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Memo to Steve Shuey 2 Apri120, 2006 <br />Evaluation of Rock Fall Potential Proposed Red Shale Pit. File M-2005-071 <br />Without blasting, the potential for operations at the proposed Red Shale Pit to destabilize proximate <br />cliff forming sandstone ledges is essentially non-existent. The levels of ground vibration, measured as <br />peak particle velocity, regardless of frequency, that might cause extension ofpre-existing cracks in <br />plaster-on-lathe artesanal construction, is about 0.5 inches per second. The levels of vibration at the <br />Rollins sandstone cliff face in question that maybe caused by operations at the proposed quarry are <br />likely to be an order of magnitude less that those required to increase pre-existing cracking in plaster. <br />While it cannot be stated with absolute certainty that vibrations from the proposed quarry will not be <br />the ultimate trigger of some future rock fall event, it is clear that the only way that quarry generated <br />vibrations could trigger rock fall would be in a situation where loose rock was going to fall in the very <br />near term from some other triggering mechanism. <br />cc: Bruce Humphries, DMG (via email) <br />Rick Wenzel, DMG (via email) <br />c:\Documents and Settings\acs\My Documentsked shale rock fall potential.doc <br />