• Title/Summary/Keyword: shallow groundwater

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Frture mapping and deep-seated ground water exploration in the crystalline rocks by integrated geophysical techniques (종합적 물리탐사에 의한 파쇄대 및 심부 지하수 탐사)

  • 정승환;김정호;조인기;전정수
    • The Journal of Engineering Geology
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    • v.2 no.2
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    • pp.113-130
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    • 1992
  • Groundwater in crystalline basement is controlled primarily by tectonic fractures. It is evident that the delineation of the heavily faulted area and/or fractures deeply developped should be considerable value in deep-seated low enthalphy geothermal water. Electrical and electromagnetic methods have effectively been employed to map hydraulic faults and shear zones for groundwater exploration. In this study VLi; dipoledipole resistivity, controlled source audio~frequency magneto-telluric(CSAMT) and magnetic methods were applied in the Bomun resort area, adjacent to Kyongju city, southeastern part of Korea. The integrated geophysical tools employed in this experiment can be manifested themselves as: 1. Magnetic high for granite intrusions which is more favorable for geothermal gradient increase in depth. 2. VLF cross-over trends for mapping linear shallow conductive fractures and shear zones. 3. Dipole-dipole resistivity distributions for the deep-seated(less than 500m in depth) fractures and shear zones. The dipole-dipole resistivity field data were inverted to the true resistivity distribution with two-dimensional automatic inversion program based on the finite-difference method. 4. CSAMT provides an efficient way of delineating fractures and fault zones if the depth is greater than about 500m.

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Variations of Soil Temperatures in Winter and Spring at a High Elevation Area (Boulder, Colorado)

  • Lee, Jin-Yong;Lim, Hyoun Soo;Yoon, Ho Il;Kim, Poongsung
    • Journal of Soil and Groundwater Environment
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    • v.20 no.5
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    • pp.16-25
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    • 2015
  • The City of Boulder is located at an average elevation of 1,655 m (5,430 feet), the foothills of the Rocky Mountains in Colorado. Its daily air temperature is much varying and snow is very frequent and heavy even in spring. This paper examines characteristics of shallow (surface and depth = 10 cm) soil temperatures measured from January to May 2015 in the high elevation city Boulder, Colorado. The surface soil temperature quickly responded to the air temperature with the strongest periodicity of 1 day while the subsurface soil temperatures showed a less correlation and delayed response with that. The short-time Fourier of the soil temperatures uncovered their very low frequencies characteristics in heavy snow days while it revealed high frequencies of their variations in warm spring season. The daily minimum air temperature exhibited high cross-correlations with the soil temperatures without lags unlike the maximum air temperature, which is derived from its higher and longer auto-correlation and stronger spectrums of low frequencies than the maximum air temperature. The snow depth showed an inverse relationship with the soil temperature variations due to snow's low thermal conductivity and high albedo. Multiple regression for the soil temperatures using the air temperature and snow depth presented its predicting possibility of them even though the multiple r2 of the regression is not that much satisfactory (r2 = 0.35-0.64).

Mapping the water table at the Cheongju-Gadeok site of the Korea National Groundwater Monitoring Network using multiple geophysical methods

  • Ju, Hyeon-Tae;Sa, Jin-Hyeon;Kim, Ji-Soo
    • The Journal of Engineering Geology
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    • v.27 no.3
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    • pp.305-312
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    • 2017
  • The most effective way to distinguish subsurface interfaces that produce various geophysical responses is through the integration of multiple geophysical methods, with each method detecting both a complementary and unique set of distinct physical properties relating to the subsurface. In this study, shallow seismic reflection (SSR) and ground penetrating radar (GPR) surveys were conducted at the Cheongju-Gadeok site of the Korea National Groundwater Monitoring Network to map the water table, which was measured at 12 m depth during the geophysical surveys. The water table proved to be a good target reflector in both datasets, as the abrupt transition from the overlying unsaturated weathered rock to the underlying saturated weathered rock yielded large acoustic impedance and dielectric constant contrasts. The two datasets were depth converted and integrated into a single section, with the SSR and GPR surveys conducted to ensure subsurface imaging at approximately the same wavelength. The GPR data provided detailed information on the upper ~15 m of the section, whereas the SSR data imaged structures at depths of 10-45 m. The integrated section thus captured the full depth coverage of the sandy clay, water table, weathered rock, soft rock, and hard rock structures, which correlated well with local drillcore and water table observations. Incorporation of these two geophysical datasets yielded a synthetic section that resembled a simplified aquifer model, with the best-fitting seismic velocity, dielectric constant, and porosity of the saturated weathered layer being $v_{seismic}=1000m/s$, ${\varepsilon}_r=16$, and ${\phi}=0.32$, respectively.

