Government of the People's Republic of Bangladesh Ministry of ...

INTRODUCTION
Geological Setting of the
Areas of Arsenic Safe Aquifers
All water below the earth surface may be called subsurface or underground or ground water. A
hole penetrating the ground, initially passes through the zone of aeration (unsaturated zone), in
which inter granular spaces are normally filled mainly with air. The hole then enters the
saturated zone in which all inter granular spaces are filled with water. The upper surface of the
saturated zone is called the water table and at any place it normally slopes toward the nearest
stream. Very considerable amount of water occurs in more or less definite layers or rock
formations that often extend at various angles for hundreds or thousands of meters into the
earth. Such water bearing layers or rock formations are known as aquifers. An aquifer is
usually bounded above and below by materials impervious to water.
In Bangladesh the most important environmental issue at present is the arsenic contamination
in the ground water of the Holocene 1 aquifers of the Recent Alluvial deposits. The present
paper deals with the aquifers of arsenic safe geological regions and superimposes them on the
Upzila Map of Bangladesh. Lists of the Upzilas totally or partially belonging to this region are
enclosed as Annex - 2 to Annex - 6.
.
GEOMORPHOLOGY OF BANGLADESH
Topographically, Bangladesh is a plain land except the hills regions of east and northeast. The
plain land mainly consists of fluvio-deltaic sediments deposited by the Ganges, the
Brahmaputra and the Meghna river systems.
Geomorphologically, Bangladesh can be divided into four distinct regions each having
distinguishing characters of its own.
1. The Holocene Floodplains of the Ganges, the Brahmaputra and the Meghna river systems.
2. The Bengal Delta
3. The Eastern and Northeastern Tertiary Hills Regions
4. The Pleistocene 2 Terrace or the Pleistocene Uplands
1. An epoch of the Geological Time Scale, approximately 10,000 years ago, to the present time; also, the
corresponding series of rocks and sediments deposits.
2. An Epoch in the Geological Time Scale that started about 1.8 million years ago and lasted until the start of the
Holocene some 10,000 years ago, also, the corresponding series of rocks and sediments deposits.
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