If the soil is saturated with clean water, even seasonally, it cannot accept any more wastewater. The untreated wastewater will then either rise to the surface or back up into the house. Physical Damage Driving, paving, or building on top of a soil absorption unit can damage the field. Pipes can shift or be crushed and the soil compacted. Damage of this sort can make it difficult to locate the septic tank and prevents access for regular pumping.
Tree roots can also clog the soil absorption field.
Plant the area in grass, not trees or shrubs. These systems usually fail in a few months because they are inadequately sized, installed in impermeable soils, or not properly constructed. In Oregon, several inches of unsaturated soil must be present between the soil absorption system and a limiting layer. Temporary or permanent water tables, bedrock, or impervious soil are all considered limiting layers. The soil is the most important part of the septic system and must be properly evaluated and protected.