• Journal of Soil and Groundwater Environment
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• v.18 no.5
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• pp.65-76
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• 2013

The water-table fluctuation (WTF) method has been often used for estimating groundwater recharge by analysis of waterlevel measurements in observation wells. An important assumption inherent in the method is that the water level rise is solely caused by precipitation recharge. For the observation wells located near a stream, however, the water-level can be highly affected by the stream level fluctuations as well as precipitation recharge. Therefore, in applying the WTF method, there should be consideration regarding the effect of stream-aquifer interactions. Analysis of water-level hydrographs from the National Groundwater Monitoring Wells of Korea showed that they could be classified into three different types depending on their responses to either precipitation recharge or stream level fluctuations. A simple groundwater flow model was used to analyze the errors of the WTF method, which were associated with stream-aquifer interactions. Not surprisingly, the model showed that the WTF method could greatly overestimate recharge, when it was used for the observation wells of which the water-level was affected by streams. Therefore, in Korea, where most groundwater hydrographs are acquired from wells nearby a stream, more caution is demanded in applying the WTF method.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.11a
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• pp.81-84
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• 2000

Two-layer aquifer system with fractional flow dimension is composed of contiguous two layers: Layer 1 (lower layer) and Layer 2 (upper layer) with different permeability and specific storage each other. For this aquifer system, we assume that groundwater flow originates only from Layer 1 on the pumping well. The aquifer system considers wellbore storage and skin effects on the pumping well. Dimensionless drawdown curves for different flow dimensions are analyzed for different lambda (λ, crossflow coefficient) values, kappa ($textsc{k}$, permeability ratio between Layer 1 and Layer 2) values and omega ($\omega$, storativity ratio between Layer 1 and Layer 2) values. The curves for Layer 1 and Layer 2 show characteristic trend each other.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.2
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• pp.101-109
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• 1998

Hydraulic property of fissured aquifers often depends on geologic structure which acts main channel of groundwater flow. We treated theories of linear flow related to vertical geologic structure. Then, we analyzed the result of two pumping tests conducted in Okmyeong-ri area (Kyeongbook province) using fractal model and found hydraulic characteristic of the fissured aquifer in this area. According to the pump test analyses, groundwater flow around the holes (pumping well D9; observation wells C3 and D7) of test 1 is linear. and is controlled by vertical geologic structure with infinite length and infinitesimally small width. On the other hand, around the hole D10 (pumping well) of test 2, groundwater flow is pseudo-radial (n=1.9) or radial (n=2). Thus, the characteristic of fractured aquifer often shows variable groundwater flow spatially and temporally.

• Journal of the Korean Society of Groundwater Environment
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• v.2 no.2
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• pp.49-57
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• 1995

Areas of Chungyang in Chungcheongnamdo, Cheju island and Georgia in U.S.A. were selected to calculate their groundwater ages and dispersion parameters using tritium. Piston flow model, Completely mixing model and Dispersion binomial model which calculate men residence times, and Dispersion normal model and Dispersion model(C$\_$FF) which calculate mean residence times and dispersion parameters simultaneously were applied. Since the input data, tritium concentrations of rainwaters, lack in part, tritium input function was prepared using the correlation of tritium concentrations of rainwaters of Pohang, Korea and Ottawa, Canada. Similar results of PFM and DBM reflect the intrinsical similarity of two models, assumption of low dispersion. The ages of sites of showing relatively higher tritium concentrations than other sites in the sam, region were not calculated by CMM. Since the calculations of DNM and DM(C$\_$FF/) provide the combination of wide ranges of parameters and groundwater ages, the ranges of dispersion parameters were narrowed down under the assumption that ages calculated by PFM and DBM are correct. Since large variation of tritium concentrations of outflows in a same region may reflect the different characteristics of each groundwater flow regime, using only one specific model on a whole region is not recommended.

• Journal of Radiation Protection and Research
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• v.28 no.3
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• pp.239-245
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• 2003

Every nuclear power plant measured concentrations of tritium in groundwater and surface water around the plants periodically. It was not easy to predict the tritium concentration only with these measurement data in case of various release scenarios. KAERI developed a new approach to find the relationship between the tritium release rate and tritium concentration in the environment. The approach was based upon a dynamic compartment model. In this paper the dynamic compartment model was modified to predict the tritium behavior more accurately. The mechanisms considered for the transfer of tritium between the compartments were evaporation, groundwater flow, infiltration, runoff, and hydrodynamic dispersion. Time dependent source terms of the compartment model were introduced to refine the release scenarios. Also, transfer coefficients between the compartments were obtained using realistic geographical data. In order to illustrate the model various release scenarios were developed, and the change of tritium concentration in groundwater and surface water around the nuclear power plants was estimated.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.5-16
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• 2002

