Abstract
Analytical models for the simulation of contaminants’ fate and transport in the unsaturated zone are used in many engineering applications concerning groundwater resource management and risk assessment. As a consequence, several scientific studies dealing with the development and application of analytical solutions have been carried out. Six models have been selected and compared based on common characteristics to identify pros and cons as well as to highlight any difference in the final output. The analyzed models have been clustered into three groups according to the assumptions on contaminant source and physico-chemical mechanisms occurring during the transport. Comparative simulations were carried out with five target contaminants (Benzene, Benzo(a)pyrene, Vinyl Chloride, Trichloroethylene and Aldrin) with different decay’s coefficient, three types of soil (sand, loam and clay) and three different thicknesses of the contaminant source. The calculated concentration at a given depth in the soil for the same contamination scenario varied greatly among the models. A significant variability of the concentrations was shown due to the variation of contaminant and soil characteristics. As a general finding, the more advanced is the model, the lower the predicted concentrations; thus, models that are too simplified could lead to outcomes of some orders of magnitude greater than the advanced one.
Highlights
The release of organic contaminants into the environment represents a growing threat for groundwater and human health, as evidenced by the concentrations measured in several groundwater bodies [1,2,3,4,5]
They share the following common features: (i) the assessment of the concentration of a single contaminant dissolved in aqueous phase that moves from a source located in the unsaturated zone to the water table; (ii) the negligible effect related to the movement of substances in the non-aqueous phase; (iii) the small number of geometrical, hydrogeological and chemical input data; (iv) the use of a set of simplifying assumptions that allows to obtain analytical solutions
The model is based on the determination of the contaminant LF, which represents the steady ratio between the contaminant concentration in the soil source and the resultant concentration in groundwater. This approach may be applied both to organic and inorganic contaminants and it is adopted by various software for risk assessment, e.g., Risk-Based Corrective Action (RBCA) Tool Kit for Chemical Releases [53]
Summary
The release of organic contaminants into the environment represents a growing threat for groundwater and human health, as evidenced by the concentrations measured in several groundwater bodies [1,2,3,4,5]. Ie f f ·Ksw R·L1 ·ρs λsource ·θw ·Ksw ρs αleach σ· exp(k·z) k·sinh(σ·z)+σ· cosh(σ·z) k= They share the following common features: (i) the assessment of the concentration of a single contaminant dissolved in aqueous phase that moves from a source located in the unsaturated zone to the water table; (ii) the negligible effect related to the movement of substances in the non-aqueous phase; (iii) the small number of geometrical, hydrogeological and chemical input data; (iv) the use of a set of simplifying assumptions that allows to obtain analytical solutions. Specific features of the models will be carefully described
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