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While North Carolina authorities and federal agencies are investigating the toxic coal ash spill from Duke Energy's power plant into the Dan River last month, the company may still be discharging harmful chemicals into waterways, the New York Times has claimed.

Aerial photographs obtained by the newspaper show two of Duke's coal ash ponds at the Cape Fear River being fitted with portable pumps and hoses that seem to be discharging water from the ponds into the river. According to Drew Elliot, spokesman for the North Carolina Department of Environment and Natural Resources, the regulator noticed the activity during a site inspection last week. In an email sent to the New York Times, Elliot explained that while the power plant's permit allows maintenance work, discharging untreated wastewater is a violation, so the occurrence will be investigated.

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Meanwhile, a spokesperson for Duke stated that the pumping was necessary to reduce the level of water in the ponds and was part of the maintenance work Duke was permitted to carry out. He also said that state authorities were informed about the activity, but was unable to provide further details.

The coal ash ponds near the power plants contain processed wastewater mixed with heavy metals that could be very harmful for the environment, according to the New York Times.