3.9 tons of marijuana confiscated by Texas Highway Patrol (Texas Department of Public Safety)

For highway patrol officers, there's no such thing as a routine traffic stop. That adage was again proven true when a Texas Highway Patrol trooper pulled over a gas tanker to perform a routine visual inspection and discovered the tanker was carrying 3.9 tons of marijuana. It's unclear how the trooper was able to make the discovery.

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In a news release, the Texas Department of Public Safety estimated the value of the confiscated pot at around $3.4 million. The truck driver was arrested and charged with possession. He's being held on $1 million bond. According to DPS spokesperson Sgt. Johnny Hernandez, more arrests may be forthcoming.

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Hernandez told NBC News that the bust was "a big, significant seizure" and among the largest in recent memory. Earlier this year, federal law enforcement seized more than 14,000 pounds of marijuana along the Arizona-Mexico border. The estimated street value of the drugs was between $7 million and $12 million, according to News 4 Tucson.