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Background concentrations in soil

Last updated on March 28, 2023

Under the Environmental Management Act (EMA), the Contaminated Sites Regulation (CSR) has provisions to address naturally occurring, locally elevated concentrations of substances in soil.

Provincial background estimate

CSR numerical soil standards (Schedule 3.1) may be adjusted to reflect natural background conditions based on a provincial background soil estimate.

When the calculated standard is less than the estimate, the estimate is selected as the final soil standard.

The soil data on the Background concentrations database page are used to derive the provincial background soil estimate.

Review Protocol 28: 2016 Standards Derivation Methods (PDF, 3.2MB) for more details.

Local background estimate

During site investigation, naturally occurring concentrations of substances may be identified in the soil in excess of the CSR numerical standards.

If this is suspected, Protocol 4: Establishing Local Background Concentrations in Soil (PDF, 565KB) may provide options for establishing local background concentrations at a site. 

The following flowchart is designed to assist in the process of determining if a background application may be appropriate:

Soil sampling approach

In addition to the requirements of Protocol 4, the following sections provide guidance for the preferred sampling approach used to assess substance concentrations in the soil at local background reference sites.

Alternative sampling approaches may be used and should be justified in the report.

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Materials classification 

The following procedures are recommended:

  • Check available soil, terrain, or surficial geology maps to determine the type of surficial material at the background reference site
  • Wherever possible, locate the local background reference site that has the same surficial material as the site of interest for which the background soil concentration is to be established
  • If the information on soils and terrain is not available for the site, complete a terrain survey for the site
  • Classification of reference site materials is a requirement in applications for background concentrations under Protocol 4: Establishing Local Background Concentrations in Soil (PDF, 565KB)
 

Soil sampling locations

Wherever possible, the local background reference site should be approximately one hectare in size.

At any reference site, a minimum of 4 randomly selected soil sampling locations should be identified as follows (see Figure 1):

  1. Locate the approximate centre of the site
  2. Divide the site through the centre point into 2 halves
    • This is the division line
  3. Draw a line perpendicular to the division line through the centre to further divide the site into 4 quadrants
    • This is the perpendicular line
  4. Randomly select one soil sampling location for each of the 4 recommended 50x50m quadrants
    • For example, using a 1 to 40 random number table, randomly select 2 numbers:
      • The first is the number of metres perpendicular to the division line
      • The second is the number of metres the sampling site is located to the right or left of the perpendicular, depending on the quadrant you're working in
 

Soil sampling

3 samples or more should be collected within each soil horizon at relevant depths:

  • Shallow
  • Mid
  • Deep

In collecting soil samples, the following should be consulted:

 

Soil analysis

Soil samples should be chemically analyzed for all potential contaminants of concern relevant to the site of interest.

Samples should be analyzed only as described under the Environmental Data Quality Assurance Regulation.

Technical Guidance 12: Statistics for Contaminated Sites (PDF, 92KB) is a useful reference for statistical outliers.

 

The information on this web page does not replace the legislative requirements in the EMA or its regulations and it does not list all provisions for contaminated site services.

If there are differences between this information and the Act, Regulation, or Protocols, the Act, Regulation, and Protocols apply.