Part Ⅰ: Hydrochemical and statistical research suggest that groundwaters from meandering riverside alluvial aquifers in Buyeo, South Korea are clustered into 3 groups both dry and wet season of 2001 and 2002. Ca-(SO_(4))-NO_(3) type (n=12) groundwaters (Group Ⅰ) are highly contaminated by nitrate (u...
Part Ⅰ: Hydrochemical and statistical research suggest that groundwaters from meandering riverside alluvial aquifers in Buyeo, South Korea are clustered into 3 groups both dry and wet season of 2001 and 2002. Ca-(SO_(4))-NO_(3) type (n=12) groundwaters (Group Ⅰ) are highly contaminated by nitrate (up to 294.6mg/L) and also high in redox potential (Eh), total dissolved solid (TDS), Ca, Mg, and SO_(4), but low in pH and alkalinity. This group is located near the Geum River, where coarse-grained sediments has been deposited and intensively fertilized. Particularly, nitrification increases acidity which enhance the dissolution of minerals and/or agrochemicals such as calcite, biotite, lime, and mixed fertilizers. Whereas Ca-HCO_(3) type (n=12) groundwaters (Group Ⅱ) are observed where fine sediment has been deposited. The lowest Eh, nitrate (NO_(3) mean=1.5 mg/L), sulfate, and highest pH, alkalinity, dissolved carbon (DOC), and Fe concentrations of Group Ⅱ groundwater indicate that the denitrification dominantly takes place in this environment. Other samples were belong to the Group Ⅲ, which were moderately contaminated by NO_(3) (n=31; NO_(3) mean=49.1 mg/L). Group Ⅲ groundwaters occupy most of study area, then this group represents the groundwater quality of this area. In a geomorphological point of view, the pattern of distribution of groups is related to the dynamical sedimentation of 'point bar'. The Group Ⅰ area, which was a sand island in 1923, was merged to point par in recent years, then the sediments and soil are not consolidated yet. On the other hand, Group Ⅱ area is located in the end and the center of point bar therefore silt and clay can be accumulated and characterized as 'riparian zone'. These fine-grained sediments contain sufficient reducing agent such as organic carbon and pyrite then prevent the oxygen and form a reducing environment. The spatial distribution of these groups doesn't change significantly with season except that of Group Ⅰ, indicating hydrochemical characteristics of groundwaters are mainly controlled by geology of this meandering riverside alluvium. The results of this study can be applied to the water use technology such as bank filtration and underground damming. In Korea, this study is the first attempt to integrated approaches, i.e., hydrology, hydrochemistry, geophysics, and sedimentology, to elucidate the hydrogeological and hydrochemical processes in an alluvial aquifer. Part Ⅱ: Inverse (mass balance) and forward (reaction) hydrochemical modeling methods are applied to explain the hydrochemistry of groundwaters from Buyeo alluvial aquifer. Groundwaters collected in 2001 are hydrogeochemically and statistically classified into three groups: highly contaminated (Group Ⅰ: NO_(3) mean=194.7 mg/L), moderately contaminated (Group Ⅲ: NO_(3) mean=58.4 mg/L) groups, and contamination-attenuated (Group Ⅱ: NO3 mean=0.9 mg/L) group. As a result of inverse and forward modeling, nitrification releases the acid to groundwater, and then maintains low pH and HCO_(3), which overwhelms the acid buffering capacity of aquifer (mineral dissolution). Because nitrification consumes plenty of oxygen, Group Ⅰ area is 6 expected to be open to atmospheric oxygen gas. On the other hand, denitrification by oxidation of organic carbon is dominant reaction in Group Ⅱ which increase pH and HCO_(3). Consequently the hydrochemical processes take place in Buyeo alluvial aquifer can be summarized by stoichiometrically balanced chemical reactions, which is validated by thermodynamic calculations and isotopes. The results of this study can be used to control the pollution sources and apply the technology for secure water supply. Part Ⅲ: Hydrogeochemical and hydrogeological studies have been performed in September and November of 2001 and June of 2002, in order to understand the nitrate behaviors in a riverside shallow alluvial groundwaters of the Osong area near Cheongju. Because of the intensive agricultural activities, large population, and extensive pumping of groundwater in the area, nitrate contamination has been expected. The Miho stream, a tributary of the Geum River, has meandered and left two large oxbow lakes in the study area and possibly caused the spatial heterogeniety of aquifer material. Thirty three percent of the samples, NO_(3) concentrations exceeded the drinking water standard (44.3 mg/L). NO_(3) might be originated from mineralized