Validation of surface-based hydrochemical investigation and the impact of underground facility construction at Horonobe URL

Abstract

We verified the surface-based hydrochemical investigation for deep underground at Horonobe Underground Research Laborator y (URL) at Horonobe, Hokkaido, Japan, and identified the hydrochemical changes during the URL construction. The evaluation of the relationship between the number of boreholes and understanding of water chemistry suggests that three basic borehole investigations and an additional borehole for high permeable geological zone (fault and fractured zone) are required to illustrate cross-sectional hydrochemical distribution including the uncertainty for kilometers scale survey line. The observation and numerical analysis of hydrochemical variation (salinity, pH, ORP) around the URL indicate that the groundwater pressure and the salinity in the vicinity of high permeable geological zone are varying due to groundwater inflow into the drift. The variation was consistent with the prediction reported previously. These results are considered to be referred to the management during surface-based investigation and construction of underground facility at the other sedimentary rock area.

Characterization of sediment and granite hosted deep underground research laboratories reveals diverse microbiome functions, limited temporal variation and substantial genomic conservation

“…Groundwater was recovered from 140 m and 250 m below the surface via tubes into defined intervals of boreholes into the surrounding rock. The Horonobe groundwater is organic rich and saline, dominated by Na + -Cl --HCO3 -(Table S3, Amano et al, 2012;. Temperatures range from 13 -25 °C, pH ranges from 6.4 to 7.2, and Eh values range from -315 to -204 mV.…”

Improvements in Drill-Core Headspace Gas Analysis for Samples from Microbially Active Depths

“…Large variations in δ 13 C CH4 values from the IsoJar™ measurements ( Figure 1) were attributed to methane-oxidizing bacterial activity using sulfate ions in the deep underground environment or to isotopic fractionation during gas migration through fractures [14]. However, these possible causes are considered unlikely because (a) geochemical studies in the Horonobe area indicate that reducing conditions are maintained deep underground and sulfate ions are either absent or present at very low concentrations [29][30][31][32]; (b) studies of iodine enrichment [33] indicates that any traces of methane oxidation by sulfate in pore waters of sediments would have been erased during upward fluid flow due to compaction during burial; and (c) there is no evidence in the study area of isotopic fractionation in gases during migration [34,35]. The δ 13 C CH4 and δ 13 C CO2 values obtained by the EV method ( Figure 1) show little scatter plotting in the carbonate reduction field.…”