Environmental Assessment of Soil and Groundwater Pollution by BTEX Leaching in Valencia Region (Spain)

Abstract

The impact of hydrocarbon spills in the unsaturated zone is a significant environmental concern, particularly in locations where contamination arises from leaks in underground fuel storage tanks (USTs). This paper presents the outcomes achieved through the utilization of VLEACH, a finite-difference numerical model, to assess the concentrations of organic contaminants in the solid, liquid, and gas phases within the vadose zone. Additionally, it evaluates the mass transfer of pollutants to the aquifer as part of an environmental assessment for the placement of a forthcoming service station. The study encompasses an analysis of 18 scenarios under realistic conditions based on actual field data. These scenarios were constructed, taking into account various factors, including the nature of the leak (one-time or permanent), the depth of the phreatic level, and the soil conditions and properties. The results highlight the potential environmental consequences of a permanent leak as compared to those resulting from a specific accident. The findings further emphasize the substantial influence of soil moisture on transport phenomena within the vadose zone. Variations in soil moisture significantly alter hydraulic conductivity, impact magnitudes, transport velocities, and even the predominant transport mechanism. Consequently, precise delineation of soil moisture becomes a crucial parameter in such simulations. Additionally, it has been observed that each component of BTEX (benzene, toluene, ethylbenzene, and xylene) experiences varying transport velocities through the vadose zone. Benzene, having a greater propensity to concentrate in the liquid and gas phases, exhibits the swiftest movement through the vadose zone. The detection of benzene in aquifers can serve as an indicator of the potential future arrival of the remaining BTEX compounds.