Introduction
Model flow of water and light nonaqueous phase liquid (LNAPL), and aqueous phase transport of up to five species in ground water with multiple pumping and/or injection wells with MARS. MARS is a finiteelement model that allows accurate representation of highly irregular material and physical boundaries in a heterogeneous and anisotropic media.
MARS 2D/3D Flow

Initial conditions and free oil volume are estimated internally from the monitoring well fluid level data.

Rectangular 2D prism or isoparametric quadrilateral elements to accurately model irregular domain and material boundaries, hydraulic, and physical boundaries.

Oil and water recovery rates vs. time are computed.

Areal distribution of residual hydrocarbon is computed and used to estimate transient contaminant loading to ground water if transport simulations are performed.

Interactive finiteelement mesh generator: rectangular/isoparametric quadrilateral mesh for areal simulations.

Spatiallyvariable water recharge, injection or LNAPL leakage.

Model multiple pumping and/or injection wells and trenches.

Model specified head and flux boundary conditions.

Simulates fractured media or granular porous media based on the dual porosity approach.
Included with MARS is the finiteelement model, BIOF&T 3D, that allows:

Transient 2D or 3D multicomponent aqueous phase transport in groundwater aquifers. This feature enables computationally efficient simulations with a model that gives due regard to the dimensionality of the problem and is hydrogeologically defensible.

Temporal and spatial variations in the source (i.e., residual dense or light nonaqueous phase liquids), and, given the initial conditions, changes in loading to ground water are computed and updated internally for aqueous phase transport.

Model specified concentration, mass flux and source/sink boundary conditions.

Convection, dispersion, diffusion, adsorption, desorption, and microbial processes based on oxygenlimited, firstorder or Monodtype biodegradation kinetics as well as anaerobic sequential degradation involving multiple daughter products. This allows realworld modeling not accomplished in similar biodegradation packages.

Computationallyefficient matrix solution by conjugate gradient method with preconditioning.
MARS 2D/3D Input

Mesh discretization data

Initial conditions for flow: water and oil pressure distribution

Boundary conditions for flow: specified head boundaries, flux boundaries, and sources and sinks

Soil hydraulic properties: van Genuchten parameters, hydraulic conductivity distribution, and porosity

Initial conditions for transport

Species concentration

Boundary conditions for transport: specified concentration, specified mass flux, and spatial distribution of contaminant loading

Dispersivities

Mass transfer rate coefficient between oil and water phase

Distribution coefficient

Bulk density

Diffusion coefficient for species

Biodegradation parameters for each species

Fraction of the mobile phase (needed for fractured media simulations only)

Mass transfer coefficient between mobile and immobile phase (needed for fractured media simulations only)
MARS 2D/3D Output
Flow

Spatial distribution of fluid pressure with time

Spatial distribution of fluid saturation with time

Fluid velocity distribution with time

Fluid pumping/injection rates and volume vs. time
Transport
For each species:

