What is the requirement for the bottom of a drainfield excavation?

The requirement for the bottom of a drainfield excavation to be 12 inches lower than the treatment outlet is based on ensuring proper gravity flow and distribution of effluent. This vertical separation is essential for maintaining adequate drainage and preventing backup or flooding of the treatment system. A minimum of 12 inches allows for sufficient settling of solids as they naturally separate from liquids, which enhances the overall effectiveness of the septic system.

This elevation difference also helps to facilitate the movement of effluent through the drainfield, ensuring that it can be absorbed into the surrounding soil effectively. Properly designed gravity systems rely on this elevation to function without requiring additional pumping or mechanical assistance, thus promoting a more sustainable and self-sufficient wastewater treatment method.

Ensuring that the drainfield is positioned correctly in relation to the treatment outlet is vital to the long-term performance and efficiency of the on-site sewage facility, thereby making this option the correct choice.