• Journal of Soil and Groundwater Environment
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• v.13 no.1
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• pp.77-91
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• 2008

In this study, we developed a technique of applying DRASTIC, which is the most widely used tool for estimation of groundwater vulnerability to the aqueous phase contaminant infiltrated from the surface, and a groundwater flow model jointly to assess groundwater contamination potential. The developed technique is then applied to Buyeo-eup area in Buyeo-gun, Chungcheongnam-do, Korea. The input thematic data of a depth to water required in DRASTIC model is known to be the most sensitive to the output while only a few observations at a few time schedules are generally available. To overcome this practical shortcoming, both steady-state and transient groundwater level distributions are simulated using a finite difference numerical model, MODFLOW. In the application for the assessment of groundwater vulnerability, it is found that the vulnerability results from the numerical simulation of a groundwater level is much more practical compared to cokriging methods. Those advantages are, first, the results from the simulation enable a practitioner to see the temporally comprehensive vulnerabilities. The second merit of the technique is that the method considers wide variety of engaging data such as field-observed hydrogeologic parameters as well as geographic relief. The depth to water generated through geostatistical methods in the conventional method is unable to incorporate temporally variable data, that is, the seasonal variation of a recharge rate. As a result, we found that the vulnerability out of both the geostatistical method and the steady-state groundwater flow simulation are in similar patterns. By applying the transient simulation results to DRASTIC model, we also found that the vulnerability shows sharp seasonal variation due to the change of groundwater recharge. The change of the vulnerability is found to be most peculiar during summer with the highest recharge rate and winter with the lowest. Our research indicates that numerical modeling can be a useful tool for temporal as well as spatial interpolation of the depth to water when the number of the observed data is inadequate for the vulnerability assessments through the conventional techniques.

• Journal of Soil and Groundwater Environment
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• v.13 no.4
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• pp.8-21
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• 2008

A series of three-dimensional numerical simulations using a hydrodynamic dispersion numerical model is performed to analyze quantitatively impacts of layered heterogeneity of geologic media and groundwater pumping schemes on groundwater flow and salt transport in coastal aquifer systems. A two-layer heterogeneous coastal aquifer system composed of a lower sand layer (aquifer) and an upper clay layer (aquitard) and a corresponding single-layer homogeneous coastal aquifer system composed of an equivalent lumped material are simulated to evaluate impacts of layered heterogeneity on seawater intrusion. In addition, a continuous groundwater pumping scheme and two different periodical groundwater pumping schemes, which withdraw the same amount of groundwater during the total simulation time, are applied to the above two coastal aquifer systems to evaluate impacts of groundwater pumping schemes on seawater intrusion. The results of the numerical simulations show that the periodical groundwater pumping schemes have more significant adverse influences on groundwater flow and salt transport not only in the lower sand layer but also in the upper clay layer, and groundwater salinization becomes more intensified spatially and temporally as the pumping intensity is higher under the periodical groundwater pumping schemes. These imply that the continuous groundwater pumping scheme may be more suitable to minimize groundwater salinization due to seawater intrusion. The results of the numerical simulations also show that groundwater salinization in the upper clay layer occurs significantly different from that in the lower sand layer under the periodical groundwater pumping schemes. Such differences in groundwater salinization between the two adjacent layers may result from layered heterogeneity of the layered coastal aquifer system.

• Geophysics and Geophysical Exploration
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• v.13 no.1
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• pp.24-30
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• 2010

This study utilises repeated numerical tests to understand the effects of variable near-surface conditions on time-lapse seismic surveys. The numerical tests were aimed at reproducing the significant scattering observed in field experiments conducted at the Naylor site in the Otway Basin for the purpose of $CO_2$ sequestration. In particular, the variation of elastic properties of both the top soil and the deeper rugose clay/limestone interface as a function of varying water saturation were investigated. Such tests simulate the measurements conducted in dry and wet seasons and to evaluate the contribution of these seasonal variations to seismic measurements in terms of non-repeatability. Full elastic pre-stack modelling experiments were carried out to quantify these effects and evaluate their individual contributions. The results show that the relatively simple scattering effects of the corrugated near-surface clay/limestone interface can have a profound effect on time-lapse surveys. The experiments also show that the changes in top soil saturation could potentially affect seismic signature even more than the corrugated deeper surface. Overall agreement between numerically predicted and in situ measured normalised root-mean-square (NRMS) differences between repeated (time-lapse) 2D seismic surveys warrant further investigation. Future field studies will include in situ measurements of the elastic properties of the weathered zone through the use of 'micro Vertical Seismic Profiling (VSP)' arrays and very dense refraction surveys. The results of this work may impact on other areas not associated with $CO_2$ sequestration, such as imaging oil production over areas where producing fields suffer from a karstic topography, such as in the Middle East and Australia.

