Contaminated Land and Bio-Remediation - Environmental Biotechnology: Theory and Application - page 95

Figure5.1 Factorsaffectingtechnologysuitability
Ex situ
The main characteristic of ex situ methods is that the soil is removed from where
it originally lay, for treatment. Strictly speaking this description applies whether
the material is taken to another venue for clean-up, or simply to another part
of the same site. The main benefits are that the conditions are more readily
optimised, process control is easier to maintain and monitoring is more accurate
and simpler to achieve. In addition, the introduction of specialist organisms, on
those occasions when they may be required, is easier and/or safer and generally
these approaches tend to be faster than corresponding in situ techniques. They
are best suited to instances of relatively localised pollution within a site, typically
in 'hot-spots' of medium to relatively high concentration which are fairly near
to the surface.
Amongst the main disadvantages are the additional transport costs and the
inevitably increased likelihood of spillage, or potential secondary pollution, rep-
resented by such movement. Obviously these approaches require a supplementary
area of land for treatment and hence they are typically more expensive options.
As Figure 5.1 illustrates, the decision to use in situ or ex situ techniques is
a comparatively straightforward 'black-or-white' issue at the extremes for either
option. However, the middle ground between them comprises many more shades
of grey, and the ultimate resolution in these cases is, again, largely dependent on
individual circumstance.
Intensive and Extensive Technologies
Though the in situ/ex situ classification has established historic precedence, of
recent times an alternative approach to categorise remediation activities has
emerged, which has not yet entirely achieved the same widespread recognition