Changes of Hydraulic Conductivity in Coastal Aquifers with the Existence of Illites

Hydraulic conductivity of aquifers is one of important hydrogeological parameters in the seawater-freshwater field, which has a great influence on the scale and extent of seawater intrusion. Columns were subject to a pulse of seawater followed by fresh water or brackish water. Outflow rates and changes in hydraulic head as well as electric conductivity and particle concentrations were monitored over time. Permeability decrease occurred and no particles were found in the outflow when seawater was flushed by fresh water. However, when the concentration of the inflow solution for this replacement decreased gradually, particle releases occurred and permeability also decreased. Results indicate that there exists a distinct variation of permeability of aquifer media in the seawater-freshwater interface, namely a critical value existing in those experiments. The analysis of the experiments suggests deflocculation and release process of illite are the main factors of permeability reduction of sand columns.