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ECOSA Evaluation AdrianBrown <br />3. ECOSA <br />3.1 Design <br />The ECOSA is an existing overburden storage area approved for construction in the MLE. It is located <br />in the northeast portion of the Cresson Project, adjacent to the East Cresson Mining area backfill (Plate <br />1). The ECOSA is planned to accept overburden primarily from the WHEX portion of the East Cresson <br />Mining area and the Main Cresson Mining area. Under MLE -2, the ECOSA footprint will expand to <br />approximately 274 acres, and it will hold approximately 120 million tons of overburden (Plate 7). The <br />design has been changed in MLE -2 to allow more efficient use of the available area for overburden <br />storage. <br />The ECOSA is located within the Grassy Valley surface drainage area and any potential surface runoff <br />from the ECOSA will flow into Grassy Valley. Ground water infiltration into the ECOSA will flow <br />directly to the Diatreme, or will be diverted by subsurface rock - filled drains into the Diatreme, from <br />there it will join the flow of the regional groundwater regime. <br />3.2 Construction <br />Initial site preparation will include vegetation salvage, growth medium salvage and stockpiling for use <br />in future surface reclamation at the Cresson Project. This will be followed by removal of clay materials <br />from select areas in the footprint for use in the construction of the VLF liner systems. Following clay <br />removal, additional surface preparation will include contour ditching to enhance capture and infiltration <br />of potential precipitation from the ECOSA into the underlying Diatreme rock, and to transfer infiltrating <br />groundwater to locations where it will infiltrate to the Diatreme. Sediment and storm water runoff <br />drainage control measures will be installed downgradient of ECOSA prior to surface disturbance. <br />For the redesigned footprint of the ECOSA, a road will be constructed to access the toe of the area. The <br />facility will then be constructed by end - dumping, initially with a 300 foot high single lift, finishing with <br />70 -foot lifts with the ultimate toe of each lift set back 100 feet from the ultimate crest of the lift below, <br />to facilitate final grading to a 2.5:1 slope. <br />Reclamation of the ECOSA facility will begin by grading the outslope to approximately 2.5:1, six <br />inches of plant growth medium will be placed on the slope, and the surface seeded during the next <br />available planting season. <br />3.3 Storm Water Management <br />CC &V has evaluated the final configuration for the redesigned ECOSA and also designed a storm water <br />management system to route potential storm water runoff flows and control sediment transport and <br />erosion during construction through completion of reclamation. This system is discussed in Section 10.3 <br />of the Project Description and Appendix 12, Volume VI. <br />The storm water management system during development and for final configuration of the ECOSA <br />uses the same criteria as previously approved. Diversion and conveyance structures are designed to <br />route flows of storm water from the 100 -year, 24 -hour precipitation event. These storm water flows are <br />1385E.20120224 5 <br />