RICHMOND, Calif. (AP) - The U.S. Environmental Protection Agency is conducting a criminal investigation of Chevron after learning the company had been routing pollutants around monitoring equipment at its Richmond refinery and burning them off into the atmosphere.

The San Francisco Chronicle reports that the Bay Area Air Quality Management District found a pipe inside the refinery used to route hydrocarbon gases around monitoring equipment about two years ago.

The EPA opened the criminal investigation in early 2012. EPA investigators want to know who at Chevron was aware of the bypass pipe and whether it was used to intentionally deceive air pollution regulators.

The probe is unrelated to the Aug. 6 fire at the Richmond plant, which reduced production at one of the nation's largest refineries. Smoke from the fire sent thousands of residents to hospitals with health complaints.

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