Evaluation of deep groundwater development for arsenic mitigation in western Bangladesh

Abstract

Groundwater contamination by arsenic frequently occurs in western Bangladesh. Integrated hydrogeological studies were carried out by the Japan International Cooperation Agency (JICA) in the Jessore, Jhenaidah and Chuadanga districts to assess the possibility of supplying safe drinking water from deep aquifers. The subsurface geology of up to 300 m in depth was classified into 5 formations (viz. A to E formations in descending order). Thick clay facies are found in C formation in the Jessore district, however, clay facies are absent in the Jhenaidah and Chuadanga districts. The clay layer separates deep aquifers from shallow aquifers, and controls vertical groundwater flow. The results of core sample analysis showed that high arsenic contents of more than 30 ppm were found not only from shallow clay but also even from deep clay below 200 m. However, the arsenic concentrations in groundwater were generally below 0.05 mg/L in the deep aquifers. The simulation study using a vertical 2-D groundwater model indicates that deep groundwater will not be contaminated by arsenic in shallow groundwater when the piezometric heads of the deep aquifers are higher than the shallow aquifers. However, the simulation results indicate that overexploitation of the deep aquifers will cause arsenic contamination in deep aquifers due to the downward movement of contaminated shallow groundwater when no sorption takes place in the sediments. These results suggest that groundwater management and control of groundwater pumpage in deep aquifers are crucial for sustainable supply of arsenic safe deep groundwater in western Bangladesh.

Keywords:

• Arsenic
• groundwater contamination
• Bangladesh
• core boring
• deep aquifer
• groundwater development
• overexploitation
• groundwater simulation
• vertical 2-D model
• groundwater management

Acknowledgments

The authors are grateful to JICA for providing permission to publish this paper. The JICA project was carried out by Kokusai Kogyo Co., Ltd. and Mitsui Mineral Development Engineering Co., Ltd. The authors wish to thank the officials of DPHE for their cooperation during the project. The authors also wish to thank the members of the JICA Study Team, especially Mr. Kazuyuki Suenaga, Mr. Masatoshi Tanaka, Mr. Kazuro Bando, Mr. Tsuguo Ishikawa, Mr. Munehiro Fukuda, and Mr. Takashi Higo are thanked for their hydrogeological work and arsenic analysis.

Notes

*kh: horizontal hydraulic conductivity, kv: vertical hydraulic conductivity, Ss: specific storage.