MONITORING OF ARSENIC CONCENTRATIONS IN GROUNDWATER PUMPED FROM 50 COMMUNITY WELLS TAPPING PLEISTOCENE AQUIFERS IN ARAIHAZAR, BANGLADESH

Tens of thousands of deep wells tapping Pleistocene aquifers characterized by orange-coated sands have been installed in recent years throughout Bangladesh by government and aid organizations. Such community wells are popular and credited for a significant reduction in the exposure of the rural population of Bangladesh to As contained in shallow groundwater associated with Holocene aquifers. This approach to mitigation has its critics, however, because of concern that As concentrations in Pleistocene might increase over time. The evidence for such increases is very limited, but there is a worrisome lack of follow-up to the deep well installations in the form of periodic monitoring. We report here monitoring data for As and other constituents of groundwater of potential health concern for 50 deep community wells installed within a 25 km2 area of Araihazar upazila, Bangladesh, where Columbia University and its local partners are involved in a study of the origin and health effects of exposure to arsenic groundwater pumped from shallow wells.

The monitoring data show that 47 out of 50 deep wells installed in 2001-2004 and ranging from 30 to 200 m in depth continue to provide water to the surrounding households that consistently meets the Bangladesh standard for As in drinking water of 50 ug/L. All but 7 of these wells also consistently meet the WHO guideline for As of 10 ug/L. We have re-installed new community wells at the 3 locations where As concentrations rose above 50 ug/L. We are investigating the origin of these failures which probably reflect the local entrainment of shallow groundwater that is elevated in As rather than whole-aquifer contamination. The results confirm that deep community wells that extend to Pleistocene aquifers are a valuable source of drinking water. The documented failures indicate, however, that it is imperative to periodically monitor deep wells. Besides setting up regional laboratories to test groundwater for As and other constituents of groundwater of potential health concern, such monitoring could be encouraged by providing access and training at the village level in the use of one of the several reliable field kits for arsenic that are now commercially available.