Large amounts of construction materials will be needed both in Sweden and other European countries for capping landfills that will be closed in the near future. In order to reduce exploitation of virgin materials and to save natural resources, an option can be utilization of various types of secondary construction materials (SCM) e.g. ash, slag, sand from fluid bed incineration and compost. However, at the same time this may represent potential risks due to the release of trace elements and other pollutants into environment. The main aim of this work is to evaluate the environmental impact of water that discharges from different parts of a landfill cover built with ashes and other SCM.From 2003 to 2005, a four hectares large test area was established at Tveta landfill, southwest of Stockholm, Sweden. Test area is divided into six sub areas with regard to different recycled materials used in different layers of the cover construction (Figure 1).Figure 1. Design of the landfill cover test area at the Tveta landfill. BA = Bottom ash; FA = Fly ash; FC = Friedland clay Infiltrating water through the landfill cover either drains off in the drainage layer as drainage water or percolates through the liner into landfill body as leachate. At Tveta landfill, leachate amounts between 1 l (m2 yr)-1 and 30 l (m2 yr)-1 have been observed below highly compacted ash liner. Results show that leachate samples have higher pH, salt forming elements (e.g. K, Na, Ca and Cl) and concentrations of Cd, Ba As, Al, and Mo, and lower concentrations of Mn, Zn, Mg, Fe, Ni, and Pb compared to drainage water. The concentrations of Cr and total N are in the same range in leachate and drainage water while NH4-N is higher in leachate. Leachate of areas 1 and 4 shows higher content of organic matter than drainage water in these areas. A strong correlation is observed between EC, K, Na and Cl as well as between Cu and TOC. The comparison of the leachate and drainage water quality with different limit values showed that the leachate had elevated concentrations of As, Mo, Cl and nitrogen while the drainage water was mainly contaminated by Ni, Zn, Cl and nitrogen with the addition of As, Cu, Mo, and Pb in areas 2 and 4.Following conclusions can be drawn by now:The hydraulic properties of the landfill cover satisfy legislative requirements for non hazardous waste landfills; in some cases/areas also for hazardous waste landfills.Most of the infiltrating water through the landfill cover is discharged as drainage water. Thus, the design of layers above the liner is most important with regard to the environmental impact of the construction. Both leachate and drainage water need treatment before discharge into the local recipient. Organic matter in the protection layer is likely to contribute to the mobilization of Cu and Ni in short term.The sea might be a suitable recipient in cases where ashes are used in landfill covers because both leachate and drainage contain salt forming elements in elevated concentrations which may harm groundwater or freshwater but do not pose a risk to salt-water.The leaching of most pollutants did not show any clear tendencies during first three years. Thus, assessing the time period for treatment needs is difficult. However, it is expected that the contaminants in the drainage water will be depleted within few decades.Leachate might be contaminated by salt forming and trace elements for one hundred years. However, generated leachate amounts are low and it is expected that leachate from landfill cover will not influence overall landfill leachate with full extent.The ageing of the ashes in connection with mineral transformations is an important process that is expected to reduce the release of pollutants. Further research is needed with regard to long term changes of the material properties and the treatment needs for water.
Cagliari: CISA, Environmental Sanitary Engineering Centre , 2007.
International Waste Management and Landfill Symposium : 01/10/2007 - 05/10/2007