Groundwater contamination control
Through computer based modeling programs
Control of groundwater contamination in a contaminated site is very important. For this reason, the effects of transport and final fate of contaminants in the subsoil should be studied. Nevertheless, due to complexity of the contamination processes that take place, different monitoring methods have been developed, as computer based modeling programs, which are able to simulate involved chemical processes, contaminant transport mechanisms based on advection, dispersion, sorption and reaction, heat flow, etc.
Generally, a wide range of software is now available for groundwater flow and contaminant transport modeling.
Modern numerical simulation programs are applied for modeling of one-, two- and three-dimensional groundwater flow, contaminant transport, heat flows. Advanced modeling programs can simulate multi-phase flows of water, air and soil gas and multicomponent fluid mixtures.
Some of the programs allow to take into account fluid density e.g. when industrial brines and/or sea water intrusion modeling.
The following table presents the codes of the programs which can be applied for one, two and three-phase simulation of different processes (groundwater flow, contaminant transport, heat flow).
Download table: Computer based simulation programs
The most powerful/commonly used computer based models that are applicable to POP’s contaminated sites are described as following:
- TOUGH2: Transport of unsaturated groundwater and heat. General purpose numerical simulation program for multi-dimensional fluid and heat of flows of multiphase, multicomponent fluid mixtures in porous and fractured media. It is applicable in geothermal reservoir engineering, nuclear waste isolation, environmental assessment and remediation and flow and transport in variably saturated media and aquifers.
- T2VOC: TOUGH2 module for three phase flow of water, air, and a volatile organic compound. Processes such as the migration of hazardous non-aqueous phase liquids in variably saturated media, forced vacuum extraction of organic chemical vapours from the unsaturated zone, evaporation and diffusion of chemical vapours in the unsaturated zone, air sparging, direct pumping of contaminated water and free product, and steam injection for removal of non aqueous phase liquids from contaminated soils and aquifers can be simulated.
- TMVOC: TOUGH2 module for simulating three-phase non-isothermal flow of water, soil, gas and a multicomponent mixture of volatile organic chemicals in multidimensional heterogeneous porous media. It is applicable for problems like hydrocarbon fuel or organic solvent spills in saturated and unsaturated zones. It can model contaminant behaviour under natural environmental conditions, as well as for engineered systems, such as soil vapour extraction, groundwater pumping or steam assisted source remediation.
- T2DM: TOUGH2 module for modeling mass transport by molecular diffusion and hydrodynamic dispersion in two dimensional flow systems.
- EOS: The various EOS (equation of state) modules included in the TOUGH2 package can represent different fluid mixtures (water and air, water, brine and air, water, brine, parent radionuclide, daughter radionuclide, and air, water, non-condensable gas, and black oil, etc.)
- VS2DT (Variably Saturated 2-D flow and solute Transport model): Program which simulates steady-state or transient groundwater flow and solute transport in variably saturated porous media. This model permits to solve by means of finite-difference advection-dispersion equation and the non lineal water flow equation. Simulated processes include: transient groundwater flow and contaminant transport through the vadose zone and leaching of contaminants to infiltrating groundwater, sorption of dissolved contaminants on soil and first-order decay contaminants. Typical application of the VS2DT model include determining the fate of agricultural chemicals, landfill leachate, underground storage tanks leaks and accidental chemical spills as they migrate through the unsaturated zone towards the water table.
- MODFLOW: Modular finite-difference flow model, which is used to simulate groundwater flow through aquifers. The groundwater flow is simulated in three dimensions, based on changes in time and for a porous heterogeneous and anisotropic medium. It is also possible to simulate stationary conditions. Generally, the model is used to simulate the movement of a fluid in a porous saturated medium, permitting the prediction of pollutants migration through groundwater. By means of this model the effects of wells, rivers, drainage systems, horizontal flow barriers, evapotranspiration and recharge can be simulated.
Some programs can be also used for hydrogeochemical processes modeling like PHREEQC (pH (pH), RE (redox), EQ (equilibrium), C (program written in C)), LEHGC (Hybrid Lagrangian-Eulerian Finite-Element Model of HydroGeo-Chemical Transport through Saturated/Unsaturated media) and EQ3/EQ6.