KEALAKEHE — Hawaii County wastewater experts hope to have the Kealakehe Wastewater Treatment Plant upgraded and able to produce quality, reusable water in the next three years.
Plans for the treatment facility would allow the plant to produce what’s referred to as “R-1 water,” water which is considered suitable enough for irrigating food crops. The recycled water won’t connect with any drinking water systems.
Craig Lekven, managing engineer of the Maui office for engineering consulting firm Brown and Caldwell, said several sites have already been identified as places to use recycled water. Lekven sat on a panel of experts at a forum Thursday night on wastewater at the West Hawaii Civic Center.
The proposed sites to be the first to use recycled R-1 water would be the Queen Liliuokalani Children’s Center, the Old Kona Airport State Recreation Area and the Kohanaiki development. It will also irrigate the land surrounding the current plant.
“That’s going to use a substantial portion of the flow from this treatment plant,” said Lekven.
A diagram included in a presentation by Brown and Caldwell indicates that water must go through several treatment phases to qualify as “R-1.” That includes rapid mixing and flocculation (which forces smaller particles to clump together into larger ones) followed by filtration and ultraviolet disinfection.
Even with the four sites, he said, there’s still going to be plenty of water that can’t be reused as a result of fluctuations in water use.
As a result, that presents a need to manage the unused water.
Lekven said the current proposal is to get rid of the current disposal system, where discharged water is deposited into a sump, a large drainage basin.
Instead, in an effort to lessen the impact on the environment, he said the proposal is to build subsurface flow wetlands, a strategy approved by the U.S. Environmental Protection Agency, around the perimeter of the treatment center.
After primary treatment, wastewater would flow into the constructed wetlands, which act as a natural treatment system designed to pull nutrients from the wastewater, effectively “polishing” the water, Lekven said. The Brown and Caldwell diagram outlines three such wetlands, altogether covering 12 acres.
The benefit of these systems, Lekven said, is that natural systems like these rely on plants and the sun to do the work of treating water rather than requiring electricity.
Once polished, Lekven said, the water will go through soil aquifer treatment which will provide additional treatment for water that will eventually make its way through the ground.
“We’re looking at reducing the impact of the community on its environment by 80 percent,” Lekven said. “So that’s a substantial reduction on our impact to the environment.”
The county hopes that the treatment plant upgrades will allow for water to be reused in about three years.
Bobby Jean Leithead Todd, director of the Hawaii County Department of Environmental Management, said the upgrade to Kealakehe treatment center is estimated to cost about $54 million.
The county already has a commitment from the state for revolving funds to go toward the upgrades.
Every year, the state’s Department of Health, Environmental Management Division’s wastewater branch receives a $10 million grant from the Environmental Protection Agency, said wastewater branch engineering program manager Sina Pruder. The state also provides a 20 percent match for those funds, for about $12 million each year.
In total, the revolving fund has about $750 million, Pruder said.
The state then provides low-interest loans to the counties for wastewater infrastructure.
One such loan is being made to Hawaii county for the R-1 upgrades. That loan came with a 1.25 percent interest rate.
A second phase of the project, which includes a distribution system and holding tanks to help distribute R-1 water, is estimated to cost another $50 million.
“So just upgrading Kealakehe and providing a distribution system, we’re looking at $104 million,” Pruder said.
Todd said the county recently met with Kohanaiki developers to confirm their interest in using the reused water, and the county has already made some changes to the original plan.
“We were thinking we would build everything at the same time, that we would do the R-1, as well as the subsurface wetlands as well as the (subsurface aquifer treatment).” she said. “But we’re moving that schedule up.”
Now, the priority is getting the water to R-1 quality first, said Todd.
She said the county has already paid the state to install reuse water pipes at Queen Kaahumanu Highway to run from Kealakehe Parkway out to Kohanaiki.
Once the plant gets into the initial phases of running R-1 water, she said, pipes will be installed running from Kealakehe Parkway to the treatment plant so water can go to Kohanaiki.
Some water reuse could happen even sooner, she said. Once the State Historic Preservation Division signs off on a project for the Old Kona Airport State Recreation Area, the treatment plant could produce R-2 water to send it down that way.
That quality of water is a step lower than R-1, but is still considered suitable for purposes such as subsurface irrigation at parks, according to the Department of Health.
That project was delayed because of further studies at the park required by the Preservation Division.