The city is planning a multi-million dollar upgrade of the Wahiawa Wastewater Treatment Plant that would increase the possible uses for the treated wastewater.

The treated wastewater and the water in Lake Wilson, where the treated water is discharged, can be used for some irrigation purposes, said city Environmental Services Department deputy director Ross Tanimoto.

He said because the city had already been planning to make improvements to the plant, officials decided to go further to upgrade the quality of the reclaimed water.

With the upgrade, the treated water and Lake Wilson would meet state health standards for more purposes, including its use on edible crops, he said.

"It makes the water more marketable, more usable, more open for everybody's use," Tanimoto said.

The total project — which includes storage improvements to address high flow periods often associated with heavy rain — is expected to cost up to $40 million. The city has allocated $18 million for fiscal 2008.

The city will solicit bids for the project this year, with construction scheduled to begin in early 2009 and run through 2011.

The Wahiawa Wastewater Treatment Plant, one of the oldest plants on the island, has gone through several upgrades since it was established in the 1920s, according to the city. The plant treats and disinfects about 2 million gallons of wastewater daily and discharges it into Lake Wilson, also known as the Wahiawa Reservoir.

The plant serves Wahiawa, Whitmore Village and the Naval Computer and Telecommunications Area Master Station Pacific facility.

There have been preliminary discussions between city environmental services officials and the Board of Water Supply to use reclaimed water for the Central O'ahu Regional Park, a use that does not require a water-quality upgrade. A board spokeswoman has said it is one of many options being considered.

But Tanimoto said the water-quality upgrade is still beneficial even if the board ends up using the water for the park. He said if there are circumstances where the board can't use the water — if it's raining or there's flooding, for example — the city still wants to be able to discharge higher-quality water into the lake.

According to state health policy, the quality of water discharged in Lake Wilson determines the possible uses for the entire lake, he said.

The plant currently conducts tertiary treatment on wastewater, including conventional biological treatment and sand filtration plus ultraviolet disinfection.

The Wahiawa-Whitmore Village Neighborhood Board supports the overall objective of the improvements, said board chairman Ben Acohido. He said project officials assured the community that the new technology would nullify any odor from the plant.

"For the good of the community, it has to be done," he said.

A "pre-final" environmental impact statement on the project is scheduled to be released next month for public review and comment, Tanimoto said. Officials have said any long-term impacts are expected to be minimal.

Reach Lynda Arakawa at larakawa@honoluluadvertiser.com.