WATER QUALITY ASSESSMENT OF DUG WELL WATERS AND ITS ADJOINING BURIGANGA RIVER REACH, OLD DHAKA, BANGLADESH

Dug wells are installed at shallow depths and are largely located in sands, gravels and other interspaces through which precipitation infiltrates and percolates into the underground aquifers due to gravity. Dug wells were mentioned as early as in 1968 as a source of drinking water for Dhaka dwellers (Khan and Stockard, 1968). Thirty six dug well water samples were collected randomly from different old houses with some of the wells located close to the river and also four Buriganga river water samples were collected at four different Ghats (boat terminals) during both the dry (April, 2010) and wet (September, 2010) seasons. The depth of these dug wells vary from 3.5m to 16m with an average depth of 10m. Water levels in the dug wells have both seasonal and diurnal fluctuations. Bad odor comes out from most of the dug wells and appears to be dark in color. Most of the samples of both the dug well waters and the Buriganga river were contaminated (in terms of trace elements) as almost all parameters and concentration levels of different chemical constituents exceeded the standard limits of World Health Organization (WHO, 2004), Department of Environment, Bangladesh (DOE, 1997) and United States Environmental Protection Agency (USEPA, 1995). But the study also shows that the range of all physical and chemical parameters of both dug wells and the Buriganga river were almost identical and did not vary with season. The hydrochemical classification shows most of the dug wells and Buriganga river water samples are Ca²⁺-Na⁺-HCO_3^--Cl^- type. It has not been deciphered whether the dug wells are being recharged from surface water flowing directly into the well or groundwater that has recharged via riverbank filtration. If the dug well water is protected from direct inundation from surface water, the shallow groundwater in this part of Dhaka city could be an alternative perennial source of water for bathing and washing especially during the dry seasons when water scarcity looms large. Thus, it is urgent to ensure the proper maintenance of these historical dug wells by the concerned authorities and improving our understanding of sources of recharge to the wells. At the same time, crash programs must be undertaken without further delay to control and mitigate the water pollution of Buriganga river.