Evidence for elevated levels of arsenic in public wells of Bangladesh due to improper installation

摘要

One of the mainstays of mitigation to reduce the exposure of the rural population of Bangladesh to arsenic (As) from private, mostly <90 m deep wells over the past 15 years has been the installation of over 300,000 deeper community wells. A comprehensive testing campaign previously conducted across a 180 km² of area of Bangladesh identified 9 out of total of 927 wells >90 m deep that contained >50 μg/L arsenic. We show here that for 5 of these 9 wells, conductivity profiles obtained after spiking the well bore with salt indicate a shallow leak that could explain the high As in the well water. In 2 out of the 5 leaky wells, the presence of additional screens at the depth of the leak was documented with a downhole camera. The downhole camera did not detect anomalies in the construction of the remaining 3 leaky wells or in the 4 wells that did not leak. The 4 wells that did not leak were all >150 m deep and located in two villages separated by less than 500 m. Excluding these two villages and a handful of leaky wells, the results indicate an aquifer that is consistently low in As over a sizeable area at depths >90 m. Isolated cases of public wells that are elevated in As that have been reported elsewhere in Bangladesh may therefore reflect improper installation rather than actual contamination of the deep aquifer.