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Duke Energy’s contractor spent its first full day on Monday 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, Tenn., 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 will collect and test 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.
Phillips and Jordan used the same separation process for ash that accumulated at the city’s water treatment plant during the filtering process following the spill. The city stored that ash until Duke Energy arranged for its removal.
The removal of ash at the plant began in late March and ended on May 5 with the removal of a total of 253 tons of dried ash and sediment. Those solids also were transported to the Upper Piedmont Landfill.
The coal ash spill into the river occurred when a pipe under the main ash pond at Duke Energy’s shuttered Dan River Steam Station – located 20 miles upstream from Danville – broke on Feb. 2 and spewed 30,000 to 39,000 tons of coal ash and 24 to 27 million gallons of water into the river.
“What we have seen along the river is varying situations,” Brooks said Monday. “In some areas, we have seen no coal ash. In other areas, we have seen a thin deposit of coal ash on the sediment layer. On others, we suspect the sediment layer may have covered the material now as part of the river’s normal circulation process.”
Of the three deposits identified as candidates for removal, this one near the Schoolfield Dam is the largest. Duke Energy estimates 2,500 tons, or 6 to 8 percent of the entire spill, accumulated near the dam, which is the first dam downstream from the Duke Energy plant.
The city closed the park on April 1 to allow Duke Energy crews and its contractor to begin mobilizing its operations for the ash removal. A security fence is in place.
Duke Energy expects its work at the park will be finished and the park re-opened to the public in early July. The EPA and other agencies have reviewed the ash removal plan and techniques.
The park features a boat access ramp and a boathouse. The boathouse opens seasonally and allows water sports enthusiasts to rent a canoe, stand-up paddleboard or kayak hourly, daily or for the weekend. The Danville Parks and Recreation Department also uses the park as a river access point when it conducts water recreational classes. The department plans to conduct many of the classes at other points along the river in the city, but the boathouse is now closed and access to the boat ramp is blocked.
The city has placed two cameras at the park to allow citizens to watch the dredging operation. Go to www.danrivercleanup.org to watch a live stream of the activity.