PORTLAND, Maine — Summit Natural Gas faces a $250,000 fine from regulators after an Augusta gas leak that utilities investigators wrote was potentially “catastrophic.”

The leak led to the evacuation of an Applebee’s restaurant in February, after reports of the odor of gas in the area and in nearby manholes.

“In some locations, gas had concentrated into an explosive mixture of gas and air, creating an immediate and extremely serious threat to life and safety,” regulators wrote in a penalty recommendation issued in March. “Had gas continued its migration and entered a nearby building — for example the Applebee’s restaurant — and ignited, the resulting damage could have been catastrophic and caused multiple fatalities.”

Regulators suggested the fine in March after determining that trenchless installation of the 2-inch gas main damaged underground electrical conduits in three spots. Arcing from the damaged power line burned through the gas main, causing the leak.

Lizzy Reinholt, a spokeswoman for Summit, said the company believes the leak is an isolated incident, but has launched an internal review of the incident and installations done during its 2013 and 2014 expansions by that contractor, ElectriCom Utility Construction.

“We believe this was an isolated incident with a unique set of circumstances,” Reinholt wrote in a statement. “However, out of an abundance of caution, we are doing a systemic review of anywhere this contractor worked.”

Harry Lanphear, spokesman for the Maine Public Utilities Commission, said the concern is with natural gas traveling through the ground and channels drilled for gas lines and other infrastructure. Mixed with sufficient oxygen, that gas can explode.

The penalty recommendation also suggests the company inspect any lines installed with trenchless technologies not covered in its review completed in December.

The requested fine from regulators tops the $150,000 suggested penalty for damaging sewer and water lines in 26 places, during installations completed about a month before the installation near the Augusta Applebee’s, on Western Avenue. The PUC in its report said the likely violations in this case were similar but unrelated to the sewer line case.

Summit and Maine Natural Gas expanded rapidly in the Kennebec Valley area in 2013 and 2014, but that pace slowed last year as oil prices plummeted and lowered the cost of heating oil, propane and kerosene. The company cut back expansion plans in 2015 and laid off about a quarter of its workforce in January.

Regulators wrote the latest recommended penalty factors in that past violation, Summit’s culpability and the company’s ability to pay. Regulators ultimately trimmed that earlier penalty to $100,000, with other changes in company practices, after Summit requested an informal conference to settle the matter.

Summit in the latest case requested an informal conference with regulators, which was scheduled for April 7.

Darren is a Portland-based reporter for the Bangor Daily News writing about the Maine economy and business. He's interested in putting economic data in context and finding the stories behind the numbers.