Groundwater dating using radiocarbon in fulvic acid in groundwater containing fluorescein

• Separation method of fulvic acid and fluorescein was proposed.
• Humic and fulvic acids were isolated from contaminated groundwater with fluorescein.
• DO14C for fulvic acid was estimated from the mixture of fulvic acid and fluorescein.
• DO14C age for fulvic acid was compared with groundwater age estimated by He.

SummaryNatural DO14C is recognized as one of the most useful tracers in the estimation of groundwater age. Fluorescent dye is commonly used as an indicator of drilling fluid contamination during borehole investigation. Fluorescein (FS) is one of the most frequently used fluorescent dyes, yet as it contains little radiocarbon it may affect DO14C age when it is mixed with natural DOC. In this study, fulvic acid (FA) was isolated from groundwater containing FS and DO14C value of isolated FA was measured. Separation methods were proposed by using the difference between sorption and desorption behavior of FA and FS onto synthetic adsorbent resin. DO14C measurement on FA from a mixture of FA and FS is estimated by removing FS from the mixture and correcting for the amount of C derived from FS.Furthermore, DO14C age is compared with the groundwater age estimated by He. The results show that the values of DO14C age for separated FA estimated by the two methods had good agreement with those that corresponded to groundwater age estimated by He. This result indicates that DO14C is a useful indicator of groundwater age even for groundwater contaminated with FS.