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Mr. Michael Cunningham 2 <br />CDRMS <br />August 16, 2013 <br />and loaded (e.g. there is confining pressure on the GCL), hydration of the GCL is no longer an <br />issue, regardless of the quantum of water contained within the perched aquifer. A letter from <br />CETCO addressing the use of GDL over groundwater seeps is attached. <br />Geocomposite Drainage Laver (GDL): <br />Therefore, the proposed placement of the geonet liner is for installation purposes only and is <br />intended to temporarily protect the GCL until the TSF liner system is; (a) installed, (b) filled with <br />water for ballast (per TR -3), and (c) the existing tailings are placed in the newly constructed <br />facility (per TR -3). <br />Since the geonet is to be placed directly on soil, geonet with a geotextile layer to keep colluvium <br />from the geonet is specified. The geonet with geotextile material is referred to as Geocomposite <br />Drainage Layer, GDL. <br />Geocomposite Clay Liner (GCL): <br />CETCO specifies that a minimum of 1ft of confining material be placed on the GCL. The water <br />and existing tailings to be placed in the TSF will exceed this requirement. <br />The installation process will be completed and tested in 4 -6 days (from the commencement of <br />liner installation). The existing tailings and ballast water will be placed in the TSF over a period <br />of 5 -7 days after the installation of the liner. This represents a timeframe of about 2 weeks <br />where the GCL will be unconfined. <br />CETCO is a leading manufacturer of GCLs, and will, through our installation contractor, supply <br />the GCL for the TSF. <br />Clarifications: <br />The liner contractor will commence TSF liner installation only if weather conditions <br />permit and low inflows from the perched aquifer are present, allowing for the proper <br />installation of the GDL. <br />UMC will work with the Division to obtain permission to install alternative inflow <br />mitigation measures should high inflows preclude the use of a GDL system. <br />Reference to "Engineer" in this document refers to Ken Curfman. Mr. Curfman was also <br />our engineer representative during embankment construction. <br />1. The Division requires the submittal of the following information in order to adequately <br />analyze this proposal: <br />a) Provide documentation which demonstrates that the transmissivity of the geonet is adequate <br />to handle up to 3 times (24gpm) the amount of inflow which has been observed. <br />Response: <br />Given that the GCL will be unconfined for a short period of time (approximately 2 weeks); UMC <br />does not believe that demonstrating a 24gpm geonet transmissivity is required. UMC commits <br />to installing the TSF liner system during a period of low inflow. <br />b) Demonstrate that the colluvium at the bottom of the TSF can handle infiltration of the <br />estimated maximum inflow rate (24gpm). <br />