A one‐dimensional numerical model is developed with oscillating velocities and dispersions to simulate the migration process of a contaminant plume within tidally influenced aquifers. Model simulations demonstrate that a major effect the tidal fluctuation has on the migration process of a contaminant plume is the exit concentration discharging to the tidal estuary. Tidal fluctuation causes the exit concentration levels to be significantly diluted by the surface‐water body of the estuary. Sensitivity analyses demonstrate that tidal fluctuation hastens the rate of plume migration near the bank of the estuary because of the relatively high advective and dispersive fluxes induced by tides. However, tides affect the migration process only over a short distance from the tidal‐water interface (about 40 ft for the parameters used in this study). If the contaminant plume is located far beyond the interface, tidal fluctuations will not affect the rate of plume migration until an existing regional ground‐water flow velocity brings the plume to the tidally active zone. With or without tides, the rate of contaminant migration increases with higher regional hydraulic gradient. Furthermore, the effects of tidal fluctuations on the transport process become insignificant with higher regional hydraulic gradients.

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Abstract, A finite element model has been developed to simulate the migration of gases in soil from a buried source such as a landfill. Using quadratic elements, the diffusion convection equation coupled with the mass conservation equation of a binary mixture of gases is solved under a combination of Dirichlet, Neumann and flux type of boundary conditions. The model is compared with an analytical solution and a set of field measurements. The model is used to display the influence of seasons on the migration of gases. The effectiveness of venting trenches in containing such migrations is examined and a method for the determination of trench depth is presented.

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