Laserfiche WebLink
A.� <br /> Mr. Brandon Guite <br /> Henderson Mill <br /> March 29, 2018 <br /> Page 2 <br /> upstream step is constructed. A schematic showing the design slope and benches is provided <br /> in Figure 1. These benches are regularly graded as part of erosion and storm water control <br /> measures and are considered standard maintenance of the impoundment. The overall slope <br /> of 4:1 provides embankment stability and this slope is maintained during any bench <br /> regrading activities. <br /> DBMS Comment 2 <br /> In the Seismic Hazard Update section of the AECOM report dated January 26, 2018, the <br /> Engineer states an updated site-specific seismic hazard analysis of the Henderson tailings <br /> dams was performed in 2015. Please provide the Division with a copy of the seismic <br /> hazard analysis report for review. <br /> AECOM Response 2 <br /> As requested, a copy of the Site Specific Seismic Hazard report is included with this letter. <br /> The Site Specific Seismic Hazard Report evaluates and characterizes potential seismic source <br /> using available geological and seismological data. The content of the Site Specific Seismic <br /> Hazard report has been reviewed by an independent third party expert and resulting ground <br /> motions are used as an input to the seismic analyses. <br /> DRMS Comment 3 <br /> In the Loading Conditions section of the AECOM report dated January 26, 2018, the Engineer states <br /> pore pressure conditions at each of the modeled sections will improve with time since dissipation of <br /> the excess pore pressures in the foundation and tailings material will continue. Please provide <br /> evidence pore pressures have not yet stabilized and will continue to improve with time. Please <br /> demonstrate the drainage features are currently adequate and a long-term monitoring program is in <br /> place to ensure any future failures of the drainage features will be detected and addressed <br /> appropriately. <br /> AECOM Response 3 <br /> The statement in the Design Report refers to the post-deposition dissipation of pore <br /> pressures. The slope stability analyses were performed at the final embankment height with <br /> maximum pore pressure (or phreatic surface) conditions. The stability of the embankment <br /> would improve as consolidation and drain down occur after deposition ceases. Currently, <br /> and as operations continue,pore pressures will remain at levels lower than those used for the <br /> final embankment height stability analysis. <br /> During operations the pore pressure conditions within the impoundment are expected to rise <br /> since active deposition is still occurring. This is observed in piezometers installed along <br /> M•1DCSIPROJECTSIWTR\60551494_HEN3_BUTTR�SW0 ELIVERABLESIDRMS REPORTORMS COMMENTMFINALIDRMS RESPONSE_AECOM_FINAL.DOCX <br />