Gwang-Ok Bae

Evaluation of spatio-temporal trends of groundwater quality in different land uses using Kendall test

The monitoring of temporal and spatial variations of groundwater quality is important for better managing groundwater resources. In a heavily cultivated agricultural site, Yupori, Chuncheon (Korea), groundwater quality has been monitored since 2002 because the groundwater in this area contains elevated levels of nitrate. Concentrations of NO3-N, SO42−, and Cl− were found to be high in vegetable fields and low in fruit orchards. For groundwater management purposes, a regional Kendall test was carried out to investigate the spatio-temporal trends of three major anion (NO3−N, SO42−, and Cl−) concentrations for various land use types: vegetable fields, fruit fields, and barns. The mean concentration of NO3-N in the vegetable fields exceeded the maximum contaminant level for drinking water (10 mg L−1) and showed the highest increasing trend with time among the various land use types. The results showed a statistically significant increasing trend in the NO3-N and SO42− concentration in vegetable fields from 2002 to 2007. The estimated slope of the NO3-N and SO42− concentration in the vegetable fields was 2.1 mg L−1 per year and 1.01 mg L−1 per year over a period of 6 years. The concentration of Cl− showed an increasing tendency in fruit fields and decreasing tendency in barns. In order to regulate groundwater quality in the study area, nitrate contamination in vegetable fields should be particularly controlled. Spatio-temporal trends for different land uses using regional Kendall test can be usefully applied to control groundwater quality in the study area.

Groundwater pumping effects on contaminant loading management in agricultural regions

Groundwater pumping changes the behavior of subsurface water, including the location of the water table and characteristics of the flow system, and eventually affects the fate of contaminants, such as nitrate from agricultural fertilizers. The objectives of this study were to demonstrate the importance of considering the existing pumping conditions for contaminant loading management and to develop a management model to obtain a contaminant loading design more appropriate and practical for agricultural regions where groundwater pumping is common. Results from this study found that optimal designs for contaminant loading could be determined differently when the existing pumping conditions were considered. This study also showed that prediction of contamination and contaminant loading management without considering pumping activities might be unrealistic. Motivated by these results, a management model optimizing the permissible on-ground contaminant loading mass together with pumping rates was developed and applied to field investigation and monitoring data from Icheon, Korea. The analytical solution for 1-D unsaturated solute transport was integrated with the 3-D saturated solute transport model in order to approximate the fate of contaminants loaded periodically from on-ground sources. This model was further expanded to manage agricultural contaminant loading in regions where groundwater extraction tends to be concentrated in a specific period of time, such as during the rice-growing season, using a method that approximates contaminant leaching to a fluctuating water table. The results illustrated that the simultaneous management of groundwater quantity and quality was effective and appropriate to the agricultural contaminant loading management and the model developed in this study, which can consider time-variant pumping, could be used to accurately estimate and to reasonably manage contaminant loading in agricultural areas.

Factors causing dynamic variations in the saltwater–freshwater transition zone in a beach aquifer, Mangsang, South Korea

