ASTM E3248-20

Standard Guide for NAPL Mobility and Migration in Sediment – Conceptual Models for Emplacement and Advection

SIGNIFICANCE AND USE
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, (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 to regulators and other stakeholders has been historically hampered by the lack of standardized terminology and characterization protocols. The complexity of NAPL movement in sediment, and the lack of agreed upon methods for analysis and interpretation of site data, has led to uncertainty in corrective action decision-making. This has sometimes resulted in misleading expectations about remedial outcomes. The emplacement and transport mechanisms for NAPL in sediments are different from those in upland environments, due to a variety of physical, geochemical, and biological differences between sediment and upland environments, thus necessitating this guide.  
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 inv...
SCOPE
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 Develo...

General Information

• Status: Published
• Publication Date: 31-Mar-2020
• ICS: 13.080.01 - Soil quality and pedology in general
• Technical Committee: E50 - Environmental Assessment, Risk Management and Corrective Action
• Drafting Committee: E50.04 - Corrective Action

Relations

• Refers: ASTM E3163-18 - Standard Guide for Selection and Application of Analytical Methods and Procedures Used during Sediment Corrective Action
• Effective Date: 01-Sep-2018
• Refers: ASTM E1739-95(2015) - Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites (Withdrawn 2024)
• Effective Date: 01-Apr-2015
• Refers: ASTM E1739-95(2010)e1 - Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites
• Effective Date: 01-Sep-2010
• Refers: ASTM E2081-00(2010)e1 - Standard Guide for Risk-Based Corrective Action
• Effective Date: 01-Sep-2010
• Refers: ASTM E1689-95(2008) - Standard Guide for Developing Conceptual Site Models for Contaminated Sites
• Effective Date: 01-Feb-2008
• Refers: ASTM E2081-00(2004)e1 - Standard Guide for Risk-Based Corrective Action
• Effective Date: 01-Oct-2004
• Refers: ASTM E2081-00 - Standard Guide for Risk-Based Corrective Action
• Effective Date: 10-Apr-2000
• Refers: ASTM E1739-95(2002) - Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites
• Effective Date: 10-Sep-1995
• Refers: ASTM E1739-95e1 - Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites
• Effective Date: 01-Jan-1995
• Referred By: ASTM E3282-22 - Standard Guide for NAPL Mobility and Migration in Sediments – Evaluation Metrics
• Effective Date: 01-Apr-2020
• Referred By: ASTM E2020-22 - Standard Guide for Data and Information Options for Conducting an Ecological Risk Assessment at Contaminated Sites
• Effective Date: 01-Apr-2020
• Referred By: ASTM E2205/E2205M-22 - Standard Guide for Risk-Based Corrective Action for Protection of Ecological Resources
• Effective Date: 01-Apr-2020
• Referred By: ASTM E3281-21a - Standard Guide for NAPL Mobility and Migration in Sediments – Screening Process to Categorize Samples for Laboratory NAPL Mobility Testing
• Effective Date: 01-Apr-2020
• Referred By: ASTM E2081-22 - Standard Guide for Risk-Based Corrective Action
• Effective Date: 01-Apr-2020
• Referred By: ASTM E3382-23 - Standard Guide for Developing Representative Background Concentrations at Sediment Sites - Framework Overview, Including Conceptual Site Model Considerations
• Effective Date: 01-Apr-2020

Overview

ASTM E3248-20: Standard Guide for NAPL Mobility and Migration in Sediment – Conceptual Models for Emplacement and Advection provides a foundational framework for evaluating non-aqueous phase liquid (NAPL) behavior in sediment environments. Developed by ASTM International, this standard is relevant for a wide range of contaminated sediment sites where NAPL presence and movement are of concern. The guide assists stakeholders in understanding the unique processes influencing NAPL mobility and migration within aquatic sediments, supplementing existing conceptual site models (CSMs) and supporting more effective site assessment and remediation efforts.

Key Topics

• NAPL Emplacement Mechanisms: The guide distinguishes between advective processes (movement driven by hydraulic gradients and NAPL pressure) and depositional mechanisms (such as oil-particle aggregate [OPA] formation and in situ deposited NAPL [IDN] sediments).
• Unique Sediment Properties: It addresses how sediment characteristics-such as porosity, stratigraphy, and hydrological interactions-differ from those in upland soils and influence NAPL transport.
• CSM Integration: ASTM E3248-20 supplements conceptual site models by outlining key components necessary to assess NAPL behavior in sediment, including source characteristics, emplacement history, physical and chemical properties, and the hydrogeological context.
• Terminology Standardization: The standard clarifies critical terms like mobile, immobile, and migrating NAPL, advection, and sediment-specific phenomena, fostering consistent communication among professionals.
• Evaluation Considerations: It identifies factors such as bathymetry, energy of the aquatic environment, salinity, and tidal conditions that can affect NAPL distribution and movement.

Applications

ASTM E3248-20 is intended for use by:

• Environmental Professionals and Consultants: Supports investigation, characterization, and remedial design at contaminated sediment sites by guiding data collection related to NAPL mobility and migration.
• Regulatory Agencies: Facilitates consistent, science-based communication regarding NAPL behavior, enhancing stakeholder engagement and the regulatory review process.
• Project Managers and Remediation Teams: Aids in decision-making for site cleanup by providing a structure for evaluating the likelihood and mechanisms of NAPL migration, crucial for risk assessment and remedy selection.
• Analytical Laboratories: Offers standard terminology and concepts, improving interpretation of sediment sampling and NAPL analysis data.

