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u • Parachute Site The Parachute Site lies on the southern end of the Piceance Creek Basin, as described in Section 7.2.1, above. In the area surrounding the Parachute Site, more than 20,000 feet of sedimentary rocks ranging in age from Cambrian to Tertiary overlie the basement crystalline rocks (ACOE 1985). The floor of the Parachute Creek valley is lined with relatively thick deposits of unconsolidated soils. These soils were deposited primarily in extensive alluvial fans created by deposition of poorly sorted soil and rock materials carried down tributaries toward Parachute Creek from the canyon slopes during periods of high runoff (ACOE 1985). Geologic Hazards Geologic surface hazards, such as landslides, rockfalls, slumps, soil creep, and mudflows are not known to be active in the project area. The topography of the area is not conducive to mass wasting hazards except during unusually intense periods of precipitation. Along the Parachute Creek valley, landslides and colluvial debris occur along the valley slopes (ACOE 1985). The Piceance Creek Basin is in a region of low seismicity (Simon 1972). The seismic frequency is less than one event per decade per square degree of latitude and longitude. • The fracture density for the Saline Zone of the Parachute Creek Member is very low and is lower than that of the rock formations above the Saline Zone. The lack of fracturing in the Saline Zone will minimize the potential for subsurface subsidence. 7.2.3 Nahcolite Resources The Piceance Creek Basin contains the world's largest and most economically significant nahcolite resource. Conservative estimates of in-place nahcolite in the basin have been reported at 29 billion tons (Dyni 1981). The nahcolitic oil shale has been estimated to cover some 257 square miles of the Piceance Creek Basin (Smith et al. 1973). The thickest and richest nahcolite-bearing stratigraphic intervals are known to occur in the depositional center of the basin in T1S and T2S, R97W and R98W. The Piceance Site encompasses approximately 4,954 acres overlying the depositional center of the basin. Current drill hole data taken from near monitoring well 20-1 and the experimental test cavities indicate the presence of significant sodium resources, with a total saline interval almost 770 feet thick at an average nahcolite content in excess of 26 percent by weight (Dyni 1974). This equates to 333 million tons of nahcolite per square mile. Considering other drill hole data at the Piceance Site, this results in an in-place average nahcolite resource of 313 million tons per square mile for a total Piceance Site resource estimate of some 2.44 billion tons of nahcolite. American Soda, L.L.P. 7-10 Commercial Mine Plan August 18, 1998