Evaluation and characteristics of commercial Portable ground-water in Korea

  • Cho, Byong-Wook;Sung, Ig-Hwan;Choo, Chang-O;Lee, Byeong-Dae;Kim, Tong-Kwon;Lee, In-Ho
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • 1998.11a
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    • pp.119-122
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    • 1998
  • Chemical analysis, measurement of pumping rates of 60 production wells and depth to water tables of 57 monitoring wells were carried to protect depletion of water resources and deterioration of water quality for the commercial portable ground-water. Borehole depth of production well averages 149m(31 boreholes), casing depth is 28m(29 boreholes), production rate is 70 $m^3$/day and depth to water table of monitoring well is 23.26m, respectively. The geology of 60 wells can be divided into Daebo granite(20), Okchun metarmorphic complex(18), Precambrian granitic gneiss(15), Bulguksa granite(4), Cheju volcanics(2), Cretaceous sedimentary rock(1). Average electrical conductivity and pH are 152$\mu$S/cm, and 7.35, respectively. The contents of major cation and anion predominantly $Ca^{2+}$>N $a^{+}$>M $g^{2+}$> $K^{+}$ and HC $O_{3}$$^{-}$ >S $O_{4}$$^{2-}$>Cl ̄>F ̄. Water type is predominantly $Ca^{2+}$-HC $O_{3}$$^{-}$(81.7%). It's possible that water chemistry of some wells were affected not only by the geology of boreholes penetrated but by inflows of surface water or shallow ground-water. Therefore, it is strongly necessary to steadily monitor the water quality and hydrogeologic conditins of production wells.ells.ls.ells.

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In-situ Monitoring of Matric Suctions in a Weathered Soil Slope (풍화토 사면에서 강우로 인한 간극수압 변화에 대한 실험연구)

  • 이인모;조우성;김영욱;성상규
    • Journal of the Korean Geotechnical Society
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    • v.19 no.1
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    • pp.41-49
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    • 2003
  • Rainfall-induced landslides in a weathered granite soil slope usually happen on shallow slip surfaces above the groundwater table. The pore-water pressure of soil above the groundwater table is usually negative. This negative pore-water pressure (or matric suction) has been found to make a large contribution to the slope stability. Therefore, the variation of in-situ matric suction profiles with time elapse in a soil slope should be understood. In this study, a field measurement program was carried out from June to August, 2001 in order to monitor in-situ matric suctions and volumetric water contents in a weathered granite soil slope. Finite-element transient seepage analyses are also conducted using SEEP/W. The influence of climatic conditions on the variation of in-situ matric suctions could be found to decrease rapidly with the change of depth. It could be found that decrement of matric suction induced by precipitation is affected not only by the amount and duration of rainfalls but also by the initial matric suction just prior to rainstorms. The soil-water characteristic from the field monitoring tends toward the wetting path of SWCC obtained from the laboratory test.

Watershed Classification Using Statistical Analysis of water Quality Data from Muju area (무주지역 수질특성자료의 통계학적 분석에 의한 소유역 구분)

  • 한원식;우남칠;이기철;이광식
    • Journal of Soil and Groundwater Environment
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    • v.7 no.3
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    • pp.19-32
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    • 2002
  • This study is objected to identify the relations between surface- and shallow ground-water and the seasonal variation of their qualities in watersheds near Muju area. The water type shows mainly Ca-$HCO_3$type. Heavy-metal contamination of surface water is locally detected, due to the mixing with mine drainage. In October nitrate concentration is especially high in densely populated area. Cluster Analysis and Principal Component Analysis are implemented to interpret the complexity of the chemical variation of surface- and ground-water with large amount of chemical data. Based on the cluster analysis, surface-water was divided into five groups and ground-water into three groups. Principal Component Analysis efficiently supports the result of cluster analysis, allowing the identification of three main factors controlling the water quality. There are (1) hydrogeochemical factor, (2) anthropogenic factor and (3) heavy metal contaminated by mine drainage.