By using ASTM E3248-20, practitioners can:

• Develop robust, site-specific conceptual models to evaluate the potential for NAPL movement in sediment environments
• Identify key data needs for site assessment, including sediment stratigraphy, NAPL source history, and physical property measurement
• Assess environmental and human exposure risks posed by mobile NAPL in aquatic ecosystems
• Support the selection and design of effective remediation approaches based on NAPL mobility potential

Related Standards

ASTM E3248-20 is designed to supplement a number of other widely-used ASTM standards, including:

• ASTM E1689: Guide for Developing Conceptual Site Models for Contaminated Sites
• ASTM E2531: Guide for Development of Conceptual Site Models and Remediation Strategies for Light Nonaqueous-Phase Liquids Released to the Subsurface
• ASTM E1739 / ASTM E2081: Guides for Risk-Based Corrective Action (RBCA)
• ASTM E3163: Guide for Selection and Application of Analytical Methods and Procedures Used during Sediment Corrective Action

Together, these standards enable comprehensive environmental site assessment and management by promoting standardized, technically-sound approaches to NAPL assessment in both upland and sediment environments.

Keywords: ASTM E3248-20, NAPL mobility, NAPL migration, sediment conceptual site model, NAPL emplacement, advective transport, contaminated sediment, sediment remediation, environmental site assessment

Standards Content (Sample)

