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., ~• • Existing and proposed coal mining attached Figure 1, include: Mine File No. Newlin Creek C-045-81 Dorchester No. 1 C-014-81 Twin Pines No. 2 C-058-83 G.E.C. Strip C-037-81 -15- operations in the general area as shown on Operator • A. Geology Harrison-Peltron Joint Venture, Dorchester Coal Company Twin Pines Coal Company, Inc. G.E.C. Minerals Geology of the Canon City Coal Field is expressed by a belt of sedimentary rocks of Cretaceous age. the Trinidad Sandstone and the Vermejo Formation (see Figure 4). These units are overlain by the Raton and Poison Canyon Formations of Paleocene age. The Yermejo Formation, which contains eleven coal seams of mineable thickness, lies conformably on the Trinidad Sandstone. The Trinidad Sandstone is thick, horizontally extensive and is relatively permeable. Transgression of the sea over the sands resulted in the development of the Vermejo Formation, a prograding coastal lagoonal deposit intersected by deltaic erosion and depositional features. As a result of this depositional environment, coal deposits which are lenticular and discontinuous were formed. The coal outcrops are obscurred by piedment alluvial-colluvial material from zero to 120 feet in thickness derived from erosion of the mountains to the west. Structurally, the Canon City Coal Field is a closed eliptical synclinal basin bounded on the west and south by the arcuate border of the Wet Mountains. The mountains, formed of Precambrian metamorphics, were thrust up and over the younger coal bearing elastics of the Yermejo Formation, thus developing the Chandler Syncline. The doubly plunging asymmetrical syncline trends approximately north-south with a steeply inclined (nearly vertical and sometimes overturned) western limb and a much more gradual dip of from 6 to 10 degrees on the eastern limb. The Dorchester No. 1 permit area lies on the southern terminus of the Chandler Syncline. 6. Ground Water Three categories of potential groundwater aquifers occur in Lhe Canon City Coal Field. These are; 1) The Trinidad Sandstone, 2) lenticular, discontinuous sandstones and coals of the Vermejo and Raton Formations, and 3) localized, shallow alluviwm along drainages. The first water-bearing zone, the Trinidad Sandstone, is the most extensive aquifer in the region. A few domestic wells within the general area tap the Trinidad Sandstone near the Arkansas River, approximately nine miles north of the permit area. These wells have yields ranging from 20 to 100 gallons per minute. Data on the Trinidad Sandstone from the Raton Basin indicate permeabilities of 1 to 200 millidarcys. This sandstone formation lies approximately 350 feet below the lowest coal seam to be mined by any of the proposed mines. Because of the stratigraphic distances between the Trinidad Sandstone and the coat seams proposed for mining and the existence of many aquitards between the units, the probable hydrologic impact to the Trinidad Sandstone as a result of the proposed mining in the Canon City Coal Field is negligible.