EN 
DE When investigating contaminated sites, one often comes across old sites where petrol stations used to be located. The underground tanks in particular are usually contaminated with soil and groundwater. These have been caused by leaks in the tanks or quite simply by overflow damage during refilling. The main contaminants in petrol, diesel or heating oil tanks are usually mineral oil hydrocarbons. These have 10 to 40 carbon atoms, which are strung together like a chain, and are highly odour-perceptible. Due to the long molecules, however, this group of substances is not categorised as highly volatile pollutants.
Volatile substances do not play a major role in diesel and heating oil. In petrol, on the other hand, the volatile component is formed from the so-called BTEX aromatics. This abbreviation stands for the substances benzene, toluene, ethylbenzene and xylenes, which used to be added to petrol as anti-knock agents. They are still contained in petrol today, but only in a maximum permitted concentration of 1 %.
Benzene has a proven carcinogenic and mutagenic effect and can also cause blood disorders and temporary blindness.
To check whether a contaminated site poses a risk to human health and groundwater due to BTEX aromatics, soil air samples are taken in addition to soil and groundwater samples and the levels are assessed according to the standard assessment principles (e.g. LAWA). If there is significant contamination that makes remediation necessary, soil replacement or continuous soil vapour extraction and purification using activated carbon can be carried out, for example. However, the pollutants can also be broken down over time by microorganisms.
In addition to BTEX aromatics, we have also recently had to deal with other highly volatile substances from the group of trimethylbenzenes (TMB). These belong to the so-called C3-aromatics and can attack the central nervous system, among other things. The three TMB isomers mesitylene, pseudocumene and hemimellithine are naturally contained in coal tar, but also in fuel and are often used as solvents. Unlike BTEX aromatics, there is no clear assessment strategy for TMB in Lower Saxony. In addition, TMB are more persistent, i.e. less degradable, which is why they often make up a significant proportion of old damage cases. If the BTEX aromatics (especially benzene and toluene) at a petrol station damage have already been degraded due to the high age of the damage, often only the TMB with higher contents remain. However, as it can be assumed that the source of the damage has already dried up and the levels will continue to fall, the TMB are only considered to be an artefact of earlier damage.
