The Las Virgenes Municipal Water District is only 25 miles up the 101 freeway from the bright lights of Hollywood and a few minutes’ drive from the gleaming beaches of Malibu, Calif. But it is a world apart.
Situated in the Santa Monica Mountains, the district serves about 70,000 customers in a 122-sq-mile corridor of western Los Angeles County. The area is a mix of suburban and rural—a dry, arid landscape accentuated by large swaths of chaparral.
The Santa Monica Mountains Conservancy and the Malibu Creek Watershed protect much of the land, which means the district maintains a high level of environmental stewardship.
“Our challenge is how to best manage and utilize resources,” said Eric Schlageter, the district’s senior engineer. “Our vision is of a world that values every drop and brings water full circle.”
The district works to extract full value from everything it handles. Under an agreement with the Triunfo Sanitation District, the Las Virgenes – Triunfo Joint Powers Authority (JPA) treats wastewater and converts the biosolids removed during the process to nutrient-rich compost, which it offers at no charge to customers.
Solution
It takes weeks of processing and curing to convert waste to shovel-ready compost. It also requires a dependable, secure system for storing centrate, which is the liquid extracted from the solids. Schlageter points to the district’s three Aquastore tanks from CST—two of which date to 1980 and still perform like new.
Aquastore’s glass-fused-to steel technology meets the demands of liquid storage for the long term. The Aquastore is built using hydraulic jacking, which allows for top-down construction that is safer, faster and takes up less space than traditional steel tank erection.
Aquastore tanks are resilient and require minimal maintenance with low life-cycle costs. They are virtually seamless, which reduces the likelihood of leaking from inside or contamination from the outside. That is critical when storing and processing biosolids, which can cause corrosion and caking.
The Aquastore is also resistant to extreme weather (e.g., brilliant sunlight and 100°F temperatures) and retains its luster for decades, which means it does not need to be repainted. A municipal water provider in South Dakota estimates that maintenance for a glass-fused-to-steel tank over a 60-year span would cost $266,000.
Results
The Las Virgenes Aquastores measure 81 ft (diameter) by 23 ft (height), and over the years they have proven their versatility and adaptability—first simply for storing sludge, and now both are outfitted with internal equipment for aeration and mixing.
“California Aquastore helped us with the conversion from sludge to centrate,” Schlageter said. “When we drained the tanks, we were amazed to find the glass was in tip-top shape, the sealant was intact and didn’t need recoating.”
Schlageter said having three tanks gives the district more flexibility and, ultimately, efficiency and savings. Since two tanks are required—one for storage and one for treatment—the district can take one out of service at any time for maintenance and inspection without having to suspend operations.
Being able to switch between tanks without interruption is important to Schlageter, who said the decision to remain with Aquastore was important from a continuity standpoint.
“We’ve been working with California Aquastore for a long time, and we’ve been extremely happy with them,” Schlageter said. “Whether it’s additional treatment or upgrading the cathodic protection to minimize corrosion, they’ve always been helpful in providing information and direction or suggestions.”
Harper said it is not uncommon for Aquastore tanks to last so long, and points out the company has a stake in the game to make sure the tanks hold up well.
“Anytime you drill into the tank, perform work, or an outside source comes into contact with it, we’re there to provide guidance,” Harper said. “They’re the resource management experts and we’re the tank experts, so they look to us for specific expertise whenever they need to make a change or alter the tank in any way.”
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Schlageter said he appreciates that Harper and the team from California Aquastore were involved from the beginning of the third tank installation—working with the design consultant, and assisting during early stage planning and preliminary design through construction.
“They were needed for more than just erecting the tank, and we were glad they were at our side,” Schlageter said.
