One Excavator Sets StormVault Stormwater Detention System

On paper, installing a massive underground stormwater detention system capable of capturing 2.4 million gallons of runoff sounds like a job destined for colossal cranes and months of coordination. But, at the Moxy Hotel project in Glendale, Arizona, it was handled by something far more familiar to most civil contractors: a CAT 352 excavator and a forklift. 

Sitting on the edge of the Westgate Entertainment District, just steps away from State Farm Stadium, the Moxy Hotel brand is constructing its third property in the Grand Canyon state. The district has become a major tourism hub, drawing a wide array of folks from football fans and concertgoers to foodies and business travelers. 

But there was an issue. The planned site for the new luxury hotel had long functioned as a drainage field easement, holding stormwater runoff from neighboring properties. So, when the Moxy Hotel project was introduced, stormwater management became one of its biggest challenges. 

To make room for the new hotel and the parking lot required to support it, the drainage easement, which served as an above-ground retention pond, had to be moved underground. 

One of the major design hurdles was the site’s geometry. Utilities, tree wells, and perimeter constraints left little room for traditional rectangular detention layouts. 

“This was one of the more complex designs I’ve ever worked on,” says Zach Kent, Vice President of Stormwater Solutions for Jensen Infrastructure. “Between everything inside and around the system, the layout looked like Swiss cheese. We had to use every square foot we had.” 

Jensen worked closely with Rick Engineering, going through five to six design iterations over several weeks to refine the layout. AutoCAD overlays were passed back and forth until the system met volume and code requirements without sacrificing available site area. 

The StormVault™ detention system was selected to do the job. It thrives on unique designs. Since the system relies on the simple yet proven marriage of box culvert and spanning slabs, it’s easy to tinker with designs as new problems arise. 

“We didn’t reinvent the wheel,” says Buddy Hensley, an Outside Sales Representative based out of Jensen Infrastructure’s Phoenix facility. “We utilized typical type 2 precast box culvert already approved and on the market since the 1970s. We were able to model it to be a detention system application to continue with what has been existing in the market for decades.” 

The Moxy Hotel StormVault system stacked modules to achieve a 12′ interior height and a void ratio approaching 90 percent. This results in a detention system with approximately 2.4 million gallons of storage capacity, roughly equivalent to four Olympic-size swimming pools. 

And don’t forget about the hotels right next door. This StormVault structure also had to tie into an existing 96″ corrugated steel pipe, which required a custom inlet structure sporting a massive opening. Additionally, inlets from catch basins, surface grates, and curb inlets feed onsite runoff into the system before overflowing into an adjacent open detention basin during larger storm events. 

But what truly set the project apart was how it was installed. 

Aside from the large custom inlet structure, every StormVault component was engineered to weigh less than 25,000 lbs, allowing installation with standard civil equipment. A single CAT 352 excavator handled setting duties, while a forklift offloaded precast pieces from delivery trucks. No crane was required. 

“Most systems of this size would need a crane,” Kent says. “Here, everything was installed with equipment most contractors already have.” 

In total, 755 precast concrete pieces were set without the cost, logistics, or scheduling challenges that come with heavy crane rentals. Ultimately, saving time while simplifying coordination and removing congestion on a tight urban site. 

Midway through construction, the engineering team faced another test. Portions of the system were originally assumed to have at least 2′ of cover, but field conditions revealed areas with as little as 6″ of cover. Jensen’s engineering team quickly reanalyzed the design, recalculated reinforcement, and incorporated additional rebar and structural gussets into production without delaying the project. 

“The ability to reengineer that mid-job and keep moving speaks volumes about the team,” Kent says. 

In the end, close collaboration between Jensen, Rick Engineering, general contractor Porter Brothers, and installing subcontractor Clearwater Pipelines delivered a stormwater solution that met extreme design constraints without sacrificing constructability. 

The crane-free StormVault installation provides nearly 322,000 cubic feet of storage, meets 100-year storm event criteria, and was installed using familiar equipment already on site. 

Sometimes, it turns out, the little excavator really can. 

Learn more about StormVault and the full suite of  stormwater management solutions now. To start on your next project, contact us today.