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Janice Lynn Bennett - 81422.PDF Page 16 <br />Blasting Impacts Assessment for the Proposed GCC Rio Grande, Inc Quarry in Pueblo County, Colorado <br />4.0 SPECIFIC RED ROCK QUARRY BLASTING I M PACTS ANALYSESI M PACTS <br />ANALYSES OF PROPOSED BLASTING AT GCC RED ROCK MINE <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 is assuming that the largest diameter charges that GCC will use in their blasting <br />operations is 6.75 inches,made calculations based on a 6.75 diameter charge, which is typically <br />the largest size hole drilled in limestone quarries. <br />3.1 I mpacts 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 Red Rock 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 fragmented <br />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 characteristics. <br />In one test, the fracturing produced around 6 1/2 - inch - diameter blastholes, loaded with ANFO was <br />measured and it was found that the maximum cracking extended 26 charge radii. <br />AtBased upon my assessment of the limestone characteristics at the Red Rock Site, the maximum <br />fracture radius for a 6.75 -inch blastholes, at 26 charge radii, will likely not exceed 88 inches or 7.3 <br />feet. Since all water wells and other utility pipes will beare located much farther than the limits of <br />ground rupturing, any physical harm to these facilities is extremely unlikely. The nearest water <br />well on the Blake property is located more than 4,000 feet from the permitted blasting areas. <br />Ground rupture damage will also not impact the nearest water - bearing aquifer (Dakota sandstone) <br />located more than 400 feet below the ground surface. <br />REVEY Associates, Inc. <br />Page 13 July 2002 <br />