DETERMINATION OF SUSTAINABLE ZONES FOR GROUNDWATER ABSTRACTION FROM THE MULTI-LAYERED AQUIFER SYSTEM IN THE BENGAL BASIN, BANGLADESH

The use of deep groundwater (±300 m deep) is becoming an important issue in the Bengal Basin, due to both water quality problems and an acute shortage of available water in upper aquifers. In southeastern Bangladesh, multi-layered aquifer conditions exist with arsenic contamination at shallow depths, and high iron and brackish groundwater occurring mainly in the deeper layers. Many previous studies have offered explanations for the high concentrations of dissolved arsenic in groundwater - most of which proposed that the arsenic is derived from geo-genic sources and its release in groundwater is through natural processes, not the result of anthropogenic practices. About three million tube-wells, installed at shallow depths (10 to 50m), discharged groundwater with arsenic concentrations more than the Bangladesh drinking water standard of 50 µg/l. Toxic levels of arsenic typically occur in the middle Holocene sediments deposited in low-lying delta and floodplain areas, which adversely affects the health of millions of people. Aquifers are recharged by vertical percolation as well as water from a long distance traveling from highly elevated eastern hilly terrain to deeper aquifers. Arsenic or chloride-rich groundwater in the upper aquifers is not likely to be drawn into the deep aquifer under conditions of moderate use from the deep aquifer water. Under the current trend of groundwater abstraction, the possibility of a mass transport of arsenic in the lower part of the first aquifer, just below the arsenic-contaminated zone, will increase in future (?).

Keywords: Groundwater model, Aquifer stress, hydraulic conductivity and aquifer zoning.