Paper No. 7
Presentation Time: 3:30 PM
POTENTIALITY OF SHALLOW BROWN SAND AQUIFERS AS SAFE SOURCE OF DRINKING WATER IN ARSENIC AFFECTED REGIONS OF BENGAL BASIN
BISWAS, Ashis1, BHATTACHARYA, Prosun2, NATH, Bibhash3, MUKHERJEE, Abhijit4, HALDER, Dipti2, CHATTERJEE, Debashis5, MÖRTH, Carl-Magnus6 and JACKS, Gunnar7, (1)Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N5E2, Canada, (2)KTH-International Groundwater Arsenic Research Group, Department of Land and Water Resources Engineering, Royal Institute of Technology (KTH), Teknikringen 76, Stockholm, SE-10044, Sweden, (3)School of Geosciences, University of Sydney, Sydney, 2006, Australia, (4)Department of Geology and Geophysics, Indian Institute of Technology (IIT), Kharagpur, 721302, India, (5)Department of Chemistry, University of Kalyani, Kalyani, 741235, India, (6)Department of Geological Sciences, Stockholm University, Stockholm, SE-106 91, Sweden, (7)KTH-International Groundwater Arsenic Research Group, Dept of Sustainable Development, Environmental Science and Engineering, KTH Royal Institute of Technology, Teknikringen 76, Stockholm, SE-10044, Sweden, ashis@kth.se
Identification of safe aquifer that can be targeted by cheap drilling technology is extremely important to prioritize arsenic (As) mitigation management. This study explores the potentiality of brown sand aquifer (BSA) as a safe drinking water source within shallow depth (<70 m) by delineating its regional distribution and hydrogeochemical contrast to grey sand aquifer (GSA), over an area of 100 km
2 in Chakdaha Block of Nadia district, West Bengal, India. The drilling of 14 boreholes recorded the formation of BSA around the depth of 35 m along central (north-south transect) and southwestern part of the study area. Additionally, drilling of 2 boreholes at the southwestern region was stopped at 50 m even before reaching any aquifer; however the driller confirmed the presence of BSA at the base of red clay layer around the depth of 70-80 m. The GSA was encountered at 13 boreholes along the west and east margin of the study area parallel to river Hooghly and Ichamati. At central northern part of the study area, drilling of 6 boreholes revealed the formation of GSA on the top of the BSA, with a separating red clay layer between two aquifers. The
14C dating of the sediment from the top of red clay layer indicates the age of 8506 ± 60 yr BP.
The hydrogeochemical investigation indicates that despite close similarity in major ion composition, the redox condition is markedly different in groundwater of the two studied aquifers. In BSA redox status is limited to the Mn oxides reduction stage; while in GSA Fe oxides reduction to SO42- reduction processes are prevalent. In groundwater of BSA, though the concentration of dissolved As is very low (<10 µg/L) the concentration of Mn is very high (>400 µg/L). The enrichment patterns of As and Mn in groundwater of GSA are opposite to that of BSA. This study warrants rigorous assessment of attendant health risk for Mn prior to considering mass scale exploitation of the BSA for possible sustainable drinking water supply. However, considering the severity of As health risk in rural Bengal due to limited availability of As safe drinking water sources, the BSA can be targeted temporarily for As safe drinking water with regular monitoring program until alternate As as well as Mn safe drinking water sources are explored and made available to the affected population.
