2012-01-06_PERMIT FILE - C1982057 (34)

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• OIL WELL SITE BLASTING SENE CA 1!-W Colorado Cessation Order (CO) No. C-93-141 was issued to Peabody Western Coel Company (PWCC) on October 16, 1993. Abatement step number two states: "Submit a revision to the Seneca II-Y permit that will establish maximum allowable ground vibrations from blasting to provide protection from damage to the oil well and holding tanks." Vibra-Tech Engineers, Inc. was contacted to address the above abatement plan requirement. This firm has been processing and evaluating seismograph is date from the Seneca II-W Nine since operations began. Vibra-Tech's response provides references and related documentation that affirms engineered structures such as wells and tanks can withstand peak particle velocities of at least five inches-pe r-second (ips). Their response to PWCC is attached. PWCC will continue to maintain peak particle velocities at the well site of five ips or • less, and will continue to utilize a seismic monitor at the well site to verify compliance with the five ips maximum limit. Of more importance, is the reason why fly rock occurred. The cast blest that created the fly rock which caused damage to en oil well facility at Seneca II-W was investigated by Peabody Western management. The consensus of opinion is that fly rock was caused by an unknown mud slip or void within the solid strata which was being Last. The mud void was not of competent nature to contain the energy intended to fragment the solid strata typically encountered in this area. Solid competent strata were present in the face of this particular shot. The presence of this suspected void could not have been detected when inspecting the face, nor was it identified when analyzing core drill holes. To prevent a reoccurrence of this event, PWCC proposes to increase bore hale column stem in areas where mud seams are encountered in upper strata. The powder column will be contained in the solid strata and the hole will be stemmed throughout any mud seams. Stem height has been historically set at 23 feet in this pit area, which is substantially greater than the 17 to 18-foot stem height normally associated with 10-5/8•inch drills, • but will be increased as dictated by the depth of the mud. When mud in the upper strata is more than 35 percent of the Cotal hole depth, test holes will periodically be drilled 1 Revised 10/26/93