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All surface water control structures have been built to enough of a size to withstand the 10-YR(2 <br /> HR) storm event. The time of concentration for runoff within the drainage basins present is less <br /> than an hour.NRCS Technical Release 55 guidelines recommend a storm duration in excess of <br /> the time of concentration for a basin as sufficient. <br /> 6. Revegetation and Final Reclamation <br /> Revegetation of Zones 2 through 4 will be completed in 2020. Zone 1 will have revegetation <br /> conducted on the north sloping portion of the zone in 2021. The upper, flat area of Zone 1 will be <br /> used for stockpile storage by APC. <br /> Final release of all revegetated areas is anticipated to be achieved by 2022. <br /> 7. Monitoring <br /> T-posts and stakes have been placed within the completed slide repair work for monitoring with <br /> GPS. GPS and visual monitoring will continue to be conducted over the next two years as part of <br /> the approved permit. Annual reports will summarize this monitoring, starting next year. <br /> 8. Conclusion <br /> The work completed by APC and their contractors has seen the establishment of permanently <br /> stable slopes in the area of recent and historic earth slope slides. The installation of subgrade <br /> drainage pipes along with the removal of all toe-based stormwater ponds will ensure that <br /> saturation conditions do not exist in the tailings or colluvium material on the slope. The <br /> installation of appropriately mixed and compacted Design Fill will ensure that the slope is not <br /> susceptible to water build up or the generation of weakness planes within it. Construction <br /> modifications put into place allowed the slide repairs to be a success while accommodating <br /> safety and practical limitations of the earthwork required. <br /> Please contact me if you have any further questions or concerns. <br /> Sincerely, <br /> :Q Z: <br /> :2 0047151 m= <br /> �3% o• Ben Langenfeld, P.E. <br /> '+�.. •. �� Greg Lewicki and Associates <br /> SS�ONALV <br /> Ralston TR 03 17 (:ng lxe icki and Avuwiatcs,PI AA <br />