Environmental isotope study of groundwater discharge from the large karst springs in West Syria: a case study of Figeh and Al-sin springs

Environmental isotopes (delta O-18, delta D and H-3) in precipitation and groundwater were integrated for the description of groundwater discharge from the large karst springs of Figeh and Al-sin located in West Syria. The two springs are considered as the most important springs in this Middle East country due to their huge discharge. The delta O-18 values are -8.91 and -6.49aEuro degrees for Figeh and Al-sin, respectively. The regression line for both precipitation and groundwater is described by the equation: delta D = 7.9 delta O-18 + 19.7, which shows no evaporation during precipitation and suggests that the groundwater is mainly from direct infiltration of precipitation. The altitude gradients in the precipitation were estimated to be -0.23aEuro degrees/100 m for delta O-18. The main recharge areas are 2,100 and 750 m.a.s.l., for Figeh and Al-sin springs, respectively. The tritium concentrations in groundwater are low and very close to the rainfall values of 4.5 and 3.5 TU for Bloudan and Kadmous meteoric stations, respectively. Adopting a model with exponential time distribution, the main residence time of groundwater in Figeh and Al-sin springs was evaluated to be 50-60 years. A value of around 3.9 and 4.2 billion m(3) was obtained for Figeh and Al-sin, respectively, as the maximum groundwater reservoir size.