How far below the lid should the suction pipe not extend?

The correct choice, indicating that the suction pipe should not extend below the lid by 1 inch, is based on safety and efficiency in radon mitigation systems. Maintaining this distance prevents the suction pipe from becoming submerged in water or sediment, which could lead to a variety of issues including reduced efficiency of the system and potential for blockage.

If the pipe extends too far below the lid, it can create a pathway for water or particles to enter the system, compromising its ability to function effectively in mitigating radon gas. Moreover, having a specified distance helps ensure that the radon mitigation system can create the necessary vacuum and not draw in unwanted materials that could impair performance.

The specific measurement of 1 inch strikes a balance, allowing for adequate operation of the system while minimizing risks associated with overextending the pipe.