In rural Bangladesh, the drinking water supply is mostly dependent upon manually operated hand pumped tubewells, installed by the local community. The presence of natural arsenic (As) in groundwater and its wide scale occurrence has drastically reduced the safe water access across the country and put tens of millions of people under health risk. Despite significant progress in understanding the source and distribution of As and its mobilization through sediment-water interactions, there has been limited success in mitigation since the problem was discovered in the country’s water supply in 1993. This study evaluated the viability of other kinds of alternative safe drinking water options and found tubewells are the most suitable due to simplicity and technical suitability, a wide acceptance by society and above all low cost for installation, operation and maintenance. During planning and decision making in the process of tubewell installation, depth of the tubewell is a key parameter as it is related to groundwater quality and cost of installation. The shallow wells (usually &lt; 80m) are mostly at risk of As contamination. One mitigation option are deep wells drilled countrywide to depths of around 250 m. Compared to safe water demand, the number of deep wells is still very low, as the installation cost is beyond affordability of the local community, especially for the poor and disadvantaged section of the society. Using depth-specific piezometers (n=82) installed in 15 locations spread over the 410 km2 area of Matlab (an As-hot spot) in southeastern Bangladesh, groundwater monitoring was done over a 3 year period (pre- and post-monsoon for 2009-2011 period). Measurements were performed for hydrogeological characterization of shallow, intermediate deep and deep aquifer systems to determine the possibility of targeting safe aquifers at different depths as the source of a sustainable drinking water supply. In all monitoring piezometers, As was found consistently within a narrow band of oscillation probably due to seasonal effects. Hydrogeochemically, high-As shallow groundwaters derived from black sands are associated with elevated DOC, HCO3, Fe, NH4-N and PO4-P and with a relatively low concentration of Mn and SO4. Opposite to this, shallow aquifers composed of red and off-white sediments providing As-safe groundwater are associated with low DOC, HCO3, Fe, NH4-N and PO4-P and relatively higher Mn and SO4. Groundwaters sampled from intermediate deep and deep piezometers which were found to be low in As, are characterized by much lower DOC, HCO3, NH4-N and PO4-P compared to the shallow aquifers. Shallow groundwaters are mostly Ca-Mg-HCO3 type and intermediate deep and deep aquifers’ groundwaters are mostly Na-Ca-Mg-Cl-HCO3 to Na-Cl-HCO3 type. A sediment color tool was also developed on the basis of local driller’s color perception of sediments (Black, White, Off-white and Red), 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 a depth of 100 m from all 15 nest locations. All samples were assigned with a Munsell color and code, which eventually led to identify 60 color varieties. The process continued in order to narrow the color choices to four as perceived and used by the local drillers for identification of the targeted As-safe aquifers. Munsell color codes assigned to these sediments render them distinctive from each other which reduces the risk for misinterpretation of the sediment colors. During the process of color grouping, a participatory approach was considered taking the opinions of local drillers, technicians, and geologists into account. In addition to the monitoring wells installed in the piezometer nests, results from 87 other existing drinking water supply tubewells were also considered for this study. A total of 39 wells installed in red sands at shallow depths producing As-safe water providing strong evidence that red sediments are associated with As-safe water. Average and median values were found to be less than the WHO guideline value of 10 μg/L. Observations for off-white sediments were also quite similar. Targeting off-white sands could be limited due to uncertainty of proper identification of color, specifically when day-light is a factor. Elevated Mn in red and off-white sands is a concern in the safe water issue and emphasizes the necessity of a better understanding of the health impact of Mn. White sediments in shallow aquifers are relatively uncommon and seemed to be less important for well installations. Arsenic concentrations in more than 90% of the shallow wells installed in black sands are high with an average of 239 μg/L from 66 wells installed in black sediments. It is thereby recommended that black sands in shallow aquifers must be avoided. This sediment color tool shows the potential for enhancing the ability of local tubewell drillers for the installation of As-safe shallow drinking water tubewells. Considering the long-term goal of the drinking water safety plan to provide As-safe and low-Mn drinking water supply, this study also pioneered hydrogeological exploration of the intermediate deep aquifer (IDA) through drilling up to a depth of 120 m. Clusters of tubewells installed through site optimization around the monitoring piezometer showed a similar hydrochemical buffer and proved IDA as a potential source for As-safe and low-Mn groundwater. Bangladesh drinking water standard for As (50 µg/L) was exceeded in only 3 wells (1%) and 240 wells (99%) were found to be safe. More than 91% (n=222) of the wells were found to comply with the WHO guideline value of 10 µg/L. For Mn, 89% (n=217) of the wells show the concentration within or below the previous WHO guideline value of 0.4 mg/L, with a mean and median value of 0.18 and 0.07 mg/L respectively. The aquifer explored in the Matlab area shows a clear pattern of low As and low Mn. The availability of similar sand aquifers elsewhere at this depth range could be a new horizon for tapping safe drinking water at about half the cost of deep tubewell installation. All findings made this study a comprehensive approach and strategy for replication towards As mitigation and scaling-up safe water access in other areas of Bangladesh and elsewhere having a similar hydrogeological environment. / <p>QC 20151211</p> / Sida-SASMIT project (Sida Contribution 75000854).

