Federal Contaminated Site Risk Assessment In Canada Part I: Guidence on Human Health Preliminary Quantitive Risk Assessment (PQRA)

Appendix A

Screening Contaminants of Potential Concern for Local or Regional Background (Natural) Soil, Groundwater and Surface Water Concentrations

Before a site is considered contaminated, on-site concentrations of contaminants, particularly natural elements, should be compared to data from local or regional surveys of soil quality, groundwater quality, or surface water quality in uncontaminated areas. If possible, such surveys should be conducted at the time of the site environmental assessment, although the collection of background samples at that time is generally a rare occurrence. However, the results of many regional soil surveys are available in the open scientific literature. Soil survey data are also available from provincial ministries of natural resources, which have conducted surveys and compiled soil survey data for purposes of mineral exploration and mineral mapping. Similarly, the Geological Survey of Canada (GSC) has compiled data from numerous large-scale and small-scale soil surveys for purposes of mineral exploration and mapping across Canada. These GSC surveys are publicly available as GSC Open Files, which can be searched and reviewed with the assistance of the local GSC office or library.

If it is found that concentrations of contaminants of potential concern at the site are representative of background levels, the site may not be considered contaminated despite the fact that generic guidelines are exceeded.

Many contaminants, particularly metals, are naturally occurring, and natural levels can exceed Canadian Council of Ministers of the Environment (CCME) guidelines and other generic guidelines without representing industrial or anthropogenic contamination. A prime example is arsenic. The CCME soil quality guideline for arsenic is 12 ppm. This guideline was derived on the basis of a "national" natural background concentration of 10 ppm arsenic in agricultural soils from southern Ontario and the Prairies, with an additional 2 ppm which represented the additional contamination (above background) associated with a 1-in-1-million cancer risk (Health Canada, 1995). Although natural levels of arsenic in those agricultural soils are only 10 ppm, the regional background of arsenic established for Ontario is 17 ppm (Ontario Ministry of Environment and Energy (OMEE), 1997b), and in various regions of British Columbia it ranges up to 25 ppm (British Columbia Ministry of Water, Land and Air Protection (BCMWLAP), undated). In Sydney, Nova Scotia, local sampling determined that the local urban background concentration of arsenic ranged up to 200 ppm (JDAC Environment Ltd., 2002). In Yellowknife, NWT, the natural soil-borne levels of arsenic average approximately 150 ppm, with natural levels occasionally exceeding 1500 ppm (Richardson, 2002).

Yellowknife is situated on a geologic anomaly known as a greenstone belt. Greenstone belts and other geologic deposits are rich in mineral deposits, of which arsenic is a natural contaminant.

Soils derived from such geologic deposits will have naturally high concentrations of those elements. In fact, prospecting for mineral deposits is often accomplished by surveying soils for anomalously high arsenic levels (see Richardson, 2002). Therefore, arsenic and other metals can be present in soils at levels far in excess of national or provincial guideline values, but such levels do not represent anthropogenic or industrial pollution.

When setting national guidelines, the CCME derives guideline values by determining the tolerable or essentially negligible concentration of a contaminant above the background (natural) level (CCME, 1996a). The CCME also recognizes that natural levels in soil vary spatially, and recommends that local soil quality objectives be established that incorporate local or regional background concentrations if they are significantly different from the background value used in the derivation of the national generic guideline for a particular contaminant (CCME, 1996b).

In some cases, it may be appropriate to use "urban" background concentrations, rather than those associated with more rural areas. This may be particularly true for carcinogens where risk assessment and risk management are targeted at incremental risks above background levels. If the local urban environment and/or adjacent properties have elevated concentrations from sources other than the subject property, and those elevated concentrations are accepted and not slated for remediation or risk management, then these urban background levels may constitute the appropriate background concentrations for risk assessment and risk management purposes. However, professional judgment will be required to determine the most suitable basis for defining background concentrations.

The Ontario Ministry of Environment and Energy presents the main elements of a background approach and Ontario-specific criteria (OMEE, 1997 - Table F). Similar guidance is also provided by the BC Ministry of Water, Land and Air Protection (BCMWLAP, undated).

References

British Columbia Ministry of Water, Land and Air Protection (BCMWLAP) (undated). Protocol 4: Determining Background Soil Quality. Section 53, Contaminated Sites Regulation, Waste Management Act. Government of British Columbia, Victoria, BC. Available online at:
http://wlapwww.gov.bc.ca/epd/epdpa/contam_sites
/policy_procedure_protocol/protocols/background_soil.html

Canadian Council of Ministers of the Environment (CCME). 1996a. A Protocol for the Derivation of Environmental and Human Health Soil Quality Guidelines. Report CCME EPC-101E, CCME. March 1996.

Canadian Council of Ministers of the Environment (CCME). 1996b. Guidance Manual for Developing Site-specific Soil Quality Remediation Objectives for Contaminated Sites in Canada. CCME, Winnipeg, Manitoba. March 1996.

Health Canada. 1995. Canadian Soil Quality Guidelines for Contaminated Sites, Human Health Effects: Inorganic Arsenic. Air and Waste Section, Environmental Health Directorate, Health Canada, Ottawa. Unpublished report. February 1995.

JDAC Environment Ltd. 2002. Background Surface Soil Concentrations, Urban Reference Area, Human Health Risk Assessment North of Coke Ovens (NOCO) Area - Sydney, NS. Contract report submitted to Public Works and Government Services Canada.

Ontario Ministry of Environment and Energy (OMEE). 1997. Guideline for Use at Contaminated Sites in Ontario. OMEE, Toronto. Revised February 1997.

Richardson, G.M. 2002. Determining Natural (Background) Arsenic Soil Concentrations in Yellowknife NWT, and Deriving Site-Specific Human Health-Based Remediation Objectives For Arsenic in The Yellowknife Area. Final report, submitted by Risklogic Scientific Services Inc. to the Yellowknife Arsenic Soils Remediation Committee (YASRC), Yellowknife. April 2002.