ASTM E3382-23

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: E3382 − 23
Standard Guide for
Developing Representative Background Concentrations at
Sediment Sites — Framework Overview, Including
Conceptual Site Model Considerations
This standard is issued under the fixed designation E3382; 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 and forensic considerations) and then how to use them to
calculate representative sediment background concentrations.
1.1 This guide provides an overarching framework for the
Relevant content contained in Guides E3163, E3164, E3242,
development of representative sediment background concen-
and E3344 is summarized herein, but the individual guides
trations at contaminated sediment sites. It is intended to inform,
should be consulted for more detailed coverage of these topics.
complement, and support but not supersede the guidelines
established by local, state, tribal, federal, or international 1.4 Representative sediment background concentrations are
agencies. typically used in contaminated sediment corrective actions
performed under various regulatory programs, including the
1.2 Technically defensible representative sediment back-
Comprehensive Environmental Response, Compensation, and
ground concentrations are critical for several purposes (Guide
2 Liability Act (CERCLA). Although many of the references
E3242) (1) . These include sediment site delineation, establish-
cited in this guide are CERCLA oriented, the guide is appli-
ing remedial goals, remedy selection, assessment of risks posed
cable to corrective actions performed under local, state, tribal,
by representative background concentrations, and establishing
federal, and international corrective action programs. However,
appropriate post-remedial monitoring plans.
this guide does not provide a detailed description of the
1.3 As part of the overall framework presented in this guide,
requirements or existing background guidance for each juris-
Guide E3240 provides a general discussion of how Conceptual
diction.
Site Model (CSM) development fits into the risk-based correc-
1.5 This guide would optimally be applied at the start of any
tive action framework for contaminated sediment sites.
sediment corrective action program but can be initiated at other
However, not all elements of a sediment CSM need to be
points in the program as well.
considered when developing representative sediment back-
1.6 This standard does not purport to address all of the
ground concentrations; those that do are discussed in detail in
safety concerns, if any, associated with its use. It is the
Section 7 of this guide.
responsibility of the user of this standard to establish appro-
1.3.1 As additional data are collected and analyzed, the
priate safety, health, and environmental practices and deter-
CSM should be updated as needed.
mine the applicability of regulatory limitations prior to use.
1.3.2 This guide is related to several other guides. Guide
1.7 This international standard was developed in accor-
E3344 describes how to select an appropriate background
dance with internationally recognized principles on standard-
reference area(s). Guide E3164 covers the sampling method-
ization established in the Decision on Principles for the
ologies used in the field to obtain sediment samples (whether
Development of International Standards, Guides and Recom-
from the sediment site or background reference area[s]), and
mendations issued by the World Trade Organization Technical
Guide E3163 discusses appropriate laboratory methodologies
Barriers to Trade (TBT) Committee.
to use for the chemical analysis of potential contaminants of
concern (PCOCs) in sediment samples. Guide E3242 describes
2. Referenced Documents
how to evaluate candidate background data to obtain represen-
2.1 ASTM Standards:
tative background data sets (including statistical, geochemical,
E178 Practice for Dealing With Outlying Observations
E1689 Guide for Developing Conceptual Site Models for
This guide is under the jurisdiction of ASTM Committee E50 on Environmental
Contaminated Sites
Assessment, Risk Management and Corrective Action and is the direct responsibil-
ity of Subcommittee E50.04 on Corrective Action.
Current edition approved May 1, 2023. Published June 2023. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
E3382–23 contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3382 − 23
E2993 Guide for Evaluating Potential Hazard as a Result of the exposure pathways as incomplete, potentially complete, or
Methane in the Vadose Zone complete. (Guide E3242)
E3163 Guide for Selection and Application of Analytical
3.1.7 corrective action, n—the sequence of actions that may
Methods and Procedures Used during Sediment Correc-
include site assessment and investigation, risk assessment,
tive Action
evaluations of potential remedial action alternatives, interim
E3164 Guide for Sediment Corrective Action – Monitoring
remedial action, remedial action, operation and maintenance of
E3240 Guide for Risk-Based Corrective Action for Contami-
the remedy, monitoring of progress, making “No Further
nated Sediment Sites
Action” determinations, and completion of the remedial action.