A hydrogeomechanical numerical model is presented to evaluate rainfall impacts on groundwater flow in slopes and slope stability. This numerical model is developed based on the fully coupled poroelastic governing equations for groundwater flow in deforming variably saturated geologic media and the Galerkin finite element method. A series of numerical experiments using the model developed are then applied to an unsaturated slope under various rainfall rates. The numerical simulation results show that the overall hydromechanical slope stability deteriorates, and the potential failure nay initiate from the slope toe and propagate toward the slope crest as the rainfall rate increases. From the viewpoint of hydrogeology, the pressure head and hence the total hydraulic head increase as the rainfall rate increases. As a result, the groundwater table rises, the unsaturated zone reduces, the seepage face expands from the slope toe toward the slope crest, and the groundwater flow velocity increases along the seepage face. From the viewpoint of geomechanics, the horizontal displacement increases, and the vertical displacement decreases toward the slope toe as the rainfall rate increases. This may result from the buoyancy effect associated with the groundwater table rise as the rainfall rate increases. As a result, the overall deformation intensifies toward the slope toe, and the unstable zone, in which the factor of safety against shear failure is less than 1, becomes thicker near the slope toe and propagates from the slope toe toward the slope crest. The numerical simulation results also suggest that the potential tension failure is likely to occur within the slope between the potential shear failure surface and the ground surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.5
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• pp.321-326
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• 2011

Recently, ground source heat pump (GSHP) systems have been introduced in many modem buildings which use the annually stable characteristic of underground temperature as one of the renewable energy uses. However, all of GSHP systems cannot achieve high level of energy efficiency and energy-saving, because their performance significantly depends on thermal properties of soil, the condition of groundwater, building loads, etc. In this research, the effect of thermal properties of soil on the performance of GSHP systems has been estimated by a numerical simulation which is coupled with ground heat and water transfer model, ground heat exchanger model and surface heat balance model. The thermal conductivity of soil, the type of soil and the velocity of groundwater flow were used as the calculation parameter in the simulation. A numerical model with a ground heat exchanger was used in the calculation and, their effect on the system performance was estimated through the sensitivity analysis with the developed simulation tool. In the result of simulation, it founds that the faster groundwater flow and the higher heat conductivity the ground has, the more heat exchange rate the system in the site can achieve.

• Geomechanics and Engineering
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• v.27 no.5
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• pp.433-445
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• 2021

Artificial ground freezing (AGF) is a commonly used geotechnical support technique that can be applied in any soil type and has low environmental impact. Experimental and numerical investigations have been conducted to optimize AGF for application in diverse scenarios. Precise simulation of groundwater flow is crucial to improving the reliability these investigations' results. Previous experimental research has mostly considered horizontal seepage flow, which does not allow accurate calculation of the groundwater flow velocity due to spatial variation of the piezometric head. This study adopted vertical seepage flow-which can maintain a constant cross-sectional area-to eliminate the limitations of using horizontal seepage flow. The closure time is a measure of the time taken for an impermeable layer to begin to form, this being the time for a frozen soil-ice wall to start forming adjacent to the freeze pipes; this is of great importance to applied AGF. This study reports verification of the reliability of our experimental apparatus and measurement system using only water, because temperature data could be measured while freezing was observed visually. Subsequent experimental AFG tests with saturated sandy soil were also performed. From the experimental results, a method of estimating closure time is proposed using the inflection point in the thermal conductivity difference between pore water and pore ice. It is expected that this estimation method will be highly applicable in the field. A further parametric study assessed factors influencing the closure time using a two-dimensional coupled thermo-hydraulic numerical analysis model that can simulate the AGF of saturated sandy soil considering groundwater flow. It shows that the closure time is affected by factors such as hydraulic gradient, unfrozen permeability, particle thermal conductivity, and freezing temperature. Among these factors, changes in the unfrozen permeability and particle thermal conductivity have less effect on the formation of frozen soil-ice walls when the freezing temperature is sufficiently low.

• Journal of Soil and Groundwater Environment
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• v.20 no.3
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• pp.41-50
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• 2015

Hydrogeologic environment of the Mega City such as Seoul, suffers from rapid changes caused by urbanization, construction of underground subway or buildings, and contaminant loading by diverse anthropogenic activities. Understanding the present condition of groundwater environment and water budget is necessary to prevent natural and manmade disasters and to prepare for sustainable water resource management of urban environment. In this study, regional groundwater flow and water budget status of Seoul was analyzed using numerical simulation. Modeling result indicated that groundwater level distribution of Seoul generally followed the topography, but the significant decreases in groundwater level were observed around the subway network. Steady-state water balance analysis showed groundwater recharge by rainfall and leakage from the water supply network was about 550,495 m³/day. Surface water inflow and baseflow rate via Han River and major streams accounted for 799,689 m³/day and 1,103,906 m³/day, respectively. Groundwater usage was 60,945 m³/day, and the total groundwater leakage along the subway lines amounted to 114,746 m³/day. Modeling results revealed that the subway could decrease net groundwater baseflow by 40%. Our study result demonstrated that the subway system can have a significant influence on the groundwater environment of Seoul.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.99-101
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• 2003

Unsaturated hydraulic conductivity models have been widely used for the numerical modeling of water flow and contaminant transport in soils. In this study, a simple hydraulic conductivity model is developed by using information of particle-size distribution from the lognormal distribution model and its results are compared with those from the Kosugi-Mualem (KM) model. The accuracy of the proposed model is verified for observed data chosen from the international UNSODA database. Results showed that the proposed model produces adequate predictions of hydraulic conductivities. Performance of this model is generally better than the KM function.