Regional air quality managers said Tuesday that inspectors had cracked the mystery of the epic stink that had descended over much of Southern California.
They confirmed that the rotten egg odor traveled about 150 miles from the Salton Sea to Los Angeles.
"We now have solid evidence that clearly points to the Salton Sea as the source of a very large and unusual odor event," said Barry Wallerstein, executive officer of the South Coast Air Quality Management District.
How unusual? As late as Monday night, AQMD officials weren't even sure it was scientifically possible for a malodorous scent to trek the distance the Salton Sea's fumes did. So they asked an air quality modeler to use sophisticated computer modeling to find out if it was "theoretically possible" for a stench to fly that far.
"I think we've shown it was theoretically possible," said Sam Atwood, an AQMD spokesman. "But this is just something we did not expect."
Air samples collected in the Coachella Valley, near the Salton Sea and elsewhere clinched inspectors' suspicions of the 376-square mile, murky body of water as the source of the pervasive smell. Atwood said AQMD inspectors collected air samples that contained hydrogen sulfide.
Inspectors found concentrations of the gas, a product of organic decaying matter, heaviest close to the Salton Sea, with a pattern of decreasing concentration farther away. Still, it added up to footprints indicting the sea as the guilty party.
Inspectors ruled out landfills, oil refineries and a natural springs site as possible culprits.
"The air samples were the final piece of the puzzle," Atwood said. "Our inspectors did go out to the Salton Sea and did smell some very strong odors at the sea, as well as at the locations leading up to it."
But it took the might of a powerful storm blowing from the southeast to bring the stench of the Salton Sea to L.A. All in all though, L.A. got lucky, compared to the town of Mecca, just north of the Salton Sea, and nearby Indio, which received a much heavier concentration of the gaseous, funky odor.
"The storm originated in the Gulf of California and the Sea of Cortez, and hit the Imperial Valley and Salton Sea," said Tim Krantz, a professor of environmental studies at the University of Redlands. "We had huge squalls and pretty heavy winds in the Coachella Valley. The winds pull the surface layers of the sea off from the southeast to northwest, and that surface water is replaced from the depth."
And those depths are all kinds of stinky.
Experts said the winds from the Sunday night storm probably unsettled the fetid layers of water near the bottom of the Salton Sea, bringing them to the surface.
Andrew Schlange, general manager of the Salton Sea Authority, said in the last week a large number of fish had died in the water, probably exacerbating the problem. But he said the fish die-off, which is a normal occurrence, was not significant enough on its own to explain the well-traveled odor.
Rather, he said, the storm upset an anaerobic — or oxygen-deprived — lower layer of the Salton Sea, where organic material lay decomposing, releasing the noxious hydrogen sulfide gas, with its distinct rotten egg smell.
The good news was that by Tuesday the odor had greatly diminished. As of about 5:30 p.m. Monday, there had been 235 complaints about the smell, Atwood said. Since then there have been less than 10, though the "sulfur-type" odor still lingered in some parts.
Atwood said that an AQMD meteorologist has looked at the thunderstorm reports, and that along with wind-measuring instruments in the Coachella Valley, it was determined that winds of more than 60 mph blowing from the southeast probably sent the rank odor to the Los Angeles Basin.
"That's unusual because usually the winds are blowing in the opposite direction," he said.
The Salton Sea has lost much of its depth, being only about 50 feet at its deepest point, with an average depth of about 30 feet, Schlange said. That means it doesn't take as potent a weather event as it did in the past to cause an upswell that sends the water near the bottom to the top.
Schlange said the Salton Sea was losing much more water through evaporation than was being replenished through agricultural runoff and other sources. If water wasn't flowing into the sea, it would lose a depth of about 4 to 6 feet a year through evaporation.
If something isn't done to better replenish the Salton Sea, Schlange said, issues with wide-ranging odor could be more common in the future. He said there's a plan to do mitigation work on the sea, but money to fund it is lacking.
"All of a sudden Sunday evening we had all these conditions that came together to allow something like this to occur," Schlange said. "It's occurred before, but not at this magnitude."