[A-HW25] Near Surface Investigation and Modeling for Groundwater Resources Assessment and Conservation

[AHW25-02] Apply THMC Software to Simulate the Porosity Reduction in a Permeable Reactive Barrier-Aquifer System

*Thi-Tuyet-Han Nguyen¹、Jui-Sheng Chen^1,2 (1.Graduate Institute of Applied Geology, National Central University, Taoyuan, Taiwan、2.Center for Advanced Model Research Development and Applications, National Central University, Taoyuan, Taiwan)

キーワード：Permeable reactive barrier (PRB), Zero-valent iron (ZVI), Thermal-Hydrology-Mechanic-Chemical (THMC), Porosity reduction

Permeable reactive barrier (PRB) involving zero-valent iron (ZVI) is an in-situ technique for treating groundwater contaminants. Chemical reactions take place inside the PRB, promoting secondary mineral precipitation and leading to a decrease in the porosity of the PRB. When the porosity reduction, flow path reorientation, residence time changes, and bypassing occur. This study used THMC software, a numerical model of Thermal-Hydrology-Mechanical-Chemical (THMC) through multiple phases, to determine porosity reduction through flow modelling and the chemical reactions occurring within the PRB. According to the groundwater flow model, PRB has a permeability higher than the neighbouring aquifer materials, allowing water to pass through quickly and preserving the groundwater's hydrogeology despite removing contaminants. The model result indicates that porosity loss is most significant at the entrance face, followed by a fall and stabilisation after 0.2 m at the PRB entrance. Aragonite, siderite, and ferrous hydroxide reduce porosity by more than 99%. This model highlights the relative effect of concentration by illustrating porosity losses for the high and low levels of bicarbonate and sulfate entering groundwater. The concentration of bicarbonate significantly impacts the reduced porosity caused by the formation of precipitated carbonate minerals. The rate coefficient also influences porous reduction, while the anaerobic iron corrosion rate coefficient is highly sensitive to porous reduction due to iron corrosion influencing the formation of Fe²⁺, OH^-, and the precipitation of Fe(OH)₂. Therefore, this research aims to use THMC to simulate the decrease of porosity in PRB, investigate the factors that should be considered when predicting porosity loss from mineral clogging in PRB and analyze the reduction of porosity over time.