Contaminant transfer in coastal aquifers

Groundwater flow and contaminant transport processes in coastal aquifers can be complicated by tidal effects adjacent to the coast. This study was designed to evaluate the significance of tidal influences on contaminant transport by focusing on one-dimensional homogeneous coastal aquifers. This study formulated a conceptual model and corresponding flow and transport equations, analyzed coastal boundary conditions, numerically solved the contaminant transport equations, and used experiments to verify the numerical results. Based on the results of the numerical and experimental studies, it was concluded that tides can have a significant impact on contaminant transport in coastal aquifers, especially in unconfined aquifers subject to moderate/high tidal amplitudes, when groundwater flow velocity in the aquifer is low, and within areas of the aquifers adjacent to coastal waters. Quantitatively, under these favorable conditions, contaminant discharge can be enhanced by tides by a factor of two or three during the early stages of contaminant discharge, and the enhanced discharge can still be substantial during later stages by 30 to 50 percent. When the groundwater flow is close to stagnant, the tidal impact is most apparent, resulting in significant contaminant discharge tens of years ahead of the case without tides