Beurteilung der natürlichen Abbau- und Rückhalteprozesse der Schadstoffgruppen MKW und BTEX in der wasserungesättigten Bodenzone - Ergebnisse aus Untersuchungen im Labor-, Technikums- und Feldmaßstab

The potentials and limitations of natural degradation and sorption processes of petroleum hydrocarbon and BTEX contaminants in the vadose zone were investigated in laboratory and technical scale as well as in field scale.On a former military site, soil investigations and a monitoring of soil air, seepage water and groundwater were carried out for three years. Although the contaminants in soil were inhomogenously distributed, a decrease in the concentration of petroleum hydrocarbons attributable to biodegradation, volatilization and leaching processes was observed in several sampling areas. In particular, microbial degradation processes were confirmed by soil air and ground water monitoring. The microbial activity at the site is limited by low nutrient concentrations and a low pH-value. Batch experiments with disturbed and homogenised soil samples showed an increase of the pH value up to 7 following the addition of a calcareous buffering agent, although column experiments demonstrated that the amendment of the soil pH affected only the upper soil layer. The stimulation of nutrient ratios caused a higher degradation rate of petroleum hydrocarbons and BTEX, but also a leaching of nitrate and ammonia by seepage water.The potentials of natural degradation processes and of possible stimulation enhancement could be confirmed through Batch experiments. Column experiments with disturbed and undisturbed soil samples evidenced transport and leaching processes of contaminants, providing at the same time a measurement of the effectiveness of stimulation activities in relation to the soil depth. For Upscaling laboratory experiments to field scale, options and limitations of the test systems have to be further considered.