There is an urgent need for Bangladesh to identify the arsenic (As) contaminated tubewells (TWs) in order to assess the health risks and initiate appropriate mitigation measures. This involves testing water in millions of TWs and raising community awareness about the health problems related to chronic As exposure from drinking water, and providing alternative safe water option for the exposed population of the country. The use of spatial maps in a participatory context emerged as an important tool for an effective and rational distribution of alternative safe water options for the exposed population of the country. Field test kit offers the only practical tool available to screen all the TW water considering the time frame and financial resources of the country. A comparison of the field test kit results and laboratory measurements by atomic absorption spectrometry (AAS) as “gold standard” for As in water of 12,532 TWs in Matlab upazila (sub-district) in Bangladesh, indicates that the field test kit correctly determined the status of 87% of the As levels compared to the Bangladesh Drinking Water Standard (BDWS) of 50 μg/L, and 91% of the World Health Organization (WHO) drinking water guideline value of 10 μg/L. In order to identify the sustainable alternative safe water options, different type of safe water options were distributed in Sonargaon and Jhikargachha upazilas (sub-district) in 2001 and later revisited the options in 2004 to identify the sustainable ones. It was observed that community acceptability of the distributed options was not encouraging; less than 2% of the provided options were found to be in use. However, two new approaches emerged from people’s initiatives, which were making rapid and positive contributions to safe water coverage: switching to the existing As-safe TWs and reinstalling TWs at 50-100 m depths by looking at particular type of sediment colours. A study was conducted in Matlab upazila to validate the concept of installation/reinstallation of TWs at certain depths, a new concept promoted by local drillers (masons). The study revealed that locally a thick layer of black to grey sediments overlies an oxidized unit of yellowish-grey to reddish-brown sediments. The correlation between the colour of both units and the groundwater redox conditions was investigated to provide an easy tool for targeting low-arsenic groundwater. The water abstracted from black sediments contained high amount of As concentration but the concentration decreased towards the yeallowish to red sediments. Three boreholes verified the driller's perception of the subsurface lithologic conditions. Discrepancies between the driller's and the research team description of the sediment colours were insignificant. This study shows that sediment colour is a reliable indicator of high and low As-concentrations in TW water and can be used by local drillers to install TW. Lack of financial resources and identification of an appropriate distribution tools are some of the major obstacles to provide sustainable solution to the exposed population of the country. Spatial mapping exercise along with community participation can help maximize the safe water coverage of different alternative safe water options by reducing financial involvement. Combining people’s voice with that of spatial information gave better results and the method is already been proved useful in targeting non-served areas. Participatory Rural Appraisal (PRA) methods along with geographical information system (GIS) used in the study to obtain relevant information. Participants from different focus groups were asked to determine their ‘own priorities’ for spatial planning of alternative arsenic-safe water options. The study discusses community perspectives on demand-based safe water options and reveals the suitability of using participatory geographic information system (PGIS) technique to target non-served areas for rational distribution of safe water options. / QC 20100716