Duke Energy’s contractor spent its first full day yesterday removing the deposit of coal ash and sediment found in the Dan River across from Abreu-Grogan Park on Memorial Drive, which is just upstream from the Schoolfield Dam.
The operation took place in view of local and North Carolina media who gathered Monday to tour the site and hear Duke Energy officials explain the restoration process.
“We have surveyed the river all the way down to the Kerr Reservoir and what you are seeing is the largest deposit that we have identified for removal,” Duke Energy spokesman Jeff Brooks told the media. “It is a deposit estimated at about 2,500 tons. That is coal ash and river sediment. Coal ash is only a part of that, but we are removing all of that material.”
Duke Energy’s contractor, Phillips and Jordan of Knoxville, Tennessee, is using a more sophisticated dredging technique than simply scooping into the river bottom as is common. The technique it is using works somewhat like a household vacuum cleaner, with the dredging tool sweeping up the ash, minimally disturbing the river bottom.
Brooks said the nozzle of the dredging tool, mounted on a barge, is six feet in width and is capable of removing up to 1,500 gallons of coal ash, sediment and water per minute.
The barge is pulled back and forth along the river. A safety crew riding in a small boat shadows the barge.
“This crew also monitors the environmental impact, so if we see anything that begins to stir or anything that seems out of place, then we are going to stop operations,” Brooks said. “We want to make sure this material does not migrate farther down the river.”
Turbidity barriers, also known as silt barriers or silt curtains, are in place in the river. These special curtains are designed specifically to contain and control the dispersion of silt – or in this case, coal ash – in a water body. They surround the submerged parts of the dredging tool.
The deposit of coal ash and sediment is located on the north bank of the river, across from Abreu-Grogan Park and the city’s water intake. The deposit spans 350 yards by 20 yards, according to Duke Energy. It measures up to one foot in depth.
As added precaution, the city of Danville has shifted the hours of operation at its water treatment plant due to the dredging. The shift in hours of operation at the water treatment plant means the water intake valve is closed during the daytime when dredging is taking place. The value is open during the evening and overnight when there is no dredging.
During the dredging operation, the city is collecting and testing raw water samples at the intake pipe where it draws its water from the river. In addition, the city will collect and test samples of the water after treatment.
The coal ash, sediment and water dredged from the river goes through a multi-stage filtering process that separates the ash and sediment from the water. Clean water is discharged back into the river. The settled solids are conveyed to roll-off containers for disposal.
Brooks said these containers will be transported to Person County, N.C., where the solid waste will be deposited at the Upper Piedmont Landfill. The landfill is double-lined.
Press Release, May 13, 2014