The smell came from the canyons and drifted over their neighborhoods in late October, but most residents who live in the gated communities of Porter Ranch thought the northerly gusts of wind common to their area would sweep the stench of rotten eggs away.

Instead, the odor persisted.

It became a phantom that haunted them during their twilight jogs and on their morning walks on dusty horse trails. It was there in their dens where they watched TV and in bedrooms where their children slept. It was even there on the playgrounds of nearby elementary schools.

“It was smelling really bad,” said Susan Gorman-Chang, who along with her husband, George, has lived in Porter Ranch for more than 20 years. Now, the couple has chosen to leave the area. “Our neighbor called the fire department. It was that bad.”

The Southern California Gas Co. knew what was happening a day before the fire department was called. They knew methane was leaking from a 40-year-old well in Aliso Canyon above the Santa Susana Mountains, that it was spewing tons of gas into the air. Several days later, they informed residents through letters that the agency would plug the leak as fast as possible.

Eight weeks after that call was made, the leak continues. It has caused massive disruption in the northwestern San Fernando Valley community of Porter Ranch, an affluent community of nearly 31,000 residents about 28 miles from downtown Los Angeles. More than 1,800 families have been relocated by the gas company and more than 1,000 remain on a waiting list. Some say they can’t remember a displacement of residents this large since the Northridge earthquake in 1994, when 20,000 people were left homeless. Two local elementary schools have been impacted, with nearly 2,000 schoolchildren and staff slated to be moved to other schools in January.

Enough methane gas is being released to fill the Empire State building each day, state officials have said, and the concern has even reached the Federal Aviation Administration, which issued temporary flight restrictions over the area for small aircraft and helicopters.

The gas company has apologized but has said the leak may take four months to plug and to create a relief well.

“It’s like the BP spill on land,” said environmental activist Erin Brockovich, who was made famous by successfully battling Pacific Gas and Electric Co. over groundwater contamination in the community of Hinkley in the Inland Empire in 1996. “I’ve really never seen anything like this. I think the magnitude is enormous. Its like a volcano, and the gas is like the lava that can’t be shut off.”

An abandoned oil field with 115 wells, the Aliso Canyon storage facility became the second largest in the nation when it was repurposed in the 1970s, with a capacity to hold 86 billion cubic feet of natural gas.

Gas continues to leak from a narrow pipe enclosed in a breached 7-inch well casing. The affected well, known as SS 25, is 8,750 feet deep.

Aging infrastructure may be to blame. In a report presented to California’s Public Utilities Commission last year, concerns were raised by the gas company regarding well casings that were “further amplified by the age, length and location of wells,” according to the report. “Some SoCalGas wells are more than 80 years old with an average age of 52 years.”

The number of wells that have needed repairs has increased, from three repairs in 2008 when tracking of repairs began, to nine in 2013.

“Without a robust program to inspect underground storage wells to identify potential safety and/or integrity issues, problems may remain undetected,” last year’s report stated.

The affected well passed its pressure tests, including the latest one in 2014, according to the California Department of Conservation’s Division of Oil, Gas and Geothermal Resources.

The 1,200 tons of methane gas being released daily by the affected well is adding 25 percent more greenhouse gas to the atmosphere per month than normal, said Dave Clegern, spokesman for the California Air Resources Board. Methane is about 9 percent of the total annual greenhouse gas emissions in California, Clegern added.

“You can figure that a million metric tons — which is about the estimated monthly amount — is the equivalent of putting about 200,000 more cars on the road for a year.”

Methane lives in the atmosphere for about 12 years, according to the U.S. Environmental Protection Agency. Unlike carbon dioxide, which can live longer in the atmosphere, methane can be more devastating to the climate because of how well it absorbs heat, according the Environmental Defense Fund.

That may be bad for the environment, but families who live in Porter Ranch are wondering what the gas leak is doing to their lungs, hearts and the health of their children. Residents have reported headaches, nausea and nosebleeds. Even their dogs and cats were getting sick.

The nurse’s office at two nearby elementary schools reported increased visits by children, up to 38 one week. The most common symptoms reported by the students were headache and stomachache.

Earlier this month, county health officials said the gas leak did not pose any long-term health risks but then changed course after as the leak entered its sixth week and gas company officials said it might take four months to plug the well.

Prolonged exposure to trace chemicals, county health officials later said, some of which are known carcinogens, can cause long-term health effects.

However, they cautioned that levels examined so far in Porter Ranch are not believed to be associated with long-term health problems.

