Natural attenuation of airport pollutants in the unsaturated zone - Studies at Gardermoen, Norway

Field experiments conducted at Oslo airport, Gardermoen during the period 1994 - 1999 investigated the transport and degradation of two potential pollutants - de-icing chemicals and water soluble jet-fuel. The experiments were performed in two lysimeter trenches under different boundary conditions. Laboratory experiments and numerical simulations were also performed to increase the understanding of the natural system and to quantify the natural attenuation capacity. The work revealed gravity dominated unsaturated flow in the coarse sandy soil, but also sub-horizontal displacement within dipping layers. The unsaturated zone provides natural capacity for pollutant degradation with a strong positive correlation observed between degradation and initial biomass, temperature and available nutrients (N and P). Whether de-icing chemicals reach the groundwater level or not depends on the degradation potential and retention times in the unsaturated zone. If the chemicals do not reach the ground water during the spring, high evapotranspiration during summer months can increase retention times by about two months.