Atlantic RBCA V4 User Guidance

TECHNICAL ADVISORY – Effective August 30, 2021

Atlantic PIRI has released the technical document Atlantic RBCA for Impacted Sites in Atlantic Canada V4 User Guidance (July 2021). The associated Atlantic RBCA V4 Toolkit for Atlantic Canada will be available for purchase. The V4 User Guidance and V4 Toolkit take effect August 30, 2021, with some exceptions as outlined in the Atlantic RBCA V4 and EQS/PSS Implementation Procedure.

Important changes to the technical document and Toolkit include the following:

Updated Chemical Toxicity Database

The Atlantic RBCA V4 Toolkit includes updates to the chemical toxicity database to reflect the most recent toxicity reference value (TRV) updates for benzene, toluene, ethylbenzene, and xylene (BTEX).  The chemical toxicity database has also been expanded to include selected chlorinated volatile organic compounds (CVOCs). The Atlantic RBCA V4 User Guidance includes risk-based screening levels (RBSLs) and pathway specific screening levels (PSSLs) that reflect the updated toxicity information.

Adjustment Factors

The Atlantic RBCA V4 Toolkit applies an Adjustment Factor (AF) of 10x individually to each fraction specific site-specific target level (SSTL) within the Toolkit so the SSTLs from the Toolkit can be used directly (i.e., there is no need to multiply the SSTLs for BTEX and total petroleum hydrocarbons (TPH) by 10).  The tables of RBSLs and PSSLs reflect the application of the AF to each fraction specific SSTL prior to the calculation of the SSTL for TPH.

Oxygen-Limited Biodegradation

The Atlantic RBCA V4 Toolkit includes an option to consider oxygen-limited biodegradation in the calculation of volatilization factors for petroleum hydrocarbons (PHCs) in subsurface soil, soil gas, and groundwater.

If the “no biodegradation” option is selected, the Johnson and Ettinger model is applied as has been done for the derivation of the RBSLs and PSSLs.

Hazard Quotients

The Atlantic RBCA V4 Toolkit incorporates the following target hazard quotients (HQ) for parameters in the Toolkit: 0.2 for CVOCs, 0.5 for BTEX, and 1.0 for TPH.

Carcinogenic vs. Non-carcinogenic SSTLs

The Atlantic RBCA V4 Toolkit output now indicates the driving basis of the SSTL (i.e., carcinogenic endpoint, non-carcinogenic endpoint, drinking water quality guideline).

Implementation Procedures

The updated technical document is now available and takes effect as of August 30, 2021, with some exceptions as outlined in the Atlantic RBCA V4 and EQS/PSS Implementation Procedure.