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<br />CAMAS America, Inc. <br />11 January 1996 <br />Page 2 <br />2. The geometry of the East Higfivall of the Central Quarry is such that drill holes <br />for highwalls will be positioned closer to the outside edge of each subsequent <br />bench as lower benches are excavated and, in some cases, may be beyond the <br />edge of the bench. In order to improve the ease of drilling and match the geome- <br />try of the slope better, it is recommended that the fourth {lowest present bench) or <br />fifth bench width be reduced to approximately 45 feet. The 45-foot width is <br />measured from the toe of one bench to the toe of the next, excluding the effect of <br />angle holes. With the angle holes inclined at 20 degrees, approximately 15 feet of <br />bench width is lost and the actual horizontal bench width would be approximately <br />30 feet. If the 30-foot working width is not adequate, then two "catch-up" <br />benches each 50 to 55 feet wide (toe-to-toe) are recommended as an alternative. <br />This change is presented in the Geotechnical Stability Exhibit of the Annual <br />Report. <br />3. It was observed that angle drilling of the highwalls of the east slope of the Central <br />Quarry has had a very beneficial effect on the condition of individual highwalls. <br />Haley & Aldrich recommends that angle holes and precision (smooth wall) <br />blasting techniques continue to be used. <br />As you are aware, the quality of rock at the south end of the Central Quarry is <br />relatively poor. Current mine plans for the Central Quarry reservoir are for an 80 <br />x 80-foot highvvall/bench configuration in this area. It is unlikely that steeper <br />slopes would be stable due to the poorer quality of the rock. Additionally, <br />problems with the stability of individual benches and highwalls may be reduced <br />with the use of a 40 x 40-foot configuration as opposed to an 80 x 80-foot <br />configuration. Ultimately, a configuration flatter than 1 H:1 V may be necessary. <br />We would also like to point out that a rock rib is to remain at the south end of the <br />Central Quarry to separate the reservoir from the future South Quarry. It is <br />recommended that precision blasting methods be employed for t7nal highwalls in <br />this area and also for intermediate highwalls which will exist for over a decade <br />above the reservoir prior to development of the South Quarry. <br />c:~:o:am~os~ev.zao <br />