Groundwater dating using radiocarbon in fulvic acid in groundwater containing fluorescein

Summary Natural DO 14 C 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 DO 14 C age when it is mixed with natural DOC. In this study, fulvic acid (FA) was isolated from groundwater containing FS and DO 14 C 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. DO 14 C 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, DO 14 C age is compared with the groundwater age estimated by He. The results show that the values of DO 14 C 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 DO 14 C is a useful indicator of groundwater age even for groundwater contaminated with FS.