High levels of wastewater near the TJ River were measured weeks before the charges were filed

Raymond Johnson remembers the stench near his home being particularly bad this summer.

“You feel like you’re going to throw up, you feel sick inside,” says Johnson, who bought his home in San Ysidro on the Tijuana River in 2008, not knowing that the smell of sewage would increasingly plague the neighborhood in the years to come.

“A few years after this problem arose, it should have been fixed,” he said.

As authorities field hundreds of complaints from residents about the pungent smell in their neighborhoods due to the binational sewage crisis, data shows that hydrogen sulfide levels in the South Bay exceeded state limits on 15 days last year.

Nine of those days were recorded after the Hollister sewage pumping station failed on June 16, when about 300,000 gallons of raw sewage flowed into the river. But it wasn’t until late July, after residents began receiving complaints, that the San Diego County Air Pollution Control Authority first complained about the plant.

Infrastructure problems in both countries have led to sewage overflows along the U.S.-Mexico border for decades. In recent years, it has been particularly bad due to mechanical failures at sewage treatment plants. Researchers have estimated that more than 100 billion gallons of toxic waste, including raw sewage, have flowed through the Tijuana River Valley in the past five years.

Pollution has blocked access to predominantly Latino beach communities—the main stretch of Imperial Beach, for example, has been closed for more than two years. A new wastewater treatment plant currently being built in Baja California is expected to help reopen the beaches.

A byproduct of the high levels of sewage in the river is hydrogen sulfide, a colorless gas that smells like rotten eggs and is also known as sewer gas. Its health effects depend on how much of the gas someone inhales and for how long, ranging from headaches, nausea and loss of smell at lower concentrations to rapid unconsciousness and death at high concentrations.

The California Air Resources Board sets the nuisance limit at 30 parts per billion. That’s the level at which the smell is bad enough to significantly affect quality of life but not health. The Occupational Safety and Health Administration sets the level that most people can smell at 10 parts per billion, but some people can smell it at much lower levels.

In the South Bay, readings reached as high as 58 parts per billion this summer.

However, the district only collects readings in a small area. Data has only been collected at a fire station on San Ysidro Boulevard since September. Three more sensors still need to be moved to planned locations throughout the South Bay.

Before June, the sensors recorded only five days with readings above the CARB limit: four in October and one in late April, according to a public records request.

A month before the Hollister pump station was reported—and in the middle of the week with the most days of exceedances recorded by the sensors—a county official discussed the high readings in an email to local authorities and said he did not have the authority to address the root cause of the odor.

“The unfortunate side of ambient air monitoring is that it can be very passive – collecting data (typically) over several years to develop future policies, determine the health impacts of pollution, etc.,” Kevin Bradley, director of Community Air Monitoring, wrote in his June 27 email.

The exceedances alone are not enough to take action.

The county, which received about 150 odor complaints last month, is still investigating the Hollister plant outage. Officials confirmed they launched the investigation because of the large number of complaints from residents, not because of the high hydrogen sulfide levels.

“State law essentially says that these odors or this public nuisance have to affect a significant number of people,” said Jeff Lindberg, chief of the district support division of CARB’s enforcement division. “In enforcement, we have to trace it back to the people. We can’t trace it back to a number that comes off a monitor.”

Lindberg said that while the sensors could still serve as additional evidence to support public testimony, their real value lies in their function as a diagnostic tool.

The sensors deployed by the district are equipped to collect meteorological measurements such as wind speed, wind direction and humidity. Once all the sensors are installed throughout the South Bay, the district can use them to determine the source of the gas.

Regardless of what data is collected, Lindberg says it is very difficult to determine nuisance if there are no complaints from the public.

“When you start getting these masses of several hundred complaints, you now have really clearly and simply demonstrated that this is affecting a significant number of people, and that’s kind of what the district is looking for,” he said. “That’s why complaints are so important in this process.”

David Soderman, director of San Diego’s air pollution monitoring agency, said the data is too complex to determine whether the high gas levels were caused by the power plant outage. The agency has not yet analyzed the data more thoroughly.

“We’re still trying to get the sites up and running, and we have a limited number of people available,” he said. “To investigate and actually do this kind of analysis is resource intensive.”

Although the smell of hydrogen sulphide can be disgusting, experts say there is no evidence that even close to the levels detected by the sensors are harmful to health.

The state limit of 30 parts per billion was set in the 1980s to determine when the smell of the gas was strong enough to affect quality of life, but not health. Dr. Tee Guidotti, a consultant and former professor of environmental and occupational health, said there was no credible scientific evidence that the levels detected by the sensors posed a threat to human health during acute or chronic exposure. The hydrogen sulfide level that is strongly considered harmful to health is about 5,000 parts per billion, a level that causes an acute toxic reaction very quickly.

The highest value measured by the sensors was 58 ppb. The assumption that chronic, low hydrogen sulfide concentrations, such as those measured by the sensors in South Bay, have health effects is not supported.

However, he said the measured levels created an “unbearable” stench that made it “difficult to do anything to lead a normal life.”

“The burden of something like this in society is not neutral, it is not a figment of the imagination, it is a psychological response to a real problem. Because bad smell, like other harmful stimuli, triggers fear, and that triggers a fight-or-flight response,” Guidotti said. “But that’s where the evidence ends.”

Limited data

Despite residents across the region complaining about the smell, the Air Pollution Control Agency has delayed additional monitoring throughout the South Bay.

The agency used a $100,000 federal grant to purchase six solar-powered sensors. Until recently, all were located at the same site in San Ysidro.

Officials cited a range of problems ranging from paperwork delays to security clearances.

Sibi Sutty has lived in the northeast corner of Imperial Beach since August 2023 and said the smell has gotten much worse since he moved in. He has been closely monitoring the data since the sensors came online.

“When I noticed the smell near my house, I looked at the data and couldn’t really see any connection there,” Sutty said. “The sensor was reading zero, but you could obviously smell it outside my house.”

A sensor was installed near his home on Aug. 7, but data was not online as of last week. County officials said the sensor was having technical issues, needed to be calibrated, and they weren’t sure when it would start transmitting data.

Three other sensors are also waiting to be moved to a new location. A land use agreement with San Diego County is currently being finalized to install a sensor at the Tijuana River Valley Campground. The county previously said in a statement that this sensor should be operational soon, as should another sensor at the South Bay Wastewater Treatment Plant.

A sensor to be installed on the roof of the Imperial Beach Fire Department has been reviewed by air pollution district safety consultants who are waiting for the safety equipment to be installed. The sensor is expected to be operational in a few months.

The district has also purchased a reference monitor, which is more accurate but very expensive. It can be used to improve the accuracy of the sensors and allow comparisons between individual sensors installed at different locations. Officials said they are not sure when it will be operational because parts are still needed.

Despite the delays and the intensity of the smell this year, Sutty is optimistic about the future. He looks forward to seeing the data near his home and hopes it can be used to tell regulators and residents whether the upcoming improvements will reduce residents’ exposure to hydrogen sulfide.

“It would really help us understand how low the flow needs to be for this to no longer be a problem,” Sutty said. “I’m not hopeful that this can be 100% fixed. But I’m hopeful that the significant deterioration we’ve seen over the last few years will return to the level it was maybe three or four years ago.”

Earlier this month, federal officials announced they had awarded a contract to expand the South Bay wastewater treatment plant, with construction set to begin later this year. The expansion, combined with infrastructure improvements in Mexico, is expected to prevent up to 90 percent of the untreated wastewater that reaches the coast from reaching the coast.