The measurement of total petroleum hydrocarbons (TPH) has been a key measure of site assessment and corrective action at leaking underground fuel tank (LUFT) sites as well as other sites with suspected petroleum contamination. In the past, TPH has been measured by freon-113 extraction followed by infrared spectrophotometry (EPA Method 418) or by gas chromatography with flame ionization detection (Modified EPA Method 8015). For the relatively volatile fraction of gasoline, or TPH-gasoline (TPH-G), samples are analyzed with purge-and-trap GC-FID. This fraction is more accurately called volatile petroleum hydrocarbons (VPH), since the results may or may not include gasoline contamination. For the semi-volatile fraction, e.g., diesel contamination, samples are extracted, usually with methylene chloride, and analyzed by GC-FID (TPH-D); this is similarly more accurately called extractable petroleum hydrocarbons (EPH). The TPH results in water and soil have been used in California and elsewhere to assess contamination and to monitor cleanups.

The advent of Risk-Based Corrective Action (RBCA) may end, or severely limit, the use of TPH for LUFT site assessment. The American Society for Testing and Materials (ASTM) has adopted a standard for the use of RBCA at petroleum sites. The RBCA standard has a tiered approach to site assessment and corrective action. Tier one includes examples of Risk-Based Screening Levels (RBSLs) which are used in the first tier of corrective action.

The RBSL examples include contamination with benzene, ethyl benzene, toluene, xylenes, naphthalenes, and benzo[a]pyrene. The use of TPH measurement in risk assessment is discouraged because “. . . the general measure of TPH provides insufficient information about the individual chemical(s) of concern present (RBCA, p. 9).” The use of RBCA criteria may encourage the use of field tests for aromatics, e.g., the immunoassays which are sensitive to benzene and substituted aromatics. The implementation of the RBCA model has resulted in leaving much higher levels or residual contamination of some petroleum fuels. In fact, TPH may still be used in an RBCA system to ensure that soils saturated with fuels are removed even though other RBCA criteria are not exceeded.

The California SB1764 Committee, in the review of the California LUFT program, received many comments about the limited use of TPH. Complaints about TPH were that the measurement was not risk-based and also could include naturally-occurring organics. Many sites have extractable petroleum hydrocarbons which is arguably due to naturally-occurring organics and not due to the release of petroleum products.

The TPH Criteria Working Group is a national group with diverse representation from industry, the Department of Defense, U.S. Environmental Protection Agency, and state governments. Their approach has been to develop a new scheme of TPH measurements which are risk based and could be used in a RBCA structure. It includes the measurement of individual components plus the fractionation of extractable petroleum hydrocarbons, e.g., with alumina, into aliphatic and aromatic fractions. The fractions are then analyzed by GC-FID and the fraction corresponding to specific carbon ranges are reported. The carbon range results would be compared with the corresponding risk-based criteria.

The movement toward risk-based corrective action will eliminate much of the need for TPH measurements. However, the use of risk-based TPH measurements may resurrect TPH from the dead with a reincarnated mission.

Bart Simmons is the Acting Chief, Hazardous Material Laboratory, Department of Toxic Substances Control, Berkeley, CA.