Hydrogen sulfide readings near a South Bay elementary school raise renewed concerns over Tijuana River pollution

Monitoring shows repeated spikes near a campus close to the Tijuana River Valley

Hydrogen sulfide readings tracked in San Diego’s South Bay near the Tijuana River Valley have at times risen well above California’s long-standing odor-control threshold, intensifying concerns for families and staff at a nearby elementary school and surrounding neighborhoods.

Hydrogen sulfide is a colorless gas commonly associated with sewage and the “rotten egg” odor frequently reported in communities bordering the Tijuana River. Local and regional monitoring efforts have expanded since 2024 as cross-border sewage flows and stagnant, contaminated water in the river corridor have been linked to recurring air-quality impacts, particularly overnight when concentrations can rise quickly.

What the numbers mean — and what they do not

California uses an odor-based standard for hydrogen sulfide of 30 parts per billion (ppb) averaged over one hour, intended to limit nuisance impacts. In the South Bay, publicly reported monitoring has shown periods when hourly averages exceeded that threshold, including multi-hour events. Separate research and public-agency summaries have described short-term peaks that can approach several hundred ppb in the area during certain conditions.

While hydrogen sulfide can cause irritation and other symptoms at elevated levels, public health agencies have emphasized that odor and symptoms reported by residents do not necessarily indicate an immediate life-threatening emergency. At the same time, the persistence of repeated spikes has raised questions about chronic exposure, the adequacy of existing guidance for schools, and the need for clearer action thresholds tied to protective measures.

Why a school has become a focal point

One of the region’s fixed monitoring locations has been placed at an elementary school in the Nestor area, close to the river valley. The school site has been used as a real-time indicator of neighborhood exposure because it sits near documented river “hot spots” where contaminated water can release gases into the air under specific wind and temperature patterns.

Local guidance associated with the monitoring program generally recommends reducing outdoor activity when concentrations reach the odor threshold. For campuses, that can translate into shifting recess or physical education indoors and increasing attention to building filtration and ventilation practices during odor events.

Current response measures and longer-term constraints

• Expanded real-time monitoring in multiple South Bay locations to help residents and institutions track conditions.
• Distribution of air purifiers to households in affected communities as an immediate indoor-air mitigation step.
• Ongoing coordination among local, state, and federal entities around health assessments and environmental tracking tied to the sewage crisis.

Officials have consistently described a central limitation: meaningful reduction in hydrogen sulfide episodes is closely tied to controlling sewage and polluted flows in the Tijuana River system. That requires infrastructure and operational improvements on both sides of the border, along with sustained funding and project delivery timelines that extend beyond near-term mitigation at individual sites.

Residents continue to report that odor events are intermittent, weather-sensitive, and often strongest at night or early morning—patterns consistent with how hydrogen sulfide can accumulate and move under changing wind and atmospheric conditions.

For families near the affected campus, the immediate question remains how often elevated readings occur during school hours, what steps are taken during spikes, and how quickly longer-term sewage and water-quality fixes can reduce the underlying emissions driving the problem.