A New Model in Θ-STOCK to Numerically Model NAPL Contaminant Transport through Unsaturated Porous Media
Kiarash Jafarzadeh, Behrouz Gatmiri, Omid Ghasemi‐Fare, Mohammad Amin Hassani
Abstract
The present paper aims to study the spatial-temporal behavior of insoluble pollutants in unsaturated soils. Soil, serving as the primary habitat for most animal and plant species and as a major source of drinking water, is constantly subjected to various environmental damages. The introduction of hydrocarbon pollutants into the soil and groundwater aquifers is highly dangerous and, unfortunately, common in nature. The transport phenomenon of insoluble pollutants in porous media is governed by the complex interactions between capillaries, viscous forces, gravity, mass transfer between different phases, and chemical and biological reactions. Understanding the behavior of pollutants in the soil subsurface is essential for providing effective solutions for the recovery of contaminated sites, risk assessment, and addressing damages caused by reservoir leakage, as well as quality control of groundwater resources. In this study, a numerical model was developed using the numerical code of Θ-STOCK finite element. The insoluble pollutant phase was introduced into the model, forming an environment consisting of solid earth, water, gas, and insoluble pollutants. The permeability of each fluid is one of the most important parameters that should be determined, as it is related to fluid saturation and capillary pressure; therefore, the constitutive relationship between relative permeability, saturation, and capillary pressure governing the transport of Non-Aqueous Phase Liquids (NAPLs) in porous media has been incorporated into the model. The three-phase k-S-P model was idealized as two interrelated sub-models: saturation–capillary pressure and relative permeability–saturation. A parametric study was conducted to evaluate the performance of the developed code. The comparison of the obtained results with other numerical and physical models showed that the performance of the developed model is satisfactory.