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Reconstruction and Realignment of Upper Grassy Valley after WHEX Pit Backfill <br />After the WHEX pit is backfilled the soils can be expected to consolidate over <br />time. Simple restoration to the pre- existing topography without consideration for such <br />behavior could result in low areas along the stream system caused by settling. The <br />result would be undesirable interception of storm water into the backfilled mine pit. <br />Consolidation and settling is generally related to the depth of fill. The amount is also <br />sometimes predictably on the order of 1 percent of the fill depth. The depth of backfill in <br />WHEX may be as high as 500 feet near the center of the pit, and near the natural <br />alignment of Upper Grassy Valley. Therefore, settling on the order of five feet would not <br />be out of the ordinary. <br />The proposed remedy is to reestablish Upper Grassy Valley in a constructed <br />tributary north of its present alignment and where the backfill is the shallowest, along the <br />northern boundary of the pit. The expected consolidation through that corridor should be <br />on the order of one foot, an acceptable amount. The relocation of the stream to that <br />alignment will include sculpted landforms (a ridge) and the stream will be lined with clay <br />to prevent exfiltration into the mine. Detail 7 on Sheet 4 shows the proposed <br />realignment of Upper Grassy Valley. That alignment and its profile have been chosen <br />for minimum depth of backfill as for north as possible (as describe above) but at a low <br />enough elevation so that storm water discharges from EMP -18 can flow to Grassy Creek <br />(rather than pumping) after mining of WHEX has been completed and the area is <br />backfilled. That will occur, according to the mine plan, in 2018 and will be completed in <br />2019. <br />Implementing the Use of Perforated Outlet Pipes in non - Terminal EMPs <br />The EMP ponds in Upper Grassy Valley were previously designed (MLE1 and <br />Amendment 8) to hold twice the 10- year /24 -hour storm. Observation of two such ponds <br />(EMP -10 and EMP16) has revealed that accumulation of storm water could be a <br />continual issue because of the impermeable nature of underlying soils. The Storm <br />Water Management Plan (SWMP) allows for pre - planned "regenerative release" of storm <br />water to natural streams such as Grassy Creek, but only with extra precautions to <br />protect water quality. Those additional measures can be averted if the storm water <br />accumulations can be used within the mine instead of discharging to the stream. This <br />Client: CC &V Gold Mining Co. <br />Title: Storm Water Management, MLE2 <br />2/2/12 <br />Page 10 <br />