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North Fork Valley Seismic Network — Second Quarter 2010 <br />SUMMARY <br />During the three -month period from 1 April to 30 June 2010, 35 mining - related seismic events of <br />approximate Richter local magnitudes (ML) 1.7 and larger were relocated using data recorded on <br />the North Fork Valley Seismic Network. Most of the seismic events were located in two areas: <br />at the Elk Creek Mine and at the Bowie Mine. Only 5 seismic events occurred within the West <br />Elk Mine permit area. The largest event during this quarter was a coda magnitude (M 2.5 <br />event at Bowie Mine. The largest event at the West Elk Mine was a M 2.2 event on 26 April <br />north of the area of active mining. The highest peak horizontal ground acceleration (PGA) <br />observed during the second quarter was 0.002 g recorded at station BWK in the Bowie Mine area <br />resulting from a M 1.9 event at a distance of approximately 0.94 km (0.58 mi). The largest <br />PGA recorded at the West Elk Mine was only 0.0004 g at station MCD resulting from the 18 <br />April Mc 1.9 event located approximately 4.68 km (2.91 mi) away. <br />INTRODUCTION <br />This report has been prepared in partial fulfillment of a commitment by Mountain Coal Company <br />(MCC) to monitor seismicity (including the microseismic activity near the longwall mining <br />activity) in the North Fork Valley just east of Paonia, Colorado. This commitment is to the <br />Colorado Department of Natural Resources, Division of Reclamation, Mining and Safety. This <br />report contains analyses of the data collected for the second quarter of 2010 (1 April through 30 <br />June). <br />The area included in this study encompasses the West Elk Mine, operated by MCC and Bowie <br />No. 2 Mine, property of Bowie Resources, LLC (BRL) (Figure 1). Seismicity from Elk Creek <br />Mine, owned by Oxbow Mining, Inc. is also recorded on the North Fork Valley Seismic Network <br />(NFVSN). <br />The 10- station NFVSN was established to (1) monitor the mining- related seismicity occurring in <br />the vicinity of the West Elk and Bowie No. 2 mines at a detection threshold magnitude of M <br />1.0, (2) provide event locations and magnitudes and estimates of ground motions, and (3) <br />determine focal mechanisms when feasible. Installation of the NVFSN was begun in 2006 and <br />by October of that year, 5 stations were in operation (Swanson et al., 2007). By July 2006, 10 <br />stations were operational. <br />NETWORK OPERATIONS <br />The NFVSN consists of 10 permanent stations (Table 1 and Figure 1), which were installed as a <br />cooperative effort between MCC, BRL and the Spokane Research Laboratory of the National <br />Institute of Occupational Safety and Health/Centers for Disease Control and Prevention <br />(NIOSH/CDC). One temporary station OXM was installed in February 2009 and has remained <br />as part of the network (Table 1 and Figure 1). A semi - permanent station, NOB, was installed in <br />November 2009 in the Bowie Mine area. The following factors were used to determine the <br />station locations: access, permission of land owners, network geometry, radio line -of -sight to the <br />common recording site at Paonia Airport or a repeater station, and uniform coverage of the target <br />I= W:\X_WCFS \PROJECTS \WEST ELK -MTN COAL \2010 Q2 \Q2_2010_ MCC. DOC\31 -AUG-1 0\\OAK 1 <br />