Spatial distribution of concentration with time

Mass dissolved in water vs. time

Mass remaining in NAPL phase vs. time

Mass adsorbed on the solid phase vs. time
MARS 3D with Transport

MARS 3D comes with BIOF&T 3D and all features included in BIOF&T 3D.
MARS 2D/3D Technical Information
MARS (Multiphase Areal Remediation Simulator) can be used to model recovery and migration of light nonaqueous phase liquids in unconfined heterogeneous, anisotropic aquifers. MARS writes input flow files for the BIOF&T model which simulates multispecies dissolved phase transport in heterogeneous, anisotropic, fractured media, or unfractured granular porous media.
Groundwater contamination from hydrocarbon spills/leaks is a serious environmental problem. Nonaqueous phase liquids (NAPL) are immiscible fluids that have insignificant solubility in water. NAPLs in the subsurface migrate under the influence of capillary, gravity, and buoyancy forces as a separate phase. Light NAPLs (LNAPLs) float and migrate on top of the water table posing a continuous source of contamination to the ground water. Due to water table fluctuations, some of the NAPL gets trapped in the unsaturated and saturated zones. NAPL trapped in the soil and ground water acts as a continuing source of groundwater contamination resulting in expensive restoration of these aquifers.
MARS consists of:
1. The MARS flow module simulates recovery and migration of water and LNAPL in unconfined aquifers following an LNAPL spill or leakage at a facility. It can also simulate NAPL recovery with skimmers and trenches, and optimize the number, location, and recovery rates for water and oil.
2. MARS writes input files for BIOF&T, a transport model that simulates decoupled 2D or 3D multispecies aqueous phase transport from the free and residual NAPLs.
The MARS flow module invokes an assumption of nearequilibrium conditions in the vertical direction. This reduces the nonlinearity in the constitutive model and transforms a 3D problem into a 2D areal problem, thereby drastically reducing computational time for the simulation.
MARS gives the initial distribution of NAPL specific volume in the domain for BIOF&T which models the aqueous phase transport, and computes and updates the temporal and spatial variation in the source during the simulation.
This software is accompanied by a userfriendly preprocessor, mesh editor and postprocessor. The preprocessor and mesh editor can be used to create input data files for MARS. They include modules for: mesh generation; allocating heterogeneous and anisotropic soil properties to zones; defining fixed head, flux, source/sink boundary conditions for water and oil phases; and allocating spatiallyvariable recharge in the domain. Twodimensional rectangular or isoparametric quadrilateral elements are permissible to accurately model irregular domain and material boundaries.
Required input for flow analyses consists of initial Zaw, Zao distribution, soil hydraulic properties, fluid properties, time integration parameters, boundary conditions and mesh parameters. The van Genuchten constitutive model, along with fluid scaling parameters, is used to compute water and oil phase volumes.
MARS output includes a list of the input parameters, initial and boundary conditions, and the mesh connectivity. It also includes simulated water and oil phase pressures, water and oil phase velocities at each node, total volume of water and oil versus time, and water and oil recovery/injection rates for each sink/source location versus time. Volume of free oil and residual oil and their spatial distributions are also printed versus time. Flow simulations can be performed in stages. MARS creates an auxiliary file at the end of the current stage that can be used to define initial conditions for the next stage.
MARS 2D/3D Input Parameters
Estimation of Soil Properties
Soil properties needed for a MARS flow simulation are: saturated hydraulic conductivity in principal flow directions, anisotropy angle of the main principal flow direction in the areal plane with the xdirection of the model domain, soil porosity, irreducible water saturation, and van Genuchten retention parameters. SOILPARA, 1995, a proprietary computer model, provides an easytouse tool for estimating soil hydraulic parameters from soil texture based on: 1) the public domain model RETC developed by M. Th. van Genuchten et al., 1991, 2) the work of Shirazi and Boersma, 1984 and Campbell, 1985, and 3) a selection of USDArecommended typical parameter values for various texture classes available in the SOILPARA database are included in the MARS document.
Fluid Properties
Fluid properties required by MARS are specific gravity, oil to water dynamic viscosity ratio, and fluid scaling parameters. Methods to estimate these parameters are included in the MARS document.
Creating Input Data Files
The sequence of the input parameters and their definitions has been furnished in Appendix D of the MARS document. This section explains the procedure for spatial discretization and mesh generation, defining initial conditions, boundary conditions, and the maximum permissible array dimensions.
Spatial Discretization and Mesh Generation
The MARS modules allow use of rectangular and isoparametric elements. The element size and shape can be changed to obtain mesh refinement that is necessary to obtain accurate results.
Initial Conditions for Flow
Initial head distribution in the domain for water and oil can be specified by:

bilinear interpolation with heads defined on the left and right boundaries

a nonuniform head distribution defined by fluid levels in the monitoring wells
Boundary Conditions
Specified pressure head (type1) boundary conditions can be defined at selected nodes versus time.
Type2 (specified flux) and source/sink boundary conditions can be defined by specifying the volumetric rate [L3 T 1] versus time for respective nodes. For a type2 boundary condition, when flux [L T 1] is known at a node, the user should multiply flux with the area represented by the node in a plane perpendicular to the flux.
MARS 2D/3D Windows Interface
What is the MARS preprocessor?
The Windows preprocessor for MARS is designed to help users create and edit input files for the MARS numerical model. The preprocessor works in concert with the mesh editor to allow users to assign boundary condition schedules, soil types, recharge zones, etc. to the finiteelement mesh used in the MARS numerical model. The preprocessor contains all control parameters that determine model run options, initial conditions, monitoring well information, fluid properties, boundary schedule data and soil type definitions as well as serving as a binder for mesh editor files. The preprocessor also contains a module for writing input files for the MARS numerical model and for actually running the numerical model.
Using the MARS preprocessor
