Effective contaminant source geometries and their implications for final plume extension - ESTIMATE

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Dense non-aqueous phase liquid (DNAPL) contaminants have been found to persist in groundwater bodies for several decades due to their very low solubility in water as well as biodegradation properties. A proper risk assessment of each contaminant site is required as DNAPLs additionally pose a tremendous environmental and health hazard.Up to now, numerous investigations (field studies, laboratory experiments, analytical and numerical modelling) were carried out in order to characterise sub-surface contaminant migration, transport within plumes, and governing reactive processes. Source zone architecture is found to have significant influence on steady-state plume extension, which is the critical assessment property. However, the relevance of different impacts (i.e. aquifer properties, external stresses) with respect to the final state of a source zone could not sufficiently be clarified and quantified. Hence, more information on geometric measures of a contaminant source and its major dependency on impacts are required. Complex source geometries are valid for a single scenario only, and depend on a large number of processes. However, in analytical or numerical analyses, source geometry is mostly incorporated very rudimentarily as simple geometrical structures due to time and data limitations. Therefore, straightforward effective source geometries that condense information, and emerge from sub-surface properties and external stresses are required for an improved prediction of contaminant plumes. Effective source geometries could be used to predict final plume lengths with same accuracy as complex source geometries. We consider this as the currently most critical knowledge gap that restricts our ability to adequately predict contaminant plume lengths. Therefore, we want to characterise the influence of aquifer properties and external stresses on DNAPL source zone architecture which will allow us to derive transformation techniques to convert complex to effective source geometries under consideration of impacts. To achieve this, we will utilize a combination of laboratory-scale experiments, and numerical modelling. Our main research challenges are to (i) enhance the understanding of the final extent of complex DNAPL source zone architectures, (ii) quantify the influence of external stresses and site-specific characteristics on the final extent of complex source zones, (iii) derive effective source geometries from complex source geometries, and (iv) provide a functional relationship of external stresses and site-specific characteristics to acquire effective source geometries for the use in analytical or numerical assessment tools. Based on a combination of a plume length model and a source characterisation model, we hypothesise that improved description of source geometries will yield better estimations of maximum plume length and, therefore, much better opportunities for DNAPL remediation techniques.