Monday, November 5, 2007 : 9:20 a.m.

A Forensic Method for Discerning Hydrocarbon Sources During Vapor Intrusion Pathway Investigations

Gina Plantz, Allen D. Uhler, Ph.D., Kevin McCarthy and Stephen Emsbo-Mattingly, NewFields Environmental Forensics Practice LLC

Determining the sources of hydrocarbons in soil gas and indoor and ambient air is an issue at many vapor intrusion sites.  Vapor and air samples collected for chemical characterization at vapor intrusion sites are typically analyzed following EPA Method TO-15.  The BTEX (benzene, toluene, ethylbenzene and xylenes) compounds, among the few petroleum- or tar-derived hydrocarbons included as target analytes in the standard TO-15 method, are commonly used by investigators to determine if hydrocarbons are present in subsurface soils, and to infer the source(s) of such hydrocarbons. Unfortunately, using only BTEX chemicals for identifying specific hydrocarbon sources is problematic because BTEX is present in virtually every type of hydrocarbon product commonly encountered in the subsurface.

 

In order to accurately characterize the nature and type or types of hydrocarbons sources in soil gas, indoor and ambient air, environmental samples must be analyzed using a descriptive method of analysis that employs a more robust target analyte list.   This paper presents a forensic air method (Forensic TO-15) specifically developed to differentiate hydrocarbon sources during VI investigations.  The robust target analyte list includes many paraffin, isoparaffin, aromatic, naphthene, olefin, and heteroatomic hydrocarbon compounds. 

 

Forensic TO-15 has proven to be a critical tool for source characterization.  By having the ability to produce distinct fingerprints for source determination, Forensic TO-15 can allow for a reduced number of samples thereby leading to reduced costs.  The importance and advantages of being able to fingerprint hydrocarbons in the subsurface and ambient air will be discussed and case study data will be presented.

Gina Plantz, NewFields Environmental Forensics Practice LLC GINA PLANTZ is a senior scientist and consultant with NewFields Environmental Forensics Practice in Rockland, MA. She has over 10 years of experience in the field of environmental chemistry where her area of expertise is Vapor Intrusion (VI) pathway analysis, with focus on air chemistry, soil gas analysis and analytical techniques. Ms. Plantz is has participated in the development of several state VI guidance documents and has been an invited speaker many VI conferences and workshops, including the US EPA’s VI training workshops held at the AEHS meetings in 2004-2007.


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Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Detection, and Remediation® Conference