UNFILLED TUNNELS A WEAK LINK AT BORDER

Seven of the largest tunnels discovered under the U.S.-Mexico border in recent years have yet to be filled in, authorities said, raising concerns because smugglers have tried to reuse such passages before.

Among the unfilled tunnels, created to ferry people and drugs, is the longest one yet found -- extending nearly half a mile from San Diego to Tijuana. Nearby, another sophisticated passageway once known as the Taj Mahal of tunnels has been sitting unfilled for 13 years, authorities say.

Though concrete plugs usually close off the tunnels where they cross under the border and at main entrance and exit points, the areas in between remain largely intact. Filling the seven tunnels would cost about $2.7 million, according to U.S. Customs and Border Protection officials. Accessing tunnels that run under private property is also a problem, as is a lack of coordination with Mexican authorities.

Mexican authorities have told their U.S. counterparts that they’ve filled their end of the tunnels. But U.S. officials express doubt, citing the high costs and examples of tunnels being compromised. The Mexican attorney general’s office, which handles organized crime, did not respond to numerous requests for interviews.

In recent years nearly 50 tunnels have been discovered running under the border from San Diego to Arizona. Most are small, crudely constructed passages -- called gopher holes -- that are easily destroyed.

But filling the larger, more elaborate tunnels requires enormous amounts of material and expertise, especially because some were probably designed by mining engineers.

To prevent break-ins, authorities say they install motion sensors, which alert them to incursions.

But smugglers in some cases have been able to access existing tunnels by digging around the plugged entrance points, according to the U.S. Border Patrol and Immigration and Customs Enforcement, which heads the San Diego-based U.S. Border Tunnel Task Force.

In Nogales, Ariz., traffickers have used one tunnel three times over a four-year span. Tijuana smugglers were suspected of reusing a tunnel in 2004, one year after its discovery inside a house in Mexico. U.S. authorities have had to reinspect several other tunnels in response to suspicious activity or tips.

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Unclear jurisdiction

Because of overlapping jurisdictions among federal border agencies, the responsibility for subterranean work was unclear for years. The Border Patrol and the Drug Enforcement Administration each had some responsibility.

After the Department of Homeland Security was created in 2003, the responsibility for filling tunnels was assigned to one agency: Customs and Border Protection.

Authorities cite this streamlining as progress. But Customs and Border Protection has not filled any tunnels, and has capped only two since assuming control. Michael Friel, an agency spokesman, said the agency is trying to find money in its budget to complete the work. The 2007 budget for Customs and Border Protection is $7.8 billion.

Critics say the existence of so many unfilled tunnels poses a needless -- and inexcusable -- national security risk.

“I was shocked to learn that these tunnels haven’t been filled in. They should be,” U.S. Sen. Dianne Feinstein (D-Calif.) said in a statement. “The department should move, find money, and do it. This is a huge department with a huge budget. And if they don’t have the money, they should tell us, and we will seek to get it in the emergency supplemental.”

Among the unfilled passages:

* The so-called Grande Tunnel connecting warehouses in San Diego and Tijuana. Nearly half a mile long, the tunnel was discovered in January 2006 and attracted global media attention as well as groups of local and national politicians, who were given tours of its cave-like depths. The tunnel prompted Feinstein to propose legislation outlawing the construction of tunnels under the border.

* The 1,400-foot tunnel called the “Taj Mahal” because of its lighting system and reinforced concrete walls. The tunnel was discovered in 1993. Five years later, authorities suspected the passage had been reentered after 33 illegal immigrants were found covered in mud near the opening. A metal lid over the tunnel opening had been cut. Border Patrol agents say they never determined for sure if the passage was reused.

* Two long tunnels leading from Mexicali, Mexico, to a quiet residential area in Calexico, Calif. One of them, discovered in 2005, was equipped with a ventilation system, phone line and video surveillance equipment.

