The Pennsylvania Department of Environmental Protection (DEP) finalized more than $374,000 in penalties Aug. 20 against three of the state’s leading natural gas producers for methane migration violations that affected private drinking water wells.

All of the violations date back to 2011 or 2012. The DEP said the investigations were “complex and lengthy,” adding that it was ultimately able to “conclusively determine that methane gas from natural gas wells had migrated off-site and impacted private wells” serving homes and hunting clubs in Northeast Pennsylvania.

The agency said Chesapeake Energy Corp., ExxonMobil Corp. subsidiary XTO Energy Inc. and Royal Dutch Shell plc affiliate SWEPI LP had all been cited and have already paid the penalties.

Chesapeake paid the most, for casing issues at a well in Bradford County. The DEP said four private water wells had been impacted by the methane migration. Chesapeake paid a fine of $193,135.

XTO paid $95,753 for casing and cementing issues at two natural gas wells in Lycoming County that impacted seven private water wells. And SWEPI paid $85,593 for problems caused by the communication between an abandoned gas well and one or more of its own in Tioga County. Methane migrated from those wells and impacted water wells at two nearby hunting clubs.

Both Chesapeake and SWEPI notified the DEP of the problems in 2012. An investigation into the problems at XTO’s wells in Lycoming County, however, was prompted by a citizen complaint that the agency received in 2011, DEP said.

The DEP said all of the affected water wells have been permanently replaced with treatment systems installed by the companies. Repairs on the defective gas wells have also been completed.