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J CHAPTERTWO Proposed Action and Alternatives <br />' Weii Construction <br />Figure 2-5 shows a typical vertical solution mining well section. The wells aze anticipated to be <br />completed as follows: <br />' • A surface hole would be drilled to a depth of about 120 feet, and surface casing (20- to 30- <br />inch) would be set and cemented in the hole. <br />• The solution mining well would then be drilled to total depth, which corresponds to the <br />bottom of the nahcolite-bearing zone. The bottom of the mining interval would typically be <br />750 to 800 feet below the Dissolution Surface, which defines the bottom of the lowest <br />' aquifer. At the Piceance Site, the Dissolution Surface varies from about 1,200 feet to 1,900 <br />feet below the ground surface. At a representative surface elevation of about 6,200 feet, <br />where the Dissolution Surface is at approximately 1,400 feet below the ground surface, the <br />total depth of a solution mining well would be approximately 2,200 feet. <br />• Intermediate casing would be set from the surface to the top of the tazget mining interval. <br />Typically, the casing would extend to approximately 150 feet below the Dissolution Surface <br />to isolate and protect the overlying aquifer system from any effects of mining. The casing <br />would be cemented to the surface with a suitable heat-resistant cement. At a representative <br />surface elevation of about 6,200 feet, the intermediate casing would extend to a depth of <br />about 1,550 feet. <br />' • The well would be completed with injection and production tubing (also known as injection <br />and production strings). <br />A system of monitoring wells would be constructed to monitor potential environmental impacts. <br />t Monitoring wells aze discussed further in Section 2.2.5.3. <br />' Mining <br />Injection of pressurized hot water in the cavity through the injection tube would dissolve bedded <br />' and disseminated nahcolite deposits. The fluid, now called production fluid, would exit the well <br />through the production tube carrying the dissolved nahcolite in solution. The nahcolite-bearing <br />solution would then be transported through a network of solution piping from the well field to <br />' the initial processing plant. Although it is not actually a void, the leached azea is referred to <br />herein as a solution mining cavity. <br />The water used in the mining process would be pumped to the Piceance Site from the Pazachute <br />t Site via a 43.4-mile-long return water pipeline. The water would be a combination of recycled <br />water from the processing system and make-up water that is added to replace evaporative losses <br />during processing and wastewater that is sent to the ponds. The pipeline is described in Section <br />' 2.2.2. <br />The water, called "injection fluid", would be injected into the solution mining wells at elevated <br />' temperatures of 300°F to 420°F and at pressures ranging from 300 to 700 pounds per squaze inch <br />gage (prig). Pressure tests performed at the test facility indicate that the proposed inlet pressure <br />is not expected to cause fracturing. Volumetric flow rates would range from 20 to 200 gallons <br />' per minute (gpm). Once the heated, pressurized injection fluid reaches the mining interval, it <br />' 2-5 <br />