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[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]

Summary: Groundwater is nearly the sole source for freshwater supply on Jeju volcanic island because there are no perennial streams and rivers. Rain harvesting and subsequent artificial recharging have been conducted to meet growing freshwater demand in the island. We performed sequential samplings of harvested rainwater prior to the artificial injection in summer of 2008 at an artificial recharge site of western Jeju. Field measurements and chemical analyses of 313 rainwater samples revealed that there was a variation in chemical composition but the Na+K+SO4 +Cl type was dominant. Predominance of Na and Cl was likely to be from sea salts while substantial amount of SO4, NO3 , and NH4 is attributed to anthropogenic air pollution. The enrichment factors of SO4, HCO3, K, Mg, and Ca suggested that their non-marine contribution ranges from 75.4% to 99.98%. However, the sea salt contributed substantially to Cl concentration up to 73.5%. Most of the rainwater parameters generally decreased with time and they were generally stabilized after 20min, which is an effect of the first flush and thus some diversion (rerouting) is required for suitable artificial injection of the harvest rainwater in this study area. [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]

Summary: Groundwater is being now seriously considered as heat sources for space heating and cooling in Korea. This study evaluated groundwater temperature data obtained from 266 Korean national groundwater monitoring stations. Spatial distribution of the groundwater temperatures is mainly affected by geographical latitude, air temperature, and local topographic elevations. The distribution pattern for the groundwater temperatures is most similar to that of the air temperature. Annual variations of the groundwater temperatures were classified into four main patterns. The P (periodic) type representing periodic annual variation was mainly found in shallow groundwaters (62.5%). Most peculiar is F (flat) type, in which the groundwater temperatures showed nearly no variation, and was mostly observed in deep wells (47.9%). Water levels are seemingly related to the classifications. Water levels of P or WP (weak periodic) types were shallowest while those of F type were deepest. Magnitude of annual temperature variation was within 8°C for 76.6% of the shallow wells while 97.1% account for the variation within 8°C in the deep wells. The highest groundwater temperatures mostly occurred in the coldest months (November–February) and the lowest temperatures in March–June, immediately before the hottest months (July–August). A simple exponential relationship between the amplitude and the phase difference with respect to the air temperature was found, which indicates propagation of the air temperature mainly due to conduction. Considering stability of groundwater temperatures, F type in bedrock aquifers appeared most suitable for the heat pumps in respect to efficient system design and maintenance. For practical application of the groundwater heat pumps, detailed investigation of hydrogeologic conditions and potential environmental changes is required. [Copyright &y& Elsevier]

Summary: The Korean Ministry of Construction and Transportation (MOCT) and the Korean Ministry of Environment (MOE) manage the National Groundwater Monitoring Stations (NGMS) and the Groundwater Quality Monitoring Stations (GQMS) under Article 17 of the Groundwater Act. Under the same legislation, local government will install or designate an additional 10,000 monitoring wells as Subsidiary Groundwater Monitoring Stations (SGMS) by 2011. However, a standard for the installation and management of the SGMSs has not yet been developed. This study focuses on the development of a model for the determination of optimal monitoring frequencies during the manual measurement of the SGMSs. The groundwater level time series for the 81 deep and shallow monitoring wells making up the NGMSs were analyzed using an AR(p) model, and a harmonic series model was then made for the determination of groundwater level sampling frequency in the SGMSs. The result showed that the average sampling frequency necessary for groundwater level monitoring is about once every 8.9 days. Moreover, it indicates that water level sampling needs to be performed more frequently in steeply inclined sites, deep wells, and in monitoring wells belonging to an AR(2) rather than an AR(1) model. [Copyright &y& Elsevier]