N-fertilizer and livestock manure. An abrupt change of nitrate concentration was observed around the oxbow lakes, ranging from 123 to 0.1 mg/L in the fall of 2001 and from 217 to 1.2 mg/L in the summer of 2002. Assuming that groundwater flow is continuous in the area, nitrate eliminated by the denitrification rather than dilution, biological uptake, and nitrogen reduction, because low Eh, and O_(2) indicated the environment where lower NO_(3) sample is located is sufficient to denitirify the nitrate by oxidation of organic carbon. Nitrate concentration from monitoring wells increase with season (dry and rainy season), although the average values were not significantly different. Surface contaminant such as manure dump (organic fertilizer) and chemical fertilizer, and sewage effluence from Osong can be recharged by heavy rainfall. As a result of factor analysis, two factors explained about 60% of variance of hydrochemical data in 2001 and 2002. The first factor in both 2001 and 2002 show high factor loading in Ca, Mg, TDS, and NO_(3) which indicate that this factor represent the nitrification and following dissolution of agrochemicals. The second factor in both 2001 and 2002 show the positively high values of factor loading in pH, HCO_(3), and SiO_(2) and negatively high values of factor loading in SO_(4) and NO_(3), which indicate that this factor represent the inter relations among parameters which were affected by background water quality (silicate hydrolysis) and reduction. The spatial distribution of these two factors were presented by kriging. The higher first factor score is observed in the upper stream area of oxbow lake (residential area), and low first factor score is distributed between the oxbow lakes. On the other hand, the second factor score are high in the upper stream area and around oxbow lakes. Consequently, the two oxbow lake are play a key role in controlling the groundwater quality in this area: 1) clean groundwater might be recharged to the area between two oxbow lakes; 2) pollution is hindered by hydraulic barrier of upper lakes; 3) fine sediments around oxbow lakes make reducing environment. The results of this study can be applied to the water use technology such as bank filtration and underground damming. In Korea, this study is the first attempt to integrate related approaches, i.e., hydrology, hydrogeochemistry, geophysics, and sedimentalogy, to elucidate the hydrogelogical and hydrochemical processes in an alluvial aquifer.
Part Ⅰ: Hydrochemical and statistical research suggest that groundwaters from meandering riverside alluvial aquifers in Buyeo, South Korea are clustered into 3 groups both dry and wet season of 2001 and 2002. Ca-(SO_(4))-NO_(3) type (n=12) groundwaters (Group Ⅰ) are highly contaminated by nitrate (up to 294.6mg/L) and also high in redox potential (Eh), total dissolved solid (TDS), Ca, Mg, and SO_(4), but low in pH and alkalinity. This group is located near the Geum River, where coarse-grained sediments has been deposited and intensively fertilized. Particularly, nitrification increases acidity which enhance the dissolution of minerals and/or agrochemicals such as calcite, biotite, lime, and mixed fertilizers. Whereas Ca-HCO_(3) type (n=12) groundwaters (Group Ⅱ) are observed where fine sediment has been deposited. The lowest Eh, nitrate (NO_(3) mean=1.5 mg/L), sulfate, and highest pH, alkalinity, dissolved carbon (DOC), and Fe concentrations of Group Ⅱ groundwater indicate that the denitrification dominantly takes place in this environment. Other samples were belong to the Group Ⅲ, which were moderately contaminated by NO_(3) (n=31; NO_(3) mean=49.1 mg/L). Group Ⅲ groundwaters occupy most of study area, then this group represents the groundwater quality of this area. In a geomorphological point of view, the pattern of distribution of groups is related to the dynamical sedimentation of 'point bar'. The Group Ⅰ area, which was a sand island in 1923, was merged to point par in recent years, then the sediments and soil are not consolidated yet. On the other hand, Group Ⅱ area is located in the end and the center of point bar therefore silt and clay can be accumulated and characterized as 'riparian zone'. These fine-grained sediments contain sufficient reducing agent such as organic carbon and pyrite then prevent the oxygen and form a reducing environment. The spatial distribution of these groups doesn't change significantly with season except that of Group Ⅰ, indicating hydrochemical characteristics of groundwaters are mainly controlled by geology of this meandering riverside alluvium. The results of this study can be applied to the water use technology such as bank filtration and underground damming. In