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Identification of dominating factors affecting vadose zone vulnerability by a simulation method

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ABSTRACT

The characteristics of vadose zone vulnerability dominating factors (VDFs) are closely related to the migration and transformation mechanisms of contaminants in the vadose zone, which directly affect the state of the contaminants percolating to the groundwater. This study analyzes the hydrogeological profile of the pore water regions in the vadose zone, and conceptualizes the vadose zone as single lithologic, double lithologic, or multi lithologic. To accurately determine how the location of the pollution source influences the groundwater, we classify the permeabilities (thicknesses) of different media into clay-layer and non-clay-layer permeabilities (thicknesses), and introduce the maximum pollution thickness. Meanwhile, the physicochemical reactions of the contaminants in the vadose zone are represented by the soil adsorption and soil degradability. The VDFs are determined from the factors and parameters in groundwater vulnerability assessment. The VDFs are identified and sequenced in simulations and a sensitivity analysis. When applied to three polluted sites in China, the method improved the weighting of factors in groundwater vulnerability assessment, and increased the reliability of predicting groundwater vulnerability to contaminants.

No MeSH data available.


Conceptual diagram of maximum pollution thickness (M) (generated by Microsoft Office 2010 software for Windows 2003/XP/VISTA/7).
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f6: Conceptual diagram of maximum pollution thickness (M) (generated by Microsoft Office 2010 software for Windows 2003/XP/VISTA/7).

Mentions: The most popular model for assessing groundwater intrinsic vulnerability is the DRASTIC model5 developed by a committee of the United States Environmental Protection Agency (EPA). However, as DRASTIC operates on regional scales, some of the DRASTIC factors are unsuitable for assessing vadose zone vulnerability and protecting unconfined groundwater at the site scale. Therefore, we must select the factors that most influence the vadose zone vulnerability4. The vadose zone is most closely associated with the groundwater level (D) and impact of the vadose zone (I), where D represents the distance from the ground surface to the groundwater table. In practice, the pollution sources occupy both the ground surface and the vadose zone. The further the pollution source from the groundwater table, the longer the time of reaction between the contaminants and the soil media. Consequently, the reaction will be more sufficient, and the vadose zone will be less vulnerable. In this paper, we replace D by the maximum pollution thickness (M), which defines the distance between the pollution sources and groundwater table, and which more accurately reflects the influence of the pollution source on the groundwater (Fig. 6).


Identification of dominating factors affecting vadose zone vulnerability by a simulation method
Conceptual diagram of maximum pollution thickness (M) (generated by Microsoft Office 2010 software for Windows 2003/XP/VISTA/7).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384093&req=5

f6: Conceptual diagram of maximum pollution thickness (M) (generated by Microsoft Office 2010 software for Windows 2003/XP/VISTA/7).
Mentions: The most popular model for assessing groundwater intrinsic vulnerability is the DRASTIC model5 developed by a committee of the United States Environmental Protection Agency (EPA). However, as DRASTIC operates on regional scales, some of the DRASTIC factors are unsuitable for assessing vadose zone vulnerability and protecting unconfined groundwater at the site scale. Therefore, we must select the factors that most influence the vadose zone vulnerability4. The vadose zone is most closely associated with the groundwater level (D) and impact of the vadose zone (I), where D represents the distance from the ground surface to the groundwater table. In practice, the pollution sources occupy both the ground surface and the vadose zone. The further the pollution source from the groundwater table, the longer the time of reaction between the contaminants and the soil media. Consequently, the reaction will be more sufficient, and the vadose zone will be less vulnerable. In this paper, we replace D by the maximum pollution thickness (M), which defines the distance between the pollution sources and groundwater table, and which more accurately reflects the influence of the pollution source on the groundwater (Fig. 6).

View Article: PubMed Central - PubMed

ABSTRACT

The characteristics of vadose zone vulnerability dominating factors (VDFs) are closely related to the migration and transformation mechanisms of contaminants in the vadose zone, which directly affect the state of the contaminants percolating to the groundwater. This study analyzes the hydrogeological profile of the pore water regions in the vadose zone, and conceptualizes the vadose zone as single lithologic, double lithologic, or multi lithologic. To accurately determine how the location of the pollution source influences the groundwater, we classify the permeabilities (thicknesses) of different media into clay-layer and non-clay-layer permeabilities (thicknesses), and introduce the maximum pollution thickness. Meanwhile, the physicochemical reactions of the contaminants in the vadose zone are represented by the soil adsorption and soil degradability. The VDFs are determined from the factors and parameters in groundwater vulnerability assessment. The VDFs are identified and sequenced in simulations and a sensitivity analysis. When applied to three polluted sites in China, the method improved the weighting of factors in groundwater vulnerability assessment, and increased the reliability of predicting groundwater vulnerability to contaminants.

No MeSH data available.