There’s a disconnect when it comes to designers and backflow prevention installation. Outside, above ground backflow enclosures are safer and more cost-effective, but many designers fail to realize it. That’s because many water jurisdictions don’t have standard details in place for this design. But the push to change that has already started.
Without a standard detail in place, most designers won’t take the time to inquire with the water jurisdiction. Instead, they’ll fall back on what they always do: put the backflow prevention assembly in an underground vault. Since the backflow prevention installation is such a small part of their design, if standard detail does not exist, the design engineer won’t investigate or take the risk of designing a backflow enclosure that’s outdoors and above ground.
In many U.S. cities, finding a standard detail for an above-ground backflow enclosure is almost impossible. In comparison, a standard detail for the vault installation is commonplace. But as we’ve talked to water jurisdictions, most say they will accept an above-ground design. And support is growing to make above-ground backflow enclosures the norm.
Backflow Preventers Protect Water Systems
The objective of a backflow preventer is to protect water supplies. The backflow prevention device is required on domestic water lines, fire lines and irrigation systems. If there’s a cross-connection the results could be disastrous. If the objective is to develop and implement cross-connection control programs to safeguard public drinking water, why then does the industry continue to allow underground vaults to be designed?
The reasons probably vary from jurisdiction to jurisdiction, but underground vaults are dangerous, prone to flooding, put your water supply at an increased risk of cross-contamination, and your staff in harm’s way. That’s where the University of Southern California comes in.
USC Supports Installing Backflow Preventers Above Ground
The University of Southern California’s Foundation for Cross-Connection Control and Hydraulic Research continues to recommend that a backflow device should not be installed below grade. The reason for this recommendation is the safety of the public drinking water. USC periodically publishes recommendations in their “Cross Talk” publication. Some of their most recent recommendations include:
Summer 2005 - "The Foundation would like to recommend that all backflow prevention assemblies be installed above grade. There have been instances where double check valve assemblies have been installed below grade to prevent freezing and they have ended up completely under water due to a flooded vault. In other cases, they have become completely buried because of mud filling in the vault during a rainy season."
Spring 2014 - "The DC and RP must be installed between 12” and 36” above grade...When a backflow preventer is installed below grade, the vault or pit in which an assembly is installed may fill up with water — possibly contaminated water. The water in the pit could 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."
Winter 2016 - "The Foundation recommends assemblies be installed 12” to 36” above grade. If an assembly needs to be hidden from view for aesthetic reasons, consideration should be given to installing it behind a wall or landscaping. For freeze protection or the threat of vandalism think about installing an assembly in an enclosure instead of a pit or vault. In some cases, an RP is replaced with a double check valve assembly (DC) since the DC has “no openings,” therefore reducing 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. "
Designing your backflow preventer installation in a vault is risky. It increases the chance your backflow assemblies will end up underwater and covered in a layer of grime — including the test cocks.
Industry Agrees: Backflow Enclosures Are Needed
Safe-T-Cover representatives also meet regularly with water jurisdictions. We know the industry is aware of the risk. Many water purveyors know vaults are prone to flood. But many fail to provide a standard detail for above-ground backflow enclosure installations. Will the industry require tombstone legislation to make this change? We hope not.
After polling more than 1,200 professionals from civil engineering firms across the United States, we found 74 percent agreed or strongly agreed that “the local water guidelines for commercial and industrial construction lack needed standard details for above-ground backflow preventer installation."
If you want to see examples of standard details for above ground backflow enclosure installation, we’d be glad to send them to you. Complete the form below, and we will send a few examples. As a water jurisdiction, this might prove helpful in adding this standard detail. As a design engineer, you could take these examples to the water jurisdiction and encourage them to include them in their standard details. You can also request a consultation to let us know how we can help.