace elements, and salinity. Unquantifiable increases in nutrients, coliform organisms, and trace elements are probable because of the increased domestic wastewater treatment plant effluent from Durango and Aztec which would be produced as the cities grow. Low flows in the Animas River, which are critical in waste-loading levels, would not be affected. A slight temperature 12