COMPREHENSIVE APPROACH IN DEVELOPING COLOR BASED TOOL TO TARGET ARSENIC SAFE AQUIFER SEDIMENTS IN BANGLADESH

In Matlab region of SE Bangladesh more than 80% tubewells contain elevated arsenic (As) concentrationin concenrations about the WHO (10 µg/L) and the Bangladesh (> 50µg/L) drinking water standards. A color based classification of the sediments could be quite simple and useful in targeting arsenic safe aquifers for the installation of community driven tubewells. Currently, local drillers are installing tubewells either in the reddish brown sediment layers that occur relatively in shallow depth or in the deeper sediments which produce water with very low or no As. The relationship of sediment color and corresponding As concentrations in water has already been demonstrated by our earlier studies and a followup monitoring has ben carried out in a limited area in Matlab South Upazila. The present work undertakes to scale up this observation with an aim to develop and provide a handy tool to the local drillers for targeting safe aquifers by themselves. A total of 1920 sediment samples have been considered from 15 locations bored up to a depth of 800 feet and scientifically evaluated according to the color codes following the Munsell Color Chart. The use of Munsell color codes to these sediments made them distinctive from each other and thus reduces the risk for misinterpretation of the sediment colors. A total of sixty varieties have been observed which are ultimately grouped into four categories. In grouping exercise, participatory approach was considered taking the opinions of local drillers, technicians, and geologists into account. All these sixty varieties observed were then finally concluded into four major colors viz. black, white, off-white and red. Despite some discrepancies observed between the drillers' color conception of the sediments and the Munsell description, all the sediment samples could broadly be classified into four distinct color groups. This study shows the potential for educating local drillers to target safe aquifers on the basis of the color characteristics of the sediments, which might be replicable to obtain arsenic safe water in many areas of Bangladesh. Practically, if local drillers can target safe aquifers based on this color tool, it will play a significant role in As mitigation where the practice of using tubewells is well rooted and most acceptable method among the users.