ASSESSMENT OF NITRATE CONTAMINATION IN GROUNDWATER OF DELHI USING MATHEMATICAL MODELLING

Abstract

National capital territory of Delhi is facing severe problems in management of groundwater quality and quantity. The quality of ground water within Delhi varies from the place to place along with the depth of the water table. Dissolved nitrate is most common contaminant in groundwater. Rising nitrate concentrations in rivers and groundwater in regions have been of concern for several decades. Diffuse pollution from agricultural activities and livestock are often the main sources of elevated nitrate concentrations in groundwater. These activities pollute superficial water courses as well as groundwater through percolation. The fertilizers deteriorate the water quality inducing economical and ecological problems. In the last century automation of agriculture and the introduction of high yield crops has raised the use of fertilizers, increasing nitrate concentration in groundwater. Initially, the main concern was about human health, reflected in the Drinking Water Directive. More recently, legislation, the Nitrates Directive, has included reference to nitrate’s role in eutrophication. Realizing the importance of groundwater quality in urban areas and its deterioration due to the various pollutants, leading by nitrate, study was carried out to determine the nitrate contamination of ground water in Delhi using the mathematical models. Groundwater models describe the groundwater flow and transport processes using mathematical equations based on certain simplifying assumptions. These assumptions typically involve the direction of flow, geometry of the aquifer, the heterogeneity or anisotropy of sediments or bedrock within the aquifer, the contaminant transport mechanisms and chemical reactions. Groundwater flow models are used to calculate the rate and direction of movement of groundwater through aquifers and confining units in the subsurface. These calculations are referred to as simulations. The finite difference method of mathematical modeling has been used for the solution of convective dispersion equation of transport of nitrogen in the sample.Model with the least limitations and assumption have been selected for the calculation of the flow and transport of the nitrogen. The simulations using a uniform nitrogen to nitrate conversion ratio provides greater details of nitrate behavior. The results from the transport simulation are compared with the results of mass balance equation, which predict the average the nitrate concentration. Modeling errors are common in the simulations, due to the various assumptions taken in the modeling. For the reduction in the modeling errors, there is a need to apply best hydro-geological judgment. Hydro-geochemical data shows the great variation in the nitrate concentration. This data provide the basis for conversion of nitrogen to nitrate ratio in the simulation.