It isn’t cost alone that can keep tunnels unfilled. Owners of private property also can slow the process. In 2002, after a tunnel was discovered running under part of his property in eastern San Diego County, David Field, a San Diego building inspector, feuded with the DEA over how to fill the quarter-mile-long passage. The DEA wanted to use a concrete-soil mix. Field, for environmental reasons, said he wanted the portion under his land filled only with dirt.

The tunnel featured a battery-operated cart on rails and was used to ferry what may have been tons of drugs over a 10-year period, according to authorities.

In 2002, the DEA sent Field a letter saying that drug traffickers would probably reuse the tunnel if it wasn’t completely closed off and threatened to seize Field’s property if the tunnel was compromised. Field said the letter surprised him because he knew the agency had never filled the Taj Mahal tunnel found in 1993.

“I said that tunnel is still open.... So how could this be a national emergency?” Field said.

Authorities say they have had to check the tunnel twice to investigate tips that it had been reopened, but have found no evidence.

Smugglers can be determined about reclaiming their tunnels. Take the case of the little light-blue house in Nogales. The vacant building with barred windows is at 438 W. International St., right across the street from the border, where a 20-foot fence provides a formidable above-ground barrier.

Several years ago, smugglers, starting from a drainage canal in Mexico, dug under the border fence, under International Street, and under the yard, to a front room in the house. Wooden slats and carpeting covered the opening, said Agent Mario Cano, a U.S. Border Patrol spokesman.

In December 2001, U.S. authorities discovered the 85-foot tunnel -- equipped with a rail and cart system -- and plugged it. But the smugglers soon dug around the cap at the border and found their way back to the tunnel, Cano said.

Diggers used about 15 feet of that tunnel, then branched off and burrowed an additional 40 feet. They surfaced near the house’s driveway and covered the new opening with trash cans. In March 2002, that opening was discovered and sealed, Cano said.

Smugglers went to work again, this time using portions of the first and second tunnel before branching off to surface in another area of the yard, where they covered their latest opening with a tarp. That branch and its opening were discovered in October 2005.

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Digging a new route

This month, authorities returned to the house again. This time, two men were digging a new route, starting inside the home, Cano said. They had progressed only 15 feet, Cano said, but may have intended to link up again with one of the existing tunnels under the property.

None of the passages have been filled, Cano said, although he believes portions may have collapsed because of heavy rains. Even if the tunnels were filled, he said, the problem might not go away.

That’s because smugglers have used the concrete fill to make support walls and ceilings for new tunnels, he said. The filled-in passages also serve as markers, guiding crews to new areas where they want to go below ground.

The tunnel diggers’ determination has bedeviled U.S. authorities, who have teamed with structural and civil engineers and geologists to devise the best ways to close tunnels. They’ve experimented with a type of concrete that will cave in if smugglers use it for support.

The cost to close the unfilled tunnels ranges from $200,000 to $700,000.

But addressing the problem here solves only part of the problem because some tunnels extend hundreds of feet into Mexico, where U.S. authorities have no control.

Though Mexican authorities promise to fill tunnels, it’s hard to know if they’ve followed through, said Assistant Special Agent in Charge Frank Marwood, who heads the U.S. Tunnel Task Force.

Mexican authorities have occasionally permitted their U.S. counterparts to inspect tunnels for suspicious activity, including one time when a corpse was discovered on the Mexican side. But it’s not routine.

In 2004, smugglers in Tijuana are believed to have reused a tunnel that Mexican authorities said they had filled. The smugglers broke into a tunnel discovered a year earlier and formed a new tunnel heading toward a parking lot near the San Ysidro Port of Entry, U.S. authorities said.

The tunnel has since been filled in on the U.S. side, but the status of the Mexican side is unknown.

Corruption in Mexican border agencies complicates matters. Last year, two Mexican customs officers were arrested on suspicion of being involved in the construction of a tunnel near the San Ysidro Port of Entry.

U.S. authorities also believe Mexico can’t afford to fill tunnels. If so, the U.S. should provide assistance, some say. “It’s a binational security breach, and I think the way to handle it is by a binational effort,” Marwood said.

“If they’re not filled in, [smugglers] just branch out at one end or another.”

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richard.marosi@latimes.com