Dynamic variation in the saltwater–freshwater transition zone below a seafront beach in South Korea was investigated with long-term monitoring of the groundwater in relation to the precipitation, wave height, and tide. Correlation, spectral analysis, and regression analysis of monitoring data were performed to deduce the relationships between these factors. The general shape of the transition zone was affected by the seasonal groundwater levels, but temporary fluctuations were predominantly affected by local rising-groundwater-level events. The distinct increases in the groundwater level were closely related to the wave height. Different patterns of electrical conductivity (EC) change were detected in the shallow and deep zones, and these differences indicated that the transition zone was highly dynamic. The EC values at shallow depths were temporarily increased by the wave setup and tidal fluctuations during the rising-groundwater events, but the EC at greater depths was reduced by the seaward or downward movement of the relative freshwater. In exceptional cases, during extreme increases in the groundwater level resulting from seawater flooding, the rapid downward flow of the flooding saltwater through the well bore caused synchronous EC fluctuations at all depths.RésuméLa dynamique de la variation de la zone de transition eau douce-eau salée en bordure de mer en Corée du Sud a été étudiée à partir de suivis des eaux souterraines sur une longue période en relation avec les précipitations, la hauteur des vagues et la marée. Des corrélations, des analyses spectrales et des analyses par régression des données de suivi des eaux souterraines ont été réalisées pour déterminer une relation entre ces facteurs. La forme générale de la zone de transition est affectée par les variations saisonnières des niveaux piézométriques mais des fluctuations temporaires sont affectées de manière prédominante par des évènements de montées locales des eaux souterraines. Les phases d’élévation des niveaux piézométriques sont clairement corrélées à la hauteur des vagues. Des gammes différentes de conductivité électriques sont détectées dans les zones profonde et peu profonde. Ces différences indiquent que la zone de transition est hautement dynamique. Les valeurs de conductivité électrique dans les faibles profondeurs sont temporairement augmentées par la mise en place des vagues et des fluctuations de marée durant les épisodes de montée des eaux souterraines, mais les conductivités à des profondeurs plus importantes sont réduites par le mouvement vers la mer ou vers la profondeur de l’eau douce. Dans les cas exceptionnels, durant des crues extrêmes des eaux souterraines résultant d’une inondation par la mer, la pénétration verticale rapide de l’eau de mer par forage entraine des fluctuations synchrones de conductivité électrique à toutes les profondeurs.ResumenSe investiga la variación dinámica en la zona de transición agua dulce – agua salada por debajo de una playa del frente marino en Corea del Sur con un monitoreo a largo plazo del agua subterránea en relación a la precipitación, alturas de las olas y la marea. Se llevaron a cabo análisis de correlación, espectral y de regresión de los datos de monitoreo para deducir la relación entre estos factores. La forma general de la zona de transición fue afectada por los niveles estacionales de agua subterránea, pero fluctuaciones temporarias fueron predominantemente afectadas por los eventos locales de ascenso de niveles del agua subterránea. Los distintos incrementos en el nivel de agua subterránea fueron estrechamente relacionados con las alturas de las olas. Se detectaron diferentes patrones de conductividad eléctrica (EC) en zonas someras y profundas, y estas diferencias indicaron que la zona de transición fue altamente dinámica. Los valores de EC en aguas somera fueron incrementados temporalmente por la elevación de las olas y las fluctuaciones de marea durante los eventos de ascenso del agua subterránea, pero la EC a grandes profundidades se redujo por movimiento hacia el mar o de descenso del agua relativamente dulce. En casos excepcionales, durante incrementos extremos del nivel de agua subterránea que resultan de inundaciones de agua de mar, el flujo de descenso rápido del agua salada de la inundación a través de los pozos produjo fluctuaciones de EC sincronizadas a todas las profundidades.摘要通过长期监测地下水与降水、波高和潮汐的相关性来研究韩国滨海沙滩含水层海水-淡水过渡区动态变化。进行了相关的频谱分析和监测数据的回归分析来推断这些因素之间的关系。过渡带一般的形状受季节性地下水水位影响,而临时波动主要受局部地下水水位上涨活动影响。地下水位显著的增加与波高密切相关。在浅部和深部带检测到不同模式导电率(EC)变化,这种差异表明过渡带是高度动态的。浅深处随着地下水上涨活动中波的上扬和潮汐波动EC值临时增加,而在更深处随着较淡的水朝海或向下移动EC减小。例外情况下,由于海水注入,地下水水位极度增长,盐水通过井口快速向下流动,整个深度上EC同时出现波动。ResumoInvestigou-se a variação dinâmica de uma zona de transição água salgada-água doce subjacente a uma praia na Coreia do Sul, com monitorização a longo prazo das águas subterrâneas em relação com a precipitação, altura da onda, e maré. A fim de deduzir as relações entre estes fatores, fez-se correlação, análise espetral e análise de regressão dos dados de monitorização. A forma geral da zona de transição foi afetada pelos níveis sazonais das águas subterrâneas, mas as flutuações temporárias foram predominantemente afetadas por eventos locais de aumento dos níveis de águas subterrâneas. Os diferentes aumentos no nível da água subterrânea estavam estreitamente relacionados com a altura da onda. Padrões diferentes de variação da condutividade elétrica (CE) foram detetados nas zonas de pequena profundidade e profundas, e estas diferenças indicaram que a zona de transição era altamente dinâmica. Os valores de CE em zonas pouco profundas aumentaram temporariamente pela configuração da onda e pelas flutuações de maré durante os eventos de subida de águas subterrâneas, mas a CE a maiores profundidades foi reduzida pelos movimentos em direção ao mar, ou para baixo, da água relativamente mais doce. Em casos excecionais, durante subidas extremas do nível de águas subterrâneas resultantes de inundações pela água do mar, o rápido fluxo descendente da água salgada da inundação através do poço causou flutuações de CE síncronas a todas as profundidades.

