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confirms that the surface materials that will remain in part at the base of the ECOSA and that <br /> will be used to reclaim the ECOSA have sufficient hydraulic conductivity to conduct the <br /> measured infiltration of 6" per year under post-closure drainage conditions3. <br /> 4. Evaluation of vertical head conditions in the footprint of ECOSA and more generally in Grassy <br /> Valley. This data from a total of 27 nested well or vertical piezometer string installations,4 of <br /> which are within the footprint of ECOSA, confirms that within the footprint of ECOSA all bedrock <br /> flow is vertically downward'. <br /> 5. Construction of a groundwater flow model of the Cripple Creek Mining District and its environs. <br /> This model was constructed using the topography and geology of the district and observed <br /> surface infiltration rates, and was calibrated against the observed stream baseflow and three <br /> dimensional head conditions measured at the sites. It confirms that all seepage that enters the <br /> bedrock in the footprint of ECOSA flows through the diatremal rockmass and exits with the <br /> natural groundwater via Carlton Tunnel. <br /> The reliability of these evaluations is very high in locations where the ECOSA is underlain by the Tertiary <br /> volcanics of the diatreme,which constitutes 87%of the footprint'. The remaining 13%on the western <br /> edge of ECOSAis underlain by Precambrian rock, which has lower hydraulic conductivity and higher <br /> hydraulic head than is observed in the Tertiary bedrock. While the evaluations described above <br /> conclude with high reliability that seepage infiltrating from the ECOSA in this area will also infiltrate into <br /> the bedrock and flow to the diatreme to exit via the Carlton Tunnel, it is possible that in some <br /> unobserved locations this may not occur, and water might instead flow to the north on the surface of <br /> the remaining colluvium at the base of ECOSA. To mitigate this possibility a seepage collection ditch <br /> system has been included in the proposed ECOSA foundation design to intercept any infiltrating ECOSA <br /> water that may not be drained to the underlying rock and conduct it at a 1%eastward slope over the <br /> diatremal bedrock area,terminating in the vicinity of the Cameron Mine workings'.These drains will <br /> conduct any ECOSA seepage to locations where it will infiltrate to and pass through diatremal rock to <br /> ultimately exit with the natural groundwater via the Carlton Tunnel.The mitigation is implemented at <br /> construction time, as it cannot be added once the ECOSA is constructed. <br /> Adequacy Issue#3: Mitigation of Potential for Seepage from the Toe of the ECOSA to Grassy Valley <br /> DRMS Adequacy Comment <br /> In order to mitigatethis occurrence[flow on a preferential pathway from ECOSA to Grassy Creek], the <br /> Division believes the addition of a three foot inert low infiltration layer above the overburden would limit <br /> moisture contact, thereby minimizing impact to the prevailing hydrologic balance. <br /> 3ECOSA Report, Plate 11. <br /> 4 ECOSA Report, Plate 13. <br /> ECOSA Report, Plate 15. <br /> 6 ECOSA Report, Plate 12. <br /> 'Drainage ditch design shown in ECOSA Report, Plate 14. <br /> Adrian Brown Consultants, Inc. Page 3 of 8 <br />