APPLICATION OF A COUPLED GROUNDWATER FLOW - REACTIVE CHEMICAL MODEL TO A PERMEABLE REACTIVE BARRIER

摘要

The removal of pollutants from groundwater with permeable reactive barriers (PRB) is an increasingly popular remediation technology. PRBs incorporate hydrogeological features which direct groundwater through a chemically reactive zone where organic contaminants may be decomposed and other contaminants including radionuclides may be immobilsied through precipitation and sorption. At various stages in the design of a site specific PRB hydrogeological and geochemical models can be employed to optimise the design. This paper presents an overview of the functionality and testing of a coupled 3D, finite-element biogeochemical reaction-transport model (TRAFFIC) which can be used to model both hydrogeological and geochemical effects in PRBs and thus provides a useful design tool. Equilibrium and rate limited geochemical processes are considered using a module based on the PHREEQC geochemical code. A wide range of processes can therefore be simulated, which can include processes of metal corrosion, microbiology, mineral precipitation and contaminant sorption which are relevant to the reactions utilised in PRB designs. A PRB model application is presented which considers a scenario where cesium (Cs) contaminant plume present in groundwater is remediated using a zeolite based permeable reactive barrier. The barrier considered is of the funnel and gate design. The PRB model representation considers the combined hydrogeological effects of the barrier design, and chemical effects of ion exchange of the reactive zeolite. The model takes account of geochemical effects of cations present in the groundwater that compete for available ion exchange sites present in the zeolite PRB. The model can be used to predict lifetimes of the barrier for varying loadings of zeolite. It is shown that such models can be used to assist the design of such barriers.