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ABSTRACT
This paper describes the requirements to use controlled natural attenuation for the management of a contaminated site. After the presentation of the regulatory environment, the components of natural attenuation are detailed. The geochemical conditions required for biodegradation of BTEX and chlorinated solvents are analyzed in detail using examples. In conjunction, the role of the models for prediction is analyzed. In addition, the contribution of isotopic measurements is presented. And, finally, two typical cases illustrate situations in which the attenuation is applicable for which it is not.
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Read the articleAUTHORS
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Olivier ATTEIA: Professor EA 4592 – Institut polytechnique de Bordeaux
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Elicia VERARDO: BRGM doctoral student
INTRODUCTION
Natural attenuation (NA) refers to all the mechanisms that lead, without human intervention, to a reduction in the mass, toxicity, mobility, volume, flow or concentration of pollutants in soil or groundwater. Like any other management measure, natural attenuation involves reducing the concentration at the target.
Different scenarios and the types of targets involved are considered. For the technique to be applicable on a site, it must be controlled, which is why the term "controlled natural attenuation" is often used.
There are two main processes:
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non-destructive mechanisms, including dilution, dispersion, adsorption and volatilization;
the transformation of pollutants and destructive mechanisms adapted only to certain organic molecules (metallic pollutants are never destroyed).
On the majority of sites, natural attenuation is only envisaged where there is significant destruction of pollutants.
Due to their presence on numerous sites (Basol database of polluted sites and soils), the objective is to focus on the biodegradation of BTEX (benzene, toluene, ethybenzene, xylenes), followed by that of chlorinated solvents (perchloroethylene, trichloroethylene and their derivatives). The extent of this biodegradation is quantified using models at two sites, demonstrating different efficiencies for different substances. This approach can be completed by setting up microcosms and monitoring pollutant isotope levels.
Because of the slow rate of flow and the quantities of pollutants in source areas, AN is essentially a process that extends over several years, and the timescales that can be envisaged can be defined on the basis of real-life examples.
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KEYWORDS
degradation | numerical model | | | isotopes
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Unit operations. Chemical reaction engineering
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Controlled natural attenuation of organic pollutants: tools and models
Regulatory aspects
Bibliography
Software tools
PHAST – A Computer Program for Simulating Groundwater Flow, Solute Transport, and Multicomponent Geochemical Reactions http://wwwbrr.cr.usgs.gov/projects/GWC_coupled /phast/index.html
PHT3D http://www.pht3d.org
...Websites
ADEME – French Environment and Energy Management Agency http://www2.ademe.fr
including
Natural attenuation of aliphatic organochlorine compounds in aquifers, methodological guide, R Macaoh program (2001-2006). http://www2.ademe.fr/servlet/getDoc?sort=1=96=3=51390=...
Events
Intersol, the international congress and exhibition on soil, sediment and water, is held in Paris every year at the end of March. http://www.intersol.fr
Contaminated Site Management in Europe Congress, held every year in a European city at the end of November. http://www.redoxtech.com
...Standards and norms
- Soil quality – Services relating to polluted sites and soils (studies, engineering, rehabilitation of polluted sites and remediation work)" - NF-X-31-620-2 -
- Soil quality – Pollution detection and characterization methods – Groundwater sampling in a borehole - NF-X-31-615 - 12-00
Regulations
MEEDDAT, 2007. Note ministérielle. Polluted sites and soils – Management and redevelopment of polluted sites New Ministry texts on preventing soil pollution and managing polluted soils in France – Appendix 2: Management and redevelopment of polluted sites. How to identify a (potentially) polluted site. Comment gérer un problème de site pollué, February 2007.
Directory
Companies
A number of companies in France practice natural attenuation treatment. These include the Union des Professionnels de la Dépollution des Sites (Union of Site Remediation Professionals), which is the trade association for professionals in the polluted sites and soils sector. http://www.upds.org/
Organizations
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