The groundwater of the Quaternary and Upper Cretaceous aquifers forms an important source for water supply at Wadi Hodein area. The main objective of the present work is to study and evaluate the hydrogeochemical characteristics of these aquifers. To achieve that, field and laboratory measurements were carried out for 27 groundwater samples.
The groundwater salinity of the Quaternary aquifer increases from the upstream portions (ranged between 1363.29 and 2419.19 ppm) to downstream (ranged between 4969.5 to 5171.8 ppm) reflecting brackish to moderately saline water, respectively. At the upstream portions, the main sources of groundwater salinization are the dissolution of minerals due weathering with a consequent evaporation and concentration of salts. At the Delta of Wadi Hodein, the main sources of salinization are the leaching of the residual old saline water between rock pores and dissolution of sabkha deposits. Besides, heavy exploitation of hand dug wells increases the leaching process and dissolution of salts causing salinization. The study of the hydrochemical parameters as well as Base Exchange Index excludes the possibility of any significant seawater infiltration. The rCl/rBr, rBr/rI and rB/rCl ratios indicate groundwater enrichment with bromide, iodide and boron concentrations. This is attributed to the breakdown of organic matter, weathering of granitic and meta-gabbroic rock fragments and leaching of evaporites and clay.
The groundwater salinity of the Upper Cretaceous aquifer varies from 287.56 ppm to 3137.15 ppm, reflecting fresh to brackish water types. 75% of groundwater samples reflect normal good groundwater, while 25% of samples indicate contamination due to leaching of marine sediments. The hydrochemical composition of groundwater reflects that 80% of groundwater samples have Na2SO4 and NaHCO3 salts of meteoric origin, whereas MgCl2 salt of marine origin dominates 20% of groundwater samples. The presence of MgCl2 salt indicates that, the groundwater still reflect the marine water characters due mixing and leaching of marine sediments.
The saturation indices of relevant minerals in the Quaternary and Upper Cretaceous groundwater samples were calculated using WATEQ-F computer-program. The results indicate that, the saturation indices of dolomite, magnesite, talc, goethite, magnetite and hematite are positive values, indicating super-saturation and precipitation of these minerals. On the other hand, the saturation indices of celestite, halite, anhydrite and gypsum are negative values, indicating sub-saturation and potential for dissolution of these minerals in groundwater.
*-The groundwater of the Quaternary aquifer is unsuitable for drinking, irrigation, livestock and poultry purposes, whereas 75% of groundwater samples of Upper Cretaceous aquifer are classified as suitable for the same purposes.
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