SOIL-GIS is an ArcView 3.X extension developed by GECOsistema s.r.l. and requires ArcView Spatial Analyst to WORK. It contains interfaces to the following models:

•         USGS MODFLOW 2000  (Saturated zone, flow);

•         USEPA MT3D-MS  (Saturated zone, solute transport);

•         USEPA HSSM 1.03  (Unsaturated zone, non aqueous phase liquids - NAPL);

•         USEPA VLEACH 2.2 (Unsaturated zone, dissolved (organic) chemicals).

All models present some simplifications in order to provide an easy–to-use tool for geohydrologists with limited modeling experience. In addition, SOIL-GIS implements some explorative modelling tools which can be used for screening level assessment of aquifer pollution from specific sources, and support to environmental forensics.

MODFLOW 2000

MODFLOW is a model of flow in saturated soil. Therefore it cannot be applied to the vadose zone. For what regards MODFLOW 2000 the main simplifications introduced in SOIL-GIS are:

•         Single layer aquifer;

•         Discretization domain in constant dimension rectangular cells;

•         Boundary conditions given by constant border piezometric head;

•         Steady flow with a single stress period;

•         External forcing limited to wells and drains;

•         Rivers as constant head cells.

MT3D-MS

MT3D-MS uses a flow field, which can be imported from results of MODFLOW, to simulate solute transport when solute concentration does not influence the flow field itself (as in the case of saline stratification) . The main simplifications introduced in SOIL-GIS consist of:

•         Only one chemical species for each simulation;

•         Constant dispersion coefficient;

•         Constant reaction kinetics parameters;

•         Boundary condition given by constant concentrations.

HSSM

HSSM estimates the release of hydrocarbons in the unsaturated zone analyzing NAPL (Non-Aqueous Phase Liquids) transport from the source to the aquifer. It can be applied for the case of oil spill or leakage from NAPL reservoirs. It describes multiphase flow in the vadose zone, the formation of a floating oil lens on the water table, and the migration of soluble constituents of the NAPL in the aquifer, following simplified schemes of the processes. Soil-GIS allows launching HSSM with site-specific parameters.

VLEACH

VLEACH describes pollutant transport in the unsaturated zone considering the partitioning in solid, liquid and gaseous phase, and the loading of solutes to groundwater. The main simplifications are:

•         Monodimensional flow;

•         Domain divided in polygons with homogenous subsurface;

•         Dispersion not considered[1];

•         Conservative contaminant.

Soil-GIS allows launching HSSM with site-specific parameters.

Explorative modelling tools

Soil-GIS also contains some explorative modelling tools:

•         Capture area:  delineates the area from which water flows to a user-specified point, based on the flow directions on the water table;

•         TOT:  calculates the time of travel of a pollutant through diffusive/dispersive and advective mechanisms, inside the capture area;

•         AT_inst:  implements the simplified analytic solution of the advection-dispersion equation in the case of instantaneous release (e.g. spills);

•         AT_const:  implements the simplified analytic solution of the advection-dispersion equation in the case of constant concentration source (e.g. leaking reservoirs).