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MAR-17-98 15:11 From:CCBV GOLD MN~ <br />1119669325! • T-317 P 06/10 Joh-647 <br />4. Ground-water investigation. To investigate the finding that the highwall rock is not <br />saturated. and that no water pressure exists within the highwalls. two holes were drilled <br />into the highwall. The holes were inclined °, which oriented the hole petpendiculaz <br />to the highwall. The holes were 750 feet to g. One week after completion, one hole <br />was dry and the other had 70 feet of water at the base of the hole. The zone of <br />saturation indicated by the water that was encountered is located well outside of any <br />highwall failure surface. <br />Based on these observations, it is evident that the ground-water pressure in the Mine highwatls <br />~ is zero. The drained rock masses are believed to be the result of the continuing function of the <br />underlying network of drainage tunnels connected to the underground mine workings, and by <br />the rela[ively porous nature of the underlying strata. <br />Summary. of Rock Conditions at the Cresson Mine <br />These continuing observations have confirmed that the Cresson Mine highwalls are comprised <br />of the "hard, competent rock (Urtiaxiel compressive strengths is the range of 5500 co 25000 <br />psi)" that was projected in the application for permit amendment Ntunber ti (see statement in <br />Enclosure 19 of Volume VIII of CC&V's Permit Amendment Application -prepared by Call & <br />Nicholas. Inc. in report dated 23 February 1994). The jointing. which has been encountered <br />during mining, has fewer significant joint sets than was projected in that application, and the <br />rock has been found to be unsaturated and experiencing no hydrostatic head. <br />Slope Design <br />Original design <br />The original mine slope design projected the following: <br /> <br />1. Mined slope. Each mined bench was designed to be 20 Feet high. The interbench <br />slope (the outslope of the 20-foot bench) was recommended to be 72°. A 2-foot offset <br />was planned above each 20-foot bench. <br />2. Catch benches. Catch benches were planned to occur every 4th level (resulting in <br />80-foot total height between catch benches. The catch-bench width was planned to be <br />between 31 and 48 feet, with the difference a function of the orientalion of the Mine <br />highwall rela[ive [o the Pracntres and joints. <br />3. Overall slope. The total offset between catch benches was between 37 and 52 feet. <br />This, combined with the 72° intorbench slope and the vaziable catch bench width. <br />provides a range in overall highwall slope angles from 48 to 52°. <br />5 <br /> <br />