StormVault Biofiltration Lands on Oahu

Mililani, Oahu

A 60-year-old community built atop a former pineapple plantation, Mililani traces its origins to developers seeking to relieve a housing shortage on the Hawaiian Island of Oahu. Mililani sits a short distance from Hawaii’s state capital, Honolulu, and continues to evolve with two main developments and about 50,000 residents.

Along with houses, schools, businesses, and community centers comes another fact of Mililani modern life: the self-storage unit. As Mililani has grown, so has the need for residents to store belongings and businesses to supply new facilities. In nature rich Hawaii where land and sea are precious resources, starting a new venture begins by examining the environmental impact. Storage buildings are no different.

Developers of the new Mililani Self-Storage facility needed to comply with local regulations for managing stormwater. Jensen Precast had a solution – the economical, modular StormVault Biofiltration System will treat area stormwater runoff before it discharges from the storage site to the Waikakalaua stream running adjacent to the development. After years of research and development of the system, Jensen Precast gained approval from the City and County of Honolulu. It’s now entering the Hawaiian biofiltration market with this initial project in Mililani.

The concept of biofiltration has been around for many years but only recently has caught on as a way to tackle urban stormwater runoff. Commonly known as green infrastructure development on the East Coast and low impact development on the West Coast, biofiltration captures and filters stormwater at the source instead of routing it to a detention pond or a mammoth stormwater detention facility.

At the Mililani Self-Storage site, stormwater runoff will be diverted to a Jensen Precast StormVault Biofiltration System, which includes three precast concrete vaults with treatment chambers, piping, bridging stone, and proprietary Sierra Blend engineered bio-soil media. With space at a premium in Mililani, the system offers a more compact – and natural – solution for managing stormwater.

“There is a very prescriptive amount of engineered bio-soil media that assists in biofiltration for water quality and volume control,” says Walter Stein, PE, Jensen Stormwater Systems Division Manager in Sparks, Nevada. “We spent two and a half years developing it. Our Sierra Blend media achieved performance verification from the New Jersey Corporation of Advanced Technologies, passing one of the most stringent testing protocols for this type of product. It was then certified by the New Jersey Department of Environmental Protection.”

With credentials in hand, the City and County of Honolulu listed Jensen Precast as an accepted provider for biofiltration systems, and the Mililani project soon followed.

The Jensen Precast manufacturing plant in Honolulu built the vaults, which were installed by Mana Construction under a parking lot at the Self-Storage facility. The bio-soil media for this first project comes from Jensen Precast plants in California, but plans are to eventually source the media locally.

Tommy Chock, Mana Construction Project Manager, says past engagements provided a comfort level with Jensen Precast, even though the biofiltration system was a new product. The contractor had worked with Jorelle Flint, Jensen Precast Project Manager, and his team on several previous jobs. “We’ve worked with Jorelle on many projects, and he’s really good,” Chock says. “So those were the guys to go with. Jensen Precast matched all our drawings and met all our needs. So we just keep moving.”


Modular Biofiltration More Economical

The Jensen Precast StormVault Biofiltration System is a nonmechanical, self-operating unit that engages whenever stormwater enters the system. The Sierra Blend bio-soil media consists of layers of material each with a specific function to filter the stormwater and, in Mililani’s case, discharge it under the road to the Waikakalaua stream.

Jensen Precast has partnered with Honolulu for years in a quest to protect its beautiful blue near shore waters – one of its most valuable resources.

“Honolulu has been very aggressive at providing improvements in their septic systems, and we’ve been integral in helping them address that wastewater improvement effort,” Stein says. “They’ve been doing it since the 1990s and every year they get better water management processes in place. Now their clean water program has advanced to non-point source stormwater.

“For the biofiltration initiative, we’re providing a highly modular, economical system, because the vaults are off the shelf rather than custom. The owner doesn’t have to buy specialty structures. We have compliance with stormwater regulations, emulation of predevelopment conditions, and a biofiltration process for control of both the water quality and water volume. Plus, we have a good set of hydraulics with an adjustable weir. It’s just a sweet layout all the way around.”

The entry into the biofiltration market is exciting for the team in Honolulu, says Garret Lau, Jensen Precast Hawaii Region General Manager. He lives in Central Oahu, not far from the Mililani Self-Storage facility, and has been working to add biofiltration systems to his plant’s product lines.

“The approval for stormwater here is difficult,” Lau says. “Swaraj came up with the design, Walt looked at it and said ‘Perfect,’ and we got it approved locally. So everything kind of fell into place at that point. Our team works hard pushing the locally manufactured concept.”

With the new StormVault Biofiltration System entering the market, cooperation was key in bringing the project to a successful conclusion. After seeing the system up close, Chock says there is a lot of potential for more biofiltration units on the island, especially in the Mililani region.

“One thing about using it here, it’s actually really muddy,” Chock says. “This is one of the rainiest spots on the island. It just pours over here, so that biofiltration system is going to be very good for cleaning the water before it leaves the site.”

Jensen Precast is a leading provider of stormwater solutions for large and small projects. Get a quote for your project.

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