Southern California Gas Company has temporarily plugged the ruptured natural gas well near Porter Ranch that forced thousands of families to relocate since October. Now, some of those families question how they will know when the air has cleared.
Part of the answer will come from an SUV that uses mirrors and lasers to measure the gas it as it cruises the hilly streets around Porter Ranch.
Andrea Polidori, quality assurance manager at the South Coast Air Quality Management Distsrict, laughed recently at the prospect that he's been driving round Porter Ranch using lasers to ferret out pockets of methane.
"I'm not a Jedi, or anything like that, but yeah, I guess," he joked.
Polidori, at the wheel of the plug-in hybrid Ford Escape SUV, started a recent methane survey near the entrance to Southern California Gas Company's Aliso Canyon Natural Gas Storage Facility just after dawn Wednesday.
He didn't know then that he might be tracking the last big blasts of natural gas that have been pouring from a blown out well since at least Oct. 23. Some 5 billion cubic feet of natural gas has been lost from the underground storage field since the leak was discovered. A temporary halt to the leak was achieved Thursday about 8 a.m., SoCalGas announced. A permanent fix using cement to seal the leak will likely take days to complete.
Polidori's has been testing for solely for methane since natural gas is more than 80 percent methane.
"Right now the concentrations are definitely low," he said as he began driving west along Sesnon Boulevard, which is the street closest to the leaking well. "Today, it's early in the morning, I think concentration most likely will be about background level."
Background level refers to the amount of methane in the air under normal circumstances. It's about 2 parts per million in the sometimes windy foothills of Porter Ranch and surrounding areas. The background level tends to be higher in the L.A. Basin where there is more traffic and industry, about 5 parts per million.
Just a few blocks to the west he saw the level of methane rise.
"Right now we are actually getting an increased methane concentration. I've seen a lot higher here," Polidori said.
The instrument on top of the SUV was taking readings that will be plotted on a map and posted to the AQMD website a few hours later. Polidori could see preliminary readings immediately.
"Yellow means relatively low methane, near background methane. Orange is four to five times methane, and red is very high methane," he said.
The methane is 40 parts per million -- that's 20 times higher than usual. Wednesday was a red day for this portion of Porter Ranch. This area has gotten the worst of the methane since the mobile testing began in late December. Later analysis showed the highest level that morning was 58 parts per million.
"It think the highest I've ever seen with this vehicle was about 1:40 in the morning, I don't remember the day, but I saw up to 70 ppm which is about 35 times the background level," he said.
The instrument taking the measurements is called an open path methane analyzer.
It looks like two halves of a big white metal egg, about a foot around, that's been pulled apart to reveal, not a yolk, but two mirrors facing each other. It shoots a laser beam that bounces back and forth on the mirrors before returning to be measured. The difference in the strength of the infrared signal beam going out and the one coming back in shows how much methane is in the air.
The instrument takes one reading per second. Polidori said he slows the SUV when levels appear to be higher so that he can get additional readings for a more precise measurement. Methane is typically measured in parts per million, and the equipment is sensitive enough to detect much smaller particles, as small as 2 parts per billion.
On Wednesday, there wasn't much traffic for his sudden slowing to be a problem, partly because so many families had moved from Porter Ranch to sleep away from the rotten egg smell, which can cause short-term symptoms like headaches and nosebleeds and nausea. It's strongest at night.
The odor comes from smelly chemicals called mercaptans that are added to odorless methane while it's being shipped by pipeline and stored underground so that a leak is easier to detect.
The methane machine cost $55,000, part of about $370,000 in emergency spending the AQMD has approved for air testing equipment and personnel since the leak began. That includes placing trailers with air testing equipment at three locations around the area. One is at Porter Ranch Community School, whose students were relocated to a campus in Northridge until the end of the semester.
The trailers test for methane around the clock. They also collect air samples to detect volatile organic compounds including benzene, which can cause cancer.
Other testing is also happening.
SoCalGas and the Department of Public Health are testing for methane, benzene and other chemicals within the gas storage field and along the perimeter. The state Air Resources Board is testing for methane at the well site, and from towers, airplanes and satellites. UCLA scientists are doing independent tests.
Polidori has driven the methane mobile around the area nearly two dozen times since he got it December 21, including on Christmas Day. He varies the route and time to get a more complete picture of how the methane moves around in different weather and wind conditions.
AQMD wanted to get good information about air quality levels while the leak was active to compare against when the leak is completely plugged.
Dr. Cyrus Rangan, the top toxicology expert with the Los Angeles County Public Health Department, said the testing won't stop for the foreseeable future.
"We want to make sure that we watch the environmental conditions and we want to see them return back to normal, that's the most important thing to us," Rangan said.
On Wednesday, Polidori had gone about 15 miles, and he found some elevated methane levels, about 40 parts per million.
"Methane itself is not even at 40, 50, 60ppm is not a health concern," he said, echoing public health officials.
Even so, the natural gas leak has been an invisible, smelly disruption and left many uncertain about the health of their environment.
Local and state agencies have ordered up studies to answer questions about the long term effects of mercaptans and the extent of exposure to cancer-causing benzene.