The indictment charges Werner Transportation Services Inc., of Gainesville, Ga., violated the U.S. Clean Air Act when it negligently released anhydrous ammonia and "negligently placed another person in imminent danger of death and serious bodily injury," The (Columbia, S.C.) State reported Thursday.
If convicted of the criminal misdemeanor, Werner could be fined up to $500,000.
South Carolina state regulators said the leak occurred after a hose blew out as ammonia was being transferred into a Werner tank truck from the Tanner Industries Inc. plant outside Swansea.
A car driven by Jacqueline Ginyard was enveloped in the resulting toxic cloud as she drove by the plant on her way to work. She died after inhaling the fumes.
At least seven other people were hospitalized.
State health officials fined Tanner $91,000 in 2010 for a series of emergency preparedness procedures that failed during the spill. Tanner was also fined $23,625 by the state Labor Department for workplace safely violations.