Though likely to cause irritation, the foul odor plaguing Huntington Beach poses no immediate danger, city officials said.
Residents report that the odor causes headaches, nausea and sore throats.
"The Fire Department is aware of this issue, and we do not believe it is an immediate life safety issue," according to a Wednesday post on the city website.
The post came after several residents, including Ocean View School District board President Gina Clayton-Tarvin, showed up to Monday's City Council meeting to complain. They said the problem has been occurring off and on for about two years, with a particularly bad occurrence Aug. 29.
"It was so overwhelming — I thought I had a gas leak in the home," Clayton-Tarvin said.
South Coast Air Quality Management District spokesman Sam Atwood said monitoring equipment in the area recorded the highest measured concentration of hydrogen sulfide odor this year on Aug. 29 — some 16 parts per billion.
Thirty parts per billion is the state standard, he explained, but 16 ppb is enough to cause reactions.
"At the 30-ppb level, most individuals can smell the odor and some may experience symptoms, such as headaches and nausea," he said. "However, the symptoms associated with this level of exposure are temporary and do not cause any long-term health effects. Humans can detect hydrogen sulfide odors at extremely low concentrations, down to a few parts per billion."
Due to multiple sources in the area with the capability of producing gas-like odors, and the periodic nature and unknown location of the source, the agency has had a difficult time assessing the cause, though analysis of complaints and wind directions point to an offshore source, Atwood said.
The Huntington Beach Fire Department has been working with the AQMD to collect air-quality samples.
The Fire Department is in the area and can respond more quickly in the effort to detect odors, which have sometimes subsided by the time air-quality regulators arrive to investigate complaints, Atwood said.
Seal Beach and Long Beach residents have reported similar odors.
The origin has yet to be identified but potential sources are being investigated, the AQMD page says.
Huntington resident Adam Plesniak started a Change.org petition to raise awareness about a year ago. He had 1,181 signatures as of Friday.
Plesniak said the movement has made headway in the past week.
The city's webpage says residents who smell the odor should call (800) CUT-SMOG or report the issue to the AQMD online.