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SUMMIT ENGINEERING C 0 1 ENGINEERS & LAND SURVEYORS <br /> Mail: P.O. Box 1897 Alamosa, CO 81101 P: 719-589-6147 E: summitengco@gmai1.com <br /> STATE OF COLORADO <br /> DIVISION OF RECLAMATION,MINING AND SAFETY <br /> Department of Natural Resources <br /> 1313 Sherman St.,Room 215 C O L O R A D O <br /> Denver,Colorado 80203 D I v i s 1 o N Of <br /> Phone:(303)86&3567 RECLAMATION <br /> FAX:(303)832-8106 MINING <br /> Sc— <br /> DATE: December 19,2007✓� SAFETY <br /> ail!R4u,Jr. <br /> TO: Kate PiCkfoId °Otef <br /> Huns D,She <br /> s/ ExeoAwe Dxew <br /> FROM: Allen Sorenson / <br /> r/ Rdeald w Catlany <br /> Division Dnecwr <br /> RE: Review o BlaSdX -braden Coats)Plan,Robiaa C~VUetion,LLLP., —'W ae, —Tnasee <br /> Robtxs Rock Pi;File No.M-2007-080 <br /> The Division of Reclamation,Mining,and Safety(DRMS)minerals program engineering section has <br /> reviewed the blasting report for the proposed Robins Rock Pit,prepared by Merritt LS,L.L.C.and dated <br /> December 17,2007(Merritt Report). The Merritt Report provides a good structure and template for the <br /> regulation of blasting at the proposed Robins Rock Pit. However,a number of details must be sufficiently <br /> addressed prior to DRMS consideration to approve or deny the permit application. <br /> 1. The maximum charge weight per delay criterion suggested in the Merritt Report was published in <br /> the 1960s,and has been superseded by the Scaled Distance Equation,which is based on <br /> investigations conducted by the U.S.Bureau of Mines in the 1980s. The Scaled Distance Equation <br /> is: <br /> W=(D/Ds)' <br /> Where W=the maximum charge weight per 8 millisecond delay period,in lbs. <br /> D—the distance from the blast location to potentially affected structures,in feet <br /> Ds=the minimum scaled distances,which by definition are: <br /> for D=0 to 300 ft.,Ds=50 <br /> for D=301 to 5000 ft.,Ds=55 <br /> and for D=50011 and beyond,Ds=65 <br /> The DRMS will require that all blasting at the proposed quarry be conducted in accordance with the <br /> Scaled Distance Equation. The following table illustrates how the Scaled Distance Equation is <br /> used,and that anomalies occur at the regulatory Ds change distances of 301 and 5001 feet. These <br /> anomalies will not affect operations at the proposed Robins Pit because as explained in item no.2 <br /> below,the location of the Haberkon House 0.8 miles from the blast site is the controlling factor for <br /> blasting. <br /> DISTANCE—Fr. MINIMUM Ds MAX.CHARGE WT./DELAY,LBS. <br /> 100 50 4.0 <br /> 300 50 36.0 <br /> 310 55 31.8 <br /> 330 55 36.0 <br /> 500 55 1 82.6 E� <br /> Office of Office of <br /> Mined Land Reclamation Denver•Grand)unction . Durango Acne and Inactive Mines <br /> Job # 1200710MP - A Page 172of78 <br />