Field Observations of Small Scale Spatial Variability of Snowmelt Drainage and Infiltration

De-icing chemicals (containing 1,2 propane diol and potassium acetate) used on airports in winter time mix with snow and start infiltrating along the runways in spring. The distribution of the chemicals over the area, and the infiltration pattern during the snowmelt period will strongly affect the efficiency of the unsaturated zone for degradation of these chemicals before entering the groundwater. Transport of de-icing chemicals and tracers in the unsaturated zone was studied in a lysimeter trench at Gardermoen, Norway during the snow melt periods of 1994 and 1995. Simultaneously, volumes of meltwater were registered from melt plates. Observations in 1994 indicated a typical diurnal process in contrast to observations in 1995 where large volumes of meltwater entered from each melt plate within a limited number of days. Temperature seemed to be the main regulating factor and cause for the observed differences between years. The overall melt pattern was well captured by a simple model based on air temperature and global radiation. Large differences in melt volumes collected from melt plates on the surface indicated a spatially variable drainage pattern strongly related to micro-topography. Infiltration rates estimated from breakthrough curves of tracers moving through the unsaturated zone at the same location were in the same order of magnitude as drainage rates found from melt plates.