Soil Protection and Contaminated Sites Rehabilitation Policy

The risk assessment procedure makes it possible to:

• Assess the risk that a site constitutes to human health, wildlife and flora;
• Establish specific decontamination criteria for soils and groundwater;
• Determine what types of corrective measures are required to manage the risk;
• Assess the residual risk resulting from application of these measures.

The steps to follow to select the decontamination objectives from the risk assessment procedure are diagrammed in Figure 1 and described in the following text.

In all cases, anyone opting for the use of the risk assessment procedure must carry out a toxicological risk analysis, an ecotoxicological risk assessment and an assessment of impact on groundwater and surface water.

3.1.1 Toxicological Risk Analysis

The analysis of toxicological risks is defined as a systematic and forward-looking approach aimed at identifying and quantifying the risks associated with the exposure of a target individual or population to contaminants present in various environments.

The analysis of health risks includes several stages and various levels of refinement. The MSSS and MEF have developed standardized guidelines describing the various stages and methodological choices to be made (see Section 11. 6). Anyone wishing to carry out an on-site analysis of toxicological risks must follow these guidelines. Risk analyses carried out according to other procedures will be considered only to the extent that the differences with the procedure drawn up by the MSSS and MEF are indicated and justified.

Figure 1: Risk Assessment Procedure Flowchart

3.1.2 Ecotoxicological Risk Assessment

The assessment of ecotoxicological risk constitutes a rational process of identifying, comparing and analysing descriptive measures aimed at assessing the possibilities and probabilities of harmful responses occurring with an ecological receptor as the result of its exposure to one or more contaminants.

Ecotoxicological risk assessment involves various stages and levels of refinement. The MEF has drawn up a document entitled Ecotoxicological Risk Assessment Procedure, which describes the various stages and the methodological choices to be made. Anyone wishing to carry out an on-site ecotoxicological risk assessment must follow this procedure. Risk assessments carried out using other procedures will be considered only to the extent that differences with the procedure recommended by the MEF are indicated and justified.

3.1.3 Assessment of Impacts on Groundwater and Surface Water

This assessment is identical to the one that must be carried out for groundwater when the firm responsible chooses to decontaminate its site using generic criteria (See Appendix 2). The impact on surface water is assessed using the use-based criteria associated with this water.

Once the risk analyses are carried out to the satisfaction of the MEF and its associate the MSSS (for the health aspect), the applicant must determine, where appropriate, what corrective measures he intends to take to render the risk associated with the site insignificant. To do this, he has a choice among various management modes (see Figure 2, main document).

APPENDIX 4 / Confinement, control and monitoring (ccm) measures

Action must be taken on contaminated sites that have an impact on the environment or that constitute a significant risk to health, wildlife or flora. The objective of this action is to manage the risk in a way that ends the impacts and ensures that the site no longer represents significant risks in the short or long term. Recourse to confinement, control and monitoring (CCM) measures can make it possible to attain this result.

CCM measures consist in:

• confining, that is, isolating contaminants so as to prevent their propagation;

• controlling, that is, ensuring that the measures put in place are maintained;

• monitoring, that is, ensuring the effectiveness of these measures.

The CCM measures to be put in place shall be chosen and adapted according to the special conditions of each case, such as the nature and scope of the contamination, the geological and hydrogeological characteristics of the site, the biological sensitivity of the environment and the use made of it (e.g., groundwater used as source of drinking water...) and, where appropriate, the specific features of the project under consideration (single family dwellings, gardens, etc.).

The confinement measure are called active, when they require the installation and operation of active equipment to maintain their effectiveness. For example, the pumping of groundwater to permit hydraulic confinement is an active confinement measure. On the other hand, passive confinement measures require no active equipment. For example, any measure to cover contaminated soils that makes it possible to prevent contact with the contaminants is a passive confinement measure.

Passive measures must be designed so that the normal uses of the site for the expected category of use may take place without raising the question of the adequacy of the measures adopted. For example, adding a 5-cm layer of clean earth on a playground is clearly insufficient because normal recreational activities would quickly remove the protective layer put in place.

Similarly, a review of the literature and consultations with experts were carried out in order to establish a minimum thickness of clean soils that could ensure the viability of biological receptors such as vegetation and invertebrates. It has been found that the majority of land-based organisms living at our latitudes reproduce and feed in the first metre of soil below the surface. As well, about 90% of the roots of plants found in Québec are generally located within this layer. Consequently, from a strictly ecotoxicological point of view with respect to landscaping, a minimum thickness of one metre of clean soil (contamination = A criteria) is recommended in cases where the CCM measures call for the addition of soil covering.

CCM measures may also be introduced to eliminate or reduce the active contribution of contaminants in groundwater (see Appendix 2, Section 2. 2. 2). Depending on the case being treated, these measures may take the form of the encapsulation of the contamination sources or the placing of a water-proof surface membrane (clay materials or geomembrane liner) that limits the percolation of surface water through contaminated soils or waste materials. Some technical specifications for the constitution and the installation of impervious membranes are given in the Guideline regarding Implementation and Management of Secure Landfill Sites (July 1994).

Moreover, the construction of new buildings, the waterproofing of certain areas of the developed site resulting from the construction of highway infrastructures, and the installation of storm sewer networks may be designed so as to reduce the percolation of rainwater through the ground and the active contribution of contaminants to groundwater.

To be effective, any confinement measure must be accompanied by control measures that make it possible to ensure its integrity. The site must be checked regularly to ensure that the confinement measure are still in place and functioning and that the use made of the site does not threaten the integrity of these measures. In certain cases. it may be necessary to set up a structure maintenance program. As well, when confinement measures require, the physical movement of the site, pumping system or water collection, the condition of the infrastructures in place (e.g., fences, barriers, drainage ditches) must be monitored.

Monitoring must make it possible to ensure the effectiveness of the confinement measures implemented. Most often, this will consist in taking samples of groundwater or surface water to verify its quality and keep up with changes. In some cases, monitoring will be carried out to ensure that no new contaminants are entering the environment. On occasion, it will be carried out in order to confirm the attenuation or a stabilization of contamination already in the environment.

An atmospheric emissions (dust, gaseous or other emissions) monitoring program may also be adopted, where appropriate.