MT3D⁹⁹

1. Implicit Solver: The iterative solver is based on generalized conjugate gradient methods with the highly efficeint Lanczos/ORTHOMIN acceleration scheme and enables the user to solve a wide array of problems using much less computational effort (also included in MT3DMS).
2. TVD Solution Scheme: MT3D⁹⁹ combines three major classes of transport solution techniqies in a single code, namely, the standard finite difference method; the particle tracking based Eularian-Lagrangian methods; and the third order finite-volume TVD (total-variation-diminishing) method. The new TVD method for solving the advection term is mass conservative and minimizes numerical dispersion and articicial oscillation (also included in MT3DMS).
3. Dual Porosity: The optional dual porosity (dual domain) advection-diffusion mass transfer model provides a more effective approach than the standard single-porosity advection-dispersion model for simulating solute transport in fractured media or extremely heterogeneous porous media (also included in MT3DMS).
4. Nonequilibrium Sorption and Monod Kenetics: The nonequilibrium sorption model enables the user to examine the role of sorption in solute transport and remediation processes without the restrictive local-equilibrium assumption. In addition to the first-order kinetics, MT3D⁹⁹ also supports zero-order and mixed-order Monod kinetics.
5. Multi-Species Reactions: MT3D⁹⁹ includes an enhanced reaction package to handle BIOPLUME-type aerobic and anaerobic reactions between hydrocarbon contaminant and any user-specified electron acceptors, and parent-daughter chain reactions for organic or inorganic copounds. This enables MT3D⁹⁹ to analyze natural attenuation and bioremediation without using a third-party add-on reaction package. The multi-species reactions are fully-integrated with the MT3D⁹⁹ transport solution schemes, including the implicit solver (MT3DMS supports multi-species contaminants but does not support any reactions or interactions between the various contaminant species).
6. Automatic Restart Option: MT3D⁹⁹ supports a new automatic restart option to greatly facilitate the continuation run from a previous simulation.
7. Complete Mass Budgets: MT3D⁹⁹ computes and saves cell-by-cell mass budgets. This enables the user to compile a detailed mass budget for any sub-region of the model grid (MT3D⁹⁶ also includes a cell-by-cell mass budget but only for a single species of contaminant).