(CNN) - A gas leak that forced the evacuation of some 100 people in Lawrence, Massachusetts, last week happened when road workers inadvertently closed a gas valve that should have been disabled previously, state authorities told CNN.
Friday's evacuations came a year after Lawrence and two nearby communities were hit by a string of gas explosions that killed at least one person.
Power was cut early Friday to 1,900 homes in the city, about 30 miles north of Boston, due to the most recent leak, National Grid spokesman John Lamontagne told CNN. About 80,000 people live in Lawrence.
Friday's leak happened when road workers who were checking water valves inadvertently closed a gas valve, puncturing an active main line, the Massachusetts Department of Public Utilities told CNN Monday in a joint statement with the city and Columbia Gas.
The workers had been checking water valves to prepare for road paving, the statement reads.
The gas valve in question was not in compliance with state requirements, and had been slated to be disabled last year as part of pipeline reconstruction, according to the statement.
Following Friday's leak, 45 additional valves were identified for inspection over the weekend, the statement reads.
The department has deployed so-called "sniffer trucks" to detect any additional leaks and has characterized an investigation into the incident as ongoing.
No injuries, fires or explosions were reported as a result of Friday's leak, Lawrence Fire Chief Brian Moriarty said.
About 100 people are took shelter at a nearby school, Lawrence Mayor Dan Rivera said.
Poor oversight caused 2018 blasts, per NTSB
At least one person was killed last September when a string of gas explosions hit Lawrence and two other towns north of Boston. Nearly 40 homes and business were affected by the explosions and fires, and at least 22 people were taken to hospitals.
The "probable cause" of those blasts was inadequate management of a construction project by Columbia Gas, the National Safety Transportation Board announced last week. Also a factor was inadequate protection of a low-pressure natural gas distribution system, the agency concluded.
"Columbia Gas of Massachusetts' weak engineering management ... did not adequately plan, review, sequence, and oversee the construction project that led to the abandonment of a cast-iron main without first relocating regulator sensing lines to the new polyethylene main," NTSB's Managing Director Sharon Bryson said last week.
"Contributing to the accident was a low-pressure natural gas distribution system designed and operated without adequate over-pressure protection," she said.
Columbia Gas' findings align with those of the NTSB, the utility said in a statement.
"We welcome today's action by the NTSB because it will help us, our industry partners, the public, and others learn from this tragedy. As we've said since that tragic day, we take responsibility for what happened," the statement said.
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