Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

A. S. M. Woobaidullah ¹, K. M. Ahmed ¹, M. A. Hasan ¹, M. K. Hasan ²

Affiliations
1 Department of Geology, University of Dhaka, Dhaka 1000, BD
2 Dept. of Geological Sciences, University College, London, Gower Street London, WCIE 6BT, GB

Abstract

The study area is dependent on ground water for irrigation during the dry months of the year as sufficient surface water resources are not available. Occurrence of saline ground water in some parts of the area, particularly at Kashopara and Kasab unions. restricts the use of ground water for irrigation purposes. Ground water electrolytic conductivity (EC) monitoring and resistivity sounding show a distinct vertical ground water zoning with varying salinity, viz .. an upper zone (0-30 m) of relatively fresh Na/CaHCO₃-type ground water with EC values <1000 μS/cm and a lower zone (below 30 m) of NaCI-type (brackish) ground water with EC values >2000 μS/cm. It is suggested that salinity prohlems in the affected area can be managed through minimum abstraction of saline ground water, proper selection of crops, land development and by changing methods of irrigation.

Keywords

Hydrogeology, Ground Water, Salinity, Ground Water Management, Bangladesh.

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K. M. Ahmed ¹, M. Hoque ², M. K. Hasan ³, P. Ravenscroft ⁴, L. R. Chowdhury ⁵

Affiliations
1 Department of Geology, University of Dhaka, Dhaka 1000, BD
2 Bangladesh University Grants Commission, Agargaon, Dhaka 1207, BD
3 Department of Geological Sciences, University College London, Gower Street, London, WCIE 6BT, GB
4 Mott MacDonald International Ltd., 122 Gulshan Avenue, Dhaka 1212, BD
5 Laboratory Division, BAPEX, House #39, Road #116, Gulshan, Dhaka 1212, BD

Abstract

Gas occurrences in irrigation wells have been reported from most parts of the country, and in some parts of the southeast region, gas occurrences have become a limiting factor for groundwater development. Methane is the main component of water well gases and is readily identified by its ignition characteristics. It has been found that conditions required for gas formation, such as the amount of total organic carbon and organic matter, depth of burial, hydrothermal gradient and degree of compaction, are all favourable for the generation of biogenic gases in the deltaic regions of the Bengal Basin. Biogenic gas from water wells contains only methane as the hydrocarbon gas and along with more than one per cent (by volume) of carbon dioxide. On the other hand thermogenic gas from deep wells contains methane and other higher hydrocarbon gases along with less than one per cent of carbon dioxide. Areas marked by high groundwater salinity generates more methane than other parts of the country and this is suggestive of estuarine environment of deposition of the aquifer materials in those areas.

Keywords

Groundwater, Methane, Bangladesh.

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K. M. Ahmed ¹, M. A. Hasan ¹, S. U. Sharif ¹, K. S. Hossain ²

Affiliations
1 Department of Geology, University of Dhaka, Dhaka 1000, Bangladesh, IN
2 Groundwater Circle. Bangladesh Water Development Board, 72 Green Road, Dhaka, IN

Abstract

Groundwater abstraction in Dhaka city has increased more than 700% during the last three decades. Consequently, water level has dropped to 20 m below sea level in the south central part of the city, where the ground surface elevation is 5.7 m. The rate of water level decline varies from 0.75 to 1.5m/year at different observation points within the city.

Iso-conductivity map of the groundwater depicts higher electrolytic conductivity (EC) value (500 to 800 μ1S/cm) in the southern part of the city, particularly along the river Buriganga. compared to the northern part (l00-2oo μ1S/cm). Contamination in the aquifer of southern part is attributed to recharge by polluted water from the Buriganga. Monitoring results of deep tube wells (DTWs) and hand tube wells (HTWs), located in municipal waste and industrial effluent disposal sites, show a marked depth variation in groundwater EC. Higher EC values in the HTWs demonstrates contamination in upper part of the aquifer from the disposal sites. Major ions and trace element concentrations of the water samples also reveal similar pattern. Increasing trend in the ionic concentrations. particularly cl^- and N0₃ , as observed in the historical record indicates gradual quality deterioration.

Keywords

Groundwater, Dhaka City, Bangladesh.

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A. A. Seddique ¹, K. M. Ahmed ¹

Affiliations
1 Department of Geology, University of Dhaka, Dhaka 1000, BD

Abstract

In Narayanganj, a rapidly growing and densely populated industrial town, groundwater abstraction has been increasing continuously to keep pace with urban development Groundwater is being tapped from the shallow. Holocene Alluvial aquifer and deeper Dupi Tila sands aquifer of Plto-Pleistocene age. As a consequence of the large-scale exploitation, water level has dropped to 15 m below ground surface and declining at a rate of 0 4 to 0 9 m/year. Groundwater electrical conductivity map depicts higher values (1000 to 2900 uS/cm) in the central and southern part, close to the Sitalakhya. River Analyses of hand tubewell (alluvial aquifer, 20-40m deep) and deep tubewell (Dupi Tila aquifer, 80-180m deep) water samples from different parts of the town reveal that there are marked vertical variations in groundwater quality. Shallow groundwater has higher dissolved solids, which demonstrates contamination in the upper aquifer and this is most pronounced in the industrial and thickly populated areas. Arsenic, lead, manganese, cadmium, etc are found to occur above the Bangladesh and WHO drinking water standards in a number of samples Present quality of the deeper aquifer is better in all respects, though there is a long-term risk of quality deterioration if proper water management is not practiced.

Keywords

Groundwater Pollution, Industrial Activity, Narayanganj Town, Bangladesh.

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