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iii iiiiiiiiiiiiiiii 999 DIVISION OF MINERALS AND GEOLOGY Department of Natural Resources 1313 Sherman St., Room 215 Denver, Colorado 80203 Phone: (303j 866-3567 FAX: (303) 832-8106 To: Tony Waldron From: AI Amundson STATF OF COLOI~~O DIVISION OF Memo MINERALS GEOLOGY April l2, 2002 I MENINGMSAFEOrY Subject: M-2002-004 Red Rock Plant and Limestone Mine Blasting Review Bill Owens Governor Greg E. Walther Executive Director Michael B. Long The Division of Minerals and Geology has evaluated the portion of the mining plan (ExhibitD~~on Direetnr pages D4 and DS and pages 4 through 12 of rule 6.5) dealing with blasting at the subject property. A site visit was conducted to verify the location of nearby residences and man-made structures that may be affected by blasting. The mapped locations were found to be accurate. These distances are an integral part of the "scaled distance calculation" that blasters use to determine the maximum amount of explosive that can be detonated per 8 milisecond delay in order to remain under the guidelines for peak particle velocity and noise pressure. The values and distances represented in the permit application were entered in a spreadsheet using factors commonly used by blasters to calculate burden, spacing, depth of drill holes, and stemming. The scaled distance equation and an equation to calculate peak particle velocity are then calculated from these values. The values presented in the permit application appear reasonable. It appeazs that their plan follows accepted blasting practices in all areas with the exception of 2 feet of stemming proposed at the top of page D-5. While it is anticipated that the blasting contractor will utilize more stemming than 2 feet to contain the energy of the blast, the Division would like the stemming increased and expressed in a fashion that allows the operator flexibility with additional safety. Calculating the scaled distance formula for the weight of explosive proposed (360 pounds) yields a safety factor of approximately 2 (see attached sheet) with respect to a (appazently hypothetical) house located 1500 feet away from the blast. This indicates that two holes containing 360 pounds each can be safely detonated on the same delay within the guidelines of the scaled distance equation. The house is apparently hypothetical as the initial mining will take place over 7,000 feet from the Blake Ranch (the nearest house), with mining occumng between 4,000 and 5,000 feet away in years 35 through 50. Since it appears to this reviewer that the Blake house is located well in excess of 4,000 feet away from blasting through year 50, the limitation of 360 pounds per delay based upon 1,500 feet is extremely conservative.