If you’re still installing backflow preventers in utility vaults, it’s time for a change. None of us like change. We get it. Especially when there’s no need. After all, “if it ain’t broke, don’t fix it,” right?
But we’re traveling all over the United States and learning more every day about backflow design. We’re meeting with water jurisdictions and civil engineers regularly. We’re talking with backflow device manufacturers and trade groups, including ABPA and AWWA. We’re listening to what the University of Southern California’s Foundation for Cross-Connection Control and Hydraulic Research has to say on the subject. It’s led us to discover two compelling reasons to keep backflow preventers out of underground utility vaults.
Water jurisdictions often tell us they know a vault can flood. In fact, a Safe-T-Cover poll found 70 percent of water purveyors and engineers admitted it. Some water purveyors say at least half the vaults they look at have water in them.
One Texas backflow tester sends us pictures and videos of flooded vaults. We also interviewed a tester and instructor who works in Virginia. He says 100 percent of the vaults he works on have flooded at least once.
A cross-connection control investigator in a large midwestern city told us something very scary. He says he’s opened thousands of vaults during his 30-year career and only one out of 100 is dry. And when the vault floods, the backflow prevention device is often completely under water.
Experts at the University of Southern California write about the dangers of flooded utility vaults in their publication, Cross Talk. They recommend that all backflow prevention assemblies be installed above-grade. Double-check valve assemblies are often installed below-grade to prevent freezing, but typically end up underwater in a flooded vault.
Those same experts state DC and RP must be installed between 12 inches and 36 inches above-grade because a backflow preventer installed in a vault or pit is exposed to a flooding risk. Then there's the possibility of contaminated water, which would create a cross-connection between the water in the pit and the backflow preventer through the test cocks. This may occur whether the test cocks are opened or closed.
The USC Foundation also recommends assemblies be installed 12 inches to 36 inches above grade. Their experts recommend placing backflow prevention installations in an aluminum enclosure. They say the benefits of using an outdoor backflow enclosure include:
Keeps vandals away
Outdoor backflow enclosures reduce the risk of a cross-connection. Yet, the test cocks found on the DC could be the site of a cross-connection. If a test cock leaks or is broken off and becomes submerged, backflow could occur through the test cock. So, instead of preventing backflow, a cross-connection has been created through the assembly.
Additionally, most states require each water jurisdiction to have a cross-connection control program with language similar to this: Each public water supply shall develop a comprehensive, ongoing program for the detection, elimination, and prevention of cross connections. If vaults can create a cross-connection, how are they in compliance with this requirement? Knowing this, why would the vault ever be an acceptable design if the responsibility is to provide a design that prevents cross-connections and safeguards clean drinking water?
For more visual proof of how often vaults flood, watch the video below for footage sent to Safe-T-Cover by testers.
OSHA considers water utility vaults or pits confined spaces. Statistics from the National Institute for Occupational Safety and Health show an average of 92 fatal injuries in confined spaces each year.
You might be thinking, "these testers are trained professionals, surely they know how to manage a confined space." That’s a good observation. But what about the building's maintenance person, property owner, or the adventurous kids that can get in the vault by merely opening the lid?
Testers agree that there is little stopping curious people from opening them.
The two main reasons engineers and water districts cite for installing backflow preventers in vaults are heating and aesthetics. In terms of backflow enclosure aesthetics, all you require is strategic placement on the grounds and possibly some landscaping. And backflow enclosures are heated and insulated. Knowing this, why would you continue to design a vault for the backflow when an above ground enclosure is an already accepted design in most major cities across the nation?
We see installing backflow preventers in a water utility vault as a clear problem. Unfortunately, the utility vault has been the standard for backflow design for decades. We now know the best practice of using an above-ground backflow enclosure should replace the vault.
Change in any industry can be hard, but it’s in your best interest to protect potable water supplies, irrigation systems, sprinkler systems, fire hydrants and water lines by placing backflow preventer installations in backflow enclosures.
For more information, check out our “Engineer's Guide to Industrial Enclosure Design.” Or download our checklist below to help get you started.
The civil engineering community is already implementing changes, and now it’s your turn. Please contact us if we can provide support or help you on your next project.