Development of risk-based soil quality guidelines for selected trace metals

Ian Mitchell

The Alberta Tier 1 Soil and Groundwater Remediation Guidelines (Alberta Environment and Sustainable Resource Development, ESRD, 2010) are used for the assessment and remediation of contaminated sites in Alberta; the Canadian Environmental Quality Guidelines (Canadian Council of Ministers of the Environment, CCME, 2012) are used for Federal Government lands and in several other provinces. Typically, if concentrations of chemical contaminants exceed these guidelines, the contamination requires remediation, risk management, or site-specific risk assessment.

Both the Alberta and CCME soil quality guidelines were derived based on a Protocol for the Derivation of Environmental and Human Health Soil Quality Guidelines (CCME, 2006). This protocol describes the approach, assumptions and models for deriving widely applicable soil quality guidelines that are protective of both human and environmental health. However, some substances, particularly certain metals, have not been evaluated using the CCME (2006) protocol or its 1996 precursor, and are still assessed using prior interim guidelines from 1991. Specifically, antimony, beryllium, boron, cobalt, fluoride, molybdenum, silver, sulphur, tin and several organic substances (primarily chlorinated organics and phenolics) do not have modern risk-based guidelines.

In the absence of risk-based guidelines, concentrations of these substances measured during contaminated site investigations cannot be readily related to potential risks to human and environmental health. Without this information, it is unknown whether remediation is necessary to protect human and environmental health, or whether remediating to guidelines will achieve human and environmental health protection. The available options for cost-effective site-specific risk assessment for the metals in particular are also very limited without a risk-based guideline as a starting point. Risk management plans are also difficult to develop, since the 1991 interim guidelines do not provide any information on what receptors or exposure pathways may be affected by different chemical concentrations in soil.

Based on our discussions with federal and provincial government departments, we do not expect significant government resources to be invested in further soil quality guideline development for the foreseeable future. Therefore, guideline development will likely need to be driven by the industries that would benefit from having additional risk-based soil quality guidelines. It is our belief that the upstream oil and gas industry would benefit from having risk-based soil quality guidelines for certain metals, including molybdenum, cobalt, antimony and beryllium, and that these benefits would far exceed the cost of funding the guideline development. The timing of the proposed work is also considered to be optimal, since considerable data have been generated recently in support of European Union REACH (Registration, Evaluation, Authorization and Restriction of Chemical Substances) requirements that are expected to substantially reduce the cost of soil quality guideline development for many metals.

The proposed project will involve the development of risk-based soil quality guidelines for one or more metals (see Section 6) using the approach specified by CCME (2006). The end result will be soil quality guidelines that meet all requirements of both Alberta and CCME, with a complete scientific supporting document provided with each guideline. The guidelines could be used immediately as internal guidelines by the oil and gas industry, and eventually adopted by ESRD, CCME and other jurisdictions. The guidelines will be developed in cooperation with ESRD, Health Canada and Environment Canada to maximize the potential for eventual formal adoption.

Policy Issue
Additional Science for the Refinement of Regulatory Guidelines/Directives/Policies/Criteria. The degree of conservatism current in some regulatory guidelines can be linked to some unnecessary remedial efforts throughout the petroleum industry. The development of accepted scientific studies to reduce these conservatisms would ultimately lead to a reduction in perceived waste going to landfill and a reduction in remedial costs.

Knowledge Gap
Refinement or development of risk?based soil quality guidelines for selected trace metals (eg. Molybdenum, antimony, beryllium, and cobalt).