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' CNAP'iEBFOUR Environmental Consequences <br />' Additionally, it was determined that subsurface collapse in and surrounding the solution cavities <br />would not likely cause caving in the Mahogany Zone (approximately 550 feet above the roof of <br />the solution cavities) but could induce fracturing in this formation (Agapito 1998a). <br />' Several methods of mining oil shale which were carried out in the past in the Piceance Creek <br />Basin included: <br />• conventional mining with above-ground retorting <br />• modified in situ retorting <br />• (true) in situ methods <br />Conventional mining was conducted at several pilot operations (Unocal, Colony, Anvil Points, <br />Mobil, etc.) on the southern boundary of the Piceance Creek Basin. They all targeted the rich <br />Mahogany Zone between the A- and B- Grooves. Conventional mining used drill-and-blast <br />mining with truck haulage and room- and- pillar layout with above-ground retorting (Agapito <br />' 1998a). <br />Mining of oil shale using modified in situ retorting was demonstrated by Occidental Oil Shale, <br />Inc. at Logan Wash and Rio Blanco Oil Shale Co. at the Ca tract and was planned at the Cb tract <br />' by Occidental Oil Shale, Inc. and others. Multi Minerals, Inc., who had control of the White <br />River Nahcolite lease adjacent to the Yankee Gulch Lease, based an unapproved mine plan on <br />this concept in the 1970's. With the modified in situ method, after solution mining the nahcolite, <br />~' the cavity contains rubblized, porous, permeable oil shale available for in situ retorting (Agapito <br />' 1998a). <br />True in situ methods include both multiple and single borehole methods. Heating of the rock <br />mass can be accomplished using a variety of methods. Permeability between boreholes may be <br />enhanced using hydraulic fracture or blasting techniques where multiple boreholes are used. A <br />single-hole technique, using steam injection to recover oil from oil shale, was demonstrated by <br />Shell in the 1970's (Prats et al. 1977). <br />' In summary, the proposed action does not appeaz to adversely impact minability of oil shale in <br />the Mahogany Zone which contains the richest oil shale resource in the Piceance Creek Basin. <br />Although current technologies are not feasible for recovery of oil from oil shale, future <br />' technologies could be. Since future technologies aze not known, potential impacts from solution <br />mining of nahcolite on the minability of oil shale, particulazly in the Saline Zone, can not be <br />assessed at this time. <br />r Piaeline <br />Impacts to geology from the proposed pipelines would be minimal because the pipes would be <br />buried only 3 to 5 feet deep. The pipeline comdor is in an area of low seismicity. The impacts <br />to geology along the majority of the pipeline route would be limited to minor subsurface <br />' disturbances where rock would be excavated, crushed, and reapplied as base material for the <br />pipes. The only areas of potential concern from a geological standpoint are those areas with <br />significantly steep slopes, particularly Davis Point. At Davis Point, bedrock exposed at the <br />' ground surface would likely be impacted in an attempt to create both an adequate base and a <br />direct route for the pipes. In addition, pipeline construction in areas of very steep slopes and <br />' Geology 4-3 <br />