“Running out of room” seems to be a common theme regarding municipal landfills, particularly in the more densely-settled parts of the country. Even in less-dense areas there’s a shortage of permitted space and long delays in obtaining further permits. In addition to growing volumes of municipal solid waste, another material stream is adding unnecessarily to the landfill burden.
This is “excess fill” — generally meaning soil removed from con struction sites. As governments seek to limit urban sprawl by encouraging “infill” developments, there’s greater potential for some of the soil to have been impacted by previous industrial use. Regulators naturally want to be sure that the potential environmental and health risks of this material are managed.
Another type of increasing excess fill is sediment dredged from storm-water management ponds. These ponds are growing in number as municipalities seek to manage the flow of precipitation off hard surfaces such as roofs, roadways and parking lots and into their storm sewer systems. Sediment that accumulates in these ponds must be removed periodically to maintain the retention capacity of the ponds, and may contain road salt, antifreeze, hydrocarbons and other materials washed off the paved surfaces, and pesticides and herbicides from lawns and gardens.
Much of the cost from excess fill is seen in landfill fees. For example, if tip fees are, say, $50 per cubic metre, for a pond 100 metres square dredged to the depth of one metre, the disposal costs alone would be $500,000. Add to this the cost of trucking the fill to the landfill, multiplied over several ponds which are emptied regularly, and the costs mount substantially. As well as these costs, unnecessary trucking of soil to landfills has air-quality and noise impacts from trucks.
Regulations and risk solutions
Provincial regulations have the laudable goal of protecting public health and the environment from the improper disposal of materials that may pose a danger. However, current regulations are in some cases behind the times with regards to science. While these issues concern virtually all jurisdictions in Canada, we focus here on Ontario as it has the most complete regulations regarding excess fill.
In Ontario all wastes must be disposed of at a site operating under a Certificate of Approval. The challenge lies in defining “waste.” Under the provincial Environmental Protection Act and O. Reg. 347, virtually any soils removed from a site are considered waste by the environment ministry. While the Regulation does exempt inert fill, its definition as “earth or rock fill or waste of a similar nature that contains no putrescible materials or soluble or decomposable chemical substances” is unworkable. This has led the ministry to adopt a working definition of inert fill as all fill materials in which the concentrations of the measured parameters are below the Guideline’s Table 1 values. Under this definition, material that exceeds even a single parameter by only a minor amount must be considered “waste” and sent to a landfill.
Since the Table 1values are based on background concentrations, not measured effects, this regulation ignores the fact that some contaminants are much more dangerous than others. Similar legislation in other provinces can result in excess fill being sent to landfill more than is necessary.
One alternative is a Site-Specific Risk Assessment (SSRA) approach. This is probably most appropriate for soils whose contaminants are not considered highly toxic, but which have some parameters in excess of legislated contaminant criteria, if it has been determined that there will be no adverse effects on humans or non-human biota.
SSRA points to the heart of the issue; it’s not the simple presence of the compound or element of concern, but rather the possibility of its causing an adverse effect. It makes more sense to discuss contaminants in terms of their potential for toxicity, leaving out those where toxicity is only a minor concern or is a concern only at levels higher than usually encountered.
Bio-accumulation is a major consideration for this suggested tiered approach. The form of the compound is a major consideration, and in the soil environment, most chemicals are not freely available. Bio-availability depends on several site-specific factors. For example, metals are typically most reactive in free ionic form, but the presence of free ions is usually controlled by the pH of the system, Most metals are only available at a pH below that of most soils, which is generally pH 6 to 8.
The SSRA approach being proposed has already been honed through a similar process for brownfields redevelopment, basing decisions on the actual effects of the contaminants. It would likely be most applicable on large sites, and where the degree of “contamination” is low, as these would likely provide the best return on the money invested in the additional testing and evaluation. These assessments might be best done through a phased approach that focuses initially on compounds of concern and how they are distributed, to see if a risk assessment approach is warranted.
The SSRA approach would address the issue of toxicity, and determine the level of risk, recommending appropriate disposal. It would be based on testing to determine the level of effects, which in turn would be determined partly on the bio-availability of the compound. In place of the restrictive and rather arbitrary definition of “contamination” an SSRA approach would weigh all the risks, costs and opportunities in support of decisions favouring the best possible outcome.
Rein Jaagumagi is a Senior Environmental Specialist with Golder Associates in Mississauga, Ontario. Contact Rein firstname.lastname@example.org