Influence of seawater intrusion and heavy metals contamination on groundwater quality, Red Sea coast, Saudi Arabia.

Groundwater samples were collected from 115 boreholes and dugwells to document the influence of seawater intrusion and heavy metals contamination on groundwater quality of the Al Qunfudhah region along the Red Sea coast, Saudi Arabia. The groundwater quality index (GWQI), metal index (MI), and heavy metal pollution index (HPI) were calculated and multivariate analyses were conducted. pH, EC, TDS, Cl-, HCO3-, SO42-, NO3-, NO2-, PO43-, SiO2, F-, NH4+, Ca2+, Mg2+, Na+, K+, B, Ba, Cd, Cr, As, Ni, Pb, Se, Sb, Hg, Cu, and Zn were analyzed and interpreted. The average values for TDS, Ca2+, Mg2+, Na+, K+, Cl-, HCO3-, SO42-, B, and Se were greater than the permissible limit of WHO standards for drinking water. Piper plots indicated three types of groundwater facies, Na-K-SO4-Cl (72.50%), Ca-Mg-So4-Cl (25.50%), and Na-K-CO3-HCO3 (2%). Based on GWQI, MI, and HPI, approximately 37-70% of the groundwater samples fell under poor quality to unsuitable waters (strongly to severely affected), especially in the western part along the Red Sea coast. This proven the role of seawater intrusion through the NE-SW fault system, dissolution/precipitation of carbonates, silicates, fluorite, and gypsum, as well as anthropogenic factors in increasing the concentrations of heavy metals and controlling the chemistry and quality of the groundwater in the study area. These findings provide an important information on heavy metals pollution in coastal aquifer with seawater intrusion along the Red Sea.