The outdated and understaffed Hilo Wastewater Treatment Plant, which is operating under an administrative consent decree with the federal government, accidentally discharged an estimated 607,000 gallons of effluent into Hilo Bay on Friday morning.

The Department of Environmental Management described it as “non-chlorinated secondary treated effluent” in a news release Sunday.

Treatment plants use chlorine to disinfect wastewater by killing viruses and bacteria in it. The discharges released into the ocean in Hilo did not undergo chlorination.

The accident happened between 8:15 a.m. and 12:30 p.m. Friday, according to the department. 

“The cause of the failure was determined to have occurred when the chlorine was being replenished. Restoration of the system was completed at approximately 12:30 p.m.,” the release says.

The Department of Health issued a water quality advisory for Hilo Bay outside of the Hilo breakwater. 

United Public Workers Hawaii, which represents plant operators, issued a statement on April 19 that said its workers are “overwhelmed and overworked” due to understaffing.

The Hilo wastewater plant is severely outdated. It has incurred numerous fines by the U.S. Environmental Protection Agency for having derelict equipment and for allowing illegal discharges into the ocean.

A top EPA enforcement official recently described the Hilo plant as the worse she has seen in her career with the federal agency.

The administrative consent order sets strict timelines for the county to repair treatment plants in Hilo, Kulaimano, Papaikou and Kealakehe.

Civil Beat’s coverage of environmental issues on Hawaii island is supported in part by a grant from the Dorrance Family Foundation.