The vulnerability of the Dupi Tila Aquifer, Dhaka, Bangladesh
The Dupi Tila aquifer in Bangladesh is of national importance, providing over 95% of the water supply for the capital city, Dhaka. The demand for water is rising inexorably. There is concern about the sustainability of the aquifer and its vulnerability to contamination. In Dhaka, the Dupi Tila aquifer is confined by the Madhupur Clay. Natural recharge to the aquifer is by vertical leakage through the Madhupur Clay. However, large-scale development of the aquifer since 1971 has continued beyond the rate which could be sustained by vertical leakage. Piezometric levels have steadily declined, aquifer storage has been depleted, the aquifer has become unconfined over large parts of the city, and an extensive cone of depression has developed outwards to the rivers bounding the city. The extent to which groundwater abstraction can be balanced by induced river recharge and enhanced vertical leakage has been explored by development of a groundwater flow model. Both types of recharge are potential sources of contamination. To assess aquifer vulnerability to contamination, a detailed survey of groundwater quality across Dhaka has been made and related to previous data. A plume of contaminated groundwater is shown to have intruded the aquifer. In addition, a preliminary survey of organic contamination suggests that contaminants from industrial areas are entering the aquifer through the Madhupur Clay. To evaluate the relative impact on groundwater quality of induced river recharge and enhanced vertical leakage, a solute transport model was developed from the groundwater flow model. Induced recharge from the contaminated River Buriganga is responsible for the plume of low quality groundwater in the South West of the city. Vertical leakage of contaminated urban recharge may affect groundwater quality more widely in the longer term. Recommendations are made for the protection of the Dupi Tila aquifer as a source of high quality groundwater.