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.
Designation: E3248 − 20
Standard Guide for
NAPL Mobility and Migration in Sediment – Conceptual
Models for Emplacement and Advection
This standard is issued under the fixed designation E3248; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This guide is designed for general application to a wide
mendations issued by the World Trade Organization Technical
range of sediment sites where non-aqueous phase liquid
Barriers to Trade (TBT) Committee.
(NAPL) is present or suspected to be present. This guide
describes multiple emplacement mechanisms that can result in
2. Referenced Documents
NAPL presence within the sediment stratigraphic profile and
2.1 ASTM Standards:
how the characteristics of the sediment, aquatic environment,
and NAPL properties influence NAPL movement within sedi- E1689 Guide for Developing Conceptual Site Models for
Contaminated Sites
ments. This guide provides example conceptual models for
NAPL emplacement in sediments in order to establish a E1739 Guide for Risk-Based Corrective Action Applied at
Petroleum Release Sites
common framework that can be used to assess conditions
influencing NAPL movement by means of advection. E2081 Guide for Risk-Based Corrective Action
E2531 Guide for Development of Conceptual Site Models
1.2 This guide supplements methodologies for characteriza-
and Remediation Strategies for Light Nonaqueous-Phase
tion and remedial efforts performed under international,
Liquids Released to the Subsurface
federal, state and local environmental programs, but does not
E3163 Guide for Selection and Application of Analytical
replaceregulatoryagencyrequirements.Theusersofthisguide
Methods and Procedures Used during Sediment Correc-
should review existing information and data available for a
tive Action
sediment site to determine applicable regulatory agency re-
quirementsandthemostappropriateentrypointintoanduseof
3. Terminology
this guide.
3.1 Definitions of Terms Specific to This Standard:
1.3 ASTM standard guides are not regulations; they are
3.1.1 immobile NAPL—NAPL that does not move by ad-
consensus standard guides that may be followed voluntarily to
vectionwithintheconnectedvoidspacesofthesedimentunder
support applicable regulatory requirements. This guide may be
specified physical and chemical conditions, as may be demon-
used in conjunction with other ASTM guides developed for
strated by laboratory testing, or may be interpreted based on
assessing sediment sites.
mathematical calculations or modeling.
1.4 Units—The values stated in SI units are to be regarded
3.1.2 in situ deposited NAPL (IDN) sediments—NAPL-
as the standard. No other units of measurement are included in
containing sediment resulting from the deposition of Oil-
this standard.
Particle Aggregates (OPAs).
1.5 This standard does not purport to address all of the
3.1.3 migrating NAPL—NAPL that can move at the NAPL
safety concerns, if any, associated with its use. It is the
body scale, such that the NAPL body may advectively expand
responsibility of the user of this standard to establish appro-
in at least one direction under observed or reasonably antici-
priate safety, health, and environmental practices and deter-
pated field conditions.
mine the applicability of regulatory limitations prior to use.
3.1.4 mobile NAPL—NAPL that may move by advection
1.6 This international standard was developed in accor-
withintheconnectedvoidspacesofthesedimentunderspecific
dance with internationally recognized principles on standard-
physical and chemical conditions, as may be demonstrated by
ThisguideisunderthejurisdictionofASTMCommitteeE50onEnvironmental
Assessment, Risk Management and Corrective Action and is the direct responsibil- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ity of Subcommittee E50.04 on Corrective Action. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Current edition approved April 1, 2020. Published June 2020. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
E3248–20. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3248 − 20
laboratory testing, or as may be interpreted based on math- differentfromthoseinuplandenvironments,duetoavarietyof
ematical calculations or modeling. physical, geochemical, and biological differences between
sediment and upland environments, thus necessitating this
3.1.5 NAPL—Chemicals that are insoluble or only slightly
guide.
soluble in water that exist as a separate liquid phase in
environmental media.
4.2 This guide is intended to supplement the CSM devel-
3.1.5.1 Discussion—NAPL may be less dense than water
oped according to the principles outlined in the contaminated
(Light Non-Aqueous Phase Liquid [LNAPL]) or more dense
sites conceptual site model Guide E1689, the standard guide
than water (Dense Non-Aqueous Phase Liquid [DNAPL]).
for developing a CSM for Light Non-Aqueous Phase Liquid
(LNAPL) sites Guide E2531, and the Risk-Based Corrective
3.1.6 NAPL advection—the process of NAPL movement in
Action (RBCA) Guides E1739 and E2081, by considering
the subsurface due to pressure and gravitational forces.
conditions for NAPL emplacement and movement (that is,
3.1.7 NAPL body—Sediment where the NAPL present ex-
advection) that are unique to a sediment environment. This
hibits movement.
guide will aid users in understanding the unique and funda-
3.1.7.1 Discussion—The NAPL is mobile at the pore scale
mental characteristics of sediment environments that influence
and either stable or migrating at the NAPL body scale. The
the occurrence and behavior of NAPL in sediments. Under-
NAPLbody excludes any portion of the NAPLzone where the
standing the sources of NAPL encountered in sediment, the
NAPL is immobile at the pore scale.
mechanisms for NAPL to become emplaced in sediments, and
3.1.8 NAPL emplacement—the process by which NAPL is
the site characteristics that influence the advective movement
set in, or enters, sediment by either advective forces or by in
of NAPL within the sediment column will aid in identifying
situ deposition (IDN) through the water column.
specific data requirements necessary to investigate these con-
3.1.9 NAPL movement—Any process where NAPL exhibits
ditions and to provide a sound basis for remedy decisions.
advective flow at any scale within the sediment; NAPL
4.2.1 Advective transport is the primary NAPL migration
movement includes NAPL mobility at the pore scale and
mechanism that is addressed within this guide.
NAPL migration at the NAPL body scale.
4.2.2 In addition to advective transport, biogenic gas
3.1.10 NAPL zone—sediment where NAPLis present in any bubbles moving through sediments (that is, ebullition) may
also facilitate NAPL migration; however, this process is
state; the NAPL can be mobile or immobile at the pore scale,
or stable or migrating at the NAPL body scale. beyond the scope of this guide.
4.2.3 Processes associated with NAPL movement due to
3.1.11 oil-particle aggregate (OPA)—a particle formed in a
erosion (for example, propwash) are not within the scope of
surface water body resulting from the adherence to an oil
this guide.
droplet by minerals and/or organic material.
4.3 This guide describes the emplacement mechanisms and
3.1.12 pore scale—the scale of the connected void spaces
advective processes, and identifies the relevant information
