Environmental regulators in North Carolina consulted Duke Energy last year before seeking to exclude citizen activists from talks to settle charges that the utility’s coal ash ponds had polluted the state’s groundwater, newly released email exchanges among the regulators indicated on Thursday.

Duke officials and the state later settled the charges by proposing a fine and a requirement that Duke study the potential for further pollution before offering solutions. That agreement collapsed in February after one of the utility’s coal ash ponds spilled tens of thousands of tons of toxic slurry into the Dan River.

Federal prosecutors have since opened a criminal investigation into the spill and the relationship between Duke and the state’s environmental bureaucracy. Critics charge that environmental regulation has been hobbled by political interference since Gov. Pat McCrory, a Republican, a former mayor of Charlotte and a Duke Energy employee for 29 years, took office last year.

The emails were obtained in legal proceedings by the Southern Environmental Law Center, which had announced in January 2013 that it planned to sue Duke over charges that its coal ash pollution violated the federal Clean Water Act. The act allows citizens to sue over pollution violations unless governments move to correct them — and to go to court if a settlement is too weak.