Significance and Use
4.1 Many contaminants, including chlorinated solvents and petroleum products, enter the subsurface in the form of an immiscible liquid, known as a NAPL. 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, (2) evaluating if (and how) human and ecological receptors may be exposed to NAPL, and (3) assessing remedial alternatives. In addition, demonstrating the potential movement of NAPL in sediments is hampered by the lack of standardized terminology and characterization protocols, thus necessitating this guide.
4.1.1 Understanding the presence and movement of NAPL in sediments is complicated by the lack of standardized protocols for characterizing NAPL movement in the diverse range of sediment environments. Literature searches have indicated that there is a limited body of available, applicable research. Current research has focused on site-specific sediment NAPL mobility assessment approaches, but application of common methods or decision-making processes identified across sites were limited.
4.1.2 The movement (or lack of movement) of NAPL in sediments is a key factor in developing protective remedial options for NAPL-impacted sediments and for the long-term management of sediment sites. Typical exposure pathways that are addressed through risk management decisions at upland sites are usually not applicable to sediment sites. Rather, “contaminants in the biologically active layer of the surface sediment at a site often drive exposure” (1)5, because in aquatic environments, benthic organisms live in the surface sediment to maintain access to oxygenated overlying water. NAPL that is present in subsurface sediment below the biologically active layer that is not migrating and has an overlying sediment that is expected to remain in place (that is, is not dredged or eroded) does not pose a risk to human or ecological receptors, because there is no pathway for exposure. Therefore, remediation of the NAPL may not be warranted. Thus, understanding NAPL presence, extent and potential movement is a key factor in managing contaminated sediment sites.
4.2 This guide will aid users in developing the scope and method selection for investigating the presence and characteristics of NAPL in a sediment environment. This guide provides an overview of the sample collection, field screening and sample handling methods for investigating the presence or absence of NAPL, as well as characteristics of NAPL in the sediment environment.
4.2.1 Use of this guide supports a multiple lines of evidence approach to evaluate NAPL movement in sediments.
4.2.2 This guide should be used to support existing decision frameworks for field screening and sample collection for NAPL-impacted sediments.
4.2.3 This guide is not intended to provide specific guidance on sediment site investigation, risk assessment, monitoring or remedial action.
4.3 Assessment of NAPL movement in sediments is an evolving science. This guide provides a systematic, yet flexible, decision framework to accommodate variations in approaches by regulatory agencies and users, based on project objectives, site complexity, unique site features, programmatic and regulatory requirements, newly developed guidance, newly published scientific research, use of alternative scientifically based methods and procedures, changes in regulatory criteria, advances in scientific knowledge and technical capability, multiple lines of evidence approach, and unforeseen circumstances.
4.4 The use of this guide is consistent with the sediment risk-based corrective action (RBCA) process that guides the user to acquire and evaluate appropriate data and use each piece of data to refine goals, objectives, receptors, exposure pathways, and the CSM. As the sediment RBCA process proceeds, data and conclusions reached at each tier help focus subsequent tiered evaluations. This integrated process results in efficient, cost-effective decision-making and timely, appropriate response actions for NAPL-impacted sediments.
4.5 This guide is not intended to replace or supersede federal, state, local, or international regulatory requirements. Users of this guide should confirm the regulatory guidance and requirements for the jurisdiction in which they are working. This guide may be used to complement and support such requirements.
4.5.1 This guide may be used by various parties involved at a sediment site, including regulatory agencies, project sponsors, environmental consultants, site remediation professionals, environmental contractors, analytical testing laboratories, data reviewers and users, and other stakeholders.
4.5.2 This guide does not replace the need for engaging competent persons to evaluate NAPL emplacement and movement in sediments. Activities described in this guide should be conducted by persons familiar with NAPL-impacted sediment site characterization and remediation techniques, as well as sediment NAPL movement assessment protocols. The users of this guide should consider assembling a team of experienced project professionals with appropriate expertise to scope, plan, and execute sediment NAPL data acquisition activities.
4.6 The user of this guide should review the overall structure and components of this guide before proceeding with use, including the following sections:
4.6.1 Section 1: Scope;
4.6.2 Section 2: Referenced Documents;
4.6.3 Section 3: Terminology;
4.6.4 Section 4: Significance and Use;
4.6.5 Section 5: NAPL Mobility Field Investigation Overview;
4.6.6 Section 6: Sediment Sample Collection Procedures;
4.6.7 Section 7: Sediment Sample Field Characterization;
4.6.8 Section 8: Sediment Sample Handling, Storage, and Transport;
4.6.9 Section 9: Field Methods for Determining Hydraulic Conditions;
4.6.10 Section 10: Keywords;
4.6.11 Appendix X1: Additional Sediment Sample Collection Considerations; and
4.6.12 Appendix X2: Case Study.
Scope
1.1 This guide provides considerations to inform sample collection, field screening, and sample handling of sediments impacted with non-aqueous phase liquid (NAPL) to assist in data collection for the evaluation of NAPL movement in sediment. The conditions affecting NAPL emplacement and movement in sediments are significantly different than in upland soils. As such, the framework for the assessment of NAPL movement in upland soils has been determined to have limited applicability for sediments.
1.2 This guide is applicable to sediment sites where the presence or suspected presence of NAPL has been identified. Sediments are the subject media considered in this guide, not surface water or groundwater.
1.3 The goal of this guide is to provide a technical framework for sample collection, field screening, and sample handling activities used to evaluate NAPL conditions, in particular NAPL movement (that is, mobility at the pore scale and migration at the NAPL body scale) in sediments, which can be used to inform the development and selection of remedial options and post-remedial monitoring activities.
1.4 This guide discusses sample collection procedures, including direct methods (that is, core and grab samples) and indirect methods (that is, DART®2, laser-induced florescence, and porewater samplers) for assessing NAPL presence or absence in sediment.
1.5 This guide discusses field characterization procedures for assessment of NAPL-impacted sediments including visual screening, stratification assessment, shake test, ultraviolet (UV) light test, NAPL FLUTe™3, and headspace vapor monitoring.
1.6 This guide discusses considerations to obtain samples representative of in situ conditions. This includes methods used to evaluate sediment integrity, sample retrieval from the sediment bed, core identification, sample storage onboard the vessel, sample retrieval from the coring device, sufficient sample recovery, core cutting techniques, sample removal from the core, and sample freezing/cooling considerations.
1.7 This guide discusses the objectives, approaches, and materials for the storage and transport of NAPL-impacted sediment, focusing on samples taken for laboratory NAPL mobility and geotechnical tests. Considerations include sample packaging and handling, storage temperature, and hold times.
1.8 NAPLs such as fuels, oils, coal tar, and creosote are the primary focus of this guide.
1.9 Units—The values stated in SI or CGS units are to be regarded as the standard. No other units of measurement are included in this standard.
1.10 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.
1.11 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.
