Six Mexican national guardsmen wielding flashlights form the front line, tracking shovel-bearing drug traffickers through the seven-mile stretch of drainage and sewage lines on the Mexican side. They wonder out loud how many tunnels they haven’t been able to find.
“Nogales is the capital of cross-border tunnels between Mexico and the United States,” said Ricardo Santana Velázquez, the Mexican consul general in neighboring Nogales, Ariz.
The subterranean challenge of stopping drug trafficking and human smuggling is on daily display here. Once traffickers discovered the Nogales drainage system, they learned to drill and hammer into the walls of the channel. Authorities don’t know how much contraband makes it through the tunnels before they are found and blocked. But they say a narrow hand-dug passage could be worth tens of millions of dollars to drug cartels.
On a scorching recent Monday afternoon, Santana and the team of Mexican national guardsmen crawled into the underground drainage system. Traffickers seemed to enter every day, drilling tunnels that bisect the sewer like holes in Swiss cheese, each of them connecting the pipeline to Arizona.
One tunnel led to the bathroom of an Arizona home — and 211 pounds of cocaine and fentanyl, meth and heroin. Another opened up in an overgrown patch of grass just north of the border wall.
Traffickers dug one access point in a Mexican cemetery, removing a corpse so they could enter the pipeline through the grave.
The aging drainage system, built in the 1930s as a Depression-era joint project between the two countries, connects the twin cities of Nogales, Mexico, and Nogales, Ariz. It has been a boon for traffickers: More than half of the tunnels found beneath the U.S.-Mexico border since 1990 have been discovered here.
One guardsman descended into the sewer and surveyed the sidewall.
“You can tell they’re working on something new,” he said. Members of the unit spoke on the condition of anonymity because they said publishing their names would make them and their families targets for the cartels.
The guardsman pointed to a pile of rock and soil that appeared to have been disturbed recently, not far from a makeshift altar with candles. The pipeline was illuminated only by his flashlight. Untreated water dripped from the rocky ceiling. The stench was putrid.
“The hard part now is finding the newest tunnel,” he said. “It’s here somewhere.”
Patrolling the 2,000-mile U.S.-Mexico overland border is hard enough. The frontier cuts through inhospitable deserts, traces the zigzag of the Rio Grande and slices between multiple sister cities, where downtown streets are a few feet apart across the border. But patrolling underground in an aging drainage system?
“With six men, it sometimes feels impossible,” one guardsman said.
The Nogales Wash Channel was built to solve a simple problem. Each year during monsoon season, a rush of water flowed downhill from Nogales, Mexico, to Nogales, Ariz., flooding the U.S. side with sewage. Engineers from both countries determined that the only solution was an international drainage system — a roughly 16-mile combination of pipeline, tunnel and open channel that crosses the border.
“This project is designed to protect the important border city of Nogales,” the Daily News in Amarillo, Tex., explained in June 1935.
Now 11 million to 15 million gallons of water flows north through the system each day from Mexico to the United States, where it’s treated. About seven miles of the system are in Mexico’s Sonora state; nine are in Arizona.
When it was finished in the early 1940s, there was little reason to believe that the infrastructure connecting what were then sleepy communities on either side of the border would be used by transnational criminals. Even when the drug trade took off in the 1970s and 1980s, there was no need to move marijuana or cocaine through sewer pipes when so much of the frontier was easily traversed.
But as security has tightened, the sewage system became one of the greatest vulnerabilities on the U.S.-Mexico border. The U.S. Border Patrol says 127 tunnels have been found in the Nogales area since 1990. Many of them tap directly into the drainage system.
“There’s a reason why they call Nogales the tunnel capital of the border,” said John Mennell, a spokesman for U.S. Customs and Border Protection. “But it also underscores the importance of the wall. These traffickers have been driven underground because the easier routes are no longer available to them.”
Traffickers float bags of drugs on the northbound wastewater and alert colleagues who are waiting in Arizona to snag the packages. In the past, those drugs have clogged the sewage system, causing massive flooding. Border Patrol officers have raised questions about the public health implications of consuming drugs that have arrived on a river of human waste.
To deter the traffickers, the Border Patrol has welded shut the manholes used to access the sewage system in southern Arizona. Local officials in Arizona have discussed adding mesh nets to the pipeline that would catch packages of drugs.
Engineers and local officials say the nature of the Nogales border, where Mexico has little water-treatment capacity and waste flows downhill into Arizona, necessitates the use of a binational sewage pipeline.
“People are flushing their toilets every day,” said Luis Ramirez, an adviser to the Greater Nogales Santa Cruz County Port Authority who has been working on the binational sewage system for 25 years. “You can’t just stop the flow.”
For decades, the United States patrolled the border alone, trying to block traffickers’ increasingly creative attempts to smuggle drugs. But over the past decade, Mexican security personnel have joined the effort.
The American tunnel team uses cutting-edge technology, including devices that monitor oxygen levels and noxious gases. They’ve created a tunnel simulator to train new agents.
“The Americans have everything,” said one member of the Mexican unit. “We don’t even have helmets.”
The six-member Mexican unit is responsible for all border enforcement, above and below ground, over a 30-mile stretch. They’re able to conduct only two brief patrols in the sewage system each week.
On the Mexican side, the ceiling of the tunnel system appears to be weakening, and local officials have expressed concern about the possibility of collapse. During a patrol last month, the team identified a new leak. The men jumped over a widening pool of wastewater.
“Every time someone drills into the side of the infrastructure, it further weakens it,” Ramirez said. “At some point, you begin to worry about the integrity of entire sections.”
When the Mexicans find signs of a tunnel, they call U.S. Border Patrol agents to investigate where it might lead in Arizona.
“The collaboration is now very strong,” said Kevin Hecht, the head of the Border Patrol’s tunnel team.
“Police agencies on both sides frequently patrol the tunnels jointly,” said Santana, the Mexican consul general. “We understand that this criminal activity affects border security.”
The illicit tunnels are often as narrow as two feet and as long as 90 feet, depending on what the traffickers are trying to transport. One of the tunnels identified last year was being used by migrants who surfaced on the U.S. side near a patch of brush. The passage was spotted when a Border Patrol camera trained on the area captured people emerging from the earth before sprinting into the distance.
Traffickers use welding tools to break through the pipes. They dig through soil and rock with small shovels they bury when they aren’t being used. They sometimes conceal their work with gray clay.
The Mexican patrols often find crack pipes in the drainage system. They suspect that the people who are trafficking in drugs are also consuming them. During monsoon season, Mexican and U.S. teams have found bodies swept up by the rushing water. It’s usually not clear if they were traffickers or homeless people seeking shelter in the pipes.
In several cases, the Mexican patrol has found men in the sewer who appeared to be digging. But because they were still technically on Mexican soil and not in possession of drugs, no charges were filed.
“Cross-border tunnels are the parallel and underground reality of the illicit trafficking of arms, money, drugs and people, which can no longer be ignored,” Santana said.