within the sediment.
necessary for a technically reliable and comprehensive CSM in
3.1.13 sediment—a matrix of pore water and particles in-
support of the investigation and/or remediation of NAPL in
cluding gravel, sand, silt, clay and other natural and anthropo-
sediments.Atechnically reliable and comprehensive CSM will
genic substances that have settled at the bottom of a tidal or
result in more efficient and consistent investigation of NAPLin
non-tidal body of water (E3163).
sediments (for example, assessment of risks associated with
3.1.14 stable NAPL body—NAPL that does not move at the
NAPL in sediment, and/or remedy decisions). The key ele-
body scale, such that the NAPL body will not advectively
ments in assessing the presence and mobility of NAPL in
expand in any direction under observed or reasonably antici-
sediment include (1) the hydrological setting, (2) the physical
pated field conditions.
and chemical characteristics of the sediment, (3) the physical
and chemical characteristics of the NAPL, and (4) the physical
4. Significance and Use
extent of the NAPL zone. The means and methods for
4.1 Understanding the potential emplacement and transport
collecting this information, including evaluating the mobility
mechanism for NAPL in sediment is an important element of
of NAPL in sediments, is not addressed in this guide.
an overall conceptual site model (CSM) that forms a basis for
4.4 Many contaminants (for example, chlorinated solvents,
(1) investigating the nature and extent of NAPL, (2) evaluating
petroleum products and creosote) enter the subsurface as an
if (and how) human and ecological receptors may be exposed
immiscible liquid, known as NAPL. NAPLs may flow as a
to NAPL, and (3) assessing remedial alternatives. In addition,
separate phase from water. If the NAPL is denser than water
demonstrating the potential movement of NAPL in sediments
(known as dense non-aqueous phase liquid, or DNAPL), it will
to regulators and other stakeholders has been historically
sink under the influence of gravity. If the liquid is less dense
hampered by the lack of standardized terminology and char-
than water (known as a light nonaqueous phase liquid, or
acterization protocols. The complexity of NAPL movement in
LNAPL), it will float on water.
sediment,andthelackofagreeduponmethodsforanalysisand
interpretation of site data, has led to uncertainty in corrective 4.5 This guide provides a logical framework for the initial
action decision-making. This has sometimes resulted in mis- assessment of NAPL movement in sediment environments. It
leading expectations about remedial outcomes. The emplace- will help users understand the physical conditions and em-
ment and transport mechanisms for NAPL in sediments are placement mechanisms that influence NAPL movement and
E3248 − 20
aid in prioritizing methods for gathering data to support 4.6.9 Appendix X1 – Emplacement Models: Potential
development of a CSM. NAPLInteractions at SurfaceWater Boundaries and Effects on
NAPL Movement;
4.5.1 The elements of a CSM for NAPL at sediment sites
4.6.10 Appendix X2 – Sedimentary Processes and Ground-
describe the physical and chemical properties of the
water – Surface Water Interactions;
environment, the hydraulic conditions, the source of the
NAPL, the emplacement mechanisms, and the nature and 4.6.11 Appendix X3 – NAPL Movement Terminology.
extent of the NAPL zone. The CSM is a dynamic, evolving
4.7 This guide provides an overview of the unique charac-
model that will change through time as new data are collected
teristics influencing the presence and potential movement of
and evaluated and/or as physical conditions of the site change
NAPL in aquatic sediment environments. This guide is not
due to natural or engineered processes. The goal of the CSM is
intended to provide specific guidance on sediment site
to describe the nature, distribution, and setting of the NAPL in
investigation, risk assessment, monitoring or remedial action.
sufficient detail, so that questions regarding current and poten-
4.7.1 This guide may be used by various parties involved in
tial future risks, longevity, and amenability to remedial action
a sediment site, including regulatory agencies, project
can be adequately addressed.
sponsors, environmental consultants, site remediation
4.5.2 The unique elements for a CSM for a NAPLsediment
professionals, environmental contractors, analytical testing
site (compared to an upland NAPL site) include, but are not
laboratories, data reviewers and users, and other stakeholders.
limited to:
4.7.2 This guide does not replace the need for engaging
(1) Characteristics of the sediment and water body.
competent persons to evaluate NAPL emplacement and move-
(a) Physical characteristics: hydrology (for example,
ment in sediments. Activities necessary to develop a CSM
river currents, tidal conditions), sedimentology (for example,
should be conducted by persons familiar with NAPL impacted
native water body bottom characteristics, deposited sediment
sediment site characterization techniques, physical and chemi-
characteristics, sedimentation rates, erosive forces), and hydro-
cal properties of NAPL in sediments, fate and transport
geology(forexample,groundwater-surfacewaterinteractions).
processes, remediation technologies, and sediment evaluation
(b) Geochemical: for example, redox conditions
protocols. The users of this guide should consider assembling
(c) Biological characteristics: for example, presence of
a team of experienced project professionals with appropriate
benthic community
expertise to scope, plan, and execute sediment NAPL data
(2) Characteristics of the NAPL release(s) including
acquisition activities.
sources, mechanisms, and timing unique to surface water and
sediment that affect the conditions under which the NAPLwas
5. Unique Aspects of Sediment Sites
emplaced in the sediment.
5.1 This section discusses unique aspects of sediment sites
(3) Mechanisms of NAPL emplacement in sediments,
for evaluating NAPL emplacement and NAPL movement in
which include:
sediment, compared to evaluating NAPL emplacement and
(a) Advective transport from upland sources,
movement in upland soil. For the purposes of this section,
(b) Deposition on a competent sediment surface from
sediment is considered a saturated material that is below a
direct releases to surface water, with potential burial by
surface water body and soil is considered a saturated and
sediment deposition (applies to DNAPL only), and
unsaturated material below a ground surface.
(c) Formation and deposition of OPAs, with potential
burial by sediment deposition.
5.2 NAPL may be emplaced within sediments through a
(4) Indicators for the potential presence and extent of
varietyofprocesses,includingadvectionanddeposition.These
NAPL, including observance of seeps, droplets and/or sheens
mechanisms and their effect on NAPLmovement are described
within a water body.
in Section 6. In contrast, the primary mechanism of NAPL
(5) The potential for human and ecological exposures to
emplacement in soil is advection.
NAPL in sediment or by means of NAPL release to overlying
5.2.1 The distribution of NAPL within sediment pores
surface water.
varies based on the processes of emplacement. Depending on
