A federal grand jury convened in Raleigh yesterday as part of a criminal investigation into Duke Energy, following the company’s coal ash spill into the Dan River last month.

Details of the grand jury’s exact purpose have been kept secret. US attorney Thomas Walker would say only that the investigation is looking at whether criminal activity occurred, WSCO TV reported.

Charlotte attorney Tony Scheer said jurors may look at evidence about the spill itself, or about the relationship between Duke and state regulators.

The February 2 spill dumped 39,000 tons of coal ash into the Dan River, coating 70 miles of the waterway. State regulators have charged Duke with violations at Dan River and five other power plants.

Public health officials advised residents to avoid contact with the Dan River and not to eat the fish, the AP reports.

Prosecutors have issued at least 23 grand jury subpoenas to company executives and state officials, following claims that regulators were too cozy with Duke.

Last week Duke president Lynn Good said it would take the company at least two years to clean up the Eden dump, which caused the Dan River spill. Duke plans to move the remaining ash away from the river to either a lined landfill or a “lined structural fill solution.”

She said the company will move ash dumps in the Asheville and Charlotte area. Duke is looking at options for the Sutton pits near Wilmington, and will work on long-range plans for 11 other sites, Good said.

She has said that Duke expects its customers to pay the costs of emptying the utility’s 31 coal ash ponds in North Carolina.

State regulators are also investigating whether Duke broke the law by pumping contaminated water from a coal ash dump near the Cape Fear River, as the Waterkeeper Alliance recently alleged.