Econ. Environ. Geol. 2006; 39(1): 27-38

Published online February 28, 2006

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Hydrogeochemical Evolution Related to High Fluoride Concentrations in Deep Bedrock Groundwaters, Korea

Kyoung-Ho Kim1, Seong-Taek Yun1*, Gi-Tak Chae1, Seong-Yong Kim2, Jang-Soon Kwon1 and Yong-Kwon Koh3

1Department of Earth and Environmental Sciences and the Environmental Geosphere Research Lab (EGRL), Korea University, Seoul 136-701, Korea
2Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Korea
3Korea Atomic Energy Research Institute, Daejeon 305-353, Korea

Correspondence to :

Seong-Taek Yun

styun@korea.ac.kr

Received: February 1, 2005; Accepted: January 10, 2006

Abstract

To understand the geologic and hydrogeochemical controls on the occurrence of high fluoride concentrations in bedrock groundwaters of South Korea, we examined a total of 367 hydrochemistry data obtained from deep groundwater wells (avg. depth=600 m) that were drilled for exploitation of hot springs. The fluoride concentrations were generally very high (avg. 5.65 mg/L) and exceeded the Drinking Water Standard (1.5 mg/L) in 72% of the samples. A significant geologic control of fluoride concentrations was observed: the highest concentrations occur in the areas of granitoids and granitic gneiss, while the lowest concentrations in the areas of volcanic and sedimentary rocks. In relation to the hydrochemical facies, alkaline Na-HCO3 type waters had remarkably higher F concentrations
than circum-neutral to slightly alkaline Ca-HCO3 type waters. The prolonged water-rock interaction occurring during the deep circulation of groundwater in the areas of granitoids and granitic gneiss is considered most important for the generation of high F concentrations. Under such condition, fluoride-rich groundwaters are likely formed through hydrogeochemical processes consisting of the removal of Ca from groundwater via calcite precipitation and/or cation exchange and the successive dissolution of plagioclase and F-bearing hydroxyl minerals (esp. biotite). Thus, groundwaters with high pH and very high Na/Ca ratio within granitoids and granitic gneiss are likely most
vulnerable to the water supply problem related to enriched fluorine.

Keywords fluoride, deep bedrock groundwater, hydrogechemical evolution, water-rock interaction

Article

Econ. Environ. Geol. 2006; 39(1): 27-38

Published online February 28, 2006

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Hydrogeochemical Evolution Related to High Fluoride Concentrations in Deep Bedrock Groundwaters, Korea

Kyoung-Ho Kim1, Seong-Taek Yun1*, Gi-Tak Chae1, Seong-Yong Kim2, Jang-Soon Kwon1 and Yong-Kwon Koh3

1Department of Earth and Environmental Sciences and the Environmental Geosphere Research Lab (EGRL), Korea University, Seoul 136-701, Korea
2Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Korea
3Korea Atomic Energy Research Institute, Daejeon 305-353, Korea

Correspondence to:

Seong-Taek Yun

styun@korea.ac.kr

Received: February 1, 2005; Accepted: January 10, 2006

Abstract

To understand the geologic and hydrogeochemical controls on the occurrence of high fluoride concentrations in bedrock groundwaters of South Korea, we examined a total of 367 hydrochemistry data obtained from deep groundwater wells (avg. depth=600 m) that were drilled for exploitation of hot springs. The fluoride concentrations were generally very high (avg. 5.65 mg/L) and exceeded the Drinking Water Standard (1.5 mg/L) in 72% of the samples. A significant geologic control of fluoride concentrations was observed: the highest concentrations occur in the areas of granitoids and granitic gneiss, while the lowest concentrations in the areas of volcanic and sedimentary rocks. In relation to the hydrochemical facies, alkaline Na-HCO3 type waters had remarkably higher F concentrations
than circum-neutral to slightly alkaline Ca-HCO3 type waters. The prolonged water-rock interaction occurring during the deep circulation of groundwater in the areas of granitoids and granitic gneiss is considered most important for the generation of high F concentrations. Under such condition, fluoride-rich groundwaters are likely formed through hydrogeochemical processes consisting of the removal of Ca from groundwater via calcite precipitation and/or cation exchange and the successive dissolution of plagioclase and F-bearing hydroxyl minerals (esp. biotite). Thus, groundwaters with high pH and very high Na/Ca ratio within granitoids and granitic gneiss are likely most
vulnerable to the water supply problem related to enriched fluorine.

Keywords fluoride, deep bedrock groundwater, hydrogechemical evolution, water-rock interaction

    KSEEG
    Jun 30, 2024 Vol.57 No.3, pp. 281~352

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