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ilJ?7~O Assessment of Impacts of Proposed Coal-Resource and Related Economic Development on Water Resources, Yampa River Basin, Colorado and Wyoming-A Summary Compiled and Edited by Timothy Dock Steele and Donald E. Hillier :\HSTRACT Expanded mining and use of coal resources in the Rocky Mountain region of the western United States will have substan- tial impacts on water resources, environmental aInenities, and social and economic conditions. The U.S. Geologica! Survey has completed a 3-year assessment of the Yampfl River basin, Colorado and Wyoming. where increased coal-resource develop- ment has begun to affect the environment Clnd quality of life. Economic projections of the overall effects of coal-resource development were used to estimate water use and the types and amounts of waste residuals that need to be assimilated into the environment. Based in part upon these project-ions, several physical-based models and other semiquantitative assessment. methods were used to determine possible effects upon the basin's water resources. Depending on the magnitude of mining and use of cool resources in the basin, an estimated 0.7 to 2.7 million tons (0.6 to 2.4 million metric tons) of waste residuala may be discharged annually into the environnlent by coal-resource development and associated economic activities. If the assumed development of coal resources in the basin occurs, annual cOllBumptive use of water, which was apprOXimately 142,000 acre-feet. (175 million cubic meters) during 1975, may almost. double b)' 1990. In a related analysis of alternative cooling systems for coal- conversion facilities, four to five time8 as much water may be used consumptively in (I wet-tower, cooling-pond recycling system as in once-through cooling. An equivalent amount of coal transported by slurry pipeline would require about one-third the water used consumptively by once-through cooling for in-basin conversion. Current conditions and a variety of possible changeg in the water resources of the basin resulting from coal-resource development were assessed. Basin population may increase by as much as threefold between 1975 and 1990. Volumes of wastes requiring treatment will increase accordingly. Potential problem8 associated with ammonia-nitrogen concentrations in the Yampa River downstream from Steamboat Springs were evaluated using a waste-load assimilative-capacit.y model. Changes in sediment loads carried by streams due to increased coal mining and construction of roads and buildings may be ap- parent only locally; projected increases in sediment loads relative to historic loads from the hasin are estimated to be 2 to 7 percen t. Solid-waste residuals generated by coal-conversion processes ZUld disposed of into old mine pits may cause widely dispersed ground-water contamination. based on simulation-modeling results. Projected increases in year-round water use will probably result in the oonstroction of several proposed reser- voirs. Current seasonal patterns of streamflow and of dil'lsolved- solids concentrations in streamflow will be altered appreciably by these reservoirs. Decreases in time-weighted mean~annual dissolved-solids concentrations of as much as 34 percent are an- t.icipated, based upon model sinluJations of several configura- tions of proposed reservoirs. Detailed st.atist.icalanalyses ofwater~quality conditions in the Yampa River basin were made. Regionalized maximum water- Quality concentrations were estimated for possible comparison with future condit-ions. Using Landsat imagery and aerial photographs, potential remote-sensing applications were evaluated to monitor land-use changes and to assess both snow cover and turbidity levels in s.treams. TIle technical information provided by the several studies oft.he Yampa River basin assess- ment should he useful to regional pl81lners and resource managers in evaluating the pos8ible impacts of development on the basin's water resources. INTRODUCTION Water is an important resource contributing to the physical and economic well-being of any region. The amount and quality of "available" water are factors affecting the economic development. that may occur. With time, economic development will affect the water resources of a region through withdrawals and consumptive use of water in various economic activities and discharge of waste residuals (that is, byproducts of a process that have no economic value) that eventually may enter the hydrologic system (Kneese and Bower, 1968). The Yampa River basin in northwestern Colorado and Bouthcentra! Wyoming is a region of natural beauty which has remained largely unaf- fected by the activities of humans (fig. lA-C). Its