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AZ� <br /> Mr. Brandon Guite <br /> Henderson Mill <br /> March 29,2018 <br /> Page 6 <br /> Cyclic DSS tests. These lab tests are based on relatively undisturbed samples that <br /> represent the in-situ conditions. <br /> • The material properties used in analysis have been developed using the state of the <br /> practice in laboratory tests and CPT soundings state parameter review. The material <br /> properties have been reviewed extensively and accepted by the third party TRB. <br /> • Phreatic surface and pore pressure regime have been developed based on various CPT <br /> measurements and regularly monitored piezometer readings. As discussed earlier <br /> under Response 3,threshold values have been established and are part of a long-term <br /> monitoring program. <br /> • Calibrated seepage model has been used to develop and estimate the phreatic surface <br /> at the various stage of analysis. As discussed in the report, a phased construction <br /> method has been developed for Henderson 3 Dam buttress and at each stage the <br /> phreatic surface will be reviewed and updated to actual measured conditions. <br /> We also note that the DRMS comment specifically refers to completing a sensitivity analysis <br /> on Stage 4 of the 3 Dam buttress. While this TR is specific to Stage 1,the same comments <br /> above would apply on why a sensitivity analysis is not warranted at any stage of the buttress <br /> design. As described in our response to DRMS comment#3,phreatic levels are monitored <br /> continuously, and any differences in the measured phreatic level to the projected levels will <br /> be taken into consideration at each stage of the buttress design. <br /> CLOSING REMARKS <br /> We hope this document helps clarifies any concerns the DRMS has with the buttress design. In <br /> addition,the DRMS should take comfort that Freeport has taken the initiative to have a TRB of <br /> tailings dam experts review the design. However, if further clarification is needed please let us <br /> know. <br /> Sincerely, <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 /> Updated site-specific seismic hazard analyses report <br /> M MDCSIPROJECTSIWTR6055149/_HEN3_BUTTR1500.DELIVERABLESIDRMS REPORTIDRMS COMMENTSTINALIDRMS RESPONSE_AECOM_FINAL DOCX <br />