Some countries use risk based approach while others might ask for a certain level of final hydrocarbons in the treated soils (e.g. 3% or even 1%). The initial contaminated soils can contain up to 10% hydrocarbons. But if there is no risk on receptors, should we allow for natural remediation only or should there be a certain level to achieve in the final treated soil before sending the soils to the landfill?
technically it is very difficult to go beyond 5%, the allotted time would be much, that is why we usually stop the treatment when we arrived at a balance.
but it also depends on the specifications, in this case we would have to resort to several treatment processes
Hi Mahad,
The risk based approach is definitely the way to go. The target residual contamination must be set based on the risk to human / environmental receptors. It will depend on the setting, pathways and sensitivity of receptor. In some cases it may be valid to leave contamination to naturally degrade and attenuate, in others it may be an unacceptable risk. If you are looking for standard for soils going to landfill - that would be quite different to leaving soils in-situ. Landfills in Queensland Australia that are built to accept "regulated waste" (ie more contaminated than household waste), will generally accept 10% by weight TPH or
Treatment in t he range 5-8% will be fine because natural attenuation will further degrade the hydrocarbon.
Adewale; Guess it will depend where. Natural attenuation may vary on soil texture-parent material, soil nutrient, climate, groundwater, Soil bacteria-microorganisms-macroorganisms', vegetation, land use.
This is where baseline/reference studies are so crucial in terms of understanding natural bioremediation. Microbes are incredible organisms, but there is still a lack of understanding in terms of their capabilities to degrade oily soils depending on soil properties, available nutrients, physical conditions etc. Sure it's pretty well understood that microbes will degrade oil when in the presence of it, but the array of aerobic and anaerobic metabolic pathways involved in these degradation pathways are incredibly diverse in some instances. At what percentage does bioremediation take place? at what percentage is the oil perhaps passed by in favour of a more energetically favourable carbon source?
Many credible answers have been given, but, I would like to add: the level to which any cleaning up, or remediation of a site that is polluted, is guided by the intended future use of that site. If the site shall be a playground for children for example, then, cleaning up should be taken up to a level where natural mechanisms can finish up the job. However, is the intended use is for parking space, say for long distant trucks; then, we don't need very thorough cleaning-up.
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