Uncertainty in biokinetic parameters on bioremediation: health risks and economic implications.

Human health risk assessment is one of the rapidly evolving tools used in the management of contaminated aquifers. Health risk assessments have been traditionally based on the point estimate approach. Due to the uncertainty and variability inherent in subsurface properties and exposed human population characteristics, probabilistic risk assessment is becoming widely accepted. This study is focused on understanding the uncertainty in biokinetic parameters in describing biodegradation under natural and enhanced remediation conditions. The uncertain parameters considered in this work are key biokinetic parameters and the uncertainty is assessed using the predicted receptor maximum concentration, maximum of 30-year average concentration, time to reach maximum concentration, maximum mass of decay, and the time for maximum decay. The results of this analysis were extended to health risk assessment and risk-based economic analysis. The paper discusses the approach and methodology adopted in this study and the implication of uncertainty of key parameters on decision-relevant information.

Extended phase relations and load effects in MSW.

The moisture retention and compression characteristics of municipal solid waste under self-weight are likened to those of an unsaturated soil. By assuming that the solid organic fraction in waste retains a relatively immobile micropore moisture and that deformation at low confining stress occurs at the expense of a relatively large macropore system, an insight into the variation of density and moisture with depth can be gained. With data on the composition of the waste, the phase composition can be extended to distinguish between solid organic and solid inorganic fractions, resulting in a four phase material model. The model is developed using detailed moisture and waste composition data from the Lyndhurst Sanitary Landfill site in Victoria, Australia. Finally, comparison of the model with large scale compression test results provides an insight into the nature of waste compression and moisture content data at low confining stress.

Observations of the impacts of some landfill leachates with clays.

Compacted clay liners are common, major, components of landfill leachate (fluid) containment systems. This is sensible, but knowledge and understanding of the longterm performance and behaviour of day mineral/landfill leachate systems remain very limited. The authors studied the reactions of day soil with leachate simulants related to three different climates and waste cultures. The day came from a Tertiary sequence near Melbourne, Australia, a type in common use locally for landfill engineering. X-ray diffraction was used to observe mineralogical change in 3 mm clay plugs caused by reactions with the leachate simulants. Changes in hydraulic conductivity were also measured. The results show both that the different leachates have distinct effects on the clay minerals, and that the leachate/day reactions have direct measurable and distinct impacts on hydraulic conductivity. The laboratory studies were completed at the University of Melbourne. The X-ray diffraction work was completed at The Natural History Museum in London. The experimental results are discussed here and indications given of some potential implications.