GENERAL32057 - Laserfiche WebLink

Home Browse Search

The next underlying zone, which is approximately 2-20 ft. in thickness, exhibits moderate disintegration and contains numerous points and slickened sides. This zone generally has undergone moderate weathering and has become weaker, and is especially unstable in the presence of water. The third and lower most zone has more widely spaced joints and slickened sides. Surface moisture content and thus the degree of weathering is variable end not as extensive in this zone. This material exhibits an overall higher strength then the overlying weathered clay materials. No preferred orientations of slickened sides, point planes or fault plane surfaces have been determined in the Brea, however, regional geological structure may suggest strike orientations of larger features (faults, etc.) in a northwest-southeast direction. Physical and chemical properties of the stratum within the overburden and interburden ere found at the end of Section 4.4 Individual Laramie coal beds ere often lenticular, do not extend laterally for any great distance and vary considerably in thickness. Areas free of coal were probably channel end channel-margin environments consisting of fine to coarse grained sandstones. Fine, well cemented sandstone boulders encountered in the Keenesburg Mine active pit are representative of channel environments. Light gray claystones • (generally massive in the Denver Basin) were deposited in well dr-i^°d swer.~s, and light colored silts and c].a;/s d°po=+.*°d ^n levees. The cool, developed from peat layers, along with dark gray, organic rich claystones and clay-shales, accumulated in poorly drained swamps in overbank or flood bank areas. Some coal deposits may hove been developed in abandoned channels. The thickest coal beds were formed in more stable parts of the swamp. The Laramie sandstone and Fox Hills sandstone (Laramie-Fox Hills aquifer) lie approximately 210 foot below the expected maximum depth of mining and should not be affected by ash disposal activities. The Laramie Formation overlying the Fox Hills Sandstone consists of yellow-brown and gray to blue-grey soft carbonaceous shale and clay-shales interbedded with sand and shaly send. It contains cross-bedded gray to buff sandstone, which is slightly to well-cemented, and contains coal seams in the lower portion. The Laramie forms the bedrock across ell of the mine site end ~is covered by unconsolidated Tertiary and Quaternary deposits consisting of dune sand, alluvium and terrace deposits dipping slightly westward. All beds below the Tertiary end Ouaternery • deposits dip slightly to the west. -10-