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Blasting Impacts and Rock Slope Stability Assessment for Cottonwood Quarry m Grand County,CO <br /> 4.0 IMPACTS ANALYSES OF PROPOSED BLASTING AT COTTONWOOD SITE <br /> In the following sections, potential effects of blasting are analyzed and where appropriate, <br /> practical and proven mitigation measures are recommended. For purposes of estimating blast <br /> effects, the author made calculations based on a 6.75 diameter charge, which is typically the <br /> largest size hole drilled in aggregate quarries of this scale. <br /> 4.1 Impacts on Water Resources <br /> From the author's experience at many other blasting operations throughout the United States, <br /> concerns about blasting impacts on water resources have involved physical damage to existing <br /> water wells, reservoirs, springs and aquifers or chemical contamination of ground water. A <br /> discussion of these potential physical and chemical impacts at the Cottonwood site follows. <br /> Physical Damage,to Water Resources <br /> In a study (RI 790I, 1983) conducted by the US Bureau of Mines (USBM), researchers set up <br /> tests designed to determine.the maximum zone of physical rock damage zone that can occur <br /> around blastholes. In this study, core logs, borehole periscopes, permeability tests and various <br /> other measures were used to determine the extent of blast damage to adjacent rock not <br /> fragmented and removed by blasting. <br /> Data from the study indicated that the extent of localized blasthole damage in the form.of radial <br /> cracking is generally a function of radial charge diameter, explosive type, and rock <br /> characteristics. In one test,the fracturing produced around 6 V2 -inch-diameter blastholes, loaded <br /> with ANFO was measured and it was found that the maximum cracking extended 26 charge <br /> radii. <br /> At the Cottonwood site, the maximum fracture radius for a 6.75-inch blastholes, at 26 charge <br /> radii,will likely not exceed 88 inches or 7.3 feet. Since all water wells and other utility lines are <br /> located much farther than the limits of ground rupturing, any physical harm to these facilities is <br /> extremely unlikely. <br /> Since quarrying operations will occur in rock formations located at higher topographic elevations <br /> than any water-bearing rock aquifers, rock blasting and mining operations will have no impact <br /> on area wells or the water that feeds them. <br /> REVEY Associates,Inc. Page 12 April 2004 <br />