Background concentrations

Local background concentrations are naturally occurring substance concentrations in a geographic area that exceed the numerical standards in the Contaminated Sites Regulation (CSR). Once established, a local background concentration is used to determine whether a site is considered contaminated.

This page describes how you can establish local background concentrations for soil and groundwater with ministry-approved regional background concentrations or seek approval for site-specific concentrations. 

If you believe you have naturally occurring substances at your site, you may establish a local background concentration before applying for:

• Approval in Principle
• Certificate of Compliance
• Determination of Contaminated Site
• Scenario 3 release notice under the site identification process

For all other media, submit a preapproval application under Protocol 6: Applications with Approved Professional Recommendations and Pre-approvals (PDF 360KB)

On this page

• Establishing local background concentrations in soil
• Establishing local background concentrations in groundwater
• Using statistics

Establishing local background concentrations in soil

Protocol 4: Establishing Local Background Concentrations in Soil (PDF, 565KB) provides options for establishing local background concentrations in soil. 

Option 1: Use ministry-approved regional background soil concentrations

This option allows for direct use of ministry regional background concentrations to establish local background concentrations. Option 1 does not require approval from the director.

• Use Table 1 and Figure 4 in Protocol 4 to determine the local background concentration for your region. This table was created using the Background Soil Database (XLSX, 118KB to establish local background concentrations in various regions throughout B.C.
• Data from the background soil database can also be used to derive a local background concentration at your site. However, the data available is limited and special considerations are required when analyzing the data  

Use Option 2 to determine a local background concentration if substances are not listed in Table 1 of Protocol 4. 

Option 2: Get director approval for site-specific local background concentrations

Request approval from a director to establish site-specific local background concentrations based on:

• Data from the ministry background soil database, supplemented with data from reports or from soil sampling results, or
• Soil sampling conducted at an appropriate reference site

Approval from a director is not required under Option 2 if you are applying for a certification document or a director's release notice and:

• The substance is not a potential contaminant of concern at the reference site or the site of interest; and
  • There are no detectable concentrations of hydrocarbons or volatile organic compounds in the samples used to calculate the background concentration; and
  • The substance is not present above CSR numerical soil standards in fill material
• The site of interest is located within a known mineralized area, as determined by a qualified professional using verifiable records such as government databases, geological assessments or maps; and it has not been previously mined or disturbed.

The ministry has soil analytical data for other parameters that may not be considered naturally occurring but may be useful for comparison purposes. Submit an information request to the Remediation FAQs inbox to access:

• Analytical data for organic analytes (e.g., pesticides, herbicides, PAHs, chlorinated phenols) and miscellaneous parameters (e.g., pH, certain inorganics)
• Background sampling site locations and soil descriptions by region 

Establishing local background concentrations in groundwater

Protocol 9: Establishing Local Background Concentrations in Groundwater (PDF, 400KB) provides options for establishing local background concentrations in groundwater.

Option 1: Use ministry-approved regional background groundwater concentrations

This option allows for direct use of ministry regional background concentrations to establish local background concentrations. Option 1 does not require director's approval. 

Use the approved regional background concentrations in Table 1 of Protocol 9.  Local background concentrations of inorganic substances in groundwater have been calculated using the ministry's Background Groundwater Database (PDF, 215KB) for three regions in B.C.: The Lower Mainland region (includes sub-regions 1 and 2), Southern Vancouver Island region and the Thompson Okanagan region. 

Table 1 of Protocol 9 provides background groundwater concentrations of inorganic substances in select regions of the province. iMapBC can help:

• Determine if your site is in one of these regions,
• Identify the location and analytical data for specific regional background ground water wells, and
• Determine the background groundwater concentration for a region.

How to use iMapBC

1. Launch iMapBC
2. Select 'Data Sources'
3. Select 'Add Provincial Layers'
4. Scroll down to the 'Waste' tab and select it
5. Choose the appropriate boxes to view "Background Groundwater Concentrations":
   • Individual background sample sites concentration data
   • Regional concentration areas for the regional background concentrations
6. Review boundaries of regional areas.
7. On the “Find” tab, select the region or individual site using “point” to view the background concentration data

Use Option 2 to determine a local background concentration if substances are not listed in Table 1 of Protocol 9, or if your site is not located in one of the listed background regions.

Option 2: Get director's approval for site-specific local background groundwater concentrations

Request approval from a director to establish site-specific local background concentrations using:

• Site-specific concentration data collected from representative background monitoring wells located on or adjacent to your site; or
• A combination of site-specific concentration data collected at your site supplemented with concentration data from nearby background groundwater wells listed in the background groundwater database

Approval from a director is not required under Option 2 if:

• The substance is not a potential contaminant of concern at the site of interest, and
• The substance is not present above the CSR numerical soil standards in fill material where background wells are located.

Using statistics

When using Option 2 of Protocols 4 (soil) and 9 (groundwater), local background concentrations can be developed using site-specific data and basic statistical tools. This involves collecting samples from areas that represent natural conditions and checking that the data are reliable and appropriate to use. Common methods include plotting the data (for example, using Q–Q plots or histograms) to understand how it is distributed, and using simple statistical tests (such as t‑tests) to confirm that the data represent natural background conditions rather than site contamination. See Technical Guidance 12, Statistics for Contaminated Sites for more information.