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2023-07-14_PERMIT FILE - C1981010A
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2023-07-14_PERMIT FILE - C1981010A
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Last modified
8/25/2023 9:05:37 PM
Creation date
8/4/2023 11:13:46 AM
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Template:
DRMS Permit Index
Permit No
C1981010A
IBM Index Class Name
Permit File
Doc Date
7/14/2023
Doc Name
pgs 3-1 to 3-101
Section_Exhibit Name
3.0 Project Plan
Media Type
D
Archive
Yes
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3.4.3.1 Blasting Near Archaeological Site 5MF948 <br />As requested by Trapper Mining Inc. (Trapper), Agapito Associates Inc. (AAI) completed an analysis of the <br />potential for damage to an archaeological rock art site from nearby blasting operations in existing and <br />planned mining areas. The archaeological site in question (5MF948) contains examples of ancient rock art <br />(petroglyphs) and is nominated as a National Register site. The site is projected to potentially be as close <br />as 700 feet from the pit edge. The rock art is located on a south -facing cliff in the Twentymile sandstone <br />formation and is protected from flyrock and air blast but may be susceptible to damage from blasting <br />vibrations. The rock art elevation is approximately 200 feet below the lowest planned mining elevation <br />corresponding to the Q seam. The rock art objects are located at ground level on a vertical face of the <br />Twentymile sandstone cliff outcrop under a shallow overhang. <br />To better define what, if any, modifications to the blasting plan may be required to protect the rock art site, <br />AAI conducted an analysis in two parts: (1) determination of the maximum allowable value for the peak <br />particle velocity (PPV) measured at the rock art site to prevent damage to the cliff face, and (2) <br />determination of a representative equation relating particle velocity to distance and charge weight in order <br />to design blasting rounds that will not exceed the criteria determined in Part 1. Existing seismic data from <br />Trapper, including recent measurements at the rock art site, were reviewed and evaluated for relevancy to <br />future mining areas and specific ground conditions near the rock art site. <br />The vibration level measured at the ground surface that causes damage to an above -ground structure is <br />normally less than the level that would cause damage to rock or other structures at the ground surface. <br />Likewise, damage criteria developed to protect buildings may be overly conservative for structures such <br />as the rock art cliff located on the surface. AAI determined through a literature review that tensile slabbing <br />could occur in a ground vibration range of 10-25 in/s, while tensile and radial cracking of a rock mass <br />could occur in the 24-100 in/s range. <br />AAI found a particle velocity of 10 in/s to be the threshold for rock fracturing at the rock art site. However, <br />an increased factor of safety was advised due to the presence of jointing and overhanging blocks at the <br />site which increases the likelihood of rock falls and damage to the rock art features on the exposed rock <br />surface. Since rock falls have been reported in the range of 2-4 in/s, AAl advised that ground vibrations <br />be restricted to less than 2 in/s. However, they further advised that it may be possible to construct a <br />protective structure around the limited exposure length of the rock art panels to deflect rock falls away <br />from the face. With sufficient protection from rock falls, a maximum vibration level of 5 in/s might be more <br />appropriate, and still provide a safety factor of 2 for protection of the face from fracturing. Trapper <br />proposes to use the 2 in/s (5 in/s with rock fall protection) PPV recommended by AAI. <br />AAI collected vibration measurements at the rock art site for 68 production blasts conducted between <br />December 10, 2015 and June 7, 2016. They analyzed data for the 68 shots and developed an equation, <br />representative of actual conditions, based on production blasts and actual vibration levels at the rock art <br />site. The data set consisted of a wide variety of blast designs involving distances of 2,180-6,380 ft <br />between the blast and the rock art site, charge weights per 8 -msec delay of 320-6,480 lb and scaled <br />distances (SD) of 30-230 ft/Ib° 5. The measured peak particle velocity (PPV) ranged from 0.021 to 0.491 <br />in/s. The data were analyzed using a log -log plot of PPV versus SD to determine the linear regression <br />through the transformed data and the 95% prediction intervals. The equation was calculated as the best -fit <br />curve plus two standard deviations (approximately; the upper limit is based on the maximum 95% <br />prediction interval for the data set, which is slightly greater than two standard deviations) and is given by <br />the following: <br />PPV = 71.61 * SD -1.311 (2016 production blasts) <br />The maximum charge weight per delay for the on-site production blasts was 6,500 Ib. For the <br />3-31 b <br />T-�� <br />
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