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Following is a summary of the probable hydrologic consequences of the Meadows IJo. 1 Mine and the Eckman Park Mine Complex Cumulative Hydrologic Impact Study. Probable Hydrologic Consequences The Yampa River Basin is an area of intensive coal mining activity. Section 34-33-114(2) of the Act requires that the Division assess the potential cumulative impacts that these mines might impose upon the hydrologic system. The following assessment focuses on the potential cumulative impacts on the ground water and surface water resources of the Yampa River Basin. Description of Ground Water Resources The study area for this assessment is essentially the Yampa River Basin from Steamboat Springs to May bell, Colorado. Figure 1 shows the study area and the locations of the coal mines in the basin. Table 1 lists the coal mines and their status and production levels. Figure 2 is a generalized stratigraphic column for the Yampa River Basin. Figure 3 is a cross-section which shows the relationship of the mined area to the Trout Creek Sandstone - the nearest regional aquifer. Ground water occurs in both bedrock and alluvial aquifers in the study area. Regional bedrock aquifers include the Trout Creek sandstone, the Middle sandstone, the Twentymile sandstone, and the White sandstones. Many other strata are also water-bearing. However, they either yield insufficient amounts of water to wells, or are not continuous through the basin and, therefore, cannot be considered regional aquifers. Post-depositional folding of these strata has resulted in the formation of several bedrock ground water sub-basins. Generally, these sub-basins constitute separate ground water basins with individual recharge and discharge areas. This tends to localize bedrock ground water and inhibit regional flow patterns. The Meadows Mine is located on the eastern flank of the Hayden Syncline, a sub-basin of the Sand Wash basin. Currently, four other mines are at least partially located within the Hayden Syncline: the Seneca II, the Grassy Gap, Seneca II West, and the Hayden Gulch mines. All of the mines obtain coal from the Mesa Verde formation. Operators at Meadows and Grassy Gap mined coals in the lower coal group, below the Trout Creek sandstone. The two Seneca mines obtain coal from the middle coal group, and at Hayden Gulch coals were mined in the upper coal group, above Twentymile sandstone. Transmissivities of the bedrock aquifers are usually low. High yields are only obtained in wells completed in fracture zones. The aquifers usually exhibit confined artesian characteristics, except near outcrops. Many wells completed in the aquifers discharge water at the surface. Water quality in the aquifers is usually too poor for domestic purposes, marginal for irrigation purposes, and acceptable for stock watering purposes. -7-