Changes in Geochemical Composition of Groundwater Due to CO2 Leakage in Various Geological Media

Improving monitoring network design to detect leaks at hazardous facilities: Lessons from a CO2 storage site

Exploring the challenges posed by uncertainties in numerical modeling for hazardous material storage, this study introduces methodologies to improve monitoring networks for detecting subsurface leakages. The proposed approaches were applied to the Korea CO2 Storage Environmental Management (K-COSEM) test site, undergoing calibration, validation and uncertainty analysis through hydraulic and controlled-CO2 release tests. The calibration phase involved inter-well tracer and multi-well pumping tests, leveraging the Parameter ESTimation (PEST) model to determine the aquifer flow and solute transport properties of the K-COSEM site. To tackle uncertainties with limited observation data, we adopted Latin Hypercube simulation. Our uncertainty analysis confirmed model accuracy in simulating observed CO2 breakthrough curves. We also explored a probabilistic method to identify the environmental change point (EnCP) through correlation analysis with the distance from the CO2 injection well, revealing a linear trend and pinpointed potential preferential flow pathways by assessing detection probabilities. Evaluating CO2 detection capabilities was crucial for optimizing monitoring well placement, highlighting strategic well selection based on detection probabilities. This study advances managing uncertainties in hydrogeological modeling, underscoring the importance of sophisticated models in designing monitoring networks for hazardous leak detection in complex subsurface conditions.

Design, construction, and validation of an in-situ groundwater trace element analyzer with applications in carbon storage

It is estimated that carbon emissions should reach net-zero by 2050 to meet important climate targets. Carbon capture is likely necessary to reach these targets, requiring a long-term storage solution such as geological carbon sequestration. However, as with any subsurface activity, leakage can occur, potentially impacting groundwater quality near the storage site. Rapid detection is essential to mitigate damage to this resource. Since CO₂ will acidify groundwater, the concentrations of acid soluble minerals and associated cations will increase. Thus, an in-situ, real-time element analysis system based on laser-induced breakdown spectroscopy (LIBS) is under development to monitor these elements. The system splits the traditional LIBS system into a miniature, all-optical sensor head built around a passively Q-switch laser fiber coupled to a control unit. Previous work has validated the LIBS technique for use at high pressure as well as the split system design. In this work, a fieldable prototype sensor is developed and tested in an onsite monitoring well where trace elements concentrations (approx. 0-3 ppm) were tracked over 20 days. These concentrations varied in response to local rainfall, diluting with increased rain, demonstrating the ability of a LIBS-based sensor to track trace elements under real-world conditions.

Spatio-temporal variation of groundwater chemistry in the Upper Oti Basin of Ghana

The Oti Basin is located at northeastern part of Ghana. Two major geological formations of Voltaian sedimentary supergroup exist: Kwahu-Morago and Oti-Pendjari groups. A total of 133 groundwater samples and 7 surface water samples were collected for two major seasons, viz. dry season (February, 2020) and wet season (November, 2020), and analysed for cations and anions. This is to determine the sources of ions, including pollutants and the reactions that promote them for sustainable groundwater management. Results of major ions revealed groundwater is potable base on the WHO permissible limits. Wet season nitrate and sulphate were higher than that of dry season, suggesting anthropogenic influence. Pearson's correlation shows major contributors of total dissolved solids were Mg, Na and HCO₃ with a correlation (r = 0.439, 0.874 and 0. 945) respectively. In the wet season, major contributors were TH, Mg, Na, SO₄ and HCO₃ with correlation (r = 0.548, 0.537, 0.856, 0.530 and 0.936) respectively. Gibbs plot suggests chemical weathering and precipitation to be the main contributors to the water chemistry. The dominant hydrochemical facies within the basin for both seasons was Na-K-HCO₃ water type. The plot of Ca²⁺  + Mg²⁺ vs. HCO3^-  + SO4^2- suggests both silicate weathering and ion exchange processes are taking place within the basin. Mineral stability diagrams signify kaolinite as the most stable mineral phase in the groundwater. Chloro-alkaline indices were negative for both seasons leading to base-exchanged softened water production. Consequently, majority of ions evolved from natural geochemical processes whilst nitrate and sulphate presence might be due to anthropogenic sources.

