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STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Department of Natural Resources 1313 ShemFan St., Room 215 Denver, Colorado 80203 Pholre: (303) 8663567 FAJ(: (303) 832A706 DATE: September 23, 2005 TO: Tom Schreiner FROM: Allen Sorenson ~~ RE: Blasting Plan Review of Third Adequacy Review Response, Clear Creek District Water Providers, LLC, MMRR Quarry, File No. M-2004-067 COLORADO DIVISION OF M[NF~RALS GEOLOGY RE CLANATION•MINING SAFFTY•SCIENCE Bill Owens Governor Russell George ERecutive Diretlor Ronald W. Cattany Division Director Natual Resourm Trustee The Division of Minerals and Geology (DMG) engineering staff' have reviewed the Applicant's blasting plans as contained in the third adequacy review response dated September 14, 2005. The blasting vibration control plan provided will be protective of offsite structures, and the DMG can recommend approval of that plan. It is DMG's understanding that the Applicant is preparing a list of best management practices (BMPs) for dust control to be submitted for DMG review and approval. The BMPs for dust control during blasting operations, in addition to those already committed to in September 14, 2005 adequacy response, must nclude the following (a diagram with nomenclature is enclosed with this memo): Blasting with low density explosives such as Ammonium Nitrate and Fuel Oil (ANFO) will be done with a minimum burden to charge diameter ratio of 25. Blasting with higher density explosives (density greater than 0.95 grams per cubic centimeter) must use a minimum ratio of 30. If the Operator determines that lower ratios are desirable, a written proposal with justification must be submitted to DMG, and written approval from DMG must be obtained prior to employment of the lower ratios in blasting operations. DMG notes that the blast patterns shown in figure 2 of the Applicant's "Response to 2"d Adequacy Review" dated August 19, 2005 are incompliance with the required burden to charge diameter ratios. 2. For initial blasting operations, the collar distance (stemming) will be equal to burden. Collar distance can be gradually reduced to a minimum of 70 percent of the burden if cazeful observations of each blast indicate that dust generation is not increasing with decreasing stemming. Dust observations must be recorded in all blasting reports where collar distance is less than burden. If the Operator determines that coltaz distances less than 70 percent of burden aze desirable, a written proposal with justification must be submitted to DMG, and written approval from DMG must be obtained prior to employment of the lower collaz distances in blasting operations. Once an acceptable minimum collar distance is approved by DMG, dust observation recording in blasting reports may be discontinued. As discussed in DMG's September 9, 2005 engineering memo, and as agreed to in the Applicant's September 14, 2005 "Response to 3`d Adequacy Review" letter, blasting mats or application of thick dirt cover may be used in lieu of the required minimum stemming. DMG notes that the blast patterns shown in figure 2 of the Applicant's "Response to 2"d Adequacy Review" dated August 19, 2005 do not specify minimum stemming requirements. Office of Office of Colorado Mined LarFd Reclamation Mive and Inactive Mines Geological Survey