About the Guidance Document:
This ITRC project reviewed, updated, and developed guidance on methods and procedures used for evaluating risk and establishing cleanup requirements at TPH contaminated sites. Much, if not all, of the information required was already published by states and other entities over the past 20 years (e.g., TPH carbon range chemistry and toxicity, methods to develop weighted toxicity factors and screening levels for different fuel types, models, and approaches to develop screening levels for direct exposure, vapor intrusion, drinking water and aquatic toxicity, gross contamination, etc.). The ITRC document is primarily a compilation of the existing information presented in an easy-to-use manner for regulators and consultants. This document also incorporates updated TPH information being collected concurrently by the American Petroleum Institute (API).
Comprehensive guidance on making scientific, risk-based decisions at petroleum-contaminated sites helps states develop guidance to address this common class of contaminants.
The following technical areas and regulatory barriers are addressed by this project:
- • Overview of petroleum fuel and vapor chemistry
- Review of published, TPH carbon range toxicity factors including those that are part of ongoing API review
- Review of methods to develop risk-based, TPH carbon range screening levels for soil, water, and air/vapor (e.g., standard EPA RSL models)
- Review of lab methods for testing of carbon ranges and TPH in soil, water, and air
- Example use of risk-based TPH screening levels for the remediation and long-term management of petroleum-contaminated sites.
- Possible review and consideration of approaches to develop weighted toxicity factors and screening levels for specific petroleum fuels and mixtures;
Complete remediation at petroleum release sites is often infeasible for technical or cost reasons. Many of these sites may be depleted in typical indicator compounds, such as BTEX, but still heavily contaminated in terms of Total Petroleum Hydrocarbons (TPH). In many cases, states have closed such sites with long-term strategies involving institutional control mechanisms (ICs). However, TPH contamination at sites closed with ICs can cause problems associated with future redevelopment of the site when conditions change and contractors are directly exposed to petroleum contamination in soil, groundwater, and vapor containing elevated TPH levels. Some common problems encountered include the following scenarios:
- Concerns of workers over potential health effects from exposure to contaminated soil, water, and vapor
- Fouling of heavy equipment with oil
- The sudden need to store and dispose of large volumes of contaminated soil and/or water
- Need for a redesign of dewatering system due to high levels of dissolved TPH (or TPH-related degradation products) in groundwater, etc., and
- Need to redesign engineering plans to address concerns over potential vapor migration into utility corridors or new buildings.
- Discoloration of soils.
- Odors that may alarm workers and nearby residents.
These problems can lead to work stoppages, temporary losses of jobs, disruptions to small businesses involved in the project, unrepaired roads and utilities, etc., and impose economic hardships on a community. A process that allows a more informed use of TPH data to identify potential problems ahead of time is an important part of the solution.
The traditional single-compound approach of managing petroleum contaminants does not fully identify short- and long-term potential environmental concerns. It also can create delays and cost run ups due to residual petroleum contamination encountered during subsurface utility work or redevelopment. States should utilize a risk-based approach to more effectively incorporate TPH data in addition to traditional BTEX data in cleanup and long-term management decisions.
A 2011, Alaska Department of Environmental Conservation (ADEC) survey of all 50 states and Canada found wide variation in RBCA Tier 1 cleanup approaches using TPH cleanup levels:
- TPH cleanup levels ranged from 50 mg/kg (OK) to 4,100 mg/kg (AZ)
- GRO cleanup levels ranged from 3.1 mg/kg (OH) to 1,500 mg/kg (UT
- DRO cleanup levels ranged from 2.7 mg/kg (OH) to 5,000 mg/kg (UT)
- RRO (ORO) cleanup levels ranged from 99 mg/kg (TX) to 10,000 mg/kg (UT)
Methods and techniques for characterizing the risk of petroleum mixtures were refined during the period 2004 to 2014 using a variety of methods, which lead to a wide range of cleanup values. Better guidance was needed to help states develop a consistent methodology for establishing risk-based cleanup levels and for establishing and approving methods for risk-based corrective actions.