Trent Biggs, a watershed scientist at San Diego State University, displays a protective case that surrounds a water quality sensor that once stood in the San Diego river. Similar sensors now sit testing water quality in the Tijuana River. Nov. 11, 2022. / MacKenzie Elmer
Trent Biggs, a watershed scientist at San Diego State University, displays a protective case that surrounds a water quality sensor that once stood in the San Diego river. Similar sensors now sit testing water quality in the Tijuana River. Nov. 11, 2022. / Photo by MacKenzie Elmer

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An Election Day storm sent one billion gallons of water and muck over the U.S.-Mexico border into San Diego in a dramatic brown gush captured on video by the International Boundary and Water Commission. As gross as that water looked, nobody really knows what was in it.

A team of researchers at San Diego State University is trying to change that by installing a pair of real-time water quality sensors where the Tijuana River crosses the border and spills into the Pacific Ocean. The instrument looks like a big white PVC pipe stuck in the mud protecting a cylindrical tube filled with sensors sending live water quality data to a website managed by the SDSU team.

Trent Biggs, a watershed scientist, and Natalie Mladenov, director of the Water Innovation and Reuse Lab, are collaborating on the project funded in part by the U.S. Environmental Protection Agency.

Trent Biggs, a watershed scientist at San Diego State University, points to a tryptophan sensor in a new real-time water quality instrument for the polluted Tijuana River. / Photo by MacKenzie Elmer

“Our scientific goal is to determine if we can measure sewage contamination and bacterial concentrations in real time,” Biggs said.

These new sensors measure a number of sewage indicators including the amount of oxygen in the water, which gets eaten up quickly by bacteria living in wastewater. Low dissolved oxygen means the water quality is not good enough to support life for other animals.

The team is also tracking conductivity, or how much salt the river water contains which is another indicator of sewage. They’re also tracking tryptophan, an amino acid known commonly for its presence in turkey and chicken. But it’s also found in the organic matter that’s in sewage and it actually glows in water under ultraviolet light, which is precisely how the sensor tracks it.

Sure enough, Biggs’ water quality data from the early November storm showed an upward bounce in tryptophan concentrations as the Tijuana River flowed its course to the ocean.

Trent Biggs, a watershed scientist at San Diego State University, points to new real-time water quality data in the Tijuana River. The bright green line indicates tryptophan, an amino acid that’s an indicator of sewage, which spiked during a Nov. 8 rain in the Tijuana River watershed. Nov. 11, 2022. / Photo by MacKenzie Elmer

One goal for these sensors is to serve as an early-warning system when poor water quality barrels toward the shores of Imperial Beach, which experiences beach closures a majority of the year, and Coronado, which until this summer didn’t typically feel the side-effects from the Tijuana River sewage crisis. But a new technology rolled out earlier this year detecting fecal bacteria in water by its DNA led to a spate of daily consecutive summertime beach closures, sending shockwaves throughout San Diego’s southernmost beach communities.

“We have these apps where you can look up what the air quality is like today. In the long term, we’d like to have something similar where you can check the water quality,” Biggs said.

Last week’s storm was the research team’s first real test of the sensors, which are expensive and take a lot of routine maintenance – one reason real-time water quality sensing systems aren’t more common. And the data take a trained eye to interpret.

Another goal of this project is to eventually measure the success of a $330 million investment from Congress in expanding a wastewater treatment plant at the border. The current border plant can only handle 25 million gallons of wastewater pumped from Tijuana per day. But it’s over-loaded when heavy rains generate more wastewater than any border infrastructure can handle, often forcing Mexico to turn off pumps that divert sewage to the U.S. for treatment. That sewage, then, ends up spilling elsewhere, and eventually over the border.

The Election Day storm was so large there was a spill inside the South Bay International Wastewater Treatment plant, which is managed by the IBWC. Morgan Rogers, the IBWC’s plant manager, reported that the plant was taking in over twice the water it was built to handle over a 12-hour period, causing tanks that settle-out solids from sewage to overflow.

South Bay residents and elected leaders called for more regular water quality monitoring in the valley for years, but no agency took it up. There are a few short studies, like one by the IBWC in November of 2020 revealing the water contained not only raw sewage but byproducts of banned soaps and cleaners, harmful metals, parasitic worms and chemicals from plastics production.

The SDSU instruments won’t reveal that level of detail about the water quality. But researchers hope it will fill the knowledge gap in communicating the presence of pollutants to the public.

“The holy grail here is identifying indicators that are reflective of a risk to human health as well as ecosystem impacts,” Biggs said.

Around Our Environment

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  • A voter ballot measure that would allow the city to charge everyone for trash pick-up is on track to fail, ever so slightly, but it gained a bit of ground in the latest vote count. (Politics Report)
  • Vince Vasquez plotted how districts voted on Measure B, with coastal communities largely voting no and northern and southeastern San Diego strongly in favor.
  • A new report shows two water districts that want a divorce from the San Diego County Water Authority would save money by doing so. (Union-Tribune)
  • More evidence that bird flu isn’t going away: The San Diego Zoo Safari Park found a dead wild pelican on its grounds that tested positive for avian flu. (Union-Tribune)

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