• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.217-217
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• 2019

해안과 하천이 위치해 있는 낙동강하구의 담 염수 경계면 추적 연구에서 담 염수 경계면의 담수기원특성을 분석하기 위해서는 담 염수 경계면을 이루는 담수의 기원이 하천 혹은 지하수 인지를 규명하는 것이 매우 중요하다. 담 염수 경계면에 있는 담수는 일반적으로 하천과 지하수에 의한 것으로, 낙동강하구 일원을 대상으로 지하수공 내 해수침투 여부 파악을 위해 화학적(유기물) 분석을 실시하였다. 이와 아울러 낙동강하구 일원에서 담 염수 경계면에서 채취한 수질시료의 담수기원을 분석하기 위하여 K-water연구원 수질안전센터에 지하수공 7개지점(BH-1~7호공)의 심도별 물시료 2~4개지점(총 23개 지점), 하천(1개 지점), 해수 및 해안유출수(각 1개 지점)를 포함한 26개 시료를 LC-OCD(Liquid Chromatography-Organic Carbon Detector)로 분석하였다. LC-OCD 분석결과 특성은 기본적으로 유기물질이 물에서 유래한 aquagenic 혹은 토양층에서 유래한 pedogenic 유기물질 인지에 달려있다. 댐 또는 하천에서 pedogenic 유기물의 농도는 일반적으로 유역분지의 수문 또는 수리지질학적 경로에 의존한다. pedogenic 유기물들은 주로 상대적으로 작은 분자량을 갖는 친수성, 높은 사슬밀도 및 내화성 분자특성을 갖는 펄빅산으로 구성된다. aquagenic 유기물질은 수생 식물성 생물이나 플랑크톤의 분해 산물로서 세포벽에서 유래된 peptidoglycans와 고분자량의 polysaccharides 등을 포함한다(Chio & Jung, 2008; Buffle, 1988). 담 염수 경계면 추적을 위한 7개 관측공의 심도별 수질시료는 하천, 해수, 그리고 해안유출수의 용존유기탄소를 분석하기 위하여 LC-OCD로 정밀분석하였다. 그 결과, humic, 휴믹물질의 산화물질인 building blocks, 생물고분자 물질(bio-polymers), neutrals, acids로 분석되었으며, 일반적인 자연유기물질의 기원은 pedogenic과 aquagenic 유기물질로 분류된다. IHSS 표준물질 분석 등을 통한 SUVA 값으로부터 자연유기물질의 기원정보를 제공하는 HS-Diagram으로 도시한 결과, 2018년 11월 2일 조사한 26개의 원수시료 전체는 pedogenic fulvic acid〉aquagenic fulvic acid으로 하천의 기원이 우세한 것으로 분석되었다. BH-1호공과 BH-6호공의 특정 1개구간 GL.-6m를 제외한 모든 구간에서 aquagenic FA의 지하수 기원으로 분석되었으며, 나머지 지하수공(BH-2, 3, 4, 5, 7)과 하천 및 해안유출수는 유역분지 수문학적 경로인 pedogenic FA의 하천 기원의 담수인 것으로 분석된다.

• Economic and Environmental Geology
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• v.27 no.2
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• pp.191-199
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• 1994

We have developed an algorithm based on the method of integral equations to simulate the magnetotelluric (MT) responses of three-dimensional (3-D) bodies in a layered half-space. The inhomogeneities are divided into a number of cells and are replaced by an equivalent current distribution which is approximated by pulse basis functions. A matrix equation is constructed using the electric Green's tensor function appropriate to a layered earth, and is solved for the vector current in each cell. Subsequently, scattered fields are found by integrating electric and magnetic Green's tensor functions over the scattering current About a 3-D conductive body near the earth's surface, interpretation using 2-D transverse electric modeling schemes can imply highly erratic low resistivities at depth. This is why these routines do not account for the effect of boundary charges. However, centrally located profiles across elongate 3-D prisms may be modeled accurately with a 2-D transverse magnetic algorithm, which implicitly includes boundary charges in its formulation. Multifrequency calculations show that apparent resistivity and impedance phase are really two complementary parameters. Hence, they should be treated simultaneously in broadband MT interpretation.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.205-215
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• 2009

