In March 2013, DHEC identified a preferred cleanup alternative for the Congaree River sediments and soils as No. 4 - Removal of the TLM and Impacted Sediments.
Federal and state laws govern activities in (or affecting) navigable waters, therefore various permits will be required if it were selected as the final cleanup alternative. The United States Army Corps of Engineers (USACOE) and DHEC have established a joint application process for activities requiring both federal and state reviews or approvals. The permit processes require SCE&G to submit detailed information for the project addressing, but not limited to, the following:
- Potential impacts on public navigation practices within the Congaree River;
- Temporary dam construction design and operation;
- Techniques for the temporary removal of water, also known as dewatering;
- Land disturbance activities;
- Management of impacted water and sediments from the river and uplands;
- Impact to wetlands (as applicable);
- Historic impacts and recovery of historic artifacts (as applicable and through approvals from the State of South Carolina Historic Preservation Office and/or South Carolina Institute of Archeology and Anthropology); and
- Endangered or threatened plant and animal species (as applicable and through approvals from National Marine Fisheries, the South Carolina Department of Natural Resources and/or United States Fish and Wildlife Agencies).
During the permitting process, several significant design issues with the cofferdam were identified and caused the need for a re-evaluation of the proposed removal action. These issues included:
- Risk of increased erosion to the shoreline on the west bank;
- Risk of creating flooding on the west bank;
- Risk of overtopping of the cofferdam;
- Risk of catastrophic overtopping where cofferdam material and exposed tar material would be washed downriver; and
- Risk of construction, potential for leakage and concerns that the cofferdam could not be adequately removed when complete.
DHEC is currently re-evaluating the cleanup alternatives outlined in the Engineering Evaluation/Cost Analysis (EE/CA). The Administrative Record includes documents that DHEC is using to evaluate the alternatives.