Technologies for Treating Contaminated Soil
This technology facilitates the removal of volatile and semi volatile contaminants (VOC and SVOC), such as fuel fumes and liquid fuels, from the sub saturated strata of the ground. Air or steam is used as an agent and are injected into the sub strata through boreholes. Pressure pumps adjacent to the boreholes create a negative gradient, which causes the steam or the water, bearing the contaminant, to rise to ground level. Heating the ground streamlines the process because the heat increases the evaporation of the contaminant by increasing its gaseous pressure. The heating process is carried out by subterranean heat exchanger systems. When the contaminant reaches the surface, the SVE system separates the contaminant fumes and the liquid and each of the phases is handled specifically. The process is relatively quick and inexpensive.
However, take note that the method is not suitable for heavy oil, metals, diesel fuel, PCBs, dioxins and kerosene.
In addition, in those area where the water table level is close to the surface it is possible that pumps will be required to lower the surface level because the vacuum is liable to also draw the ground water upwards into the non saturated strata and, in such a situation, the ground water may come into contact with the contaminating fuels. The SVE method is not suitable where the level of the ground water table is less than one meter from the surface.
Prior to commencing activities, it is crucial to investigate the ground using geophysical methods, is order the profile the attributes of the soil, such as: Hydraulic conductivity, fume composition of the soil, permeability and damp attributes. Thereafter, the ground gas is to be monitored and a map of the contaminated area should be drawn up. Take into account that the SVY system is not effective in damp soil or in clay.
The advantages of the system
A relatively short treatment period of 6 months to 2 years.
Proven effectiveness, available equipment and simple installation.
Minimal interference in activities conducted at the site.
Relatively low cost
Can be combined with other treatment methods.
Limitations of the Method:
Very saturated soil requires a greater vacuum to be created thus making the process more expensive
Extracting the gas from the contaminated area depends upon the permeability of the soil. When the permeability of the soil is lower, the effective of the system is reduced.
Very dry ground or high concentrations of organic material in the soil hinders the process.
The air emitted at the end of the process is liable to cause additional environmental damage should it not be treated. Generally, a license to emit air is also required.
Occasionally, the treatment of liquid remnants is required at the end of the process.
The system is not effective in subterranean saturation strata.
The level of the ground water table relative to the ground surface must be taken into account.