the emplacement mechanism, NAPL may preferentially oc-
4.6 The user of this guide should review the overall struc-
cupy either the larger pores or the smaller pores in sediment. In
ture and components of this guide before proceeding with use,
contrast, since NAPL emplacement in upland soil tends to be
including:
through one mechanism (advection), the general distribution of
4.6.1 Section 1 – Scope;
NAPL within soil pores tends to be similar from site to site –
4.6.2 Section 2 – Referenced Documents;
thatis,NAPLinuplandsoiltypicallyoccupiesthelargerpores.
4.6.3 Section 3 – Terminology;
Differences in the NAPL distribution within the sediment pore
4.6.4 Section 4 – Significance and Use;
network and stratigraphic sequence affect the potential move-
ment of NAPL.
4.6.5 Section 5 – Unique Aspects of Sediment Sites;
4.6.6 Section 6 – NAPL Emplacement Mechanisms;
5.3 The key differences in NAPL movement in sediment
4.6.7 Section 7 – NAPL Movement Decision Analysis compared to soil are summarized below.
Framework;
5.3.1 Vertical hydraulic gradients and upward NAPLmigra-
4.6.8 Section 8 – Keywords; tion to the sediment surface and the surface water are typically
E3248 − 20
of primary interest for NAPL movement evaluations in sedi- 5.3.6 SurfacewaterbodiesmayhavemoresourcesofNAPL
ment. Conversely, horizontal gradients and lateral NAPL than upland sites. Each type of NAPL has unique physical
migration are often the primary focus of NAPL movement properties that affect NAPL movement. Thus, sediment may
assessments in soil. have more variability in NAPL physical properties and poten-
5.3.2 In sediment, there is often a short vertical distance tial for NAPL movement than soil.
between the NAPL and potential receptors. In soil, the vertical 5.3.7 Surface water bodies can be dynamic environments
distance between the NAPL and receptors is typically much with erosion and deposition. Combined with the focus on
greater. vertical NAPLmigration, as described in 5.2.1, these processes
5.3.3 Sediment lithology tends to vary more vertically than can affect NAPLmovement. For example, erosion may expose
horizontally over the same distance.As a result, upward NAPL sediments containing NAPL, enabling NAPL migration into
migration may encounter multiple lithologic layers with sig- the surface water. Conversely, surface sediment containing
nificant differences in pore size and pore entry pressure. In NAPLmay be buried under depositing sediment, eliminating a
contrast, horizontal NAPL migration may encounter similar potential NAPLmigration pathway. In contrast, soil tends to be
lithology with less variability in pore size and pore entry a more static system, with negligible erosion or deposition.
pressure.As vertical NAPLmovement is of primary interest in 5.3.8 NAPL emplacement and movement mechanisms in
sediment, there tends to be more vertical variability in sediment may differ significantly from upland sites. These
lithology, pore size, and pore entry pressure in sediment concepts are discussed in greater detail in the following
compared to a similar horizontal distance in soil. sections and Appendix X1.
5.3.4 Surface water elevations may fluctuate more fre-
6. NAPL Emplacement Mechanisms
quently than groundwater elevations. Some common causes of
fluctuating surface water elevations are tides, precipitation, and 6.1 Considerations for Developing NAPL Emplacement
anthropogenically controlled water elevation (for example, Conceptual Site Models:
dams). Fluctuating surface water elevations can produce vary- 6.1.1 Site Conditions—Many physical and chemical condi-
ing hydraulic gradients in strength and direction. The fluctuat- tions influence the potential for NAPL movement. These
ing hydraulic gradient may affect NAPL movement in sedi- conditions may be spatially variable and temporally limited.
ment. In contrast, groundwater elevations typically fluctuate The relative importance of each site condition is site depen-
more slowly than surface water elevations do, resulting in less dent. As such, characterization programs should consider each
variability in NAPL movement in soil. condition to determine their relative importance to NAPL
5.3.5 Sediments typically have higher porosity than soil. movement. These components are briefly described below, and
With higher porosity, a given volume of NAPL in sediment their significance with respect to NAPL emplacement is
pore spaces has a lower NAPL saturation and may have less outlined in Tables 1-4.
continuity and mobility. In contrast, the same volume of NAPL 6.1.1.1 Bathymetry / Topography—The bathymetry influ-
in lower porosity soil would have a higher NAPL saturation ences the movement of DNAPL along the sediment-water
and possibly higher mobility. interface. After accumulating at the sediment interface, the
TABLE 1 NAPL Emplacement Conceptual Model Components
CONCEPTUAL MODEL ADVECTIVE EMPLACEMENT OPA DEPOSITION / IDN SEDIMENT SURFACE FLOW ON SEDIMENT
COMPONENTS SURFACE
Site Conditions
Bathymetry / Topography . . X
Energy of the Environment (erosion, . X X
deposition, settings)
Saline / Fresh Water Quality . X .
Groundwater Elevation X . .
Surface Water Elevation X . .
Tidal Conditions X . .
NAPL Conditions
Source of NAPL X X X
NAPL Source History X X X
NAPL Distribution Relative to Source X X X
NAPL Lateral Distribution in XXX
Sediments
NAPL Vertical Distribution / Depth in XXX
Sediments
NAPL Physical Properties (density, XXX
viscosity, etc.)
Sediment Conditions
Sediment Texture / Particle Size X X X
Sediment Hydraulic Conductivity X . .
Sediment Stratigraphy X X X
NAPL-Stratigraphic Correlation X X X
“.” = Not Applicable to emplacement conceptual model
E3248 − 20
TABLE 2 NAPL Emplacement Conditions: Advective Emplacement
ADVECTIVE EMPLACEMENT
Site Conditions
Bathymetry / Topography .
Energy of the Environment (erosion, deposition, settings) .
Saline / Fresh Water Quality .
Groundwater Elevation Location of LNAPL
Surface Water Elevation Location of Potential Seep
Tidal Conditions Thickness of Smear Zone
NAPL Conditions
Source of NAPL LNAPL / DNAPL Source
NAPL Source History Active or Terminated
NAPL Distribution Relative to Source Connected to Source
NAPL Lateral Distribution in Sediments Proximal to Shoreline
NAPL Vertical Distribution / Depth in Sediments At Depth - Upward Movement
NAPL Physical Properties Controls Emplacement / Velocity
Sediment Conditions
Sediment Texture / Particle Size Important to Migration Potential
Sediment Hydraulic Conductivity Important to Migration Potential
Sediment Stratigraphy NAPL Emplaced after Strata
NAPL-Stratigraphic Correlation Potentially Cutting Across Strata
“.” = Not Applicable to emplacement conceptual model
TABLE 3 NAPL Emplacement Conditions: OPA Deposition and IDN Sediment Formation
OPA DEPOSITION / IDN SEDIMENT
Site Conditions
Bathymetry / Topography .
Energy of the Environment (erosion, deposition, settings) Deposition Required
Saline / Fresh Water Quality Influences OPA Formation
Groundwater Elevation .
Surface Water Elevation .
Tidal Conditions .
NAPL Conditions
Source of NAPL LNAPL Source
NAPL Source History Active or Terminated
NAPL Distribution Relative to Source Disconnected
NAPL Lateral Distribution in Sediments Potentially Large Footprint
NAPL Vertical Distribution / Depth in Sediments Generally thin, shallow depths
