CHARACTERIZING CONTAMINANT GROUNDWATER AND SEDIMENT FROM COASTAL AQUIFERS OF SOUTHWEST BANGLADESH

The coastal aquifers of Bangladesh at the southwest portion suffer from severe salinity intrusion and arsenic (As) pollution.Lithological characterization from inter-layering of sand-silt-clay reveals that the aquifer sediments distribution and hydrogeological settings are relatively complex here. Aquifer-aquitard alterations change rapidly even within a short distance. Analysis of core sediments and groundwater from the present study reveals that the aquifer sediments consist of very fine sand, fine sand, and medium sand in the southern margin of Satkhira district, in southwest Bangladesh. Very fine sand, silt, and clay dominate the shallow (< 50 m) deposits of the study area. Dissolution of soil, rock, and organic matter allows salts and arsenic entering into the groundwater which persists for a longer time and are unable to naturally degrade. Groundwater analysis from 12 monitoring wells shows that average As concentration is 0.0475 mg/L and average salinity is 533.75 mg/L which is much higher than the EPA permissible limits (0.01 mg/L for As and 250 mg/L for Cl respectively).Textural studies suggest major aquifer sediments comprise 92% of fine to medium sand and 8% fine grained particles of silt and clay fractions. Concentration of bulk of heavy minerals is noticed at the 0.063 size fractions.

The present study has established a standard hydrologic and GIS model to interpret the ongoing and future extents of arsenic and salt contamination in southwest Bangladesh. Quantitative cross-sectional studies from a household questionnaire survey have assessed severe health implications among the local communities who are exposed to both climate and non-climate induced hazards. This study also reveals that anthropogenic and geogenic sources of arsenic and salinity mobilization and combined biogeochemical processes play major roles in public health problems as well as affect the socioeconomy of coastal Bangladesh.

Key Words: groundwater contamination, sediment characterization, coastal aquifers, arsenic and salt contamination, GIS modeling.