Identification of high nitrate concentration in shallow groundwater of an arid region: a case study of South Kuwait's Bay

Coastal aquifer is a fragile environment due to the interaction of groundwater with seawater, especially in arid environments. Groundwater along Kuwait's Bay is polluted due to discharge of waste from desalination plants, power plants, and other anthropogenic activities. Earlier studies on submarine groundwater discharge in Kuwait's Bay region have reported the transfer of nutrient flux from the groundwater to Kuwait's Bay. The current study focused on nitrate sources and processes governing their distribution in groundwater samples collected from the southern part of Kuwait's Bay. The concentration of nitrate in the samples ranged from 22.7 to 803.9 mg/L. Higher values were noted in the samples collected inland and a few samples adjacent to the Bay. Spearman's correlation analysis of the data indicated that NO₃- has a strong positive correlation with SO₄^2- and moderate positive correlation with Na ⁺ , TDS/EC. The PCA analysis and factor scores revealed the different sources for groundwater nitrate contamination as follows: leakage of sewer lines in the urban region has led to the infiltration of contaminated sewage, high saline environment due to seawater intrusion, chemical weathering, and influence of denitrifying bacteria. The health risk has resulted due to the NO_3- concentration being above the standard limit for adults. Furthermore, the nitrate concentration was higher in the region adjoining the landfills. In addition, the discharge of groundwater with higher nitrate to the adjacent open water in the Bay may lead to eutrophication. Hence, proper management strategies are to be adopted to control the nitrate pollution in groundwater.

Application of Inductively Coupled Plasma Spectrometric Techniques and Multivariate Statistical Analysis in the Hydrogeochemical Profiling of Caves-Case Study Cloșani, Romania

The aim of the study was to develop the hydrogeochemical profiling of caves based on the elemental composition of water and silty soil samples and a multivariate statistical analysis. Major and trace elements, including rare earths, were determined in the water and soil samples. The general characteristics of water, anions content, inorganic and organic carbon fractions and nitrogen species (NO₃⁻ and NH₄⁺) were also considered. The ANOVA—principal component analysis (PCA) and two-way joining analysis were applied on samples collected from Cloșani Cave, Romania. The ANOVA-PCA revealed that the hydrogeochemical characteristics of Ca²⁺-HCO₃⁻ water facies were described by five factors, the strongest being associated with water-carbonate rock interactions and the occurrence of Ca, Mg and HCO₃⁻ (43.4%). Although organic carbon fractions have a lower influence (20.1%) than inorganic ones on water characteristics, they are involved in the chemical processes of nitrogen and of the elements involved in redox processes (Fe, Mn, Cr and Sn). The seasonal variability of water characteristics, especially during the spring, was observed. The variability of silty soil samples was described by four principal components, the strongest influence being attributed to rare earth elements (52.2%). The ANOVA-PCA provided deeper information compared to Gibbs and Piper diagrams and the correlation analysis.

Association of Physicochemical Characteristics, Aggregate Indices, Major Ions, and Trace Elements in Developing Groundwater Quality Index (GWQI) in Agricultural Area

The aim of this study was to propose a groundwater quality index (GWQI) that presents water quality data as a single number and represents the water quality level. The development of the GWQI in agricultural areas is vital as the groundwater considered as an alternative water source for domestic purposes. The insufficiency of the groundwater quality standard in Malaysia revealed the importance of the GWQI development in determining the quality of groundwater. Groundwater samples were collected from thirteen groundwater wells in the Northern Kuala Langat and the Southern Kuala Langat regions from February 2018 to January 2019. Thirty-four parameters that embodied physicochemical characteristics, aggregate indicator, major ions, and trace elements were considered in the development of the GWQI. Multivariate analysis has been used to finalize the important parameters by using principal component analysis (PCA). Notably, seven parameters-electrical conductivity, chemical oxygen demand (COD), magnesium, calcium, potassium, sodium, and chloride were chosen to evaluate the quality of groundwater. The GWQI was then verified by comparing the groundwater quality in Kota Bharu, Kelantan. A sensitivity analysis was performed on this index to verify its reliability. The sensitivity GWQI has been analyzed and showed high sensitivity to any changes of the pollutant parameters. The development of GWQI should be beneficial to the public, practitioners, and industries. From another angle, this index can help to detect any form of pollution which ultimately could be minimized by controlling the sources of pollutants.