President Donald Trump’s proposed wall won’t stop Mexican cartels from smuggling drugs into the U.S. through illegal tunnels, which increased significantly after a border fence was built and security was considerably tightened.

“Illegal tunneling activity on the southwest border of the United States represents a significant and persistent threat to border security and will likely remain so in the near future,” the Immigration and Customs Enforcement Homeland Security Investigations (HSI) office warned in a 2010 report that only became public April 2, 2017.

“The rise in illegal tunneling is likely a response to increasingly heightened border security,” said the report, which was posted this month by the Government Attic web site.

Data on tunnels dug since 2010 is scarce, but there is no doubt the number has increased, Lance LeNoir, supervisor of the U.S. Border Patrol Entry Team in San Diego, told The Daily Caller News Foundation’s (TheDCNF) Investigative Group.

And the Department of Homeland Security’s Inspector General (IG) called illegal tunnels “a significant homeland security vulnerability” in a 2012 report, saying “law enforcement has recovered approximately 169,000 pounds of narcotics, valued at more than $200 million, from drug traffickers using tunnels.”

Federal officials had discovered 146 tunnels as of 2010, 62 of which were completed. Another 67 were found before completion, often prior to crossing the border into the U.S. The status of the remaining 17 was not reported.

“Tunnel activity has been on the rise since the first reported discovery in 1990, though the trend has accelerated since 2006,” the heavily-redacted HSI report said.

Just four tunnels were found before 1999. The number of tunnels uncovered annually slowly rose before spiking to 17 in 2006 – more than double the number found the year prior. More were discovered in the following years, hitting 25 and 23 in 2009 and 2010, respectively.

The acceleration coincides with the Secure Fence Act of 2006, which authorized up to 700 miles of border fence, and Operation Jump Start, which increased the number and aggressiveness of enforcement officials. (RELATED: America’s Heroin Epidemic Fueled By Flood Of Illegal Immigrants)

“The success of Operation Jump Start, the newly created border fencing and subsequent elevation in Border Patrol agent levels may have caused [transnational criminal organizations] to seek alternative methods for transporting drugs across the U.S./Mexico border,” the HSI report said.

“It is possible that the simultaneous rise in tunneling activity during this time period was the result of heightened border security,” the report said.

Similarly, “the increase in the number of tunnels over the past four years may be attributed to border fencing and an increased number of Border Patrol agents,” the watchdog’s 2012 report said. (RELATED: War Against Heroin Being Lost In Bureaucratic Fog)

Customs and Border Protection (CBP) spokesman Ralph DeSio told TheDCNF: “As our borders become more hardened, this is one of the reasons they’ll take to tunneling.”

The tunnels are highly sophisticated and difficult to detect. Entrances are typically found in covered shelters, such as warehouses, and can have their own lighting and ventilation or may connect to existing underground infrastructure, like sewers.

One tunnel discovered in 2010, for example, was nearly half a mile long, 90 feet deep, and was estimated to have taken more than a year to build at a cost of $1 million.

More recently, traffickers have started using a drill that can dig tunnels as narrow as six inches to transport drugs, making it even more difficult for federal agents to locate. Unfortunately, effective tunnel-detecting technology isn’t available, thus magnifying the challenge.

“CBP does not have the technological capability to detect illicit cross-border tunnels routinely and accurately,” the 2012 IG report said. “Until CBP has this capability, criminals may continue to build cross-border tunnels undetected.”

LeNoir added that “we’ve been testing every viable technology on the planet. We’re talking about a very small, niche market here. If there was something out there that worked, we would be using it.”

He noted that existing equipment is only somewhat effective and it would be expensive to develop technology specific to his team’s needs. Instead, law enforcement officers rely on more traditional approaches.

“We put our emphasis on human intelligence … hardened investigative techniques, outreach programs … and old-fashioned police work,” said LeNoir, whose team is “affectionately known as the Tunnel Rats” after a Vietnam War group of the same name. “It’s a lot of man-hours and a whole lot of patience,” which sometimes involves staking out potential tunnel sites.

Outreach programs are ways authorities spread awareness by teaching locals about spotting potential tunnel sites.

Meanwhile, tunnels aren’t the only way drugs are trafficked across the border.

“There’s peaks and valleys,” LeNoir said. Tunnels “tend to be trendy one year, not trendy the next.”

Essentially, drug smugglers shift their emphasis to a different trafficking method after enforcement agencies more effectively or more aggressively crack down on another.

“I think they utilize whatever transportation method gets drugs across the easiest with the least resistance,” Mark Spencer, who spent 25 years as a Phoenix police office and now the southwest project coordinator for the watchdog group Judicial Watch, told TheDCNF.

Ultimately, traffickers will find any way possible to get their drugs into the U.S.

“They have to move a perishable product and a lot of it in a short amount of time,” LeNoir said.

[dcquiz] Regardless, it’s likely Trump’s proposed border wall will still be helpful.

“I think that a wall is definitely going to help,” CBP officer and president of the Arizona chapter employee union Patricia Cramer told TheDCNF. “It’ll make it a lot harder on [drug traffickers]. I haven’t met one officer that isn’t for it. The wall we have now is a joke.”

She noted that drug smugglers will eventually find new methods, but it’ll be especially effective in keeping out illegal immigrants who forgo a vetting process.

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