A $536 million upgrade to the city’s 45-year-old Honouliuli Wastewater Treatment Plant in Ewa Beach has been completed, the city says.

The completed work at the wastewater plant — which serves communities from Ha­lawa to Makakilo, including Barbers Point and Mililani — fulfills a second major milestone in a 2010 consent decree mandated by the federal government, designed to prevent untreated sewage from entering Oahu’s marine and shoreline environments.

On Friday the city Department of Environmental Services unveiled the newly constructed, full secondary treatment upgrades at an approximately 10-acre portion of the treatment plant at 91-1000 Geiger Road. The Honouliuli plant, built in 1978 with its deep ocean outfall 1.76 miles offshore, at a depth of 200 feet, was completed in February 1979, the city says.

The new plant was commissioned in January, and turned over to ENV operations staff ahead of the consent degree deadline of June 1, the city says.

“A project like this takes a village and a lot of time, a lot of years,” ENV Director Roger Babcock said during a news conference. “This project is to bring the treatment plant to (a) full secondary treatment plant, where all wastewater is treated to a secondary level.”

Although secondary treatment does not make the water drinkable, it does turn it into recycled water that can be used for things like landscaping.

In 2010 the negotiated consent decree included three phases and a 25-year implementation schedule. Under the settlement, Honouliuli would need to be upgraded to secondary treatment by 2024. The Sand Island wastewater plant at 1350 Sand Island Parkway would need to be upgraded by 2035, the city says.

According to the U.S. Environmental Protection Agency, mandated upgrades will reduce the public health risk caused by exposure to pathogens in raw sewage, and the amount of harmful pollutants affecting the island, its inhabitants and wildlife.

In 2010 the comprehensive settlement, involving EPA and the U.S. Department of Justice, was reached with the city to address Clean Water Act compliance at Honolulu’s wastewater collection and treatment systems, the EPA states. The settlement also resolved lawsuits brought by the Sierra Club, Hawaii’s Thousand Friends and Our Children’s Earth Foundation, and included a full compliance schedule for the city to upgrade its wastewater collection system.

The city’s waste collection system consists of about 2,100 miles of pipes, 72 waste­water pump stations and associated force mains. The city collects and treats nearly 100 million gallons of wastewater daily, the city says.

According to the EPA, the city had illegal sanitary sewer overflows throughout its collection system and effluent violations from its two largest wastewater treatment plants — Honouliuli and Sand Island — that caused violations of the city’s National Pollutant Discharge Elimination System permit and parts of the federal Clean Water Act.

The overflows also caused millions of gallons of untreated sewage to be discharged into waters off Oahu. Those violating acts included the March 24, 2006, Beachwalk force main break, which spilled about 50 million gallons of sewage into the Ala Wai Canal alone, the EPA states.

As a result, the city had to pay a total fine of $1.6 million — to be split between the federal government and the state of Hawaii — in order to resolve violations of the Clean Water Act and Hawaii’s water pollution law, the EPA states.

Ultimately, the consent decree meant work on the city’s wastewater collection system included rehabilitation and replacement of both gravity and force main sewer pipes; backup strategies to minimize the risks of force main spills; a cleaning and maintenance program; improvements to Hono­lulu’s program to control fats, oils and grease from entering into the wastewater system from food establishments; and repair to pump stations, according to the EPA.

Phase one work involved the upgrade of the city’s sewer collection system; phase two involved secondary treatment upgrades at Honouliuli; and phase three for secondary treatment upgrades at Sand Island treatment plant, the city says. From 2010 through fiscal year 2020, the city notes it spent approximately $1.3 billion in capital costs on phase one upgrades to the collection system.

At Honouliuli, the city says comprehensive upgrades included installation of new aeration basins, a blower building equipped with turbo blowers, a mixed liquor distribution box, secondary clarifiers and a secondary process pump station.

“Basically, they’re taking out a lot more solids,” ENV spokesperson Markus Owens told the Honolulu Star- Advertiser at Friday’s event. “The secondary treatment is taking out a lot more of the organic material.”

He noted what’s left is essentially cleaner, treated sewage water that can be shared.

“We send 13 million gallons a day over to the Board of Water Supply’s reclamation facility,” Owens said. “Some of it is R-1 (recycled water) for landscaping and golf courses.”

To date, the state Department of Health is the delegated authority under the Clean Water Act and is therefore the primary agency to conduct inspections of the Honouliuli plant, according to EPA spokesperson Alejandro Diaz.

“The inspections by DOH and EPA of Honouliuli are to determine compliance with the facility’s National Pollutant Discharge Elimination System permit,” Diaz told the Star-Advertiser via email. “The regular compliance checks are done at least every two years.”

The upgrades were completed at the plant on Jan. 31, five months before the deadline, Diaz said.

The final milestone for the 2010 consent decree is upgrading the Sand Island plant to secondary treatment standards, which must be completed by Dec. 31, 2035, Diaz said.

According to the city, Sand Island currently uses an enhanced primary plant that includes ultraviolet disinfection of effluent prior to discharge through a deep ocean outfall. Secondary upgrades to Sand Island are being accomplished in two phases, with the first 50% complete, to be finished in 2026.

The second upgrade will begin in 2029 and be completed by the consent decree deadline of Dec. 31, 2035, the city says.

“The Sand Island plant will need to be upgraded by 2035, but could be extended to 2038 based on a showing of economic hardship,” Diaz said, adding that the city has not asked for more time. “The city is still projecting that they will meet the Dec. 31, 2035 construction deadline for Sand Island.”