TPH Risk Evaluation at Petroleum-Contaminated Sites

The United States Interstate Technology and Regulatory Council (ITRC) Total Petroleum Hydrocarbons (TPH) Risk Evaluation team has developed this guidance to assist state regulators and practitioners with evaluating risk and establishing cleanup requirements at petroleum release sites. This guidance focuses on factors that are unique to petroleum hydrocarbon releases and builds on other available documents published by the TPH Criteria Working Group (TPHCWG) (1997a1997b1997c1998a1998b1999), ITRC Risk-3 (2015), Massachusetts Department of Environmental Protection (MADEP) (2014), California State Water Board–San Francisco Bay Region (CASWB-SFBR) (2016a), and Texas Commission on Environmental Quality (TCEQ) (2017b).

Risk evaluations for petroleum release sites present complex and unique challenges to site managers, risk assessors, regulators, and other stakeholders. Mischaracterizing risks associated with petroleum contamination can lead to unnecessary cleanups, inappropriate property use limitations, or, most importantly, inadequate protection of human health and ecological receptors. Once released to the environment, petroleum contamination changes over time and space due to natural and anthropogenic weathering processes. Although traditional indicator compounds (e.g., benzene, toluene, ethylbenzene, xylene, and naphthalene [BTEXN]) may be present below levels of concern in impacted media, unidentified petroleum fractions or degradation products (metabolite compounds) could potentially still pose a risk to human health and ecological receptors. Summarizing approaches to evaluate this topic in more detail is one of the primary objectives of this document and it is hoped that this document will assist in further research regarding this subject.

A common assumption at petroleum release sites is that the carcinogenic indicator compounds (e.g., benzene, naphthalene, and, for some regulatory agencies, ethylbenzene and additives such as methyl tertiary-butyl ether [MTBE]) typically drive risk-based decision making rather than other petroleum compounds that may be present. However, very few field-based studies comparing risks posed by individual compounds found in TPH (such as benzene) to risks posed by the broader spectrum of TPH-related compounds have been published (Brewer et al. 2013). Additionally, concentrations of carcinogenic compounds might be reduced to low concentrations relative to other hydrocarbons due to natural attenuation processes. At such sites, the remaining petroleum hydrocarbons and petroleum-related degradation products (e.g., petroleum-related metabolites) can be expected to contribute to the potential human health noncarcinogenic risk at petroleum release sites.

This guidance will improve regulators’ and project managers’ understanding of the unique properties of TPH and provide the tools, techniques, and lessons learned to improve risk characterization and to make better-informed risk management decisions at petroleum-contaminated sites.

To access the guidance document, visit the ITRC website.