Agenda - 06-01-2010 - 4k - Laserfiche WebLink

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Charleston County, South Carolina 42 General Engineering and Environmental Management Services HDR began work with Charleston County in 2002 to permit, design, and manage construction of the proposed US 17 South Subtitle D MSW Landfill. The County acquired the 750 -acre site in the early 1990's to replace the currently active Bees Ferry Landfill. The initial work included a site evaluation by preparation of a Preliminary Hydrogeologic Characterization Report (PHCR). The site was reviewed for threatened and endangered species, as well as cultural resources. HDR delineated over 400 acres of jurisdictional wetlands and coordinated with the U.S. Army Corps of Engineers (USACE) to gain approval of the delineation and to obtain approval of proposed wetland disturbances. During this work, the County was reviewing its long -term solid waste management program, and HDR evaluated the Bees Ferry Landfill for potential expansion in lieu of immediate development of the 17 South site. HDR reviewed expansion options and determined that continued waste management at Bees Ferry was both feasible and economical. The County transitioned HDR to permit, design, Key Elements. and manage construction of a lined Subtitle D P ■ D ermittin and -acre lined landfill n expansion at the Bees Ferry Landfill. Through ■ desi The combination of piggybacking over the old waste and taking the ash monofill out of service increased the design capacity of the lined unit from 3.5 MCY to nearly 10 MCY. U to • Lined landfill piggybacks over initial concept planning, HDR determined that closed landfill piggybacking the new lined expansion over the sideslope of the unlined unit would • Unlined landfill grades afford more capacity at less cost, while providing a more environmentally sound cap redesigned over the unlined landfill. HDR and the County met with SCDHEC to discuss the • Old waste area reclaimed to optimize lined capacity piggybacking option, and after review of other facilities where HDR had • Construction Administration for piggybacked over old waste, they agreed the approach was permittable. Cell 1 and leachate facilities The expansion capacity without piggybacking was initially estimated to be 3.5 MCY, while utilizing the piggyback concept would yield 6.2 MCY. After further design, the expansion area was modified to include decommissioning of the existing ash monofill, which boosted the expansion capacity to a gross airspace of nearly 10 MCY. This significant airspace is expected to provide MSW disposal capacity at Bees Ferry for more than 30 years. During the permitting of the lined expansion, HDR prepared a permit modification for the current, unlined MSW site in order to accurately match the permitted contours to the construction grades. The permit modification was prepared in a manner to give the County flexibility with regard to closure date and tonnage received. The design also allowed co- disposal of C &D waste within the MSW area, which improved the site life of the existing C &D landfill and optimized the use of the soon to be closed MSW area. An 11 -acre area that had received waste was also reclaimed in order to construct the new liner system over the unlined area of the landfill. HDR proceeded to complete the Site Hydrogeologic Characterization Report (SHCR) and the Permit Application for the site. The Bees Ferry Landfill is located near the centroid of the most seismically active area on the eastern seaboard according to USGS seismic mapping. This is due to the historic Charleston Earthquake of 1886. This fact required a rigorous seismic evaluation, including in -situ shear wave analysis to determine the most sensitive frequency for the site. HDR has designed completely new infrastructure for the Bees Ferry Landfill including a new Convenience Center, Scalehouse, Administration Building, Roads, and Landscaping. HDR is currently providing Construction Administration for Cell 2 expansion. Page 27 11. R