After more than three months and several failed attempts to stop one of the worst natural gas leaks in U.S. history, the spewing methane above Porter Ranch — which has forced thousands of residents to flee the community since October and prompted numerous health and environmental concerns — has been halted, Southern California Gas Co. officials said Thursday.

The moment came early Thursday, when crews at Southern California Gas Co.’s Aliso Canyon storage field intercepted the base of the leaking well — more than 8,000 feet deep, at the depth of the natural gas reservoir — via a relief well and began pumping heavy fluids to temporarily control the flow of gas upward.

Now that the flow of gas has been stopped, the process of “killing” the well has begun. That process, to be confirmed by regulators, includes injecting cement into the well to permanently kill it.

“We have … begun the process of sealing the well and permanently stopping the leak,” said Jimmie Cho, SoCalGas senior vice president of gas operations and system integrity, and SoCalGas incident commander. “I was very glad we achieved this for the community and our customers. And I am most pleased that we did it without any safety incidents with the workers, who have been working on this from Day One.”

Since its detection on Oct. 23, the leak has pumped more than 100,000 tons of the greenhouse gas methane into the air and has left SoCalGas officials investigating why this particular leak has been so hard to stop.

Reaction

The news quickly spread throughout the Porter Ranch community, which for months has dealt with droves of relocating residents and odors that have prompted many to complain of nosebleeds and nausea. Many looked forward to moving back immediately. Some were skeptical. Others who had remained at home simply were happy to begin opening their windows after weeks of being shut.

“I am relieved to hear that SoCalGas has ‘intercepted’ the Aliso Canyon gas leak,” Los Angeles Mayor Eric Garcetti said in a statement. “This is a critical step for the health and safety of the residents of Porter Ranch and Los Angeles.”

While a lot of work remains to ensure the neighborhood’s safety, Garcetti said, “this is welcome and long-overdue good news.”

Company officials signaled they were getting close to a solution when they announced there would be an eight-day return home deadline rather than the original time frame announced earlier.

Porter Ranch resident Yvette Washington, who did not relocate from the area, said the latest development was welcome news and hoped a sense of normalcy would soon return to her community.

“I’m concerned abut the long-term — housing values, health. I’m concerned about my family,” she said. “I don’t want to wake up 10 years from now and have a third eye.”

Resident Connie Hayden returned to the area Thursday afternoon to see if what she had heard was true.

“I can’t believe it,” said the Porter Ranch resident of 10 years, wiping away tears. She, her husband and children relocated to a hotel in December.

“I’m moving back immediately” she said. “All those little things we lost became so big. But I’m a positive person. I’m just so happy right now.”

A long road to Thursday

Many residents complained of effects like nausea and bloody noses that they said were related to compounds in the gas that give it a rotten egg odor.

SoCalGas gave up to $7,000 in relocation expenses to families who left the community. At one point, residents from more than 5,000 households were in temporary housing.

The leak and a communication breakdown early on between the company and the community outraged residents and elected officials. And it resulted in a series of lawsuits, including claims of wrongful death and allegations that the gas company did not inform authorities of the leak in a timely manner.

Gas company executives said they believe the leak started on a Friday in late October 2015, and the crew at the well site focused on trying to stop it and failed to tell the utility’s communications and customer service unit.

• VIDEO: Porter Ranch resident Connie Hayden talks about stopping the gas leak

Though SoCalGas discovered the leak on Oct. 23, it wasn’t until Oct. 26 — at a previously scheduled meeting with Porter Ranch neighbors to discuss a turbine replacement project — that company officials first spoke publicly about the leak, according to a spokeswoman. The first letter on the subject was emailed to several key contacts on Oct. 27, including the Porter Ranch Neighborhood Council, two schools and four adjacent Home Owner Associations. The next day, the company hand-delivered 1,500 letters to community members and launched a website. On Oct. 31, the company mailed letters to some 8,000 residents about its efforts to stop the leak.

The first attempt to kill the well was made on Oct. 24 by forcing fluids down the SS 25 shaft. That attempt failed, and SoCalGas contacted Halliburton’s Boots & Coots, the company formed in the late 1970s by Asger “Boots” Hansen and Ed “Coots” Matthews, veterans of Red Adair Service and Marine Co.

That company extinguished several hundred oil-well fires in Kuwait during the Gulf War. And in 1974, Adair was brought in to put out an oil-well fire in the field above Porter Ranch.

Special well-kill equipment was then brought in from the Gulf Coast, and Boots & Coots made six other attempts to kill SS 25, the last in late December, but none was successful.

Gov. Jerry Brown finally declared a state of emergency regarding the gas leak on Jan. 6.

Questions remain

There are 115 wells at Aliso Canyon, and some — like SS 25 — date back to the early 1950s. The facility under the Santa Susana Mountains is a sandstone formation, and natural gas is stored in the rocks’ pores.

The gas is injected under pressure, and the state ordered the company to draw out as much as possible. The facility — the biggest west of the Mississippi River — can hold 86 billion cubic feet of natural gas; there were 77 billion cubic feet in storage when the leak erupted.

In late January, the California Public Utilities Commission ordered that the withdrawals be stopped when there were 15 billion cubic feet left in the field.

The leak raised concerns among environmental groups and residents about the safety of storage facilities like Aliso Canyon.

“The leak may be stopped, but huge questions remain about the risks of gas-storage wells across California,” Maya Golden-Krasner, an L.A.-based attorney with the Center for Biological Diversity, said in a statement. “State oil officials have left people across the state at risk from these unsafe wells, and the Aliso Canyon facility is clearly just too dangerous to stay open. It’s appalling that the state’s new emergency rules for gas storage are actually weaker than the industry’s own suggested safety practices.”

The Environmental Defence Fund said the leak exposed failings in the regulatory system.

“Now comes the critical process of making sure this doesn’t happen again and holding the company accountable,” Tim O’Connor, California Oil & Gas Director at the Environmental Defense Fund, said in a statement. “SoCalGas can’t respond with its checkbook alone. It has to take care of the neighbors it has harmed and take enough methane out of the air to make up for the damage this leak has caused.

“This disaster is what happens when aging infrastructure meets lax oversight, and it’s just one example of a problem that is plaguing the oil and gas industry across the country. We need comprehensive national action to hold industry accountable for reducing these emissions and keeping disasters like this from happening again in the future.

The leak is expected to cost the company, a division of Sempra Energy, $250 million to $300 million, according to a filing with the Securities and Exchange Commission. However, that number does not include potential damages from scores of lawsuits, penalties from government agencies and expenses to mitigate pollution, The Associated Press reported.

When to move back?

Regulators on Thursday emphasized there was a way to go in the process of retiring the well.

“This is an important step toward stopping the gas leak, however, additional steps must be taken before the well is officially confirmed to be sealed,” said California Department of Conservation Chief Deputy Director Jason Marshall in a statement. “After Southern California Gas Co. injects cement into the leaking well to form a permanent seal and that cement seal has dried, several tests mandated by the Division of Oil, Gas, & Geothermal Resources will be conducted to confirm the leaking well has been sealed. We will issue a public notice that the well is officially sealed only after this state verification and testing is complete.”

Once the permanent sealing of the well has been confirmed by DOGGR, SoCalGas will start winding down its temporary relocation program, officials said Thursday. Residents who have temporarily relocated to short-term housing, such as hotels, will have up to eight days/seven nights to transition back home. Residents who have been placed in rental housing will have until the agreed term of their leases to return home.

Staff writers Brenda Gazzar and Dana Bartholomew contributed to this report.