Physicochemical patterns observed in a groundwater well with CO2 stratification: Learnings from an automated monitoring from South Korean national groundwater monitoring network

Hyun Kwon Do, Yon Gyung Ryuh, Soonyoung Yu, Kyoung Ho Kim, Seong Taek Yun

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1 Citation (Scopus)

Abstract

Unusual episodic fluctuations of electrical conductivity (EC) were observed twice a year in a national groundwater monitoring network well in South Korea where EC was automatically monitored at a depth of 20 m below ground level (bgl). To address the causes of the observed EC fluctuations, this study examined the depth profile of wellbore water in the 70-meter-deep monitoring well screened between 50 and 70 m bgl and cased down to 50 m bgl. The results of well logging, borehole video recording, and hydrochemical analysis of wellbore water indicated that the CO2-rich groundwater entering through the screened zones below 50 m bgl was physicochemically stratified into three layers with distinct EC that were separated by two transition zones in the well: a bottom layer (70–43 m bgl) with an EC of ∼3900 μS/cm, intermediate layer (35–24 m bgl) of ∼1800 μS/cm, and top layer (16–3 m bgl) of ∼300 μS/cm. The first transition zone at depths of 43–35 m bgl was attributed to CO2 exsolution in the open system and the subsequent physicochemical changes of wellbore water, while the second transition zone at depths of 24–16 m bgl was formed by the precipitation of hydrous ferric oxides with consequent sorption of remaining ions due to a sudden change toward the oxidizing environment. The monitoring probe installed at a depth of 20 m bgl was found to be located within the upper transition zone, which caused EC peaks when the well was purged at a depth of 25 m bgl for well maintenance twice a year. This study shows that automated groundwater monitoring systems may misguide one about the groundwater quality if an unexpected physicochemical variation (such as stratification) occurs in a monitoring well. Therefore, the presence of interface zones caused by abrupt changes in EC must be carefully considered when an automated monitoring well is designed. The screened zone is a suitable location for installing an automated monitoring probe to measure the representative water quality (i.e., EC), in particular, in an aquifer that is under the influence of inputs of low-pH and high-TDS fluids (e.g., CO2-rich groundwater and acid mine drainage).

Original languageEnglish
Article number127229
JournalJournal of Hydrology
Volume604
DOIs
Publication statusPublished - 2022 Jan

Bibliographical note

Funding Information:
The completion of this work was financially supported by the Korea CO2 Storage Environmental Management (K-COSEM) Research Center and partly the Subsurface Environment Management Research Project (no. 2021002440003), which were supported by Korea Ministry of Environment through the Korea Environmental Industry & Technology Institute (KEITI). The early-stage field campaigns were supported by the 2010 Eco-Technopia 21 Project of KEITI. A few geologists at the Korea Water Corporation (KOWACO) and graduate students of the Environmental Geochemistry Lab of Korea University helped the field campaigns. We acknowledge anonymous reviewers for providing constructive comments and suggestions on the manuscript.

Funding Information:
The completion of this work was financially supported by the Korea CO 2 Storage Environmental Management (K-COSEM) Research Center and partly the Subsurface Environment Management Research Project (no. 2021002440003), which were supported by Korea Ministry of Environment through the Korea Environmental Industry & Technology Institute (KEITI). The early-stage field campaigns were supported by the 2010 Eco-Technopia 21 Project of KEITI. A few geologists at the Korea Water Corporation (KOWACO) and graduate students of the Environmental Geochemistry Lab of Korea University helped the field campaigns. We acknowledge anonymous reviewers for providing constructive comments and suggestions on the manuscript.

Publisher Copyright:
© 2021 Elsevier B.V.

Keywords

  • Automated monitoring
  • CO exsolution
  • CO-rich groundwater
  • Iron oxy-hydroxides precipitation
  • Physicochemical stratification

ASJC Scopus subject areas

  • Water Science and Technology

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