• Journal of Soil and Groundwater Environment
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• v.6 no.4
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• pp.73-81
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• 2001

With the development of industry and standard of living, the quantity of groundwater consumption has been increasing. For the analysis of groundwater, to determine the hydraulic parameters of aquifer is very important. Various numerical methods have been developed to solve aquifer tests and eliminate the subjectivity of traditional graphical type curve methods. The slope-matching method, which matches the slope of the Theis type curve to the slope of the field data, can be used to numerically solve pump tests for both leaky and nonleaky aquifers. A FORTRAN program on based slope-matching method was developed to obtain the transmissivity, storage coefficient, and leaky factor from pumping test data automatically. Results derived from published data show that the improved slope-matching method gives parameters close to the ones derived by the slope-matching method.

• Journal of Soil and Groundwater Environment
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• v.24 no.3
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• pp.13-23
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• 2019

The purpose of this study is to suggest conceptual models based on finite numerical method that can be used to assess contaminant transport through subsurface and estimate exposed concentration at contaminated site. This study tested various assumptions of the numerical models for contaminant transport in unsaturated and saturated zones to simulate the pathways to the human exposal point. For this purpose, models for seven possible scenarios of contaminant transport were simulated using the numerical code MODFLOW and MT3D. The simulation results that showed different peak concentrations and travel times were compared. In conclusion, the potential utility of the numerical models in the site specific risk analysis suggested as well as future research ramifications.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2007.04a
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• pp.353-356
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• 2007

본 연구는 현재 충주호 주변의 수치지도 및 위성영상자료를 이용하여 기존의 DEM 자료로부터 3-D 영상을 생성하고 공간분석을 수행하였으며, 영상의 시계열분석을 하기 위하여 2000년 영상과 2003년 영상의 비교 분석하였다. 현재 연구중인 충주호 주변 토양도와 위성영상을 이용하여 토사유출특성 및 토양유실량을 산정 평가하였다. 충주호를 대상으로 유역특성과 유역내에서 발생되는 토사유출에 관한 정보를 분석함으로서 충주호 유역의 효율적인 관리방안을 모색하고 호수로 유입되는 하천수의 오염을 줄일 수 있도록 하였다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.272-276
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• 2004

화강암에 대한 화학적 풍화특성과 풍화 정도의 정량적으로 표현하기 위한 방법으로 조사지역의 지형자료에 기초한 습윤지수(wetness indes)를 산정하였으며, 중화속도 및 등급을 산정하였다. 습윤지수는 지형 고도를 이용하여 2-5m 크기의 격자로 구성 된 수치고도모형을 작성하여 계산하였으며 풍화속도와 등급은 Profile model을 이용하였다. 연구대상지역은 마산지역과 서부산지역으로 집수지형을 지시하는 습윤지수의 분포는 마산지역에서 다소 높은 지수 값을 보인다. 임계부하량(critical loads)에 의한 풍화등급은 마산 가포동 지역과 서부산 견마도 지역은 각각 3등급과 4등급에 해당하여 견마도 일원에서 높은 풍화 정도를 지시한다. 이와 같은 결과는 동일한 화강암 분포지의 경우에도 구성 광물의 비율과 기온과 강수량과 같은 지역적인 특성에 따라 상이한 풍화 경향이 나타남을 지시한다.

• Microbiology and Biotechnology Letters
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• v.19 no.6
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• pp.624-630
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• 1991

Sixty five phenol degrading bacteria were isolated from soil and identified. Sirnility values calculated on the basis of total 46 morphological, biochemical and physiological characteristics of the isolated strains. 65 isolates were divided into 6 clusters at the 70% simility lavei, The dominant organisms were belonged to Azotobacter, Pseudomonas and Flavobactwium.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1998.11a
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• pp.27-31
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• 1998

Most models for the simulation of multi-phase flow and multi-species transport employ the capillary approach which uses the Darcy's law for the representation of mass flux of each phase. The capillary approach based on the Darcy's law require many empirical coefficients with complex functional dependencies rather than rigrous mathematical and physical formulation. The shortcoming of the capillary approach cause the numerical errors in the simulations by the multi-phase flow and transport models. This study discuss some of the problems related with the use of models.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.04a
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• pp.202-205
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• 2001

In this study, the electrokinetic remediation test for the kaolin contaminated by lead was performed and voltage, zeta potential, pH distribution, current, contamination transport in soil sample were studied and finite differential numerical analysis program(HERP) for a contaminated soil were compared with those of test. From the result of HERP, in the anode it was represented that the rest concentration was decreased with the voltage. Hence, if treatment time was continued for a long in the constant voltage, comparing with sample having no change in the rest concentration, it is considered that the voltage gradient is the control factor of the rest concentration.