The Analysis of hydrochemical buffering process at Horonobe Underground Research Laboratory, Japan

Iwatsuki, Teruki  ; Amano, Yuki   ; Murakami, Hiroaki  ; Nanjo, Isao; Aoki, Kazuhiro ; Sasaki, Yoshito ; Yoshikawa, Hideki

This study aims to develop the evaluation methods of environmental changes and the recovery process around a large underground facility. To this end, hydrochemical changes in response to shaft excavation are analyzed based on the observation of water pressure, groundwater chemistry and microbial community structure around the URL. Regarding the chemical disturbance in the area, the redox potential (ORPSHE) of the groundwaters in the monitoring boreholes showed reducing condition (around -200 - -250 mV with pH of approx. 6-7) nevertheless the gallery is in oxidized condition. Theoretical calculation and chemical/microbial analysis of water sample suggests that the dominant redox buffering process around gallery is water-mineral-microbe interaction including iron-, sulphur-bearing materials (mineral and solutes).