An Important 2nd-Look at the Reported Concentrations of Indoor Air Total Petroleum Hydrocarbon

Environmental Forensics
Oral Presentation

Prepared by

Contact Information:; 713-372-2190


When indoor air (IA) samples are taken to evaluate potential vapor intrusion risk at petroleum-impacted sites, many states require analysis of total petroleum hydrocarbon (TPH) or air-phase petroleum hydrocarbon (APH) fractions. Then the lab reported TPH/APH concentrations are compared against the generic screening levels. There are two potential problems with the lumpsum TPH/APH fraction concentrations: 1) Some chemicals reported as part of the TPH or APH fractions may not be related to subsurface petroleum impacts but are sourced from common IA sources; 2) Some chemicals reported as part of the TPH or APH fractions can be non-petroleum hydrocarbons compounds. Given the screening levels of IA TPH and/or APH fractions are usually very conservative, if non-petroleum compounds are counted into the lumpsum of TPH/APH fraction, a subject site can be kept open for a long time due to those erroneously reported TPH/APH fraction concentrations.
Air phase TPH or APH fractions are usually analyzed by EPA Method TO-15 which cannot discern the source of IA or APH easily. In this case study, a former retail site in Massachusetts has been kept open for a long time partially due to the reported concentrations of APH fractions have been over the stringent state IA VI screening levels. Recently, a detailed examination was performed with the level-IV TO-15 data report from this site. It was found that three out of the four IA samples contained non-petroleum hydrocarbons compounds (such as 1,2-dichloroethane and isopropanol, which are commons solvents) but included in the reported APH fractions. Those identified non-petroleum hydrocarbon compounds are usually found in household consumer products. After the removal of all the non-petroleum hydrocarbon compounds, the actual IA sample APH fraction concentrations dropped below the state IA VI screening levels. Due to the ubiquitous usage of petroleum hydrocarbons in consumer products, it is also not clear if the petroleum hydrocarbon compounds in the actual APH fraction concentrations are linked to the subsurface contamination or simply due to the IA background.
This case study has demonstrated 1) it is important to recognize the contribution of background IA sources to the detected TPH/APH fractions; 2) it is important to only report the site-relevant IA TPH/APH values; 3) if the reported data is over the regulatory limits, recommend to perform a close look on the composition of the detected TPH/APH fractions. 4) It would be ideal to develop an additional step in air sample collection or some other APH fraction analysis method that can at least eliminate the non-petroleum fractions.