OTAY MESA, CALIF. – Not even the site where President Trump's massive border wall project is coming to life is impervious to illegal border crossings.

Several immigration officials told the Washington Examiner during a trip to the border Wednesday that agents have apprehended unauthorized immigrants inside the construction zone where eight border wall prototypes are currently being built.

"There have been arrests made where individuals crossed illegally into the United States," said U.S. Customs and Border Protection San Diego division chief Mario Villarreal. "We've had additional resources there in the form of our horse control and ATVs."

The prototype construction zone is situated behind two barriers – one made of corrugated landing mats, the other of steel wire mesh – just north of Mexico, where border patrol agents have dealt with a particularly high volume of foot traffic for decades.

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Flanked by rolling brown hills and sprawling beaches just 12 miles west, the Otay Mesa area is a primary target for border crossings. In August, border patrol officers discovered a 328-foot smuggling tunnel near the Otay Mesa Port of Entry, culminating in the arrest of 30 Chinese and Mexican nationals who had emerged from the underground structure.

After scaling the primary barrier down here, one of the most common ways illegal immigrants will overcome the steel mesh barrier is by cutting a small hole with power tools.

"It takes less than a minute," U.S. Border Patrol agent Eduardo Olmos told the Washington Examiner after he pointed out parts of the barrier appeared to have been patched. "We had one to two cuts a day last year, and about 500 total."

Despite the apprehensions that occurred at the site of prototype construction, Villarreal said the overall project has gone smoothly so far, with one week left until the evaluation process begins.

"The companies that have come in have come with the right equipment, the right staffing, and they've been very thorough," he said. "There hasn't been any worksite-related injuries ... and the weather has been typical San Diego. It's gone very well."