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An Approach that Uses the Concentrations of Hydrocarbon Compounds in Soil Gas at the Source of Contamination to Evaluate the Potential for Intrusion of Petroleum Vapors into Buildings (PVI)
Citation:
Wilson, J., K. Jewell, C. Adair, C. Paul, C. Ruybal, G. DeVaull, AND Jim Weaver. An Approach that Uses the Concentrations of Hydrocarbon Compounds in Soil Gas at the Source of Contamination to Evaluate the Potential for Intrusion of Petroleum Vapors into Buildings (PVI). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-14/318, 2014.
Impact/Purpose:
This issue paper offers an alternative approach to screening that could be applied before a decision is made to do sub-slab monitoring or indoor air monitoring. The approach is based on three factors: (1) the concentrations of hydrocarbons in soil gas at the source of the vapors, (2) the separation distance between the receptor and the source of the vapors, and (3) a presumption that aerobic biodegradation will reduce the concentrations of hydrocarbons in the unsaturated zone. This issue paper provides technical recommendations. The issue paper is intended for staff of state agencies that regulate PVI, or consultants to site owners who must prepare reports evaluating PVI. This issue paper is not guidance provided by U.S. EPA OSWER or U.S. EPA OUST. This Issue Paper is not guidance provided by U.S. EPA OSWER or U.S. EPA OUST.
Description:
If motor fuels are spilled from underground storage tanks, petroleum hydrocarbons can vaporize from the spill and move as a vapor through the unsaturated zone. If a building is sited above or near the spill, the hydrocarbons may intrude into the air space of the building. This petroleum vapor intrusion (PVI) is a concern if the concentrations of individual hydrocarbons exceed the limits that are set by the states or by U.S. EPA. The conventional approach is to measure the concentrations of compounds of concern in shallow soil gas, and apply a generic attenuation factor to predict the concentration in indoor air. The conventional approach makes no allowance for biodegradation of the hydrocarbons in the soil. The issue paper is intended for staff of state agencies that regulate PVI, or consultants to site owners who must prepare reports evaluating PVI. The approach uses mathematical models to predict the concentration of the hydrocarbons in indoor air. The models incorporate an estimate of biodegradation of the hydrocarbons. The models make site specific estimates of the concentration in indoor air based on the particular circumstances at a particular site. These circumstances include the concentration of petroleum hydrocarbons in vapors at the source of the vapors and the separation distance between the source of the vapors and the building.