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Cripple Creek & Victor Gold Mining Company Squaw Gulch Valley Leach Facility Design <br />Cut material, if suitable for use as structural fill, will be used for site grading and <br />foundation preparation activities. Because a deficit of fill material currently exists, mine <br />overburden material will be provided by CC &V from the mining operations. During <br />construction, this material will be segregated to meet the 24 -inch maximum particle <br />diameter specification for structural fill. <br />A portion of the VLF will be constructed over the Squaw Gulch Overburden Storage <br />Area (SGOSA). As part of the site construction, the slopes of the SGOSA will be <br />regraded to 2.0H:1 V. Given the particle size distribution of materials within the <br />SGOSA (boulders to sand size), there is a potential for differential settlements to <br />develop on the slope as the VLF is loaded with ore. To reduce the impact of <br />differential settlements, a 3 foot thick layer of structural fill may be placed and <br />compacted over the regraded slope. In some areas, geogrid and /or geotextile may be <br />placed on the regraded slope prior to placement of the structural fill. The geosynthetic <br />materials will help bridge gaps in the regraded slope and help distribute the differential <br />settlements. <br />4.6 Underdrains <br />An underdrain system comprised of primary, secondary, and tertiary underdrains will <br />be constructed within the VLF area to intercept and convey potential shallow <br />groundwater beneath the composite liner system. Primary underdrains will collect and <br />convey flows from the secondary underdrains. The secondary underdrains will be <br />installed in topographic lows beneath the VLF area. Tertiary underdrains will be <br />installed during construction in locations observed to exhibit seeps outside of the <br />topographic lows. Details of the proposed underdrain system are shown on Drawings <br />A250 and A255, with locations of the underdrains shown in plan view on Drawings <br />A205 and A210. <br />Shallow groundwater flows collected in the underdrain system and captured via the <br />underdrain cutoff wall will flow into an underdrain sump located downstream of the toe <br />of the PSSA embankment. The dual- compartment underdrain sump will consist of <br />compartments sized to contain 24 hours of underdrain flow at an average flow rate of <br />20 gpm. The lower compartment of the underdrain sump will be fitted with a collection <br />pump and pumpback piping to route underdrain water back to the VLF. The <br />underdrain pumpback piping, illustrated on Drawing A207, will extend under State <br />Highway 67 in two 12 -inch diameter high density polyethylene (HDPE) culverts to <br />route flows back to process. <br />The primary underdrains will consist of a minimum 15 square -foot cross - sectional area <br />of underdrain fill (minus 12 -inch fill) with a 4 -inch perforated, corrugated polyethylene <br />(PCPE) pipe wrapped in a 12- oz/yd nonwoven geotextile and will be covered with a <br />minimum of 6 inches of select structural fill. The primary underdrain will be placed at a <br />Project No.: 74201125G0 Page 20 <br />1 September 2011 <br />amec° <br />