Since 2018, a team from Ashley & Vance Engineering, including structural project engineers Mika Daniel and Chelsie Taylor and civil project engineer Kathleen Allwine have been working with city planners, design consultants, and construction teams on the new City of Morro Bay Water Reclamation Facility. While water reclamation facilities may not feel glamorous, they have complicated designs and are necessary to a city’s infrastructure, community health, and environmental safety. Here’s a brief insight into some of the more unique elements that went into designing this facility.
The Morro Bay Water Reclamation Facility in Morro Bay, California, is replacing the town’s existing wastewater treatment plant, originally constructed near the beach in 1953. Its last upgrades occurred in 1984, and it has been operating under modified discharge permits ever since. In 2013, the California Coastal Commission denied requests to upgrade the existing facility due to rising sea levels, tsunami, and flood risk concerns and insisted that a new water reclamation plant be located farther inland. In 2017, new requirements adopted by the Regional Water Quality Control Board prompted the city to begin a nearly 3-year construction project to meet permitting compliance by February 2023.
City Prepares for Drought by Injecting Reclaimed Water Underground
The new state-of-the-art water reclamation facility is designed to safeguard the community’s water source from drought and saltwater intrusion by injecting clean, reclaimed water underground, effectively recycling stormwater and solving multiple problems with innovative solutions.
Kathleen Allwine participated in early civil engineering design and says, “I live less than five minutes from the new facility, and I do feel it’s a benefit to the community. The current plant is right on the beach and doesn’t treat the water to the standards it needs to. That water goes right into the ocean. I’m excited that this state-of-the-art facility has been moved inland and the water that comes out is drinking-water quality.”
Calculating for 100-Year Plus Storms
Water reclamation facilities need to operate during major weather events, which means certain water-holding basins need to be large enough to handle sudden major inflow from nearby landscapes, and shut-off valves need to be installed to control water flow within the plant.
Runoff water from the hillside must be intercepted and effectively concentrated into swales, collected in basins, then directed to a pipe outlet. “The velocity of that water is high,” Kathleen says. “Which can be very erosive to areas downstream if not distributed correctly. The outlet pipe is near a creek and the property line, so we had to distribute the water so it continues to flow toward the creek without eroding a channel or disturbing the adjacent property. The design of those level spreaders was crucial in intercepting the water, taking it around the facility, and then getting it back into flow so that adjacent property owners and the creek are not damaged.”
Many Civil Engineers Work in Partnership
Because the design was effectively laid out before Kathleen joined the project, there was limited or fixed space for putting in level spreaders before runoff reached the creek, leaving little room for adjustments. Kathleen says, “Typically, when I do the whole project, I do the civil grading and drainage, utility, layout, everything, so I get to prioritize which aspects are most efficient for construction. For this project, the water reclamation was clearly primary, so I worked hard to make sure my elements fit around the design that already existed, which made it more challenging. And the space constraints were tight.”
Matching the Rate of Water Flow
Kathleen designed swales and water systems to distribute catch water along the edges of the plant to prevent the plant from flooding and ensure the runoff rejoins the creek without causing erosion. “We added energy dissipation devices,” Kathleen says. “And I worked onsite with the civil engineer doing grading to size the pond to accommodate that much runoff. We also sized two basins and designed the outlet structure so that the runoff leaving the site flowed at the same rate as before development.”
Complicated Structural Engineering Gets Buried Underground
For structural project engineer Mika Daniel, what stood out most was just how large these tanks are. “They are up to 26-feet-deep,” she says. “And after all is said and done, they bury the tanks underground and nobody knows the extent of the design.” These aren’t just standard swimming pools either. There are myriad things to consider when designing huge tanks for water reclamation facilities, including specific code requirements that are stricter and more complex than above-ground waterless structures, the varying weight of chemicals, seismic forces of sludge, and complicated systems integrations.
