Caffeine vs Carbamazepine as indicators for wastewater pollution in a karst aquifer

Abstract. This paper presents the analysis of caffeine and carbamazepine transport in the subsurface during and after sewage discharge in the Sorek creek over outcrops of the Western Mountain Aquifer (Yarkon-Taninim) in Israel. Both caffeine and carbamazepine were used as indicators for sewage contamination in the subsurface. While carbamazepine is considered conservative, caffeine is subject to sorption and degradation. The objective of the study was to quantify differences in their transport under conditions in the carbonate aquifer. A quasi-3D dual permeability numerical model was used to simulate water flow and transport of both pollutants in a vadose zone – aquifer system. The results of this study show that each of these two pollutants can be considered as effective tracers for characterization and assessment of aquifer contamination. Carbamazepine was found to be more suitable to assess the contamination boundaries, while caffeine can be used as a contaminant tracer only briefly after contamination occurred. In instances when there are low concentrations of carbamazepine which appear as background contamination in an aquifer, caffeine might serve as a better marker for detect new contamination events given its temporal nature. The estimated caffeine degradation rate and the distribution coefficient of linear sorption isotherm were 0.091 d−1 and 0.1 L/kg, respectively, which imply a high attenuation capacity. The results of the simulation indicate that around 95 % of carbamazepine mass was retained in the porous matrix of the unsaturated zone by the end of the year, while all of the caffeine was completely degraded a few months after the sewage was discharged.