A framework for risk assessment of disposal of contaminated materials treated by solidification/stabilization

Quantitative risk assessment is a tool used at hazardous waste sites to evaluate the need for treatment and to determine which control strategies should be implemented. A general approach to conducting quantitative risk assessments at contaminated sites is reviewed and a framework for applying it to evaluating risk associated with groundwater contamination by disposal of materials treated by solidification and stabilization is presented. This approach is based on a material balance around the disposal zone and the groundwater flowing past it. Two limiting cases are identified that can control the concentration of contaminant leaving the leaching zone. The first case occurs when the leachate flow past the solid is low and the contaminant concentration in the leachate can approach that in equilibrium with the pore water in the solid. The second case occurs when the flow past the solid is sufficiently large that the concentration of contaminant in the flow is low enough that the rate of leaching is not affected. For this case, the flux from the solid can be predicted by simple leach models. Examples of applying this framework to materials treated by solidification/stabilization are presented.