IWWG Task Group on
Leaching Assessment Methodology and Tools

Chair: Hans van der Sloot


Background

Leaching assessment based on extraction tests coupled with contaminant transport models are widely used for making decisions on acceptability of environmental impact from materials used beneficially or disposed in landfills. They are used for regulatory purposes to develop criteria for acceptance, for compliance with specific regulations, for evaluation of treatment options and for periodic quality control. They are meant to cover the wide range of exposure conditions of material in practice. The range of materials covered extends from soil and soil like materials to sludges, sediments, non hazardous waste, hazardous waste, stabilised waste, mining waste to a wide range of construction materials and products. The relevant constituents include inorganic contaminants (metals, oxyanions, salts) to organic contaminants (highly water soluble to poorly water soluble) and radionuc.

Scope

The working group on Leaching Assessment is in the process of being set up. Those interested in joining can indicate their interest to the emails below. The intent of the Working group is to establish a forum for exchange of experience and data on the development, use, and interpretation of leaching assessment methodology (including test methods, interpretive models and other tools) and data for assessment of the constituent mobility, partitioning between dissolved and particulate forms, release controlling factors, geochemical modelling of chemical speciation and transport.

Topics

The following topics are of interest:

Members

Institutions/people expressing an interests to take part to the group will be added below:

DHI Water &Environment, DK: O. Hjelmar
Energy Research Centre of The Netherlands, ECN (NL): H.A. van der Sloot, A. van Zomeren.
Vanderbilt University, Nashville(USA): D.S. Kosson

Relevance of leaching

Leaching tests have become more important in recent years as a result of questions about the possible effects of using alternative materials (formerly wastes) as fuels, or alternative raw materials in construction or as fertilizers in agriculture. Until a few years ago single step leach tests were applied, but these have been shown to be too limited in scope to be able to guarantee compliance with environmental objectives at both short and longer term. It is now realized that a test can not mimic 1:1 a field application and as such the tests to be applied should also be suitable as input for modeling of release by chemical reaction transport models.

Leaching test development

As a result of these needs, leaching test development is going through rapid developments in recent years. This is prompted by the need for proper characterisation tests to assess the long term release of inorganic and organic contaminants from a variety of materials and products in support of European regulations. Such new regulatory requirements are, among others, the development of criteria for the End of Waste Directive, the Mining Waste Directive, the Biowaste Directive and  the Construction Products Directive. The EU Landfill Directive still has no provisions for stabilised waste, as at the time of its development, the modelling tools to assess impact were insufficiently developed to come to acceptable conclusions. These limitations will be eliminated soon so that a proper impact assessment can take place.
Currently, US-EPA is in the process implementing new characterisation leaching tests in SW-846 to provide a more appropriate alternatives for cases where TCLP is not scientifically appropriate. This implementation of a pH dependence leaching test, a percolation test a tank leach test and a compacted granular leach test is expected to be completed by the end of 2010, with formal release of draft methods in Spring 2009 followed by interlaboratory validation. In Japan, China and Australia, these methods are also more and more recognised as powerful tools to answer important questions of potential environmental impact.
In addition to the fields already mentioned, standardisation of characterisation leaching test has taken place in the fields of soil, sludge, sediments and biowaste. This work was carried out in ISO TC 190 (Soil) and has led to adoption of the same methods by CEN TC 345 (Soil characterisation). The Working group is now complementing the work by developing tests to quantify important modelling parameters for chemical speciation modelling to assess long-term leaching behaviour of materials (quantification of reactive hydrated Fe-oxide and Al-oxide surfaces, solid and dissolved organic matter fractionation in hydrophilic, fulvic- and humic acid fractions).

Horizontal standardisation

The above mentioned developments point at a very wide spread horizontal standardisation process. Horizontal meaning here a process of identifying suitability of tests across a wide range of different policy fields, which have been addressed traditionally in a vertical manner (test developed for individual fields (e.g. waste, soil, sediments, wood, sludge, construction, etc). What this means is that the physical and chemical aspects of assessing release from materials and products is described adequately by a limited set of tests as they cover relevant mechanisms of release.

Validation

At this point in time the standards developed so far are all listed as Technical Specifications since validation data are not yet available. In view of the wide applicability of the set of characterisation test methods, validation across multiple fields is worth considering as individual material stream validation is much more costly than carrying out an integrated validation, in which a wide spectrum of materials and products are covered. Researchers and practitioners interested in participating in such an exercise are welcome to make themselves known to the undersigned.

Decision support tools

Modelling tools are available to describe release from waste materials and (secondary) construction products. An important development is the generation of a database of leaching data to avoid unnecessary duplication of work once a sufficient reference base has been built up for a given material or product. As it turns out worldwide cements, municipal solid waste incinerator bottom ashes, coal fly ashes and slag from steel works have more characteristics in common than that they differ. This implies that the main constituents of environmental concern can be identified rather quickly from such a broad data set. To build such a data set, the relevant testing information must be made available. At least studies carried out with public funds (e.g EU research projects and national research) should be required to be made publicly available. With a database like that statistical data evaluation will be feasible, which for quality control purposes and for declarations of compliance with regulatory criteria will be highly beneficial to the industry. By combining the database with regulatory criteria for different applications and modelling capabilities, a decision support tool is created that allows one to draw more extended conclusions that would ever be possible by an individual alternative material user or waste producer.

IWWG

For the IWWG group Leaching, the development of a database of waste leaching data is a goal that the group has set itself. The unified database structure as embedded in the database/expert system  LeachXS will be the basis for developing such a dataset to be used by the members. A publicly available LeachXS Lite version is in development in cooperation with US-EPA for Coal combustion residues. This version could be expanded to cover the main fields of interest to the IWWG group.
A second action identified is the exchange of information on leaching to a wider group of interested parties by developing an IWWG monograph on leaching. This possible activity will be discussed during the next meeting of the IWWG group Leaching at the International landfill Symposium (October 2009, Sardinia)  

References   
     pH dependence leaching test
CEN/TS 14429  Waste
CEN/TS 14497 Waste  automated
ISO/TS 21268-4  Soil, sludge, sediments, biowaste
CEN/TC 351 draft method in development  Construction products
US-EPA method 1313 (draft) Waste
     Percolation test
CEN/TS 14405 Waste
ISO/TS 21268-3 Soil, sludge, sediments, biowaste
US-EPA method 1314 (draft) Waste
CEN/TC 351 draft method in development Construction products
     Tank leach test
CEN/TS DMLT-PLR (in enquiry) Waste
US-EPA method 1315 (draft) Waste *
CEN/TC 351 draft method in development Construction products *
     Modelling parameters
ISO/TS  Fe-oxide, Al-oxide, DOC fractionation (in preparation in cooperation with CEN/TC 292 Waste and CEN/TC 345 under the Vienna Agreement) Soil, sludge, sediments, biowaste
     Additional parameters (not yet assigned to standardisation)
Redox capacity (Dutch national standard NEN 7348)

* These contain an option for compacted granular materials behaving as monolith in their release behaviour

Contact person:

Hans van der Sloot
Hans van der Sloot Consultancy
Dorpsstraat 216
1721 BV Langedijk
The Netherlands
Tel: +31(0)226-341607
Fax: +31(0)84 7298428
Email: hans(AT)vanderslootconsultancy.nl

A. van Zomeren
Environmental Risk Assessment
Energy Research Centre of The Netherlands, ECN (NL)
P.O. Box 1, 1755 ZG Petten, The Netherlands
Phone: +31 224 564249/ +31 224 564768
Fax: +31 224 568163
Email: vanzomeren(AT)ecn.nl

Next Task Group Meeting: