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III IIIIIIIIIIIII III ~ /- ~~- ~~ ~ 999 Sf~~; EXHIBIT D MINING PLAN Historically, sodium bicarbonate and sodium carbonate have been manufactured synthetically using the Solvay process. This process uses salt, ammonia, carbon dioxide, and limestone. The limestone is heated to produce lime and carbon dioxide. The carbon dioxide is dissolved in the other components, and the result is a sodium bicarbonate precipitate. The sodium bicarbonate is heated and dried to form sodium carbonate (Lewis 1992). The relatively large energy requirements and the adverse environmental effects of the Solvay process have caused the industry to shift toward processing natural deposits (Lewis 1992). Processing of natural sodium bicarbonate deposits involves simple, known processes and results in less by-product. The United States is a world leader in soda ash production due to natural trona (sodium sesquicarbonate) deposits in the Green River Basin in Wyoming, which provide over 90 percent of the United States' supply and approximately 25 percent of the world's supply of soda ash. Trona ore is removed from several subsurface beds via a method similar to longwall coal mining. The nonsoluble tailings (oil shale, mudstone, and claystone), which comprise approximately 12 percent of the ore, are disposed of in surface reservoirs or in portions of the underground mine (Striven 199. Natural sodium bicarbonate deposits may also be mined using a solution mining method. In situ solution mining is an alternative to mechanical excavation of ore and is applicable to a wide range of commodities that are soluble in water, such as nahcolite. Since most waste components are not soluble, they tend to be left in place as the resource is solubilized and removed to a surface processing facility. In situ solution mining operations are characterized by the absence of mine waste piles and tailing impoundments because of the selective dissolution and recovery of the resource (SME 1992). D.1 Mining Method At the Yankee Gulch Sodium Minerals Project (Yankee Gulch Project), bedded and disseminated nahcolite deposits will be mined using a solution mining method. Nahcolite is naturally occurring sodium bicarbonate and has the chemical formula NaHCO,. Mining will be accomplished by injecting pressurized and heated water into vertical wells (solution mining wells) approximately 2,000 feet deep and removing the nahcolite in solution form. This method of mining will be used throughout the operation. Surface disturbance will include construction of drill pads, well field piping, surface structures and facilities, ponds, pipelines, utilities, access roads, and other project components. D-1