2019-05-02_REVISION - M1978208 - Laserfiche WebLink

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Items five and six are noted and do not require direct addressing. Existing available geological and geotechnical data gathered by the operator and other third- party experts over the past 15 years was reviewed and evaluated. In addition to that, Mr. Dean Misantoni conducted a preliminary site investigation to determine if there was any reason to doubt the veracity of the previously gathered geologic and geotechnical information on the site. The analysis found herein is limited by the available data provided by the operation and the third-party reports reviewed. Neither Mr. Misantoni nor any Lewicki and Associates staff make any additional geotechnical stability determinations beyond that which have already been made in previous analyses or work. This evaluation is to confirm the validity of existing analysis only. 1. Existing Highwall Description 1_1 Highwall Geology The Idaho Springs Formation makes up the Precambrian basement of much of Colorado. The different lithologies have been well described, and while it varies petrographically somewhat across the State, it can generally be described as a package of igneous and metamorphic rocks including banded gneiss, migmatite, schist, pegmatite and amphibolite. Many other lithologies can be present in lesser amounts. Moreover, the terminology used in naming such a diverse package of rock types can be confusing. While the current highwall examined is not the same one described in all of the previous reports reviewed, the overall descriptions provided by previous geo-consultants and in-house staff describe the same package of rocks noted below, and although different terms may have been used(e.g. banded gneiss is equivalent to biotite or horneblende gneiss and migmatite is equivalent to injection gneiss) all of the lithologic descriptions observed in the available historic reports accurately and competently describes the rock types exposed in the present highwall. The only additional lithology which was apparently not present in previous highwalls (to the west, earlier in the quarry history) consisted of narrow, foliation-parallel intrusions of Pikes Peak granite on the upper left wall of the current highwall. These "sill-like" intrusions are no more than 2 ft. thick and are probably derived from a nearby mass of Pikes Peak granite to the north- northeast of the property. Lithologically,these are composed of pinkish orange, blocky, equi- granular, medium—grained, quartz-biotite-feldspar granite. This granite is volumetrically estimated at less than five percent by volume of the current highwall. The remaining 95% of the highwall exposes banded gneisses (Idaho Springs Fm.). This can be further divided into biotite gneiss, migmatite or injection gneiss, and amphibolites (a gneiss with dominant horneblende instead of biotite). Figure 1 is a photo of the highwall on April 29, 2019, with the distribution of each rock type shown.None of the currently exposed rock types are weathered to any extent. The above qualitative observations were made during the site visit and based on the previously conducted analysis; however no systematic mapping or plotting of any features was performed. Based on data available and the observations made,the primary structural element that will affect the highwall stability and design, is the foliation, or layering/banding. This feature is similar to bedding in sedimentary rocks and may or may not be derived from a sedimentary protolith. A few, apparently random joints were also noted. The strike of the foliation along most of the highwall is north to south, at a slight angle (NNE-SSW)to the strike of the highwall face (roughly N-S). The foliation typically dips from ten to thirty degrees east(into the highwall and Shaffers Crossing TR 2 X (;rck I.caic►t and tswciatrs.PI