Quantification and Evaluation of Groundwater Quality Grade by Using Statistical Approaches

This study suggests a method to grade groundwater quality quantitatively using statistical approaches for evaluating the quality of groundwater in wells included in the Groundwater Quality Monitoring Network (GQMN). The proposed analysis method is applied to GQMN data from 2001 to 2008 for nitrate nitrogen, chloride, trichloroethylene, potential of hydrogen (pH), and electrical conductivity. The analysis results are obtained as groundwater quality grades of the groundwater representing each of the monitoring stations. The degree of groundwater contamination is analysed for water quality parameters, district, and usage. The results show that the degree of groundwater contamination is relatively high by nitrate nitrogen, bacteria and electrical conductivity and at Seoul, Incheon, Gwangju, Gyeonggido and Jeollado. The degree of contamination by nitrate nitrogen and trichloroethylene is especially high when the groundwater is used for agricultural and industrial water, respectively. It is evaluated that potable groudnwater in GQMN is significantly vulnerable to nitrate nitrogen and bacteria contamination.

Geological structures in the Tongri-Dogye and Sangdeog areas in the eastern part of the Samcheog Coalfield, Korea

AbstractsThe study area, the Tongri-Dogye and Sangdeog areas, is located in the eastern part of the Samcheog Coalfield and consists of Precambrian granitic rocks, Paleozoic sedimentary rocks, and Cretaceous sedimentary and volcanic rocks. The study area is characterized by the E−W trending folds and thrusts, and N−S trending faults. The E−W trending folds and thrusts are well developed and are cut by the N−S trending faults in the study area. The N−S trending faults records two components of fault movements; earlier stage of the west dipping normal fault and later stage of strike-slip fault. A series of these normal faults have a character of step faults and stratigraphic positions are younger toward the west across these faults. Cretaceous volcanic rocks have two phases, extrusive and intrusive phases. Extrusive volcanic rocks are affected by the southwards thrust movement, while others intruded into the thrust sheets. Age of volcanic rocks ranges from 66.9 Ma to 49.2 Ma. These lines of evidences indicate that thrust movement occurs between 66.9 Ma and 49.2 Ma. The Osipcheon Fault, one of the major N−S trending faults in the eastern part of the Samcheog Coalfield, is characterized by strike-slip with dextral movement. Along the Osipcheon fault, the horse tail structures are developed near the tip area in the western part and subparallel faults are dominant in the eastern part of the fault. The Osipcheon Fault is terminated in the Triassic Donggo Formation near the Tongri town. Thrust faults and related structures are also developed along the lateral tip line of the minor thrust such as ramp structures, crescent type anticline, and antiformal stack structures. Along the Osipcheon Fault, minor reverse faults and domino-type extensional faults are developed on the coaly shale beds during the strike-slip faulting.

Improving accuracy and flexibility of numerical simulation of geothermal heat pump systems using Voronoi grid refinement approach

We have developed a method and computational algorithms for implementing the method, which can generate unstructured Voronoi grids for its use in TOUGH2 simulations of geothermal heat pump systems. An adaptive gridding technique, known as Voronoi tessellation, not only is flexible to include detailed shapes of the cross-sections of pipes at any position inside the geothermal wells, but also always satisfies the orthogonal condition of the TOUGH2 grid, which is that connections between two adjacent grid blocks in a TOUGH2 grid should be orthogonal to their connection interface. A series of newly developed or already existing codes are used to create Voronoi seeds that are placed at specific positions for the geothermal wells, to calculate the x- and y-coordinates of the Voronoi vertices from the Voronoi seeds, to generate 3-D grids and TOUGH2 input files from Voronoi vertices, and to visualize the generated grid and simulation results with ParaView. We show the desired form of the grid generated from the developed method and computational algorithm and perform an example simulation to demonstrate the use of the developed grid that includes four different kinds of geothermal well systems.