Understanding the leaching behaviors of Appendix III and IV constituents from Coal Combustion Residuals (CCR) units as a function of time is an important aspect of remedy selection and corrective action design. This is particularly important in regulated or legacy units where CCR removal is not feasible, and infiltration or intermittent groundwater contact with CCR has the potential to mobilize constituents into the groundwater system.
It is well known that not all of the total mass of solid-phase constituents can be mobilized into the groundwater system. The leachable fraction of a constituent is the ratio between the amount that can be mobilized and the total amount in the solid phase assemblage. The leachable fraction is a function of the composition of the solid phase assemblage and the composition of infiltrating water.
In this study, Charles Hostetler, Ph.D., Kacey Garber, M.S., and Lindsey Hawksworth examine different methods that have been used to determine the leachable fraction of constituents from CCR and their strengths and weaknesses. We also examine various attempts to mechanistically interpret leachable fraction in terms of the composition of the stable phase assemblage and geochemical speciation, solubility, and adsorption reactions. Finally, we examine the consequences of uncertainty in leachable fractions on remedy selection and corrective action design.
