Ground water contamination at Finnish landfills

Abstract

In a field study of 43 Finnish landfills, hydrogeological site conditions were characterized, and toxic substances in ground water were analyzed at 16 sites. The concentrations of several main leachate components, harmful substances and AOX in nearfield ground water were elevated above background values. However, the concentrations of most micropollutants were dominated by small values, causing skewed and truncated frequency distributions. Frequently abundant contaminants included some heavy metals, particularly Zn (median concentration 80 μg L−1), dichloromethane (18) and 1,2-dichloroethane (26). The variation in the concentrations of many contaminants was large (CV >200%). The concentration ranges generally overlapped with those in other Finnish landfill investigations, but were below many foreign results. Some substances were less prominent in ground water than in leachate, reflecting subsurface retention and removal. The geological formations surrounding the waste deposits commonly include moraines and moors, and the shallow soils are dominated by glacial tills and peat. In eskers more porous and permeable differentiated soils occur. The range of laboratory k cvalues was 10−3.5 to 10−8.5 ms−1, with considerable areal variation. Ground water is at most sites rapidly discharged to surface from the small aquifers. Locally more widespread subsurface contamination is possible due to greater conductivities or flow regimes, depending on attenuation factors. The concentration of especially inorganic substances exceeded drinking water norms, mostly by a factor of < 10 and maximally 400 (Fe). The overall health risks caused by the observed ground water contaminant distributions are deemed relatively minor, due e.g. to limited ground water use, but are locally more significant, involve uncertainties and require further study and caution.