Hydrochemical disturbances measured in groundwater during the construction and operation of a large-scale underground facility in deep crystalline rock in Japan

Abstract

Changes in the hydrochemical conditions of groundwater were evaluated following the construction of a large-scale underground facility at the Mizunami Underground Research Laboratory (MIU), Japan. The facility was constructed to a depth of 500 m in sedimentary and granitic rocks. Drawdown of the groundwater level in the range of several tens to hundreds of meters was observed up to hundreds of meters away from the shafts during the first ten years of facility construction and operation. Subsequent changes in groundwater chemistry occurred due to upconing of high-salinity groundwater from the deepest part of the shaft and the infiltration of low-salinity shallow groundwater. We predict that future deep groundwater chemistry in the vicinity of the MIU facility will resemble that of the present-day shallow groundwater. Multivariate statistical analysis provides fundamental insights into such a site. We found that the extent of hydrochemical variability related to MIU construction and operation was dependent on the distance from the facility shafts and galleries and on hydrogeological compartmentalization resulting from lithological boundaries (such as permeable conglomerates vs. more compact lithological units) and other features (such as faults or clay layers). We conclude that hydrochemical impact assessment of groundwater in low-permeability rock is essential prior to the construction of such a facility. This should include characterization of hydrogeological structures and compartments to propose suitable location of shafts and galleries.

Ecological and genomic profiling of anaerobic methane-oxidizing archaea in a deep granitic environment

“…The lengths of horizontal boreholes named the HFDB and SFDB were~100 m. The HFDB and SFDB were located at a depth of 300 mbgl and previously referred to as 09MI20 and 09MI21, respectively (Suzuki et al, 2014;Iwatsuki et al, 2015;Ino et al, 2016). The boreholes were drilled mostly with outflowing groundwater.…”

“…The granitic bedrock of the URL has both highly fractured and sparsely fractured domains (hereafter referred to as HFDB and SFDB, respectively). At a depth of 300 m below the surface, we drilled horizontal boreholes into the HFDB and SFDB with outflowing groundwater in 2009, an approach that minimized contamination (Figures 1a and b;Suzuki et al, 2014;Iwatsuki et al, 2015;Ino et al, 2016). The evidence supporting the involvement of ANME-2d in AOM was deduced from (1) the correlated abundance of ANME-2d phylotypes with hydrologic and geochemical features, (2) the recovery of a near-complete genome from the subsurface ANME-2d from the site showing evidence of a complete reverse methanogenesis pathway but interestingly lacking nitrate reductase and large multiheme cytochromes and (3) tracer studies with 13 CH 4 showing sulfate-dependent AOM in the granitic groundwater.…”

Deep microbial life in high‐quality granitic groundwater from geochemically and geographically distinct underground boreholes

“…During the construction of underground facilities, the intrusion of shallow groundwater into the deep aquifer is extensive and significantly alters the chemistry and microbiology of the original groundwater (Banwart et al, 1996;Gascoyne and Thomas, 1997;Pedersen et al, 2014). At the Mizunami underground research laboratory (URL), mixing of shallow and deep groundwaters was artificially caused by the shaft construction in the highly fractured domain of the granitic basement (Suzuki et al, 2014;Iwatsuki et al, 2015). In contrast, artificial mixing was not evident in the sparsely fractured domain.…”

Numerical Simulation on Damage and Failure Mechanism of Rock under Combined Multiple Strain Rates

“…e similar rockburst study was experienced at the Kolar goldfield, India in the 1960s [34]. Moreover, in order to examine the excavation damaged zone (EDZ), many field laboratories were established, such asÄspö Hard Rock Laboratory (HRL) [35,36,37] in Sweden, AECL Underground Research Laboratory (URL) [38,39,40] in Canada, Kamaishi mine [41] and Mizunami Underground Research Laboratory [42] in Japan, Mont Terri Rock Laboratory [43,44] and Grimsel Test Site [45] in Switzerland, Mol Underground Research Laboratory [46,47] in Belgium, and Meuse/Haute-Marne Underground Research Laboratory [48,49] in France. In China, the rockburst studies in the tunneling of Jinping project made significant contributions to the development of rockburst prediction [50,51].…”