Leave the contaminated soil where it is 

Often, it is advisable to leave the contaminated soil where it is instead of removing it and paying a lot of money to remove it. This is the result of a specific project in Århus, where the Danish State Railways saved both the environment and a substantial amount of money by leaving an area of diesel contaminated soil where it was. Just like heavy metals and other chemical substances which do not evaporate, diesel oil, under certain conditions, stays in the soil without doing any harm.

"It is a question of having enough conviction and not just removing the soil. The legislation accepts this. If it can be justified environmentally and with regards to health, one ought to leave the soil where it is," says project manager Benny Nielsen, COWI Århus.

Before the rebuilding of a new IC4 (Inter City Train) workshop in Århus for the Danish State Railways, COWI carried out a contamination investigation and risk assessment of the area. It was known in advance that the area was contaminated as it had been the home of a locomotive workshop since the 1930s. An extensive ground investigation also showed that the soil was heavily contaminated with diesel oil. Nonetheless, the subsequent risk assessment maintained that the soil was not harmful for neither people nor the environment. Consequently, it was not necessary to remove the soil.

Contaminated concrete used

When the environmental aspects of the building of the new IC4 workshop became known to the Danish State Railways, they asked COWI to prepare environmental assessments of two building scenarios. In connection with this task, COWI found large amounts of concrete contaminated with oil. As this coincided with the Danish State Railways having to fill up an excavation in an old hall building, COWI suggested that they use the contaminated concrete as construction material instead of new gravel and sand. In this way the Danish State Railways spared the environment the pollution that the transport of the concrete would have caused, and saved money for new materials such as sand and gravel. These savings could clearly be seen in the building budget.

However, the largest saving came when the Danish State Railways had to relay a large track area in front of the IC4 workshop, where the soil was also contaminated with diesel oil amongst other sub-stances. COWI calculated that the Danish State Railways should potentially remove large amounts of contaminated soil which would be costly to the budget - and with regards to the environment. Instead, COWI's environmental and geotechnical investigations showed that the Danish State Railways could actually reuse two thirds of the soil and make savings to the budget and to the environment.

"The trend is to leave things where they are and only clean up when it is necessary," says Benny Nielsen.

Published 25.09.2002