Next Generation Leaching Tests for Evaluating Leaching of Inorganic Constituents

NEXT GENERATION LEACHING TESTS FOR EVALUATING LEACHING
OF INORGANIC CONSTITUENTS
S. THORNELOE*, G. HELMS**, D. FAGNANT**
*US EPA, Office of Research and Development, National Risk Management and Research Laboratory,
Research Triangle Park, North Carolina, USA, e-mail: Thorneloe.Susan(a}epa.gov
**US EPA, Office of Land and Emergency Management, Washington, D.C. 20460, USA
Key words: leaching, hea\y metals, waste disposal and treatment
The US EPA lias completed the development and validation of leaching tests, referred to as the
Leaching Enviromnental Assessment Framework (LEAF), that are used to r evaluate liquid-solid
partitioning of inorganic constituents found in wastes and materials being considered for disposal or
beneficial use. This paper provides an overview of the work completed to validate and implement the
methods for a range of management options for a specific material or waste. Classifications of
hazardous and nonliazardous material can be confusing, particularly when an industrial by-product
may be found to be safely used in some or many applications as an alternative to extracted or virgin
resources whereas otherwise the material would be regarded as hazardous. It can be difficult to assess
the performance of a treatment technology unless the leaching tests reflect the enviromnental
conditions under which the waste or material is managed. As a result, the next generation leaching
tests were needed to help evaluate more effective and efficient strategies for management of industrial
by-products while ensuring protection of human health and the enviromnent.
The research described was conducted collaboratively by the U.S. EPA's Office or Research and
Development and Office of Land and Emergency Management (formerly known as the Office of Solid
Waste and Emergency Response), Vanderbilt University in Nashville, Tennessee, Hans van der Sloot
Consultancy in the Netherlands, and the Energy Research Centre of the Netherlands. LEAF represents
decades of research to develop standardized leaching tests that produce comparable data and can lead
to more informed decisions regarding how best to manage industrial waste and other by-products.
In the U.S., as in other countries, there is increased interest in using industrial by-products as
alternatives or secondary materials (i.e., not primary materials or virgin resources that are typically
extracted from mines), helping to conserve virgin or raw materials. Within the U.S., beneficial use
lias been defined as the incorporation of an industrial material into a commercial product that provides
(1) functional benefit, (2) meets relevant design specifications and performance standards for the
proposed use, (3) replaces virgin or raw materials in a product already on the market and (4) is
implemented in an environmentally acceptable manner. The LEAF and associated test methods are
being used to develop a source term for leaching of any inorganic constituents of potential concern
(COPC) in order to determine what is environmentally acceptable. A source term is an estimate of
constituent release from a material or waste and is used in subsequent fate and transport modeling to
evaluate r exposure for use in a risk assessment. The results from the risk assessments are used to
inform decisions about levels that are protective of human health and the enviromnent.
The LEAF tests have advantages over single-point pH tests, which when used do not typically reflect
the conditions of how a waste is managed and therefore can result in an inaccurate estimate of the
leaching source term. For example, aresenic was found to be leaching from a K088 disposal monofill
at levels more than 100 times what a single-point test had estimated. As a result, the US EPA had to
withdraw the delisting petition and instituted disposal restrictions for the waste. In another example,
a waste from an aluminum company was evaluated for land disposal restrictions using the results of a

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single-point leaching. The US EPA was sued and the court found that models of the environment must
bear a reasonable relationship to the situation that they are intended to represent. Whether one is
concerned about the potential use of industrial by-products or the safe disposal and treatment of
industrial by-products, more accurate source terms improve the ability to ensure protection of human
health and the environment.
Rather than evaluate leaching under a single set of conditions to simulate field conditions, LEAF
measures leaching characteristics of a solid material (e.g., waste, treated wastes such as by
solidification/stabilization, secondary materials such as blast furnace slags, energy residuals such as
coal fly ash, soil, sediments, mining and mineral processing wastes) over a range of conditions that
influence leaching concentrations or rates. LEAF incorporates three factors that can affect leaching
and that can vary under plausible use or disposal conditions: leachate pH, the liquid-to-solid ratio (L/S)
of the test material and the leaching environment, and whether or not leaching is controlled by
constituent aqueous-solid partitioning under chemical equilibrium or by the rate of mass transport
through the material (e.g., the physical form of the material, diffusion from the solid). Important
factors that may impact leaching but are not readily assessed in the laboratory (e.g., changing redox
conditions, reaction with atmospheric carbon dioxide) can be evaluated using geochemical speciation
and scenario-based reactive transport models.
The leaching test methods include batch equilibrium, percolation column and semi-dynamic mass
transport tests for monolithic and compacted granular materials. By testing over a range of values for
pH, liquid/solid ratio, and physical form of the material, this approach allows one data set to be used
to evaluate a range of management scenarios for a material, representing different environmental
conditions (e.g., disposal or beneficial use). The results from these tests may be interpreted
individually or integrated to identify a solid material's characteristic leaching behavior. Furthermore
the LEAF approach provides the ability to make meaningful comparisons of leaching between similar
and dissimilar materials from national and international origins.
To assist in the implementation of LEAF, software (referred to as LeachXS-Lite) is available at no
cost for data management, evaluation, and visualization. A user's guide to support implementation
has been developed and is undergoing review prior to final release in 2016. This presentation will
focus on the guidance for LEAF implementation summarizing a series of case studies illustrating how
source terms are developed for a range of potential LEAF applications. In addition, future work to
identify drivers for leaching of semi- and non-volatile organic constituents is ongoing with the goal to
develop and validate methods for estimate leaching source terms for waste streams such as
contaminated soils and sediments, including those that may have non-aqueous phase liquids (NAPLs)
from manufacturing residues (e.g., manufactured gas sites), petroleum hydrocarbons (light- or
LNAPLs) or chlorinated solvents (dense- or DNAPLs).
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