A Mexican driver of a semi-truck was arrested Wednesday at the Nogales Commercial Facility after federal officers found more than three tons of marijuana in containers labeled vaccum pumps and lamp holders, authorities said.

The 33-year-old driver was referred to a secondary inspection, and officers detected an anomaly in the tractor-trailer, which was spotted by a commercial X-ray system, said Edith Serrano, a U.S. Customs and Border Protection spokeswoman.

A narcotics detection dog alerted to the presence of drugs, and officers found 6,219 pounds of marijuana with an estimated worth of more than $3.1 million, Serrano said.

The semi-truck and marijuana were seized, and the driver was turned over to federal authorities.