The Biogeochemistry of Contaminant Groundwater Plumes Arising from Waste Disposal Facilities

Landfills with solid waste are abundant sources of groundwater pollution all over the world. Old uncontrolled municipal landfills are often large, heterogeneous sources with demolition waste, minor fractions of commercial or industrial waste, and organic waste from households. Strongly anaerobic leachate with a high content of dissolved organic carbon, salts, and ammonium, as well as specific organic compounds and metals is released from the waste for decades or centuries.

Landfill leachate plume hosts a variety of biogeochemical processes, which is the key to understand the significant potential for natural attenuation of specific organic contaminants in a leachate plume. The complexity of this system is exemplified with the presentation of two comprehensive field studies at the Norman Landfill (United States) and the Grindsted Landfill (Denmark).

The key findings from these integrated studies and the literature are the following: (1) Local hydrogeological conditions in the landfill area may affect the spreading of the contaminants; (2) investigations of landfill leachate plumes in geologic settings with clayey till deposits and fractured consolidated sediments are lacking; (3) the size of the landfill and the heterogeneity of the source may create a variable leaching pattern and maybe also multiple plumes; and (4) significant natural attenuation of xenobiotic organic compounds occurs, but the complexity of leachate plumes with respect to compounds (inorganic and xenobiotic organic compounds) and biogeochemical processes may be an obstacle for the implementation of natural attenuation as a remedy.

These findings highlight that demonstration of natural attenuation in terms of contaminant mass reduction at the field scale is difficult. However, very few alternatives to natural attenuation exist for remediation at landfill sites. Finally, the potential chemical or ecological impact from landfills located in former wetlands or near surface water bodies may deserve attention in future studies.