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Ground water Hydrology <br />Ground water information is found in the following portions of the permit <br />application: Sections 2.04.5, 2.04.7, 2.05.6, 4.05.11 through 4.05; and <br />Exhibit 7. <br />Ground water at Colowyo occurs as isolated, perched aquifers in interbedded <br />and lenticular sandstones and coals and within isolated alluvial aquifers. <br />Base flow in the two perennial streams in the general area comes mainly from <br />ground water discharge from alluvial aquifers in the stream valleys. <br />Stratigraphically, the Trout Creek Sandstone is the major, regional aquifer in <br />the area. It is approximately 800 feet beneath the lowest coal seam to be <br />mined. The principal recharge for the aquifer is to the south of the permit <br />area in the headwaters of Taylor and Goodspring Creeks. There is no <br />continuous, regional ground water system on the permit area above the flood <br />plain of Goodspring Creek. Information contained in the permit application <br />and the Northwest Colorado EIS indicates that, in test holes drilled by W.R. <br />Grace and Company and the USGS, no saturation was encountered in any of the <br />beds to be mined. <br />The Trout Creek Sandstone outcrops north of the permit area, where ground <br />water is discharged at the surface. The Mancos Shale underlies the Iles <br />Formation and forms the base of the regional ground water system in the area. <br />This shale is exposed at the surface north of the permit area, in the southern <br />limb of the Axial Basin Anticline. Due to the impervious nature of the Mancos <br />Shale, ground water flow in either the deep bedrock units of the Williams Fork <br />and Iles Formations, or in the alluvial aquifers of Goodspring and Wilson <br />Creeks, is discharged to the streams where they flow across the Mancos Shale. <br />Surface Water Hydrology <br />Surface water information is found in the following portions of the permit <br />application: Sections 2.04.5, 2.04.7, 2.05.6 and 4.05; Maps 11, 12, 12A, 32 <br />and 37; and Exhibit 7. <br />The permit area is drained by two perennial streams; Goodspring Creek to the <br />east and Wilson Creek to the west. Taylor Creek, an intermittent stream, <br />flows into Wilson Creek north of the rail loadout. Several ephemeral <br />drainages occur on the permit area, including the Streeter Drainage. The <br />lower portion of the drainage has been relocated as a result of an excess <br />spoil fill at the mouth of Streeter Canyon, near the confluence of Streeter <br />Drainage and Goodspring Creek. These drainages are tributaries to Milk Creek, <br />which flows into the Yampa River which is located about seven miles north of <br />the permit area. Precipitation averages 18 inches annually on the property <br />and runoff is limited. Flows in the drainages are mainly in response to snow <br />melt or intense thunderstorm events. <br />Water sampled from the drainages is quite hard, dominated by calcium and <br />magnesium cations and bicarbonate and sulfate anions. The relatively high <br />alkalinity and pH of the system impedes the solubility and transport of heavy <br />cations, thus minimizing potential toxicity problems associated with heavy <br />metals or acid drainage. <br />-5- <br />