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Terry Morris Engineering, 705 Clovis Drive, Durango, Colorado 81301 <br />Analysis of the Effect of Blasting Operations on Structures Associated with <br />Mining Activity at the Mayday Mine <br />This report evaluates proposed blasting operations at the Mayday Mine relative to any potential <br />damage to structures on the site and in the Immediate area The Mayday Mine is located In La <br />Plata County, Colorado at the end of CR 124. <br />The planned mining activity will take place approximately 1,500 feet underground through the <br />Mayday No 2 workings. The nearest structures are the mine office and mill complex located <br />approximately 1,500 feet northwest of the Mayday No 2 portal and four residential buildings <br />located approximately 1,000 feet west of the Mayday No 2 portal. Conservatively no structures <br />exist within a straight line distance of 2;000 feet of the proposed blasting <br />Blasting will occur using typical underground methods utilizing high explosive dynamite or water <br />gel primers and ANFO set off by nonel or electric detonators with timing delays greater than 25 <br />milliseconds. A typical round, consisting of thirty holes, 6 -foot deep and 1-3/8 inch diameter would <br />explode up to 100 pounds of explosive. Delay timing would result In maximum of up to 30 pounds <br />detonated in any 8- millisecond or greater period. <br />The proposed blasting plan described results in very low vibration due to the small amount of <br />explosive detonated per delay. Due to the confined nature of breaking rock underground, 'blasting <br />Is only effective when small charges are detonated per delay. With proper use and storage of <br />explosives there is not a concern that the underground plan presented would cause structural <br />damage on the property surface. <br />Using the typical industry standard scaled distance approach to limit vibration, with an applicable <br />minimum scaled distance value of 60, the proposed blasting plan described above would not affect <br />the structures defined. The table below shows the predicted quantity of explosive which could be <br />detonated without expecting damage from ground vibration to structures located 2,000 -feet from <br />the blast. <br />Terry Morris, <br />Scaled Distance Formula: <br />W =(d /D,) <br />Scaled Distance, Ds = 60 <br />Distance from blast to affected structure, d = 2,000 feet <br />Allowable weight of explosive per 8 ms delay, W = 1,100 lbs/delay <br />In conclusion, the proposed plan using 100 pounds of explosive per blast (even without the benefit <br />of delay timing) falls well under the predicted 1,100 pounds of explosive which could be detonated <br />with no expected structural damage. It is recommended that vibration monitoring be utilized if the <br />size of the blasts ever reaches the unlikely amount of 200 pounds of explosive per delay to provide <br />more accurate prediction of potential vibration damage. Any other significant modification of the <br />proposed plan in loca� ) tion of structures relative to blasting activity or the size of expected charges <br />to be blasted should t;� jNyed based on the new parameters. <br />` L • ;1REZ 4 <br />Respectfully s :; °� F ��, <br />4L,,, a t'•+"� <br />• <br />l immototh <br />