Investigative strategies and risk assessment of old unlined municipal solid waste landfills

Abstract

A case study was carried out at an old landfill site (Riet site) located in Winterthur, northern Switzerland. The Riet site contains mainly municipal solid wastes (MSW) comprising four discrete unlined landfill compartments, the oldest of which dates back to 1918. One goal of the case study was to assess the investigative techniques used to determine the risk of groundwater contamination. Waste compartments and leachate plumes were delineated with the electromagnetic method EM31 and with tracer methods. The most efficient methods for a risk assessment were flow modelling based on reliable hydraulic head and hydraulic conductivity measurements, and chemical analyses. Chemical analyses of leachate and groundwater samples showed that the older compartments of the landfill pose only a small risk to the groundwater. The other goal of the study was to determine the long-term risk of groundwater contamination posed by MSW landfills of different ages. To this end, chemical concentrations of leachate from the Riet site were compared with those of other MSW landfills of various ages. The long-term risk of landfill compartments older than about 1960 can be considered in general to be considerably smaller than that of younger ones. Age of the compartment and leachate concentrations could be correlated.