Laserfiche WebLink
(4) At sites where blasting is part of the proposed mining or reclamation <br />plan, the Applicant shall demonstrate through appropriate blasting, <br />vibration, grotechnical, and structural engineering analyses, that off-site <br />areas will not be adversely affected by blasting. <br />The Division of Minerals and Geology has evaluated the portion of the mining plan <br />(Exhibit D, pages D4 and DS and pages 4, through 12 of rule 6.5) dealing with blasting at <br />the subject property. <br />A site visit was conducted to verify the location of nearby residences and man-made <br />structures that may be affected by blasting. The mapped locations were found to be <br />accurate. These distances are an integral part of the "scaled distance calculation" that <br />blasters use to determine the maximum amount of explosive that can be detonated per 8 <br />milisecond delay in order to remain under the guidelines for peak particle velocity and <br />noise pressure. <br />The values and distances represented in the permit application .were entered in a <br />spreadsheet using factors commonly used by blasters to calculate burden, spacing, depth <br />of drill holes, and stemming. The scaled distance equation and an equation to calculate <br />peak particle velocity are then calculated from these values. <br />The values presented in the permit application appeaz reasonable. It appeazs that the plan <br />follows accepted blasting practices in all areas with the exception of 2 feet of stemming <br />proposed at the top of page D-5. While it is anticipated that the blasting contractor will <br />utilize more stemming than 2 feet to contain the energy of the blast, the Division would <br />like the stemming increased and expressed in a fashion that allows the operator flexibility <br />with additional safety. <br />Calculating the scaled distance formula for the weight of explosive proposed (360 <br />pounds) yields a safety factor of approximately 2 with respect to a (appazently <br />hypothetical) house located 1500 feet away from the blast. This indicates that two holes <br />containing 360 pounds each can be safely detonated on the same delay within the <br />guidelines of the scaled distance equation. The house is apparently hypothetical as the <br />initial mining will take place over 7,000 feet from the Blake Ranch (the nearest house), <br />with mining occumng between 4,000 and 5,000 feet away in years 35 through 50. <br />Since it appears to this reviewer that the Blake house is located well in excess of <br />4,000 feet away from blasting through year 50, the limitation of 360 pounds per <br />delay based upon 1,500 feet is extremely conservative. <br />It is understood following the site visit of April 10, 2002 that no blasting will be required <br />for foundations at the plant site. If this changes, the Division must be notified, and the <br />blasting must be closely supervised to maintain compliance with both the seismic <br />monitoring and the scaled distance guidelines. The plant site is in excess of 5,000 feet <br />away from the Blake Ranch and a greater distance away from the residences along the <br />Saint Charles River. <br />13 <br />