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• provide a summary of the proposed design and construction, and incorporate design <br />information which has been previously approved by the ML1tB. <br />6.2 Phase 5 VLF and Underdrain System Design Components <br />6.2.1 Underdrain System <br />Although there is no evidence of shallow ground water seepage within the <br />footprint of the Phase 5 VLF, the design includes a similar Underdrain system to <br />the existing approved VLF Underdrain system. After the Phase 5 VLF area has <br />been cleared and the foundation prepared to grade, an Underdrain system will be <br />installed beneath the Phase 5 VLF area to intercept potential shallow ground <br />water seepage that may arise at times and carry the flows beneath and away from <br />the VLF. The Underdrain system consists of primary, secondary and tertiary <br />underdrains. The primary underdrains will collect and convey flows from the <br />secondary underdrains. Secondary underdrains will be installed in topographic <br />lows beneath the Phase 5 VLF area. Tertiary underdrains will be installed during <br />construction if seepage is observed outside of the topographic lows. The <br />underdrains will route flow into a collection pipe located at the upstream toe of <br />the PSSA embankment and designed to return any potential water collected by the <br />• system into the Phase IV VLF containment. <br />As part of the Phase 5, design the effects of increased depth of ore on the flow <br />capacity of the existing VLF underdrains was evaluated (see Appendix 8, <br />Volumes V and VI). The evaluation determined that the existing underdrains have <br />sufficient capacity and integrity under the increased depth to ensure continued <br />operation. <br />6.2.2 Ore Storage Area Liner System <br />The ore storage area will be constructed with the composite liner system as <br />previously approved for the Phase IV construction. This system consists of a <br />minimum one-foot thick soil liner fill ("SLF") with a maximum permeability of <br />1x10-6 centimeters/second ("cm/sec") placed on a prepared surface and overlain <br />by an 80-mil single-sided textured (texture side down) linear low density <br />polyethylene ("LLDPE") geomembrane. The geomembrane will be overlain by a <br />pipe drain system and a minimum of two feet of drain cover fill ("DCF") prior to <br />placement of the ore. The pipe drain system, called the high volume solution <br />collection system ("HVSCS"), consists of a network of pipes laid in a dendritic <br />• Cripple Creek & Victor Gold Mining Company <br />Cresson Project Mine Life Extension <br />6-2 <br />