Which type of backflow preventer is allowed to be installed below ground?

The correct answer highlights that the Double Check Valve Assembly (DCVA) is the type of backflow preventer that can be installed below ground. One of the main advantages of the DCVA is its design, which consists of two check valves arranged in series. This allows it to effectively prevent backflow in situations where non-health hazards are present.

The DCVA is often used in installations where there is minimal risk of contamination from the water supply, making it suitable for more protected applications. When properly installed, it provides a reliable barrier against backflow under many circumstances, specifically in environments where there is no hazard to public health. However, it's essential that these assemblies are accessible for maintenance and testing, and appropriate installation practices should be observed to ensure long-term reliability.

In contrast, other types of backflow preventers have restrictions that prohibit them from being installed underground. For instance, Atmospheric Vacuum Breakers require air pressure to function and cannot be submerged, while Pressure Vacuum Breakers can only be installed above ground for similar operational reasons. The Reduced Pressure Principle Assembly (RPZ) is also not typically buried due to the requirement for accessibility and the complexity of its design, which necessitates periodic testing and maintenance above ground to ensure proper operation.