For soil wetted to be considered unsuitable, how far must it be from the natural surface?

The statement regarding soil being considered unsuitable when it is wetted at a depth of 36 inches or less from the natural surface is based on guidelines that assess the potential for septic system performance. In septic system evaluations, unsuitable soil often refers to conditions where the soil is saturated or has poor drainage capabilities, which can impede the proper treatment and absorption of effluent from septic systems.

If the soil is within 36 inches of the natural surface and exhibits these saturated conditions, it is deemed inadequate for the installation of septic systems because it can lead to surface runoff, contamination of groundwater, or system failure. This threshold helps maintain environmental health by ensuring that septic systems are placed in areas where they can function effectively without risking contamination or failure due to saturated soils.

The other options suggest measurements that do not align with the established criteria for suitability in septic system design, making them less relevant for determining the adequacy of the soil for septic infrastructure.