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Blasting Impacts and Rock Slope Stability Assessment for Cottonwood Quarry in Grand County, CO <br />4.0 IM PACTS 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 7901, 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 />craclang is generally a fimetion of radial charge diameter, explosive type, and rock <br />characteristics. In one test, the fracturing produced around 61A -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 />