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4.3Assessment of environmental impact

Existing frameworks for the assessment of alternative materials

The framework developed by Kosson et al (2002) covers many aspects relevant to road construction materials. It covers the issue of characterisation of release behaviour. It covers also the issue of different levels of detail in the need of knowledge for the material to be judged, from conservative (total composition) to highly detailed (in specifying the leaching conditions in a field scenario). Furthermore it addresses chemical speciation, modelling of release to take the information generated beyond the duration of a laboratory leaching test. Another aspect that has been addressed in this context is the relationship between laboratory, lysimeter and field scale data (full scale application), as this may lend credibility to modelling, when shown to be capable of describing observed release. Finally also the link of the test data with regulatory criteria is of importance. On the one hand the wide range of laboratory leaching data form the basis for limit setting and on the other hand data generated in leaching can be verified against regulatory criteria. The framework as presented has resulted in a database/expert system, which links many relevant aspects of the materials together.

The framework (Kosson et al (2002)) expands on ENV 12920 and has many other aspects that are covered in it. A key aspect is the concept of linked database/expert system with characterisation data from a wide range of materials among which the materials relevant to WP3. Since characterisation is costly, the information generated in characterisation studies should be made available from at least all EU funded studies and national research programmes to ensure comparability and traceability. Many materials are produced in similar production processes and as such have common characteristics as has been shown for MSWI bottom ash for instance. This implies that storing characterisation information for referencing by others is of great importance to avoid unnecessary duplication of work.
Database/expert system

Such a database/expert system has been developed (ECN, Vanderbilt, DHI) for environmental risk assessment for different applications of construction materials including road construction materials. The first step in setting up the database has been to identify the type of questions to be answered and to ensure that data are implemented in a manner that allow the desired cross comparisons between different types of materials, the mutual comparison between test methods and establishing relationships between lab and field. The database contains results of laboratory experiments (pH-static experiments, column leaching tests, CEN tests, availability tests and diffusion tests) from a substantial number of construction material samples. It also contains data from relevant field measurements that are linked with laboratory work. This makes the database/expert system a unique tool to study the behaviour of different recycled materials, the comparison of different tests on construction materials, the comparison of data from laboratory leaching, lysimeter scale studies and field measurements. Furthermore, the system can serve as basis for modelling the chemical behaviour and release of substances in different scenarios. In Figure 4.1 an outline of the expert system is given comprising software components.

Figure 4.1: Outline of the expert system
The expert system serves as a tool for research, (capitalization of knowledge on leaching) environmental assessment, regulatory decision-making, material treatment evaluation and quality control based on understanding of the leaching behaviour of materials in the environment. The global set-up of the expert system is given in Figure 4.2. The expert system is comprised of software components that provide facilities, testing protocols and guidance in the following areas:

1. 
   Problem Definition and Test Selection - Guidance on problem definition; selection of characterization needs and methods, detailed methodologies; existing information on characteristics and behaviour of similar materials; citations.
   
2. 
   Data Collection and Management - Guidance on laboratory, lysimeter and field data collection (including experimental design and quality control considerations); data management, formatting and graphical presentation, (including consistency and quality control checking); existing information from similar pilot and field evaluations; citations.
   
3. 
   Management Scenario Description – Development of detailed description of potential management scenarios or beneficial materials use scenarios; site-specific information (including material configuration, site geometry and topography, infiltration rates, climate); design specifications.
   
4. 
   Material Properties– Guidance on test methods for obtaining material-specific properties; data management facilities.
   
5. 
   Direct data evaluation, parameter derivation and comparative data sets for
   
   1. 
      pH and L/S Ratio Dependence – evaluation of aqueous concentrations from batch testing (including cations, anions, reduction/oxidation potential, EC, DOC, ionic strength); geo-chemical speciation; acid/base neutralization capacity (ANC/BNC); leaching potential (availability).
      
   2. 
      Release With Time – Percolation Release – granular materials and monolithic materials from sequential data sets (including L/S ratio or time from column testing or lysimeter testing); associated geo-chemical speciation; mass transfer parameter estimation. This mode of release differs from surface related release.
      
   3. 
      Release With Time – Surface Related Release - granular materials and monolithic materials from sequential data sets (including tank leach testing of monolithic and compacted granular materials); associated geo-chemical speciation; mass transfer parameter estimation.
      
6. 
   Source Term Description - Development of a source term description that would estimate constituent release as a function of time for default, or user defined management scenarios. This would include selection of appropriate source term models, evaluation of the effects of potential external stresses (e.g., waste mixtures, carbonation, oxidation, reduction, acidification) and uncertainty analysis.
   
7. 
   Impact Evaluation – Assessment of potential impacts to sub-soils or groundwater; risk characterization.
   
8. 
   Judgment and Decision-Making - Algorithms for comparing evaluation results and decision-making based on regulatory criteria from different jurisdictions; recommendations on reduced-testing quality control programs, approaches to reduce constituent release, development of remediation end-points, and long-term stewardship requirements.
   

Inherent in the system would be components that would be distributed to system users (e.g., problem definition and methods guidance) and components that would be resident in centralized servers (e.g., database of related physical, chemical and leaching characterization information from other materials).



Figure 4.2: Overview of software modules for the Expert System Project
Materials considered as part of the system include, without being limited to, alternative materials, traditional construction materials and materials in recycling and “end of life” scenarios. The expert system can be used to evaluate environmental impact from construction materials to soil and groundwater, evaluate treatment processes, define quality control criteria and assess environmental aspects in recycling and “end of life” conditions. The expert system includes selection and definition of testing protocols, integrated data management, quality control procedures, geo-chemical speciation evaluation, source term models to estimate potential future constituent release under various environmental conditions and management scenarios, environmental risk characterization, uncertainty analysis, and a reference database of leaching characteristics for previously evaluated materials. The expert system will be able to integrate laboratory and field data of various types and origins. It is intended to make best-practices decision-making widely accessible. The data for a range of material to be discussed in more detail in the end of this chapter are generated with this database/expert system. A standard data representation proves to be very beneficial for understanding relationships between tests, as well as to allow conclusions to be made more easily on release mechanisms and release controlling factors.
Other recommendations and problems to be solved for alternative material use

For some materials, fairly extended information at different scales of testing (laboratory, lysimeter and field scale) is available, such as for MSWI bottom ash. However, for others the information is much more limited. For a proper and safe use of such materials in construction a suitable characterisation is necessary. Therefore, it is recommended to fill these gaps in the knowledge of leaching behaviour of still poorly characterised alternative materials for road construction.

The methodology as described in section 3.3.2 should be developed further to obtain a uniform basis of criteria development relevant not only for road construction, but also for other types of construction applications and materials.

It is recommended to work out one or more road construction scenarios and on the basis of available information on leaching characteristics, hydrology and exposure conditions provide environmental impact data for comparison with groundwater quality objectives at selected targets (for the European Landfill Directive approach – see section 3.3.2).