The present investigation has been conducted to delineate the hydrogeochemical and environmental factors that control the water quality of the groundwater resources in the north-east of Cairo. A complementary approach based on hydrogeochemistry and a geographical information system (GIS) based protectability index has been employed for conducting this work. The results from the chemical analysis revealed that the groundwater of the Quaternary aquifer is less saline than that of the Miocene aquifer and the main factors that control the groundwater salinity in the studied area are primarily related to the genesis of the original recharging water modified after by leaching, dissolution, cation exchange, and fertilizer leachate. The computed groundwater quality index (WQI) falls into two categories: fair for almost all the Miocene groundwater samples, while the Quaternary groundwater samples are all have a good quality. The retarded flow and non-replenishment of the Miocene aquifer compared to the renewable active recharge of the Quaternary aquifer can explain this variation of WQI. The index and overlay approach exemplified by the DUPIT index has been used to investigate the protectability of the study aquifers against diffuse pollutants. Three categories (highly protectable less vulnerable, moderately protectable moderately vulnerable and less protectable highly vulnerable) have been determined and areally mapped.
Nowadays, irrigation uses large amount of marginal wastewater due to continuous decline in fresh water supply. As a consequence, using this wastewater for different purposes can cause some adverse environmental impacts. Anthropogenic activities such as septic tanks, sewage ponds, and polluted drains have large influence on deterioration of shallow groundwater aquifers. So, construction of many wastewater treatment plants in these areas is mandatory to control and mitigate this deterioration. Groundwater vulnerability assessment maps and contamination simulation in unsaturated zone can be beneficial in understanding contaminants pathways and groundwater quality evolution. This work is mainly focused on aquifer vulnerability assessment to pollution and the role of vadose zone in attenuation of contaminants transport through it prior to groundwater seepage. Therefore, about 56 drainage and groundwater samples were collected and analyzed for potentially toxic elements. The most vulnerable sector was determined using GOD method revealing that central parts of the study area are the most threatened zones with some scattered sporadic zone of sensitivity to pollution and this was verified through the zonation of Pb, Fe, and Mn spatial concentrations. The leakage of these elements through the unsaturated zone was further simulated using HYDRUS-1D model for the next 10-year period to determine the extent of the pollution plumes and maximum concentration of these elements that percolate to the groundwater directly. The concentration of Fe, Pb, and Mn at the end of the simulation reached low concentrations at the bottom layer of the unsaturated zone.
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