Advanced treatment for a U.S. river diversion
Proposed
San Diego County. In design; 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.
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, with state support. Since February 2025. Cost: State incentive funds.
Free air purifiers and replacement filters for households in Imperial Beach, Nestor, San Ysidro, Egger Highlands, Otay Mesa West, and the Tijuana River Valley.
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 August 2026.
Interlocking floating modules made partly of recycled plastic span the river. Water passes underneath while floating trash is held back.
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 catches what floats. Tires, car parts, and sediment pass underneath.
- Crews cannot safely clear it during storms, when debris is heaviest.
- Hauling debris to the landfill is the main ongoing cost.
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 2021. 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.
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.
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.
What worked
Bacteria dropped sharply on treatment days, and Border Patrol agents near the site reported less odor.
Where it struggled
- 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
Funded, not built
San Diego County. Interim fix approved; timing unclear. Cost: $4 million interim; about $25 million for the full fix.
Culvert extensions would carry low flows under the road and release them below the water surface, so sewage stops churning and releasing gas.
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
- Slowed by red tape.
- The full fix is not 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