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On November 29, 2001 SCC conducted a series of three seismographic surveys of blasts for the • <br />purpose of acquiring data in order to justify the request for variance from the Scaled Distance Factors <br />of Rule 4.08.4(10). The primary purpose of the study was to define a modified scale distance factor <br />under which recommended maximum charge weights per 8-millisecond delay period would not <br />exceed approved peak pazride veloaties of 1 .25 inches per second (ips) at 0 to 300 feet, 1.00 ips at <br />301 to 5,000 feet, or 0.75 ips at greater than 5,000 feet <br />For the Yoast Mine azea, the combined results of the study indicate that blasts designed using a <br />modified scaled distance factor of 28.44 will not exceed approved peak vibration levels at the nearest <br />inhabited residences. However, at the request of the Division, Shot #1 was analyzed independent of <br />Shots #2 and 3 and resulted in a higher distance scale factor of 34.85. Based on the indications and <br />results of the regression analysis of the data from Shot #1, the Division believes that a modified <br />Scaled Distance Factor of 35, for distances of 301 feet to 5,000 feet between the structures identified <br />in Rule 4.08.4(10) and the neazest blast hole, is appropriate. <br />Using the Scaled Distance Factor of 35, two new Factors were calculated for peak pazticle velocities <br />of 1.25 ips and 0.75 ips. The +95% confidence level equation using the data from Shot #1 is: PPV • <br />=326.4 *(SDft83, where PPV is the Peak Particle Velocity in inches pet second, the y-intercept is <br />326.4, the slope is -1.63, and SD is scaled distance. Scaled distance SD = D ~, where D is the <br />distance from the neazest blasthole collaz to the seismograph in feet, and W is the charge weight per <br />8-millisecond delay period in pounds. The formula derived from the Shot #1 data set defines a <br />modified scaled distance of 30.39 for distances from 0 to 300 feet, 34.85 for distances from 301 to <br />5,000 feet, and 41.57 for distances from 5.001 feet and beyond. <br />Therefore, based on the Division's review and comments, SCC requested a variance from the default <br />Scaled Distance Factors of 50, 55 and 65 to Modified Scaled Distance Factors of 31, 35 and 42, <br />respectively. Table 142, Modified Scaled Distance Factors - Yoast Mine Area, presents a summary <br />of the requested Modified Scaled Distance Factors. <br />SCC will conduct continuous ground vibration and air blast monitoring at the Brian Valora and Gary <br />Valora residences to ensure compliance with the Peak Particle Velodty limits of Rule 4.08.4(10). <br />Monitoring at the Gary Valora residence will be conducted, particulazly during overburden shots in <br />the northern half of the pit Monitoring will also be conducted at the closest residence (Brian Valora), <br />particulazly during overburden shots in the southern half of the pit • <br />MR-24 4 Revised 9/05 <br />