The Mekong Delta, situated between Cambodia and Vietnam, is one of the most productive aquifer systems in the region. In recent years, however, several studies have shown that groundwater in several areas of the delta is highly contaminated with arsenic (As). Although more than 80% of the total area of the Mekong Delta is situated in Vietnam, most of the studies have been conducted on the Cambodian-side of the delta. In this study, borehole core samples were collected around the Tien and Hau Rivers, the two main branches of the Mekong River as it enters Vietnam. We present a raw data collection of the chemical and mineralogical composition of distinct lithological features from six borehole core samples drilled up to a depth of 40 m. The data also include the pH, Eh, EC, As, Si, Al, DOC, dissolved heavy metals (Fe and Mn) and major coexisting ions of leachates obtained by leaching the 34 selected sediment samples in deionized water. The information provided in this paper would be useful as a baseline for reactive transport or geochemical modeling to understand and predict As migration in naturally contaminated aquifers under various conditions. For more insights, the reader is referred to our paper entitled “The solid-phase partitioning of arsenic in unconsolidated sediments of the Mekong Delta, Vietnam and its modes of release under various conditions” Huyen et al., 2019.
Arsenic (As) contamination of groundwater is often caused by As leaching from geological formations. This study focused on factors affecting As content in unconsolidated sediments by using three sediment cores in the Ishikari Plain, Hokkaido, Japan. The geochemical properties of the sediments were characterized by the chemical and mineral compositions as well as leaching experiments and sequential extractions of As. The results showed that higher As content of 4-9 mg/kg was observed in peat layers with organic matter content >10 wt%, and that higher As contents deeper than 8 m below the surface were also observed. The deeper sediments were likely to be formed in brackish water conditions due to lower weight ratios of organic carbon content to sulfur content (C/S<10). The results of the leaching experiments showed that As was mobilized at slightly alkaline region. These indicate that the distribution of As depended on the organic content in the sediments and sedimentation condition, and that the mobility of As in the sediment was affected by pH.
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