Common causes of failure in septic tank seepage field systems include improper sizing and which of the following?

The correct choice highlights that nonsuitable soil is a significant factor contributing to the failure of septic tank seepage field systems. For a septic system to function effectively, the soil must possess certain characteristics that facilitate the proper absorption and treatment of effluent.

If the soil is too compacted or has low permeability, it can impede the natural filtration processes, causing the effluent to pool or back up in the system. Conversely, overly sandy soils may not retain enough water, leading to inadequate treatment of the wastewater. Soil type significantly influences a septic system's ability to disperse and treat effluent, and if the soil is not suitable, this misalignment can result in system failure.

Other factors like regular servicing, routine cleaning, and deep drainage generally support the proper functioning of septic systems rather than cause failures. However, without suitable soil, regardless of how well the system is serviced or maintained, the system may still malfunction. Therefore, understanding the soil quality is crucial for the effective design and longevity of a septic tank seepage field system.