• The Journal of Engineering Geology
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• v.23 no.4
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• pp.467-476
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• 2013

With increasing interest in environmental issues and the quality of surface water becoming inadequate for water supply, the Korean government has launched a groundwater development policy to satisfy the demand for clean water. To drive this policy effectively, it is essential to guarantee the accuracy of sustainable groundwater yield and groundwater use amount. In this study, groundwater use was monitored over several years at various locations in Korea (32 cities/counties in 5 provinces) to obtain accurate groundwater use data. Statistical analysis of the results was performed as a method for estimating rational groundwater use. For the case of groundwater use for living purposes, we classified the cities/counties into three regional types (urban, rural, and urban-rural complex) and divided the groundwater facilities into five types (domestic use, apartment housing, small-scale water supply, schools, and businesses) according to use. For the case of agricultural use, we defined three regional types based on rainfall intensity (average rainfall, below-average rainfall, and above-average rainfall) and the facilities into six types (rice farming, dry-field farming, floriculture, livestock-cows, livestock-pigs, and livestock-chickens). Finally, we developed groundwater-use estimation equations for each region and use type, using cluster analysis and regression model analysis of the monitoring data. The results will enhance the reliability of national groundwater statistics.

• The Journal of Engineering Geology
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• v.29 no.3
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• pp.265-277
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• 2019

Changes in the amount, intensity, frequency, and type of precipitation, in conjunction with global warming and climate change, critically impact groundwater recharge and associated groundwater level fluctuations. Monthly gravity levels by the Gravity Recovery and Climate Experiment (GRACE) are acquired to monitor total water storage changes at regional and global scales. However, there are inherent difficulties in quantitatively relating the GRACE observations to groundwater level data due to the difficulties in spatially representing groundwater levels. Here three local interpolation methods (kriging, inverse distance weighted, and natural neighbor) were implemented to estimate the areal distribution of groundwater recharge changes in South Korea during the 2002-2016 period. The interpolated monthly groundwater recharge changes are compared with the GRACE-derived groundwater storage changes. There is a weak decrease in the groundwater recharge changes over time in both the GRACE observations and groundwater measurements, with the rate of groundwater recharge change exhibiting mean and median values of -0.01 and -0.02 cm/month, respectively.

• The Journal of Engineering Geology
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• v.31 no.3
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• pp.395-432
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• 2021

Groundwater recharge rates vary widely by location and with time. They are difficult to measure directly and are thus often estimated using simulations. This study employed frequency and regression analysis and a classification and regression tree (CART) algorithm in a machine learning method to estimate groundwater recharge. CART algorithms are considered for the distribution of precipitation by subbasin (PCP), geomorphological data, indices of the relationship between vegetation and landuse, and soil type. The considered geomorphological data were digital elevaion model (DEM), surface slope (SLOP), surface aspect (ASPT), and indices were the perpendicular vegetation index (PVI), normalized difference vegetation index (NDVI), normalized difference tillage index (NDTI), normalized difference residue index (NDRI). The spatio-temperal distribution of groundwater recharge in the SWAT-MOD-FLOW program, was classified as group 4, run in R, sampled for random and a model trained its groundwater recharge was predicted by CART condidering modified PVI, NDVI, NDTI, NDRI, PCP, and geomorphological data. To assess inter-rater reliability for group 4 groundwater recharge, the Kappa coefficient and overall accuracy and confusion matrix using K-fold cross-validation were calculated. The model obtained a Kappa coefficient of 0.3-0.6 and an overall accuracy of 0.5-0.7, indicating that the proposed model for estimating groundwater recharge with respect to soil type and vegetation cover is quite reliable.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.4
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• pp.361-375
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• 2007

This paper presents the results of investigation on tunnelling-induced ground surface settlement characteristics in water bearing ground using finite element (FE) stress-pore pressure coupled analysis. Fundamental interaction mechanism of ground and groundwater lowering was first examined and a number of influencing factors on the results of the coupled FE analysis were identified. A parametric study was then conducted on the influencing factors such as rock type, thickness of soil layer, permeability of shotcrete lining, among others. The results indicate that the tunneling-induced groundwater drawdown results in a deeper and wider settlement trough than without groundwater drawdown, and that the Error function approach does not yield satisfactory result in predicting a settlement profile. The results of analysis are summarized so that the relationship between the settlement and the influencing factors can be identified.

• Journal of Soil and Groundwater Environment
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• v.25 no.4
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• pp.87-97
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• 2020

In this study, the applicability of the geostatistical evolution strategy as an inverse analysis method of estimating hydraulic properties of small-scale basin was tested. The geostatistical evolution strategy is a type of data assimilation method that can effectively estimate aquifer hydraulic conductivity by combining a global optimization model of the evolution strategy and a local optimization model of the ensemble Kalman filtering. In the applicability test, the geometry, hydraulic boundary conditions, and the distribution of groundwater monitoring wells of Hanlim-Eup were employed. On the other hand, a synthetic hydraulic conductivity distribution was generated and used as the reference property for ease of estimation quality assessment. In the estimations, two different cases were tested where, in Case I, both groundwater levels and hydraulic conductivity measurements were assumed to be available, and only the groundwater levels were available, in Case II. In both cases, the reference and estimated hydraulic conductivity fields were found to show reasonable similarity, even though the prior information for estimation was not accurate. The ability to estimate hydraulic conductivity without accurate prior information suggests that this method can be used effectively to estimate mathematical properties in real-world cases, many of which little prior information is available for the aquifer conditions.

