Puget Sound Energy will have to pay at least $1.5 million for last year's natural gas explosion in Seattle's Greenwood neighborhood.

In the settlement announced Monday by the Utilities and Transportation Commission, PSE could face $1.25 million extra in charges if it fails to inspect several other gas pipelines by a set deadline.

“$2.75 million is the highest penalty the commission has imposed for a violation of pipeline safety regulations and is among the highest penalties the commission has ever imposed," the commission said in a statement. "The penalty recognizes the severity of the violations and the resulting harm, as well as the company’s acceptance of responsibility, cooperation, and agreement to take appropriate steps to minimize the possibility of future violations."

The commission is made up of three members.

An investigation by the UTC revealed in September that the March explosion was the result of "damage to an above-ground service line by trespassers who regularly accessed the space where the line was located."

The explosion caused extensive damage to the entire neighborhood, leaving economic repercussions even a year later.

Related: A year later, Greenwood still recovering from gas explosion

UTC investigators also determined that the gas line was "improperly retired in 2004, and therefore remained active until it was shut off after the explosion."

As part of the settlement, PSE is required to inspect and remediate more than 40,000 retired gas lines. The gas lines needing review were separated into four groups, all requiring action within the next three years.

The Washington State Attorney General's Office helped negotiate the settlement announced Monday, but ultimately supported a higher penalty.

PSE must also review its policies and practices for deactivating service lines and create an employee training process.

The UTC says PSE operates a 12,000-mile natural gas distribution system to around 785,000 customers around Washington.