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Recently, global urbanization and industrialization have resulted in excessive groundwater exploitation, and the occurrence and damage of land subsidence to human life and property are increasing accordingly. The present study assessed the impact of tunnel excavation on the groundwater system and potential land subsidence in a Korean metropolitan area. A numerical model was established to predict groundwater level variations with tunnel excavation, and the mechanisms and cases of land subsidence worldwide were reviewed. The established model adequately represented the groundwater system in the study area. The tunnel excavation decreased the groundwater level along the tunnel line, and significant groundwater drawdown primarily occurred up to 6.1 m at locations with high permeability, leading to the temporary development of a large depression cone. The study area has favorable conditions for land subsidence, and curved tunnel excavation may induce ground disturbance, resulting in groundwater inflow and soil loss in the region. In addition, the risk of land subsidence is expected to persist owing to the lag time caused by the creep phenomenon, even though the groundwater level recovers. Efforts to effectively reduce land subsidence damage in urban areas are crucial, requiring measures such as controlling land subsidence occurrence and implementing prevention measures through early recognition, including artificial recharge of groundwater, underground cavity observation with ground penetrating radar, land subsidence observation with a borehole extensometer, and groundwater level monitoring systems. [ABSTRACT FROM AUTHOR]

Accessory minerals in granitic rocks are unlikely significant radionuclide contributions to groundwater due to their remarkable durability. However, accessory minerals incorporating U and Th may suffer structural damages due to the radioactivity and become highly susceptible to alteration. This study investigates geochemistry coupled with textural analysis of the U–Th bearing accessory minerals using a field emission scanning electron microscope and an electron probe micro-analyzer. Altered zircons with numerous open structures related to the radioactive decay show higher contents of U and Th and low analytical totals. Some thorites show high contents of U and non-formula elements due to the hydrothermal alteration in the metamicted thorite. The cerianite including U occurs as micro-veinlet in fracture with trace of Fe and Mn oxides, which indicates secondary phase formation from the decomposed accessory minerals in an oxidizing environment. Some accessory minerals with the high content of U and Th have been found in Mesozoic granite terrain in South Korea, where high concentration levels of radionuclide in groundwater were also reported. The leaching of U may be more likely when the accessory minerals are highly metamicted or altered as found in our samples. The altered zircon and thorite of the study area could be major carriers of radioelement in Mesozoic granitic aquifers where the occurrence of soluble U-minerals has not been reported. [Display omitted] • High radionuclides concentration in groundwater poses a threat to human health. • Accessary minerals can enrich groundwater with radionuclides in granite aquifers. • Altered zircons contain high U and Th levels with open structures. • Thorites show elevated U levels and non-formula elements due to alteration. • Metamicted and/or altered accessory minerals increase uranium leaching potential. [ABSTRACT FROM AUTHOR]

[Display omitted] • Groundwater Deficit (GWD) highlights delayed response to precipitation decline. • GWD characterizes and quantifies groundwater drought, including spatial extent. • GWD identifies thirteen drought events over a two-decade span in South Korea. Although South Korea is frequently subjected to monsoons, the shortage of summer monsoons and relatively dry spring and winter seasons cause droughts in the Korean Peninsula. Since the late 1960s, severe droughts in South Korea have encouraged extensive groundwater development for agricultural and economic growth. Therefore, identifying and estimating the impact of droughts on the country's groundwater resources is crucial for establishing policies and regulations on groundwater exploitation and recharge. Current drought management of the country relies on a meteorological drought index. However, these estimates lack a comprehensive understanding of absolute drought severity and propagation. This study aims to develop a quantitative method for calculating the frequency and severity of groundwater droughts based on the Groundwater Deficit (GWD) derived from NASA's Gravity Recovery and Climate Experiment (GRACE) mission data. The estimated annual GWD in mass over the country ranges from -0.07 km3 to 0.04 km3, with a trend in the mass of -1.60×10−3 km3/year from 2002 to 2021. Thirteen groundwater drought events were identified based on GWD. Among those, the highest drought severities recorded in 2015 and 2019 were -34.27 km3 months and -55.38 km3 months, respectively. Monthly deficits define the quantity of water required to restore normal groundwater storage conditions. Hence, the minimum and average days to recover from groundwater droughts were estimated based on the strength of the storage-based approaches. The GWD approach aligns with meteorological drought databases with a time lag. It illustrates the transition from meteorological drought to groundwater drought, along with their onset, cessation, propagation, instantaneous severity, and peak magnitude. [ABSTRACT FROM AUTHOR]

