The Journal of Engineering Geology (지질공학)

The Korean Society of Engineering Geology (대한지질공학회)
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Assessment of Groundwater Contamination Vulnerability by Geological Characteristics of Unsaturated Zone

불포화대 지질특성에 따른 지하수오염취약성 평가

  • Jeong, Gyo-Cheol (Dept. of Earth and Environmental Sciences, Andong National University)
  • 정교철 (안동대학교 지구환경과학과)
  • Received : 2018.12.04
  • Accepted : 2018.12.18
  • Published : 2018.12.31
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Abstract

The media in the undersaturated zone is defined as the uppermost layer of the water table at which the groundwater is unsaturated or saturated discontinuously. The properties of the unsaturated zone can affect the reduction of contaminants that flow from the lower part of soil to the water table. In recent, there have been problems in evaluating groundwater contaminations vulnerability because weighted value for permeability is given, regardless of anisotropy and heterogeneity in the unsaturated media. Geological media have various ranges of permeability. When applying the weighted value, representative of permeability for grain sizes standardized, to construction of contamination vulnerability, it will produce more exaggerated result than the case that considers unsaturated geological properties. In this study, we performed laboratory column tests considering two sets of the unsaturated layers in order to investigate the permeability in anisotropic unsaturated zone with anisotropy. On the basis of the tests, average permeability coefficients were calculated considering the properties of unsaturated media obtained from drill cores in the field. The final contamination vulnerability map constructed shows that the contamination vulnerability map applying the properties of geological media of the unsaturated zone coincides much better with the results measured in the field, compared to the case of contamination vulnerability considering the weighted value in the unsaturated zone.

불포화대 매질은 지하수면 상부층으로서 지하수에 의해 포화되어 있지 않거나 불연속적으로 포화되어 있는 층으로 정의된다. 불포화대의 특성은 토양층 하부로부터 지하수면까지 유동하는 오염물질의 저감에 영향을 미친다. 최근 지하수오염도 평가에서는 불포화대 매질의 이방성 및 불균질성을 고려하지 않고 투수성을 나타내는 가중치를 주는 문제점이 있다. 지질학적 매질들은 다양한 범위의 투수성을 갖는다. 표준화된 입도를 대상으로 투수성을 나타내는 가중치로 오염취약도 작성에 적용한다면 불포화대 지질특성을 고려하여 작성한 오염취약도보다 과대하게 작성될 것이다. 본 연구에서는 이방성의 불균질 불포화대의 투수특성을 알아보기 위하여 복수의 불포화층을 고려한 실내 칼럼실험을 실시하였으며, 이를 바탕으로 현장 시추자료에서 얻어진 불포화대 매질의 특성에 의한 평균 투수계수로 환산하여 기존의 불포화대의 가중치를 적용한 지하수오염취약도와 불포화대 매질특성을 고려한 지하수오염취약도를 비교한 결과 불포화대 매질특성을 고려한 지하수오염취약도가 현장의 수질 측정결과와 잘 일치한다.

Keywords

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Fig. 1. Mimetic diagram of column test device.

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Fig. 2. Saturation degree of column test over time.

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Fig. 3. Soil placement mimetic diagram.

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Fig. 4. Variation of the permeability coefficient according to the change of bentonite content.

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Fig. 5. Volumetric water content change of TDR (Bentonite 5%).

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Fig. 6. Volumetric water content change of TDR (Bentonite 10%).

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Fig. 7. Volumetric water content change of TDR (Bentonite 20%).

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Fig. 8. Boring long of study area.

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Fig. 9. Result value of each zone by HYDRUS-10.

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Fig. 10. Groundwater contamination vulnerability by DRASTIC.

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Fig. 11. Groundwater contamination vulnerability by improved DRASTIC.

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Fig. 12. Coincide with the results measured in the field compared to the contamination vulnerability.

Table 1. Physical property of standard sand used in experiment

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Table 2. Permeability coefficient equation

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Table 3. Permeability coefficient of TDR-1 and TDR-2

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Table 4. Variable value of soil hydraulic characteristic in study area

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Table 5. Analysis results by cation and anion of bedrock groundwater

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Table 6. Analysis results by cation and anion of alluvial groundwater

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