Effective contaminant source geometries and their implications for final plume extension - ESTIMATE
Final Report Abstract
In ESTIMATE, the formation of DNAPL source zones in the subsurface and the impact of source zone geometry on contaminant plume extension were investigated. Corresponding knowledge is essential for reliable assessment of DNAPL contaminated sites. In particular, impacts of aquifer properties and external stresses were addressed. The project followed a comprehensive approach including labscale investigations (2-D tank experiments together with numerical modeling), image and data analysis, scenario-based modeling at larger scales, as well as development of concepts and tools. Utilizing the 2-D tank experiments it was possible to mimic the DNAPL migration processes in a repeatable way under defined system conditions. Three different porous media types indicated the high relevance of porous media properties. Observation data could be transferred to DNAPL saturation distributions employing a developed image processing and analysis (IPA) framework. The measurement data could be directly compared to results of a numerical reference model. Results show good agreement between experiment and model, so that the DNAPL release scenarios are physically plausible, explainable and predictable by using the numerical model setup. It is to be emphasized that the IPA implementation appears to be used within ESTIMATE for the first time to analyze the formation of contaminant source zones. With this approach, it was possible to visualize the source formation processes in large detail under controlled ambient and defined boundary / initial conditions for all three porous media types. The experimentally generated data were introduced in a numerical multiphase flow model with comparably good calibration success, determinable uncertainties and prediction capability. Scenario-based modeling at larger scales involved analytical and numerical approaches to analyze the impacts of DNAPL source zone shapes, aquifer properties and external stresses (groundwater recharge, pumping wells) on contaminant spreading. It could be concluded that recharge significantly impacts plume length, also when the source zone geometry is regular and simple. A complex and irregular source geometry is likely to magnify the impact. The role of transverse dispersivity can be significant, especially when the stresses are of high magnitude. Similar behavior was found when the impact of water extraction by pumping wells was studied. Furthermore, it was possible to develop a mathematical approach to determine the maximum width of a contaminant plume as well as the location downstream from the source where this maximum is attained. In addition to the IPA framework mentioned above, several other concepts and tools could be developed to support DNAPL site analysis. An open-source, browser-based tool offers several simple analytical solutions to estimate plume length in early stages of site assessment. To support the selection of the most appropriate analytical solution, promising steps based on the Analytical Hierarchy Process (AHP) methodology could be undertaken. Another approach, which is specifically designed to facilitate shape characterization of DNAPL sources, is based on statistical properties (average and standard deviation) of selected shape parameters. The underlying concept is meant to cover a middle ground between the complexity of real-world source geometries and the rather regular shapes considered in many mathematical models.
Publications
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(2019), Quantification of uncertainties from image processing and analysis in laboratory-scale DNAPL release studies evaluated by reflective optical imaging, Water 11, 2274
Engelmann, C., Schmidt, L., Werth, C. J., Walther, M.
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(2019), The fate of DNAPL contaminants in non-consolidated subsurface systems – Discussion on the relevance of effective source zone geometries for plume propagation, J. Haz. Mat. 375, 233-240
Engelmann, C., Händel, F., Binder, M., Yadav, P.K., Dietrich, P., Liedl, R., Walther, M.
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(2020), Influence of recharge rates on steady-state plume lengths, J. Contam. Hydrol. 235, 103709
Birla, S., Yadav, P.K., Mahalawat, P., Händel, F., Chahar, B.R., Liedl, R.
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(2021), Contamination Assessment and Site-management Tool (CAST): A browser-based tool for site assessment, Groundwater
Yadav, P. K., Birla, S., Baliga, V., Liedl, R., Chahar, B. R., Werth, C. J.
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(2021), Towards predicting DNAPL source zone formation to improve plume assessment: Using robust laboratory and numerical experiments to evaluate the relevance of retention curve characteristics, J. Haz. Mat. 407, 124741
Engelmann, C., Sookhak Lari, K., Schmidt, L., Werth, C. J., Walther, M.
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(2022). An approach for selecting a model for the assessment of potentially contaminated sites, Groundwater
Yadav, P. K., Daulat, S., Birla, S., Nogueira Hernandes, N., Liedl, R., Chahar, B. R.
