Chemical attenuation processes perform an important role in the retardation of substances within the hydrogeological environment. The extent of attenuation as described by the distribution coefficient Kd is highly dependent on the nature of the solid substrate and also the infiltrating solution. Published studies have presented data relevant to natural attenuation processes within sediments associated with contamination from industrial sources and associated with landfill leachates. This paper presents an evaluation of the attenuation capability of artificial mineral or natural geological barriers within the UK for heavy metals, ammonium and, indirectly, for organic substances. This paper confirms the high potential for heavy metals to be adsorbed to low-permeability sediments from dilute solutions; however, it also establishes that heavy metal distribution coefficients are significantly depressed in the presence of landfill leachate. This is likely to be due to competitive surface reactions and solution complexation. Attenuation coefficients were generally depressed for cadmium and zinc by over 50%, whereas copper and nickel attenuation coefficients can be depressed by two orders of magnitude. The experimental attenuation coefficients determined through this study can be used for modelling contaminant migration in the absence of site-specific data for both landfill-related and contaminated land scenarios.

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