Korea, this study is the first attempt to integrated approaches, i.e., hydrology, hydrochemistry, geophysics, and sedimentology, to elucidate the hydrogeological and hydrochemical processes in an alluvial aquifer. Part Ⅱ: Inverse (mass balance) and forward (reaction) hydrochemical modeling methods are applied to explain the hydrochemistry of groundwaters from Buyeo alluvial aquifer. Groundwaters collected in 2001 are hydrogeochemically and statistically classified into three groups: highly contaminated (Group Ⅰ: NO_(3) mean=194.7 mg/L), moderately contaminated (Group Ⅲ: NO_(3) mean=58.4 mg/L) groups, and contamination-attenuated (Group Ⅱ: NO3 mean=0.9 mg/L) group. As a result of inverse and forward modeling, nitrification releases the acid to groundwater, and then maintains low pH and HCO_(3), which overwhelms the acid buffering capacity of aquifer (mineral dissolution). Because nitrification consumes plenty of oxygen, Group Ⅰ area is 6 expected to be open to atmospheric oxygen gas. On the other hand, denitrification by oxidation of organic carbon is dominant reaction in Group Ⅱ which increase pH and HCO_(3). Consequently the hydrochemical processes take place in Buyeo alluvial aquifer can be summarized by stoichiometrically balanced chemical reactions, which is validated by thermodynamic calculations and isotopes. The results of this study can be used to control the pollution sources and apply the technology for secure water supply. Part Ⅲ: Hydrogeochemical and hydrogeological studies have been performed in September and November of 2001 and June of 2002, in order to understand the nitrate behaviors in a riverside shallow alluvial groundwaters of the Osong area near Cheongju. Because of the intensive agricultural activities, large population, and extensive pumping of groundwater in the area, nitrate contamination has been expected. The Miho stream, a tributary of the Geum River, has meandered and left two large oxbow lakes in the study area and possibly caused the spatial heterogeniety of aquifer material. Thirty three percent of the samples, NO_(3) concentrations exceeded the drinking water standard (44.3 mg/L). NO_(3) might be originated from mineralized N-fertilizer and livestock manure. An abrupt change of nitrate concentration was observed around the oxbow lakes, ranging from 123 to 0.1 mg/L in the fall of 2001 and from 217 to 1.2 mg/L in the summer of 2002. Assuming that groundwater flow is continuous in the area, nitrate eliminated by the denitrification rather than dilution, biological uptake, and nitrogen reduction, because low Eh, and O_(2) indicated the environment where lower NO_(3) sample is located is sufficient to denitirify the nitrate by oxidation of organic carbon. Nitrate concentration from monitoring wells increase with season (dry and rainy season), although the average values were not significantly different. Surface contaminant such as manure dump (organic fertilizer) and chemical fertilizer, and sewage effluence from Osong can be recharged by heavy rainfall. As a result of factor analysis, two factors explained about 60% of variance of hydrochemical data in 2001 and 2002. The first factor in both 2001 and 2002 show high factor loading in Ca, Mg, TDS, and NO_(3) which indicate that this factor represent the nitrification and following dissolution of agrochemicals. The second factor in both 2001 and 2002 show the positively high values of factor loading in pH, HCO_(3), and SiO_(2) and negatively high values of factor loading in SO_(4) and NO_(3), which indicate that this factor represent the inter relations among parameters which were affected by background water quality (silicate hydrolysis) and reduction. The spatial distribution of these two factors were presented by kriging. The higher first factor score is observed in the upper stream area of oxbow lake (residential area), and low first factor score is distributed between the oxbow lakes. On the other hand, the second factor score are high in the upper stream area and around oxbow lakes. Consequently, the two oxbow lake are play a key role in controlling the groundwater quality in this area: 1) clean groundwater might be recharged to the area between two oxbow lakes; 2) pollution is hindered by hydraulic barrier of upper lakes; 3) fine sediments around oxbow lakes make reducing environment. The results of this study can be applied to the water use technology such as bank filtration and underground damming. In Korea, this study is the first attempt to integrate related approaches, i.e., hydrology, hydrogeochemistry, geophysics, and sedimentalogy, to elucidate the hydrogelogical and hydrochemical processes in an alluvial aquifer.
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