Mottled soil, particularly with bright and grey variations, is often indicative of what type of soil?

Mottled soil, characterized by distinct bright and grey variations, typically indicates the presence of seasonally saturated conditions. The mottling occurs due to fluctuations in the water table, where periods of saturation lead to soil anoxia (lack of oxygen), causing the grey colors to form through anaerobic processes. Once the water recedes, oxygen returns, allowing for the development of brighter colors as iron oxidizes. This cycle of saturation and drying reflects a soil that experiences seasonal changes in moisture levels.

Understanding this characteristic is crucial for assessing soil for On-Site Sewage Facilities (OSSF), as it helps determine the soil's ability to adequately drain and whether it can support a septic system effectively. In contrast, dry soil would not display these mottled colors since it would lack the conditions that promote such changes. Clay soil refers to particle size rather than saturation conditions, and saline soil pertains to sodium content rather than moisture levels. Therefore, recognizing mottled soil as an indicator of seasonally saturated soils guides appropriate septic system design and placement.