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Volume 4: Investigative approach for petroleum VIAP

3. Define extent of the vapor source – Step 1

Delineation of the vapor source for a petroleum release is necessary to identify which buildings and properties are within the LIZ (Section 4) and if there is sufficient vertical separation distance to screen out buildings (Section 5).

Applicable unrestricted residential soil and groundwater VIAC is used to define the vapor source during the investigative process to better understand the full extent of a person’s obligations that exist under Part 201. For a criterion to be applicable, all assumptions in the calculation of the criterion need to fit the conditions present at the facility. See Volume 6 – Volatilization to the Indoor Air Criteria for more information. For facilities that only need to consider their due care obligations under Sec. 20107a the applicable unrestricted residential VIAC identifies where a notice of migration is required if contamination migrates off-site.

Additional information on vapor source delineation can be found in Attachment B.

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