Three Piece Design on the Fly for Bypass Vault

With 25 million gallons of sewage flowing daily through the site, the N19 Arden Pump Station comprises a vital link in the wastewater infrastructure of Sacramento, California. When the Sacramento Regional County Sanitation District embarked on an extensive series of repairs and upgrades, it first needed to divert the flow through a bypass system to dry out the pump station.

W.M. Lyles Co., a heavy civil contractor, took on the job. That’s when Mark Schmitz, Project Engineer, placed a call to Tim Pellegrini, Jensen Precast Estimating Manager. The conversation went something like this, Pellegrini says: “We’re doing this job, we need a bypass vault. There are a number of mitigating factors. We’re trying to get this done quickly. Can you help us out?” Pellegrini’s answer was a strong, “Yes, of course. What do you need?”

When the wastewater treatment plant was built in the 1980s there was no contingency plan to bypass around the pump station when repairs were needed. “So there was no way to get in and repair, clean, and upgrade their wet well portion without developing a bypass system,” Schmitz says.

He and his team wanted Jensen Precast’s help designing a bypass vault to divert the 17,000 gallons of sewage that courses through the pump station during peak flows. It would require a structure with an inside space of 11’W x 14’L x 24’H. Then there were the “mitigating factors.”

The seismic study pointed to the need for thicker walls. The Sanitation District wanted 12″ thick walls for the risers, an HDPE liner, and pipe liners cast into the risers. After some back-and-forth refining the design, the contractor decided to cast the base onsite and needed 17′ of risers to sit on top.

Fast Submittal Package

Needing to work quickly, Pellegrini submitted an engineering request to Andy Cho, Jensen Precast Engineering Product Developer. Cho worked out a three piece design – two risers and a slab cover – while Pellegrini pulled together the submittal package.

“Normally we do not do design work until we have a purchase order, but given the time constraints and our relationship with W.M. Lyles, I went ahead and submitted an engineering request to Andy and the team to get a preliminary drawing done,” Pellegrini says. “From there we created a full calculation package and a full submittal package, and were able to get that approved before we got the purchase order. From their final draft of the plan, we had the package to them in two weeks – easily half or 60% less lead time. That was definitely part of the selling point in the whole deal.”

The Jensen Precast production team in Lockeford, California, went to work on a tight schedule. Schmitz did everything he could to keep the W.M. Lyles project on track.

“It was on short notice to the point where I was ordering pipe spools and personally driving them to the yard to get dropped into the forms,” Schmitz says. “It was redesign on the fly.”

The pieces were delivered on August 26, 2020, and the contractor’s work continues on schedule. Schmitz has praise for every aspect of the Jensen Precast portion of the project.

“Tim Pellegrini is great to work with, the Jensen Precast field guys were great to work with,” Schmitz says. “The form shop did a great job in meeting the schedule. Everyone was good to work with through and through.”

For custom design projects, contact us to work with our team of engineers.