Traditional analytical methods were focused on providing a quantitative total (i.e. TPH) with little to no qualitative information. There was also quantitative uncertainty in that the concentrations reported were dependent on the method used and the calibration. For example, potentially dramatically different TPH concentrations would be expected for the same sample analyzed by GC-FID but quantitated using differing n-alkane ranges and calibrated against differing alkane references or as fuel oil #2, as motor oil, etc. For those of you in the business a long time, any agreement between any of the GC-FID analyses mentioned above and the obsolete TPH-IR Method 418.1 would be purely dependent on chance. Given it’s shortcomings, it’s hard to believe that this 418.1 TPH method was the “go to” petroleum method of the 1990’s and that there was not a definitive US EPA GC-FID method that addressed carbon range, calibration standards, etc. until Method 8015B was introduced later on in 1996.
For risk assessment, you still need to know “what” is present. Qualitative information was typically provided on a number of different levels. The TPH could be identified as a particular petroleum product by a cursory “fingerprinting” approach with limited success and limited exposure criteria based on product. The TPH present could also be identified in terms of its n-alkane hydrocarbon range and could also be further broken out into a lower molecular weight, purge able fraction (GRO) and a higher molecular weight, extractable fraction (DRO). This information could be used as long as there was corresponding health standards to compare them to. Another approach to obtaining qualitative information that could be used for risk assessment involves the identification of specific, individual constituents such as BTEX or PAHs that can be individually identified and for which applicable exposure criteria exists.
What was, and still is needed is a comprehensive risk based corrective action (RBCA) approach to petroleum contaminated sites where the analytical methods generate definitive qualitative and quantitative data for which the applicable risk criteria has been established. This has already been done on the state level. Massachusetts, using concepts discussed by the API TPH working group, developed the volatile petroleum hydrocarbon (VPH) and extractable petroleum hydrocarbon (EPH) analytical methods. These analytical methods separate the TPH present into aliphatic and aromatic fractions and then further characterize those fractions in terms of specific hydrocarbon ranges. BTEX (VPH) and PAH (EPH) compound specific data is also determined. Significantly, cleanup standards were promulgated for each TPH category defined by the method. These methods are not perfect, but they are protective and readily facilitate the RBCA approach. Since their introduction, several other states have either adopted this approach or modified it for their own needs.
While this approach works for the states where they are utilized, there is a significant lack of consistency at the national level. This lack of consistency is not only in terms of the methodology and the TPH fraction/range data they generate, but also in the wide variation in exposure criteria, for the same compound or TPH fraction/range, on a state to state basis.
To work towards a national consensus on how to evaluate health risk from petroleum Hydrocarbons. The ITRC (http://www.itrcweb.org/Team/Public?teamID=76) has formed a TPH risk Team to develop consensus guidance on petroleum site assessment. Alpha is on the Team.
We encourage you to engage in a discussion by responding to the following questions and as always if you have other questions on this topic or comments please feel free to include them as well.
What issues have you seen in using hydrocarbon data to evaluate risk?
What kind of information would help your next petroleum hydrocarbon risk assessment?
What would you look for from regulators?
Or is it State guidance, more information on field sampling, consistent guidance on how to perform risk investigation?