NAPL Physical Properties <1.0 g/cm
Sediment Conditions
Sediment Texture / Particle Size Effects Encapsulation
Sediment Hydraulic Conductivity .
Sediment Stratigraphy NAPL Emplaced with Strata
NAPL-Stratigraphic Correlation Coincident with Strata
“.”= Not Applicable to emplacement conceptual model
DNAPL body will flow due to gravity along the interface emplacement, since LNAPLs typically migrate at the ground-
toward areas of low elevation. water table. When the elevation of the sediment surface is
6.1.1.2 Energy of the Environment (Erosional/Depositional above the groundwater table, such as might occur in a
Setting)—The environmental setting affects the potential pres- depositionalsetting(thatis,pointbars),thenLNAPLmigration
ervation of deposited NAPL. IDN sediments and DNAPL may impact these sediments. Where the groundwater elevation
bodies at the sediment surface will be potentially eroded and occurs above a sediment deposit, LNAPL will discharge
scoured in water bodies characterized by high flow velocities. directly to the surface water to form a sheen and the sediment
As such, the presence of depositionally-emplaced NAPLzones will not be directly affected.
typically reflect low energy, depositional settings. 6.1.1.5 Surface Water Elevation—The elevation of the sur-
6.1.1.3 Saline/Fresh Water Quality—Salinity may affect the face water influences the gradient and potential fluctuations in
interfacial tension (IFT) between the aqueous and NAPL the groundwater. As a result, LNAPL movement into the
phases. Typically, higher salinity will lower IFT and increase sediment is influenced by the interaction of the surface water
the potential for wettability of the NAPL phase. Increasing the and groundwater.ANAPL smear zone will result in proximity
wettability increases the potential for NAPL movement. IFT to the seepage face from LNAPL oscillations that result from
also influences the size of oil droplets that can be generated dynamic surface water fluctuations.
during the formation of an OPA. 6.1.1.6 Tidal Conditions—Dynamic fluctuating water eleva-
6.1.1.4 Groundwater Elevation—The elevation of the tions produce oscillating hydraulic gradients and pressures that
groundwater primarily influences LNAPL advective influence advective NAPL flow. These changing pressure
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TABLE 4 NAPL Emplacement Conditions: Surface Flow on Sediment Surface
SURFACE FLOW on SEDIMENT SURFACE
Site Conditions
Bathymetry / Topography Controls Gradient
Erosional / Depositional Setting Controls Exposure
Saline / Fresh Water Quality .
Groundwater Elevation .
Surface Water Elevation .
Tidal Conditions .
NAPL Conditions
Source of NAPL DNAPL Source
NAPL Source History Active or Terminated
NAPL Distribution Relative to Source Connected to Discharge Location
NAPL Lateral Distribution in Sediments Proximal to Shoreline
NAPL Vertical Distribution / Depth in Sediments At Sediment Interface / Shallow Depth
NAPL Physical Properties >1.0 g/cm / viscosity effects migration
Sediment Conditions
Sediment Texture / Particle Size Particles Incorporated into DNAPL
Sediment Hydraulic Conductivity .
Sediment Stratigraphy NAPL Emplaced with Strata
NAPL-Stratigraphic Correlation Coincident with Strata
“.” = Not Applicable to emplacement conceptual model
conditions may act to reverse hydraulic and/or the NAPL occurs at depth within the sediment, commonly due to vertical
gradients both laterally and vertically. gradient flow across different layers of strata.
6.1.2 NAPL Conditions: 6.1.2.6 NAPL Physical Properties—Density, viscosity, and
6.1.2.1 Source of NAPL—ThesourceoftheNAPLaffectsall interfacial tension are critical properties that influence NAPL
forms of emplacement. How, when, and where the NAPL was emplacement and movement. The density of a NAPL(LNAPL
emplaced are important components to determine, if possible. versus DNAPL) produces different forms of emplacement (that
The source of the NAPL can be quite variable, ranging from is, OPA formation versus DNAPL flow at the sediment
pipe and tank releases occurring at an upgradient facility, to surface). NAPL viscosity influences the movement of NAPL,
direct spills or discharges into the open water body.The source both advective and sediment surface flow. Interfacial tension
of NAPLdirectly affects such emplacement factors as the type, may influence advective wettability, as well as the size of oil
location, and extent of the NAPL zone. droplets in the formation of an OPA.
6.1.2.2 NAPL Source History—Understanding the NAPL 6.1.3 Sediment Conditions:
source history is important in evaluating the distribution, area 6.1.3.1 Sediment Texture / Particle Size—The size of solid
of impact, and longevity of the NAPL movement. Common particles affects many aspects of NAPL emplacement. Advec-
issues to resolve, if possible, are how long was the source tive movement is controlled by the pore size of the sediment,
active, what was the volume and rate of release(s), and when which is directly related to grain size. The larger the pore size
did the source end (or is it ongoing). The aspects of the NAPL (that is, the larger the particle size) the greater the potential for
source history directly affect such emplacement factors as the NAPL movement, since lower pore entry pressures are re-
type, location, and extent of the NAPL zone. quired to evacuate the water-filled void spaces within the
6.1.2.3 NAPL Distribution Relative to Source—The spatial sediment. Particle size also influences the degree of encapsu-
distribution of the NAPL zone relative to the source is an lation in OPA formation. In general, the smaller the particle
important factor in evaluating the emplacement process. size the greater the degree of encapsulation.
Typically, advective and DNAPL surface flow emplacements 6.1.3.2 Sediment Hydraulic Conductivity—The hydraulic
are directly connected to the source. However, IDN sediments conductivity influences advective NAPL emplacement.
resulting from the transport of OPAs within the water column Typically, NAPLwill migrate along the path of least resistance
may be physically separated (sometimes by large distances) (the highest hydraulic conductivity pathways). In contrast, the
from the source. occurrence of NAPL within fine grain sediments is not gener-
6.1.2.4 NAPL Lateral Distribution in Sediments— ally consistent with advection and may be reflective of other
Determining the lateral extent of the NAPL zone aids in emplacement mechanisms (for example, IDN emplacement).
definingtheemplacement mechanism.Advective emplacement 6.1.3.3 Sediment Stratigraphy—Determining the sediment
is commonly located near the upland and is localized to areas stratigraphyprovidesinformationonthethicknessofthestrata,
near the shoreline of the upland source zone. In contrast, an the location of contacts, and the stratigraphic layers that are
IDN NAPL zone may be widespread and extend over many conducive to NAPL movement. The energy of deposition and
hectares. its temporal variability is recorded in the stratigraphic
6.1.2.5 NAPL Vertical Distribution / Depth in Sediment— sequence, so this component is particularly important in
Depositionally-emplaced NAPL bodies form at the sediment- evaluating the emplacement mechanism for depositionally-
