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<br />The vertical solution mining wells will be used to provide access to the nahcolite <br />resource, which is generally located from approximately 1,400 to 2,200 feet below <br />ground surface (based on a surface elevation of approximately 6,200). All wells will <br />have a surface hole drilled to a depth of approximately 120 feet below ground surface <br />and will have surface casing cemented in place. An intermediate hole will then be <br />drilled through the surface hole to total depth. The total depth will depend on the <br />surface elevation and other geologic factors but will generally be about 2,200 feet. <br />Intermediate casing and/or tubing strings will then be placed in the intermediate hole <br />and will extend to depths between 1,550 feet and 2,200 feet. A schematic of a solution <br />mining well is presented in Figure D-1 <br />The heated, pressurized water used for solution mining, called "injection fluid," will be <br />injected into the solution mining wells at temperatures of 300°F to 420°F and at <br />pressures ranging from 300 to 700 pounds per square inch gage (psig). Volumetric flow <br />rates will range from 20 to 200 gallons per minute (gpm). Once the injection fluid <br />reaches the mining interval, it will dissolve the mineral nahcolite from the nahcolite/oil <br />shale matrix and create a leached area. Although it is not actually a void, the leached <br />area is referred to herein as a "solution mining cavity". The dissolved nahcolite <br />solution, called "production fluid," will then be extracted from the well. The solution <br />mining cavities will grow in diameter as the wells operate over time. The predicted <br />final configuration of a single solution mining cavity is roughly a cylinder with an <br />average diameter of approximately 200 feet and a height of approximately 650 feet. The <br />proposed mining interval contains 70 to 75 percent oil shale and other residual rock. <br />When totally mined, the leached area within each cavity will have had 25 to 30 percent <br />of its original volume, i.e., that part occupied by nahcolite, removed by solution mining. <br />A 200-foot diameter is considered a conservative estimate of the maximum cavity <br />diameter. Cavities could well be less than 200 feet in diameter. This conservative <br />estimate of ultimate cavity size was used in developing the well spacing and well <br />development plan because the ultimate cavity size has not been demonstrated. Well <br />spacing will be at 300-foot centers but will likely be adjusted when cavity growth rate <br />and ultimate cavity diameter have been adequately demonstrated. <br />The proposed well field layout is illustrated in Figure D-2. Areas outlined in Figure D-2 <br />will be sequentially developed over 30 years according to the 5-year time intervals <br />indicated, i.e., during Year 0 through Year 5, during Year 5 through Year 10, and so on. <br />These areas, or "mining panels," were selected for development because they are <br />located on ridgetops, which would make them the simplest areas to develop and <br />reclaim. Note that some 5-year mining panels are subdivided into sections that are not <br />located next to each other, in which case their components bear letter designations as <br />shown on Figure D-2. <br />Once the nahcolite solution has been mined, it will be initially processed at the Piceance <br />Site. The initial processing system will concentrate and prepare the solution so that it <br />D-2 <br />