has part adjacent to vadose zone An interface layer which 1) is primarily composed of solid materials, 2) separates the land surface and phreatic zone, and 3) contains groundwater at atmospheric pressure. If the vadose zone includes portions of soil, the water contained therein is termed soil moisture. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. In such soils, therefore, the unsaturated zone is the upper section of the vadose zone and not identical to it. unsaturated zone phreatic zone groundwater solid layer interface layer land