water interface and, hence, will be correlative with the sur- emplaced NAPL. Advectively-emplaced NAPL zones are not
rounding strata. In contrast, advectively-emplaced NAPL affected by the depositional environment and are located at
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depth below the sediment-water interface. Additional discus- from LNAPL), the relative density of the NAPL versus the
sion of sedimentary processes and their effect on sediment aqueous phase has a large effect on the distribution of the
stratigraphy is provided in Appendix X2. NAPL in the surface water body and associated sediments. In
6.1.3.4 NAPL-Stratigraphic Correlation—Correlating the contrast to advective emplacement, depositional emplacement
spatial distribution of the NAPL zone with the stratigraphy of NAPL occurs during sediment formation and the NAPL is
provides useful information of the emplacement process. The incorporated as part of the sediment matrix.The distribution of
occurrence of depositionally-emplaced NAPL will be correla- NAPLfrom depositional emplacement is largely influenced by
tivetothestrata,whiletheoccurrenceofadvectively-emplaced the varying densities of the NAPL.
NAPL will commonly not be correlative to the strata. 6.2.4 For an LNAPL to become deposited within the
sediment, the LNAPL, which forms a layer at the water
6.2 Physical Processes of NAPL Emplacement:
surface, must be physically separated into distinct oil beads or
6.2.1 There are two primary physical processes that em-
droplets and dispersed through the water column. Here, solid
place NAPL within sediments: (1) advective flow, and (2)
particles adhere to the LNAPL beads (Fitzpatrick et al., 2015
deposition through the water column (includes both sediment
(1)) . As particles adhere to the oil bead, the density of the
surface flow of DNAPL and formation of IDN sediments from
aggregate (that is, oil and particles) eventually exceeds the
LNAPL). A detailed discussion of emplacement conceptual
density of the aqueous phase. These oil-particle aggregates
models is included in Appendix X1, while a more detailed
(OPAs) then fall through the water column and become
discussion of interactions between groundwater and surface
deposited with the sediment. The resulting OPA-containing
water is included in Appendix X2.
sediment are termed In situ Deposited NAPL (IDN) sediments
6.2.2 The advective flow of NAPL occurs when a continu-
(Johnson et al., 2018a (2)). In contrast, a DNAPL entering a
ous phase of NAPL derived from an upland source has
surface water body (for example, discharge from a pipe) will
sufficientvolumeandporeentrypressuretoenterthesediment.
sink directly through the water column and form a layer at the
In advective flow, the NAPL pressure exceeds the pore entry
sediment surface. The DNAPL may flow along the sediment
pressure of the sediment matrix and displaces the porewater.
interface (due to gravitational forces) forming a DNAPL body
Advective emplacement occurs after sediment formation
directly on the sediment surface. Examples of NAPLemplace-
within the existing sediment pore structure. The distribution of
ment with respect to the relative density of the NAPL are
NAPL may be highly variable depending on hydraulic
illustrated in Fig. 1.
conditions, as well as the NAPL volume and NAPL gradient
6.2.5 The components requiring evaluation in developing
induced by historical releases from upland sources. Example
NAPL emplacement conceptual models are presented in Table
advective emplacement conceptual models are presented for
LNAPL and DNAPL (Fig. 1).
6.2.3 In both depositional emplacement mechanisms (sedi-
The boldface numbers in parentheses refer to a list of references at the end of
ment surface flow of DNAPLand formation of IDN sediments this standard.
FIG. 1 Example NAPL Emplacement Conceptual Models
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1. How emplacement affects NAPL movement is discussed in will have a higher potential for mobility than fully encapsu-
detail in 6.3 and 6.4, as well as Appendix X1. lated LNAPL. Critical elements to be addressed in developing
the conceptual model for IDN sediments are listed in Table 3.
6.3 Advective NAPL Emplacement:
These include the NAPL distribution in the sediment, the
6.3.1 AdvectiveNAPLemplacementresultsfromthemove-
sediment stratigraphy, and the energy of deposition.
ment of a NAPL plume from an upland source to the sediment
and/or surface water body. This emplacement produces a 6.5 NAPL Surface Flow:
6.5.1 NAPL surface flow is produced when a DNAPL is
continuous phase of NAPL within the largest pores of the
sediment matrix. The character of the NAPL distribution is discharged into a surface water body and accumulates on a
competent sediment bed. It is important to note that the
dependent upon many factors, including:
• The NAPL pressure at the time of emplacement; competent sediment surface may lie below a layer of
• The pore size distribution of the sediment; unconsolidated, “fluffy” sediment. As the DNAPL body flows
• The density of the NAPL; across the sediment surface, particles become entrained within
• The geologic conditions between the upland source and the DNAPL matrix. The resulting deposit consists of DNAPL,
the surface water body; with some sediment particles. There is a distinct boundary
• The interfacial tension conditions between the sediment, between the sediment and the DNAPL body. The flow of the
DNAPL will extend from the point of discharge, following the
water and NAPL; and
• The hydrodynamics of the surface water body. slope of the sediment surface. The flow of DNAPL will stop
when it pools, there is no slope and/or the DNAPL source is
6.3.2 In general, advectively-emplaced NAPL will be ob-
served in coarser sediments, such as sands and gravelly sands, depleted. The resultant DNAPL may become covered in
locations where deposition is occurring; but may also be
as these are more permeable and have generally lower pore
entry pressures than finer grain sediments. The area of sedi- eroded in higher energy environments, since the DNAPL
occurs directly on the sediment surface.
ment impacted by NAPL occurs proximal to the groundwater-
surface water boundary and is generally localized to areas near 6.5.2 Surface flow DNAPLemplacement may produce con-
ditions conducive to DNAPL movement. Important compo-
the shoreline of the water body. The sediment impacts are
directly connected to an upland source. nents of the emplacement conceptual model for DNAPL
surface flow sites include the physical properties of the NAPL,
6.3.3 Advective NAPL emplacement may produce condi-
tions conducive to NAPL movement. Critical elements associ- the conditions associated with the source and discharge, and
the orientation of the sediment surface (Table 4).
ated with advectively-emplaced NAPL that require defining in
the conceptual site model include the physical properties of the
6.6 Movement of Emplaced NAPL In Sediment by Advec-
NAPL and sediment, an assessment of the NAPL source, and
tion:
surface-groundwater interactions (Table 2).
6.6.1 In this guide, the term “advection” refers to the bulk
flowofNAPLthroughporespaceswithinsediment.ForNAPL
6.4 OPA Deposition Forming IDN Sediments:
to be capable of advection, it must be present as a continuous
6.4.1 The IDN sediment bed results from the formation of
