Use of the Leaching Environmental Assessment Framework (LEAF) for future fly ash management decisions

The Leaching Environmental Assessment Framework (LEAF) is a collection of leaching tests, data management tools, and leaching assessment approaches developed to identify detailed characteristic leaching behaviors of a wide range of solid materials. Cohesive integration of these components provides materials-specific “source term” release information for support of decisions involving materials management. In the U.S. and in other industrialized countries, the increasing use of secondary materials such as fly ash, foundry sands, and other industrial by-products is important economically and environmentally. Primary materials must be excavated or mined, processed, and transported. In the U.S., 130 million tons of coal combustion residues (CCRs) were generated in 2011with 44% used in a range of applications such as mine reclamation, cementitious materials, highway construction, building products, structural fill, waste solidification, and even toothpaste. The applications can have very different environmental conditions and knowledge of the leaching behavior of pollutants found in industrial by-products will vary based on the environmental conditions that the materials encounter over time. Historically, estimating the leaching of pollutants has been based on single-point extraction tests, that represent one set of possible leaching conditions (e.g., one pH level), which may not reflect the actual conditions of leaching in the field. These new methods, consider the effect of three parameters known to strongly affect constituent mobility and transport: (1) pH of the water contacting the waste, (2) amount of water contacting the waste over time, and (3) physical form of the waste. By reflecting the plausible range of environmental conditions that significantly affect constituent leaching, the LEAF methods represent a significant improvement over the past practice of relying on the results of single point leaching tests. Further, the LEAF leaching tests respond to concerns with leach testing that have been raised by EPA’s Science Advisory Board (SAB) on several occasions, going back as far as 1991. The LEAF test methods, which began as research tools, have been developed into standardized tests for routine use in commercial, academic, and national laboratories.