“As the duration of exposure increases, these trace levels can produce significant long-term health effects,” county Department of Public Health Interim Director Cynthia Harding wrote in a memo sent to the Los Angeles County Board of Supervisors. “As this incident has moved from a short-term exposure event resolved within days, to now a long-term event potentially lasting months, supplemental monitoring of potentially harmful trace chemicals is warranted.”

What is less understood is mercaptan, or what’s been described as a harmless chemical that contains sulphur that is added to natural gas to make it smell like rotten eggs and so that it can be detected.

But very little is known about the health effects of methyl mercaptan, according to the federal Centers for Disease Control and Prevention.

“The only information available is about a worker exposed to very high levels of this compound when he opened and emptied tanks of this compound,” according to the CDC. “He developed anemia, went into a coma and died about a month later.”

The last report on mercaptan offered by the Agency for Toxic Substance and Disease Registry, a division of the CDC, was presented in 1992.

“We do not know whether long-term exposure of humans to low levels of methyl mercaptan can result in harmful health effects such as cancer, birth defects, or problems with reproduction.”

Guidelines released by the Occupational Safety and Health Administration to workers say that long-term exposure of mercaptan can cause dermatitis.

There also is little information about whether mercaptan causes cancer in people or animals. Methyl mercaptan has not been classified a carcinogen by the Department of Health and Human Services, the International Agency for Research on Cancer or the Environmental Protection Agency.

The gas began leaking Oct. 23. One day later residents began calling in complaints to the Air Quality Management District. Since then, there have been more than 1,400 complaints.

“We have received a large number of complaints, not unprecedented, but a large amount,” said Sam Atwood, a spokesman for the AQMD. “This is a large number of complaints over a couple of months.”

The delay in communication by the Gas Co. to residents is what has raised distrust and anger in the community, said Alexandra Nagy of Food & Water Watch. The environmental nonprofit has helped Porter Ranch residents organize protests and rallies.

“This is an extreme health crisis and it is an extreme environmental crisis,” Nagy said. “These are real health symptoms. Residents are so fed up.”

Susan Gorman-Chang and her husband, George, said they moved into Porter Ranch in 1991 when new homes were being built. They had weathered the Northridge earthquake and even evacuated their home during wildfires that swept into the canyons above them. Last year, residents formed Save Porter Ranch to discourage Termo Co. of Long Beach, which now operates 18 wells in Aliso Canyon, from drilling 12 more within the next six years — a move that could potentially tap up to 200,000 more barrels of oil.

But the smell that was affecting them from the gas leak was too much. Gorman-Chang said she had trouble breathing after jogs. George Chang said he felt dizzy after morning walks. They were among the first families to relocate after the gas company agreed to reimburse residents who wanted to leave. Since mid-November, the Changs have lived in a two-bedroom hotel room in Chatsworth.

“We’re lucky,” Gorman-Chang said. “There are families that had to relocate down as far as Marina del Rey. And now many can’t find places to stay.”

But they miss their routine. George Chang said he still goes to his Porter Ranch home to pick up newspapers and mail. Gorman-Chang said she went back to their home about 4 miles away to make the Thanksgiving turkey because there is no stove in the hotel room.

Inside their room, there is a small Charlie Brown Christmas tree that George Chang ordered because he said it was important to keep spirits up. Their son, who attends Cal State Northridge, lives with them.

“It’s been a struggle,” Gorman-Chang said. “You have this delicate balance of life, and then all of a sudden it’s gone.”

Meanwhile, the Los Angeles County Board of Supervisors on Tuesday declared the leak in Porter Ranch an emergency to pave the way for state and federal assistance.

“This is a disaster area,” Los Angeles County Supervisor Michael Antonovich said that day. “The financial liability of Southern California Gas Co. has to be to the neighbors who have lost residential properties, the ability to sell. The home valuation has gone in the toilet.”

Los Angeles City Attorney Mike Feuer filed a civil lawsuit against SoCalGas alleging the Aliso Canyon leak has threatened residents’ health and hurt the environment. The lawsuit also alleges a public nuisance and violation of the California Unfair Competition Law from the leak.

“It is the most significant event and potentially biggest health emergency in the history of Los Angeles,” Feuer said. “There’s a huge spectrum of concern out there.”

Brockovich, who is working on behalf of the law firm Weitz & Luxenberg which filed a lawsuit on behalf of residents, said monetary compensation won’t be enough for the residents. She said the gas company should have had a contingency plan in place, in case of such leaks.

“There has to be a new plan moving forward,” Brockovich said. “As we move forward, lawsuits are not going to work anymore. There needs to be measures to change what has happened, to prevent it from happening again and to assure total safety to those people. This is, I think, a huge wake-up call.”