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Mr. Chris Oestreich <br /> June 29,2023 <br /> Page 3 <br /> 4. An overhead utility approximately 200 feet east of the mine. <br /> 5. The relocated McKay Ditch located 95-feet north of the mine. <br /> These structures are closest to the planned mine limits and will be stable per the stability analyses described herein. All <br /> other known structures are at greater distances and,therefore,will also be stable. <br /> STABILITY ANALYSES <br /> Division of Reclamation and Mining Safety(DRMS)drafted a policy regarding stability analyses of neighboring <br /> structures. The policy summarizes adequate factors of safety(FOS)for non-critical and critical structures. Most of the <br /> structures at the Jefferson County Mine are considered critical structures. The FOS are for both static and seismic <br /> (ground accelerations from an earthquake)stability analyses are listed in the DRMS policy. Soil laboratory testing has <br /> been performed at the site. For critical structures, FOS of 1.5 and 1.2 are considered sufficient for static and seismic <br /> conditions respectively. <br /> The stability of structures within 200 feet of the proposed mining limits was evaluated at the most critical representative <br /> sections under anticipated loading conditions as discussed below. The GALENA computer program was used for the <br /> analysis. The method for selecting the critical failure surface for each analyzed loading condition was the following. The <br /> Simplified Bishop's Method of Analysis was used to find the critical failure surface by randomly searching 2,001 trial <br /> failure cirdes over a broad range of the slope surface and at the structure in question to evaluate the lowest FOS. Both <br /> static stability under anticipated mining conditions and seismic stability under peak ground acceleration(PGA)loads <br /> were performed. Seismic loading was obtained from the U.S.G.S.Unified Hazard Tool attached to this report. Review of <br /> the Hazard Tool indicated a maximum horizontal acceleration of 0.132g with a return period of 2,475 years for the site. <br /> The two most critical cross sections were selected and analyzed as described below. <br /> ► Section 1 Westgate Road Section: This section is on the southeast corner of the mine where Westgate Road is <br /> at its closest(-55 feet)to the mine limit and the mine is at its deepest point on the south side. This section was <br /> analyzed with sixty-six(66)-feet of the Aggregate Unit overlying twenty-eight(28)feet of the Finer-Grained <br /> Alluvial Unit on top of daystone bedrock. The top two(2)feet of the claystone was modeled with residual <br /> strength values reflecting the weathered nature to the contact with the overlying alluvium. Unweathered <br /> bedrock was modeled beneath the residual layer. <br /> ► Section 2 Ditch Section: This section is on the northeast corner of the mine where the relocated McKay Ditch is <br /> approximately 95 feet to the mine limit and the mine is at its deepest point. This section was analyzed with one <br /> hundred(100)-feet of the Aggregate Unit on top of daystone bedrock(borings indicated there was no Finer- <br /> Grained Alluvium in this part of the mine). The top two(2)feet of the daystone was modeled with residual <br /> strength values reflecting the weathered nature to the contact with the overlying alluvium. Unweathered <br /> bedrock was modeled beneath the residual layer. <br /> Both sections were modeled for static and seismic conditions. As discussed below,all FOS required by the DRMS <br /> were met. <br />