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Koh, Dong-Chan,Genereux, David P.,Koh, Gi-Won,Ko, Kyung-Seok Elsevier 2017 Chemical geology Vol.467 No.-
<P><B>Abstract</B></P> <P>Groundwater from pristine volcanic rock aquifers on dormant Jeju Island, Korea, was investigated to identify sources and geochemical processes of dissolved inorganic carbon (DIC) and related solutes along with characteristics of groundwater flow using a multi-isotope approach. δ<SUP>18</SUP>O, δ<SUP>2</SUP>H, and <SUP>3</SUP>H of groundwater indicated the water is of meteoric origin, and is mainly derived from recent recharge, except Na-rich mineral water which has a significant contribution of <SUP>3</SUP>H-free old water. <SUP>87</SUP>Sr/<SUP>86</SUP>Sr of dissolved Sr suggests that solutes in groundwater were mainly derived from old alkali basalt in the lower part of lava flows. δ<SUP>13</SUP>C<SUB>CO2(g)</SUB> calculated using δ<SUP>13</SUP>C<SUB>DIC</SUB> and measured hydrogeochemical parameters indicated that (1) biogenic soil CO<SUB>2</SUB> is a dominant source of DIC in low mineralized water, (2) CO<SUB>2</SUB>-rich water had mostly mantle-derived magmatic CO<SUB>2</SUB>, and (3) mineral water contained both biogenic and magmatic CO<SUB>2</SUB>. δ<SUP>13</SUP>C<SUB>CO2(g)</SUB> in mineral water was affected by precipitation of calcite, which complicated the estimation of the contribution of CO<SUB>2</SUB> sources to DIC. Concentrations of mobile elements were mainly controlled by the amount of magmatic CO<SUB>2</SUB> and groundwater residence time. δ<SUP>13</SUP>C<SUB>CO2(g)</SUB> and <SUP>3</SUP>H content were used to distinguish four types of groundwater with different spatial patterns of occurrence in relation to the volcanic stratigraphy of Jeju Island. Groundwater types I and II are low mineralized water with lower levels of DIC from biogenic CO<SUB>2</SUB>, composed of either recent recharge (<40years, type I) or older water with negligible <SUP>3</SUP>H (>60years, type II). Type III is Mg-rich mineral water with significant recent recharge while type IV is Na-rich mineral water with older residence time. Types III and IV had somewhat elevated levels of DIC (up to 7.6mM) with mixed signatures of magmatic and biogenic CO<SUB>2</SUB>, while CO<SUB>2</SUB>-rich water (a subset of type III) had DIC up to 100mM with signatures of mantle-derived magmatic CO<SUB>2</SUB>. Groundwater in the eastern area of Jeju Island is mostly type I, which can be attributed to a lack of both low-permeability rocks and recent volcanic rocks in that area. Types III and IV were found in the western area where the latest volcanic rocks are distributed. In the southwestern area, type III is associated with permeable basaltic aquifers with a contribution of magmatic CO<SUB>2</SUB> and type IV is from the younger lava flows dissected by older massive trachytic rocks and shallower hydrovolcanic tuffs, which led to the higher degree of mineralization. A conceptual model is proposed to integrate the chemical and isotopic constraints of groundwater with volcanic stratigraphy and suggest the processes that generated groundwater types with different residence times and chemical compositions. This study may contribute to understanding the processes of groundwater flow and mineralization in volcanic aquifers affected by deep-source CO<SUB>2</SUB> and variable residence time of groundwater in both dormant and active volcanic areas.</P>
Dong-Chan Koh(고동찬),Beom-Kyu Choi(최범규),Yongje Kim(김용제) 대한자원환경지질학회 2007 자원환경지질 Vol.40 No.1
대기와 물에서의 CFCs (CFC-12, CFC-11, CFC-113)를 분석할 수 있는 시스템을 자체 제작된 퍼지-트랩 추출 장치와 전자포획검출기가 설치된 가스 크로마토그래피를 이용하여 구축하였다. 대기와 물에 대한 시료 채취방법도 확립되었다. 분석 시스템은 실험적으로 최적화되어 최근 대기 시료는 2% 이내, 제주도의 지하수 시료 (CFC-12 농도가 160~180 pg/kg) 는 5% 이내의 삼중복시료에 대한 재현성을 보였고, 미국지질조사소 (USGS)의 분석시스템과 교차 분석을 실시하였으며, 10% 오차 범위내에서 일치하였다. 한반도 중부 지역의 세 지점에 대해 19개월에 걸쳐 대기 중의 CFCs를 관측하여 이 지역에서 국지적인 CFCs 근원이 크지 않음을 확인하였다. 제주도의 한 농업용 공공 관정에서 2개월 간격으로 1년 동안 지하수의 CFCs를 관측한 결과 8월까지 지하수의 CFCs 농도가 감소하고 10월 이후에 다시 증가하는 계절적인 변동을 보여 주었다. 이것은 여름철 우기에 발생한 지하수 함양이 수 개월 지연되어 나타난 결과로 볼 수 있으며, 제주도 현무 암 대수층의 높은 투수성을 지시한다. CFC (CFC-12, CFC-11 and CFC-113) analytical system for air and water was constructed using a customized purge and trap extraction device and a gas chromatograph with an electron capture detector. Sampling methods of air and water for CFCs were also established. The analytical system was experimentally optimized to result in reproducibilities of triplicates less than 2% for current air samples and less than 5% for groundwater samples with CFC-12 concentration of 160 to 180 pg/kg, and verified with respect to the CFC system in USGS, which showed analytical results were in agreement within 10%. CFCs in air were monitored at three sites over 19-month period in the central part of South Korea, and the result indicates no significant local sources of CFCs in those areas. For groundwater in Jeju Island, CFCs were measured over a year with a two-month interval. The time-series data showed seasonal fluctuations which could be interpreted by the effect of recharge pulse derived from large amount of rainfall during monsoon period with a few month delay, which indicates high permeability of basaltic rocks in Jeju Island.
