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Volume 4: Investigative approach for petroleum VIAP

Vapor Intrusion Graphic
Environment, Great Lakes, and Energy

Volume 4: Investigative approach for petroleum VIAP

Thank you for taking part in the External Review of Volume 4 – Investigative Approach for Petroleum Volatilization to the Indoor Air Pathway (VIAP). It is being released as a draft document and part of the new Guidance Document for the Volatilization to Indoor Air Pathway. The review and comment period for this document begins on April 22, 2024, and ends at 5:00 p.m. on May 10, 2024. All comments should be provided on the Guidance Review Form and emailed to Comments not provided on the form will not be considered during the review process. Comments provided should be specific, suggest new or revised text, and provide additional references, if applicable. Grammar and writing-style comments are not needed.

Please email Nick Swiger at with any questions, comments, concerns, or technical challenges when accessing or commenting on these documents.

Download the Guidance Review Form

Executive Summary

Petroleum vapor intrusion (PVI) is a unique subdivision of the volatilization to indoor air pathway (VIAP) distinguished by the influence of aerobic biodegradation in degrading volatile petroleum hydrocarbon (PHC) vapors over short distances. Occurrence of this mechanism supports that risk evaluation associated with PVI should focus on contaminated groundwater at the surface (i.e., top) of the zone of saturation and areas where the non-aqueous phase liquid (NAPL) body is located above the saturation zone or where mobile NAPL intersects an underground conduit that may transport vapors to a structure. For PVI, risk evaluation can often be accomplished through application of nationally supported separation distances and strategic placement of representative soil gas samples around the NAPL body and contaminated groundwater.