In the Republic of Korea, Haean basin is the largest agricultural area in Soyang watershed which is drinking water source for more than 20 million people residing in Seoul metropolis. It is important to investigate any factor affecting the stream or groundwater quality, especially nitrate () concentration in Haean basin which can affect drinking water quality of Soyang watershed. For this purpose, multiple environmental tracers were studied, including major ions and stable isotopes of water (δ2H and δ18O). Stream and groundwater samples were collected from six predominant agricultural land uses located at different elevation points in the study area. Fields with high fertilizer amounts at intermediate to low elevation using flood irrigation method, had contaminated water. Mixing model of chloride (Cl−) and δ18O indicated groundwater recharge from precipitation and lateral inflow from fields at intermediate to low elevation, regarding solute inputs. Another mixing model and δ18O defined the existence of lateral inflow of agricultural water in fields at low elevation. The highest water contamination was found in ginseng fields located at high, intermediate, and low elevation, for (68.79 mg/L), exceeding the World Health Organization standard of 50 mg/L in groundwater. This explains that anthropogenic agricultural practices (high fertilizer amounts and flood irrigation) through precipitation and lateral inflow of agricultural water recharge processes, are the major source of groundwater contamination in Haean basin. After anthropogenic inputs, elevation complexity has played a role in spatial heterogeneity of in stream and groundwater. Findings of this study presents a need to focus on ginseng fields and their agricultural practices to maintain stream and groundwater quality of nearby aquifer. [ABSTRACT FROM AUTHOR]

We present a review of groundwater studies over the past 50 years (1968-2017) in Korea. With economic and agricultural growth, water demand has been expanding, and groundwater development is gradually increasing. Initially, groundwater studies were largely focused on using pumping and slug tests to understand aquifers in Korea. However, the interest has expanded to groundwater monitoring and data analyses, as many national and local networks for monitoring groundwater quantity and quality have been implemented. Frequent severe droughts in recent decades have led to research on the design and pilot tests for managed aquifer recharge, especially on the volcanic island of Jeju and agricultural areas. As groundwater development and its use has increased, groundwater contamination is becoming a public grievance. Thus, effective investigation of contaminated groundwater and its efficient remediation are big issues in the Research and Development (R & D) sector. The recent Gyeongju earthquake posed an additional challenge for Korean groundwater scientists to develop a method to predict earthquakes using groundwater monitoring. Furthermore, changes in precipitation patterns caused by the changing climate aggravate groundwater recharge conditions. The country has seen many academic and technical achievements in groundwater science, but many issues remain to be resolved in the near future. [ABSTRACT FROM AUTHOR]

With a growing demand for fresh water, mainly due to the rapidly developing economy, their interests focus on securing plentiful groundwater resources for drinking, domestic, agricultural and industrial purposes. In addition, remediation of contaminated groundwater has become another main interest. Hence, many environmental tracers, such as CFCs, Ra, Rn, CH, δO, δD, H, He, δC, δCl, and applied tracers, such as Cl, Br and rhodamine WT, have been widely used in the country for groundwater studies with different purposes. The main purposes include estimations of submarine groundwater discharge pathways and their quantification in coastal regions, especially in Jeju (volcanic island), as well as examinations of groundwater origin and mixing with stream water, groundwater age dating, tracing (apportioning) the contamination sources of chlorinated solvents (e.g., TCE, PCE) in industrial areas, and identification of reservoir (large dam) leakage. This paper reviews the use of environmental and applied tracers in Korean groundwater studies and provides perspectives on their use. [ABSTRACT FROM AUTHOR]

Based on water chemistry data, a rockfill dam in South Korea was investigated to identify major parts of substantial dam water leakage. Sinkholes in the dam crest and abnormal water leakage through the dam were observed since the first impounding of the dam. Previous investigations, including observational drillings, hydraulic tests, geophysical surveys, and tracer tests, revealed the development of a high permeability zone in the clay core and an abnormally high phreatic line zone in the left embankment. Sequential tracer tests provided further evidence of locations of preference and rapid water leakage pathways. In this study, we examined the usefulness of water chemistry data to confirm previous findings of water leakage. Factor analysis of the water chemistry data revealed major processes controlling the chemical composition, which include the wash-out and successive dissolution of fill materials in the dam interior, interaction between percolating water and dam core materials, and contamination of seeping water by grouting materials and previous tracer tests. Distinct spatial distribution of similar chemical groups was illustrated by cluster analysis and confirmed the location of major water leakage at the left abutment adjoining the spillway. [ABSTRACT FROM AUTHOR]

