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<br />case scenario was developed and presented in Agapito's January 7, 1999, <br />correspondence to Steigers Corporation (Agapito 1999). This realistic worst-case <br />scenario actually evaluated three cases. These cases were: <br />• 200-foot-diameter cavities spaced on 300-foot-centers, with 30 feet of <br />yielding around each cavity perimeter <br />• 260-foot-diameter cavities spaced on 300-foot-centers <br />• 200-foot-diameter-cavities spaced on 300-foot centers with 30 feet of <br />yielding around each cavity perimeter and a fault traversing the mining <br />panel. <br />The resulting surface subsidence calculated for the three above-described scenarios was <br />0.54 foot, 0.70 foot, and 0.74 foot, respectively. <br />In addition to surface subsidence, the effects of mining on subsurface strata were also <br />evaluated. The two strata of concern were the Mahogany Zone, which is an oil-shale- <br />rich zone located approximately 500 feet above the mining interval, and the Upper <br />Aquifer, which is situated approximately 720 feet above the top of the mining interval <br />and contains a potential USDW in its upper portion. The study concluded that the <br />maximum horizontal strains induced by solution mining were less than the strata strain <br />protection criteria for both the Mahogany Zone and the Upper Aquifer. Therefore, <br />there are no anticipated significant impacts to the future minability of the oil shale in <br />the Mahogany Zone or to the potential USDW. More information on the strain <br />protection criteria is provided in the Agapito Stability Report. <br />Due to the small amount of surface subsidence that is expected to occur over geologic <br />time and the fact that the strain protection criteria will not be exceeded for the <br />Mahogany Zone or the Upper Aquifer, solution mining cavities are expected to be <br />relatively stable throughout the mine life. <br />U.3 Potential Off-Site Geological Impacts <br />'The are no anticipated off-site geological impacts due to failure of any geologic <br />structure or constructed earthen facility for this project. <br />U.4 Blasting <br />No blasting is anticipated for this project. <br />U-4 <br />