Oprensning af blandingsforurenet jord

English Summary

The present report is a presentation of the different methods to remediate soil containing mixed contaminants or soil containing tar components. Counties as well as private soil cleaning companies have contributed to the project. Furthermore foreign consulting engineering companies, authorities and a few universities in Europe and USA have been contacted to achieve knowledge of the latest experiences of selected remediation techniques. An important source of information regarding environmental issues, is the American Environmental Protection Agency (EPA) that has a data base with environmental literature connected to their homepage.

During the preliminary work with the new law regarding soil contamination in Denmark, it has been estimated that there are approximately 10.000 contaminated locations and 20 km² diffuse contaminated soil with vulnerable use of area in the country. Site assessments in the City of Copenhagen show that approximately half of the topsoil contains lead as well as PAH-components at levels above the soil criteria. Soil containing mixed contaminants is also very often found by the soil cleaning companies; mostly the content of heavy metals is at lower levels than the content of organic contaminants. For several types of industries it has been observed, that the production methods have caused mixed contaminants in the soil, and the remediation technique for these types of contamination is consequently an interesting issue. Based on the facts in this report it is estimated that approximately 1 to 10 % of the excavated soil contains mixed contaminants.

Tar/PAH components are often found in urban areas and especially at former gasworks. Even though it is almost 25 years ago since the last gasworks closed down, the sites are still heavily contaminated. Cleaning of the soil from e.g gasworks, asphalt factories and from drying grounds will allso in the future be an important issue, and new efficient methods to clean the contaminated soil will be useful. There has been registered 300 locations with tar/PAH contaminants, but it is anticipated that there are still many not registered locations which have not yet been registered.

The remediation techniques for mixed contaminants are described in chapter 4 and the techniques for tar components in chapter 5. The technical background for each remediation technique is described including the fundamental chemical processes. Subsequently a status of the level of development for each remediation technique follows with an overview of the different remediation efficiencies. The efficiencies are mostly dependent of the soil type, the initial concentrations of the contaminants and specific conditions during the process. This information along with cost estimates have been included when available. Finally a summary of the collected information follows.

The remediation techniques described in this report for mixed contaminants are:

• Soil wash
• Electroreclamation
• Phytoremediation
• Stabilisation
• Combined remediation

The remediation techniques described in this report for tar/PAH-components are:

• Thermal treatment
• Bioremediation
• Extraction
• Wet oxidation

An overall summary is given in chapter 6 together with an evaluation of the relevance of each remediation technique under Danish conditions.

In chapter 7 it is recommended that especially the remediation techniques soil wash and electroreclamation are tested with regards to treatment of mixed contaminants. The results of soil wash technique seem promising but the efficiency in clay soil still needs to be proved. For soil containing tar and PAH's the soil wash remediation technique also needs to prove efficiency. The technique is recommended tested in full scale in Denmark.

The experience from foreign countries shows that electroreclamation can remove both organic contaminants and heavy metals, but it has not yet been demonstrated that it is possible to remove mixed contamination in one step if all the contaminants are present in the same soil.

There has been promising results in foreign countries with bioremediation of tar/PAH contaminants, and these results are also available in countries with climate comparative to Danish climate. Despite of the Danish experiences up untill now it is recommended to test bio remediation either with help from foreign experts or after a more intensive research in the mechanisms controlling the biological degradation of the tar components in the soil.

It is recommended to wait using phytoremediation to clean mixed contaminants and tar/PAH contaminants till the results of the present experiments in Denmark are known.

Finally it is recommended to create a program to monitor the efficiency, energy consumption, time demand and costs used for each remediation technique to compare with the results of the remediation of the soil.