Summary: The occurrence of submarine groundwater discharge (SGD) as well as its supply of many nutrients and metals to coastal seawaters is now generally known. However, previous studies have focused on the chemical and radiological analysis of groundwater, surface seawater, shallow marine sediments and their pore waters, as well as the measurement of upward flow through the marine sediments, as end members of the discharge process. In this study, chemical and isotopic analysis results of marine subsurface waters are reported. These were obtained from deep boreholes of an undersea liquefied petroleum gas (LPG) storage cavern, located about 8km off the western coast of Korea. The cavern is about 130–150m below the sea bottom, which is covered by a 4.8–19.5m silty clay stratum. An isotopic composition (δ2H and δ18O) of the marine subsurface waters falls on a mixing line between terrestrial groundwater and seawater. Vertical EC profiling at the cavern boreholes revealed the existence of a fresh water zone. An increase in the contents of ferrous iron and manganese and a decrease in levels of nitrate, bicarbonate and cavern seepage were recorded in August 2006, indicating a decreased submarine groundwater flux originating from land, mainly caused by an elevated cavern gas pressure. It is suggested in this study that the main source of fresh waters in the man-made undersea cavern is the submarine groundwater discharge mainly originating from the land. [Copyright &y& Elsevier]

The objective of this study is to examine groundwater responses before and after the November 15, 2017 Pohang earthquake (Mw=5.4) in a coastal area of Korea. The earthquake caused devastating damages to many buildings in the city. For this study, groundwater monitoring data (water level, electrical conductivity, water temperature) were obtained for January 2016 to February 2018 from the national groundwater monitoring stations, the rural groundwater monitoring wells, and the seawater intrusion monitoring wells and they are located within 25 km from the epicenter. There are eight national groundwater monitoring stations (PSG, PYI-D, PYI-S, PGB-D, PGB-S, PJH, PDH, PGR), five rural groundwater monitoring wells (PH1, PH2, PH3, PH4, PH5) and four seawater intrusion monitoring wells (GG1, GG2, YI1, YI2). Six of the monitored wells showed groundwater level decreases of 9–81 cm and two of them exhibited a recovery to the previous level within three days while the remaining wells did not. And six monitoring wells showed EC changes to the earthquake with -1,274–161 μS/cm. In addition, three wells showed discernible groundwater temperature fluctuations of -0.2–0.3oC. Here, we found the magnitude of groundwater level change is decreasing with distance of the monitoring wells from the epicenter. Some detailed analyses on the relationship between the responses and a variety of hydrogeological parameters deserve a further study. This work was supported by the Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry and Energy (No. 20183010111860) and by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF-2015R1A4A1041105). [ABSTRACT FROM AUTHOR]

Microplastic (MPs) contamination in groundwater has received massive attention since plastic waste has been released directly into the environment. This study investigates MPs contamination in groundwater on the Jeju volcanic Island, Korea. To the best of our knowledge, this is the first study to identify MPs in groundwater from volcanic islands. A total of 21 sites were sampled for groundwater wells and springs in July and September (2021). Sampling was performed without cross-contamination through quality assurance and quality control. The results showed that MPs abundance ranged from 0.006 to 0.192 particles/L in groundwater samples. Additionally, MPs were detected in deep groundwater wells where the groundwater level was 143 m below ground surface. Eight MPs polymer types, including polypropylene, polyethylene, polyethylene terephthalate, polyvinyl chloride, polystyrene, polyamide, acrylonitrile butadiene styrene, and polyurethane, were detected using Micro-Fourier Transform Infrared Spectroscopy (μ-FT-IR). Most of the detected MPs size ranged from 20 to 100 μm, accounting for 95% of the total. Fragments and fiber shaped MPs were detected, with the majority of them being fragmented in groundwater samples. The concentrations of MPs and major ions in groundwater showed a positive correlation. A negative correlation was observed between MPs concentration and topographic elevation (r = −0.59, p = 0.01). The source of MPs contamination is most likely attributed to agricultural activities, such as plastic mulching and greenhouses, which account for most of the land use in the study area. In this study, MPs entered the aquifer through the soil at the surface and seeped through cracks in fractured rock on basalt with sealed groundwater wells. This study takes 500 L of samples to prevent sample bias, reveal plastic contamination in groundwater, and indicating the characteristics and sources of contaminated plastics. [Display omitted] • Most MPs detected in groundwater were smaller than 50 μm. • Eight polymers were identified, with PP and PE being dominant types in groundwater. • Predominant shapes of MPs in groundwater were fragments. • MPs abundance and groundwater levels have a negative correlation. [ABSTRACT FROM AUTHOR]