3DFEMFAT is a 3-Dimensional Finite-Element Model of Flow And Transport through Saturated-Unsaturated Media. Typical applications are infiltration, wellhead protection, agriculture pesticides, sanitary landfill, radionuclide disposal sites, hazardous waste disposal sites, density-induced flow and transport, saltwater intrusion, etc. 3DFEMFAT can do simulations of flow only, transport only, combined sequential flow and transport, or coupled density-dependent flow and transport. In comparison to conventional finite-element or finite-difference models, the transport module of 3DFEMFAT offers several advantages: (1) it completely eliminates numerical oscillation due to advection terms, (2) it can be applied to mesh Peclet number ranging from 0 to infinity, (3) it can use a very large time step size to greatly reduce numerical diffusion, and (4) the hybrid Lagrangian-Eulerian finite-element approach is always superior to and will never be worse than its corresponding upstream finite-element or finite-difference method. Because of these advantages, 3DFEMFAT is ideal for applications to large field problems. The special features of 3DFEMFAT are its flexibility and versatility in modeling a wide range of real-world problems. . The 3DFEMFAT model is designed for:
•Heterogeneous and anisotropic media.
•Spatially and temporally-dependent element and point sources/sinks.
•Prescribed initial condition or the simulated steady-state solution as the initial condition.
•Five types of boundary conditions for the flow module: (1) prescribed heads, (2) prescribed gradient fluxes, (3) prescribed total fluxes, (4) iteratively determined infiltration, seepage, and/or evaporation boundaries, and (5) river boundaries. All boundary values are allowed to vary with space and time.
•Four types of boundary conditions for the transport module: (1) prescribed concentrations, (2) prescribed gradient fluxes, (3) prescribed total fluxes, and (4) flow direction-dependent inflow and outflow boundaries. All boundary values are allowed to vary with time and space.
•Give Three options (exact, under- or overrelaxation) for estimating the nonlinear matrix.
•Include six options (subregion block iterations, basic point iterations, and four PCG methods) for solving the linearized matrix equations.
•Provide two options (consistent and lumping) of treating the mass matrix.
•Give two options (nodal quadrature and Gaussian quadrature) for surface and element integrations.
•Provide three adsorption models (linear isotherm, nonlinear Langmuir and Freundlich isotherms) in the transport module.
•Employ hexahedral elements, triangular prism, tetrahedral elements, or the mixtures of these three types of elements to facilitate the discretization of the region of interest.
•Automatically reset time step size when boundary conditions or sources/sinks change abruptly.
•Check the mass balance computation over the entire region for every time step.