In June 2010, DHEC responded to a report of tar-like material (TLM) in the sediments of the Congaree River. The affected area begins directly south of the Gervais Street Bridge, extending approximately 200-300 feet into the river from the eastern shoreline, and approximately 2,000 feet south downriver towards the Blossom Street Bridge. At that time, DHEC began an investigation that included collecting surface water and sediment samples. DHEC also posted metal signs warning against swimming or wading in the area as a precautionary measure.
Preliminary sample results indicated that the TLM had similar chemical and physical characteristics as coal tar, a by-product of Manufactured Gas Operations which were common in cities from the late 1800s until the 1950s. Additional research found that the most likely source of the TLM was a former Manufactured Gas Plant (MGP) located northeast of the river at 1409 Huger Street that operated from about 1906 until the mid-1950s. Later this was the location of the city bus terminal until 2008.
MGPs produced a flammable gas from coal that was used for heating, cooking and lighting purposes prior to the construction of interstate natural gas pipelines. The coal tar material was a waste product from coal-gas production. Once the gas was produced, the coal tar by-product was discharged into a former stream which originated at what we know today as Finley Park, past the MGP site, and into the Congaree River just below the Gervais Street Bridge. The Huger Street MGP was operated by predecessor companies of SCE&G (now Dominion Energy) beginning in the early 1900s and ending in the 1950s, prior to the existence of environmental regulations and permitting.
SCE&G had previously entered into a Voluntary Cleanup Contract (VCC) with DHEC in August 2002 to conduct environmental assessment and cleanup activities at the former Huger Street MGP site. SCE&G has worked proactively and cooperatively with DHEC under its existing VCC to determine the extent of TLM in the Congaree River and to develop a plan for cleanup.
Cleaning up the TLM in the Congaree River is difficult because of several unique complexities which limit the options and techniques available. First, this portion of the river is underlain by granite bedrock with only a few feet of sandy sediment which eliminates the ability to place a piling wall as a barrier. Further, this portion of the river is where the Union Army disposed of much of the Confederate armory in February 1865. This creates a need to consider that unexploded ordnance (UXOs) could be buried within the sediment and requires that a removal would need to be conducted in the dry instead of using a dredging tool to remove TLM. Additionally, any items that may be found dating to the Civil War would be historical artifacts that are of interest to the State Historical Preservation Society.
On March 21, 2013, DHEC held a public meeting to discuss the Engineering Evaluation/Cost Analysis (EE/CA) and present Alternative 4 - Removal of the TLM and Impacted Sediments, as the preferred remedy for cleanup of the Congaree River sediments. All of the comments received during the public comment period were in favor of Alternative 4.
In October 2013, SCE&G began the design and permitting process for construction of a cofferdam to allow for excavation of sediments and tar-like material (TLM) in the Congaree River under dry conditions. From 2013 through the first half of 2015 meetings were held between numerous state and federal stakeholders - including DHEC, SCE&G, and the US Army Corps of Engineers (USACOE), in pursuit of the cofferdam design. 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.
In July 2015, SCE&G submitted a Work Plan proposing to try an alternate removal approach of building a temporary dam using large sandbags to allow for excavation in the river. DHEC and the USACOE agreed to allow SCE&G to conduct a pilot test to see if this alternative could work. SCE&G began the pilot test on September 29, 2015. However, on October 4, 2015, historic flooding washed out the old canal upstream of the removal area and deposited up to 5 feet of sediment over some of the areas to be excavated.
On July 12, 2016, SCE&G submitted a Field Demonstration Project Documentation Report on the pilot test to DHEC. The report concluded that the sandbag approach would not work. SCE&G requested that DHEC reconsider allowing capping of the area due to current river conditions and the negative effects of the proposed cofferdam.
On August 16, 2016, after careful evaluation of all the previously considered alternatives, DHEC sent a letter requesting SCE&G to evaluate if Alternative 3 -Sediment Capping and Institutional Controls would meet the USACOE permitting requirements. The purpose of this was to determine if the USACOE permit requirements could be met for the capping alternative, as they could not be met for a full-scale cofferdam removal alternative.
In September 2016, SCE&G submitted an application for a USACOE permit for the capping alternative. In October 2017, the USACOE approved the Nationwide Permit for capping the sediments in the river. SCE&G submitted a work plan to DHEC on November 30, 2017, for capping coal tar in the river.
In December 2017, DHEC met with SCE&G and community stakeholders to evaluate the possibility to overcome the permitting challenges of a cofferdam removal and if a modified removal action would be possible. A modified removal action would allow for the removal of contamination from the most utilized areas and remove a considerable volume of coal tar from the river. SCE&G 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. Additionally, the current Nationwide Permit for a capping alternative would remain in place and active per the permit conditions until another permit was issued.
On June 22, 2018, DHEC requested SCE&G pursue a modified removal action for the site. A modified removal action would involve constructing a smaller cofferdam or a series of smaller cofferdams to remove impacted sediments.
DHEC met with SCE&G, Congaree Riverkeeper, property owner representatives, City of Columbia, and the SC Governor’s Office in July and again in November to try to define the boundaries of a modified removal action. SCE&G submitted an updated Preliminary Removal Action Work Plan in September and then a Conceptual Plan for a Modified Removal Action in December. These documents used new data to update knowledge of the river bottom and then presented a modified removal action as agreed upon by DHEC and the stakeholders. The Modified Removal Action would allow for the removal of TLM-impacted sediment in areas of the river that are most utilized, areas where there is the most potential for exposure, and where the majority of TLM volume exists in the river.
In January 2019, Dominion Energy finalized the purchase of SCE&G. On April 2, 2019, DHEC held a public meeting to discuss the Conceptual Plan for the Modified Removal Approach. This plan was developed through the cooperative work of Dominion Energy, DHEC, and community stakeholders. The Conceptual Plan received a favorable response from the community at the meeting.
Following the public meeting, Dominion Energy began preparing the documents and submittals necessary to apply for a USACOE Permit to conduct the work in the Congaree River. The USACOE Joint Application was submitted on September 29, 2020 for review.