Hydro-geochemical and isotopic composition of ground water in Helwan area

The present study examines the hydro-geochemical and isotopic composition of eight ground water samples at Helwan governorate area in order to identify the main hydro-geochemical processes controlling their chemical content as well as to assessing the quality of these waters. For such purpose of study, many parameters have been analyzed such as pH, electrical conductivity, total dissolved solids (TDS), hardness, major cations and anions. Also, one surface Nile water sample was analyzed and compared with the results of ground water samples. Various water quality classification systems were used to characterize the different ground water types.The chemical composition of the studied ground water is strongly influenced by the lithology, especially limestone, and dolomitic limestone. The processes contributing the concentrations of major ions depend on carbonate dissolution and cation exchange. Piper diagram showed that bicarbonate is the dominant anion in all the studied ground water samples and the majority of the samples are characterized by mixed cationic composition where no dominant cation is present and thus classified into two water types: Ca–Na–Mg–HCO3 type and Na–Ca–HCO3 type. All samples are grouped as Normal-chlorinated, Normal-sulfated, while most samples are grouped as Hyper-carbonated.The source aquifers of most ground water samples are continuously replenished by fresh samples. This can be verified by studying the genetic systems of the ground water aquifers and most of the ground water samples source in an area of ground water recharge.The environmental stable isotopes oxygen and hydrogen (18O, and deuterium) were studied and used to identify the sources of recharge. The studied ground waters are enriched in D and 18O and the isotopic features suggest that most of the ground water recharged indirectly after evaporation prior to infiltration from irrigation return water as well as the contribution from Nile water.