UPDATED: Former St. Paul Park refinery owner's benzene leak 'egregious'; new owner has alleged MPCA violation

Marathon Petroleum Co., the former owner of the St. Paul Park oil refinery, paid a $700,000 civil penalty for failing to properly treat wastewater containing the chemical benzene, the Minnesota Pollution Control Agency announced.

Marathon illegally disposed of nearly 115 million gallons of wastewater containing benzene into an unprotected lagoon at the refinery rather than removing the benzene at its wastewater treatment plant, the MPCA said. The lagoon is near the Mississippi River. The company maintained there was no evidence of a release into groundwater, but state officials said that is unknown.

The company said the wastewater contained the equivalent of 128 gallons of pure benzene. Marathon paid the $700,000 penalty in November as part of an agreement with the state agency.

"It is a high penalty and it reflects the fact that the agency had a number of concerns with Marathon Petroleum about how they were handling their hazardous waste," said Sam Brungardt of the MPCA. "And then Marathon Petroleum basically continued to dispose of it in a manner that is not legal."

The company failed to properly manage wastewater off and on for 65 days between mid-June and mid-October of 2010.

Marathon spokesman Shane Pochard said in an interview that the incident was the result of a power outage and "mechanical failures."

"After that happened, additional preventative controls were put in place," he said.

Brungardt said the refinery's wastewater treatment plant is supposed to contain micro-organisms that remove chemicals such as benzene before water is discharged. In this case, however, that was not occurring before the water containing benzene was disposed in the unlined lagoon, located near the Mississippi River.

"Their bugs died," Brungardt said of the micro-organisms.

It is not clear how much, if any, benzene leaked from the lagoon.

MPCA officials said they learned of the benzene release only after Marathon called them to a meeting to discuss a separate national pollution permit violation. It was during that meeting in September 2010 that company officials mentioned the benzene release.

State officials should have been notified much earlier, said Tonya Maurice, compliance coordinator for the MPCA's industrial division.

"These are extremely egregious violations," Maurice said. "We have a company who is very large, who runs refineries, who should understand the hazardous waste violations."

She added: "They knew that their system was not working and they knew the benzene was not getting removed and they knew where they were sending that wastewater."

Benzene is a petroleum product, so it could have evaporated into the air or contaminated shallow groundwater, according to the MPCA.

Pochard said routine company testing following the benzene release showed there was "no evidence of any impact outside the refinery itself," including in surrounding groundwater.

The oil refinery's wastewater system includes two lagoons. Fluid treated by the wastewater treatment plant cycles through the lagoons, usually over five to seven days, before returning to a building to be filtered. From there the filtered wastewater is discharged into the river, Maurice said.

"We really don't know the environmental impact," she said, because of the delay between the time of the release and when officials were notified.

Marathon sold the refinery in December 2010 to Northern Tier Energy.

The MPCA currently has an "open enforcement action" pending against Northern Tier Energy, Maurice said. She said state law prohibits the release of further information while the action is pending, but she did say that an open enforcement action is triggered by an alleged pollution violation.