fluid phase, connected through the pore spaces between solid
OPAs from LNAPL beads and suspended particulates, fol-
particles.Also,forNAPLtomoveintoporespaceswherethere
lowed by deposition of the OPAs through the water column
iscurrentlynoNAPL,theNAPLmustovercometheporeentry
ontothesedimentbedoverlongperiodsoftime.AlthoughIDN
pressure of the sediment matrix; this process depends on the
sediments can range in particle size from clays to sands, finer
sediment physical characteristics, capillary pressure, NAPL-
grained IDNs are more widespread, since these can remain
water interfacial tension, and the surface interactions between
suspended within the water column over larger areas (for
NAPL, water and sediment (wettability). The rate of NAPL
example,manyhectares).ThethicknessoftheIDNsedimentis
advection, if any, depends on the sediment characteristics,
controlled by the nature and longevity of the LNAPL
hydraulic gradient, density-driven gradient, pore fluid
discharge, the concentration and particle size distribution of
saturation, NAPL viscosity, and relative permeability. NAPL
suspended particles in the water column, and the energetics of
advection can be quantified by collecting and using these types
the depositional environment. The IDN sediment resulting
of site-specific data.
from the OPA deposition consists of a collection of discrete
OPAs that form a network of small pores, where oil is either
7. NAPL Movement Decision Analysis Framework
fullyorpartiallyencapsulatedbysolidparticles(Johnsonetal.,
2018b (3)). Results of capillary pressure testing and electron 7.1 Need for a NAPL Emplacement and Movement Evalu-
microscopy suggest the OPA structure is retained upon depo-
ation:
sition. 7.1.1 Characterizing NAPL movement is not necessary at
6.4.2 Allthingsbeingequal,duetothestructureoftheOPA, all contaminated sediment sites. The obvious case where
LNAPL within IDN sediments will be less mobile than when NAPL movement is not a concern is at sites (or portions of
LNAPL is emplaced advectively. In IDN sediments, the larger sites) where NAPL has not been observed during field
LNAPL occurs in the smaller openings of the sediment matrix screening and/or identified based on laboratory analysis of
and may be totally encapsulated by solid particles. For totally sediment samples. Even in cases where NAPL presence is
encapsulated LNAPL, the original OPA structure generally confirmed in sediments, the emplacement conditions largely
inhibits the oil beads from coalescing, which limits the control NAPL movement. As such, determining the operable
potential for NAPL mobility. Partially encapsulated LNAPL emplacement process is an important component of a sound
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conceptual site model in assessing the movement of the NAPL servations of NAPL releases or sheens at the site may indicate
phase. Since laboratory NAPL mobility analyses require spe- NAPL presence. However, at most sites the presence or
cialized sample collection and handling procedures, which can absence of NAPLin sediment must be confirmed by collecting
be expensive and time consuming, it is important that such an sediment samples and performing field screening on these
evaluation only be performed if warranted. Fig. 2 is a flow samples.
chart that provides a technical framework to determine if a 7.1.3 If field screening indicates that NAPLis not present in
NAPL emplacement and movement evaluation is warranted at the sediment, then a NAPL emplacement and movement
a sediment site. evaluation is not warranted. However, if NAPL presence is
7.1.2 The initial step in a NAPL emplacement and move- confirmed, the next step is to delineate the extent of the NAPL
mentevaluationistodeterminewhetherornotNAPLisknown zone. After the NAPL zone has been delineated, at some sites
or suspected to be present. A study of potential current and the decision may be made to remove the NAPL impacted
historic NAPLsources may aid in identifying suspect locations sediments (for example, by means of dredging) – this option
and emplacement mechanisms. Current and/or historical ob- may be the selected if the NAPL zone is small and easy to
FIG. 2 Process to Determine the Need for a NAPL Emplacement and Movement Evaluation
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access for removal activities. If comprehensive removal of the 7.2.2.1 Pore scale mobility evaluations are generally con-
NAPL impacted sediment is the planned remedial option, then ducted through laboratory testing. Laboratory NAPL mobility
a NAPL emplacement and movement evaluation before the
tests can be performed under a variety of applied stresses in an
remedy would be optional. Otherwise, a sediment NAPL
attempt to mobilize NAPL from the sediment. The applied
emplacement and movement evaluation is warranted.
hydraulic pressures during pore scale laboratory NAPL mobil-
ity testing should be equal to, or more conservative than (that
7.2 NAPL Movement Evaluation Framework:
is, greater than) those observed and/or reasonably anticipated
7.2.1 After the decision has been made to perform a NAPL
in the field under natural conditions.
movement evaluation at a contaminated sediment site (or in a
portion of that site), the evaluation should consider assessment
7.2.3 NAPL body scale migration evaluations consider in
of NAPL movement at both the pore (that is, void) and NAPL
situ field conditions (that is, NAPL presence/absence; strati-
bodyscales(Fig.3).AppendixX3providesfurtherinformation
graphic conditions; calculation of horizontal and vertical gra-
on the movement of NAPLat the pore and NAPLbody scales.
dients; and sediment physical property measurements). If
7.2.2 Typically, NAPL movement by means of advection is
mathematical analysis is conducted, then some model param-
first evaluated at the pore scale. Evaluating NAPL mobility at
eter values can be supported from the results of the pore scale
the pore scale requires collecting minimally-disturbed sedi-
mobility tests and/or from additional laboratory analyses (for
ment samples and performing laboratory tests. If NAPL is
example, NAPL fluid properties such as density, viscosity and
determined to be immobile at the pore scale, then no further
interfacial tension; pore entry pressures).
NAPLmovement evaluation is required, because NAPLthat is
notadvectivelymovingattheporescalecannotbemigratingat
8. Keywords
the NAPL body scale (that is, the NAPL must be stable at this
8.1 in situ deposited NAPL (IDN); NAPL; NAPL advec-
scale). If NAPL is determined to be mobile at the pore scale,
then the evaluation must be continued to determine if the tion; NAPL body; NAPL movement; oil-particle aggregate
NAPL body is stable or migrating. (OPA)
NOTE: Each line indicates an evaluation is performed.
FIG. 3 NAPL Movement Evaluation Framework
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APPENDIXES
(Nonmandatory Information)
X1. EMPLACEMENT MODELS: POTENTIAL NAPL INTERACTIONS AT SURFACE WATER BOUNDARIES AND EFFECTS
ON NAPL MOVEMENT
INTRODUCTION
This appendix provides a description of eight different emplacement conditions by which NAPL
discharges may occur to a surface water body and its associated sediments. The models depict how
the conditions of emplacement, as well a
...