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Fora 3'/cinch diameter drill-hole, Dynomix explosive, at 3.56 #/foot, will fill about 16 feet of the 24-foot <br />deep hole, leaving 8 feet of/<-inch gravel stemming at the top of the hole to control fly-rock and sonic shock <br />with a virtually undamaging ... <br />a) less than'/z-iuch per secoud per second acceleration, <br />b) frequencies of around 200 cycles per second, and <br />c) uo measurable peak particle velocity. <br />[Note: Structural damage begins occurring at accelerations of 2 inches/sec/sec and above, in the <br />neighborhood of 10 cycles/sec and less, and with discernable peak particle velocity. ] <br />Colorado Iaw2 requires no monitoring for a scaled distance (D~ of 55 or more, where scaled distance <br />equals the actual distance (>300 feet) from the blast in feet (D) divided by the square root of the weight in <br />pounds of the explosive (VV) per delayed hole, when fired with delays of more than 8milli-seconds. <br />At a straight line distance of 820 feet from the blast site to the neazest structure (the Plateau Creek Bridge @ <br />Forest Road 514) a 57 pound load per hole, Fred at a greater than Smilli-second delay, produces a scaled <br />distance of Ds = 109 feet (.. ,nearly two times better than the minimum required monitoring threshold). <br />Ds = 820 Ft - X57 = 820 - 7.5 = 109.33 Ft <br />It would take 211 pounds/hole/delay of explosive under the same specifications to produce aColorado- <br />measurablescaled distance of Ds = 55 feet. <br />Ds = 820 Ft - X211 = 820 _ 14.5 = 56.55 Ft <br />At an explosives load of fifty-two percent (52%) of that delay hole-load limit, we consider the safety factor <br />for this blasting plan to be more than adequate. <br />Adeauacv Item #21 <br />2. The application indicates that the final slope of the benched highwall shall approximate <br />0.58H:1 V. Pursuant to Rule 3.1.10(3), rnal slopes must support rangeland post mining land <br />use and shall not be too steep fo be traversed by /(vestoc/c DMG recommends 3H: iV slopes <br />for rangeland post-mining -and use. Please clarify how the proposed 0.58H:1V slopes <br />address the requirements of Rule 3.1.10(3). <br />McStone Response #2: <br />Per Rule 3.1.10(3) the proposed slopes of the vast majority of the disturbed extraction azea are to be <br />essentially flat and nearly level. The steep perimeter headwalls and their protective crest-fencing aze an <br />intentional significant livestock and wildlife barrier at the west, north, and east property boundaries. Access <br />is to be provided via the remaining entrance road ramp at the north edge of the extraction area. A solitary <br />neaz-vertical barrier wall will be left separating the extracted areas from the Plateau Creek gorge. Of note is <br />that steep highwalls allow not only efficient extraction of the majority of the available resource, but also <br />allow for a greater portion of the remaining extracted disturbed area for a more rangeland-compatible, nearly <br />level plain. Slopes of even 3:1 and 4:1 are mazginally useful for livestock due to their steepness, and are <br />much more difficult to re-vegetate. (A box is a much more e((icietrt and use(uf comainer than a cone.) A <br />naturally occurring near-vertical slope makes up the canyon walls of the Plateau Creek gorge immediately <br />west of the extraction areas, demonstrating compatibility with existing terrain. <br />Adeauacv Item #3) <br />i. Pursuant to Rule 3.1.5(3), the application must demonstrate how the final confrguration <br />of the highwall will be sufl7cient/y stable to protect areas outside t/te affected land from slides <br />and other damage. Please submit an appropriate engine~erfng stability analyses, described <br />under Rule 6.5, for the highwall configu-ation proposed in the application. <br />2 CFR 30, Sections 715.19(e)(2)r~)(c)(1), 818.87(d(3)n, and 817.87(d)(3)~ <br />