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Vibration Study <br />Primem luninr-Senior High School <br />Primero. Colorado <br />A seismograph was placed in the track and field out building adjoining Pritnero <br />Junior-Senior hIigh school on January 22, 2002. The purpose of this vibration study <br />waa to record ground vibrations and airblast from blasting activities by Lurencito <br />Coal Company. This vibration study was prompted by a citizens complaint. <br />The seismograph and air blast monitor were located at a distance of about 3,000 feet <br />from the blasting at a location between the blasting and the home of the compliant. <br />The eyuipment was taken down on Fcbnia~y 19, 2002. <br />During this period of time one blast was recorded for both ground vibrations and <br />airblast. The trigger level for the ground motion monitor was scat at a level of O.U5 <br />inches per second (ips). This is a very sensitive trigger level and is far below the <br />regulatory limit, The airblast trigger was set at 130 dB(L). This Icvel is three dT3's <br />below the regulatoty limit of 133 dB(L) fora 2 Ii2 or lower flat frequency response <br />microphone.'1'he reason a 130 dB(i.) trigger level was selected was to avoid false <br />triggers from wind gusts that are frequent in the arcs. <br />The blast that was recopied nn February I5, 20U2 at 17:23:3$ (5:23 PM} had a peak <br />particle velocity of 0.06 ips. The maximum airblast was 114 dB(L). Ground <br />vibrations and airblast intensities on this order of magnitude are not capable of <br />causing damage to structures and arc well below the very conservative regulatory <br />limits_ <br />To put these results in perspective, the maximum peak particle velocity of U.U6 ips <br />is only 6 percent of the regulatory limit of 1.0 iPs_ Studies by trained researchets <br />and experienced observers have never found even the most superficial damage at <br />peak particle velocities of less then 0.5 ips. <br />Airblast and sound is a pressure against some object. In the case of sound it is a <br />pressure against the ear drum. For airblast it is a pressure against a wall or against a <br />window. To put the recorded airblast into perspective, the 114 dB(L) is llte <br />equivalent of the pressure caused by a wind velocity of about 10 MPH. <br />Michael F. Rosenthal <br />Senior Mining Engineer <br />Office of Surface Mining <br />Denver, Colorado <br />P~ ~ <br />