2020-02-07_REVISION - M1977211 (14)

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1100318 R0T0 0811 JRW1 10 reclamation before completion of the bench to minimize local bench instability is also discussed in the amendment and shown in Figure 6. The 1994 Amendment defines an “Area H” as seen in Figure 3. The “H” stands for “Hole.” The length of Area H shown in the 1994 Amendment and 2000 Amendment is 1,859 feet in a north-south direction. According to the amendment, the area defines the limits of excavation to be created at the base of the quarried slope; the excavation of this area allowed removal of the aforementioned undisturbed land at the north end of the quarry from the Mining Plan.19 Figure 7 through Figure 11 show the Mining Plan Map, cross sections, and Reclamation Plan Map associated with the 1994 Amendment. As a further part of its engineering and geologic evaluation and design, the 1994 Amendment discusses slope stability of Area H with particular reference to the west side of the area and considers four factors: 1) historical sliding and instability arising from the presence of clay zones (seams) in the Manitou Formation, 2) increasing the slope gradient within Area H, 3) limestone bedding plane dip, and 4) dimensions of Area H.20 With respect to historical sliding, the amendment discusses two slope failures that occurred in the mid-1970’s and one that occurred in January 1993.21 All three failures reportedly occurred on clay zones within Manitou Formation limestone and occurred as translational sliding block failures.22 Figure 12 shows the evolution of the risks associated with the presence of clay beds. The 1994 Amendment states that to increase slope stability, the upslope areas with strata containing the clay zones (Area MV in Figure 3) would be mined prior to mining Area H, thereby significantly reducing the hazard of massive landslides. With respect to the slope grading and bedding factors, the 1994 Amendment stated that prior stable performance of the quarry did not indicate these were substantial stability issues. As discussed in subsequent sections of this report, the 19 Application for Permit Amendment Pikeview Quarry, Permit Number M-77-211, received by Colorado Division of Minerals and Geology on June 2, 1994, page 8 (Appendix 12) 20 Application for Permit Amendment Pikeview Quarry, Permit Number M-77-211, received by Colorado Division of Minerals and Geology on June 2, 1994, page 19-24 (Appendix 12) 21 Mark A. Heifner, Submittal of six annual reports for Castle Concrete Company, May 21, 1993 (Appendix 23) 22 Application for Permit Amendment Pikeview Quarry, Permit Number M-77-211, received by Colorado Division of Minerals and Geology on June 2, 1994, page 20 (Appendix 12)