Sediment color tool for targeting arsenic-safe aquifers for the installation of shallow drinking water tubewells

Abstract

In rural Bangladesh, drinking water supply mostly comes from shallow hand tubewells installed manually by the local drillers, the main driving force in tubewell installation. This study was aimed at developing a sediment color tool on the basis of local driller's perception of sediment color, arsenic (As) concentration of tubewell waters and respective color of aquifer sediments. Laboratory analysis of 521 groundwater samples collected from 144 wells during 2009 to 2011 indicate that As concentrations in groundwater were generally higher in the black colored sediments with an average of 239 μg/L. All 39 wells producing water from red sediments provide safe water following the Bangladesh drinking water standard for As (50 μg/L) where mean 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 at shallow depths. A total of 2240 sediment samples were collected at intervals of 1.5m down to depths of 100 m at 15 locations spread over a 410 km(2) area in Matlab, Bangladesh and compared with the Munsell Color Chart with the purpose of direct comparison of sediment color in a consistent manner. All samples were assigned with Munsell Color and Munsell Code, which eventually led to identify 60 color shade varieties which were narrowed to four colors (black, white, off-white and red) as perceived and used by the local drillers. During the process of color grouping, participatory approach was considered taking the opinions of local drillers, technicians, and geologists into account. This simplified sediment color tool can be used conveniently during shallow tubewell installation and thus shows the potential for educating local drillers to target safe aquifers on the basis of the color characteristics of the sediments.

Hydrogeochemical controls on mobilization of arsenic in groundwater of a part of Brahmaputra river floodplain, India

“…If the environment becomes more reducing, there will be a partial reduction of Fe(III) phases, releasing As into groundwater. However, re-adsorption of As to residual FeOOH in these sediments often keeps the As concentration reasonably low (von Brömssen et al, 2007;Hossain et al 2014). If all FeOOH is reduced, the sediments will get a greyish colour (Stüben et al, 2003).…”

Preliminary Study of Heavy Metal (Zn, Pb, Cr, As, Cu, Cd) Contaminations on Different Soil Level from Post-Mining Bauxite Production for Aquaculture

“…[27]. The result of enrichment factor of arsenic which ranged extremely high enrichment EF (107.61 to 206.29) was described as a mining exploration which contains huge amounts of wastes that may increase the amounts of Arsenic [2].…”

Natural Arsenic in Global Groundwaters: Distribution and Geochemical Triggers for Mobilization

“…An analysis of 521 groundwater samples collected from 144 wells from 2009 to 2011 found that high As concentrations in groundwater correspond to black sediments with an average concentration of 239 μg/L, which by far exceeds the safe drinking water standard of Bangladesh (50 μg/L) [58]. However, average As concentrations in 39 tube wells in which red sediments were observed were lower than the WHO guideline value of 10 μg/L, implying safe water with regard to the Bangladesh drinking water standard for As (50 μg/L) [58,140]. Consuming high levels of As indeed is the main cause of the arsenicosis symptoms reported among at least 40,000 people living in the most vulnerable locations of Bangladesh.…”