SEARCHING FOR SAFE WATER IN THE ARSENIC AFFECTED COMMUNITY; SOUTH-WESTERN BANGLADESH

Groundwaters extracted from the shallow Holocene aquifers of the South-Western Bangladesh have recently been identified to be affected with high Arsenic poisoning. Limited scale in situ treatments that have been available until now might not be sufficient enough to provide ample water. It is thus urgently required to propose a safe and sustainable water source that may save millions who have heavily been dependent only on those contaminated water resources. This paper is aiming to discuss the potentiality of the safe waters that may be searched by exploring the deep aquifers with the help of a combined study including field, laboratory and numerical analysis.

Two key geochemical parameters, the reaction rate K_r and the partition coefficient, K_d were found to be very promising in explaining the As transport mechanism. In-situ K_r for natural biotite dissolution process, derived by using inverse mass balance model was found as 2.72 × 10^-16 /sec. A parametric predictor equation, that can calculate the K_d considering the aquifer sediment’s dominating minerals such as Fe and Al contents and pore-water pH was developed.Incorporating those two parameter, a 1D-Finite Difference numerical model was applied to observe and evaluate the As pollution scenario for the studied Holocene aquifer. The simulation showed very promising results introducing the idea that significant As might get reduced after 50 years from both the shallow as well as deeper aquifer. Further, the As transport particularly for the deeper aquifer was tried to simulate for its sustainability and viability for being a future source of water supply. It was noticeably found that the deeper aquifer would potentially be remained safe from being contaminated with As because of its having experienced with several natural encouraging effects including the absence of any active As leaching source minerals; presence of a silty clayey aquitard that might hinder the As to reach there; availability of adsorbing minerals like Fe, Al that may adsorb significant As, in case of leaching occurrence. As a consequence of these along with the underlying geochemical processes, the deeper aquifer would be the potential source for providing sustainable, safe, ample and adequate quantity of water in future in an affordable way for the concerned As affected poor community.