Vapor Intrusion is a common concern at properties impacted by volatile chemicals such as gasoline or chlorinated solvents. Most states have established vapor intrusion screening levels for impacted soils and/or groundwater and standards for several constituents found in the most common method used to evaluate concentrations of volatile compounds in sub-slab or indoor air samples, United States Environmental Protection Agency (US EPA) method TO-15. Generally, the evaluation of vapor intrusion concerns is related to volatile chemicals such as gasoline, jet fuel or solvents such as naphtha, toluene or trichloroethylene and its daughter products. But what about semi-volatile organic compounds such as diesel fuel? Diesel fuel is undoubtedly a common contaminant in soil and groundwater. Is vapor intrusion a concern for impacts related to diesel fuel and other semi-volatile organic compounds?
According to the US EPA, petroleum vapor intrusion can occur when vapors from petroleum hydrocarbons, solvents, or fuel additives migrate through the subsurface into overlying or nearby buildings. Vapor intrusion may pose immediate and/or long-term threats to the safety of individuals in the affected buildings, including, but not limited to, fires or explosions and possible adverse health effects. Both gasoline and diesel fuel contain BTEX (benzene, toluene, ethylbenzene and the three isomers of xylene). Therefore, in cases where vapor intrusion is a concern, identifying the makeup of the contamination is helpful in determining what measures to put into place for investigation and/or mitigation.
To determine if diesel fuel-impacted soils pose a vapor intrusion risk, the US EPA recommends analyzing bulk soil samples collected in the source area for Total Petroleum Hydrocarbon (TPH) and specific petroleum constituents such as (BTEX) (USEPA 2005). They also recommend the analysis of Light Non-Aqueous Phase Liquids (LNAPL) to determine the degree of weathering and, thus, the potential for vapor generation. More recently released, un-weathered contaminants such as diesel fuel typically contain a higher proportion of more volatile constituents than do older releases that may be more weathered and depleted in the more volatile constituents.
In addition to the age of the release, other factors should be considered, such as preferential pathways, the presence of groundwater and its movement, characteristics of the soil column and geology of the site, the amount of contamination and the presence of older contamination, to mention a few.
In summary, does a diesel fuel release pose a vapor intrusion risk? The answer is it depends. To evaluate whether vapor intrusion is a concern at diesel fuel-contaminated sites, it is essential to determine the age of the released diesel fuel, its BTEX component, and its concentrations. Under certain conditions, diesel fuel can pose a vapor intrusion concern.