1.1 This guide is a framework to facilitate moving petroleum underground storage tank (UST) release sites to closure in a manner protective of human and ecological receptors. Alternative ways to assess and address the potential for exposure to human and ecological receptors resulting from petroleum UST releases to support closure decisions are presented. Guidance is provided on navigating the closure decision-making process to achieve closure, continue the existing corrective action program, or rethink and rescope the corrective action. Alternative closure criteria are presented for contamination that is present as light nonaqueous phase liquid (LNAPL), groundwater, soil, and soil gas that can be used to document current and reasonably anticipated future threats to receptors and, ultimately, facilitate site closure. Decisions on site closure should factor in these technical criteria along with legal/regulatory concerns and other requirements, such as institutional controls. In addition, best practices for overcoming nontechnical barriers, such as nonresponsive owners and funding limitations are presented.

1.2 This guide provides best practices based on the latest scientific understanding and builds upon risk-based and sustainability principles.

1.3 This framework includes rationale for closing sites under conditions presenting a low threat to current and reasonably anticipated future receptors from releases. This approach provides for closure when the remaining portion of the release is stable or decreasing and allows for current and reasonably anticipated future uses.

1.4 In this guide, the time frame for the complete degradation of petroleum releases by natural degradation is not addressed. Accurate prediction of LNAPL depletion is not possible with today's science. While we are unable to predict the time period to full depletion, in some cases, it may be possible to predict the degradation of individual components of interest, but in this guide, this type of prediction is not addressed.

1.5 This guide is applicable to petroleum products expected at petroleum UST sites and may not be fully applicable to other hydrocarbons such as heavy crude oils or LNAPL derived from coal tar.

1.6 In this guide, methods for estimating the volume or mass of contaminants in the ground are not provided. Such estimates are difficult to make accurately, although high-resolution site characterization methods can improve estimates of the quantity of contaminants. Such estimates could help frame remediation times and possible outcomes of different remediation technologies, although they have little bearing on the methods of determining the potential for exposure or threat from a release described in this guide. Some of the models and tools referenced in this guide include methods for estimating the volume or mass of contaminants; however, LNAPL and contaminant volume estimation methods should be used with caution because of geologic and LNAPL complexity and field conditions that do not align with model assumptions.

1.7 The framework presented in this guide is not exhaustive and may not provide a closure approach suitable for every petroleum release site. Conversely, not all the tools outlined in this framework need be applied to obtain closure at the site [for example, it may be possible to obtain closure at a site without the use of institutional controls (ICs)].

1.8 The framework presented in this guide is applicable to chemical(s) of concern (COCs)commonly associated with current and historical UST petroleum releases, including gasoline and diesel fuel constituents and fuel additives (such as oxygenates and halogenated lead scavengers in leaded motor fuel). The information provided in this framework may also be applicable to petroleum releases regulated under other regulatory programs, but they are not specifically addressed in this guide.

1.9 This guide is intended to complement (but not supersede) local, state, tribal, federal, and international regulations and guidance. At certain sites, local, state, tribal, federal, or international, regulatory agency approval may also be required to implement the approaches outlined in this guide.

1.10 The framework presented in this guide is intended to complement petroleum corrective action processes including risk-based corrective action (RBCA), such as outlined in Guide . If a petroleum UST release was previously evaluated using the RBCA framework and the corrective action has not reached closure, in this guide alternative approaches to evaluate the threat posed by the petroleum release are provided.

1.11 This guide does not require the user to implement a risk-based corrective action or analysis before implementing the moving sites to closure (MStC) approach nor does it supersede or replace existing RBCA or other corrective action. The framework presented in this guide is applicable to petroleum UST releases regardless of the cleanup goals or the corrective action process used to develop them.

1.12 A variety of standards and guidelines exist that help the user develop a cleanup level for each COC and select remedial options for application in a corrective action program. In addition, most regulatory programs publish target cleanup levels.

1.13 The alternative regulatory closure criteria described in this guide include both qualitative criteria (such as, certain indicators of plume stability) and quantitative criteria (such as numerical concentrations for specific COCs).

1.14 Units—The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.15 In this guide, continued ongoing releases, worsening environmental conditions, and imminently hazardous or emergency conditions are not addressed.

1.16 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.17 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.