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 achieved the same widespread recognition or acceptance, but does, nevertheless offer certain advantages over the earlier approach. Perhaps the most significant of these is that it is a more natural division, based on genuine similarities between technologies in each class. Thus the descriptions ‘intensive’ and ‘extensive’ have been suggested.
Intensive technologies can be characterised as sophisticated, fast-acting, high intervention strategies, with a heavy demand for resources and high initiation, running and support costs. Their key factors are a fast response and low treatment time, which makes them excellent for heavy contamination conditions, since they can make an immediate lessening in pollutant impact. Soil washing and thermal treatments are good examples of ‘intensive’ approaches.
Extensive methods are lower-level interventions, typically slower acting, based on simpler technology and less sophisticated engineering, with a smaller resource requirement and lower initiation, running and support costs. These technolo-gies have a slower response and a higher treatment time, but their lower costs make wider application possible, particularly since extensive land remediation treatments do less damage to soil quality. Accordingly, they are well suited to large-scale treatment where speed is not of the essence. Examples include composting, the promotion of biological activity in situ within the root-zone, precipitation of metal sulphides under anaerobic conditions and the cropping of heavy metal accumulator plants.
All these systems of classification are at best generalisations, and each can be useful at different times, dependent on the purpose of the consideration. They are merely a convenient way of looking at the available techniques and should not be regarded as anything more than a helpful guide. As a final aspect of this, it is possible to examine the various forms of land remediation technologies in terms of their overall functional principle. Hence, the approaches may be categorised as ‘destructive’, ‘separating’ or ‘containing’, dependent on their fundamental mode of operation, as Figure 5.2 illustrates. The principal attraction of this systemisa-tion is that it is defined on the basis of representing the fate of the pollutant,
rather than the geographical location of the work or the level of complexity of the technology used, as in the previous cases. In addition, it can also be relatively easily extended to take account of any given technology.
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