• Journal of the Korean Society of Groundwater Environment
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• v.4 no.4
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• pp.199-211
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• 1997

As a part of study on geological disposal of radioactive waste, hydrogeochemical characteristics of deep granitic groundwater in Korea were investigated through the construction of a large geochemical dataset of natural water, the examination on the behaviour of dissolved constituents, and the consideration of phase stability based on thermodynamic approach. In granitic region, the contents of total dissolved solids increase progressively from surface waters to deep groundwaters, which indicates the presence of more concentrated waters at depth due to water-rock interaction. The chemical composition of groundwater evolves from initial $Ca^{2＋}$－(C $l^{－}$＋S $O_4$$^{2-}$) or $Ca^{2＋}$-HC $O_3$$^{－}$ type to final N $a^{＋}$-HC $O_3$$^{－}$ or N $a^{＋}$－(C $l^{－}$＋S $O_4$$^{2-}$) type, via $Ca^{2＋}$-HC $O_3$$^{－}$ type. Three main mechanisms seem to control the chemical composition of groundwater in the granitic region; 1) congruent dissolution of calcite at shallower depth, 2) calcite precipitation and incongruent dissolution of plagioclase at deeper depth, and 3) kaolinite-smectite or/and kaolinite-illite reaction at equilibrium at deeper depth. The behaviour of dissolved major cations (C $a^{2＋}$, $K^{＋}$, $Mg^{2＋}$, M $a^{＋}$) and silica is likely to be controlled by these reactions.

• Journal of the Korean GEO-environmental Society
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• v.12 no.2
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• pp.35-43
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• 2011

Confined aquifer, which is separated with upper clayey or silty materials, is partially distributed at the depths of the sediments in Ddan-sum area on the lower Nakdong river. Measurements of groundwater levels at 13 sites explain that groundwater flow shows seasonally various due to seasonal rainfall and agricultural water use. From 9 long-term monitoring data of groundwater levels at 7 sites, 3 types of groundwater levels time series can be classified using principal component analysis. The first type is seen in the center of Ddan-sum and has a round-shape graph due to a weak response to stream water levels. The second type exists in the outer part of Ddan-sum and shows sharply peak-shape graph due to a rapid and strong response to stream water levels and rainfall. The last type, which is seen in a deep layer, has a periodicity by tital effect. From geochemical analysis at each monitoring sites, [$Ca-HCO_3$] type happens in the center of Ddan-sum far from Nakdong river, and [$Na-HCO_3$] and [$Ca-SO_4(Cl)$] types exist in the outer of Ddan-sum affected by river quality.

• Journal of Environmental Science International
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• v.9 no.3
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• pp.229-239
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• 2000

Spring, ground and thermal waters in the vicinity of Mt. Geumjeong and Mt. Baekyang area have been sampled and analyzed for major and minor elements. According to the Piper diagram, spring water belongs to $Ca-HCO_3$ and $Na-HCO_3$ types, groundwater to $Ca-HCO_3$ type, and thermal water to Na-Cl type. Based on the phase stability diagrams of $[Ca^{2+}]/{[H^+]}^2, [Mg^{2+}]/{[H^+]}^2, [K^+]/[H^+]$, and $[Na^+]/[H^+] vs. [H_4SiO_4]$, spring water, groundwater and thermal water are mostly in equilibrium with kaolinite. The result of factor analysis shows three factors (factor 1, 2 and factor 3) for the spring water, the groundwater and the thermal water which are represented by the influence of the dissolution of feldspar, calcite, anthropogenic sources (domestic and industrial wastes) and salt water.

• Journal of Soil and Groundwater Environment
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• v.21 no.1
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• pp.104-110
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• 2016

The transport of silver nanoparticles (AgNPs) was investigated through a column packed with sand. A series of column experiments were carried out to evaluate the effect of ionic strength (IS), pH, electrolyte type and clay mineral on mobility of polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs). The deposition of PVP-AgNPs was increased with increasing solution ionic strength and decreasing pH. Furthermore, the depositon of PVP-AgNPs was affected by the electrolyte type (NaCl vs. NaNO₃) and was shown to be greater at NaNO₃ solution. Also, the transport of PVP-AgNPs was greatly increased after the pre-deposition of clay particles on sand. Our results suggest that various environmental factors can influence the mobility of PVP-AgNPs in soil-groundwater systems and should be carefully considered in assessing their environmental risks.

• Journal of the Korean earth science society
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• v.42 no.4
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• pp.425-444
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• 2021

Investigating the physical and chemical properties of riverine wetlands is necessary to understand their distribution characteristics and depositional environment. This study investigated the physical (particle size, color, and type) and chemical properties (organic, inorganic, and moisture contents) of sediments in Samrak wetland, located in the Nakdong River estuary area in Busan, South Korea. The particle size analysis indicated that the hydraulic conductivity values for the coarse grain and the mixture of coarse and fine grains ranged from 2.03 to 3.49×10^-1 cm s^-1 and 7.18×10^-3 to 1.24×10^-7 cm s^-1, respectively. In-situ water quality and laboratory-based chemical analyses and radon-222 measurement were performed on groundwater and surface water in the wetland and water from the nearby Nakdong River. The physical and chemical properties of Samrak wetland was characterized by the sediments in the vertical and lateral direction. The concentrations of chemical components in the wetland groundwater were distinctly higher than those in the Nakdong River water though the wetland groundwater and Nakdong River water equally belonged to the Ca-HCO₃ type.