Roberta Griego and Babetta Juergens (R) wear gas masks while attending a public hearing before the South Coast Air Quality Management District (AQMD) on Jan. 16, 2016. (Photo by David McNew/Getty Images)

Nearly four years after a well ruptured near Porter Ranch, unleashing the nation's largest-ever natural gas leak, an official report on the cause of the blowout has finally been made public.

The main takeaway is that this well lacked some basic protection from groundwater, which led to corrosion, eventually causing it to fail.

It also says there were things the gas field owner, Southern California Gas Company, could or should have done to prevent the leak, detect it earlier, respond to it better and shorten the four-month duration of the blowout.

The report is an independent analysis produced by Blade Energy Partners for the agencies that regulate the Aliso Canyon gas field — the California Public Utilities Commission and the State Department of Conservation's Division of Oil, Gas and Geothermal Resources.

Here are some key takeaways:

HOW DISRUPTIVE WAS THE BLOWOUT?

In October 2015, a natural gas leak was discovered at SoCal Gas's Aliso Canyon storage well.

The leak lasted for several months, spilling more than 100,000 metric tons of greenhouse gas into the atmosphere and forcing some 8,000 households in nearby Porter Ranch and other neighborhoods in the north end of the San Fernando Valley to evacuate for weeks or months.

During the 111 days that the leak was active, two schools relocated and many businesses were disrupted when their customer base disappeared to other locales. Residents found their homes and gardens speckled with petroleum-like spots, and many reported symptoms like dizziness, bloody noses, headaches and worse.

The blowout has already cost SoCal Gas $1.07 billion, about half due to the cost of relocating so many families. Some 48,000 plaintiffs have filed about 400 lawsuits alleging they were physically and financially damaged by the blowout.

SO, WHAT DO THE EXPERTS SAY HAPPENED?

This 52-year-old well should have had cement sealing the metal casing off from the corrosive dirt and rock outside it. But the top 440 feet of the well did not have that outer cement layer. That meant that water could come into contact with the outer metal surface of the casing, and potentially corrode it and get into the well.

And that's what happened. Think of a gas well as a straw within a straw within a straw. Over the years, groundwater got into the space between the outer most casing and the 7-inch inner casing of the well. There, microbes fed on carbon dioxide, and together they corroded the 7-inch inner tubing.

So on Oct. 23, 2015, while gas was being injected at very high pressure, it bulged and then split that 7-inch metal tube. And gas escaped through the corroded outer casing higher up where the cement was missing.

WHY DID IT TAKE SO LONG TO STOP THE LEAK?

SoCal Gas called in the nation's top well blowout experts — a company named Boots and Coots — but seven attempts to seal the well over two months failed.

The gas flow was eventually stopped after 111 days by drilling a second well to intercept the leaking well thousands of feet below the surface.

These well "kill" attempts involve pumping heavy fluids at high pressure into the hole. Workers can also load it with what they call "junk" things like golf balls to also try to stop the blowout.

The report says SoCal Gas should have used higher density fluids and higher pressures to kill the well. But the company had not correctly estimated the force of the gas flow that was coming out of the well. So the calculations of the amount of pressure to pump in the well kill fluids were not correct.

WHAT CONDITIONS PRIMED THE GAS FIELD FOR A BLOWOUT?

The report finds a variety of safety issues and less-than-best practices in how SoCal Gas was running the gas storage field.

For starters, the company was moving gas in and out of the gas field through both the inner tubing of the well and the donut-shaped space between the tubing and the outer casing. That is not a best practice for the gas storage industry, but it was nevertheless a common practice. It leaves no additional protective outer barrier in case of a leak. After Aliso, state rules changed and SoCal Gas now runs gas only in the inner tubing, it says.

But there were other issues.

Somebody from a different company — Termo Oil — was the first person to notify SoCal Gas that their well was leaking. But when SoCal Gas went out, they found no leak, the report said.

The report finds that SoCal Gas did not have the kind of daily surveillance to detect leaks early.

Also, the company did not investigate previous casing failures on dozens of other wells over the years. The report says 40 percent of the wells at Aliso had sustained an average of two casing failures each. Wells had sustained two other blowouts underground. But the company did not conduct analyses on those failures, the report said.

The company also had not done the kind of risk assessment needed to understand and prevent this kind of blowout.

The report said that state regulations in effect at the time of the blowout did not require casings to be a specific thickness, but that tests existed that could have revealed the deteriorated pipes and casings.

SoCal Gas said in a statement that it had done all the testing then required by state regulations, and had no indications that the casing had deteriorated.

"The Blade report confirms SoCalGas complied with gas storage regulations in existence at the time of the leak and that the related compliance activities conducted prior to the leak did not find indications of a casing integrity issue," the company said in a press release. "In Blade's opinion, there were measures, though not required by the gas storage regulations at the time, that could have been taken to aid in the early identification of corrosion and that, in their opinion, would have prevented or mitigated the leak."

Essentially, it's an issue of SoCal Gas following potentially inadequate regulation to the letter versus assertively pursuing the best practices to avoid disasters.

The report said that each of these shortcomings has since been corrected, and that state regulations and SoCal Gas' own operating polices have been updated. Each of the 114 wells at Aliso has been either shutdown or completely overhauled. About 64 are in operation now.



WITH THE REPORT FINISHED, WHAT HAPPENS NOW?

This report matters because it is an extensively-researched statement about what failed at Aliso, both mechanically in the wells, and with the company's own procedures. SoCal Gas will have some time to analyze the report and ask CPUC for any changes or additions.



The findings about safety practices could influence the many lawsuits facing SoCal Gas, especially the ones alleging the plant was negligently operated.

The report's conclusions could influence a state Legislature-required investigation underway by the CPUC into the feasibility of minimizing or ending gas storage at Aliso.

Former Gov. Jerry Brown had called on the state Energy Commission to work toward closing Aliso by 2027. The report's conclusions could be used to press Gov. Gavin Newsom, who has expressed a desire to close the place earlier than that, to act on the pledge.