New Provincial Vapour Assessment Guidelines

September 15, 2008

A potential for intrusion or migration of vapour-phase contaminants into indoor and outdoor air exists at sites where the soils or groundwater contain volatile or semi-volatile substances - such as sites where gasoline is stored. 

Inhaling the vapours can cause damage to human health, so the soil vapour intrusion pathway is usually evaluated during an environmental investigation at a site where buildings are located near subsurface volatile chemicals.  However, at present, the Contaminated Sites Regulation (“CSR”) does not provide any specific criteria for assessing vapour phase contaminants in the indoor or outdoor air.    

To address this regulatory “gap”, the Ministry of Environment has prepared Air Concentration Criteria (“ACC”) pursuant to the Director’s authority under section 63.1 (1) of the Environmental Management Act (“EMA”) and section 11 (1)(d) of the CSR.  Once the ACC are finalized and approved, which is likely to occur early next year, they will be legally enforceable.

The purpose of the ACC is to:

  •  provide guidance in assessing whether air associated with contaminated sites is contaminated and, if so;
  •  if there is a need for remedial measures, and, if so;
  •  if remediation of air at a contaminated site is satisfactory. 

Air samples and soil vapour samples must be collected for comparison with the numerical standards set out in the ACC.  To achieve a satisfactory remediation of the site, tolerable air concentration targets will have to be reached in those cases where vapour samples show higher than acceptable targets. 

To provide interim guidance to responsible persons and contaminated sites professionals until the ACC come into force, the Ministry has issued a document entitled “Interim Guidance for Contaminated Sites - Soil Vapour Assessment”.

The Interim Guidance intends to ensure that risks to human health are adequately assessed, so that appropriate remedial steps may be taken. 

Responsible persons and contaminated sites professionals should take a number of steps to achieve this.  These steps include:

  •  determining the indoor and outdoor air concentration of each volatile or semi-volatile substance using the formulas outlined in the Interim Guidance
  •  comparing the concentrations of each substance to an appropriate reference concentration.
  •  If the concentration of any volatile or semi-volatile substance is higher than the reference concentration, remedial actions are required.

The Interim Guidance is not a regulation and does not have the effect of law.  However, compliance is advisable. Non-compliance should be supported by defensible and documented professional judgment, if an Approval in Principle or Certificate of Compliance is to be obtained for a site, in cases where the application for these documents is submitted after January 31, 2008. 

Responsible persons and contaminated sites professionals should become familiar with and implement the vapour assessment requirements of the ACC and the Interim Guidance even before these standards acquire legal force.

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