Standard Guide for NAPL Mobility and Migration in Sediments – Evaluation Metrics

Importancia y uso:

4.1 Hydrophobic organic liquids (for example, petroleum hydrocarbons, coal tars) may exist in the environment for long periods of time as NAPLs. Standardized guidance and test methods do not exist to assess NAPL movement (both pore-scale mobility and NAPL body-scale migration) in sediment. Literature searches have resulted in a limited body of available and applicable research. Current research has focused on site-specific sediment NAPL movement evaluation approaches.

4.2 Standardized guidance and test methods currently exist for assessing NAPL mobility and migration at upland sites, from organizations such as ASTM International (Guides E2531 and E2856), Interstate Technology and Regulatory Council (2), and the American Petroleum Institute (3, 4). Approaches commonly used in upland sites may or may not be applicable for any given sediment site. This guide provides perspectives on the applicability of various methodologies for specific sediment conditions.

4.3 This guide describes various methodologies that are useful in sediment NAPL movement evaluation, such as laboratory test methods, calculation approaches, and field observation interpretation. The guide then provides frameworks to evaluate the data generated from these methodologies to determine if the NAPL observed in the sediments under in situ conditions exhibits movement of any kind.

4.4 Important exposure pathways in upland sites are usually not applicable to sediment sites. The U.S. Environmental Protection Agency notes, “Contaminants in the biologically active layer of the surface sediment at a site often drive exposure” (5). In aquatic environments, benthic organisms live in the surface sediment to maintain access to oxygenated overlying water. These benthic organisms are at the base of the food chain. If NAPL in subsurface sediment is not migrating, the NAPL will not move into the surface sediment and result in exposure to benthic organisms. NAPL that is stable and only present in subsurface sediment likely does not pose a risk to human or ecological receptors, because there is no completed pathway to exposure if the overlying sediment remains in place (that is, it is not dredged or eroded). With no completed exposure pathway, removal of the NAPL in the subsurface sediment may not be needed during any remedy. Therefore, understanding the potential for movement of NAPL in sediments is a key factor in the management of contaminated sediment sites. Knowledge of NAPL movement is required for developing effective remedial options for NAPL impacted sediments and for long-term management of sediment sites.

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

Section 1

Scope

Section 2

Referenced Documents

Section 3

Terminology

Section 4

Significance and Use

Section 5

NAPL Mobility and Migration Evaluation Framework

Section 6

Tiered and Weight of Evidence NAPL Movement Evaluation Approaches

Section 7

Centrifuge Test Methods

Section 8

Water Drive Test Methods

Section 9

Calculation Methods for Potential Vertical Movement of NAPL

Section 10

Field Observation Methodologies

Section 11

Keywords

Appendix X1

Laboratory Analysis Methods Commonly Used in NAPL Movement Evaluations (non-mandatory)

Appendix X2

Illustrative Examples of Tiered and WOE Approaches to Evaluate NAPL Movement (non-mandatory)

Appendix X3

Case Studies (non-mandatory)

Appendix X4

Additional Information on Centrifuge Testing Technology in NAPL Mobility Testing (non-mandatory)

Appendix X5

Laboratory Handling and Preparation of Sediment Cores (non-mandatory)

Appendix X6

Additional Information on Water Drive Test Methods in NAPL Mobility Testing (non-mandatory)

Appendix X7

NAPL Net Vertical Gradient Calculation Method (non-mandatory)

Appendix X8

NAPL Effective Hydraulic Conductivity Estimation Methods (non-mandatory)

References

 

4.6 Activities described in this guide should be conducted by persons familiar with NAPL-impacted sediment site characterization techniques and sediment remediation science and technology, as well as sediment NAPL mobility and migration assessment protocols and methodologies.

4.7 This guide may be used by various parties involved in sediment programs, including regulatory agencies, project sponsors, environmental consultants, toxicologists, risk assessors, site remediation professionals, environmental contractors, analytical testing laboratories, data validators, data reviewers and users, and other stakeholders, which may include, but are not limited to, owners, buyers, developers, lenders, insurers, government agencies, and community members and groups.

4.8 This guide is not intended to replace or supersede federal, state, local, or international regulatory requirements. Instead, this guide may be used to complement and support such requirements. Any remedial actions taken should meet the regulatory standards for the regulatory entity under which the corrective action is being performed.

4.9 This guide provides a framework based on overarching features and elements that should be customized by the user, based on site-specific conditions, regulatory context, and program objectives for a particular sediment site. This guide should not be used alone as a prescriptive checklist.

4.10 Assessment of NAPL movement in sediments is an evolving science. This guide provides a systematic, yet flexible, 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 line of evidence (LOE) approaches, and unforeseen circumstances.

4.11 Use of this guide supports multiple LOE approaches, using tiered or WOE evaluation frameworks, for the evaluation of NAPL movement in sediments.

4.12 Use of this guide is consistent with the sediment risk-based corrective action (RBCA) process that guides the user to obtain the appropriate data; acquire and evaluate additional data; and refine goals, objectives, receptors, exposure pathways, and the CSM. As the sediment RBCA process proceeds, data and conclusions reached at each step of the process help focus subsequent evaluation. This integrative process results in efficient, cost-effective decision-making and timely, appropriate response actions for NAPL-impacted sediments.

Subcomité:

E50.04

Referida por:

E3382-24, E3281-21A, E3163-24

Volúmen:

11.05

Número ICS:

13.080.01 (Soil quality and pedology in general)

Palabras clave:

centrifuge testing; contaminated sediments; migration; mobility; NAPL; permeameter testing; sediment; sediment corrective action;