Abstract
Subsurface contamination by light non-aqueous phase liquids (LNAPL) is a widespread global problem that requires appropriate techniques to remediate soil and groundwater. In this paper, the subsurface transport over multiple phases (STOMP) model was used to simulate LNAPL multiphase flow and transport during multiphase extraction (MPE) application in two Brazilian tropical soils (silty sand and oxisol) contaminated by diesel. The model was applied to a hypothetical contamination site, with the initial LNAPL thickness observed in well extraction. The first part consisted of the MPE system sensitivity analysis, varying the applied vacuum and tip tube position. The Van Genuchten α parameter and hydraulic conductivity were the properties that most affected LNAPL saturation and fluid extraction volumes. Suitable applied vacuum and tip tube position parametrization was imperative for the efficiency of LNAPL extraction. After the definition of an appropriate MPE system configuration, simulations demonstrated that the immobile LNAPL saturation affected fluid extraction and diesel oil concentrations in aqueous and gas saturation. The model applied is able to predict LNAPL contaminant behavior in porous media during MPE technique application.
Highlights
In the rapid urbanization that has taken place since the beginning of the last century, fossil fuels have become vitally important, and society still depends on these resources
The occurrence of hydrocarbon fuel leakage, which is generally lighter than water, can generate widespread subsurface contamination, resulting in potentially contaminated areas that may carry major human health and environment risks
Throughout infiltration into the subsoil and spreading, the compounds present in light non-aqueous phase liquids (LNAPL) may partition into one or more phases simultaneously, which include volatile organic compounds, compounds dissolved in water, and LNAPL immiscible in water that may be in a mobile or immobile form or may appear immobile and water-occluded (LNAPL entrapped) in the pores [1,2]
Summary
In the rapid urbanization that has taken place since the beginning of the last century, fossil fuels have become vitally important, and society still depends on these resources. The technique consists of an in situ remediation system, which performs simultaneous recovery of the contaminant constituents in its various phases (gaseous, dissolved, and free), located in the vadose zone, capillary fringe, saturated soil, and groundwater, through an applied vacuum [7]. In addition to simultaneous fluid recovery, the application of MPE predictions needs to include equations that describe both saturated and unsaturated media and the evaluation of dissolved or volatilized contaminants throughout the process, which the developed module addresses. The comparative analysis of contaminant behavior performed in each porous media and the corresponding technique’s achievements defined a suitable extraction configuration For this extraction configuration, a second stage of simulations was accomplished to evaluate the influence of LNAPL entrapment on fluid recovery, and to analyze the influence of the MPE system operation on dissolved and volatilized phases of the contaminant in the soil mass
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