HYDROGEOCHEMICAL STUDY TO UNDERSTAND MOBILIZATION OF ARSENIC AND MANGANESE IN AQUIFERS OF CHITTAGONG, A RAPIDLY EXPANDING COASTAL CITY IN BANGLADESH

While serious health effects due to extensive consumption of groundwater elevated in arsenic (As) have been documented in several South Asian countries, the source and mechanisms responsible for As mobilization in aquifers remain poorly understood. This happens particularly, in coastal city Chittagong, Bangladesh where flood plain and coastal aquifer systems occurred in the sediments of Quaternary age. The study area has the complex groundwater system; the northern part of the city is a part of Anticline associated with Tertiary aquifer system and the southern part of the city is more or less plain land. The unique geological settings of Chittagong provides opportunities to understand the geochemical processes that fuel arsenic concentrations in both Quaternary and Tertiary aquifer systems. This is a globally significant environmental and public concern because similar type of aquifers supply the drinking water to billions of people throughout the world. Preliminary studies have reported the elevated arsenic and manganese in groundwater of flood plain and coastal aquifers of proposed study area. However, as to date, no hydro-geochemical study has been conducted to understand the geochemical processes that control the arsenic distribution in water and sediments. In light of this suggestion, this study aims to investigate the detailed geochemistry of As and other redox sensitive elements in groundwater and sediments collected from the Quaternary and Tertiary aquifer systems. An improved understanding of these processes has broad implications to assess the risks posed by the As-&Mn-enriched sites and to design the mitigation strategies.