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lJIll2566 The set of coal-resource development alternatives shown in table 1 reflects a real istic range of util ization options for the Yampa River basin. Certain assumptions of scale of mines, conversion facil ities, ;lnd transport have been made for allocating coal-production amounts to the various development alternatives. These assumptions playa significant role in the amounts and forms of residuals generated ,and eventually dis- charged to the environment. In the following sections, several of the water-use and res iduals-management aspec.ts of coal-development alterna- tives wi 11 be discussed briefly. Coal Mining and Land Rehabi I itation The bulk of coal development over the next 15 years in the Yampa Riv- er basin will result from surface mining rather than underground mining. The four operations with regard to coal strip-mining are topsoil and veg- etation removal, overburden removal, coal removal, and land reclamation (Freudenthal and others, 1974). Several of the factors affecting resid- uals discharged into the environment resulting from coal-mining alterna- tives include depth of overburden, thickness of seams and the number of seams mined, quality characteristics of coal, size of the operation, and types of equipment used. Residuals generated during mIning include sediment, fugitive dust and exhaust fumes, equipment debris, and used lubrication oil for operating machinery. Increases of concentrations of certain major-inorganic and trace-metal constituents caused by geochemical alterations of overburden and low-grade waste spoils of a mine In the Yampa River basin have been reported by McWorter, Skogerboe, and Skogerboe (1975). Estimated water use for domestic and sanitary purposes during mining and for dust control on roads is 5.3 and 21 litres, respectively, per tonne of coal (I. C. James and others, written commun., 1976). The amount of water used con- sumptively increases by 60 times if land-reclamation regulations in the basin stipulate use of irrigation water to facilitate revegetation, de- pending largely upon the required level of land reclamation. These water- use estimates are in the same order of magnitude as the average estimate of 2.34 million cubic metres per million tonnes of coal (Freudenthal and others, 1974), when some irrigation for land rehabil itation is assumed. In surface mining of ,'coal, primary environmental impacts involve the effects of vegetation and overburden removal. Impacts include generation of airborne fugitive dust and increased waterborne sediment. Much of the potential sediment resulting from surface mining and construction of rail- roads and highways, conversion facil ities, and expanded urban centers may be mitigated by various means. For example, the Northwest Colorado Coal EIS estimated that more than 10,100 hectares of land surface would be disturbed by mining of coal and construction of plants, roads, and related facil ities during 1976-90. Overall, that study estimated that about 20 percent of sedi'ment loads 'generated by such activities would be discharged to the stream systems. During the 15-year period, residual-sediment load- ings due to increased coal-resource and related economic development were estimated to exceed 45,000 tonnes, and annual rate of discharged sediment is expected to increase nearly threefold over this period. However, this 6 ."'