1997-12-10_GENERAL DOCUMENTS - C1981041

Home Browse Search

a settlemettt agreement. The most recent OSM recommendation was"Other", meaning that OSM checked the accuracy of the system data,but because of the U.S.Court of Appeals recent ownership and control decision, OSM cannot recommend a permit block. Description of the Environment Geographic Setting The Roadside North and South Portals Mine complex lies in the alluvial valley of the Colorado River along Interstate 70 ([-70)just east of the town of Palisade. The river and interstate trend northeast to southwest through the mine area, with the North Portal facilities and mine workings located to the west and north, and the South Portal facilities and mine workings to the east and south. Located 12 miles from Grand Junction, the mines are situated in DeBeque Canyon in the Bookcliffs, a ridge comprised of varicolored shales and sandstones trending northwest-southeast. The Bookcliffs border the Grand Valley to the east where the Colorado River exits the highlands of the cliffs and enters the valley. Mount Garfield, a prominent peak in the Bookcliffs, lies southwest of the mine site and serves as the southwestern corner of the Piceance basin to the north. The mines can be located on the USGS 7.5 minute quadrangle maps labeled "Cameo" and "Palisade." The Bookcliffs coal field is characterized by a monoclinical structure with the strata dipping gently to the northeast. Exhibits 13 and 14 of the permit application illustrate the surface geology and geologic structure of the permit area. The mine's surface facilities are located on and adjacent to the alluvial valley floor of the Colorado River. The river alluvium ranges from a clayey to silty sand and contains scattered gravel and cobble-sized fragments. The depth of the alluvium ranges from nine to sixty feet beneath the surface disturbed areas. Historically, the valley has been mined for coal since the late 1800's, so the alluvial valley floor has been altered and affected by these operations. The Cameo power plant,a customer for coal mined at Roadside, lies just west of the mine site along Interstate 70. Geology Nearly the entire surface of the permit area consists of the Mesaverde Formation, a sequence of interbedded shales, siltstones and sandstones, indicative of a marine/alluvial depositional environment. Further to the south, the Wasatch and Ohio Creek Formations outcrop on the surface. The Roadside operation mines the Cameo coal seams found in the Mount Garfield Formation of the Mesaverde Formation of sandstones, coal and shales. The Mount Garfield Formation is an example of the transitory nature of many oceanic transgressions and regressions from the Cretaceous geologic period. The Mount Garfield Formation ranges in thickness from 472 to 536 feet in the permit area and consists of three coal zones intertonguing with three prominent sandstone members. From the top to the base, the formational sequence is as follows: the Carbonera coal seam, (stmtigraphic marker of the top of the Mount Garfield sequence), a 64-foot sandstone/shale sequence, the Cameo coal seam, 9 to 12 feet thick, Rollins sandstone member, about 114 feet thick, another shale/sandstone sequence, followed by the cliff-Forming Palisade sandstone which is 139 feet thick. Beneath the Palisade sandstone member, named for the town nearby, is the Palisade coal seam and then the Sego sandstone which forms the base of the Mount Garfield Formation. The 11