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

K. Choudhury ¹, D. K. Saha ¹, D. C. Ghosh ¹

Affiliations
1 Central Geophysics Division, Geological Survey of India, Calcutta - 700 016, IN

Abstract

Mixing of subsurface fresh and brackish/saline water has given rise to pollution in the aquifer and consequent environmental problems in the urban and semi-urban areas of the Howrah District of West Bengal. Also, overdrawal of groundwater has adversely affected the water table resulting in increase in salinity and possible threat to the civil structures. In order to suggest some remedial measures to arrest further deterioration of the environmental problems due to excessive and random pumping of groundwater, vertical electrical soundings (VES) using Schlumberger configuration have been carried out at 70 locations. Geoelectrical sections, isoresistivity maps at different depth levels as well as total transverse resistance (TTR) map of the area have been prepared. Analysis of these interpreted sections and maps have been able to (1) ascertain the resistivity and geohydrological characteristics of the subsurface layers, (2) map the aquifers and saline/brackish groundwater zones and (3) suggest measures for safeguards against groundwater pollution. Further, prospective groundwater zones and an old channel of Bhagirathi river are identified within [he highly conducting brackish deltaic area. The litho-sections brought out by the interpretation of survey data uould be useful to the city planners for land use, foundation studies and related utilities.

Keywords

Groundwater, Vertical Electrical Sounding, Geoelectrical Section, Gangetic Delta, West Bengal.

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D. C. Ghosh ¹, A. B. Mukherjee ¹

Affiliations
1 Department or Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302 (West Bengal), IN

Abstract

Hydrothermal synthesis of 1:1 type and 2:1 type trioctahedral hydrous layer lattice minerals covering the entire Mg-Ni compositional range is reported. Electronprobe microanalyses and X-ray diffraction data conform to the serpentine-type and talc-type chemistry and structure of these phases. Infra-red absorption spectra for the frequency range 4000-600 cm^-1 have been presented to characterize, their OH stretching vibrations, OH libration and the general lattice vibration modes. Optical absorption spectra between 2500 nm and 300 nm supplement the infra-red absorption data and clearly establish the d-d transition bands at about 1099 nm, 658 nm and 380 nm as caused by octahedrally coordinated Ni²⁺. Uniformity of the conditions- of synthesis between 250°C and 300°C and 350 bar P_H20 and the X-ray, infra-red and optical absorption spectra confirm the stability of the entire Mg-Ni compositional range under low pressure-temperature epizonal/hydrothermal conditions.

Keywords

Mineralogy, Hydrothermal Synthesis, Mg-Ni Layer Lattice Minerals.

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