(c) Multi-lithologic vadose zone
The multi-lithologic vadose zone consists of at least two porous media with wide
permeability differences that form three layers (e.g., silty clay layer, medium and
fine sand layer, silty clay layer) or more (Fig. 3.9). Above the groundwater are
complex layers of low-permeability clay and high-permeability sand. The permeability of multi-lithologic vadose zone differs by at least an order of magnitude.
Transformation among the above-mentioned three types may take place along
with the change of depth to water table. For example, when the groundwater table
decreases or the aquifer is dried up, the monolithologic or bi-lithologic vadose zone
may become multi-lithologic.
(3) Fissure water regions
(a) Weathering fissure type
The vadose zone of weathering fissure type contains aqueous media and includes
the upper strongly weathered zone and the lower weakly weathered zone where
groundwater exists. In view of similar structure, the weathering fissure type can be
generalized into bi-lithologic vadose zone, but the permeability ratio of strongly and
weakly weathered zones is smaller than that of the upper and lower porous media in
bi-lithologic vadose zone (Fig. 3.10).
Fig. 3.9 Structure of
multi-lithologic vadose zone
Fig. 3.10 Vadose zone
structure—weathering fissure
type
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3 Rating and Evaluation of Pollution Source Intensity …
The multi-lithologic vadose zone consists of at least two porous media with wide
permeability differences that form three layers (e.g., silty clay layer, medium and
fine sand layer, silty clay layer) or more (Fig. 3.9). Above the groundwater are
complex layers of low-permeability clay and high-permeability sand. The permeability of multi-lithologic vadose zone differs by at least an order of magnitude.
Transformation among the above-mentioned three types may take place along
with the change of depth to water table. For example, when the groundwater table
decreases or the aquifer is dried up, the monolithologic or bi-lithologic vadose zone
may become multi-lithologic.
(3) Fissure water regions
(a) Weathering fissure type
The vadose zone of weathering fissure type contains aqueous media and includes
the upper strongly weathered zone and the lower weakly weathered zone where
groundwater exists. In view of similar structure, the weathering fissure type can be
generalized into bi-lithologic vadose zone, but the permeability ratio of strongly and
weakly weathered zones is smaller than that of the upper and lower porous media in
bi-lithologic vadose zone (Fig. 3.10).
Fig. 3.9 Structure of
multi-lithologic vadose zone
Fig. 3.10 Vadose zone
structure—weathering fissure
type
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3 Rating and Evaluation of Pollution Source Intensity …