Carbamazepine breakthrough as indicator for specific vulnerability of karst springs: Application on the Jeita spring, Lebanon

• Carbamazepine breakthrough in a karst spring after a precipitation event.
• Carbamazepine used as old stored waste water indicator.
• Identification of carbamazepine mass loads and source input during event.
• Conceptual model for precipitation event flow and transport in the karst system.

The pharmaceutical drug carbamazepine is considered an effective wastewater marker. The varying concentration of this drug was analyzed in a mature karst spring following a precipitation event. The results show that carbamazepine is an indicator of wastewater entering the system through a fast flow pathway, leading to an increase of the drug concentrations in spring water shortly after a strong rainfall event. The analysis of the breakthrough curve of carbamazepine along with the electrical conductivity signal and major ions chemograph allowed the development of a conceptual model for precipitation event-based flow and transport in the investigated karst system. Furthermore the amount of newly recharged water and the mass of carbamazepine reaching the aquifer system during the event could be estimated using a simple mixing approach. The distance between the karst spring and the potential carbamazepine source was estimated by the combination of results from artificial tracer tests and the carbamazepine breakthrough curve. The assessment of spring responses to precipitation event using persistent drugs like carbamazepine helps assess the effect of waste water contamination at a spring and gives therefore insights to the specific vulnerability of a karst spring.