Characterization of groundwater quality for irrigation and drinking purposes using a modified groundwater quality index

Groundwater quality assessment is an important issue to a megacity like Delhi, where intensive agriculture, use of sewage and polluted drain water for irrigation and industrial effluents have posed a serious threat to groundwater quality. Describing overall groundwater quality over space is difficult because of multiple contaminants and its wide range of spatial variation. The present study is aimed at determination of the overall groundwater quality using a groundwater quality index after its modification and to map their spatial variation in terms of suitability for irrigation and drinking purposes. For irrigation water quality, five parameters such as electrical conductivity, sodium adsorption ratio, bicarbonate, chloride and magnesium/calcium ratio based on FAO standard and for drinking water quality, eight parameters such as sodium, calcium, magnesium, nitrate, sulphate, fluoride, total dissolved solids and hardness based on WHO standard were used. The spatial variation of groundwater quality index indicates that overall quality of Delhi groundwater is acceptable for irrigation and drinking, while highly polluted groundwater zones are mainly found at the western part. Approximately, 76.44 and 89.14% area of Delhi have groundwater suitable for irrigation and drinking purposes, respectively. Sensitivity analysis indicates that parameters, which reflect relatively poor water quality (high mean rank value) and those of significant spatial variability imply larger impacts on the index needs to be accurately assessed. The index is very robust to predict drinking water quality.