Radiocarbon loss from DIC in vadose water flow above the Judea Aquifer, Israel

The roof over the Soreq Cave in Israel was used to model the rate of transport in the vadose zone of the Mountain Aquifer of Israel. This aquifer is of great importance because it supplies 30% of the water consumption for the country. ¹⁴C was measured in drip water from stalactites and in pool water in the cave, under varying thickness of cave roof, which represent different depths in the vadose zone. The flow rate of water through the roof has been determined with tritium analysis to be ∼1 m yr^-1. From this flow rate the corresponding atmospheric ¹⁴C activity at the time of deposition of rain on top of the vadose zone could be determined. The ratio of the measured ¹⁴C activity in drip and pool water to that of the atmosphere was then calculated. From this, the initial value of ¹⁴C activity of water at the entrance to the aquifer was found to be 0.63 ± 0.03 relative to the atmosphere. A model for the chemical interaction between the DIC and the host rock was developed. The average rate of the reaction was found to be 3.5 ± 0.3% yr^-1.