Investigations

Each site has to be investigated not only for its geological, hydrogeological, and contaminant situation, but also for the site-specific degradability. The following description refers to laboratory methods for investigation of the microbiological degradability of contaminants. These methods are divided into two stages [1] (Fig. 12.3). During the first stage the general degradability is determined, i.e., whether the contaminants at the given site are sufficiently degradable. Conclusive demonstration of the fate of the contaminants can be obtained only by using tracer (e.g., 14C-labeled substances). However, this is possible only in closed laboratory systems and not on a

Fig. 12.3 Laboratory test methods for investigating and optimizing microbial degradation of contaminants (according to [1]).

technical scale. Hence, it is necessary to use indirect parameters to demonstrate biodegradation.

Investigations of numerous sites have shown that the indigenous microflora often include specific contaminant degraders. Therefore, in principle, the degradation potential is given, unless the contamination reaches toxic concentrations. Environmental conditions are usually unfavorable for rapid degradation. In the first stage of investigation the maximum degradation rate is determined, instead of a realistic rate.

During the second stage, basic data for planning the remediation, such as nutrient demand, remediation duration, and achievable end concentrations, are determined by test methods that simulate the remediation technology (benchtop scale).

The results of all site investigations and of risk assessments are considered when planning the remediation. Today, sufficient experience is available to scale up the results of bench-top scale investigations to a technical scale. Pilot scale investigations are carried out when new technologies without sufficient practical experience are being considered, recalcitrant contaminants need to be treated, or the site exhibits special complex conditions.

The data collected for a specific site are used to describe the site (conceptual site model). From this site model, laboratory investigations are designed. The laboratory results are used to plan the technical scale remediation. For in situ remediation, it is reasonable to use an additional planning instrument - modeling. These models are fed with parameters determined during site and laboratory investigations.

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