Massachusetts officials are opening their own investigation into last September's Merrimack Valley natural gas disaster.
More than 100 structures were damaged in Lawrence, Andover and North Andover in the Sept. 13, 2018, fires and explosions. One person died and dozens were injured.
Matthew Nelson, chair of the state Department of Public Utilities, said Friday his agency will look into the cause as well as the response. He said the investigation would take at least a year and could lead to penalties against Columbia Gas.
Nelson made the announcement during a forum in Lawrence focused on the National Transportation Safety Board's recently completed investigation. The agency concluded Columbia Gas poorly planned a pipeline replacement project and responded inadequately to the disaster.
The company said it will cooperate with the state's investigation.