The operating permits of a company being investigated in Ohio for allegedly dumping up to 20,000 gallons of gas drilling wastewater down a storm drain have been permanently revoked, state officials said Thursday.

The action was taken after workers at D&L Energy Group in Youngstown were allegedly seen dumping the wastewater into a storm sewer that empties into the Mahoning River watershed, according to the Ohio Department of Natural Resources.

Under the state’s orders issued Wednesday, the company will stop all injection well operations in Ohio. The company’s six injection well permits were revoked and applications for three new permits were denied. D&L must also stop all temporary storage operations at its Youngstown headquarters.

Documents obtained by The (Youngstown) Vindicator said it happened when a large storage tank capable of holding up to 20,000 gallons of waste — including oil and brine — was being cleaned by a company employee.

The company, which also has operations in Pennsylvania, said Thursday it was reviewing the state’s actions and plans to respond and perhaps appeal the decision.

U.S. Rep. Tim Ryan, a Democrat who represents the region, said he was “furious” about the alleged dumping.

The Department of Natural Resources said it’s working with the state Environmental Protection Agency to contain and clean up the dumping using containment booms, absorbent pads, vacuum trucks and other equipment.

“ODNR treats all allegations of wrongdoing involving oilfield waste very seriously and will continue to aggressively investigate each of these cases to ensure violators are held accountable,” Natural Resources director James Zehringer said in a statement.

The state has launched a criminal investigation and asked the Ohio Attorney General to look at possible civil action.