CS(AR)-1/2005 : Ground water quality monitoring and evaluation in Terai region of North Bengal

Abstract

Groundwater quality status of Cooch Behar district (under terai region of north Bengal) is presented based on the physico-chemical data as collected from 42 sampling stations of SWID. The various parameters analyzed include pH, Electrical Conductivity, TDS, Alkalinity, Hardness, Nat, Ce, Me, SO2-4, HCO-3 and Iron. T_he results were compared with water quality standards prescribed by BIS and WHO. In Cooch Behar district under Terai Region of North Bengal, rapid industrial and population growths have been taken place during the last decades. Not much of qualitative studies have been done in this region with reference to the available ground water resources. It is therefore proposed to take up study on ground water quality monitoring and evaluation in Cooch Behar district under Terai region of North Bengal with a view to see the suitability of ground water for various designated uses like drinking, agricultural, industrial etc. Seasonal quality behavior of ground water also demarcated by means of thematic maps. In the present study, different ground water classification methods on the basis of Stiff pattern diagram, Piper trilinear diagram, USSL classification, Gibbs variation classification, Durov's extended trilinear classification, Doneen's classification and Wilcox classification were applied. As per the Stiff classification, most of the samples are found as Ce-d-Me : HCO., type. On the Piper's trilinear diagram, ground water samples of the study area fall mainly in the Ce+Me : HCO-3 and mixed hydrochemical facies. Gibbs variation diagrams show that the chemistry of ground water is mainly controlled by the litho units of the area. Durov's trilinear classification shows that in cation type, majority of the samples are Ca2- and intermediate type while, in anion type, samples fall in HCO-3 and intermediate category. To evaluate the suitability of groundwater for irrigation purposes various parameters like Kelley's Ratio, Sodium Adsorption Ratios (SAR), Residual Sodium Carbonate (RSC), Magnesium hazards, Sodium % and Permeability Index have also been analyzed. According to the USSL Classification of irrigation water, samples fall under water type C 1-S 1 (low salinity and low SAR) and C2-S 1 (medium salinity and low SAR). According to Doneen's classification most of the samples are class-II type for irrigation use and few samples fall under class-1 and class-Ill. As per the Wilcox classification, most of the samples are excellent to good class. On the basis of these parameters it is concluded that the ground water is suitable for irrigation purpose. Block wise average Iron content in ground water of Cooch Behar is found much more than the desirable limit of WHO and BIS (0.3mg/I) and found unsuitable for drinking purpose without treatment.

Corrosive strength of the ground water was evaluated using different indices.

Toxicity of trace elements on human body also reviewed.