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6.3.4 MLE2 Impacts to Surface Waters <br />The progressive development of WHEX will capture an increasing portion of the <br />precipitation (snow and rain) in the upper reaches of Grassy Valley. Most of this <br />captured precipitation will infiltrate to the Diatreme. This development will reduce <br />runoff and alluvium ground water contributions to the Grassy Valley surface waters. At <br />the final disturbance limits of WHEX, the naturally low seasonal runoff at GV -01 is <br />likely to be reduced further due to the loss of the upgradient stream drainage. Flows at <br />GV -01 (or just below GV -01) may persist due to storm water management on the east <br />margin of the WHEX. Seasonal flows at the downstream surface stations GV -02 and <br />GV -03 also are likely to be decreased due to the development of WHEX. <br />The selective removal of historic mine features in the middle and upper reaches of Grassy <br />Valley during WHEX and ECOSA development (e.g., Cameron and School Section <br />materials) is likely to improve the ground water quality at GV -02 in the long -term. <br />MLE2 also will extend the ECOSA in the middle reaches of Grassy Valley (Figure 2 -2). <br />The ECOSA will manage and capture snowmelt and precipitation runoff during operation <br />to prevent erosion and sediment transport. This snowmelt or precipitation will saturate <br />the ECOSA until field capacity is reached after which the water will be captured by the <br />Diatreme drainage system. This is likely to reduce surface flows at GV -03 during <br />operation. After closure, the ECOSA cover system will manage runoff to minimize <br />erosion and sediment transport. The runoff volumes will be similar to pre -ECOSA <br />conditions. The snowmelt or precipitation that infiltrates the ECOSA cover system will <br />be captured by the Diatreme drainage system, similar to the pre -ECOSA conditions. The <br />runoff and infiltration factors for the closed ECOSA facility therefore are likely to have a <br />neutral effect on surface flows at GV -03 after closure. The operational and post - closure <br />design and runoff conditions are described "Cresson Project East Cresson Overburden <br />Storage Area Evaluation" dated February 2012 and prepared by ABC. <br />The water quality at GV -01, GV -02, and GV -03 is expected to be stable and perhaps <br />improve with removal of historic mine features in the upper and middle reaches of Grassy <br />Valley. The flow and water quality conditions in the surface waters of Grassy Valley will <br />continue to be monitored by GV -01, GV -02, and GV -03. <br />6.4 Ground Water <br />'Cripple Creek & Victor Gold Mining Company <br />Cresson Project Hydrologic Evaluation for Mine Life Extension 2 <br />33 <br />