Unsaturated Zone:
Modeling Groundwater Flow and Contaminant Transport Vol 1 No. 9

PESTAN (PESTticide ANalytical) is an analytical model for predicting the transport and degradation of dissolved pesticides through the unsaturated zone.

HELP (Hydrologic Evaluation of Landfill Performance) is a finite difference numerical model for simulating vertical percolation and lateral drainage through a landfill.
Most groundwater contamination problems can be attributed to either spills or leaks from surface or near surface storage tanks and facility operations. As a result, the behavior of the contaminants in the unsaturated zone plays a critical role in the development of a groundwater plume. However, despite this fact, the vast majority of groundwater contamination studies still neglect the contributions and influence of the unsaturated zone. This is due to several reasons:
  • lack of regulations dealing with the unsaturated zone
  • lack of data for the unsaturated zone
  • lack of easy-to-use software

Fortunately, many states are now adopting stricter risk-based policies for evaluating contamination in the unsaturated zone. In addition, software packages like UnSat Suite are making unsaturated zone modeling easier and more cost-effective.

Soil and Chemical Properties
UnSat Suite combines SESOIL, VLEACH, VS2DT, PESTAN and HELP in a Windows graphical environment specifically designed for simulating 1-D groundwater flow and contaminant transport through the unsaturated zone. UnSat Suite comes with a built-in database of soil and chemical properties for many commonly

encountered site conditions. In addition, it comes with a GIS database component for generating seasonal weather data for periods of up to 100 years for virtually any location in the world. As a result, unsaturated zone modeling studies are now being applied in many states to more accurately predict the contaminant loading rates and aquifer recharge rates.

About The Models

SESOIL is a seasonal compartment model that simulates long-term pollutant fate and migration in the unsaturated soil zone. SESOIL provides a comprehensive treatment of unsaturated zone contaminant transport processes including contaminant washload, volatilization and air diffusion of VOCs, sorption, degradation, cation exchange, hydrolysis, and metal complexation.

VLEACH (Vadose zone LEACHing) is a finite difference model for simulating the vertical mobilization and migration of dissolved organic contaminants through the vadose zone.

VS2DT (Variably-Saturated 2-D flow and solute Transport) is a finite difference numerical model for simulating steady-state or transient unsaturated flow and contaminant transport through multi-layer, heterogenous soil.

Model Output

UnSat Suite comes with a complete selection of graphical reporting tools for analyzing, interpreting and printing the simulation results. Modeling results such as recharge rates and contaminant loading rates can also be exported for use in other applications (e.g. Visual MODFLOW).

Practical Applications

  • SESOIL is widely used by both consultants and environmental agencies as a screening tool to assess contaminant fate and transport through the unsaturated zone
  • VLEACH is an easy-to-use model for evaluating VOC spills and predicting leaching of dissolved VOCs through the unsat-urated zone
  • VS2DT is used for simulating time-varying groundwater flow and contaminant transport through the unsaturated zone in multi-layered, heterogeneous soil conditions
  • The HELP model is the accepted standard for simulating landfill hydrology and predicting aquifer recharge rates

See Unsat Suite Here

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