Practice of Mass Transport Model Application for Biogeochemical Redox Process in Aquifer

Biogeochemical reduction processes are active in alluvial aquifers, because organic carbon which is indispensable for bacteria growth is abundant. As a result of reduction process, significant changes of groundwater quality take place; denitrification, reduction of manganese dioxide, iron-hydroxide, sulfate, arsenate, and methane are well known as reduction processes in an anaerobic groundwater condition. Therefore, the prediction of redox environment in an aquifer is a key subject in order to understand how the groundwater quality is affected. If the mechanism of groundwater quality formation in aquifer scale is systematically understood, impacts caused by accidents or illegal dumping can be predicted, and subsequently, an appropriate management of aquifer will be established. In the present paper, quantitative discussions are made by the numerical simulations applied for the one-dimensional column experiment and two-dimensional fresh-salt water mixing zone. Recommendation and the future subject are presented through the results of two numerical simulations. 1. Introduction Groundwater quality is strongly affected by aquifer matrix and varies in space and time. Dissolution from base rocks and minerals, ion exchange, adsorption/desorption, decay and biological degradation are the major processes which should be taken into consideration when the characteristics of groundwater quality are discussed. Hydrological and hydrogeochemical factors are needed to be simultaneously considered because the chemical species are affected by the groundwater flow also. The application of the combined mass transport model with groundwater flow is therefore useful for analyzing the above processes quantitatively. The bacteria mediated geobiochemical processes are significant amongst above processes, specifically in alluvial aquifers where human activity is intensive and impact of various waste is frequent; nitrate pollution is serious for drinking water. Dissolved manganese and iron released in the anaerobic aquifer are often the causes of unpleasant taste for drinking. Furthermore, sulfate and arsenite detected in anaerobic environment are both harmful for living beings [1, 2]. Compared to the remarkable applications of the bacteria technology in the field of medical treatment and food industry, its application to the field scale geochemical study is yet limited. As the authors view, the papers by Kinzelbach and Sch？fer [2], Lensing et al. [3], and Hunter et al. [4] have contributed to widen the modeling approaches to bacteria mediated processes taking place in aquifers.