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3.2Environmental studies in the field of road construction

3.2.1General developments

Many environmental studies on alternative materials in road construction have been carried out over the last decade (Anthonissen et al, 1990; Aalbers et al, 1998; Aalbers et al, 1999; Aalbers et al, 1996; Aalbers et al, 1990; Fällman, 1997a; Fällman, 1997b; IAWG, 1997; Kosson et al, 1996; Mulder, 1991; Mulder and Joziasse, 1992, Mammoet studies 1985-1990; Versluijs et al, 1990; Mandin et al, 1997; Sella, 1997; Mulder and Gerritsen, 1990; Musselman et al, 1994; Schreurs et al, 1996a; Eighmy et al, 1997, Schreurs et al, 1996b; Steketee, 2001; van der Sloot et al, 2001; Wrainwright et al, 2001, Eighmy, 2002). These were largely induced by the shortage of primary materials with regards to the abundance of materials going to landfill. This started with work on coal fly ash used in road construction and embankment (Schreurs et al, 1996a and b) and has expanded into a much wider range of materials to be evaluated. The WASCON series of conferences (Goumans et al, 1991, 1993, 1995, 1997, 2001) has been a basis for developments on environmental aspects and to a lesser extent on technical aspects. In view of the regulatory development of the Building Materials Decree back in 1983, the Mammoet project (Mammoet studies 1985-1990; Versluijs et al, 1990) was carried out, which dealt with most of the materials now specified in the list of relevant materials for WP3. At first the proper test methods to assess leaching had to be identified. The too simple single batch extraction procedures (van der Sloot, 1996) used in regulatory context were clearly inadequate. This process of test development has evolved from the unified approach of leaching (van der Sloot et al, 1995; Eighmy and van der Sloot, 1994; Kosson et al, 1997; Kosson et al, 2002) through the Harmonisation of Leaching/extraction network activities (van der Sloot et al, 1997) to the present standards being worked out at CEN level (PrEN 14405, 2003; PrEN 14429, 2003) and being implemented in Regulations (e.g. EU Landfill Directive, 2002). The next phase was developing the relationship between the most relevant information needed “how much of substance x is leached from this material in the short and long term under influence of external factors in a given scenario?” and the available leaching tools. An important aspect in this evaluation is the water movement in the road constructions (Scheurs at al, 1997; Johnson et al, 1999; Ludwig et al, 2000; Apul et al, 2002; Simunek and Hansson, 2004). In the development of criteria for acceptable quality of materials for a given purpose, that implies identification of target and associated quality objectives. Since long term behaviour generally can only be assessed through modelling a verification of the suitability of the predictions is essential. This in turn implies that verification of modelling predictions and field observations is of great relevance. The latter aspect is fairly costly and therefore an aspect that takes some convincing arguments before it can actually be done. And then when the material behaviour is understood and the regulatory aspects are covered, the performance of materials needs to be verified against the criteria and this needs to be done in a much simpler manner than with the more extended information obtained from characterisation leaching test. This is where compliance testing comes in. The overall management of materials and decisions that need to be taken have been embedded in a framework with a tiered approach that covers many of the aspects addressed above (Kosson et al, 2002).

3.2.2Recent developments in the USA

Whereas the previous section already includes both European and American developments, this section presents some issues which are specific to the USA situation.

Much of the developments in the U.S. are similar to advances made with the E.U. landfill directive, the CEN working groups on leaching harmonization, and efforts to develop a sound framework for interpretation of leaching data.

Presently, under federal law, wastes are either classified with subtitle C (hazardous) or subtitle D (non-hazardous solid waste). The U.S. EPA has traditionally focused on these two regulated classifications. The permitting, regulation, or statutory authorization allowing the beneficial use of waste, by-product or secondary materials has traditionally occurred at the State EPA level.

The situation in the U.S. is complicated at the state level by the many jurisdictional authorities. In 2000, a survey of State EPA beneficial use programs by the Association of State and Territorial Solid Waste Management Officials (ASTSWMO, 2000) revealed that environmental regulatory approval is very different from state to state. Over 40 states responded with 33 indicating that they have formal beneficial use processes. Some states use statutory authority, some use environmental regulations, others use more informal policies, guidance or discretionary approaches. Some have had beneficial use programs in place for over 10 years. Some were just initiated. Some processed large numbers of beneficial use permits per year (> 30). Some process very few permits (<10). Almost all states use some form of risk evaluation in their assessments (informal health risk evaluations, formal health risk assessments, ecological risk assessments).

