Abstract
We conducted multiple laboratory trials in a robust and repeatable experimental layout to study dense non-aqueous phase liquid (DNAPL) source zone formation. We extended an image processing and analysis framework to derive DNAPL saturation distributions from reflective optical imaging data, with volume balance deviations < 5.07%. We used a multiphase flow model to simulate source zone formation in a Monte Carlo approach, where the parameter space was defined by the variation of retention curve parameters. Integral and geometric measures were used to characterize the source zones and implemented into a multi-criteria objective function. The latter showed good agreement between observation data and simulation results for effective DNAPL saturation values > 0.04, especially for early stages of DNAPL migration. The common hypothesis that parameters defining the DNAPL-water retention curves are constant over time was not confirmed. Once DNAPL pooling started, the optimal fit in the parameter space was significantly different compared to the earlier DNAPL migration stages. We suspect more complex processes (e.g., capillary hysteresis, adsorption) to become relevant during pool formation. Our results reveal deficits in the grayscale-DNAPL saturation relationship definition and laboratory estimation of DNAPL-water retention curve parameters to overcome current limitations to describe DNAPL source zone formation.
Highlights
A large number of industrial sites worldwide are affected by contamination of dense non-aqueous phase liquids (DNAPLs) (Fetter et al, 2017; UBA, 2017; Gupta and Yadav, 2019)
We extended an image processing and analysis frame work to derive DNAPL saturation distributions from reflective optical imaging data, with volume balance de viations < 5.07%
Our results reveal deficits in the grayscale-DNAPL saturation relationship definition and laboratory estimation of DNAPL-water retention curve parameters to overcome current limitations to describe DNAPL source zone formation
Summary
A large number of industrial sites worldwide are affected by contamination of dense non-aqueous phase liquids (DNAPLs) (Fetter et al, 2017; UBA, 2017; Gupta and Yadav, 2019). This group of often highly persistent chemicals poses tremendous threats to ecosystems and humankind (Sakari et al, 2008; Fetter et al, 2017), especially when they persist in groundwater that is used as irrigation or potable water (Mackay and Cherry, 1989; EC, 2004). The complex geometrical and physicochemical properties of source zones are, together with subsurface characteristics such as aquifer heterogeneity and hydraulic conditions, the most sen sitive factors in controlling contaminant plume evolution (Soga et al, 2004; Falta et al, 2005; Liedl et al, 2005; Fure et al, 2006; Brusseau et al, 2007; Engelmann et al, 2019a)
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