Surface Geophysical Survey for Delineation of Weathered Zone of Chojeong Area and Investigation of Fault Fracture Zones (초정지역의 풍화대 조사 및 단층파쇄 지역의 불연속면 조사를 위한 지표물리탐사)

  • Kim, Ji-Soo;Han, Soo-Hyung
    • The Journal of Engineering Geology
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    • v.17 no.4
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    • pp.517-523
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    • 2007
  • Geophysical surveys(seismic refraction, electrical resistivity, and ground penetrating radar) were performed to delineate the weathering zone associated with vadose water in Chojeong area and investigate the fault related fracture zones. On the basis of seismic velocity structures, weathering layer for the southwestern part is interpreted to be deeper than for the northeastern part. The depth to bedrock(i.e., thickness of weathered zone) from seismic refraction data attempted to be correlated with drill-core data and groundwater level. As for the investigation of geological discontinuities such as fault related fracture zone, seismic refraction, electrical resistivity, and ground penetrating data are compositely employed in terms of velocity and resistivity structures for mapping of surface boundary of the discontinuities up to shallow depth. Surface boundaries of fracture zone are well indicated in seismic velocity and electrical resistivity structures. Accurate estimation of weathered zone and fracture zone can be successfully available for mapping of attitude of vadose water layer.

A Study on Development Potential of Shallow Geothermal Energy as Space Heating and Cooling Sources in Mongolia (몽골의 천부 지열에너지(냉난방 에너지)개발 가능성에 관한 연구)

  • Hahn, Jeong-Sang;Yoon, Yun-Sang;Yoon, Kern-Sin;Lee, Tae-Yul;Kim, Hyong-Soo
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.8 no.2
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    • pp.36-47
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    • 2012
  • Time-series variation of groundwater temperature in Mongolia shows that maximum temperature is occured from end of October to the first of February(winter time) and minimum temperature is observed from end of April to the first of May(summer time). Therefore ground temperature is s a good source for space heating in winter and cooling in summer. Groundwater temperatures monitored from 3 alluvial wells in Ulaabaatar at depth between 20 and 24 m are $(4.43{\pm}0.8)^{\circ}C$ with average of $4.21^{\circ}C$ but mean annual ground temperature(MAGT) at the depth of 100 m in Ulaanbaatar was about $3.5{\sim}6.0^{\circ}C$. Bore hole length required to extract 1 RT's heat energy from ground in heating time and to reject 1 RT's heat energy to ground in summer time are estimated about 130 m and 98 m respectively. But in case that thermally enhanced backfill and U tube pipe placement along the wall are used, the length can be reduced about 25%. Due to low MAGT of Ulaabaatar such as $6^{\circ}C$, the required length of GHX in summer cooling time is less than the one of winter heating time. Mongolia has enough available property, therefore the most cost effective option for supplying a heating energy in winter will be horizontal GHX which absorbs solar energy during summer time. It can supply 1 RT's ground heat energy by 570 m long horizontally installed GHX.

Speculation on the Water Quality for the Natural Mineral Water (국내 먹는샘물의 특정 수질 항목에 대한 고찰)

  • 조병욱;이병대;이인호;추창오
    • The Journal of Engineering Geology
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    • v.12 no.4
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    • pp.395-404
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    • 2002
  • Contents of the specific components in the natural mineral water was discussed in relation to the well depth and geology. According to water quality data during the last five years(1998~2002), the nitrate and fluoride concentrations, and pH averaged 0.89~ 1.09 mg/L, 0.37~0.45 mg/L, and 7.30~7.59, respectively. These values are the similar range to those of generalized groundwater having same well depths, implying that shallow groundwaters flow into the production wells. In general, no clear relationships between the water quality, well depth, and geology were found. The average arsenic concentration of the natural mineral water increased from 0.0024 mg/L in 1999 to 0.0066 mg/L in 2002. The percentage of production well with arsenic level higher than 0.001 mg/L also increased from 20.1% in 1999 to 64.9% in 2002. In 2002, 11 out of 57 production wells exceed 0.001 mg/L which will be announced as a new arsenic standard for drinking water by USEPA.

Analysis of Subsidence Mechanism and Development of Evaluation Program (지반침하 메커니즘 분석 및 평가 프로그램 개발)

  • Choi Sung O.;Jeon Yang-Soo;Park Eu-Sup;Jung Yong-Bok;Chun Dae-Sung
    • Tunnel and Underground Space
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    • v.15 no.3 s.56
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    • pp.195-212
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    • 2005
  • Surface subsidence which occurs with several reasons, such as collapse of gangway, discharge of groundwater, compaction of weak rock mass, and tunnel excavation in shallow depth, gives rise to a serious problem in national infra-structures. In this study, therefore, the mechanism of subsidence has been examined numerically to overcome the passive approach on subsidence occurrence area. With many kinds of numerical studies, the major geotechnical parameters have been selected and the weighted values have been defined for each parameters. Also the authors developed the numerical program which can estimate the possibility of subsidence occurrence, and proposed the decision method for objective and quantitative guideline. It is anticipated that this research will be helpful to establish the hazard map on subsidence region.