The states presently also rely on many different approaches to determining source term leaching potential and attendant risk. Some rely on the concept of total metals or total organics, some use the Toxicity Characteristics Leaching Procedure (TCLP, EPA 1311), some use the synthetic acid rain precipitation leaching procedure (SPLP, EPA 1312), some use the ASTM neutral water leaching test (ASTM 3987). Further, some approaches look at total composition and compare them to levels associated with generally accepted, risk-based thresholds associated with the land application of wastewater sludges (the 40CFR 503 regulations).

3.2.3Existing USA frameworks

The conceptual framework presented in section 2.3.2 as prepared by the Federal Highway Administration also deals with the environmental characterisation of materials. It attempted to meld the innovative European approaches designed to determine fundamental leaching properties with tests that better predict scenario-specific leaching (as discussed elsewhere in this document) with the realities of federal and state regulatory practices in the U.S. Hopefully this approach can have a strong influence on the future development of the regulatory situation in this field in the USA.

At this time, there are attempts among states to standardize beneficial use approvals (reciprocity agreements). However, the overarching federal approach to the present regulatory landscape about waste classification means that states will continue to apply their own best approaches to approval processes and risk evaluations.

There are some recent advances in the U.S. that are attempting to standardize the application of leaching methodologies so as to better predict scenario-specific risk associated with beneficial use.

Efforts by Dr. David Kosson and colleagues (Kosson et al. 2002; Sanchez et al., 2002) have looked to establish a protocol that involves a suite of mechanistic leaching tests that are used as appropriate for various use scenarios. The approach is similar to those embodied from the European perspective. The utility of the approach was demonstrated for Hg-contaminated soils. The approach was presented to the U.S. EAP Science Advisory Board in 2003 for consideration.

A workshop sponsored by the Recycled Materials Resource Center in 2004 (see http://www.rmrc.unh.edu/Research/Workshops/2004Workshop/2004Workshop.asp)

brought together experts from eight countries to explore innovations in modelling water movement and reactive transport modelling for highway beneficial use scenarios. Significant efforts by a number of groups are directed at better quantifying water movement in highway structures, refinement of deterministic models for unsaturated zone and saturated zone water movement modelling, use of appropriate source term levels of contaminants in fate/transport models, and verification of modelling efforts. These activities are directed at better predicting impacts associated with the leaching of inorganics from waste forms in highways at receptors down gradient from the highway structure.

3.2.4Eco-toxicological characterisation of materials

Among the 9 wastes studied in work package 3, most of the available data concerns the assessment of MSWI bottom ash toxicity.

Regarding MSWI bottom ash, the examination of chemical characteristics (solid material and/or leachates) is not sufficient to determine the waste toxicity. Physico-chemical and ecotoxic characteristics are complementary but do not lead to the same discrimination of waste (Ibanez et al, 2000). Ferrari et al (1999) have studied the toxicity on diverse organisms of several MSWI bottom ash samples and their leachates. The indirect toxicity evaluated thanks to the leachates led to the following sensitivity: algal growth > Ceriodaphnia test> Microtox test > plant germination and growth. The growth inhibition of Pseudokirchneriella subcapitata test has been raised by several others (Ferrari et al., 1999, Barthet, 2003) as highly sensitive. Others studies have shown that the toxic response can differ from an organism to another. It underlines the necessity to carry out several bioassays with different kind of organisms in order to assess the potential toxicity of the material (Perrodin et al., 2002). The carbonation of the MSWI bottom ash seems to decrease the toxicity evaluated on the growth inhibition test of Pseudokirchneriella subcapitata.

As far as coal fly ash are concerned, the study carried out by Pons and Leduc-Brunet (1999), dealing with the effects determination of both fresh and stored ashes on different organisms (algae, bacteria, daphnia, plants, earthworms) revealed neither direct nor indirect toxicity

The following tables introduces first the most common tests. This means the most frequently applied and the most well-documented tests. These are only a small part of the standardized tests. For this reason, we add a second table to review all the standardized tests found in the literature related to the eco-toxic properties assessment of the nine materials concerned by this report. In the both tables we include tests recommended by OECD guidelines as they also constitute reference tests.

To make easier the understanding of the tables we used common term to name the organisms. The algae tested in the tests mentioned in the table are unicellular algae (i.e. micro-algae). Photographs of some of the listed organisms are supplied at the end of the report. A list of the most common eco-toxicity tests is shown in APPENDIX 5.