Paper No. 7
Presentation Time: 2:50 PM
A SEDIMENT-COLOR BASED TOOL FOR THE INSTALLATION OF ARSENIC-SAFE DRINKING WATER TUBEWELLS IN SHALLOW AQUIFERS IN BANGLADESH
In rural Bangladesh, drinking water supply mostly comes from shallow hand tubewells which are installed manually by the local drillers, the main driving force in tubewell installation. This study was aimed to develop a color based tool on the basis of local driller’s color perception, As concentration of tubewell waters and respective color of aquifer sediments. A total of 2240 sediment samples were collected at intervals of 1.5 m up to depths of 100 m from 15 locations spread over a 410 km2
area in Matlab, Bangladesh. These sediments were characterized on the basis of grain size and color. Samples were compared with Munsell Color Chart with the purpose of standardization through a scientific method that allows a methodical re-examination and replication in the study area and elsewhere in the same manner. All samples were assigned with Munsell Color and Munsell Code, which eventually led to identify 60 varieties during the process of narrowing the colour to four colors (Black, White, Off-white and Red) as perceived and used by the local drillers. The use of Munsell color codes on these sediments made them distinctive from each other and thus reduces the risk for misinterpretation of the sediment colors. During the process of color grouping, participatory approach was considered taking the opinions of local drillers, technicians, and geologists into account.
Results of laboratory analysis of 520 groundwater samples collected from 142 wells (55 piezometers and 87 drinking water wells) during 2009 to 2011 indicate that all 47 wells producing water from red sediments provide safe water following the Bangladesh drinking water standard for As (50 µg/L). Average and median values were less than the WHO guideline value of 10 µg/L. Observations for off- white sediments were also quite similar. White sediments were rare and seemed to be less important for well installations. Groundwater arsenic concentrations were generally higher in all the black coloured sediment with an average of 235 µg/L. Through a process of simplification, this study has distinguished color shades into light, moderate and deep which led to develop a simplified color tool for convenient use. This study shows the potential for educating local drillers to target safe aquifers on the basis of the color characteristics of the sediments.