Arsenic Contamination of Groundwater in Chapainawabganj, Bangladesh: A Sustainable Mitigation Option

Abstract

About 97% Bangladeshi people use tube well water for drinking purposes. In recent time, this water has been found to contain arsenic concentration above the permissible limit. Arsenic contaminated groundwater has already become a health hazard for a large part of the population. People with long-term exposure to arsenic polluted groundwater have been affected by arsenicosis as well as related complications; and some people are reported to have died. To mitigate the arsenic contaminated groundwater problem, a sustainable mitigation is needed in the country immediately. From this point of view, an attempt has been taken to develop a sustainable mitigation technique in the present research. The developed mitigation system has been implemented in Rajarampur, a severely arsenic affected village of Chapainawabganj district. Rajarampur was selected as the site for field implementation as it has now been established as a hotspot of arsenic contaminated groundwater. It is a semi-urban locality of Nawabganj Municipality situated in northwestern Bangladesh. Physiographically, the study area lies within Ganges-Mahananda flood plain characterized by gentle topography with a mean elevation ranges from 20 meter to 25 meter. Geologically, it lies in the Rangpur Platform, which is a stable part of the Bengal Basin. Stratigraphically, the study area is characterized by a thick sequence of Cretaceous to Recent sediments overlying the Archean basement thickness of the Quaternary sediment of the area is, 60 meter to 111 meter. In the early 1990s, high concentrations of arsenic were first reported in the groundwater of Chapainawabganj of Bangladesh. It is estimated that about 25 million people are exposed to arsenic contamination, 59 districts out of 64 have arsenic contaminated groundwater, 249 upazilas out of 467 affected, and over 7000 patients have been identified. About 27% of shallow tube wells exceed the Bangladesh standard limit (0.05 ppm) and 42% exceed the WHO guideline value (0.01) for arsenic in drinking water. In the Rajarampur village, the arsenic concentration ranges from 0.035 to 1.08 ppm. On basis of regional groundwater development potentiality, the study area is characterized by simple geology comprising younger alluvium. According to the UNDP Classification (1982), the area belongs to zone F, which covers the flood plain of Rajshahi district. National Water Plan of WARPO (former MPO), however, puts the area in the catchment area no 31 of planing area no 12 of the NW region in the Catchment Planing and Regions Map of Bangladesh. According to the geological cross sections constructed on the basis bore log data, it is inferred that the aquifer of study area is more of less confined. The aquifer mostly overlies the Barind Clay layer, and sometimes the Trap Wash. According to the BOS & MML, there are three known water-bearing layers in the area. The thickness of these layers are 1 0 to 50 meter, 20 meter and 10 to 60 meter respectively The horizontal/vertical permeability of these layers is 1/0.1 to 10/1 m/d, to 20/2 mid and 1/0.1 to 50/5 mid respectively. The confined/unconfined storage of these layers is 0.001/0.1 to 0.1, 0.001/0.15 and 0.001/0.2 respectively. The porosity of these the layers is 0.1, 0.4 and .04. From the chemical analyses of groundwater of the study area it shows that the pH of groundwater ranges from 7.5 to 9.8; EC concentration ranges from 550 μSiem to 745 ~tS/cm; TDS concentration ranges from 357.5 ppm 484.25 ppm; Ca2+ concentration ranges from 67 .13 ppm to 150 ppm; Mg2+ from 2 ppm to 41.63 ppm; Na+ from 1.25 ppm to 15 ppm; K+ from 0.3 to 7.2 ppm; Fe total from 0.11 ppm to 6.4 ppm; HCO3- from 273 ppm to 483 ppm; er from 12.00 ppm to 23.37 ppm; so/· from 0.00 ppm to 1.00 ppm; NO3- from 0.00 ppm to 1.00 ppm; As from 0.035 ppm to 1.8 ppm; and the total hardness from 239.46 ppm to 367.68 ppm.------