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1 Southwestern Portland Cement Mining impacts on Montgomery School ~('S~~ SHB AGRA Project E93-7038 i Bi _ _ Page 5 ' to the mine azea. With this structure being about 1300 feet closer to the mine area than the Montgomery School building, compliance will be assured at the school site. ' S.0 PROJECTED GROUND VIBRATIONS ' An evaluation was made of the ground vibrations due to blasting at the Montgomery School site to estimate the maximum peak ground velocities due to blasting as has been historically conducted at the existing Lyons Quarry. An evaluation was also made of the change in ground vibration level and the corresponding potential for damage to offsite structures, as the mining progresses from north to south. Peak ground vibrations were estimated using the relationship ' between peak ground velocity, distance from the blast and explosive weight developed from monitoring of blasting at the existing Lyons Quarry (SHB AGRA, 1993). ' Estimation of ground vibration was done on an annual basis considering the nearest location that blasting will occur in a given yeaz. As noted in the Blast Vibration Analysis Report (SHB AGRA, 1993), blasting at the existing Lyons Quarry has used a broad range of explosive charge ' weights per delay depending on the nature of the blast. Figure 1 presents a summary of the frequency that given explosive chazges were used over the period of the blast vibration analysis. As shown in Figure 1, the range of charge weights per delay that are used range from less than ' 100 to 1600 pounds. Over 50 per cent of the shots however, used charge weights per delay in the range of 200 to 400 pounds. Ground vibration estimates were therefore made for a typical blast with a change weight per delay of 400 pounds and the maximum blast of 1600 pounds of ' explosive per delay. It should be noted that over the last 8 to 10 months of operation at the Lyons Quarry, blasting operations have been modified to use explosive charge weights per delay at the lower end of the historic range. Accordingly, the mid-range values of 200 to 400 pounds of explosive per delay may well represent the upper limits for blasting at Dowe Flats. The estimated distance from the Montgomery School site to the nearest portion of the mine at ' each year of mine development and the estimated ground vibration under the typical and maximum blasts are presented in Table 5. Figure 2 presents a plot of the variation of estimated peak ground vibration at the site with time. Also presented on Figure 2 is the Office of Surface ' Mining Reclamation and Enforcement (OSMRE) regulatory limits for control of blasting at surface coal mines. As discussed in the Blast Vibration Analysis Report, these criteria are established to control ground vibrations to levels below that which are considered to be ' damaging to structures with sheet rock or plaster interior walls. Because the OSMRE regulations consider the effects of the frequency of ground vibration on building response, the limiting peak ground vibration levels change with distance from the blast as does the frequency content of the ' ground vibration. ' An estimation of the relative levels of peak ground vibration currently experienced at the Montgomery School building site as a result of blasting at the existing Lyons Quarry was also made as noted on Figure 2. This estimation was made assuming the maximum charge weight per 1 AG RA ' Earth & Enviranmenta(Group