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..,C' "7 rJflc,'ab incremental increase in sediment yield represents less than 0.2 percent of the estimated ambient sediment yield for the entire basin (Iorns and oth- ers, 1965). Coal Processing Depending upon ultimate ,disposal of the mined coal, various degrees of processing may be required. Because the moisture content of the coal in the Yampa basin is relatively high, the coal may have to be dried dur- ing crushing and pulverizing stages for preparation either for coal gasi- fication or for. electric-power generation by coal-fired steam turbines. Coal transported by rail or slurry pipeline may have to undergo other forms of processing, such as crushing. The amounts of generated residuals and consumptive water use in coal processing are less than in other com- ponents of coal utilization. Coal-Conversion Alternatives The quantities and forms of residuals generated from the two basic energy-conversion a,lternatives evaluated for the Yampa River basin (elec- tric-power generation by coal-Hred steam turbines and coal gasification) vary considerably. The residuals-management analysis by the U.S. Geologi- cal Survey describes the processes for standard-sized conversion facili- ties and gives preliminary estimates of water-use requirements for the various processes as a function of the assumed environmental controis for both air and water and for alternative levels of residuals treatment. Ad- ditional guidelines as to water requirements for coal-conversion process- es also are reported by Freudenthal, Ricciardell i, and York (1974), and Davis and Wood (1974). The various coal utilization and water require- ments for convers i on are pr ima ril y dependen t upon assumed load factors, efficiencies of conversion, and scale of plants. The ramifications of these factors from an environmental-impact standpoint are being studied in more detail in the Yampa River basin assessment (Steele, James, Bauer, and others, 1976b) with specific examples given later in this paper. Electric-Power Generation Waste heat from steam turbines used for electric-power generation is dissipated by a condenser-cooling system. The particular cool ing-system design for a given plant is highly dependent upon water availabil ity and environmental constraints. Alternative cooling systems included in the analysis are once-through 'cool ing, evaporation ponds, and mechanical-draft or natural-draft towers (Freudenthal and others, 1974). Plant .operating modes being evaluated include assuming no constraints on residuals dis- charges to the environment, and assuming no discharge of 1 iquid residuals and flue-gas treatment to comply with present Colorado State air-quality standards. Stack gases, waste heat, and ash are the major forms of residuals from plants using steam turbines to convert coal to electric power. In order to comply with air-qual ity standards, sulfur gases emitted through coal combustion may be treated in a wet-scrubbing system using such coag- 7 ,I