Geochemistry and assessment of groundwater resource in coastal arid region aquifer (Dahab delta, South Sinai, Egypt)

Abstract

Dahab is a tourist city located in the Sinai Peninsula, downstream of the Dahab watershed, as a part of the arid coastal region. Groundwater samples have been collected from the Dahab delta and were tested for salinity, major ions, minor elements, and heavy metals to investigate the geochemical processes deteriorating the groundwater quality. The spatial distribution of major, minor, and trace elements integrated with the geochemical interrelationships using the cumulative salinity bases mixing curves have been utilized to investigate the main source(s) of groundwater recharge and salinization origin in Dahab delta aquifer. The groundwater salinity ranges from 339 upstream of Dahab watershed to 53,216 mg/L downstream in the delta area. The groundwater varies from fresh, brackish, and saline water. The spatial distributions of major ions, minor elements (Si, and Br), and heavy metals (B and Sr) confirm that the recharge comes from the upstream watershed. According to the mixing model curves, groundwater quality has declined due to interactions with the aquifer matrix, mixing with seawater, and rejected brine from the reverse osmosis desalination plants. The fresh/brackish groundwater classes have been recorded in the northwestern part of the study area close to the basement rocks, where the Quaternary aquifer receives considerable recharge through the underneath fractures, joints, and faults that enhance the subsurface recharge. The samples with a high saline groundwater class have been recorded in the eastern and southern parts of the delta, demonstrating the effects of seawater intrusion. Based on WHO guideline criteria, the assessment of groundwater for various uses has determined that most groundwater samples from the alluvial aquifer (91%) are unfit for human consumption. The Water Quality Index indicates that the groundwater in the southern part of the delta is not suitable for all uses due to mixing with the seawater, and injection of rejected brine water from the desalination plants. In the north, groundwater is unfit for drinking and aquatics, excellent for recreation, marginal for irrigation, and fair for livestock. The groundwater in coastal arid region aquifers has deteriorated due to seawater intrusion.