Distribution and attenuation of hazardous substances in uncontrolled solid waste landfills

The distribution, concentrations in various phases, attenuation and emissions of hazardous substances in Finnish municipal and industrial mixed-waste landfills were investigated in a 5 year field study. Pronounced irregular spatial variation in substance concentrations was observed within, and especially between, the sites. Most frequency distributions of contaminant concentrations in the fills were skewed toward small values. Related norms or reference values were occasionally exceeded. The attenuation of contaminants in the various phases within and around landfills varied according to the substance and site, reflecting retention and removal mechanisms. Lead and zinc were the most easily leached heavy metals in old landfills. The concentration distributions of toxicants in waterborne emissions were dominated by small values, but the maxima exceeded drinking water norms by up to 400 times. In municipal landfill gas, some halomethane concentrations (100 mg Nm⁻³) exceeded air quality norms. The estimates of contaminant fluxes were minor compared with, for example, industrial emissions. The overall toxic impacts of Finnish landfills thus seem relatively small, but may be important locally and require further study and caution. Associated issues in disposal risk assessment and management are briefly discussed.