[A-HW17] Near Surface Investigation and Modeling for Groundwater Resources Assessment and Conservation

[AHW17-P02] Role of the hydrogeochemical transport model on bioremediation of groundwater chlorinated contamination

*Sheng-Wei Wang¹, Chih-Yu Lin¹, Yen-Yu Chen¹ (1.Tamkang University)

Keywords:Groundwater, Bioremediation, Numerical model

The organic chlorinated contamination of groundwater due to industrial development over the past century poses significant threats to water safety and human health globally. Common pollutants include perchloroethylene (PCE) and trichloroethylene (TCE). The inherent complexity of chlorinated organic compounds, particularly dense non-aqueous phase liquids (DNAPL), makes remediation challenging, often requiring substantial time and cost. Traditional methods such as pump and treat and in-situ chemical oxidation (ISCO) are rapid and effective but generate wastewater and energy consumption, leading to environmental burdens or secondary pollution. In recent years, the concepts of green and sustainable remediation have gained prominence, emphasizing socioeconomic benefits and reducing carbon emissions and wastewater volumes. Bioremediation, involving the addition of substrates to stimulate the rapid growth of dechlorinating bacteria and accelerate the dechlorination of contaminants, has emerged as a popular method for chlorinated contamination remediation. However, the heterogeneity of aquifers, surface recharge, boundary conditions, and microbial diversity of dechlorinating bacteria influence the efficiency of bioremediation. This study focuses on a contaminated site in Taiwan, employing the Groundwater Modeling System (GMS) to simulate the transport of chlorinated contamination in groundwater. The RT3D and SEAM3D modules are utilized to simulate the processes of chlorinated contamination transport and degradation reactions, comparing the results with on-site remediation outcomes. Based on hydrogeological drilling investigation, historical rainfall and groundwater level data, a three-dimensional groundwater flow model is established. Based on the strategies of substrates injections, the transport and biodegradation of PCE, TCE, dichloroethylene (DCE), and vinyl chloride (VC) are simulated. The simulation results indicate that increasing substrate concentrations enhance the degradation of PCE and DCE. However, beyond a concentration of 100,000 mg/L, the dechlorination reaction rate does not exhibit a significant increase. This underscores the importance of biological analysis and a reliable simulation model at pre-remediation for determining the optimal concentration for substrate injection. Furthermore, variations in hydraulic conductivity (0.009-0.86m/day) influence the time it takes for dechlorination reactions to occur after substrate injection. Hence, a high-resolution hydrogeological investigation before deciding the remedy is necessary. Typically, in cases of chlorinated groundwater contamination, environmental authorities and responsible parties prioritize the rapid removal of pollutants. However, the results of numerical simulation indicate that a comprehensive understanding of hydrogeological and biogeochemical characteristics significantly affects the efficiency of bioremediation. The optimal design of substrate injection can reduce the PCE concentration by ~65% within 1000 days. Therefore, the numerical simulation, coupled with the hydrogeological surveys and biogeochemical determination, serve as crucial foundations for determining the practical remediation strategies.