Determination of dissolved oxygen concentration in groundwater

Aosai, Daisuke; Hagiwara, Hiroki  ; Shingu, Shinya; Yamamoto, Yuhei; Fukuda, Akari; Suzuki, Yohei*; Mizuno, Takashi   

The hydrochemical investigation focused on the deep groundwater is generally conducted by using groundwater samples taken from deep boreholes. It is impossible to avoid the contamination of the groundwater from drilling fluid during borehole drilling. Although the groundwater samples taken from borehole is contaminated with drilling fluid, the ratio of the contamination can be evaluated based on the tracer (e.g. fluorescence dye) concentration that is added to the drilling fluid, quantitatively. This methodology can apply to quantitative determination of major element and isotopic composition in groundwater by extrapolating. However, it is not argued about the applicability of this methodology for the quantitative and/or qualitative determination of minor elements, microbes, organics and colloid in groundwater. This study aimed to understand the impact caused by borehole drilling to hydrochemical properties focused on the concentration of dissolved oxygen (DO). As the result, some knowledge was obtained as follows; (1) Oxygen intruded into in-situ groundwater during drilling even though borehole was artesian condition. (2) The contamination of DO during borehole drilling can be monitored by measurement of DO concentration. (3) It is recommended that DO concentration should be measured by Winkler method in addition to common electrode method for obtaining the reliable result.