Geotechnically, a contaminated soil will behave in very much the same way as an uncontaminated soil. Contamination of whatever nature, ie hydrocarbons or VOCs, will be held within the soil matrix either in a dissolved phase within the pore fluid, free phase within the pore space or as a coating around the soil particles themselves.
It is well accepted that gross disturbance of soil during sampling can significantly effect the geotechnical characteristics measured in the soils laboratory. Mechanical disturbance will affect the soil matrix, stress changes will affect the water and/or gas within the pore spaces, as will the handling process once the sample is removed from the ground. Just as they affect geotechnical properties of soil, such disturbances should be considered as having similar effects on the nature and extent of contamination within the sample.
To minimise disturbance and maximise the understanding of the insitu nature and behaviour of soil, the geotechnical community has developed a wide range of sampling techniques, eg push sampling, piston sampling and insitu testing, which in different ways attempt to overcome the shortcomings of traditional site investigation. Just as such techniques are relevant to non-contaminated soils, they are equally applicable to those which are contaminated.
To this end Fugro has developed a range of insitu probes which give good quality and representative data cost effectively. For example the laser induced fluorescence cone and membrane interface probes can provide real-time contamination analysis, saving time in the interpretative process and improving the overall risk assessment.
As in geotechnical investigations, the pressure to obtain information quickly should never override the need to obtain good quality, representative data. Failure to do so generates an additional uncertainty and increases the risk component within the overall objective of risk assessment.