Long-term risk assessments comparing environmental performance of different types of sanitary landfills

Landfilling of non-pretreated, mixed municipal solid and similar waste remains a major method of waste management in many parts of the world today, particularly in developing countries. Modern dry-type and bioreactor landfills are considered to be relatively safe facilities in contrast to less engineered sanitary landfills. However, highly-engineered landfills are often not applicable in low-income countries because of their high cost. Performance of low-cost types of sanitary landfills deserve further exploration, because uncontrollable dumpsites pose real long-term threats to aquifers and the most reliable means of improving the situation is by upgrading these sites into technically similar, but environmentally safe facilities. Risk assessments can provide some insight into differences in environmental performance between major types of low-cost and high-cost landfills simulating the essential landfill processes. The risk of contamination at a presumed aquifer that resides directly below a presumed landfill was quantitatively assessed in this study comparing long-term environmental performances of four different types of facilities. A risk assessment software tool which explicitly enables inclusion of uncertainty present in the estimates to generate results with a wide range of possible outcomes was used to fulfill this purpose. It was demonstrated that contaminants derived from a modern, dry-type landfill would likely leech into an aquifer with the greatest impact occurring several decades after landfill closure. However, a specifically designed and properly operated, passive semiaerobic above-ground landfill was shown to be a comparatively safe facility.