Prediction of subsurface migration of contaminant through soils involves analyses of unsaturated
and saturated flow of water and advective dispersive transport of contaminant species. A finite element
model is developed here for such an analysis. It is based on the transient nonlinear Richard's
equation for the unsaturated flow and the mass transport equation using advective dispersive
transport phenomenon. The model makes it possible to make advance predictions of the spread
of the contaminant with respect to time and space, into the ground water system. The hydraulic
properties of the unsaturated soils and the dispersion characteristics need to be obtained for such
an analysis. The unsaturated flow parameters are obtained from a functional relationship between
capillary pressure head and moisture saturation, and can be determined from laboratory tests on
simple column samples of soils. A general expression is assumed to account for the effect of velocity
dependence of the hydrodynamic dispersion coefficient in the mass transport problem. A computer
program POLUT2D is developed based on the above assumptions. Pre and post processors for
the computer program POLUT2D are also developed for interactive input of data and graphics
displays of results. The computer program is ftrst evaluated by comparing the results of a problem
given in the literature with the results obtained by POLUT2D. The factors affecting the contaminant
movement and distribution such as dispersivities, hydraulic conductivities and the effect of
cutoff walls in controlling the spread of contaminant plume are studied. Also in this regard, the
movement and spread of a contaminant at a landfill site in New Castle County, Delaware, is studied
by comparing the simulated pattern of plume with the observed pattern.
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