the pollution sources sit on the ground, the maximum pollution thickness refers to
the depth to water table. Where the pollution sources are located in the vadose zone
below the ground, the maximum pollution thickness equals the thickness of vadose
zone minus the buried depth of pollution sources.
The permeability and adsorption of rocks and soils reflect the migration rate of
pollutants in the vadose zone, which is closely related to the duration of pollutant
existence in the groundwater. The permeability is described by the permeability
coefficient (K) of rocks and soils, and the adsorption described by the distribution
coefficient or adsorption coefficient (Kd) of pollutants in the media.
The degradability of rocks and soils mainly reflects the ability of microorganisms to degrade pollutants in the vadose zone, so it is closely related to the composition of microorganisms in the vadose zone. The degradability is described by
the rate of degradation (l).
(b) Bi-lithologic type
A total of six factors are considered, of which maximum pollution thickness, clay
layer thickness, clay layer permeability, sand layer permeability and clay adsorption
examine the impact on the duration of pollutant migration, and clay degradability
examines the impact on pollutant concentrations.
The maximum pollution thickness means the same as that for monolithologic
vadose zone.
The thickness, permeability and adsorption of clay layer reflect the dominant
role of the clay layer in the vadose zone in blocking pollutant migration. The clay
layer refers to a layer of such soils as clay, mucky clay, silty clay and silt, and the
adsorption is described by the distribution coefficient (Kd) of pollutants in the
media.
The sand layer consists of silt, fine sand, medium sand, coarse sand, pebble and
gravel. The sand layer thickness is not deemed a main factor for two reasons: the
sand layer thickness can be calculated based on the maximum pollution thickness
and clay layer thickness; and with high permeability, the sand layer hardly blocks
pollutant migration. The sand layer permeability is described by the permeability
coefficient (K).
The degradability of rocks and soils is defined and described the same as that for
monolithologic vadose zone. For the sake of conservatism, the degradation
parameters of least-degradability layer should be adopted for the bi-lithologic
vadose zone.
(c) Multi-lithologic type
Totally six factors are selected, of which maximum pollution thickness, clay layer
thickness, equivalent permeability of clay layer, equivalent permeability of sand
layer, and clay adsorption examine the impact on the duration of pollutant migration, and the degradability of rocks and soils examines the impact on pollutant
concentrations.
The clay layer in the multi-lithological vadose zone contains such soils as clay,
mucky clay, silty clay and silt.
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3 Rating and Evaluation of Pollution Source Intensity …
the depth to water table. Where the pollution sources are located in the vadose zone
below the ground, the maximum pollution thickness equals the thickness of vadose
zone minus the buried depth of pollution sources.
The permeability and adsorption of rocks and soils reflect the migration rate of
pollutants in the vadose zone, which is closely related to the duration of pollutant
existence in the groundwater. The permeability is described by the permeability
coefficient (K) of rocks and soils, and the adsorption described by the distribution
coefficient or adsorption coefficient (Kd) of pollutants in the media.
The degradability of rocks and soils mainly reflects the ability of microorganisms to degrade pollutants in the vadose zone, so it is closely related to the composition of microorganisms in the vadose zone. The degradability is described by
the rate of degradation (l).
(b) Bi-lithologic type
A total of six factors are considered, of which maximum pollution thickness, clay
layer thickness, clay layer permeability, sand layer permeability and clay adsorption
examine the impact on the duration of pollutant migration, and clay degradability
examines the impact on pollutant concentrations.
The maximum pollution thickness means the same as that for monolithologic
vadose zone.
The thickness, permeability and adsorption of clay layer reflect the dominant
role of the clay layer in the vadose zone in blocking pollutant migration. The clay
layer refers to a layer of such soils as clay, mucky clay, silty clay and silt, and the
adsorption is described by the distribution coefficient (Kd) of pollutants in the
media.
The sand layer consists of silt, fine sand, medium sand, coarse sand, pebble and
gravel. The sand layer thickness is not deemed a main factor for two reasons: the
sand layer thickness can be calculated based on the maximum pollution thickness
and clay layer thickness; and with high permeability, the sand layer hardly blocks
pollutant migration. The sand layer permeability is described by the permeability
coefficient (K).
The degradability of rocks and soils is defined and described the same as that for
monolithologic vadose zone. For the sake of conservatism, the degradation
parameters of least-degradability layer should be adopted for the bi-lithologic
vadose zone.
(c) Multi-lithologic type
Totally six factors are selected, of which maximum pollution thickness, clay layer
thickness, equivalent permeability of clay layer, equivalent permeability of sand
layer, and clay adsorption examine the impact on the duration of pollutant migration, and the degradability of rocks and soils examines the impact on pollutant
concentrations.
The clay layer in the multi-lithological vadose zone contains such soils as clay,
mucky clay, silty clay and silt.
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3 Rating and Evaluation of Pollution Source Intensity …