The 90 UC San Diego students hard at work in a canyon neighborhood in Tijuana on a Saturday afternoon are learning about environmental sustainability, municipal infrastructure and border economics one street paver at a time.

The UC San Diego Urban Studies and Planning Club is part of a binational pilot project to reduce water pollution by applying porous or "pervious" surfacing technology to dirt roads. The project focuses on the Tijuana River Watershed, which stretches across the U.S.-Mexico border, and its Los Laureles Canyon where 80,000 Tijuanans live in makeshift homes with no streets, sewers or power.

With support from both the U.S. and Mexican governments, the students are helping residents build and install 35,000 pervious street pavers to absorb wastewater and prevent runoff into the Tijuana River Estuary and the adjoining San Diego Bay.

"There is one thing you might keep in mind," Oscar Romo told the students at a midweek orientation. "We're doing this project in Mexico in part because we're trying to save wetlands in the United States."

Romo, a pioneer in transborder environmental protection efforts, works at the Tijuana River National Estuarine Research Reserve and teaches at UC San Diego. He has spent decades trying to alert the public that runoff from unsustainable development creates hazardous erosion, pollutes dwindling water supplies and spreads disease.

Border demographics and economics have given Romo's campaign a new urgency. With a population that has increased sixfold from 235,000 in 1964 to more than 1.5 million today, Tijuana has outpaced Las Vegas as North America's fastest-growing city. Those numbers have spiked over the past decade since the North American Free Trade Agreement ushered in border manufacturing plants, called maquiladoras, that attract low-wage workers from throughout Latin America.

The Los Laureles neighborhood of Colonia de San Bernardo has sprung up as a settlement for maquila workers and their families. Homes are thrown together from scrap plywood, used cinder blocks and even discarded garage doors, much of it from San Diego.

As student club leader Adam Krohn explained on the bus ride to the project site, "The people of the colonia can't afford building materials, so they've become very good at using things that we throw out."

Krohn reminded the students that the maquilas are thriving (and driving the population surge that strains the environment) because they produce electronic goods that are wildly popular with young U.S. consumers.

"This isn't meant as a guilt trip on you guys," he said. "I just want you to recognize while we're here that everything is interconnected. An international border doesn't stop pollution, and it doesn't stop poverty."

The interdisciplinary value of the Tijuana project extends to cross-cultural studies. During the orientation, a student asked if she could bring bags of used clothing to donate to the impoverished canyon residents.

"Thank you, that is a kind offer," Romo said gently. "But I would advise against it. The people of the colonia are very proud. They appreciate our help with the pavers, but any kind of gift would be an affront to their dignity. The kids might like it, but the parents would not."

Colonia residents have set a goal of laying 70,000 pavers to cover a half-mile stretch of the main road. The foot-wide hexagonal pavers are made of gravel, cement and water poured into wooden frames and allowed to harden. Once in place, they drain wastewater into the ground where naturally occurring bacteria remove harmful effluent. If the pilot project succeeds, its binational backers, which include the city of Tijuana and the California Coastal Conservancy, will look to replicate the low-cost technology throughout the region.

For the UC San Diego students, paver construction is a hands-on lesson about how good science can produce good public policy through local empowerment.

"This is a wonderful example of civically engaged service-learning with a strong research component of deploying new biomolecular tools in a community setting," said Keith Pezzoli, a UC San Diego professor in the Urban Studies and Planning Program who also does research for UC San Diego's Superfund Basic Research Program.

The ultimate payoff of the students' Tijuana project may occur back home in San Diego. Krohn, whose senior thesis is on best practices in watershed management, believes that pervious paving technology could catch on in the United States, where construction of roads, sidewalks, parking lots and driveways has typically relied on impervious surfacing.

"The fact that it can be done here in Tijuana on an informal basis gives students a one-of-a-kind opportunity to see how sustainability and planning theory can be directly applied to the world around them," Krohn said.

Kate Callen is a staff writer in UCOP Strategic Communications.