The U.S. Army Corps of Engineers, Buffalo District, recently completed repairs to a confined disposal facility (CDF) at the Buffalo Outer Harbor, Buffalo, NY.
Since 1970, four CDFs were built in the City of Buffalo. Only one remains active, Buffalo CDF 4, which is used primarily to store contaminated sediment which could not be otherwise placed in the lake according to EPA guidelines.
The sediment recently placed in the CDF 4 came from portions of the Buffalo River identified by the Great Lakes Legacy Act as “Areas of Concern”.
The Buffalo CDF 4 is different from typical CDF designs; it is designed to be a filtration dike. Through the dike center is steel sheet piling that rests upon filtering stone. The piling forces dredging water through the filtering stone into the lake by gravity flow, leaving the sediment in the CDF.
Since its construction in 1977, the CDF has incurred storm and ice damage in some areas. Over time, wave forces moved large armor stone out of position and broke many of the stones. Storm action also caused localized dike settlement and the sheet pile had lifted in places along the wall.
Funding limitations required the Corps of Engineers to focus repair to the areas that sustained the worst damage. Repair was broken down into two phases. The first phase was completed in 2010. It involved concrete grouting between the raised sheet piling and the filtering stone to block dredging water from flowing around the filtering stone, restoring the dike’s filtering ability.
“The contractor used a sophisticated computerized grouting system to track and document the grout volumes, flow rates and pressures. This insured the creation of a continuous wall of grout within the compromised reaches,“ said Michael Mohr, Corps of Engineers’ Coastal Engineering Regional Technical Expert.
The second phase of the repair was finished in early September 2016.
It involved removal of broken armor stones on the dike and rebuilding the crest with precast concrete block and replacing the old stone with new stone.