For pipes less than 24 inches in diameter, what pressure relative to groundwater pressure must the air exfiltration test be conducted at?

• A. 3.0 psi greater
• B. 5.3 psi greater
• C. 7.0 psi greater
• D. 10.0 psi greater

Answer: (B)

The test checks how well a pipe and its joints hold air when the internal pressure is raised above the surrounding groundwater pressure. Expressing the test pressure relative to groundwater pressure accounts for the hydrostatic head of soil water around the installation, so the pressure difference truly reflects the potential for air to escape through leaks.

For pipes smaller than 24 inches, the standard specifies setting the internal pressure to groundwater pressure plus 5.3 psi. This specific margin gives enough pressure to reveal leaks without over-stressing the pipe or its joints. It balances sensitivity to defects with safety for the piping system. The other options represent different margins that aren’t used for these smaller pipes—the required increment is 5.3 psi for pipes under 24 inches, while larger pipes use higher increments. Thus, groundwater pressure plus 5.3 psi is the correct approach for these pipes.