Using isotopes for dating and residence time of groundwater in an aquifer, a case study at Al-Najaf, Middle Iraq
Groundwater is the main source for sustaining life when surface water and rivers are scarce. Groundwater in the Najaf Desert helps sustain human and animal lives. The Dammam aquifer is considered the main source of groundwater in the study area. The isotope elements were used as a geochemical indicator to determine the age, direction of flow and the effect of rainwater on this formation. Stable isotopes δ18O and δD (Deuterium) are analyzed in rainfall and groundwater. Their values ranged between -2.56‰ and -1.99‰ and between 7.12‰ and -4.84‰ for δ18O and 2H with an average of -2.32‰ and -6.20‰ in rainfall respectively. Their values ranged from -3.26‰ to -2.01‰ for δ18O and from -27.00‰ to -16.21‰ for δ2H with an average of -2.70 and -22.27 in the Dammam groundwater respectively. Radioactive isotopes 3H (tritium) and 14C are analyzed in groundwater. The groundwater is old and does not mix with modern water, because tritium was not detected. The δ18O and δD values indicate the rainwater, which supplies the aquifer, is not from the continental lands in addition and reflects a humid and cold climate and the high amount of rainfall in the past. Analyses of 14C indicate that the groundwater date is approximately 4176.075 years before the present. The groundwater is moving from the West and southwest to the North and Northeast directions.