A U.S. District Court judge, in one of the largest clean water fines in recent Georgia history, ordered an Atlanta manufacturer of parking lot sealant to pay $10 million for polluting the Chattahoochee River.

American Sealcoat Manufacturing LLC, which appears to have halted business at its factory near Six Flags Over Georgia in unincorporated Fulton County, knowingly and repeatedly dumped a “black oily substance” into a tributary of the Chattahoochee, Judge Orinda Evans ruled August 13. The company violated the Clean Water Act by discharging pollutants and polluted stormwater without a permit.

The Chattahoochee Riverkeeper uncovered the dumping and sued American Sealcoat claiming that pollution flowed into the stream harming water quality and leaving behind “high levels of toxins and carcinogens in the stream bed.”

“They are one of the most egregious violators we’ve come across in the 21 years that the Chattahoochee Riverkeeper has been working to protect this river,” riverkeeper Jason Ulseth said Monday.

A company representative couldn’t be reached for comment. American Sealcoat’s attorney withdrew from the case last December, according to the judge’s default judgement.

The nonprofit environmental group visited the company and discussed ways to comply with the Clean Water Act to keep the sealant materials from flowing into a creek which flows 1,000 feet into the Chattahoochee River.

“On a follow-up visit we discovered that they were actively dumping this black oily material straight into the stream,” Ulseth said. “It was a large volume flow coming out of the storm drain. They knew what the requirements of the law were and they just blatantly dumped it into the stream.”

The riverkeeper is working with M&K Warehouses, which owns the property, to clean up the toxic mess.