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Memo to Tom Schreiner 2 September 9, 2005 Review of Geotechnical Exhibit File No. M-2004-067 (c) From 5001 feet and beyond distance from blast to structure, maximum PPV is 0.75 ips (d) For any structures with plaster and lath walls, the limit is 0.5 ips at all distances If the Applicant selects this compliance option, initial blasting at the site must be done in accordance with the Scaled Distance Equation (described below) until sufficient data is collected to determine the acceptability of charge weights in excess of those allowed under the Scaled Distance Equation. If this compliance option is selected, the Applicant must provide DMG with a plan showing where the seismographs will be located, and must commit to blasting in accordance with the Scaled Distance Equation until a report is submitted to the DMG with seismograph data, justification, and proposed charge weights per delay that will result in compliance with the foregoing listed PPV limits. Written approval of the plan must be issued by DMG prior to using blasting weights in excess of those allowed under the Scaled Distance Equation. 2. Scaled Distance Equation This method does not require that blasts be monitored; it relates a permissible minimum scaled distance (Ds) to distance of the blast site to a structure to be protected, as follows: (a) From 0-300 feet distance: Minimum Ds = 50 (b) From 301-5000 feet distance: Minimum Ds = 55 (c) 5001 feet distance and beyond: Minimum Ds = 65 The maximum charge weight (W) per 8 ms. delay period, in pounds, is related to the distance (D) from blast location to structure location by the equation: w = (D/Ds)2 As an example, production blasting at the MMRR Quarry is proposed for as close as 920 feet from the Blackhawk/Central City Sanitation District wastewater treatment facility. The Scaled Distance Equation yields a maximum charge weight per delay as follows: W= (920/55)2 = 280 pounds of explosive This is compared to 550 pounds of explosive per delay proposed by the Applicant for production blasts. Blasting for access road construction will occur within 235 feet of Highway 119. The Scaled Distance Equation yields: W = (235/50)2 = 22 pounds of explosive This is compared to 65 pounds of explosive per delay proposed by the Applicant for access road blasts. One of the chief drawbacks to the Scaled Distance Equation method is its impracticality at short distances. The charge weights per delay permissible maybe too small to permit any practical production blasting. For this reason, the Applicant may want to consider other less restrictive compliance options for implementation as soon as sufficient data to develop these other options is available.