Koh, Dong-Chan,Kim, Eun-Young,Ryu, Jong-Sik,Ko, Kyung-Seok John Wiley Sons, Ltd. 2009 Hydrological processes Vol.23 No.20
<P>Shallow and bedrock groundwater from granitic aquifers were investigated for the hydrogeochemistry of major and minor constituents in an agricultural area. Nitrate concentrations were observed up to 49 mg/l as NO<SUB>3</SUB>-N, with 22% of samples exceeding the drinking water standard, which could pose a significant threat because most residents rely on groundwater as their drinking water source. Principal component analysis revealed three principal components (PCs): (1) nitrate contamination, contributed by major cations, Cl<SUP>−</SUP>, SO<TEX>$_{4}^{2-}$</TEX> and NO<TEX>$_{3}^{-}$</TEX>, (2) reduction processes positively involving Fe, Mn and B, and negatively involving dissolved oxygen and NO<TEX>$_{3}^{-}$</TEX> and (3) natural mineralization, involving HCO<TEX>$_{3}^{-}$</TEX> and F<SUP>−</SUP>. Cluster analysis, performed on the PC scores, resulted in seven sample groups, which were successfully identified by total depth, elevation and land use. The nitrate-contaminated groups had mixed land uses, with locally concentrated residential areas. Uncontaminated groundwater groups were found in the natural environment, including high-altitude spring water and bedrock groundwater with a higher degree of natural mineralization. Shallow groundwater groups in paddy fields in lowlands were affected by reducing environments, of which one group was characterized by high Fe, Mn and B, and negligible nitrate. Groundwater with intermediate nitrate and lower Cl<SUP>−</SUP> and SO<TEX>$_{4}^{2-}$</TEX> was found primarily in hilly terrains with orchards and vegetable gardens, indicating lower contaminant loadings than lowland areas. Higher concentrations of F<SUP>−</SUP> and nitrate were observed in the nitrate-contaminated water, which seemed unlikely to be explained by groundwater mixing. The strong acidity generated from nitrification may infiltrate deeper into the aquifer, induce accelerated weathering of bedrock and result in the coexistence of F<SUP>−</SUP> and nitrate, which may be an evidence of intense nitrate loading, leading to soil acidification. Multivariate statistical analysis successfully delineated hydrochemical characteristics of groundwater attained by natural and anthropogenic processes in an agriculturally stressed area with complex topographic land use patterns. Copyright © 2009 John Wiley & Sons, Ltd.</P>
Koh, Dong-Chan,Chang, Ho-Wan,Lee, Kwang-Sik,Ko, Kyung-Seok,Kim, Yongje,Park, Won-Bae John Wiley Sons, Ltd. 2005 Hydrological processes Vol.19 No.11
<P>Ground water from springs and public supply wells was investigated for hydrochemistry and environmental isotopes of <SUP>3</SUP>H, <SUP>18</SUP>O and D in Jeju volcanic island, Korea. The wells are completed in a basaltic aquifer and the upper part of hydrovolcanic sedimentary formation. Nitrate contamination is conspicuous in the coastal area where most of the samples have nitrate concentrations well above 1 mg NO<SUB>3</SUB>&bond;N/l. Agricultural land use seems to have a strong influence on the distribution of nitrate in ground water. Comparison of stable isotopic compositions of precipitation and ground water show that ground water mostly originates from rainy season precipitation without significant secondary modification and that local recharge is dominant. <SUP>3</SUP>H concentration of ground water ranged from nearly zero to 5 TU and is poorly correlated with vertical location of well screens. The occurrence of the <SUP>3</SUP>H-free, old ground water is due to the presence of low permeability layers near the boundary of the basaltic aquifer and the hydrovolcanic sedimentary formation, which significantly limits ground water flow from the upper basaltic aquifer. The old ground water exhibited background-level nitrate concentrations despite high nitrate loadings, whereas young ground water had considerably higher nitrate concentrations. This correlation of <SUP>3</SUP>H and nitrate concentration may be ascribed to the history of fertilizer use that has increased dramatically since the early 1960s in the island. This suggests that <SUP>3</SUP>H can be used as a qualitative indicator for aquifer vulnerability to nitrate contamination. Copyright © 2005 John Wiley & Sons, Ltd.</P>