Miljøprojekt, 1157; Teknologiudviklingsprogrammet for jord- og grundvandsforurening – Miljøvurdering af termisk assisteret jordrensning (dampoprensning)

Miljøvurdering af termisk assisteret jordrensning (dampoprensning)

Summary and conclusions

Remediation of contaminated soil with vapour is a relatively new method, which has only been used a few times in Denmark. This project investigated whether vapour stripping is likely to affect the biological and the physical properties of soil. The project was conducted on contaminated areas in Hedehusene, Denmark in the period 1999-2002. The results from the remediation project have been reported elsewhere /1/.

To elucidate the problem three sub-projects were initiated. 1) An investigation of the effects of vapour injection on soil fauna and plants, 2) the effects of thermal remediation on the microbial communities and 3) the effect on physical properties of the soil including its hydraulic conductivity.

It is likely that local changes in soil fauna and plant communities will occur as a result of the vapour injection, i.e. the increased temperature and the lower water content of the soil. On the basis of the results from this project it is not possible to draw conclusions on how long these changes will last. Trees and smaller bushes with deeply penetrating roots will most likely die, whereas grass and most other plant species will survive and in some areas probably with increased growth as a result.

The minor changes in soil properties, which were observed in this project, are not likely to cause any significant negative changes in drainage conditions for secondary groundwater resources. An increase in soil density and hydraulic conductivity was observed. This is probably due to a combination of settlement of the soil and removal of organic carbon by wet oxidation.

Large changes in the microbial communities were observed during and after the thermal mediated remediation. Emergence of a diverse heat tolerant micro-flora was documented during the period of remediation. This lasted at least half a year after the termination of the vapour injection. Two potentially human pathogens, i.e. Pseudomonas aeruginosa and Aspergillus fumigatus, were identified in significantly increased numbers. These were the only species specifically looked for and it cannot be ruled out that other pathogens were present.

After the termination of this project, additional studies were conducted in order to follow the presence of pathogens for up to 18 months after the end of the vapour injection /4/. The conclusion from this project was that the number of heat resistant bacteria decreased just as the number of potential pathogen bacteria. However, the pathogen fungus Aspergillus fumigatus was still observed in significantly higher numbers in the thermally treated soil.