While key entrance and exit points have been plugged in some of the biggest tunnels used to ferry people and drugs across the U.S.-Mexico border, the passageways remain largely intact raising concerns smugglers reuse them, according to a published report.
In recent years, dozens of tunnels have been discovered running under the border. The smaller, more crudely constructed passages are easily destroyed, authorities say. But the larger, more elaborate tunnels require enormous amounts of material and expertise to fill.
The task to jam up an entire route also is costly and sometimes complicated if the tunnels run under private property, authorities say.
According to a report in Tuesday's Los Angeles Times, seven of the largest tunnels discovered under the U.S.-Mexico border have yet to be filled in, including the so-called Grande Tunnel found in January 2006 that extends nearly half a mile from San Diego to Tijuana.
Filling those tunnels would cost about $2.7 million, according to U.S. Customs and Border Protection officials, the newspaper said.
Michael Friel, an agency spokesman, said the department is trying to find money in its budget to complete the work. But critics say the unfilled tunnels pose an unnecessary national security risk.
"The department should move, find money, and do it," said U.S. Sen. Dianne Feinstein, D-Calif. "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."
The responsibility for filling tunnels was assigned to Customs and Border Protection in 2003, after the Department of Homeland Security was created. The 2007 budget for the border agency is $7.8 billion.
A concern with leaving the tunnels open is the reuse of them by smugglers, who dig around the plugged entrance points.
In Nogales, Ariz., traffickers have used one tunnel three times over a four-year span, said Agent Michael Cano, a U.S. Border Patrol spokesman. Smugglers also have used the concrete that plugs tunnel exits and entrances to make support walls and ceilings for new tunnels, he said.
U.S. authorities have teamed with structural and civil engineers and geologists to devise ways to close tunnels. They've experimented with a type of concrete that will cave in if smugglers use it for support.
But addressing the problem in the U.S. is only one part of the issue. Many of the tunnels extend into Mexico, where U.S. authorities have no control.
Mexican authorities have told their U.S. counterparts they've filled their end of the tunnels, but U.S. officials express doubt citing the high costs and examples of tunnels being compromised.
Special Agent in Charge Frank Marwood, who heads the U.S. Tunnel Task Force, said the situation should be handled "by a binational effort."
"If they're not filled in, (smugglers) just branch out at one end or another," he said.
The Mexican attorney general's office, which handles organized crime, did not respond to numerous requests from the Times for interviews.