Tijuana River Valley

The combination of significant transboundary sewage flows and deficient wastewater treatment infrastructure in the United States and Mexico, has created an environmental crisis affecting air, water, and soil quality.

The untreated sewage and wastewater crossing the border can release hydrogen sulfide gas (or H2S), a colorless compound with a distinctive "rotten egg" odor, contributing to local health and environmental concerns.

Investigation into Odor Complaints

One of our key responsibilities is enforcing regulations that prevent air pollution from causing public nuisances, including odors that may injure, disturb, or endanger the public’s comfort, health, or safety. These regulations are outlined under SDAPCD Rule 51 and the California Health and Safety Code, Section 41700.

While SDAPCD is dedicated to improving air quality and addressing odor complaints, it's important to note that our agency does not measure or regulate pathogens or disease-causing organisms.

Action:

In response to hundreds of odor complaints from communities near the Tijuana River, SDAPCD has documented strong odors that are significantly impacting local communities. On July 29, 2024, SDAPCD issued Notices of Violation (NOV) (A) (B) to the U.S. International Boundary and Water Commission (IBWC) and its contractor, Veolia, alleging violations of SDAPCD Rule 51 and state law. On August 30, 2024, SDAPCD issued subsequent NOVs (A) (B) to the IBWC and its contractor, Veolia, alleging violations of SDAPCD Rule 51 and state law.

Investigation Findings:

The public nuisance odors are primarily attributed to outdated infrastructure and inadequate maintenance at the South Bay International Wastewater Treatment Plant and associated equipment (pump stations and collectors), which are the responsibility of the USIBWC and its contractor. You can view the USIBWC's letters (1), (2) to SDAPCD in response to the Notices of Violation and SDAPCD's response here.

What’s Next:

SDAPCD is committed to ensuring full compliance with all applicable air quality regulations before considering any settlement discussions. Once compliance is achieved, violations of this nature typically result in monetary penalties, reflecting the severity of the infraction or litigation. Factors such as the extent of harm, the nature and persistence of the violation, the duration of the violation, and efforts to correct the issue will all influence the determination of penalties. For more information, visit our statutory penalties page.

We will continue to monitor the situation closely and take necessary enforcement actions until compliance is achieved.

Air Quality Monitoring

Action:

SDAPCD is in the process of enhancing its hydrogen sulfide monitoring network in the Tijuana River Valley with reference grade monitors to report levels of hydrogen sulfide in the community beyond trend analysis. One monitor is currently located at San Diego Fire Station #29 and we are working to place additional ones in the community of Nestor and in Imperial Beach. Monitoring locations will be shared as specific sites are identified.

Monitoring data:

The following graph shows hourly hydrogen sulfide readings of the past week from our monitoring network in the Tijuana River Valley. This chart will be updated on a weekly basis. For real-time hourly data, please click here.

As we work to enhance our hydrogen sulfide monitoring network in the Tijuana River Valley, we continue to partner with local, state, and federal agencies and research institutions to provide more information regarding health impacts from the exposure to hydrogen sulfide.

Air Monitoring Update:

On the late evening of September 12, 2024, our partner agency South Coast AQMD deployed a mobile air monitoring platform to measure instantaneous ambient H2S concentrations and to survey areas potentially impacted by the odors. Mobile monitoring was conducted along a route going from Imperial Beach and traversed along the communities and areas to the north and to the east of the Tijuana River until reaching near the international border (Figure 1). Overall, results showed mostly typical levels of H2S. There were elevated levels of H2S in some neighborhoods, and the highest levels observed were specifically near the intersection of Hollister Street and Sunset Avenue.

Hydrogen sulfide concentration map and wind rose for the duration of mobile monitoring survey, September 12-13, 2024

An instantaneous (grab) air sample was collected on Hollister Street, between Sunset Avenue and Saturn Boulevard. The sample was analyzed at the South Coast AQMD laboratory for H2S and gaseous air toxic compounds (i.e. benzene, toluene). The data showed no elevated levels of those pollutants. Note that levels of pollutants can fluctuate, even within a short time, based on the source, wind, and weather patterns.

Understanding Hydrogen Sulfide Readings:

These readings help illustrate fluctuations in gas concentrations over time. While the data gives a broader view of potential air quality issues from the ongoing sewage flow, it is important to note that these readings are informational only and are not designed to assess individual health risks.

Factors such as weather conditions, distance from the sewage flow, and equipment sensitivity can affect readings. This monitoring effort is part of our commitment to keeping the public informed about the air quality impacts caused by the transboundary sewage flows.

Health Guidelines and Standards:

The California Office of Environmental Health Hazard Assessment (OEHHA) provides health-based guidelines that agencies like SDAPCD use to assess potential health risks to the public. Short-term (1-hour) exposure to levels of hydrogen sulfide above 42 micrograms per cubic meter (equivalent to 30 parts per billion (ppb)) can cause symptoms like headaches or nausea, while longer or higher exposures can pose more serious health risks. Click here to learn more.

Our monitoring data can highlight potential health risks based on these guidelines, but they are not a direct measure of personal exposure. For specific health concerns, we recommend consulting healthcare professionals.

For information regarding health concerns, please visit the County of San Diego’s website.

To stay up to date with the latest air quality information at the Tijuana River Valley, sign-up for email updates here.