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• (Page 3) • MINE ID # OR PROSPECTING ID # M-88-081 INSPECTION DATE 10/11/95 INSPECTOR'S INITIALS ACS required. '.Che beet way to prevent flyrock ie to properly design the blast initially, particularly in terms of burden, collar distance and stemming. Since surface blasting at the Phil Sheridan Lode would be conducted in a residential area, the posting of guards prior to the blast an~9 notification of nearby residents would be considered reasonable precautions. Also, use of blasting mate may 6e required for surface blasting. The operator should contact the Division prior to any future surface blasting at the site. Once it ie assured, through application of the Scaled Distance Equation or, if necessary, vibration monitoring, that ground motions from blaetinq at the Phil Sheridan Lode are at or below acceptable limits on vibration amplitude, nearby residents may continue to be disturbed and annoyed by the blasting vibrations. This is because the level of vibration that can be felt, and can be disturbing to people, are well below levels that are required to cause structural damage. The Mined Land Reclamation Act and the Regulations do provide protection to prevent damage to private or public property outside the permit area, but do not provide any real degree of protection against annoyance. Several complainants indicated that the blaetinq would not be as worrisome if they knew when to expect the blasts to occur. It is a common practice when blasting in a populated area to notify reeidente by providing blaetinq times and schedules. Although such a requirement ie outside of the scope of the Mined Land Reclamation Act, the operator is strongly encouraged to provide nearby reeidente with such schedules. :several nearby reeidente expressed a concern that the operator not blast when children are at the nearby school bus stop. The operator ie advised not to blast when children are present. Several complainants expressed the concern that blaetinq vibration could impact the fracture controlled aquifer tapped by their domestic supply wells. While this ie an understandable concern, the Division finds that this ie not likely to occur, and provides the following discussion in this report in an effort to reassure concerned reeidente. First, the Office of Surface Mining, "Blasting Guidance Manual" states: Incidentally, ground motion has to be far above these levels to threaten wells or aquifers, although these problems are frequently feared and complained of. The "levels" referred to in this quote are the permissible ground vibrations that can be analyzed using the Scaled Distance Equation. More quantitatively, various studies have demonstrated that blast fractures are radial to the individual blaetholee, and are limited in extent (sere the attached figure taken from Morhard et al, 1987). Calder (1977, p 6) reported the radius of rupture around blaetholee in various rocks using different explosives. He reported that the blast damage zone (radius of rupture) around fully-coupled, ANFO loaded, 2-in. diameter blaetholee in Lithonia granite extended a maximum distance of approximately 2 feet, 12 diameters, from the center of the hole. Morhard, et al (1987, p 177) presented a compilation of blast damage zones. For hard rock, such ae the unaltered granite at the Phil Sheridan site, the rupture radius ranged from 7 to 15 diameters of the blaethole from the center of the blaethole. one complainant was concerned that the operator was not properly permitted to use and store explosives. It has been confirmed that an explosive permit has been issued for this site in compliance wi*_h Title 34; Article 24 C.R.S. Explosive Permits for mine sites are issued by the Office of Mine Safety within the Division of Minerals and Geology. other complaints received regarding operations at the Phil Sheridan Lode involved the operator's right to mine in a populated eubu[ban mountain environment, fumes from diesel equipment, truck traffic, and noise. These are all impacts and concerns outside the jurisdiction of the Mined Land Reclamation Act and of this Division. Some of these items may be regulated by the local land-use authority, although it is the Division's understanding that underground mining ie a use by right in the Forestry Zone of Boulder County. The potential for surface and groundwater quality impacts, and their regulatory framework, were discussed with the operator during this inspection. Mr. Conner explained that they are sinking the shaft in order to connect with the historic Phil Sheridan Tunnel. The tunnel is located approximately 100 feet below the surface at the shaft collar location, and Mr. Conner reported that the shaft was at about 80 feet at the time of this inspection. The shaft ie currently above the level of the static groundwater table, with no dewatering required. The portal to the Phil Sheridan Tunnel was inspected. The portal ie located down the hill from the permit area, across the county road, and at the east end of the Harry Covey property.