Amid questions about long-term exposure levels to potentially dangerous chemicals, public health officials Wednesday called for more sampling and testing of air in Porter Ranch near a leaking gas storage well.
Since the leak was first reported in October, hundreds of residents have complained of a noxious odor, and also of health symptoms including headaches, nausea, burning eyes, and respiratory discomfort.
The Los Angeles County Department of Public Health has repeatedly offered assurances that such symptoms are short-term phenomena tied directly to nontoxic odorants in the gas, and that there is no reason to expect long-term, chronic health effects.
However, official say those conclusions are based on sampling done to determine "instantaneous" chemical levels, and do not provide as accurate a picture of average concentrations as do samples taken over a 12 to 24 hour period.
"We are recommending what we call an expanded air monitoring program," said Jeffrey Gunzenhauser, MD, MPH, interim health officer.
The concern is not so much the odorless methane that is the primary constituent of natural gas, nor even the odorants that are placed in the gas as indicators, but contaminants such as benzene, a known carcinogen which can also cause immediate acute symptoms after short term exposure at concentrations above a threshold level.
The state of California's Office of Environmental Health Hazard Assessment sets limits for exposure both short-term and long term.
The short-term limit for benzene is 8 parts per billion, or "ppb." The highest benzene level found outside the storage facility was below the limit at 5.55 ppb, according to Angelo Bellomo, deputy director for health protection. Consequently, officials see no short-term risk from released benzene. Bellomo said levels on-site were measured above 20 ppb, but workers have been shielded by required protective gear.
Long-term health consequences can result from exposure to much lower levels over a longer period of time. The California threshold for long-term benzene exposure is one ppb.
"One part per billion for months or years, then you are also becoming at risk for chronic long term health effects," Bellomo said.
Based on aggregating "instantaneous" readings, Public Health estimates the average community exposure at half the limit, a level Bellomo said is routinely observed as the ambient level throughout the county. But officials say the better way to make that evaluation is to take samples over a longer period of time, 12 to 24 hours, and that method of testing is now underway.
"We can't really say what the average level of community exposure is," said Bellomo, expressing confidence the longer term monitoring project would provide that answer.
The leaking well is one of 115 in the Aliso Canyon Storage Facility that is the Gas Company's largest, and deemed essential to its distribution network. To stop the leak, SoCalGas crews are drilling a "relief" well nearly 9,000 feet to intercept and "kill" the leaking well.
Monday, the Gas Company estimated that work would be completed at the end of next month.
SoCalGas is responsible for the air sampling and for covering the cost of the analysis by a certified laboratory. The work is done under the direction of the South Coast Air Quality Management District.
Some integrated 24-hour sampling began in December, according to SCAQMD spokesman Sam Atwood.
Interim public health director Gunzenhauser said he hopes that by next week his department will begin seeing the longer term data it seeks.