Lab testing shows the tar-like material (TLM) is consistent with coal tar created at a former manufactured gas plant (MGP) that operated in Columbia about a century ago. MGPs produced gas from coal, oil and other feedstocks, which was used for lighting, cooking and heating homes and businesses. TLM was a byproduct of gas production.

Under the MRA, crews will install a cofferdam and dewatering pumps in the removal areas so they can work on a dry riverbed. They will then remove sediment containing the material for disposal in an approved landfill. We estimate the work will take approximately three years, with crews authorized to work from May until October of each year. However, potential high river levels and flooding could delay the work.

Dominion Energy originally proposed a full removal. However, regulatory agencies had concerns about water displacement over the larger area, particularly around the western shoreline of the Congaree River. The Modified Removal Action plan, created with active participation from stakeholders, addressed those concerns by focusing on areas that are:

• Closer to the shoreline and therefore more susceptible to human skin contact or exposure (e.g. river users such as kayakers, waders/swimmers, fishermen, etc); and
• Where more concentrated, thicker deposits of TLM are known to exist.

While this approach will result in the removal of the majority of TLM, a minor amount will remain in areas of the river where people are less likely to come in contact with the material. Routine monitoring before removal has confirmed that the Congaree River has not suffered water quality impacts nor have aquatic organisms been harmed. The river will continue to be monitored after the removal for any potential impacts.

Dominion Energy began preconstruction work in May 2022. To minimize impacts on aquatic organisms during spawning season, crews will be limited to working in the riverbed between May and October. The work will take approximately three years, with crews working within that timeframe each year. However, potential high river levels and flooding could delay the work.

Current estimates for the project are approximately $20 million, although they could increase due to weather or other construction delays. The costs associated with this project will be recovered over time with the Company's other environmental remediation projects, but it will not increase the rates themselves charged to customers.

Crews will stage operations out of the Senate Street extension, just south of the Gervais Street bridge. The work will require closing the Senate Street parking access and surrounding area for the duration of the project. The western side of the Congaree along the West Columbia shoreline will remain navigable for boaters.

Dominion Energy is taking several steps to minimize the potential impacts flooding would have. This includes tracking weather forecasts and available US Geological Survey river gauges to remain informed of any potential changes in water level. In the event of forecasted flood levels, crews will pause work and remove equipment from the cofferdam until the water has dropped back to a safe level.

It is important to note that during a 100-year storm event, the cofferdam will have no effect on the river elevation. Changes during smaller storm events will not be significant.

Dominion Energy has implemented a site traffic control plan, we plan to limit the hours that trucks use Senate Street and ensure they are staged as required at a remote location to avoid congestion. We are also monitoring road vibrations for the benefit of nearby residents to ensure minimal impact.

Dominion Energy is committed to communicating openly about the project as it progresses. We are providing quarterly reports for all interested parties that highlight communications, submittals, and project status updates. The quarterly updates are available on SCDHEC's website.