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NA-Screening: The Proof of Natural Attenuation Downstream of Landfills

The "NA-Screening" is a tool to distinguish between those contaminated sites, were Natural Attenuation (NA) is sufficiently effective to contain and minimize the groundwater contamination, and those sites, were it cannot be used because of neighboring sensitive environment or insufficient NA effectiveness. The "NA-Screening" has a hierarchical structure with three steps (Kühn et al. 2011). Only when these three steps have a positive result the monitored natural attenuation (MNA) can commence. Even as these investigative tools are cheap, the method is scientifically sound and a cost effective measure to control and contain groundwater contamination.

The effectiveness of NA is proved by three lines of evidence. In step A the reduction of the emission along a centre-line is measured geochemically and the results are summarized by the main ions, the trace elements, AOX and the DOC/TOC. These parameters are compared to the regional baseline values and the evidence of retention is positive, when the baseline values are approached within an appropriate distance. This distance depends on multiple factors such as groundwater velocity and the distance to the next sensible protective goods. As the depletion should not only be achieved by dilution, it is necessary to use a method to prove that NA is as well achieved by mineralization and metabolization. In step B the Theta-method (Θt/Θ) (Holzbecher et al. 2010) is used as a second check for effects of NA in the groundwater emissions. This method is based on the comparison of concentrations for a tracer and the attenuation-suspect substance. Examinations of the mathematical analytical solutions show that the ratio of normalised concentrations θt/θ is expected to increase in space and time in the presence of NA, but to remain constant in case of dilution and diffusion only or no degradation. In step C the contamination reduction by microbiological organisms is demonstrated, as NA effects should not solely attributable to physico-chemical factors, but also to microorganisms. The contribution by groundwater microfauna can be checked with the newly developed DNA-Microarray method (Charlé et al. 2010). This method is used to differentiate bacteria and archea as well as their activity. Only when all three methods are positive, NA can be used for the reduction of the groundwater contamination. Based on the results of the NA-screening the monitored natural attenuation concept is used (MNA is used to control the reduction of the pollution for as many years as necessary until the agreed sanitation target is reached.

Copyright:	© Lehrstuhl für Abfallverwertungstechnik und Abfallwirtschaft der Montanuniversität Leoben
Quelle:	Depotech 2012 (November 2012)
Seiten:	4
Preis:	€ 2,00
Autor:	Dr. Stephan Kühn Thomas Struppe C. Charlé
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