Numerical studies of vertical chloride concentration profiles in the aquitards in the Pearl River Delta by diffusion-sedimentation model

Abstract

The effect of sedimentation on solute transport in the aquifer-aquitard system in the Pearl River Delta has not been considered in previous studies. However, sedimentation could have an important influence on the transport of solutes in sediments. A one-dimensional numerical diffusion-sedimentation model is built to reconstruct the observed vertical chloride concentration profiles in a borehole in the Pearl River Delta and a finite difference scheme is applied to solve the model. A reasonably well agreement is obtained between the observed and simulated chloride concentration profiles. The model also presents the chloride concentration profiles at different times of sedimentation. The variation of effective diffusion coefficients and porosities with depth are also included in the numerical simulations. Sensitivity of groundwater velocity on chloride distribution is studied to investigate the effect of groundwater flow on the evolution of the chloride concentration profiles. Results show that the flow of groundwater only has a relatively minor influence on the distributions of the chloride concentrations and diffusion is the dominant mechanism for the transport of chloride. This study presents a theoretical basis for the evolution of chloride distributions in the sediments of the Pearl River Delta.