Transport and degradation of propyleneglycol and potassium acetate in the unsaturated zone

De-icing chemicals used during the winter season are potential pollutants f or the groundwater underneath the new main airport of Norway. Several field experiments examining the transport and degradation of propyleneglycol (PG ), potassium acetate (KAc) and non-reactive tracers were performed in a lys imeter trench under natural snowmelting conditions. Chemicals were applied underneath the snow cover and the transport in a heterogeneous coarse sandy soil was examined by extracting soil water from 30 or 40 suction cups plac ed at five depths between 0.4 and 2.4 m depth. Transport and degradation wa s analysed by spatial moment calculations. The de-icing chemicals showed th e same basic displacement as chemically inactive tracers, an initial fast t ransport during the melting period followed by a period of stagnation throu ghout the summer season. PG seemed to be displaced to greater depths compar ed to non-reactive tracer after the first application. However, computer si mulations of transport and degradation in a heterogeneous unsaturated soil showed that decreasing degradation constants with depth can generate a down ward movement of the centre of mass without any flow occurring in the syste m. Potassium acetate showed some adsorption, with calculated retardation fa ctors of approximately 1.3 and 1.2. The degradation rate constant for PG wa s calculated to be 0.015 day(-1) in 1994 and increased to 0.047 day(-1) in the second application made in 1995. The degradation rate constant for acet ate was estimated to be 0.02 day(-1). Increased manganese concentrations se em to be a good indicator of degradation of PG and Ac. (C) 2001 Elsevier Sc ience B.V. All rights reserved.