Elsevier

Computers & Geosciences

Volume 32, Issue 7, August 2006, Pages 890-896
Computers & Geosciences

A new model for polluted soil risk assessment

https://doi.org/10.1016/j.cageo.2005.10.025Get rights and content

Abstract

In this paper, we discuss the most important theoretical aspects of polluted soil Risk Assessment Methodologies, which have been developed in order to evaluate the risk, for the exposed people, connected with the residual contaminant concentration in polluted soil, and we make a short presentation of the major different kinds of risk assessment methodologies. We also underline the relevant role played, in this kind of analysis, by the pollutant transport models. We also describe a new and innovative model, based on the general framework of the so-called Cellular Automata (CA), initially developed in the UE-Esprit Project COLOMBO for the simulation of bioremediation processes. These kinds of models, for their intrinsic “finite and discrete” characteristics, seem to be very well suited for a detailed analysis of the shape of the pollutant sources, the contaminant fates and the evaluation of target in the risk assessment evaluation.

In particular, we will describe the future research activities we are going to develop in the area of a strict integration between pollutant fate and transport models and Risk Analysis Methodologies.

Introduction

In recent years, the problem of evaluating risk related to soil pollution has become increasingly important, worldwide. The increasing number of polluted soils in industrialised counties has required the formalisation of well-defined methodologies for defining the technical and economical limits of soil remediation. In many situations, these limits are defined in terms of general threshold values that, often, cannot be reached even with the so-called best available technology (BAT). This occurs, for example, as a consequence of the characteristics of the pollutants or of the affected soil, or of the extremely high cost or duration of the remedial intervention.

For these reasons, both in North American and European countries, many alternative methodologies based on systematic and scientifically well-founded approaches have been developed in order to determine the real effects of the pollution on receptor targets. Typically, these methodologies are organised into different levels of detail, the so-called “Tiers” (ASTM, 1998). Tier 1 is based on a conservative estimation of the risk for the targets that come from very general and “worst case” general situations. Tier 2 is based on a more detailed and site-specific estimation of the hazard, evaluated by the use of semi-empirical, analytical formulas for the source characterisation, the transport of the pollutant and the target exposition evaluation. Tier 3 is the more detailed and site-specific level of application of the risk assessment methodologies and requires the use of numerical methods with many detailed data from the site and on the receptors (e.g. chemical/physical parameters of the pollutants, hydro-geological data, exposition data, etc.).

Section snippets

The general characteristics of risk assessment methodologies

The increasing use and application of risk assessment procedures has produced a diversification and specialisation of different methodologies, depending on the case under consideration. The polluted soil risk assessment methodologies differ from each other mainly in the way they model the targets and effect of the pollutants (e.g. damages to the human life, chronic health effects, acute health effects, damages to the ecosystems, possible genetics modifications, etc.)

Generally speaking, the risk

The pollutant fate and transport model

Now, we want to focus our analysis on the aspect of the transport of the pollutant from the sources to the receptor sites and on the importance of the correct modelling of the pollutant fate. In particular, we are going to describe in detail a simulation model for the pollutants redistribution among phases at the source points and for the simulation of the effect of pollutants absorption by the receptors. The model we would analyse in detail is an innovative simulation model for the pollutants

The fluid dynamical layer

The flow of a fluid in a saturated porous medium is governed by the Darcy equation, whose generalisation for a multiphase flow is given by the equation:qα=-krαkμα(pα+ραgz),where qα (m s–1) is the volumetric flow rate per unit volume, k (m2) the intrinsic permeability of the solid matrix (it depends on the shape and the size of the pores through which the phase flows), and pα (Pa), k, μα (Pa s) and ρα (kg m–3) are the pressure, the relative permeability, the viscosity and the density of the

Modelling the transport of chemicals

In the polluted soils, chemicals can then be present in all the phases: as gas in soil air, as a dissolved chemical in the soil water and as a dissolved chemical in the nonaqueous phase, adsorbed to the soil organic matter. Consequentially, the total chemical concentration Ct can be written asCt=ρbCa+θCl+πCnw+aCg,where Ca is the adsorbed chemical concentration (expressed as the mass of sorbant per mass of dry soil), Cl the dissolved chemical concentration in the wetting phase (expressed as the

Chemical reaction modelling

Typically, many different chemical reactions take place in soils: chemicals contained in a phase can react with other chemicals to form both soluble and/or insoluble (in a certain phase) products (it must be noted that products which are insoluble in water could be soluble in the NAPL phase and vice-versa); soluble species in water may also enter into oxidation/reduction, acid/base reactions, chelations, complexations, and several other types of association that result in soluble products. It

Some possible application to detailed risk analysis evaluation

Besides the possibility of application of this model to the project and analysis of “in situ” bioremediation interventions (Villani et al., 2001), our model can be usefully applied in detailed risk analysis evaluation. For example, it can be used for detailed simulation of the shape of the contamination source and for the simulation of the fate of the pollutant through the migration pathways. In this way, it is possible to integrate the results of this simulation model with the procedures for

References (6)

  • M. Andretta et al.

    Comparison among polluted soils hazard ranking systems and absolute risk analysis methodologies

  • Standard Guide for Risk-Based Corrective Action

    (1998)
  • J. Bear

    Hydraulics of Groundwater

    (1979)
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