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construct mine portals and other facilities to support an underground mine is not considered surface <br /> mining; and the PSC reclamation bond includes any remaining facilities from the Seneca II Mine. <br /> Topography <br /> The PSC permit area is located in the Yampa Coal Field, on the southern margin of the Sand Wash <br /> Basin in the foothills of the Williams Fork Mountains. The Williams Fork Mountains extend <br /> approximately 30 miles from east to west across northwestern Colorado. Elevations in the permit <br /> area and adjacent areas are between 6,600 feet and 7,800 feet. The average elevation of the permit <br /> area is approximately 7,040 feet. Most of the permit area is covered by rolling hills with <br /> agricultural fields and rangeland. These low hills extend to higher elevation ridges and steep <br /> slopes in the eastern and southwestern parts of the permit area. The perennially flowing Grassy <br /> Creek crosses the permit area from south to north, and is joined by its two ephemeral tributaries, <br /> Little Grassy Creek and Scotchman's Gulch, near the northern boundary of the permit area. The <br /> lower portion of Little Grassy Creek within the permit boundary has perennial flow as a result of <br /> coal spoil spring inflow from Pond 002 on lands transferred from the Seneca II Mine to the PSC. <br /> Grassy Creek flows into the Yampa River two miles north of the permit area. The Yampa River is <br /> one of the largest tributaries of the upper Colorado River system. <br /> Geologic Setting <br /> Section 2.04.5 of the PSC permit application describes the geology and hydrology in the permit <br /> and surrounding areas, which includes information from the following two U.S. Geological Survey <br /> Water-Resources Investigations Reports (WRIRs): Hydrology and Geochemistry of a Surface coal <br /> Mine in northwestern Colorado_ WRIR 92-4187, by R.S. Williams, Jr. and G.M. Clark and <br /> Geohydrologic Evaluation of the upper part of the Mesaverde Group, Northwestern Colorado. <br /> WRIR 90-420, by S.G. Robson and Michael Stewart. <br /> The PSC permit area extends from the crest of the Tow Creek anticline westward to the axial area <br /> of the Hayden syncline. This area is on the southern edge of the regional Sand Wash structural <br /> basin. The local stratigraphic sequence exposed at the surface is of Cretaceous age. The sequence <br /> is,in ascending stratigraphic order,the Iles Formation, Williams Fork Formation, and Lewis Shale. <br /> The Iles and Williams Fork Formations are part of the regionally extensive Mesaverde Group. <br /> Quaternary alluvial deposits, generally derived from the Mesaverde Group, are locally present in <br /> stream valleys. Recent colluvial slides and slumps may also be present in canyons and gulches <br /> throughout the area. <br /> The Seneca II Mine extracted coal on approximately 1,800 acres of land that was transferred to the <br /> PSC. Coal seams were surface mined at the Seneca II Mine from the lower member of the Williams <br /> Fork Formation. The lower member of the Williams Fork Formation is approximately 300 feet <br /> thick in the permit area. Approximate thicknesses of the coal seams, in ascending stratigraphic <br /> order are: the Wolf Creek seam, 15 ft;the Wadge seam, 10 ft; and the Lennox seam, 4 ft. Shale, <br /> siltstone, and sandstone separate the coal seams. The Wadge seam is approximately 150 above the <br /> Wolf Creek seam and approximately 40 feet below the Lennox seam. The PSC planned to mine <br /> coal from the Wadge seam in the Hayden syncline. <br /> Page 6 of 27 <br />