Vadose zone defined

Soil organic matter is found wherever organic matter is decomposed, mainly in the near surface. However soil organic matter may also be transported as suspended particles into deeper layers of the vadose zone or via surface- and groundwaterforming sediments. Although these components form a minor part of the total solid phase, they are of major importance in defining the surface properties of the solid phase and have a great impact on the chemical behavior. 

Contaminants retained on colloid surfaces may be transported by flowing water through the vadose zone and reach the groundwater or be relocated on the land surface by runoff processes. Operationally defined as particles between 1 j,m and 1 nm in size, colloids in the subsurface may be of mineral, organic, or biological origin. 

Figure 8.1 defines the different types of subsurface-waters. The zone above the water table is called the zone of aeration, vadose zone, or unsaturated zone. Moving downward in this zone we encounter first soil water or soil moisture, then intermediate vadose water, and then capillary water. Capillary water rises into rock and sediment pores above the water table because of capillary forces. The capillary zone may be as much as 30 ft (9 m) thick in clayey sediments. To the extent the unsaturated zone can truly be called the zone of aeration, then air and atmospheric oxygen are present and conditions are oxidizing. 

Impact of Vadose Zone. The vadose zone is defined as that zone above the water table and below the soil media which is unsaturated. For purposes of this document, this strict definition can be applied to all water table aquifers. However, when evaluating a confined aquifer, the "impact" of the vadose zone is expanded to include both the vadose zone and anysaturated zones which overlie the aquifer. The significantly restrictive zone above the aquifer which forms the confining layer is used as the type of medium which has the most significant impact. 

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