An Integrated Approach for Deciphering Hydrogeochemical Processes during Seawater Intrusion in Coastal Aquifers

For managing the freshwater in the worldwide coastal aquifers, it is imperative to understand the hydrogeochemical processes and flow patterns in the mixing freshwater/saltwater zone. The Egyptian Nile Delta aquifer is a typical example. The management of seawater intrusion (SWI) requires detailed investigations of the intrusion wedge and the dynamic processes in the mixing zone. Thus, a multidisciplinary approach was applied based on holistic hydrogeochemical, statistical analysis, and DC resistivity measurements to investigate the lateral and vertical changes in groundwater characteristics undergoing salinization stressor. The results of cross plots and ionic deviations of major ions, hydrochemical facies evolution diagram (HFE-D), and seawater mixing index (SMI) were integrated with the resistivity results to show the status of the SWI where the intrusion phase predominates in similar to 2/3 of the study are (similar to 70 km radius) and the compositional thresholds of Na, Mg, Cl, and SO4 are 600, 145, 1200, and 600 mg/L, respectively, indicating that the wells with higher concentrations than these thresholds are affected by SWI. Moreover, the results demonstrate the efficiency of combining hydrogeochemical facies from heatmap and resistivity investigations to provide a large-scale characterization of natural and anthropogenic activities controlling aquifer salinization to support decision-makers for the long-term management of coastal groundwater.

Automated summary

Understanding the hydrogeochemical processes and flow patterns in the mixing freshwater/saltwater zone is crucial for managing freshwater in worldwide coastal aquifers. This study focuses on investigating the seawater intrusion in the Egyptian Nile Delta aquifer through a multidisciplinary approach involving hydrogeochemical, statistical analysis, and DC resistivity measurements. The results show the status of the seawater intrusion and provide insights into the compositional thresholds of certain ions, indicating wells affected by the intrusion. The study also demonstrates the effectiveness of combining hydrogeochemical facies and resistivity investigations for large-scale characterization and management of coastal groundwater.