Methodology for scenario-based assessments and demonstration of treatment effectiveness using the Leaching...

A methodology for developing scenario-based leaching assessments as part of the Leaching Environmental Assessment Framework (LEAF) is illustrated using a hypothetical management/treatment scenario of contaminated soil from a copper and lead smelter. Scenario assessments refine the process beyond screening-level assessments by considering site- and scenario-specific information about the disposal or utilization environment. LEAF assessments assume (i) granular materials leach at local equilibrium with percolating water, while (ii) monolithic materials (e.g., low permeability solidified/stabilized soils) leach by diffusion-based mass transport toward surrounding contact water. Leaching concentrations, estimated using LEAF leaching test data and estimated or measured scenario information, are compared to threshold values. Demonstration results indicate that leaching from untreated soil is significantly (>10x) greater from solidified/stabilized soil than treated material, except for highly soluble constituents (Cl^-, NO₃^-2) or when constituents have similar equilibrium concentrations in both materials (As, Pb). Comparison between wet and dry environments show that while dry environments lead to lower COPC mass-based rates of leaching, the leaching concentrations may be higher due to lower liquid-to-solid ratios. The presented assessment methodology can be used to evaluate treatment effectiveness when both physical and chemical retention characteristics of the material are altered.