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AOXOM <br />Henderson 3 Dam Buttress Design <br />January 26, 2018 <br />Page 11 <br />CONSTRUCTION DETAILS AND CONSIDRATIONS <br />The construction of the buttress will be completed in four stages as discussed earlier in this letter. <br />The volume of the buttress and filter material required for each stage as well as total material needed <br />are presented in Table 4. These quantities are based on neat line quantities. <br />Table 4: Volume of Construction Fill and Excavation <br />Construction <br />Stage <br />Estimated Fill Volume (CY) <br />Buttress <br />Material <br />Filter <br />Material <br />1 <br />108,200 <br />17,800 <br />2 <br />30,400 <br />500 <br />3 <br />65,800 <br />0 <br />4 <br />57,100 <br />2,000 <br />TOTAL <br />261,500 <br />20,300 <br />A representative from AECOM will be on-site during construction to observe fill placement. <br />Additionally, AECOM's representative will understand the design and can help facilitate design <br />changes required, based on field conditions. AECOM will prepare a design construction summary <br />letter complete with as -built drawings at the end of the project. <br />Infrastructures_ Mgglifcafiyns <br />The buttress construction will impact existing infrastructure as shown in the drawings. Infrastructure <br />impacted includes horizontal drains, foundation drains and the seepage collection channel. The <br />design is planning on maintaining the existing functioning horizontal drains and extending them to <br />allow them to continue to function throughout operation. The foundation drains will also be extended <br />and impacted portions of the seepage collection channel will be re -located and tied back into the <br />current seepage collection channel to maintain the current operational system. <br />Instrumentation on the dam currently includes piezometers, movement monuments and <br />inclinometers. Some of this instrumentation will also be impacted by the buttress. As part of the <br />buttress construction and post -construction monitoring, additional instrumentations are proposed to <br />be installed in the impacted areas. <br />Surface Water Runoff <br />Each bench will be constructed with a slight slope towards downstream slope, as shown in the design <br />drawings, to provide a drainage path for surface water runoff. Surface water will be collected by <br />existing stormwater collection boxes following current operation of embankment. Annual <br />maintenance of the benches and the area around the stormwater collection box should be expected <br />similar to the current operation. Upon closure, the surface water runoff management plan should be <br />revisited for long-term management solutions. <br />M�DCSWwj�tWYil►M6SSI�F MFJU_8 040.1w�64a1DRM9 RwwMAw"odwsnn 3 own Rftm GnYp Law R"wLRw 8 Fklad= <br />