Congaree River Sediment Cleanup

Congaree River
View of the Congaree River looking south from the Gervais Street Bridge

The Congaree River begins in Columbia where the Saluda River and Broad River join together. It is bordered on the east by the City of Columbia and on the west by the Cities of Cayce and West Columbia. It flows for approximately 47 miles until it merges with the Wateree River. Congaree National Park is located about halfway down the river's course.The Congaree River is a popular area for swimming, canoeing, fishing and other recreational activities.


The South Carolina Department of Health and Environmental Control (DHEC) has confirmed the presence of a tar-like material (TLM) in the sediments and soils of the Congaree River between the Gervais and Blossom Street bridges. The source of the TLM was determined to be from discharges of coal tar from a former manufactured gas plant (MGP) originally located between Huger, Hampton, and Williams Streets and owned by SCANA. This MGP operated from 1906 until the mid-1950s. DHEC has been overseeing the investigation and assessment of TLM in the river since June 2010.

By 2013, DHEC had evaluated potential cleanup alternatives and narrowed the viable alternatives down to four. DHEC initially decided to pursue Alternative 4 – Removal of the TLM and Impacted Sediments – and identified it as the preferred alternative. SCANA began the permitting process for the Removal Alternative with the US Army Corps of Engineers (USACOE).

In October 2015, the Columbia area was hit with a massive rain event causing widespread flooding and the river reached record levels. This rain event also breached the Columbia Canal (just upstream from the TLM impacted area) and deposited thousands of tons of “new” sediment downstream. Much of the TLM impacted sediment was covered with a significant layer of new sediment.

During the permitting process several challenges surfaced which were compounded by the flood. A large cofferdam approach in a very dynamic river created concerns about overtopping, catastrophic failure from overtopping, creating a rise in the river which could create potential impacts to the western bank, and whether a USACOE permit would be approved. Due to these obstacles, SCANA requested DHEC to allow SCANA to pursue Alternative 3- Sediment Capping and Institutional Controls.

In August 2016, after discussion with the USACOE and SCANA, DHEC requested SCANA evaluate Alternative 3 –Sediment Capping and Institutional Controls. SCANA submitted an application in September 2016 to the USACOE to determine if a permit could be obtained for the capping alternative. USACOE issued a Nationwide 38 Permit in October 2017 to allow for capping of the TLM.

In January 2018, DHEC met with SCANA and community stakeholders to evaluate the possibility of overcoming the permitting challenges of a full-scale cofferdam removal by targeting a smaller area for removal. A modified removal action would allow for the removal of TLM-impacted sediment in areas of the river that are most recreated, areas where there is the most potential for exposure, and where the majority of TLM volume exists in the river. SCANA requested additional information from USACOE in March 2018 for the potential modified removal approach. USACOE responded in May 2018 and indicated that a permit may be achievable for a modified removal approach. On June 22, 2018, DHEC requested SCANA pursue a modified removal action for the site.

 

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