LAWRENCE, Mass. — The reminders of last month’s gas explosions are everywhere in the Merrimack Valley. It’s difficult to go more than a few blocks here without seeing workers in neon yellow safety vests digging up streets and yards, heading into basements, loading new appliances into trucks.

They are part of a massive effort to overhaul the nearly 45 miles of gas main lines and 10,000 residential hookups in three adjacent towns, where cast-iron pipes were laid generations ago. All of it was compromised in what federal authorities said was a grave gas company error while working on the lines, an error that overpressurized the system, sent gas streaming into people’s homes, and started an alarming series of explosions and fires across a large area just north of Boston.

The work is daunting but also on a tight timeline: As nighttime temperatures in New England begin to dip below freezing this time of year, many residents are without heat, are taking cold showers and lack stoves for cooking.

Lawrence, Andover and North Andover were shocked on the afternoon of Sept. 13, when there were 80 near-simultaneous reports of explosions and fires. According to a preliminary report from the National Transportation Safety Board, the blasts came shortly after contract workers for Columbia Gas replaced a century-old iron pipe with a new plastic one but failed to realize that pressure sensors were still active in the abandoned section of pipe. That, in effect, created a communication problem: The gas system thought pressure had dropped and compensated by forcing more and more gas into the region’s lines.

Five minutes passed after a Columbia Gas office in Lawrence was notified of the increasing pressure and the first emergency calls, according to the report, and almost 20 more minutes passed before the regulator station, which keeps gas at the required pressure, was shut down.

One teenager in Lawrence was killed when a chimney was blown off a house and onto the car in which he was sitting. At least five homes were destroyed and another 126 homes and businesses were damaged within a few minutes. And all 10,000-plus customers were considered vulnerable because of potentially damaged appliances and gas connections.

Several lawsuits already have been filed against Columbia Gas and NiSource, its parent company, including one filed this week on behalf of 10 affected residents. The lawsuit argues that the company has not kept its system in good repair, citing numerous examples that show “a pattern of reckless and willful conduct intended to secure profits to the detriment of public safety.”

Columbia Gas has now launched an immense repair effort, promising to get affected residential customers’ gas back in service by the Monday before Thanksgiving — Nov. 19. Any customer who wants new gas appliances — high-efficiency name-brand water heaters and boilers, clothing dryers, and stoves — is getting them, dispensed from a former factory that has been turned into a distribution center in the heart of the affected area.

Instead of turning the damaged system back on, Columbia Gas vowed to replace the whole thing, including underground piping, meters and home appliances. It already has laid nearly 40 miles of an estimated 45 miles of main line pipe and replaced service lines to 3,865 out of about 6,100 houses and apartment buildings.

The company would not disclose how much it is spending on the repairs.

“We have the resources of a large public company to support this work,” said Pablo Vegas, chief restoration officer for Columbia Gas. “Also, we have insurance partners helping us with all the claims and damage issues.”

There are so many crews working — 218 digging up thoroughfares and side streets, paths and yards in the three towns — that they’re practically within sight of one another.

One recent day, under bright sunshine, three crews worked along a stretch of Balmoral Street, north of downtown Andover. One team was laying a main line under Balmoral Street; the other two were on side streets, laying new service lines and attaching a new meter to each house. The meters and pipe each have a new safety feature that shuts off gas flow if the pressure builds up too much.

“We’re way ahead of schedule as it relates to construction in the street — subject to weather, which is really the biggest unknown here,” said Joe Albanese, the project’s chief recovery officer, who was appointed by Gov. Charlie Baker (R).

Lawrence Mayor Dan Rivera praised Albanese but said that while Columbia Gas workers have done a great job with the repair work, the company continues to inadequately communicate with affected families and businesses.

“It’s always been the top leadership that has had issues,” said Rivera, whose own home is in the impacted area of South Lawrence, bemoaning a lack of communication and delays in the claims process. “Every time we roll out something new that’s big and important for people, it gets broken and they take a long time to fix it,” he said. “And the last thing we have is time. Winter’s coming.”

Some people are making do with replacement heating systems and microwave dinners, but many gave up on staying in their cold homes. As of Oct. 16, Columbia Gas has placed 1,829 families in substitute housing — the bulk in nearby hotels, some of them in New Hampshire. Four mobile home communities have been established on public properties, becoming fully operational this week, with more than 457 residents in 114 trailers, said Christopher Besse, a spokesman for the Massachusetts Emergency Management Agency. Another 115 trailers are assigned but people have not checked in yet, and there are more than 100 still available, he said.

Joaquin Colon was just moving into one of the Lawrence mobile homes on a recent afternoon. “They’re beautiful inside,” he said. Disabled by a bad back and with his wife recovering from surgery, the couple was happy to have heat and hot water again, he said. “Last night was cold.”

He’s not thrilled with the situation but is no longer angry at Columbia Gas. “They’re helping everybody,” he said.

A few blocks away, forklift drivers were busy loading stoves, dryers and hot water heaters onto delivery trucks. They’d retrofitted an abandoned factory for the job but didn’t have a proper loading dock, so they had to quickly design ramps that would allow the forklifts to drive directly into the trucks.

“Six weeks ago, there wasn’t a chair in the building,” said Kevin Kissane, branch operating manager for Ferguson Enterprises, the contractor that is supplying the appliances from a number of different manufacturers. Within a week of launch, the warehouse was fully stocked and bustling with dozens of workers.

Kyle Ruggieri, a project manager with Gilbane Building, which is running the appliance replacement operation, said he and others have been putting in 15-hour workdays to get people back into their homes with working appliances ahead of the coming winter.

“It’s a really good feeling to know you’re making a difference in people’s lives,” Ruggieri said. “I love what this project’s all about.”

Most of the attention so far has been directed at homes, but the 676 affected businesses in the three communities are getting new pipes and appliances, too. About 80 percent of the businesses have already reopened, mostly with help from their insurance providers. Columbia Gas is now prioritizing businesses that rely heavily on gas service, such as restaurants and laundromats, Vegas said.

Lisa Rodriguez, who lives on Springfield Street in Lawrence, said she sometimes gets envious that businesses such as the store on her corner are up and running again, while she’s still cooking on a hot plate.

“I’m mad because they got priority,” she said. “But we need food.”

Rodriguez said she was recently able to get a portable shower that, when fed with boiling water, provides a decently long hot shower.

She also bought a couple of space heaters to warm up the apartment. But with the memory still fresh of her block’s three fires last month, she’s afraid to leave them on at night: “I’d rather be awake and cold.”

Weintraub is a freelance journalist based in the Boston area and is a frequent contributor to The Washington Post. Frances Stead Sellers contributed to this report from Washington.