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-6- <br /> <br /> Hydrogeology <br /> T:,'ae geology of the area of the Colocvyo Coal 1`:ine has been des- <br /> cribed and mapped by Hancock (1925) and Hancock and Eby (1930). <br /> The mine is located in and on the ?9illiams Fork formation, ; <br /> which consists of interbedded lenticular sandstones, sandy ~ <br />I shales, carbonaceous shales and coal beds, most of which are <br />( a few inches to a few feet thick. Zones of baked shale and red <br /> szindstone found in the area are formed by the burning of coal <br />Th <br />hi <br />b <br />d <br />d <br />l <br />i <br />Il <br />f <br />i <br />h <br />l <br />t <br />f <br />i <br /> ea <br />e un <br />er <br />s. <br />y <br />ng <br />ormat <br />on, w <br />c <br />a <br />so cons <br />s <br />s o <br />es <br /> sandstones, shales and coals, contains the only extensive lat- <br /> ex~ally consistent bed. This bed, which is called the Trout <br /> Creek sandstone, is at the top of the Iles formation, about' <br />1 1200 feet below the coals being mined, and crops out approximate- <br /> ly one mile north of the mine. Below the Iles formation is the <br /> Mancos Shale, about 5,600 feet thick. It crops out to the north <br /> in. the Axial Basin. The coals of the {9illiams Fork formation <br /> average from three to twelve feet thick and have a sulfur level . <br />I__ ranging from 0.33 per cent to 0.57 per cent. The soils in the <br /> lease area are naturally calcareous. The pH values at 25°C in <br /> a 1:5 dilution ranged from 7.0 to 8.8, showing their slight ~ <br /> alkalinity. Electrical conductivity indicated only slightly <br /> saline soils; readings were generally less than 1000 micromhos~cm <br />hr (mmhos) (Final EIS, Northwest Coals, 1976). <br /> <br /> Th.=_ regional structure is a series of approximately east-west <br /> oriented anticlines and synclines. The axis of the Axial anti- <br />~_ cline lies about ten miles north of the mine and another anti- <br /> clinal axis occurs about 15 miles south of the mine. In the, <br />i immediate vicinity of the mine are two broad synclinal systems. <br /> 1 Thcese are indicated on Figure 1. The axis of the northwest-, <br />( southwest trending syncline is almost under the mine and they <br />l axis of the northeast-southwest trending syncline lies to the <br /> southeast of the mine. The structural features determine the <br />`- rec{ional direction of ground water flow. The general direction • <br />L ', <br />Leonard Rice Consulting Waler Engineers.lnc <br />\~ <br />