(Reuters) - A grand jury has indicted Phillips 66 for violating the Clean Water Act by illegally discharging hundreds of thousands of gallons of industrial wastewater into Los Angeles County's sewer system and failing to report the violations to authorities, the U.S. Attorney in Los Angeles said on Thursday.

Phillips 66 is expected to be arraigned in the coming weeks in Los Angeles federal court. It faces a maximum sentence of five years probation on each count and up to $2.4 million in fines.

(Reporting by Jonathan Stempel in New York)