June 14, 2019
LEAF Methods Added to SW–846
EPA has added four new test methods to SW–846 that make up the Leaching Environmental Assessment Framework or LEAF. The four test methods evaluate the leaching potential of inorganic constituents from solid materials under varying conditions. First and foremost, these new test methods do not replace the TCLP for determining whether a solid waste exhibits the toxicity characteristic under RCRA. Additionally, the LEAF test methods do not supersede or replace existing land disposal restriction requirements. In fact, there are no RCRA requirements to use LEAF methods. Instead, the LEAF methods are simply provided as tools to evaluate leaching potential.
The purpose of the LEAF framework is to provide an estimate of the extent and rate of constituent release to the environment through waterborne pathways under a wide range of environmental conditions. In addition, leaching assessments via LEAF can provide insights into material durability under various conditions, based on the dissolution of the primary constituents that comprise the solid matrix. The four LEAF methods are described in the following table.
Final Leaching Environmental Assessment Framework (LEAF) Test Methods
Method | Title | Description |
|---|---|---|
Liquid-Solid Partitioning as a Function of Extract pH Using a Parallel Batch Extraction Procedure | Evaluates the partitioning of constituents between liquid and solid phases at or near equilibrium conditions over a wide range of pH values. The method consists of 9–10 parallel batch extractions of solid material at various target pH values. |
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Liquid-Solid Partitioning as a Function of Liquid-Solid Ratio for Constituents in Solid Materials Using an Up-Flow Percolation Column Procedure | Evaluates constituent releases from solid materials as a function of cumulative liquid-to-solid ratio. The method consists of a column packed with granular material with moderate compaction. Eluent is pumped through the column to minimize air entrainment and preferential flow. |
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Mass Transfer Rates of Constituents in Monolithic or Compacted Granular Materials Using a Semi-Dynamic Tank Leaching Procedure | Determines the rate of mass transport from either monolithic materials (e.g., concrete materials, bricks, tiles) or compacted granular materials (e.g., soils, sediments, fly ash) as a function of time using deionized water as the leaching solution. The method consists of leaching a sample in a bath with periodic renewal of the leaching solution at specified cumulative leaching times. |
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Liquid-Solid Partitioning as a Function of Liquid-to-Solid Ratio in Solid Materials Using a Parallel Batch Procedure | Provides eluate solutions over a range of liquid-to-solid ratios. This method consists of five parallel batch extractions of a particle-size-reduced solid material in reagent water over a range of liquid-to-solid ratios. At the end of the contact interval, the liquid and solid phases are separated for constituent analysis. |
Source: EPA’s Leaching Environmental Assessment Framework (LEAF) Methods and Guidance website.
Although the titles and descriptions of the four new test methods provide a fair amount of details regarding the methods themselves, they provide little information on their intended use (and the use of the framework in general). To address this, EPA has also developed a LEAF How-To Guide (dated May 2019) to help the regulated community understand the LEAF approach and how and when to use it.
LEAF estimates the leaching of constituents from a wide range of solid materials, including as-generated wastes, treated wastes (e.g., solidified/stabilized materials), secondary materials (e.g., blast furnace slags), coal combustion residues (e.g., fly ash, air pollution control residues), industrial processing residues (e.g., mining and mineral processing wastes), and contaminated soil or sediment. The LEAF test methods consider the effect on leaching of pH, liquid-to-solid ratio, and physical form of the material. Thus, a single set of leaching data can be used to evaluate multiple management options or scenarios.
The LEAF methods are not regulatory tests, but the framework may be useful in support of non-RCRA assessments. Two such potential uses are discussed below.
- LEAF may be useful in estimating the environmental impacts of beneficial use of secondary materials, primarily as construction materials. In addition, under EPA’s sustainability initiatives, the agency promotes the beneficial reuse of industrial nonhazardous secondary materials (e.g., coal ash). Leaching data from LEAF can be used for evaluating potential adverse impacts to human health and the environment from the reuse of a wide range of these materials.
- LEAF may also find application in support of cleanup decisions under CERCLA that address specific contaminants on a site-specific basis. It may be used in the leaching evaluation of a material as part of a risk assessment. For example, site-specific data are used to determine whether action is warranted at a site. LEAF testing in support of such an evaluation could be used with the approval of the appropriate regulatory agency.
A FAQs document is also available that provides EPA’s answers to frequently asked questions about the LEAF methods and how-to guide.
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This document addresses issues of a general nature related to the federal RCRA regulations. Persons evaluating specific circumstances dealing with the RCRA regulations should review state and local laws and regulations, which may be more stringent than federal requirements. In addition, the assistance of a qualified professional should be enlisted to address any site-specific circumstances.
