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Sci Total Environ. 2019 Mar 1;654:1100-1109. doi: 10.1016/j.scitotenv.2018.11.200. Epub 2018 Nov 14.

Occurrence of metal-rich acidic groundwaters around the Mekong Delta (Vietnam): A phenomenon linked to well installation.

Author information

1
Department of Environmental Engineering, Kunsan National University, Jeonbuk 54150, Republic of Korea.
2
Department of Environmental Engineering, Kunsan National University, Jeonbuk 54150, Republic of Korea. Electronic address: kangjoo@kunsan.ac.kr.
3
Division for Water Resources Planning and Investigation of the South of Vietnam, Ho Chi Minh City, Viet Nam.
4
Faculty of Geological and Petroleum Engineering, Ho Chi Minh City University of Technology, Ho Chi Minh City, Viet Nam.
5
Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea.

Abstract

Acidic groundwaters enriched with heavy metals are frequently observed in the coastal plain aquifers. The acidic pHs are observed even in the deep confined aquifers in southern Vietnam. This study geochemically explores the causes of these acidic groundwaters by investigating 41 groundwater samples, 4 soil samples and a 54 m long sediment core and the long-term monitoring data (4189 observations) obtained from 178 wells of the National Groundwater Monitoring Network for the South of Vietnam (NGMNS). The groundwater data show elevated Fe, Mn, Al, Pb, and Zn concentrations as the pH becomes acidic and suggest pyrite oxidation be the major cause for the groundwater acidification. This is further confirmed by pyrite framboids observed in the sediment or soil samples taken from the sites where strongly acidic groundwaters were observed. Results of leaching experiments using sediment and soil samples indicate that high metal concentrations in the acidic pH are associated with the increased metal solubility and mineral dissolution kinetics. The acidification of deep groundwaters is revealed to be associated with well installation, indicating the importance of proper well-installation techniques to protect water quality of deep confined aquifers.

KEYWORDS:

Acid sulfate soil; Aquifer disturbance; Coastal plain aquifer; Heavy metal; Pyrite oxidation

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