The lawyer hired to represent North Carolina's environmental agency during a federal investigation into its regulation of Duke Energy's coal ash dumps previously represented the utility company in a different criminal probe.

The state Department of Environment and Natural Resources has hired Mark T. Calloway of Charlotte to help respond to 20 grand jury subpoenas the agency has received following the Feb. 2 spill at Duke's Eden plant that coated 70 miles of the Dan River in toxic sludge. Duke has been issued at least two subpoenas.

Calloway represented Duke in a 2004 federal investigation into the company's accounting practices. Duke was cleared of wrongdoing.

Environmental agency spokesman Drew Elliot says he sees no conflict of interest in Calloway's prior representation of Duke.

Legal experts say the arrangement likely doesn't violate ethics rules.