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A=COM <br /> Mr. Ron Hickman <br /> Henderson Mill <br /> July 15, 2020 <br /> Page 3 <br /> were used to refine the fine tailings extent and to confirm pore pressure conditions. The CPT <br /> investigation showed that the fine tailings material located on the northern side of the original <br /> 3 Dam buttress are isolated and confirmed pore pressure conditions. An updated 2D post- <br /> earthquake loading stability analysis was completed on design section 4A with the updated <br /> fine extents. This analysis was completed using the same procedures described in the 3 Dam, <br /> Phase II Buttress Design letter report dated June 1, 2020. Figure 4 presents the updated slope <br /> stability analysis results for post-earthquake loading condition which meets the stability <br /> criteria. As a result, the proposed regrade or slope flattening of the northern original 3 Dam <br /> buttress is no longer required. Remainder of the design remains consistent with the 3 Dam <br /> Phase II submission. <br /> CLOSING REMARKS <br /> We hope this document helps clarifies any concerns the DRMS has with the Phase II 3 Dam buttress <br /> design. In addition, the DRMS should continue to take comfort that Freeport has taken the initiative <br /> to have a Technical Review Board of tailings dam experts review the design. <br /> Sincerely, <br /> 0 -e— <br /> A"�� a-, <br /> Lisa Yenne, P.E. Richard R. Davidson, P.E. <br /> Project Manager Vice President and Principal <br /> Engineer <br /> cc: File <br /> Attachments: <br /> Figure 1 <br /> Figure 2 <br /> Figure 3 <br /> Figure 4 <br /> C\USERS\ZANA KARIMI\DOCUMENTS\HENDERSON STABUMDRMS PH 11 RESPONSE FINAL DOCX <br />