The East Bay Municipal Utility District has agreed to pay a $99,900 penalty as part of a settlement with federal regulators over allegations of improperly managing hazardous waste at its West Oakland sewer treatment plant.

The U.S. Environmental Protection Agency said Wednesday a 2014 inspection of the EBMUD facility, which treats wastewater before it is discharged to San Francisco Bay, found the facility accepted shipments of regulated hazardous materials without proper permitting and failed to label certain containers of hazardous waste.

"EPA's oversight role is pivotal to ensuring compliance with hazardous waste laws," Jared Blumenfeld, EPA regional administrator for the Pacific Southwest, said in a statement. "The state permitting process must be followed to have the necessary safeguards in place."

Details on the types of materials in question were not released.

In accepting the settlement, EBMUD contends all materials were handled safely and any discrepancies were "procedural" and the result of a "difference of opinion," according to EBMUD spokeswoman Andrea Pook.

"It wasn't an issue of materials or how materials were handled," Pook said in an interview Thursday. "We believe we were following all regulations and keeping all regulators informed, but the EPA felt differently."

EBMUD has since returned to compliance with federal regulations, according to the EPA.

The EPA routinely conducts inspections under the federal Resource Conservation and Recovery Act, which grants EPA the authority to control all aspects of the handling of hazardous waste.

EBMUD provides water service to most of the San Ramon Valley, but not sewer service. The Oakland facility at the center of the EPA case treats wastewater from EBMUD's sewer service area.

At the wastewater facility, EBMUD in 2012 started accepting various organic wastes -- such as restaurant grease, food scraps and blood from poultry -- and feeding the grid with electricity converted from methane gas produced when these wastes decayed.

With the waste-to-energy conversion system, EBMUD became the nation's first wastewater treatment facility to produce enough energy from organic waste to sell some back to the grid.