Utility Vaults: The One Place You Should Never Install a Backflow Preventer

If you're still installing backflow preventers in utility vaults, it's time for a change.

We've traveled all over the United States to meet with water jurisdictions and civil engineers. 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 (USC) Foundation for Cross-Connection Control and Hydraulic Research has to say.

All of this led us to two compelling reasons why you should keep backflow preventers out of underground utility vaults, and why above-ground enclosures are the right design for any site.

1. Flooded Utility Vaults Create Cross-Connections

Water jurisdictions often tell us they know a vault can flood. In fact, 70 percent of water purveyors and engineers admitted as much in a Safe-T-Cover poll. Some water officials say at least half the vaults they inspect have water in them.

One Texas backflow tester sends us pictures and videos of flooded vaults. We also interviewed a Virginia-based tester and instructor. 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 alarming. 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 underwater.

Experts at USC write about the dangers of flooded utility vaults in their publication, Cross Talk. They recommend 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.

Outdoor backflow enclosures reduce the risk of a cross-connection. Yet, test cocks found on a DC could be the site of a cross-connection: if a test cock leaks or is broken off and submerges, backflow may occur. So, instead of preventing backflow, a cross-connection gets created through the assembly!

Additionally, every state requires 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 evidence of how often vaults flood, take a look at this video sent to us by testers:

Aluminum Enclosures Mitigate Cross-Connection Risk

Outdoor backflow enclosures significantly reduce cross-connection risk. The two reasons engineers and water districts have historically cited for installing backflow preventers in vaults are freeze protection and aesthetics. Both are solved above ground.

1. Backflow enclosure aesthetics are easily managed through thoughtful placement, landscaping, custom colors or graphics.
2. Backflow enclosures that meet the ASSE 1060 Class I standard are heated and insulated — making freeze protection a non-issue for above-ground installations of any configuration.

2. Precast Concrete Utility Vaults Create Confined Space Hazards

The second major problem with vaults has nothing to do with water performance. OSHA considers water utility vaults or pits confined spaces. Data collected by the U.S. Department of Labor (USDOL), Bureau of Labor Statistics (BLS) Census of Fatal Occupational Injuries (CFOI) program 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 true, but what about the building's maintenance person, the property owner, or adventurous kids that can get in the vault by just opening the lid?

Testers agree that there is little stopping curious people from opening and accessing a vault. Limited interior space, slippery surfaces, poor air quality and restricted access make these environments genuinely dangerous — and no standard size of vault eliminates those hazards.

The two main reasons engineers and water districts have historically cited for installing backflow preventers in vaults are heating and aesthetics. In terms of backflow enclosure aesthetics, thoughtful placement on the grounds and possibly some landscaping or custom colors or graphics can help. What's more, backflow enclosures that meet the ASSE 100 Class I standard are heated and insulated.

Precast Utility Vaults vs. Above-Ground Enclosures: Change Your Approach

Installing a backflow preventer in an underground utility vault has been standard practice for decades. The durability of that habit is the main obstacle to change — not the durability of the solution itself.

Many utility vaults are precast concrete structures, fabricated off-site and available in both standard sizes and custom configurations. That underground installation carries a significant cost premium; estimates place the expense of below-grade utility infrastructure at six to 30 times more than comparable above-grade alternatives.

Above-ground aluminum enclosures offer a variety of configurations and sizes designed to house the full range of backflow equipment, including all needed piping and accessories, with adequate clearance for easy access. They're suitable for virtually any site and are already an accepted design in most states and cities across the country. Las Vegas Valley Water District made the switch and documented savings of up to $60,000 per installation compared to underground vault construction and rehabilitation.

The civil engineering community is already implementing this change. Arlington, Texas, became the first city in north-central Texas to publish containment and isolation backflow preventer guidelines specifying above-ground installations and other municipalities are following.

We now know using an above-ground backflow enclosure should replace the vault. Change in any industry can be hard, but it's in everyone's best interest to protect potable water supplies, irrigation systems, sprinkler systems, fire hydrants and water lines by placing backflow preventer installations in backflow enclosures.

Upgrade your standards with our free Standard Details Guide, including free CAD templates to spec your next enclosure.