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i • a. The Probable Hydrologic Consequences of Mining at the Coal Ridge #1 tKi ne: The Coal Ridge No. 1 Mine is located adjacent to the Colorado River in Garfield County, Colorado. The location is approximately 7 miles west of Glenwood Springs and 1.5 miles southeast of the town of New Castle. The Probable Hydrologic Consequences section of the original Findings Document describes in detail the local and regional geography, hydrology, and geology, and is incorporated by reference into this document. The surface facilities of the mine are located on the north flank of the Grand Hogback, a geological structure which exposes parts of the Upper Cretaceous Mancos Shale and Mesaverde Group. The elevation of the site ranges from 5,600 feet near the Colorado River to 7,585 feet at the crest of the Grand Hogback. The Mancos Shale is at least 4,000 feet thick in the area, is easily erodible, and intertongues wiUi the lower part of the Mesaverde Group. The lower Mesaverde Group is referred to as the Iles Formation, which consists mostly of shale with several sandstone members known, from oldest to youngest, as the Corcoran, Cozzette, and Rollins Sandstones. The Williams Fork Formation conformably overlies the Iles Formation, and includes in its lower section the Wheeler Coal seam which was to have been mined at Coal Ridge. Above the Wheeler seam are two mappable sandstone members, the Middle and the Upper Sandstones, as well as several uneconomic coal seams. The Wheeler Seam is separated from the underlying Rollins Sandstone by approximately 75 feet of shale and sandstone. In places the Wheeler Seam is split into two seams which total up to 35 feet in thickness. The formations exposed in the Grand Hogback dip to the south and southwest, into the Piceance Basin, at approximately 60 degrees. The depth to the formations in the Basin has greatly limited their potential for water development. Potential aquifers in the section include the Rollins Sandstone, Wheeler Coal, and the Middle and Upper Sandstones. The Middle and Upper Sandstones in the permit area do not yield water, while the Rollins Sandstone and Wheeler Coal typically yield less than 5 GPM, and are saturated only in deeper areas. The Grand Hogback is thought to be principally a recharge zone for these formations. Ground water development in the area is dominated by wells producing from the alluvium of the Colorado River and its tributaries. Water level and quality of the alluvial ground water are closely related to that of the Colorado River surface water. The Probable Hydrologic Consequences section of the original Findings Document stated that mixing of ground waters of the Rollins Sandstone and Wheeler Coal was possible due to fracturing as~~ciated with mine development. However, the mine tunnels extend only 613 feet (N o. 1 mine) and 576 feet (No. 2 mine) into the hogback, and are still approximately 900 feet from the Wheeler Seam. Only very minor, unmeasurable water inflow has occurred up to this time in the No. 2 mine tunnel, and none in the No. 1 tunnel. It is highly unlikely that the tunnels have modified the ground water conditions in the Mesaverde Group.