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/~atheson <br />M fining <br />•C onsultants, Inc. <br />SENECA COAL COMPANY <br />YOAST MINE <br />GROUND MOTION ATTENUATION STUDY <br />Routt County, Colorado <br />November 29, 2001 <br />• <br />11460 W. 44th Ave., Suite 6 <br />Wheat Ridge, Co 90033 <br />30356-5638 <br />Fax 303.456-5639 <br />Matheson Mining Consultants, Ino. (MMC) was retained by Seneca Coal Company to acquire <br />ground motion data in order to perform a statistical ground motion attenuation study for the Yoast <br />Mine. The ground motion was produced by the detonation of three overburden shots on November <br />29, 2001. <br />The current mine permit with the Colorado Division of Minerals and Geology allows shooting to a <br />scaled distance of 55 when distances from the blasting site are from 301 feet to 5000 feet. The <br />maximum allowable peak particle velocity in this distance range is 1.00 inch per second (ips). The <br />primary purpose of this study is to define a modified scaled distance under which recommended <br />maximum chazge weights per 8 millisecond delay period will result in no greater than 1.00 ips peak <br />particle velocity at the closest residence. The closest residence is a trailer owned by Mr. Brian <br />Valora, currently at a distance of approximately 2500 feet. Other points of concern in the area <br />include residences, water wells, springs, and pond dams. <br />For the Yoast Mine azea, shooting with the modified scaled distance of 28.44 will result in a + 95% <br />confidence level not to exceed 1.00 ips at the nearest inhabited structure. Applying a peak vibration <br />limit of 1.00 ips provides a high degree of protection for engineered structures. The +95% <br />confidence ground motion attenuation formula derived from this study is: PPV = 226.6 * (SD)"1'6' , <br />where PPV is the peak particle velocity in inches per second, SD is the scaled distance, 226.6 is the <br />y-intercept at a scaled distance of one, and -1.62 is the slope of the curve. <br />The following chazge weight per 8 ms delay period table for a constant peak particle velocity of <br />1.00 ips at distances from 1000 feet to 5000 feet in the Yoast Mine Area was derived from this <br />study: <br />• <br />