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Scope of Work:
¨ Site preparation at the T11a site required clearing and construction of a 1,800’ temporary haul road along side the tributary ravine. Topography on the site, including steep slopes, ravine depths greater than 60’, and a total elevation change greater than 100 vertical feet, further complicated accessibility and construction.
¨ The support area for the project included a 60’x140’ lined staging pad for sediment dewatering, equipment decontamination, and wastewater treatment operations. The support area pad was constructed with 40-mil liner, loading ramps, interconnecting drainage, and collection sumps.
¨ Prior to sediment removal, the total stream flow was blocked with temporary dams and diverted with a series of 4” submersible pumps to points below the active work areas. Additional dewatering and diversion was required on other areas downstream of the primary dams due to the influence of rain water and groundwater seeps.
¨ In order to protect the morphology of the stream, all sediment removal methods were designed to minimize intrusive damages wherever possible. The objective of the project was to remove the fined grained sediments, and associated PCB contamination, without removing the larger rocks. Initially, the selected removal method utilized 3,500 cfm wet/dry vacuum trucks to convey manually loosened sediments as far as 200’ from the bottom of the ravine to points on the haul road. Later in the project, when cold weather prevented vacuum truck operation, sediment was loosened and loaded with a mini-excavator and conveyed to the haul road using a 200 ton crane equipped with a 1.5 CY skip bucket.
¨ Wet sediments were trucked to the support pad where dewatering and solidification was performed using lime kiln dust. After solidification, sediments were shipped off-site for disposal via TSCA and non-TSCA landfills.
¨ Contaminated water collected from removal areas and dewatering efforts at the support pad was treated via a 100 gpm portable water treatment system. Water discharge criteria required treatment to proceed until PCBs were non-detectable.
¨ In addition to general restoration activities, the USACE permit required the construction of several environmental structures in the streambed to replace morphological structures lost during remediation. These structures included a variety of weirs, check dams, pools, and riffle complexes.
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