Dugwells vs. Shallow Tube well

Professor Charles Harvey MIT (immediately following)

I don't have any direct experience with dug wells. Two thoughts come to mind --

(1) If the water in the dug well is mixed, then I like your idea about oxidation, although the oxidation of iron is likely most important for lowering arsenic concentrations. The relative amounts of iron, arsenic, phosphate and silicate have to be such that arsenic is taken out with iron precipitation.   Stephan Hug's work with photooxidation in PET bottles has shown that the concentrations in well water are often such that arsenic is naturally removed,   however in some areas iron is too low relative to phosphate and silicate. (Of course a dug well does not have the benefit of photoxidation.) So, where there is enough iron relative to the competing anions, the safety may be basically a matter of timing, i.e. competing rates -- the rate that pumping mixes oxygen in, the rate that new groundwater enters the well, and the kinetic rates of the chemistry. It also helps that the shallowest groundwater often has less arsenic than deeper.

Deep Wells Can Target Low Arsenic Aquifers in Bangladesh, New Study Shows
Columbia researchers advance plan to mitigate arsenic crisis

A solution to arsenic-poisoned drinking water in Bangladesh has come two steps closer with two new research papers by Lex van Geen, Doherty Senior Researcher at the Lamont-Doherty Earth Observatory, part of the Earth Institute at Columbia University, and a team of researchers from Columbia.

A new study by Columbia University researchers shows highly variable arsenic levels in water drawn from wells in the 10-25 m depth range, while wells deeper than 30 m in this particular village are consistently low in arsenic. The upper panel based on an IKONOS satellite image of the village and surrounding rice fields shows the location and arsenic content of individual wells. The lower panel is a depth section of the same wells. The large blue circle indicates the location and depth of a communal well installed and monitored by the program. Satellite image by: spaceimaging.com

The first paper, titled "Spatial variability of arsenic in 6000 tube wells in a 25km² area of Bangladesh," was published in a recent issue of the highly-ranked journal Water Resources Research and was selected by the American Geological Union for highlighting in July. The paper describes a study that involved testing all tube wells in a portion of Araihazar upazila, one of 490 sub-districts of Bangladesh. The study confirms that although the arsenic content of aquifers shallower than 30 meters is spatially very variable and difficult to predict, wells that tap into deeper sandy deposits that are over 10,000 years old yield groundwater that is consistently low in arsenic ( Less than 10 micrograms of arsenic per liter, the WHO guideline value).

A complication is that the depth of these safe aquifers varies from less than 10 meters to up to 300 meters, even varying over an unexpectedly wide range from village to village as this new study shows. The challenge, therefore, is to provide the expertise and equipment needed to target these aquifers at the village scale. Click HERE to download the paper in PDF format.

Further research by the team, in a study published in the Bulletin of the World Health Organization, shows that when communal wells producing safe drinking water are provided to a village, they are surprisingly well accepted and widely used by the local population, serving an average of 500 people living within a 200 meter radius. On the basis of geographic information obtained with hand-held Global Positioning System (GPS) receivers, the study documents that most women started to walk hundreds of meters each day to fetch water from these communal wells once they were installed, switching from their private wells that had tested high for arsenic.

Local-level mapping of arsenic content in groundwater, used as a tool to site deep, safe community wells in Bangladesh, could therefore be used extensively to reduce the exposure of the population to arsenic. "On the basis of these two studies and the experiences of many other scientists and engineers," Van Geen explains, "we are beginning to form a new strategy to propose to the government of Bangladesh to mitigate the arsenic crisis."

Columbia University has been central to a five year, $11 million grant from the NIEHS Superfund Basic Research Program aimed at understanding and addressing the health impact and origin of elevated arsenic levels in groundwater in the US and in Bangladesh. The Columbia team, led by Joe Graziano of the Mailman School of Public Health and Lex van Geen, is approaching the problem from a unique, multidisciplinary perspective that spans the health, social, and earth sciences. The Columbia team also collaborates with NGOs active in Bangladesh, universities and research organizations in Bangladesh and the US, as well as with UNICEF.

The Earth Institute at Columbia is the world's leading academic center for the integrated study of Earth, its environment, and society. The Earth Institute stresses cross-disciplinary approaches to complex problems. Through its research, training and global partnerships, it mobilizes science and technology to advance sustainable development, while placing special emphasis on the needs of the world's poor.