What must the natural soil surface level be for soil wetness to be classified as suitable?

The classification of soil wetness in relation to the natural soil surface level is crucial for determining the suitability of a site for septic system installation. For soil to be deemed suitable, it must typically have a natural soil level that does not retain excessive moisture, which could hinder the effective filtration and treatment of wastewater.

When evaluating the depth of the natural soil surface, a depth greater than 48 inches below the surface indicates that the soil is sufficiently distant from the groundwater table or any saturated zones. This distance allows for adequate drainage and reduces the risk of saturated soils that could lead to system failure. This criteria is established to ensure that the soils can adequately treat effluent, thus protecting public health and the environment.

The other options suggest either shallower depths, which could lead to issues with soil saturation and potential failure of the septic system. In particular, being within 48 inches or above the surface may indicate proximity to groundwater or other moisture sources that could compromise the septic system's effectiveness. Hence, establishing greater than 48 inches as the reference point helps to ensure that the soil conditions are optimal for septic system operation.