The proposed project submitted to the Corps for permit consideration consists of conducting annual maintenance dredging, the discharge of sediment laden water from an existing Dredged Material Containment Area (DMCA), and the transportation of dredged material from CST to the Charleston Ocean Dredged Material Disposal Site (ODMDS) for the purpose of ocean disposal. In detail, the applicant has proposed to dredge approximately 60,000 cubic yards of accumulated material each year in order to maintain the depth of the berth at CST (-45 feet Mean Lower Low Water +2 feet of advanced maintenance + 2 feet of extreme low tidal variation + 2 feet of allowable overdepth). The berth at CST is 2 feet deeper than the adjacent Federal navigation channel so there is sufficient depth for cargo ships to rise and fall with the tide while they are being loaded and unloaded at CST.
The existing DA permit (SAC-2011-00078) authorizes the SCPA to use a hydraulic cutterhead or a mechanical dredge to remove accumulated sediment from the berth at CST. As shown on drawing sheets 2 and 3 of 8, the existing berth is 4,076 feet long and 125 feet wide (11.70 acres), and the total depth is -51 feet Mean Lower Low Water. Depending on the method of dredging, maintenance material is hydraulically pumped to an existing DMCA (e.g., Clouter Island, Daniel Island, and/or Drum Island) or placed in scows before being pumped into one of these existing DMCAs. The existing DA permit is scheduled to expire on December 31, 2021.
The proposed work is consistent with the existing DA permit and would not alter the length, width, or depth of the berth at CST. In addition, the SCPA has proposed to use the same two dredging methods to remove accumulated sediment, and the dredged material would be hydraulically pumped or placed in scows before being pumped into an existing DMCA. The only difference is that the SCPA has also proposed to transport dredged material from CST to the Charleston ODMDS for the purpose of ocean disposal. The Charleston ODMDS is located approximately 9 nautical miles southeast of Charleston, South Carolina and is identified as “Dump Site (dredged material)” on NOAA Nautical Chart 11521, Charleston Harbor and Approaches.
The Charleston ODMDS was designated by the U.S. Environmental Protection Agency (EPA) for the long-term placement of dredged material associated with the Charleston Harbor Federal navigation channel and other dredging projects near Charleston, South Carolina. Over the past 20 years more than 22 million cubic yards of new work material and approximately 1 million cubic yards per year of maintenance material has been placed within the ODMDS (a total of more than 42 million cubic yards). Since the existing berth at CST is located immediately adjacent to the Federal navigation channel, the SCPA believes there may be opportunities for contractors to use the same dredging equipment to conduct work associated with both projects.