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competent sandstone zone was found in anon-mineralized area at the very top of the Salt <br />Wash Formation. This proposed seal location is shown on Figure L3. The sandstone is <br />fine-grained, non-mineralized, and there are no observed bedding planes or fractures in <br />this sandstone that could serve as conduits. As is seen in Figure L3, the estimated vertical <br />distance from the seal location to the water entrance point is 23 feet. Figure L4 shows a <br />conceptual layout of the 1.6-foot thick bulkhead, including forms, timber, piping, and the <br />surrounding rock. <br />The sandstone was sampled and laboratory tests were conducted for compressive strength <br />and hydraulic conductivity. These test results are presented in Attachment A. The <br />compressive strength was found to be 8,490 pounds per square inch (psi). This is about <br />twice the compressive strength of cured, high-quality concrete and more than adequate <br />for the seal installation. The tested hydraulic conductivity of a 3-inch diameter coring of <br />the sandstone was 2.5 x 10"2 m/d (equivalent to 2.9 x 10-5 cm/s). A long-term test of a <br />larger 8-inch core resulted in a calculated hydraulic conductivity of 1.5 X 10-3 m/d <br />(equivalent to 1.7 x 10-6 cm/s). Although not completely impermeable, it is within the <br />range of an aquiclude. The plan for the seal is to employ low-pressure grouting of the <br />surrounding sandstone to ensure that water does not bypass the seal. <br />Mr. White also inspected the updip extent of the sandstone lens from which the ground <br />water is seeping to determine the maximum elevation of the water pool that would be <br />created by the seal. He concluded that if the sandstone lens were completely saturated, <br />the expected water level above the seal would be no more than 15 vertical feet above the <br />current high-water entrance point. Because the seal will be located about 23 vertical feet <br />below the current entrance point, the total estimated head on the seal will be no more than <br />38 feet. Using the Einarson and Abel (1990) template, this would result in a theoretical <br />seal concrete thickness of 0.40 feet. Because a seal of this thickness would be difficult to <br />adequately anchor in the surrounding sandstone, Energy Fuels commits to using a seal <br />thickness of 1.6 feet. This seal would be capable of handling 147 feet of head, which is <br />very conservative for this site-specific application. <br />The seal will be approximately 380 feet downdip (at a 6% grade) of the current ground <br />water inflow into the decline. As discussed above, after sealing the water levels could <br />potentially increase by a maximum of approximately 15 vertical feet above the current <br />high-water inflow point. This is equivalent to an additional 250 feet of flooded drift or <br />about 630 feet of total drift that is partially or totally under water. Given that the drift has <br />nominal dimensions of 9 feet by 12 feet and assuming the current inflow rate of 1.5 gpm <br />will continue over time, the expected time for the pool to form and equilibrate is about <br />six to nine months. The pool is not expected to migrate because it will be contained <br />within low-permeable Brushy Basin mudstones and shales. A schedule for taking water <br />level measurements and water quality samples will be proposed to DRMS and the BLM <br />prior to sealing based on the inflow rates measured at that time. Once the pool reaches <br />equilibrium, the portal will be backfilled and reclamation of the site can be completed. <br />• <br />2