Eversource Energy announced Wednesday that it has reached an agreement to purchase the Massachusetts natural gas assets of Columbia Gas for $1.1 billion from NiSource.

The acquisition will bring Columbia Gas operations in Massachusetts under local ownership by the largest energy company in New England, Eversource said in a news release after the stock markets closed.

Eversource and NiSource expect to close the transaction by the end of the third quarter of this year.

The announcement came the same day as the announcement that Columbia Gas of Massachusetts has agreed to pay a criminal fine of $53 million in a plea agreement with federal prosecutors over the 2018 gas explosions in the Merrimack Valley region that killed one person, injured many others and damaged homes and businesses.

Contacted after the announcement, spokesman Reid Lamberty said Eversource didn’t know that the plea agreement would be announced Wednesday.

The transaction will require approval from the Massachusetts Department of Public Utilities and the U.S. Justice Department under the Hart-Scott-Rodino Act.

The companies said that, under the asset purchase agreement, liabilities related to the Merrimack Valley explosions will remain the responsibility of Columbia Gas’ current parent company, NiSource.

Columbia Gas was also held at fault for a 2012 gas explosion in Springfield. The city reached an $850,000 settlement with NiSource in 2013. NiSource also reached private agreements with individual landowners and businesses.

Columbia Gas currently serves 330,000 natural gas customers in more than 60 communities in Massachusetts including Springfield, where it has a service center on Roosevelt Avenue and about 200 employees.

Eversource has its own electrical maintenance depot nearby at 300 Cadwell Drive.

Eversource has 300,000 natural gas customers already, in addition to its 1.5 million electric customers in 51 communities across the state. Many communities that Columbia Gas serves with natural gas already receive electric service from Eversource. That includes Springfield, which currently has both companies.

In total, Columbia Gas has more than 700 employees across its Massachusetts service territory. Eversource has more than 8,000 employees across Massachusetts, Connecticut and New Hampshire.

Eversource will be making offers of employment to all Columbia Gas employees on terms and conditions similar to those that apply to its own workforce, Lamberty said.

He said Eversource will work with consumer groups and regulators over the next 30 days as the purchase is reviewed by regulators.

In its news release, Eversource said it will bring these advantages to Columbia Gas customers:

Ownership by a larger, locally focused company with expertise and resources to excel at delivering safe and reliable energy for customers

Improved safety and reliability through additional investments in infrastructure upgrades

The advantage of locally based gas dispatch and emergency response in Massachusetts

Expanded opportunities to benefit from Eversource’s energy efficiency programs

Improved potential to participate in demand response and other clean energy initiatives

Potential for reduced gas supply costs and increased reliability through portfolio optimization and management

A commitment to maintain appropriate staffing levels that enable safe and reliable operations

Strong financial profile with access to Eversource’s top-tier credit ratings, which helps to lower financing costs for customers

Springfield Mayor Dominic Sarno said he communicated Wednesday with Eversource executives.

“They have reassured me that they will continue to serve our community and provide the quality of service that our residents and businesses deserve,” Sarno said. "I look forward to again meeting with the leadership team of Eversource in the very near future. To continue to build on our good working relationship for the betterment of our Springfield residents and business community.”