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MINE ID # OR PROSPECTIN~ID#: M-1978-305 • PAGE: 2 INSPECTION DATE: 9-11-00 INSPECTOR'S INITIALS: ACS This inspection was conducted to further evaluate the Dickerson Quarry and requirements to satisfy the Geotechnical Stability Exhibit (Rule 6.5) for the pending application to convert Permit M-1978-305 to a Section 112 Regular Operation Reclamation Permit (conversion application CN-O1). The Applicant, Gunnison Gravel, provided a conversion application with Geotechnical Stability exhibit that relied on qualitative discussion of the competence and hardness of the rock to be quarried and a proposal to finish the highwall by creating 40 foot high 0.5:1 faces and 20 foot wide benches. Gunnison Gravel believes that this is a highly stable configuration and is sufficiently conservative to negate the need for rigorous quantitative stability analyses. The Division of Minerals and Geology provided Gunnison Gravel with a memo dated July 31, 2000 describing a stepwise analytical procedure for determination of ultimate quarry highwall stability. The July 31, 2000 memo is incorporated into this inspection report by reference. Following their review of the memo, Gunnison Gravel stated a willingness to modify the conversion application by increasing proposed bench widths to 25 feet and by committing to make a future evaluation of the need for perimeter blasting techniques as mining operations approach the final highwall. Gunnison Gravel requested a site visit by the Division's engineering staff to further evaluate the stability of the quarry and use onsite observations in the decision of whether the concessions by Gunnison Gravel would allow an approval of the conversion application. The existing highwall in the Section 110(2) Limited Impact Permit area was inspected. This highwall was a focus of the inspection because it provides the best exposure of rock types in the quarry at the present time. Mr. Wilcox stated that the near vertical highwall had last been mined in the 1960s. The following rock types were observed: decomposed granite, West Elk Breccia, and hard biotitic gneiss referred to locally as Gunnison Granite. The decomposed granite is soft and friable. This material would be subject to rapid erosion and would have a residual strength that is less than in situ strength. The in situ decomposed granite stands at a steep, near vertical slope, but there is a wedge of granite sand at the toe of the highwall indicating that the material has eroded over the years. The West Elk Breccia is a. soft breccia made up of volcanic pumice and ash enclosing boulders and cobbles of harder volcanic rock. The quartzite occurs with and as inclusions in the gneiss. When unweathered the quartzite and gneiss are hard and durable. Gunnison Gravel anticipates that the final highwalls will be constructed primarily in the unweathered gneiss. All of the rock types observed in the quarry are jointed, and the gneiss is foliated. Some of the joints are healed with a mineral in filling; others are open and continuous over distances of tens of feet. No slickensides or clay gouge was observed in any of the joints that were inspected. The quarry face and the inspected joints were completely dry at the time of this inspection. Gunnison Gravel does not anticipate encountering ground water during operation of the proposed expanded quarry. The following measurement was taken from a joint surface that is dipping out of the existing quarry highwall: strike N39E, dip 60NE. An area of cliffs on the backside of the knob to be quarried was inspected. These cliffs are just north and west of the proposed quarry area above a Park Service picnic area adjacent to Highway 50.~ The rocks in the lower part of the cliffs are hard gneiss and minor quartzite. The following measurements were taken from joint surfaces in the gneiss: strike N60W, dip 79NE; strike N8 E, dip 73 E. It could not be determined if the gneiss persists to the pinnacles that form the upper cliffs. The pinnacles appear to have been formed at least partially as a result of near vertical jointing in the rock. A quick windshield inspection was made of steep and stable Highway 50 road cuts located east of the quarry and of canyon walls on the opposite side of the Gunnison River. Proposed quarry zone #5 was inspected (see exhibit C-mine plan map, included in the conversion CN-O1 application for quarry zone locations). Hard gneiss crops out at the surface in this zone. The following measurement was taken from a joint surface in a zone #5