Methodology for Site-Specific, Mobility-Based Cleanup Standards for Heavy Metals in Glaciated Soils

A framework was developed for establishing site-specific, mobility-based cleanup standards for heavy metal contaminated sites that incorporates a detailed soil characterization, laboratory mobility studies, and mathematical modeling. This framework was applied to a chromium contaminated soil from a metal finishing facility. A series of column leaching experiments were conducted at two different flow rates and influent pHs. A mathematical model was used to describe the fate, speciation, and transport of heavy metals in porous media. In this model, dissolved heavy metals interact with oxide coatings and soil organic matter on the outer surfaces of soil grains via surface complexation reactions. In addition, dissolved heavy metals diffuse into the soil matrix and react with intragranular reactive sites. Model simulations were performed for chromium to determine apparent mass transfer coefficients. A long-term simulation of the unsaturated zone at the site was performed to estimate cleanup levels for chromium under natural attenuation conditions. Applying this framework for the site-specific, mobility-based determination of cleanup levels provides a solution to the problem of estimating a practical cleanup goal.