Electric-power Co. Duke Energy has dredged up approximately 2,500 tons of ash and sediment in its cleanup efforts in the aftermath of the huge spill into the Dan River, the Associated Press has reported.

According to Myles Bartos, on-scene coordinator with the U.S. Environmental Protection Agency, the removal of pockets of coal ash in the river downstream from the North Carolina power plant where the spill occurred has been completed. A further 500 tons were removed from other pockets and settling tanks at water treatment plants in Virginia.

Coal ash contamination can be very harmful to waterways and aquatic life as it contains a number of heavy metals, such as mercury, arsenic and selenium. Tests on samples of water from the river and sediment at its bottom showed levels of toxic metals below federal limits, Bartos told the Associated Press.

In the incident in February about 39,000 tons of coal ash spilled into the Dan River, according to estimates by Duke Energy. Even though just a small part of the total discharge has been recovered, the cleanup operation is considered complete, Bartos said. However, if any significant deposits of contamination occur later, Duke will be required to remove them. Despite the fact that their concentration is close to levels detected prior to the spill, state and federal agencies will still monitor the river.