NUMERICAL MODEL OF RADIAL CONTAMINANT TRANSPORT IN GROUND WATER AQUIFERS

Abstract

Ground water pollution is very frequent in nature these days. The pollutant travel from a source due to the natural/forced movement of ground water (convection) and due to the pollutant concentration gradient present in space (dispersion). Because of the ever increasing environmental awareness in public and due to the potential fatal consequences the pollution has, it becomes necessary to examine the pollutant transport phenomenon in ground water aquifers. The present work deals with the development of a numerical 'model of two-dimensional axis-symmetric transient radial transport of pollutant from a recharge well for known velocity distribution in space and time. The model is based upon numerical solution of the transport equation by Finite Elements. The. Finite Element program developed in FORTRAN-77 incorporates numerically integrated isoparametric serendipity element. Though a quadratic element has been incorporated in the computer code/model linear, cubic or even higher order isoparametric elements can be incorporated easily by just adding the appropriate function subroutines corresponding to these. The computer code with a working documentation is appended in the thesis. Algorithm is checked for simple case of convection transport. The computed solution displays numerical dispersion and overshoot/undershoot phenomenon. For combined convection and dispersion case, result has been found to deviate from the corresponding analytical solution. The deviation increases with the increase of time. This discrepancy could be due to errors on account of inappropriate discretization. In the present study, the space and time were discretized in accordance with the recommendations in respect of transient radial flow, as given by Rushton. No literature on this aspect could be found to be available.