Coal tar removed from Cofferdam 1 on the Congaree River, work on Cofferdam 2 has begun, Civil War artifacts found, turned in for preservation

Workers have completed the removal of coal tar and sediment from the Area 1 Cofferdam on the Congaree River, near the Gervais Street Bridge.

According to an online post from the SC Department of Health and Environmental Control, “Over 26,000 cubic yards of material has been removed. DHEC completed a final inspection within the Area 1 Cofferdam on August 7, 2023, and determined that all coal tar and sediment has been removed to the extent practicable as envisioned in the Modified Removal Action Work Plan.”

Link to DHEC report

Once the coal tar and sediment was excavated, workers used high pressure water cannons to remove any remaining coal tar and sediment until until they reached the granite river bottom. The water used during pressure washing was maintained within the cofferdam and pumped up to a water treatment system to be processed before going to the City of Columbia Sewer system.

After all material was removed and cleaned with pressure washing, workers placed rock along the river’s edge to stabilize the banks from erosion. In the next few weeks, the Area 1 Cofferdam will be removed. The large sand bags will be removed first and then the pumps will be moved from the cofferdam. River water will begin to infiltrate into the cofferdam. Workers will remove the concrete fabriform armoring from the cofferdam. In the last step, workers will start from the middle of the cofferdam and remove the rock until they complete the removal at the shore line.

As this is taking place, workers will begin to construct the Area 2 Cofferdam, which is closer to the Blossom Street Bridge. Some of the material from the Area 1 Cofferdam will be utilized in the construction of the Area 2 Cofferdam. The Area 2 Cofferdam is much smaller and only a fifth of the size of the first cofferdam. Depending on weather conditions, the Area 2 Cofferdam will be completed during this working season.

The Unexploded Ordnance team completed clearing of Cell 2 of the Area 1 Cofferdam on June 17, 2023. They have recovered a fair amount of Civil War era artifacts that have been turned over to the archaeologists for preservation. DHEC photos

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