ASTM E3248-20

4.1 Understanding the potential emplacement and transport mechanism for NAPL in sediment is an important element of an overall conceptual site model (CSM) that forms a basis for (1) investigating the nature and extent of NAPL, 4.2 This guide is intended to supplement the CSM developed according to the principles outlined in the contaminated sites conceptual site model Guide E1689, the standard guide for developing a CSM for Light Non-Aqueous Phase Liquid (LNAPL) sites Guide E2531, and the Risk-Based Corrective Action (RBCA) Guides E1739 and E2081, by considering conditions for NAPL emplacement and movement (that is, advection) that are unique to a sediment environment. This guide will aid users in understanding the unique and fundamental characteristics of sediment environments that influence the occurrence and behavior of NAPL in sediments. Understanding the sources of NAPL encountered in sediment, the mechanisms for NAPL to become emplaced in sediments, and the site characteristics that influence the advective movement of NAPL within the sediment column will aid in identifying specific data requirements necessary to investigate these conditions and to provide a sound basis for remedy decisions.

4.3 This guide describes the emplacement mechanisms and advective processes, and identifies the relevant information necessary for a technically reliable and comprehensive CSM in support of the investigation and/or remediation of NAPL in sediments. A technically reliable and comprehensive CSM will result in more efficient and consistent investigation of NAPL in sediments (for example, assessment of risks associated with NAPL in sediment, and/or remedy decisions). The key elements in assessing the presence and mobility of NAPL in sediment include (1) the hydrological setting, 4.4 Many contaminants (for example, chlorinated solvents, petroleum products and creosote) enter the subsurface as an immiscible liquid, known as NAPL. NAPLs may flow as a separate phase from water. If the NAPL is denser than water (known as dense non-aqueous phase liquid, or DNAPL), it will sink under the influence of gravity. If the liquid is less dense than water (known as a light nonaqueous phase liquid, or LNAPL), it will float on water.

4.5 This guide provides a logical framework for the initial assessment of NAPL movement in sediment environments. It will help users understand the physical conditions and emplacement mechanisms that influence NAPL movement and aid in prioritizing methods for gathering data to support development of a CSM.

4.6 The user of this guide should review the overall structure and components of this guide before proceeding with use, including:

4.7 This guide provides an overview of the unique characteristics influencing the presence and potential movement of NAPL in aquatic sediment environments. This guide is not intended to provide specific guidance on sediment site investigation, risk assessment, monitoring or remedial action.

1.1 This guide is designed for general application to a wide range of sediment sites where non-aqueous phase liquid (NAPL) is present or suspected to be present. This guide describes multiple emplacement mechanisms that can result in NAPL presence within the sediment stratigraphic profile and how the characteristics of the sediment, aquatic environment, and NAPL properties influence NAPL movement within sediments. This guide provides example conceptual models for NAPL emplacement in sediments in order to establish a common framework that can be used to assess conditions influencing NAPL movement by means of advection.

1.2 This guide supplements methodologies for characterization and remedial efforts performed under international, federal, state and local environmental programs, but does not replace regulatory agency requirements. The users of this guide should review existing information and data available for a sediment site to determine applicable regulatory agency requirements and the most appropriate entry point into and use of this guide.

1.3 ASTM standard guides are not regulations; they are consensus standard guides that may be followed voluntarily to support applicable regulatory requirements. This guide may be used in conjunction with other ASTM guides developed for assessing sediment sites.

1.4 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.

1.5 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.

1.6 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.