HIGH ARSENIC CONCENTRATION IN GROUNDWATER RELATED TO SEDIMENTARY FACIES IN THE MEKONG RIVER DELTA, VIETNAM

Abstract

Arsenic (As) contamination in groundwater has been recognized in the Mekong River Delta (MRD) since 2001, especially in Dong Thap and An Giang provinces. The investigations were carried out during 2008-2009 and from 2012 to present. The investigations of As distribution in groundwater and sediments were based upon the field, and laboratory analyses using field kit (Hironaka, 1998) and AOAC laboratory - Vietnamese standard 6626-2000 (Vilas). Results show that the As concentrations ranging from 15 to 1,650 µg/l is found in 520 private tubewells at depth between 15 and 90 m, while being rare or very low at depth between 200 and 300 m. High As content is usually found in 15-70m tubewells in which approximately 70 - 80% of tubewells having arsenic levels of >500µg/l are located at some areas in Dong Thap and An Giang provinces in the upper MRD plain. Bore core drilling records show a probable relationship between As concentration in groundwater and sedimentary facies in the MRD. The highest As content is found along the Mekong River valleys in the Late Pleistocene and Holocene aquifers.

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