Underground Storage Tanks

PIRI's (Partnership in RBCA Implementation) official members include representatives from the major oil companies (i.e., Amoco, BP, Chevron, Exxon, Mobil, and Shell), ASTM, EPA's OUST, and States. The paper presented here represents the points of view of the various PIRI authors and not the companies or states with which they are affiliated. This document is not an EPA document. This document will be updated as changes in technologies and policies require. It is critical that readers check with the implementing agency in their States before acting upon the policies discussed in these papers.

When State regulatory agencies are integrating risk-based corrective action (RBCA) into their UST programs, they may need to reconsider their definition and use of terms such as contaminant, contamination, and contaminated media. Historically, many programs have defined a contaminant as any detection of a chemical in environmental media. To be consistent with the underlying concepts of RBCA, it may be more appropriate to define contaminant in terms of the conditions that pose an unacceptable threat to human health and/or the environment.

Defining Contaminant

In adopting a RBCA program, the acceptance that limited quantities of chemicals of concern (COCs) may remain in environmental media without presenting an unacceptable threat to human health and the environment is fundamental. In other words, the mere presence of a chemical in a medium does not necessarily make that medium contaminated. One of the goals of RBCA is to establish those specific conditions which pose an unacceptable threat to human or environmental receptors. As a starting point for defining the key terminology, the following questions must be addressed:

• What is a chemical of concern (COC) and how does it differ from a contaminant?
• When does the presence of a COC result in contaminated media?
• How does a State agency regulate contaminated media?
• How does one determine which concentration levels of COCs will pose an unacceptable present or future threat to human health or the environment?

Chemical of concern (COC) can be defined by referring to the statutory and regulatory definitions for solid waste, industrial solid waste, municipal solid waste, radioactive waste, hazardous waste, hazardous substance, petroleum substance, and other regulated substances. To define these substances, individual States should look to their own administrative code and/or the Code of Federal Regulations. For petroleum underground storage tanks, the list of COCs should be relatively limited.

A COC becomes a contaminant when the COC occurs at a concentration that poses an unacceptable threat to human health and the environment. The RBCA program will establish that particular concentration limit specific to land use and exposure scenario.

Contaminated media means soil, sediment, groundwater, surface water, or air that contains COCs at levels which exceed human health or environmentally protective levels as determined consistent with the State's RBCA program. Most States regulate contaminated media, that is, specific chemicals as they occur in air, water, soil, and sediment.

Historical Perspective

Historically, it has not been unusual for a State to use contaminant to mean any occurrence of a regulated chemical in soil, sediment, groundwater, surface water, air, or other media above the currently established level of detection. By defaulting to this definition, the State may feel that it is enacting its responsibility for protecting the public; the State cannot provide the regulated community with anything that may be misinterpreted as a permit to pollute or discharge. This definition of contaminant may be perceived to be protective [of human health and the environment], but it has not necessarily resulted in the remediation or removal of more contaminated media or other measurable benefits of reducing human health risks or ecological impacts. The following problems have been identified with a definition based on limit of detection:

• Many chemicals occur at background concentrations in soil, water, or air by their natural occurrence in the environment. Typically, these chemicals are not regarded as contaminants solely because they are detected in the laboratory.
• There is a stigma associated with the words contaminant and contamination, potentially resulting in property devaluation and/or third-party concerns. By defining contamination on the basis of occurrence only, unnecessary concern is generated and this stigma is automatically attached to a property before the potential risks associated with the occurrence of a chemical have been evaluated. This thinking is certainly not consistent with rational risk-based decision-making.
• There are inherent problems with the use of the laboratory levels of detection that will impart much uncertainty to the definition.
• The level of detection for a chemical may be specific to the laboratory method used to analyze for that particular chemical; one chemical can have various detection limits depending on the laboratory method used in that particular State or agency program.
• Detection limits are ever changing with advances in analytical chemistry and availability of better laboratory equipment. In many cases, chemicals can be detected well below background levels.
• The accurate detection of a chemical in a sample can be impeded by the occurrence of other chemicals in the sample (e.g., matrix interference).

Alternatively, the risk-based definition for contaminant takes into account the acceptable level of risk, land-use definitions (i.e., current and reasonable potential future), and exposure scenario (i.e., completed pathways). Inherent in the State-implemented RBCA program will be the demonstration that the regulated chemical is present at a concentration that is deemed to pose an unacceptable risk to human health or the environment and, therefore, is undesirable. A critical change in philosophy as it applies to these definitions might help to eliminate the automatic assignment of the "contamination" stigma to all properties where COCs are detected.

Precedent Setting Programs

There is a precedent in many State and Federal regulatory programs to allow levels of chemicals of concern to remain in environmental media without becoming contaminated media. Most States have accepted this concept in their adoption of MCLs or State drinking water standards and permitted air emissions and surface water discharges. Each State can look to its specific programs for numerous examples of situations when acceptable levels of chemicals in soil, water, or air do not create contaminated media.

Recommendation

Establish the goals of the State-specific RBCA program. Develop definitions that are consistent with the goals as part of the implementation process. Consider existing statutory and regulatory definitions to avoid conflict with existing State regulatory programs.

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