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Scope of Work:
¨ Site preparation required clearing and grubbing, removal of surficial debris, and installation of all temporary facilities including an on-site laboratory.
¨ Prior to installation of the final cover system, the entire landfill was rough graded. Over 110,000 cubic yards of stripped soils and excavated materials were relocated and compacted along with 46,000 cubic yards of imported structural fill.
¨ The gas collection system consisted of a 760’ subsurface cut-off trench, gas cutoff barrier, cap vents, header piping, 120 gas monitoring peizometers, and five activated carbon vapor treatment units.
¨ The leachate collection system consisted of 140 extraction wells, stone-filled collection trenches, a 2,300 linear foot, watertight PVC sheetpile cutoff wall, over 1,000’ of gravity drain pipe and force mains, and related connections to the leachate treatment system.
¨ The leachate treatment system collected leachate at the pumphouse where volatiles were removed with an air stripper and iron precipitation inhibitors were added prior to wetland treatment.
¨ Leachate was then pumped to one of three 1.5 acre constructed wetland treatment systems (CWTS), configured in parallel, where Phragmites australis was used to perform phytoremediation of remaining leachate contaminants. The CWTS cells are visible at the bottom of the photo (above)
¨ In order to prevent compaction during the planting of the CWTS cells, a low ground pressure (Snow Cat) dozer was used to spread the high organic topsoil material. Manual plantings were performed with special footwear. All plantings were subject to survivability requirements which included isolation from invasive species.
¨ The CWTS cells were subjected to three successive test phases during four months of startup testing and analysis. Treated water discharged to an effluent collection pond prior to off-site drainage through existing channels.
¨ Wetland disturbance from CWTS construction and landfill closure activities required the installation of an additional 2 acres of wetlands, in addition to the CWTS cells.
¨ Installation of the 144,000 square yard landfill cover included a multi-layered cover system, drainage swales, culverts, channels, downchutes, slope stabilization, aggregate roadways, gabion basket barriers, and stilling basins. Final restoration work placed topsoil and seed over 32 acres and installed 6,000’ of security fence.
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