Arsenic mobilisation in a new well field for drinking water production along the Red River, Nam Du, Hanoi

Research output: Contribution to journalArticle

Abstract

Arsenic enrichment of groundwater in the Red River (Song Hong) delta in Vietnam was discovered in 1998. Several studies performed in this area found concentrations of As exceeding the WHO-guideline of 10 lg/L. This study focuses on an area south of Hanoi city, Nam Du, where a new well field came into operation in 2004. The new well field is situated on the bank along the Red River in order to facilitate induced infiltration. The Nam Du area receives surface water with a high load of nutrients and organic matter from the Hanoi sewage system, and is subject to recently increased groundwater extraction from the Pleistocene aquifer system. The objective of the study was (1) to assess the situation in the Nam Du area by mapping the distribution of As, (2) to identify possible sources of As in the
groundwater and (3) to investigate the mobilisation processes releasing As into the groundwater. Two main field campaigns were carried out, in 2006 and 2007, both during the dry season. Groundwater and surface water levels were measured and water- and sediment samples were collected. The water in the Pleistocene aquifer shows the same
water-level variations as the Red River at a distance of 2.5 km from the riverbank, while the Holocene aquifer heads are recharged by surface water ponds and show less seasonal variation. The concentration of As in the groundwater in Nam Du exceeded the WHO provisional guideline value at all sampled locations. The main conclusions are summarised as (i) the distribution of As is highly variable but the zones with the highest concentrations of As are near the Red River in the Holocene aquifer and just down gradient from this in the Pleistocene aquifer, (ii) the sediments within the aquifers are considered to be the source of the As, where the Holocene aquifer is believed to act as the main source of As into the Pleistocene aquifer as reduced groundwater containing As from the Holocene aquifer is flowing downwards due to the downward gradient, and (iii) two different processes appear to take part in the mobilisation process. In the Holocene aquifer, reductive dissolution of FeOOH and the release of adsorbed As appear to be the main mobilisation processes. In the Pleistocene, however, mobilisation of adsorbed As due to competition from HCO3 ions for surface sites on FeOOH may be a major mechanism of As mobilisation. It is suggested that the drinking water supplier undertakes the following actions to ensure acceptable levels of As in the treated drinking water: (a) to implement a long-term monitoring program, (b) implement alternative treatment technologies; and (c) to possibly consider an alternative drinking water source.

Details

Authors
  • Jenny Norrman
  • Charlotte Sparrenbom
  • Michael Berg
  • Dang Duc Nhan
  • Pham Quy Nhan
  • Håkan Rosqvist
  • Gunnar Jacks
  • Emma Sigvardsson
  • David Baric
  • Johanna Moreskog
  • Peter Harms-Ringdahl
  • Nguyen Van Hoan
External organisations
  • Swedish Geotechnical Institute (SGI)
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Earth and Related Environmental Sciences
Original languageEnglish
Pages (from-to)3127-3142
JournalApplied Geochemistry
Volume23
Issue number11
Publication statusPublished - 2008
Publication categoryResearch
Peer-reviewedYes
Externally publishedYes