CONTAMINATED SEDIMENTS SUCCESSFULLY REMOVED AND CAPPED, ENABLING WATERFRONT DEVELOPMENT IN BUFFALO, NEW YORK

摘要

Sediments contaminated with coal tar were present in a 488 meter (1,600-foot) reach of an urban waterway in Buffalo, New York. Remedial action involved damming and diverting the streamflow around the work area, excavating and stabilizing 15,290 cubic meters (20,000 cubic yards) of hot-spot sediments, placing 8,826 square meters (95,000 square feet) of geosynthetic clay liner (GCL) and sand/armor stone cap, installation and operation of two deep DNAPL recovery wells, restoring aquatic and terrestrial plants, and long-term site monitoring. Capping entailed placement of an impermeable GCL followed by 45 cm (18 inches) of sand, geofabric, and a minimum of 15 cm (6 inches) of armor stone. Scour modeling and design calculations were performed to determine the size of the armor stone and thickness of the sand layer to ensure the long-term physical stability of the cap. Diffusion modeling was done to ensure the long-term mitigation of contaminant migration. The GCL was a reinforced composite liner consisting of a layer of sodium bentonite between two geotextiles which are needlepunched together and laminated to a membrane liner of 0.10 millimeter (4 mil) polyethylene. Topsoil was placed over selected cap sections and then planted with aquatic and emergent species. The cap was completed in 1999. Annual monitoring of the physical condition of the cap has been conducted, including two underwater video surveys. No sheens or other evidence of cap failure have been observed during the past 6 years. No erosion or uplifting of the cap is evident to date. The banks and shallows throughout the capped area have complete vegetation coverage. Numerous fish and animal species have been observed in the area, such as turtles, ducks, crayfish, and beavers. The project has enabled esthetic and economic improvements to the local community, including a recreational pathway adjacent to the waterway which is part of the City of Buffalo Local Waterfront Revitalization Plan.