How deep should soil evaluation pits be excavated?

To determine the appropriate depth for soil evaluation pits during a site assessment for a drainfield, it’s crucial to consider the necessary stratification and characteristics of the subsurface soils to ensure adequate drainage and treatment of effluent. Excavating to a depth of 24 inches below the proposed drainfield allows for a comprehensive evaluation of the soil profile, including the topsoil and underlying layers that may impact the performance of the septic system.

This depth strikes a balance between assessing the pertinent soil characteristics, such as texture, permeability, and drainage capabilities, which are critical for the effective operation of the system. Evaluating soil at this depth ensures that any restrictive layers or conditions can be identified, thus informing the design and installation of the drainfield.

Excavating deeper than 24 inches, such as 36 or 48 inches, may provide additional information about the soil conditions but is often not necessary for routine evaluations, considering that most design criteria are based on the upper layers of soil that directly influence the drainfield. Conversely, a depth of only 12 inches may not adequately reflect the true conditions impacting drainage and treatment in the context of a septic system. Therefore, the choice of 24 inches below the proposed drainfield is considered the most suitable and