ISTD treatment of contaminated soil in urban area
By M. MAKOUDI, A. JORDENS, J. HAEMERS
In-Situ and Ex-Situ Thermal Desorption (ISTD and ESTD) are technologies based on thermal conduction that can effectively treat volatile and semi-volatile contaminants, independently of large soil heterogeneity. One of its applications is for contaminated properties in urban areas and under existing buildings.
The main principle of the technology resides in installing a network of steel pipes acting as an air/soil heat exchanger to heat up the soil by conduction to temperature and pressure conditions at which the contamination is volatilized. The soil is put under negative pressure through an extraction network and the pollutants are recovered for further treatment.
The object of this article is the study of the application of In-Situ Thermal Desorption (ISTD) for the treatment of VOCl-contaminated soils (i.e. DCE, TCE, PCE) in urban areas. A concrete case of soil remediation project that Haemers Technologies® has conducted in the residential area of Stockel (Brussel – Belgium) is presented. The remediation work was conducted under the supervision of AB Ecoglobe (accredited consultancy firm). The contamination was due to the onsite activities of a former dry-cleaning facility using chlorinated solvents.
Two treatment zones were defined: Zone 1, located outside the building (25 m²) and Zone 2, located in the basement (17 m²). The treatment was applied to the unsaturated zone up to 6.5 m deep (from soil level) in Zone 1 and 4.5 m deep (from basement level) in Zone 2. In total, the project led to the treatment of 230 m³ of contaminated soil with average PCE concentration of 300 mg/kg-dry soil. The particularity of this project also resides in the characteristics of Zone 2, namely a not easily accessible basement with low ceiling.
After the treatment, a maximum concentration of 3.2 mg/kg-dry sol of PCE was observed in the soil. This corresponds to minimum remediation rate of more than 98.9% (compared to the average concentrations before treatment).