Advanced treatment for a U.S. river diversion
Proposed
San Diego County. In early study (about 18 months from September 2026); construction depends on the November 2026 sales tax measure. Cost: Bonds of roughly $700 million to $1 billion under discussion.
Treatment for captured river water could use ultrafiltration membranes, reverse osmosis, advanced oxidation, and UV disinfection.1
What worked
Proven technologies in other settings, and the only approach aimed at storm flows.
Risks
- Not yet tested here. Membranes are sensitive to the trash and sediment that wrecked the ozone pilot.
- High energy and maintenance costs.
- Storm flows are several times larger than any plant is sized for.
Lesson
Lessons from the ozone pilot apply: screen debris first, and design for sudden surges.
Problems it targets: Nothing handles storm flows
Free home air purifiers (AIRE program)
Running
San Diego County Air Pollution Control District. Since February 2025. Cost: State incentive funds at launch, expanded with $4 million in county funds in July 2026.
Up to three free air purifiers, with replacement filters, for households in Imperial Beach, Nestor, San Ysidro, Egger Highlands, Otay Mesa West, and the Tijuana River Valley.23
What worked
Immediate indoor relief for residents.
Where it struggled
- Only protects indoor air, and only where the units run.
- Does nothing about the source.
Lesson
A stopgap while infrastructure catches up.
Problems it targets: Hydrogen sulfide in the air
Floating trash boom in the main channel
Running, funded through 2026–27
Alter Terra and the Rural Community Assistance Corporation, funded by the State Water Board. Installed November 2024 for two storm seasons, now extended. Cost: $4.7 million, plus $2 million approved in July 2026.
Interlocking floating modules made partly of recycled plastic span the river. Water passes underneath while floating trash is held back.4567
What worked
It held up under large storm surges and kept tons of trash out of the valley and estuary.
Where it struggled
- It only stops floating debris. Sewage, dissolved contaminants and sediment pass through.
- It cannot be cleared during storms, when debris is heaviest, because rising water makes it unsafe for crews.
- Hauling debris to the landfill is the main ongoing cost.
- State contracts run through 2027, but the money is projected to run out at the end of the 2026–27 season.
Lesson
Simple, rugged designs survive this river. The pilot is meant to inform a permanent structure.
Problems it targets: Trash reaching the valley, PB-CILA shuts off in storms and clogs, Contaminated estuary
Trash boom and paid collection in Los Laureles Canyon
Running
WILDCOAST and Tijuana residents. Since January 2021; a second boom added in Matadero Canyon in October 2024. Cost: Grant funded.
The first trash boom in Mexico, paired with a network of residents paid per kilogram of plastic collected before it reaches the creek.8910
What worked
Stops trash close to its source and builds local support by paying residents.
Where it struggled
- Small scale compared with the number of canyons and dumpsites.
- Depends on continued grant funding.
Lesson
Source capture works best when it pays the community doing the work.
Problems it targets: Illegal dumpsites in the canyons, Canyon collectors clog and overflow, Gaps in trash collection
Hydrogen sulfide monitoring
Running
San Diego County Air Pollution Control District and Scripps researchers. Ongoing. Cost: Public agency and research funding.
A network of continuous air monitors in southern San Diego, plus research measurements that traced where the gas comes from.1112
What worked
Pinpointed the Saturn Boulevard hotspot as the main source and confirmed long-dismissed community reports.
Where it struggled
- Monitoring measures the problem; it does not reduce it.
Lesson
Good data turned complaints into a targeted fix.
Problems it targets: Hydrogen sulfide in the air
Ozone nanobubble treatment in the river
Stopped early
USIBWC with contractor Greenwater Services. September 9 to October 15, 2025. Cost: Reported at $1.1 million by the company; local reporting cites a $2.5 million contract.
Four floating units injected tiny ozone-filled bubbles into the river just downstream of the border, to kill bacteria and cut the odors that come from sewage.1314
What worked
Bacteria dropped sharply on treatment days, and U.S. Customs and Border Protection staff near the site reported less odor.
Where it struggled
- Planned to run around the clock for about 60 days, it lasted 36 days and ran only in daytime for 22 of them.
- Trash clogged the intake and nozzles during nighttime surges from Mexico, so the units could only run in daytime.
- Operations paused for a flood warning in September and again to install a trash boom.
- On October 14, a storm surge flooded the site overnight, damaging the units, generators, and fuel cells and causing a small diesel spill. The pilot ended there.
- Even after treatment, bacteria stayed far above standards for human contact.
Lesson
The chemistry worked; the river setting did not. The contractor estimates about 40 units, debris filtering, and round-the-clock operation would be needed at scale. The IBWC called it successful but said major design changes are needed; a county supervisor called it a failure.
Problems it targets: Hydrogen sulfide in the air, Contaminated estuary
Saturn Boulevard culvert redesign
Interim fix underway; permanent fix in design
San Diego County. Interim pipe extension underway, construction expected 2027; permanent fix in design. Cost: $2.5 million interim; $4 million for design and permitting; about $25 million to build the permanent fix.
Culvert extensions would carry low flows under the road and release them below the water surface, so sewage stops churning and releasing gas.151617
What worked
Grounded in research: when a sudden diversion cut nighttime flows, odor reports dropped sharply, pointing to the turbulence here as the main source.
Where it struggled
- Construction of the permanent fix is not yet funded.
Lesson
Some of the biggest air-quality gains may come from plain engineering at one hotspot, not new technology.
Problems it targets: Hydrogen sulfide in the air
Sources
- CalMatters, the county river diversion plan and the sales tax measure, September 2026
- San Diego County Air Pollution Control District, AIRE program
- California Air Resources Board, verified air cleaners
- State Water Board, trash booms funding extension, July 2026
- Border Report, rising water levels stop crews removing debris from the trash boom
- RCAC, Tijuana trash boom passes 1,000 tons, February 2026
- RCAC, Imperial Beach project profile, 2026
- WILDCOAST, Los Laureles trash boom, 2022
- The Inertia, on the tsunami of trash at the border, and residents paid by the kilogram
- KPBS, WILDCOAST installs a second trash boom, October 2024
- San Diego County News Center, public health guidance on hydrogen sulfide, June 2026
- Scripps Institution of Oceanography, the Tijuana River's toxic water pollutes the air
- USIBWC, ozone pilot project report, December 2025
- The Coronado News, what happened during the ozone pilot, February 2026
- Science, heavily polluted Tijuana River drives a regional air quality crisis — the source for the 4,500 ppb reading
- The Spokesman-Review, county greenlights the Saturn Boulevard plan, September 2026
- CalMatters, the Saturn Boulevard fix, May 2026