Viability of alternative water supply technologies for drinking purposes at a severely arsenic and salinity affected area

Abstract

Detection of Arsenic in 1993, posed a great threat to ground water based rural water supply in Bangladesh. The national screening revealed that 29% hand pump tubewells were contaminated with arsenic more than Bangladesh Standards of 50 ppb. Comilla is one of the highest arsenic contaminated districts in Bangladesh. In addition, pockets of salinity have also been found within Comilla district. The study area Manohorganj Upazila under Comilla district is one of the most vulnerable upazila in context of arsenic and salinity. Through this study the scale of water quality problem has been identified through random water sampling in shallow and deep aquifer, hydro- stratigraphy of the area has been analyzed through borelog analysis and performance of existing safe water technologies has been analyzed through socio –economic survey. The data of 754 GPS location has been collected for plotting GIS maps on water quality and safe water coverage which could be used for future reference. Union wise safe water technologies has been recommended based on the technical, social and economic findings from the study. From Water Quality analysis it has been found that shallow aquifer of the 100% upazila is severely arsenic contaminated with concentration more than 300 ppb. Deep aquifer is found arsenic safe. But iron and manganese content exceeding more than Bangladesh standards are found all over the upazila. From the combined water quality map it has been found that almost 46% of the study area are vulnerable to iron (> 1.0 mg/L), manganese (>0.4 mg/L) and chloride (> 600 mg/L) in deep aquifer. From hydrostratigraphy of the area and aquifer model it has been found that two distinct deep aquifer are present in the southern to central portion of the study area whereas in the northern portion, there is no 2nd deep aquifer up to the depth of 800 feet. Again in the eastern to central portion of the study area have two deep aquifer whereas in the western part there is one deep aquifer upto the depth of 800 feet. Slurry conductivity test during the drilling of deep tube wells successfully identified the fresh aquifer in each union. It has been found that layers with slurry conductivity value less than 60 μS/cm mostly provided water with EC value less than 1500 μS/cm. Variations were observed in static water tables in Shallow and Deep wells. In STWs water levels are still in suction limit whereas in DTWs the water levels are mostly beyond suction limit. From data of safe water coverage, still 68.4% population are in dare need of arsenic safe water in the study area. The highest coverage union is Hasnabad (54% coverage) and the least covered union is Natherpetua (11% coverage). GIS based Union wise safe water coverage map has been produced for future reference. From household survey and focus group discussion on existing technology performance, it has been found that Deep Tubewell (suction mode) and multiple connection are the preferred technology among others. Next preference is Piped Water Supply System (PWSS). Rainwater Harvesting System become the 3rd or 4th choice of people and last choice but not the least is other arsenic removal and treatment units. Considering the hydrogeological context, hydro stratigraphy of the aquifer, site observation, water quality and water table situation and people’s opinion a number of technologies has been recommended for future planning and interventions at union level. Thus the study will contribute to making effective investments on safe and sustainable water supply for the 244,943 people of Manohorganj, wherein 4,172 arsenicosis patients will be benefitted from arsenic safe water and reduced health risk.