The conventional numerical models to analyze flow in subsurface porous media under the transient state usually generate numerical oscillation and unstability due to local flux domain for critical cases such as infiltration into initially dry soil during rainfall period. In this case, it is required refined mesh and small time step, but it decrease efficiency of computation. In this study, numerical unstability in discontinuity domain is removed by applying particle tracking algorithm to simulate unsteady subsurface flow with inflow boundary condition. Finally the hybrid LE FEM improving numerical stability is proposed. The hypothetical domains with unsteady uniform and nonuniform flow field were used to demonstrated algorithm verification. In comparison with analytic solution, we obtained reasonable results and conducted simulation of hypothetical 3-D recharge/pumping area. The proposed algorithm can simulate saturated/unsaturated porous media with more practical problems and will greatly contribute to accuracy and stability of numerical computation.

• The Journal of Engineering Geology
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• v.9 no.1
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• pp.59-68
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• 1999

To clarify the geological structure of Yangsan fault around Sangchon-ri in the southern part of Kyungsang Basin the resistivity (dipole-dipole profiling) and VLF surveys carried out on the four profiles, crossing the inferred trace of the fault. The resistivity contrast across the fault is clearly shown on the profiles: higher resistivity and lower resistivity on the east and west, respectively. It is most likely from the uplift of the granitic bedrock on the east park due to the strike-fault raulting with vertical movement. The zero-crossing points of VLF anomalies, associated with near-surface fracture zone, are found to well correlate with the resistivity boundaries from the dipole-dipole profiling. Consequently, southern segment of Yangsan fault (at Sangchon-ri area) is interpreted to be vertically developed strike-slip fault with a difference more than 10m depth of basement rock at both sides.

• Economic and Environmental Geology
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• v.37 no.5
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• pp.543-554
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• 2004

Analysis of multi-channel seismic reflection and well data serves to detail the structural evolution of the northern Okinawa Trough, southern offshore Korea. The overall structural style of the area is characterized by a series of half grabens and tilted fault blocks bounded by basement-involved listric normal faults. Most half grabens and tilted fault blocks developed in the direction of NNE-SSW, parallel to the axis of the Okinawa Trough. Orientation and distribution of the listric faults also suggest the development of transfer faults in NW-SE direction. The rifting phase of the northern Okinawa Trough have been established on the basis of structural and stratigraphic analyses of depositional sequences and their seismic expressions. Major phase of rifting probably started in the Late Miocene and the most active rifting occurred during the Early Pliocene. The rifting produced a series of half grabens and tilted fault blocks bounded by listric normal faults. It appears that the rifting activity has become weaker since the Late Pliocene, but the Pleistocene sediments faulted by listric faults bounding tilted fault blocks suggest that the rifting activity is probably still in progress.

• The Journal of Engineering Geology
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• v.25 no.3
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• pp.369-376
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• 2015

Numerical models simulating groundwater flow are often used to estimate groundwater discharge into a tunnel. In designing numerical models, the grid size should be carefully considered to ensure that groundwater discharge is accurately predicted. However, several recent studies have employed various grid sizes without providing an adequate explanation for their choice. This paper suggests the optimal grid size based on a comparison of numerical models with analytical solutions. Discrepancies between numerical and analytical solutions result from the effect of model boundaries as well as the grid size. By nullifying boundary effects, the errors solely associated with the grid size could be analyzed. The optimal grid size yielding accurate numerical solutions was thus derived. The suggested relationship between tunnel radius and optimal grid size is analogous to the relationship between the equivalent well block radius and grid size.

