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2.04.7 HYDROLOGY INFORMATION • This section provides a description of the ground and surface water hydrologic systems including specific topographic, lithologic, and structural factors, which affect water quality and quantity in the RAG EC permit adjacent, and regional areas. The regional and site specific hydrologic information presented herein is the result of research from available literature and records, exploration drilling, development, mining, testing of wells, and various field studies and ongoing monitoring work. The following hydrologic description details: the depth, extent, and characteristics of ground water aquifers, the quality and quantity of groundwater resources, the seasonal variations in Flow and water quality of azea streams, data on surface and ground water use in the area, and the location of hydrologic monitoring sites monitored by RAG EC. Ground Water Resources General Description of Aquifers in the Permit Area A total of four (4) sandstone aquifers underlay the RAG EC pennit area, all of which are Cretaceous in age. These sandstone aquifers are, in ascending order: Trout Creek Sandstone Middle Sandstone Twentymile Sandstone White Sandstone All four (4) sandstone aquifers outcrop within the permit boundary, generally on the valley walls of the Yampa and Williams Fork Rivers. Generally, the sandstone aquifers dip gently to the northeast, toward the center of the structural basin. The hydraulic properties of bedrock aquifers in the region are presented on Table 1 I, Aquifer Characteristics in the Region. • These sandstones have similar lithologic characteristics consisting of very fine to medium grain calcium carbonate cemented sandstone. The sandstones are separated from underlying and overlying sandstone units by sil[stone and shale interbeds. The relative position and thickness of each sandstone unit is indicated on Figure 11, Typical Stratigraphic Section found in Section 2.04.6 Geology Description. The relative position of the "E" and "F" coal seams being/to be extracted at the No. 5 and No. 6 mines are shown on [his Figure. Hydrologic properties of these sandstone aquifers generally result from the primary permeability and storativity of the sandstone and from fracturing, which locally renders them more permeable. Yields of wells in the sandstone aquifers are variable due to the heterogeneity in [he hydrologic properties resulting from local fracturing and faulting. All of the sandstone aquifers are artesian throughout most of the permit area, and many of the wells drilled in the valley bottoms flow at ground surface. Ground water levels have declined in both the Middle and Trout Creek Sandstones. This decline is probably related to drainage of the sandstones to the No. 5 and No. 6 mine workings. Water levels also appear to have dropped slightly in [he Trout Creek Sandstone due to continued use of the aquifer for mine water supply. There are other unnamed sandstone units underlying the RAG EC permit area; however, these sandstones are thin and generally discontinuous. Where saturated, these sandstones can store and transmit water, but their role as aquifers is minor because of their limited thickness and discontinuous nature. There are up to 42 coal beds underlying the permit area. These coals range in thickness from less than I foot to as much as 20 fee[. For [he most part, the coals are more continuous than the sandstones. The coal beds can stare and transmit water; however, the coal beds are not used for water supply in the permit or immediate area because they are thin relative to the sandstone unit. • Permit Renewal No. 3 2.04-11 Revised 7/10/00