Hydrochemical and isotopic comparison of crystalline bedrock aquifers in two geological disposal research sites in South Korea using samples collected during and after borehole drilling

Soonyoung Yu, Jang Soon Kwon, Hyun Kwon Do, Gitak Chae, Junghoon Park, Sun Ju Park, Jaehoon Choi, Seong Taek Yun

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

Hydrochemical and isotopic characteristics of crystalline bedrock aquifers were investigated down to 500 m below ground level at two geological disposal research sites. Groundwater samples were collected every 50 m during drilling including water from several fracture zones (n = 24) and at water-conducting fracture zones after the drilling was completed (n = 27) to understand the impact of sampling times, i.e., during versus after drilling, on the characterization result. Both aquifers were highly weathered and showed transport in fractured rocks, which made it difficult to determine the effect of sampling times. Despite the similar ranges of hydraulic conductivities, the BH (gneiss) groundwater showed higher total dissolved solids including Na, F, and HCO3 and carbon-13 isotopes of dissolved inorganic carbon, older carbon-14 ages, but lower dissolved oxygen, oxygen and hydrogen isotopes of water, and sulfur isotopes of sulfate than the AH (granite) groundwater, indicating the extensive water rock interaction through long pathways in BH. Sulfate reduction was also observed in deep anoxic environment in BH, whereas the AH groundwater seemed to be affected by recent recharge through permeable fractures regardless of depth. Redox potential (Eh) increased in samples collected after drilling, in particular in AH, and Fe and negative Eh were not detected in groundwater collected after drilling in both areas, which implied oxidization after drilling in particular in aquifers with recent recharge. The study result suggests isotopic investigations combined with hydrochemical characterization to assess anoxic conditions for geological disposal, if possible, during drilling before grouting to accurately assess the redox condition in crystalline bedrock aquifers.

Original languageEnglish
Article number105560
JournalApplied Geochemistry
Volume149
DOIs
Publication statusPublished - 2023 Feb

Bibliographical note

Publisher Copyright:
© 2023 Elsevier Ltd

Keywords

  • Crystalline bedrock aquifer
  • During and after drilling
  • Fracture
  • Hydrochemistry
  • Isotopic composition

ASJC Scopus subject areas

  • Environmental Chemistry
  • Pollution
  • Geochemistry and Petrology

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