EPA LEAF methods for leaching assessment

The Leaching Environmental Assessment Framework (LEAF) is an evaluation system consisting of EPA methods, data management tools, and scenario assessments designed to identify and accurately describe the release of inorganic, semi-volatile organic, and non-volatile organic constituents of potential concern (COPCs) in solid materials. Introduced as an extension to the Toxicity Characteristic Leaching Procedure (TCLP) from the EPA, the Leaching Environmental Assessment Framework (LEAF) was designed to provide a flexible and customizable framework for distinguishing leaching characteristics under a range of specified conditions and for a variety of solid materials in contact with ground or surface water (including wastes, treated wastes, secondary materials, energy residuals, industrial processing residuals, and contaminated soil).

What are LEAF Methods?

The EPA LEAF program includes four different EPA methods:

• Method 1313 – Liquid-solid partitioning as a function of extract pH using a parallel batch extraction process
  Used to evaluate leaching of inorganic, semi-volatile organic, and non-volatile organic components from solid materials at specified pH values from pH 2 to 13
  
  
• Method 1314 – Liquid-solid partitioning as a function of liquid-solid ratio for constituents in solid materials using an up-flow percolation column procedure
  Used to evaluate leaching of inorganic and non-volatile organic components from solid materials in a packed column
  
  
• Method 1315 – Mass transfer rates of constituents in monolithic or compacted granular materials using a semi-dynamic tank leaching procedure
  Used to measure release rates of inorganic components from solid materials by diffusion as a function of time
  
  
• Method 1316 - Liquid-solid partitioning as a function of liquid-to-solid ratio in solid materials using a parallel batch procedure
  Used to evaluate leaching of inorganic and non-volatile organic components from solid materials at their natural pH

When can LEAF methods be used?

LEAF methods provide an alternative to TCLP when on-site testing conditions differ greatly from actual or projected conditions, or in circumstances where there is no regulatory requirement for TCLP or TLCP is not technically appropriate. LEAF can also be employed in evaluating and addressing specific contaminants in support of the Comprehensive Environmental Response, Compensation and Liability ACT (CERCLA).

How do LEAF methods differ from TCLP methods?

LEAF methods take into consideration how pH, the liquid-to-solid ratio (L/S), and the physical form of the material affect leaching. The rate and extent of leaching from a material are determined by a number of chemical and physical factors that vary between sites due to changing environmental media, including local conditions and solid materials. Slight changes in key factors can have substantial effects on the magnitude of leaching by altering the rate at which a constituent can be released or the equilibrium water concentration.

The Leaching Environmental Assessment Framework (LEAF) How-To Guide from the EPA highlights several key factors including:

• Eluate or leachate pH that controls the aqueous solubility of inorganic COPCs (constituents of potential concern), dissolution of organic carbon, and sorption of COPCs to mineral surfaces
• Liquid-to-solid ratio (L/S) defined as the volume of liquid in contact with a dry mass of solid
• Conditions that change the oxidation state of COPCs (e.g., Cr^III to Cr^IV) and the quantity of available surfaces for sorption (e.g., reduction of Fe^III to Fe^II results in decreased sorption to iron hydroxide surfaces)
• Increased measured concentration of COPCs through the formation of soluble dissolved organic carbon (DOC) complexes
• Ionic strength and ion effects suppress mineral dissolution
• Biological activity resulting in pH or redox changes

Utilizing LEAF methods to test samples in the laboratory allow for better control of key factors affecting leaching.