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Content archived on 2024-05-07

Improving in Situ Biodegradation at Light -NAPL contaminated sites: Removing constraints with Extensive Measures


Ail EU-countries face the problem of soils and aquifers contaminated with hydrocarbons lighter than water (called LNAPLs: Light Non Aqueous Phase Liquids). The light hydrocarbon spills accumulate at the phreatic water table in the form of free (liquid) product. The contaminated sites are partly industrial plants (tar production, oil refinement), partly small enterprises (metal rectification, dry cleaning), but sometimes also due to massive bombing of industrial plants during world war 11.
Such LNAPLs hydrocarbons are usually volatile but relatively insoluble in water. Nevertheless, even at small concentrations they pose a risk to the consumability of water. Among others, major (toxic) components are light oil, gasoline/kerosene, PAHs, phenols, BTEX, and chlorinated hydrocarbons.
Different forces act on the LNAPLs and determine their fate in the soil environment:

- Organic phase transport
- Evaporation to the gas phase
- Dissolution in the water phase
- Sorption to the solid phase
- Degradation by microorganisms and enzymes

The specific problem arising from an oil phase floating on top of (unconfined) groundwater aquifers is the distnbution of the oil phase in the groundwater fluctuation zone. This leads to a vertical lubrication of the hydrocarbon phase, resulting in a drastic increase of the oil covered surface (oil-film formation) in the zone of water table fluctuation. This oil film not only is the source of a number of different contaminants but also changes almost all structural and functional properties of the aquifer.

The light hydrocarbons are generally (bio)degradable under aerobic conditions. Nevertheless, spills formed during the massive bombing of industrial plants during WWII, which may involve polluted areas of tens of km2, have been persistent against degradation until now. This suggests that the conditions at the contaminated layers are unfavourable for degradation.

The main objectives for the project group are

(i) to assess how large spills of LNAPLs behave in the subsurface strata in physical, chemical and biological respect,

(ii) to assess which conditions are favourable for extensive in situ biodegradation;

(iii) to investigate whether such favourable conditions can be created at actually contaminated sites with labour - and cost effective remediation strategies, i.e. natural attenuation, as intensive in situ bioremediation may not be achievable in view of the large areas and many sites involved;

iv) to quantify the release rate of the 'subsurface' contaminant source to the surroundings during extensive remediation, because of the hazard of further spreading of the contamination during the time span needed for degradation

The project will focus on light NAPL with major emphasis on natural attenuation or intrinsic bioremediation. The proposed research provides basic understanding of processes involved in extensive and passive remediation and gives guidelines to identify which combination of site parameters are likely to facilitate these options.
Furthermore, it provides the possibility to identify which factors constrain biodegradation and which actions may successfully remove these constraints. Therefore, the proposed research may improve the scientific and technological understanding of various in situ remediation management options, especially intrinsic bioremediation, and gives confidence in choosing for these options where these are applicable. This may improve cost effectiveness of in situ remediation and reduces the risk of adverse effects due to improperly choosing extensive or passive remediation as the option.

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Participants (4)