HYDROCHEMICAL CHARACTERISTICS AND QUALITY ASSESSMENT OF GROUNDWATER IN HATIYA ISLAND, SOUTHERN COASTAL REGION OF BANGLADESH

Groundwater is the major source of fresh water in coastal areas of Bangladesh. Drinking water is mainly extracted from deep tube wells. The southern part of Bangladesh is vulnerable to natural disasters. One of the possible freshwater drinking supply alternatives is deep groundwater. However, the overexploitation of deep groundwater is increasing due to the growing population that depends on this resource. In addition, various anthropogenic activities on coastal water resources usually reduce the flows of fresh water to estuaries, and modify the estuarine mixing processes, further resulting in an increase of salinity in the coastal aquifer. The availability of water at a sustainable quality and quantity is a prime issue at present in the coastal region.

Evaluation of the groundwater quality and arsenic contamination has been done in different aquifers of Hatiya Island of Noakhali district by analyzing and assessing major ion chemistry and other parameters. Borehole lithology data reveals the presence of three aquifers separated by relatively thick aquitards. Results show that the mean arsenic concentration in groundwater is found more than 50 µg/L in the tube wells shallower than 50 m in depth where the surface elevation is less than 10 m. The mean concentration of arsenic in the intermediate aquifer (90 m) has been found to be around 30 µg/L. Arsenic mobilization in groundwater also appears to be triggered by intensive extraction of groundwater for irrigation and application of phosphate fertilizers. Salinity is the main water quality hazard of the area with conspicuous occurrences of arsenic at shallow depths. The study area seems to contain higher amounts of dissolved solids in the shallow aquifer which is evident from their hydrochemical data analysis. From hydrochemical facies analysis, it can be seen that most of the shallow and intermediate aquifers contain Na-Cl type water and indicate the influence of saline water. In contrast, most of the deep aquifers show Na-K-HCO3 type water and indicate freshwater. Water Quality Index (WQI) and Irrigation Indices have been calculated to assess the suitability of groundwater for drinking and agricultural purposes which reveal that deep aquifer contains good quality water compared to shallow and intermediate aquifers.