Nitrate-nitrogen (NO₃-N) contamination in groundwater is a major problem of drinking and domestic waters in rural areas. This study revealed the influence of land use type on shallow alluvial groundwaters in a typical rural area in South Korea by applying a self-organizing map (SOM), principal component analysis (PCA), and hierarchical cluster analysis (HCA). The uncertainty of spatial information on land use was improved by using a buffer zone of the average influence radius of 32.65 m surrounding wells. Two major land-use types, forests (44.9%) and rice fields (28.8%), occupied a total of 73.7% of the rural area. The higher concentrations of NO₃-N in public facilities and livestock areas were demonstrated to directly recharge groundwater pollutants. NO₃-N contamination in rice paddies, which also contained chlorine (Cl) and sulfate (SO₄), was assessed according to the nutrients and residual salt in the soil. In addition, different NO₃-N concentrations for the same land use indicate various biochemical reactions and NO₃-N recharge types into the groundwater system. The shallow groundwaters in the study area were classified into three clusters according to their chemical constituents and land-use properties, especially NO₃-N concentration, including pH, Cl, and SO₄, using a SOM, PCA, and HCA. Unlike existing studies, we applied a buffer zone based on the Cooper-Jacob equation to obtain an improved SOM model prediction accuracy approximately 10% greater than that using the original dataset.

Uranium (U) is one of the typical naturally occurring radioactive elements enriched in groundwater through geological mechanisms, thereby bringing about adverse effects on human health. For this reason, some countries and the World Health Organization (WHO) regulate U with drinking water standards and monitor its status in groundwater. In Korea, there have been continuous investigations to monitor and manage U in groundwater, but they have targeted only public groundwater wells. However, the features of private wells differ from public ones, particularly in regard to the well’s depth and diameter, affecting the U distribution in private wells. This study was initiated to investigate U concentrations in private groundwater wells for potable use, and the significant factors controlling them were also elucidated through statistical methods. The results obtained from the analyses of 7036 groundwater samples from private wells showed that the highest, average, and median values of U concentrations were 1450, 0.4, and 4.0 μg/L, respectively, and 2.1% of the wells had U concentrations exceeding the Korean and WHO standard (30 μg/L). In addition, the U concentrations were highest in areas of the Jurassic granite, followed by Quaternary alluvium and Precambrian metamorphic rocks. A more detailed investigation of the relationship between U concentration and geology revealed that the Jurassic porphyritic granite, mainly composed of Daebo granite, showed the highest U contents, which indicated that U might originate from uraninite (UO₂) and coffinite (USiO₄). Consequently, significant caution should be exercised when using the groundwater in these geological areas for potable use. The results of this study might be applied to establish relevant management plans to protect human health from the detrimental effect of U in groundwater.

The hydrogeochemical properties of bottled waters (n = 37) were examined to evaluate the factors governing their quality and to suggest the natural background levels (NBLs) of groundwater. The bottled waters were sourced from bedrock aquifers of various geological types and analyzed for 14 physicochemical parameters and 48 trace elements. The bottled waters mainly consisted of the Ca-HCO₃ type with low TDS (mean = 158.4 mg/L; n = 33) regardless of geological type, indicating low degrees of water–rock interaction. The results of principal component analysis (PCA) showed that these waters were characterized by the dissolution of calcite and Ca-plagioclase (PC1) and the weathering of Na-plagioclase and cation exchange (PC2). The PCA results with low concentrations of TDS and F (mean = 0.4 mg/L) revealed that the waters represent slightly mineralized groundwater, probably because the boreholes were installed in fractured aquifers, avoiding high F concentrations (>1.5 mg/L). The 90th percentiles for the Ca-HCO₃ type bottled waters were proposed as the NBLs for Korean groundwater for 11 major elements and 20 trace elements. The NBLs of NO₃ (7.9 mg/L) and F (0.9 mg/L) were similar to the 90th percentiles of EU bottled waters (n = 1785), implying the suggested NBLs are acceptable for groundwater quality management.

Approximately 40,000 chemical products are currently used in Korea; these products can contaminate the groundwater/soil, the surrounding environment, and organisms for extended periods of time. In this study, a hydrological field survey, a water quality analysis, and groundwater modeling were performed to identify the source and transport path of pollution that was caused by inorganic matter and artificial sweeteners, especially acesulfame, in the groundwater of an agricultural area in Chungnam Province, Korea. In the study area, a higher concentration of acesulfame displayed a spatial distribution similar to nitrate-nitrogen concentration. The characteristics of the groundwater flow and the distribution of the acesulfame were simulated using the Visual MODFLOW Classic Interface ver. 2014.1 and the MT3DMS module, respectively. The modeled area was divided into hilly (southern), residential (northwest), and agricultural (northeast) zones. The stream’s boundary was set to be the drainage channel in the southern hilly zone. From the simulation, we found that acesulfame spread actively from the source for 1–3 years before it reached equilibrium in the northern part of the model domain (the area downstream of the stream’s boundary). The concentration of acesulfame in the agricultural zone of the model domain decreased after five years, and it reached the steam boundary and residential zone within 10 years. After 10 years, most of the acesulfame was discharged from the agricultural zone and the hilly zone, while the concentration in the residential zone was approximately the same. Acesulfame is considered to be a potential indicator of man-made contamination for use in the management of groundwater quality.

The concentrations of natural radioactive elements in the groundwater environment are regulated by several factors, including aquifer geology, groundwater hydrochemical properties, and changes in environmental conditions. Many studies have explored these factors, but few have systematically elucidated the mechanisms underlying the dissolution of radioactive elements from their host minerals into groundwater. This study investigated the petrological, mineralogical, and weathering properties of aquifer materials and their effects on the leaching of uranium (U) and thorium (Th) into groundwater. The time required for the U concentration to reach the drinking water standard (30 μg/L) was estimated through artificial weathering experiments performed under diverse environmental conditions. Rock core samples were obtained from three sites differing in their geology and groundwater U concentrations. Mineralogical analyses revealed that thorite, a representative radioactive mineral that contains large amounts of U and Th, was present in samples from all collection sites. Thorite minerals differed in terms of their sizes, shapes, cracks, and chemical compositions between samples from different sites, indicating that geological features, mineral alteration characteristics, and environmental conditions controlled the behavior of U and Th. These factors appear to play crucial roles in regulating the mobility and potential long-term leachability of U and Th. Artificial weathering experiments confirmed that a neutral pH with surplus bicarbonate ions favored U leaching. Under these environmental conditions, aquifer U concentrations were estimated to require 8.7–226 years to reach the drinking water standard, depending on the groundwater dissolved oxygen content. Our results provide scientific evidence that may be used for managing radioactive elements in the groundwater environment, and are likely to inform new environmental policies and regulatory standards.