When America's worst-ever natural gas leak stank up the air around Porter Ranch in late 2015 forcing thousands of families to flee a pervasive rotten-egg smell and potential health impacts, a few public and private entities installed monitors to sniff the air and publicly display methane measurements in close to real time.
A well at the Aliso Canyon natural gas storage field had blown out on October 23, 2015, and spewed 109,000 metric tons of methane into the atmosphere until it was sealed in mid February of the following year.
During the leak, air monitors showed excessive amounts of methane in the air around Porter Ranch.
But now after months of normal readings, the last two public-funded monitors operated by the South Coast Air Quality Management District will be pulled out in June. The California Air Resources Board removed all five of its Porter Ranch monitors last year.
That departure will leave two companies conducting real-time testing for methane and displaying the results on line. One is Southern California Gas Company, whose blown-out well triggered the disaster.
The other is Argos Scientific, a Washington State firm whose methane monitor remains in place thanks to the sponsorship dollars of a law firm that is suing SoCal Gas over the leak on behalf of thousands of residents.
The withdrawal of the government-run methane monitors is one more signal that life in Porter Ranch is returning to normal following the nation's largest-ever uncontrolled natural gas release. But the loss of the monitors is disquieting to some Porter Ranch residents who fear they are losing a neutral source of information about their air quality at a critical time.
SoCal Gas has been petitioning state authorities for permission to resume operations at the Aliso Canyon facility.
Meanwhile, Los Angeles County Department of Public Health officials insist the area needs a multi-million dollar health study to gauge the past and potentially ongoing effects of the leaked gas on local residents.
It's not unusual for the SoCal Gas and Argos monitors to show different readings on the same day, generating some confusion among residents who often check the methane levels when they have symptoms like bloody noses or headaches that they attribute to the nearby Aliso Canyon gas field.
For example, screen shots taken April 11 show each of SoCal Gas' eight monitors reading 2 parts per million of methane.
That 2 parts per million level matches the background level of methane found in most of the Los Angeles Basin. On the same day, the Argos monitor shows a lot more fluctuation over the course of the day, often spiking above 3 parts per million.
AQMD readings for the same day were slightly above 2.0 parts per million.
Jacki Swift, a Porter Ranch resident who moved away from the area to avoid the methane and other pollutants said she relied on the monitors daily while the leak was active.
"I used to see spikes of benzene, which was great information. Although, I must admit I do not fully trust any system that's not being run by a [neutral] party. And, I certainly do not trust the readings of the SoCal gas system."
Why do different methane monitor readings vary?
The location of monitors and the wind speeds they encounter partially explain why different monitors would show different levels of methane, said Francesca Hopkins, a climate scientist at UC Riverside.
Other variations could come from different methane monitors using different measurement and collection methods. The monitors at Porter Ranch are not all the same make, however they operate with similar technology. They bounce a laser beam between mirrors and measure how the laser is affected by the presence of methane particles. The different instruments may collect data at different time intervals, and average the data points over different durations, Hopkins said.
Hopkins was among a group of scientists who measured high levels of methane -- in the 50 parts per million range -- at Aliso Canyon in the days immediately following the gas well rupture. She had previously worked on projects measuring methane levels in the Los Angeles area.
The background level of methane that is present through most of the L.A. Basin is about 2 parts per million, while a level of 3.5 parts per million is at the 99th percentile of levels found in the air basin, showing the presence of methane, Hopkins said.
A 3.5 ppm level of methane by itself is not harmful to most people. But the health concerns of public officials and residents stem from the fact that natural gas is 94 percent methane and six percent other substances which could include the carcinogen benzene. Hydrogen sulfide and sulphur dioxide are also present in natural gas and can harm health.
The AQMD recognizes 2 parts per million as the Los Angeles background level, and it set 4 parts per million as its threshhold point above which the agency would consider methane to be at a problem level.
"ARB and AQMD had established what we considered the typical air criteria as published on February 16, 2016, and as far as meeting those guidelines, especially in the more recent months, it has met those conditions," said Jason Low, AQMD's assistant deputy executive officer who oversees air quality monitoring.
"In establishing a bright line, they chose 4 parts per million," AQMD spokesman Sam Atwood said.
The monitors were initially due to be withdrawn in January, but the AQMD agreed to requests from the Porter Ranch Neighborhood Council to leave them in place through June, Atwood said. If complaints from residents about new methane emissions are verified by the AQMD's field inspectors using their sense of smell and scientific instruments, the agency could return the methane monitors to the community, Atwood said.
Most residents don't notice the small spikes in methane when they occur, but some residents say they have developed acute sensitivity to the Porter Ranch environment, reporting nosebleeds, headaches and other illnesses they attribute to the gas storage field next door.
Who's monitoring methane?
California Air Resources Board: Installed five monitors in December 2015, and removed them in July 2016.
South Coast AQMD: Installed three methane monitors while the leak was active, including two that could also detect the carcinogen benzene and the toxic chemical hydrogen sulfide. The monitor at Porter Ranch Community Center is still operating, and the monitor at Porter Ranch Community School is down temporarily during some construction at the school. Both are due to be removed in June at the end of the Los Angeles Unified School District school year. A monitor that had been at Castlebay Elementary School has been removed. SCAQMD's instruments can record data every second or every few seconds, and hourly averages are reported.
Argos Scientific: The Washington State company has had one monitor installed in a residential backyard near the gas field's southern boundary since before the gas leak was plugged. The company plans to add another backyard monitor in the Highlands area of Porter Ranch soon, said Robert Crampton, senior scientist with Argos. The monitor -- a Boreal Gasfinder -- records a methane reading once every second and those readings are averaged over five minutes and posted online.
Southern California Gas Co.: The company installed eight monitors and displays readings on a website. Viewers can click on any of the eight monitor icons to see recent past levels.
"The system is calibrated to reflect a steady 2.0 ppm unless and until readings go above 2.0. On the website, zero represents the monitor being offline due to weather or maintenance," said company spokeswoman Melissa Bailey.
The system checks the air for methane every 30 seconds and readings are averaged every five minutes and posted on the public website, The fenceline monitoring system uses General Monitors model IR 5500, Bailey said.
The system of monitors on the southern perimeter of the Aliso Canyon gas field is not the primary means the company uses to find leaks in its pipes and wells. The company can see data from pressure monitors that are installed on every well. SoCal Gas technicians inspect each well four times a day, including the use of sensitive infrared cameras to detect leaks smaller than what human senses can detect, Bailey said.
The monitors were installed in compliance with the company's settlement of misdemeanor charges brought by the Los Angeles County District Attorney's office.