• Economic and Environmental Geology
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• v.29 no.3
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• pp.345-355
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• 1996

The effectiveness of various electrode configurations in horizontal mappings and 1-D inversions of vertical sounding data for delineating 2-D structures was studied. Apparent resistivity values of three point, dipole-dipole, Wenner, and Schlumberger mappings were simulated for such structures as vertical dyke, tabular prism, buried vertical fault, ramp and complex structure by finite difference method (FDM) and they were compared with each other. Also 2-D cross sections for three structures obtained by interpolation of 1-D inverted sounding data in terms of three layers were compared for Schlumberger and Wenner arrays. On these cross sections, horizontal and vertical resistivity interfaces of the 2-D structures are revealed relatively clearly. Apparent resistivity curves of Schlumberger mapping show vertical resistivity discontinuities very well. On the whole, Schlumberger array is superior to the other arrays in electric sounding as well as mapping. This study clearly indicates that interpretations of 2-D structures based on 1-D inversion are possible.

• Economic and Environmental Geology
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• v.2 no.2
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• pp.1-35
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• 1969

The structure and geologic history of the Triassic basin in southern Connecticut have been interpreted by using gravimetric data. A gravity survey of 800 gravity stations was made by the U.S. Geological Survey in the southern Connecticut area. The resulting data were reduced by the Bouguer method and then plotted and contoured along with the generalized geology. Residual gravity maps were prepared by different methods to obtain the most plausible agreement with the known geology of the area. Seven gravity profiles across the basin are presented to show the distribution of the Triassic deposits that could produce the measured anomalies. It is concluded that the basin was formed by successive step faulting in the late Triassic period and that the sediments accumulated progressively in this basin. The deepest portion of the basin is located in the middle of the present Triassic belt and reaches a depth of about 2 miles below the surface. The data also appear to indicate the possible source areas for the basalt which at present forms the lava flows, sills, and dikes exposed in the Cheshire and Gaillard regions. The information concerning the tectonic history of the Connecticut Triassic Valley aids considerably in establishing the geologic history of the Appalachians in late Triassic time.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.11 no.3
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• pp.253-257
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• 2013

Geology, hydrogeology, and geochemistry are the main technical siting factors of a geological repository for spent nuclear fuels. This paper evaluated the siting criteria of overseas geological repository with related to hydrogeologic properties, such as hydraulic conductivity, partitioning coefficient, dispersion coefficient, boundary condition, and water age. Each country establishes the siting criteria based on its important geological backgrounds and information, and social environment. For example, Sweden and Finland that have decided a crystalline rock as a host rock of a geological repository show different siting criteria for hydraulic conductivity. In Sweden, it is preferable to avoid area where the hydraulic conductivity on a deposition hole scale (~30m) exceeds $10^{-8}m/s$, whereas Finland does not decide any criterion for the hydraulic conductivity because of limited data for it. In addition, partitioning coefficients should be less than 10-1 of average value in Swedish crystalline bedrock. However, the area where shows 100 times less than average partitioning coefficients of radionuclides in crystalline rock should be avoided in Sweden. In German, the partitioning coefficients for the majority of the long-term-relevant radionuclides should be greater than or equal to $0.001m^3/kg$. Therefore, it is strongly required to collect much and exact information for the hydrogeologic properties in order to set up the siting criteria.

• The Journal of Engineering Geology
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• v.25 no.2
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• pp.251-263
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• 2015

Geological mapping, borehole drilling, electrical resistivity, and seismic tomography surveys were conducted in order to map underground cavities and better understand the mechanisms driving subsidence in a limestone region in Korea. Limestone outcrops in the study area generally alternate between calcite-rich and calcite-poor rock. The results reveal that in areas experiencing subsidence, cavities occur mainly around soil-rock boundaries at depths of 7~14 m. These results are based on comparative analyses of electrical resistivity, seismic tomography, and borehole logging data. The volumes of the cavities are relatively small in a range of 558~835 ㎥ and they have a shape typical of suffosion sinkholes, which are typically found where sandy soils overlie bedrock cavities.