A recent storm overwhelmed Windward Oahu’s sewer infrastructure, spewing a mix of raw sewage and rainwater massive enough to fill 12 or 13 Olympic-sized swimming pools. It flowed onto streets, surrounding land and into ocean waters. The malodorous spillage — totaling 8.8 million gallons — was touched off by 8 inches of rain dumped on Kaneohe, which normally averages 6 inches for the entire month.

The city’s sewers cannot be expected to entirely tough-out Mother Nature’s unexpected spurts of especially tough weather. But last month’s spillage underscores the need to push forward with much-needed wastewater system upgrades on Oahu.

After the Windward side’s collection system, pump stations and treatment plant buckled under flow that quadrupled during the Feb. 17-18 storm, Lori Kahikina, director of the city Department of Environmental Services, pointed out that a project is underway that promises to ease future surges in the area.

Once construction wraps up in late June, the Kaneohe-Kailua Waste Water Conveyance and Treatment Facilities Project will deliver sewage to the Kailua Regional Wastewater Treatment Plant from the Kaneohe Wastewater Pre-Treatment Facility by way of gravity. Begun in 2013, the project was prominently in the news a few years ago when a 13-month drilling effort succeeded in creating a 3-mile tunnel beneath Oneawa Hills. The puka is now being fitted with a 10-foot-diameter sewage-delivery pipe.

The tunnel, which runs from a depth of 35 feet below ground level on the Kaneohe side to 62 feet on the Kailua side, can be tapped to hold storm waters. While the upfront price tag for its gravity-flow design is higher than that for a force main, the no-pressure option requires no electricity (or other energy source) to pump the flow. Plus, in the absence of pumping, a sewer line break typically releases a smaller spill.

The project is among 422 sewer-related construction upgrades required by a 2010 court consent decree reached by the city with the state Department of Health, U.S. Environmental Protection Agency and three environmental groups. So far, 367 projects have been completed. The city’s ongoing $3.5 billion effort, funded with sewer fees, will wrap up in 2035.

Among the other projects are refits at two sewage plants — Honouliuli and Sand Island — to meet standards required by the Clean Water Act. The decree settled years of litigation and helps secure a healthier future for our shorelines — including coral reef ecosystems — that had been threatened by city sewer overflows reaching ocean waters.

Like the $371 million Kaneohe- Kailua gravity-flow project, the upcoming $85.7 million Dowsett Highlands Relief Sewer in Nuuanu Valley is needed to reduce the risk of sanitary sewer overflows. Soliciting bids for Dowsett Highlands contracts are expected to open this week, and construction starts this summer. It’s good to hear the project will add a larger pipe down the Pali Highway and Nuuanu Avenue to divert sewage flow from two mains that no longer have the capacity to sufficiently support homes in the area.

In the aftermath of last month’s storm, advisories were issued about possible runoff contamination from sewers and manholes as well as cesspools, pesticides, animal fecal matter, dead animals, pathogens, chemicals and other flood debris. It was an unsettling situation that heightened health and environmental concerns, as well as the perception that such notices are increasingly a storm-related routine.

To the contrary, however, Kahikina noted that the city’s annual count of unsanitary overflows dropped to 54 in 2017 from 200 in 2006 — the year that 48 million gallons of sewage spilled into Waikiki following a rain-induced sewer line rupture.

The downward trend is encouraging. For the sake of public health and a healthier environment, upkeep of the city’s sewer infrastructure must be constant and vigilant to safeguard our land and waters from pollution threats.