Which of the following is a common sign of a failing septic system?

Pooling water above the drain field is indeed a common sign of a failing septic system. When a septic system functions correctly, wastewater is processed and absorbed into the soil in the drain field. However, when the system fails, it can lead to a backup or saturation of the soil, preventing proper absorption. This causes water to pool on the surface, indicating that the septic tank or drain field is not handling wastewater properly.

In contrast, increased water flow could be related to several issues, but it does not specifically indicate a failing septic system. Clear drinking water typically suggests there are no immediate contamination issues related to the septic system, which would not be the case if the system were failing. High soil fertility, while it might indicate good soil management, does not specifically demonstrate the health or functionality of a septic system. Therefore, pooling water directly signals a malfunction or failure in the septic system, making it the correct identification of a common problem.