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5/ L/ III IIIIII'IIIIII'll Doc Date:12/11/2001 <br />-(-- -- - -, - ~~ sss <br />2.04.7 HYDROLOGY INFORMATION <br />Occurrence of Groundwater <br />General Area <br />Colowyo Coal Company's general area of operation is defined by the <br />area bounded by Goodspring and Wilson Creeks, both of which are <br />tributaries to the Yampa River. The mine permit area and its <br />relationship to Goodspring and Wilson Creeks are shown on Map 32. <br />Colowyo Coal Company's mining operations are in an area of limited <br />hydrology. Precipitation averages 21.5 inches for the drainages in <br />the "general area" and runoff is limited. Flows in Wilson, Taylor <br />and Goodspring Creeks are mostly from snowmelt or thunderstorm <br />events. Groundwater resources on and adjacent to the mine property <br />are also limited. Base flows observed in Goodspring and Wilson <br />Creeks are mostly groundwater discharged from the thin and limited <br />alluvial/colluvial aquifers that can be found in the valleys of <br />both creeks. There are no known places of groundwater discharge <br />from bedrock units to Goodspring, Taylor, or Wilson Creeks from the <br />sandstones between the coals to be mined. <br />Rocks on the property are part of the Mesa Verde Group. These rock <br />units are almost entirely interbeds of sandstones and shales. The <br />uppermost geologic unit in the permit area is the Williams Fork <br />Formation. The coals to be mined on the property are part of the <br />Fairfield Group, the principle coal-bearing zone in the area. The <br />sandstones are predominately fine to medium-grained, poorly sorted <br />and calcareous. In the upper part of the formation they are <br />generally channel sandstones and exhibit unilateral and vertical <br />continuity. In the lower part of the formation the sandstones are <br />more continuous than in the upper part. The thickness of the <br />Williams Fork Formation, in the general area, is estimated to be <br />about 1600 feet. <br />Underlying the Williams Fork Formation is the Iles Formation. <br />Little data are available to describe the characteristics of the <br />Iles Formation, principally because of its great depth. However, <br />based on information from adjacent areas, the general <br /> <br /> <br />2.04.7-1 <br />