In addition to the massive amounts of concrete required to construct each tank, there are complicated forces imposed on the tanks themselves. “It’s not just the water pressure we had to take into consideration,” Mika explains. “It’s the sloshing effects during seismic events that impose different forces.” And the liquid she’s referring to is not just water. It’s sludge. It’s whatever wastewater gets collected from sewers and drain pipes from the city’s sewage system.
The Weight of Water
Some tanks hold certain chemicals that need special consideration. By doing research and taking the time to really understand what types of chemicals are used to treat wastewater, structural project engineer Chelsie Taylor was able to better understand the overall project design. Chelsie explains, “There are certain areas that use chemicals that weigh around double what water weighs, which changes the loading and calculations.” Her initiative and due diligence guided early conversations that enabled the structural team to ask important questions about what each tank was used for.
“It’s critical for the engineer to know what type of liquid, sludge, or chemicals are going into which tanks because that change in weight changes everything,” adds Mika. “And clients don’t often think to flag it. It’s more our responsibility as engineers to ask clarifying questions and not make assumptions.”
To help process wastewater, specialized equipment like aerators are placed inside sludge-holding tanks. “There are a lot of different systems and components attached to the structure, including substantial mechanical equipment that may not be stagnant,” Chelsie says. “The attachment to the structure may be a fixed point, but the actual mechanical equipment moves around. There’s a lot of active motion in some of these tanks because of the equipment they put in there.”
Additional systems integration components needing incorporation were things like drains, piping, pipe supports, generators, and so much more. “It offers a bit of perspective into the actual water reclamation process because you have to think through so many systems that aren’t typically incorporated into regular structural projects,” Chelsie says.
1 Project, 18 Structures
In addition to tank design, this project includes 18 different buildings and areas/pads that Ashley & Vance Engineering designed and detailed. It was a mix between equipment pads, pre-engineered metal building foundations, concrete tanks, and other elements and areas. Considerations needed to be made for how to service equipment in the future. And don’t forget the frog wall: a 2-foot-tall concrete wall designed with a lip specifically to prevent frogs from climbing over, a critical environmental consideration to protect frogs from entering the facility.
“It’s all integrated,” says Chelsie. “The mechanical, plumbing, all the systems are integrated with the structure, which means members of every team were involved from the start. Having everyone coordinate early on was important because when a sub-consultant would bring something up in a meeting, which we might not have been thinking about but it impacts structural, we could catch it and work that into our plans. We always have to be considering all these other players and their components.”
Working in conjunction with AV’s Revit team, Chelsie and Mika modeled everything, then virtually cut sections and detailed connections to arrange rebar and configure interfacing elements. Then they would go back and edit it again. “It was a very iterative process,” Chelsie says. “And it took a team to do it.”
What Are Some of the Lessons Learned on This Project?
Kathleen: “Something I learned from this project was how presenting information to each stakeholder in a way that met their needs really helped with communication. We’re all working as a team, but each team member has their own focus, their own particular set of concerns. My job was to communicate calculations to the civil engineer who was drafting the plans, meet with the project manager, and work with the city to make sure their stormwater systems were in compliance. Meanwhile, the contractors wanted to know the calculations in order to price things and build the swales. And the City of Morro Bay was focused on meeting requirements. Identifying how to communicate what and when was crucial. Sending the appropriate email and maintaining channels of communication was key.”
Chelsie: “Be curious. There’s value in knowing how something works, or at least having an idea of the scale of what you’re working on. Ask what is this project serving and doing? Understanding how certain equipment functions, for example, allows you to understand how to properly secure it to a structure and properly account for it in your analysis. So be curious about the process and what the purpose of the project actually is, especially public works projects.”
Mika: “In addition to being curious, be open-minded. You can’t just assume it’s all standard to what you normally do. You have to start questioning everything. Question if this standard, which may be normal for everyday projects, applies to this specific project you’re working on. Ask questions and brainstorm with your teammates. Figure out what the intent of the code that you’re looking at is instead of just taking it verbatim. Don’t be set in your ways or stuck in one method because each project is different.”
For more information about the Morro Bay Water Reclamation Facility, visit https://morrobaywrf.com/