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

Unexpected clear water pooling in the yard is a clear sign of a failing septic system because it indicates that the system is not properly treating and dispersing wastewater. A functioning septic system should effectively break down waste and allow treated effluent to seep through the drain field without surface pooling. When pooling occurs, it suggests that the soil is saturated or that wastewater is being pushed to the surface, indicating that the system is overloaded or compromised.

Green grass over the drain field, while it may look lush, could be misleading as it can also happen in healthy systems due to the nutrients in the effluent. Regular operation of household plumbing does not signify a failing system either, as it is expected for plumbing to operate normally unless specific signs of failure are present. Consequently, the pooling of water is the most direct indicator of a septic system that is not functioning properly.