Hydrochemical processes, bacterial contamination, and isotopic composition of mineral water and sulfur water springs, and signature on GPR observations, Helwan, Egypt

Abstract Helwan area has many sulfurous and mineral water springs known since ancient times. They were used for treatment of many kinds of rheumatoid arthritis and skin diseases. Nowadays, the area is contaminated by domestic, industrial, and agricultural wastewater and the springs’ therapeutic value is diminished by broken pipes and facilities, rendering the waters unusable.The fractured and karstified aquifer, as well as, the near-surface heterogeneity increased the vulnerability of the area to contamination from surface leakage This study addresses the springs` chemical attributes, bacterial contamination, and isotopic composition to assess the water origin, quality, and suitability for human use to retrieve the economic and therapeutic worth of the area. Water samples from eleven springs were analyzed for the major ions and trace elements. The Piper plots show that the majority of water samples exhibit Na-Cl or Na-Cl-SO 4 composition, and the water salinity has originated from dissolution of the carbonate aquifer. The majority of samples are of deep meteoric origin, and a few samples show evidence of recent marine origin. The mineral springs could be distinguished from the sulfur springs as the latter show high temperature, high salinity, a smell of rotten egg (H 2 S), and positive sulphate-reducing bacteria. Almost all of samples show high rates of fecal coliforms , meaning they are contaminated with human and animal wastes due to the near-surface groundwater and the possible leaked water from cisterns and sewage. The signature of the water contamination was clearly observed as a shadow zone and low reflectance on the ground penetrating radar images acquired around the springs. The depleted d 18 O and d 2 H ratios indicate an old Nile water recharge origin mixing with rainwater. The tritium content suggests the possibility of partial recharge from the deep Nubian aquifer. The springs` water in this state is unsafe for human use, and effective practices are needed to manage household, industrial, and livestock wastes and assimilate the springs for therapeutic practices and other human uses.