How to Predict the Efficacy of Free-Product DNAPL Pool Extraction Using 3D High-Precision Numerical Simulations: An Interdisciplinary Test Study in South-Western Sicily (Italy)

Dense nonaqueous phase liquids (DNAPLs) are known to be denser than water and immiscible with other fluids. Once released into the environment, they migrate downward through the variably saturated zone, causing severe damage. For this reason, it is essential to properly develop a rapid response strategy, including predictions of contaminant migration trajectories from numerical simulations modeling. This paper presents a series of simulations of free-product DNAPL extraction by means of a purpose-designed pumping well. The objective is to minimize the environmental impact caused by DNAPL release in the subsurface, estimating the recoverable free-product DNAPL, depending on the hydraulic properties of the aquifer medium, and estimating the leaving residual DNAPL that could act as a long-term pollution source. Coupling the numerical simulations to the bacterial community characterization (through biomolecular analyses), it was verified that (i) the DNAPL recovery (mainly PCE at the study site) through a pumping well would be almost complete and (ii) the application of other remediation techniques (such as bioremediation) would not be necessary to remove the pollution source because (iii) a natural attenuation process is provided by the autochthonous bacterial community, which is characterized by genera (such as Dechloromonas, Rhodoferax, and Desulfurivibrio) that have metabolic pathways capable of favoring the degradation of chlorinated compounds.