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1 given to blasting adjacent to the interim and final cut slopes at the east wall of the central pit is imperative to preserving slope integrity. Following is a brief summary of our understanding of your ' existing blasting techniques and a proposed perimeter control blasting design which is compatible with those techniques and your personnel's routine operations. ' We understand that production blasting at the quarry typically consists of drilling two rows of 40 ft deep holes on approximate 18 ft centers and loading those holes with about 25 ft of explosives under 15 ft of stemming. The holes are drilled to 6-112 in. diameter. Some form of delays are used to at least take out the first row toward the excavation ahead of the interior row, but we are not sure about ' the type and sequencing of delays used. We assume that an inexpensive explosive such as "ANFO" (ammonium nitrate fuel oil) is normally used for production blasting. ' Based on these data and assumptions, we estimate that approximately 350 lbs. of explosive are used per hvle. Given the drill pattern, this results in a powder factor(Ibs, of explosive(cu. yards of rock removed) of approximately 0.73. Typical powder factors for quarry operations are about 0.7 to 0.4, so these preliminary calculations seem reasonable. To augment these blasting procedures, we propose perimeter control blasting in the form of air deck presplitling using your existing materials and operations with only slight modifications tv your production blasting procedure. Air deck presplit holes will be the row of holes immediately adjacent to the interim or final cut slope. These holes should be drilled to normal production depth, but on about 9 ft centers (about half the spacing of the production holes) and loaded with an "air deck" between the explosives and the stemming. The holes should be loaded with explosive in your nvrmal manner, but only in the bottom 4 to 5 ft of borehole. The borehole should be left open above the explosive to a depth of about b to R ft below ground surface. The top 6 to 8 ft of hole should then be stemmed in your normal manner above some sort of packing (i.e. rags, etc.) set at the 6 tv $ ft depth mark, This form of blasting should still provide a clean cut slope, but using considerably less explosive close to the cut slope rock face which will, hence, be less impacted and disturbed. ' In addition, the Following requirements should be met for a perimeter control blast round using air deck presplitling: ' n Shoot the perimeter holes before the production holes using millisecond delays. ' n Space production holes adjacent to perimeter holes at 8 to 9 ft away, not 18 ft away as between production holes. ' ~ Use millisecond delay caps in each hole, using a "0" or "1" cap for the presplit holes and a higher number delay for each production hole. Not too large a delay between the presplit and the production holes should be used so that the round is essentially all shot "at the same ' time". We also considered using primacord to achieve presplitting in the perimeter holes. Based on our ' recent experience, primacord would likely blow out any stemming and we think that stemming the holes, as is presently done for production holes, is desirable. Others suggest, however, that ' 12 ~ ft-'~