Federal prosecutors are conducting a criminal investigation into the natural gas explosions and fires that rocked three communities near Boston in September.
NiSource, the parent company of Columbia Gas of Massachusetts, disclosed Thursday it is cooperating with a criminal investigation by U.S. Attorney for Massachusetts Andrew Lelling's office. The Indiana-based utility made the disclosure in its quarterly financial disclosure report to the U.S. Securities and Exchange Commission.
NiSource and its subsidiary were served initial grand jury subpoenas on Sept. 24, shortly after the Sept. 13 incident that killed one person, injured 25 others and damaged or destroyed more than 130 structures across Lawrence, North Andover and Andover, the company said in its filing.
The report didn't provide further information about the nature of the investigation, and a company spokesman declined to elaborate Thursday. Lelling's office also declined to comment.
"We are cooperating with all investigations and inquiries into the Lawrence event, including the criminal matter. However, we can't speak specifically to any of those inquiries," said NiSource spokesman Ken Stammen.
The gas explosions are also being investigated by the National Transportation Safety Board, which said in a preliminary report last month that over-pressurized natural gas lines were to blame for the deadly incident.
That investigation, which is ongoing, found the company failed to account for critical pressure sensors as it planned for upgrades to the pipeline system, parts of which are cast-iron pipes more than a century old.
The utility company also faces legal actions from victims of the explosions, including a possible class action lawsuit. Gov. Charlie Baker's administration has hired an independent evaluator and ordered all natural gas companies to review their pipeline procedures.
Thousands of customers, meanwhile, remain without natural gas service for hot water, heat and cooking.
Columbia Gas has said it will need until at least early December to fully restore service. Earlier this week, it announced it had completed a major milestone: replacement of about 44 miles (71 kilometers) of pipeline.
The company said Thursday it has restored service to 1,510 residential meters and 147 business meters, or roughly 20 percent of the total impacted area. More than 7,000 individuals are in temporary housing and about $37 million in claims have been paid out, the company said.