Determination of humic substances in deep groundwater from sedimentary formations by the carbon concentration-based DAX-8 resin isolation technique

Abstract

ABSTRACTConcentrations of humic substance (HS) in deep groundwater from sedimentary formations were determined by the carbon concentration-based DAX-8 resin isolation technique. The groundwater samples were collected from test galleries at depths of 140, 250 and 350 m at the Horonobe Underground Research Laboratory (URL) in Hokkaido, and two observation wells with different depths of 560 and 1050 m in Niigata, Japan. The analytical condition was optimized for the groundwater samples with a high salinity and a high concentration of dissolved organic matters (DOMs). The analytical results showed that the HS concentrations varied from 7.8 to 23.5 mg-C dm−3, depending on the depth and the area. The HS proportions to DOM (%HS) were evaluated to be 58 – 67% and slightly decreased in the deeper groundwater. The regression analysis showed that the HS concentrations are positively correlated with the DOM concentrations. In addition, the low deviation of the %HS values from the slope in the regression equation indicated that the slight variation of %HS can be trivial in the prediction of the concentration of HS. In previous studies, HS concentrations in the groundwater had been determined with a large uncertainty and potential usage of the regression equation for the prediction had not been elucidated. Therefore, the results in this study can provide useful information on the HS concentration and its prediction from the DOM concentration in deep groundwater from sedimentary formations.