Groundwater flow modeling in a site affected by Dense Non Aqueous Phase Liquids

Although scientific progress has shown the harmfulness and toxicity to man and the environment of certain pesticides, prohibiting their use, the residues of old productions can still give rise to environmental problems with very significant impacts. Among these, the case of DNAPL is certainly of interest, because these substances, by virtue of their specific weight, can migrate deep into the soil, reaching the bottom of the aquifer and accumulating at high depth, giving rise to contaminations difficult to be addressed. The presence of these substances determines the slow dissolution in the groundwater of compounds that can cause damage to humans and to the ecosystem. It is therefore evident the importance of a reliable characterization of such contaminated sites, and the development of accurate models to be used as a support in the design of the remediation. For this purpose, over the last years the importance of mathematical models of groundwater flow and contaminant transport at contaminated sites has dramatically increased; models are used to better understand the contamination process, to simulate long term scenarios and to support the design of the reclamation interventions, making easier the comparison of alternatives in terms of efficacy in addressing the contamination, long-term expected impacts, and of monetary costs. In this work, developed at the Technical University of Madrid, a numerical model is developed for a complex contaminated site in Spain, impacted by pesticides, using a groundwater flow and transport finite element modelling tool, Feflow. The calibrated model of the site is used to study the interactions between the impacted aquifer system and a surface water reservoir for agricultural, energy and drinking uses, adjacent to the study site, evaluating how seasonal variations in the reservoir level may impact the groundwater. Moreover, transport simulations are used to compare alternative scenarios for the site remediation, considering the injection of soluble reactants and surfactants, for a preliminary evaluation of possible remediation alternative technologies.