PERMFILE49045 - Laserfiche WebLink

Home Browse Search

July 13, 2001 To: Larry Oehler From: James Dillie Re: Review of Blasting Report and Proposed Highwall Reclamation Plan, Trout Creek Pit, M- 2001-035 Per your request, I reviewed elements of the Applicant's response to your adequacy letter regarding the blasting plan and proposed reclamation (stability) of the quarried highwalls I believe the Applicant's proposed reclamation plan of the quarried outslopes will provide stable highwalls if it includes the consultant's recommendations on page 4, second paragraph, "the risers of the ...." and comply with the recommended overall slope of 56 degrees (3/4:1). A 2.0 ips peak particle velocity (ppv) limitation is acceptable for new residential structures within 300 feet of the blast. A 1.0 ips ppv limitation should be required for structures within 301 to 5,000 feet of the quarry area. Air overpressure (airblast) should be limited to 129dBL at structures (dwellings, etc.) within 5,000 feet. It is not necessary to limit airblast at the dam. Monitoring should be required. Specifically, it is important to conduct high frequency blasts so the dam will not be adversely affected. Blast frequencies should remain above 30 Hz at the dam. Frequency, along with peak particle velocity, should be monitored during each blast at the dam. Frequency, ppv, and airblast should be monitored at all structures within 5,000 feet of the quarry area during each blast event, providing the owners of the structures allow the operator to place instruments on their property. According to the Applicant, results of the proposed blasting plan is based on a worst case scenario which includes a maximum charge of 42 pounds of explosives per delay. I would expect that this amount of explosives should not be exceeded during any blast event without prior approval by the DMG. A concrete dam should be able to withstand high frequency blasts with ppvs of 2.0 ips or less. However, since the dam is under the jurisdiction of the State Engineer's Office (SEO), I would recommend requesting input, or recommendations, from their dam safety section before approving the proposed blasting plan. I attempted to contact Mr. Michael Graver, Pueblo office, but he is out until July 23rd If the SEO is satisfied that the proposed blasting plan will minimize, or prevent, damage to the dam during blasting operations and, if the Applicant commits to the above noted limitations and monitoring, I Relieve requirements of sections 3 Fr 4 of Rule 6.5 will have been satisfied since the SEO generally requires a thorough analysis of dam stability (usually includes pseudo-static conditions) before signing off on the structure. cc: James Stevens