Analytical Study of Reactive Contaminant Transport in a Tide-Induced Groundwater Environment along Unconfined Sloping Coastal Beaches

Coastal beaches are vital to the hydrological system, yet the transport of pollutants, chemicals, bacteria, and viruses through groundwater can lead to contamination. This study develops a reactive contaminant transport model for tidally influenced beaches using various analytical approaches. A one-dimensional hydrodynamic model is established based on Boussinesq's governing equations. After linearizing the nonlinear equations, an analytical solution for sloping aquifers is derived, incorporating rainfall effects. The groundwater flow model's analytical results provide the basis for the reactive contaminant transport model, which includes a first-order decay reaction process. The analytical solution's validity is confirmed through comparisons with previous studies. A root mean square error analysis reveals higher error rates for upward sloping aquifers in both flow and transport models. Concentration profiles of the reactive contaminant plume are examined in relation to spatial and temporal variables, considering decay parameters, retardation factors, rainfall, and sloping angles to the impervious bed in a case study in Tamil Nadu, India. Higher dispersivity in upward sloping induces more dispersion, tending to decrease in concentration, while lower dispersivity causes less dispersion, resulting in the accumulation of contaminants and higher concentration. The study reveals that the concentration of contaminants is higher in sloping aquifers than in the horizontal ones. Increased retardation factor induces a fast decrease in concentration (0 ppm) before reaching the proximity surface. An increase in decay constant and retardation factor leads to a decrease in concentration in sloping aquifer systems. The skewness of concentration is negative for downward sloping aquifers, while it is positive for horizontal and upward sloping aquifers.