E3242 Guide for Determination of Representative Sediment
(Guide E3240)
Background Concentrations
3.1.8 ebullition, n—a process of gas (primarily methane)
E3248 Guide for NAPL Mobility and Migration in Sediment
generation in sediments where the quantity of gas generated is
– Conceptual Models for Emplacement and Advection
sufficient for gas bubbles to nucleate, grow, fracture the
E3282 Guide for NAPL Mobility and Migration in Sedi-
sediment, and then escape into the overlying water body.
ments – Evaluation Metrics
3.1.8.1 Discussion—Depending on the composition of a
E3300 Guide for NAPL Mobility and Migration in
particular sediment, the gas bubbles generated and released by
Sediment— Evaluating Ebullition and Associated NAPL/
ebullition may strip constituents out of the sediment and
Contaminant Transport
transport these into the overlying water. (Guide E3300)
E3344 Guide for Selection of Background Reference Areas
for Determination of Representative Sediment Back-
3.1.9 false outlier, n—measurements that are very large or
ground Concentrations
small relative to the rest of the data but represent true extreme
values of a distribution and indicate more variability in the
3. Terminology population than was expected. (Guide E3242)
3.1 Definitions: 3.1.10 natural background, n—naturally occurring sub-
stances present in the environment in forms (and at concentra-
3.1.1 anthropogenic background, n—human-made sub-
tions) that have not been influenced by human activity.
stances present in the environment due to human activities, not
(Guide E3344)
specifically related to current or historical site-related releases
or activities.
3.1.11 non-aqueous phase liquid (NAPL), n—chemicals that
3.1.1.1 Discussion—The definition of “anthropogenic back-
are insoluble or only slightly soluble in water that exist as a
ground” varies with jurisdiction. In some jurisdictions, the
separate liquid phase in environmental media.
regulator defines anthropogenic background as having both
3.1.11.1 Discussion—NAPL may be less dense than water
human-made and naturally occurring components. In this
(light non-aqueous phase liquid [LNAPL]) or more dense than
guide, the definition of anthropogenic background includes
water (dense non-aqueous phase liquid [DNAPL]).
only the human-made component. (Guide E3344)
(Guide E3248)
3.1.2 background reference areas, n—sediment areas that
3.1.12 oil-particle aggregate (OPA), n—a particle formed in
have similar physical, chemical, geological, biological, and
a surface water body resulting from the adherence to (or
land-use characteristics as the site being investigated but are
penetration into) an oil droplet by minerals or organic material.
not affected by site-related releases and/or activities.
(Guide E3282)
(Guide E3242)
3.1.13 outlying observation, n—an extreme observation in
3.1.3 background threshold value (BTV), n—a measure of either direction that appears to deviate markedly in value from
the upper limit of representative background concentrations. other members of the sample in which it appears.
(Guide E3242) (Practice E178)
3.1.4 biogenic, adj—resulting from the activity of living 3.1.14 population, n—in statistics, a comprehensive set of
values consisting of all possible observations or measurements
organisms. (Guide E2993)
of a certain phenomenon from which a sample is to be drawn.
3.1.5 cleanup level, n—the prescribed average or point
(Guide E3242)
sediment concentration of a chemical that shall not be ex-
3.1.15 potential contaminant of concern (PCOC), n—a
ceeded at the remediated site. (Guide E3242)
contaminant whose sediment concentrations at the site may
3.1.6 conceptual site model (CSM), n—the integrated rep-
exceed applicable screening levels; this includes chemicals of
resentation of the physical and environmental context, the
potential environmental concern (COPECs) and chemicals of
complete and potentially complete exposure pathways, and the
potential concern (COPCs). (Guide E3242)
potential fate and transport of potential contaminants of con-
3.1.16 sediment(s), n—a matrix of porewater and particles
cern at a site.
including gravel, sand, silt, clay, and other natural and anthro-
3.1.6.1 Discussion—The CSM should include both the cur-
pogenic substances that have settled at the bottom of a tidal or
rent understanding of the site and an understanding of the
nontidal body of water. (Guide E3163)
potential future conditions and uses for the site. It provides a
method to conduct the exposure pathway evaluation; inventory 3.1.17 sediment site, n—the area(s) defined by the likely
the exposure pathways evaluated; and determine the status of physical distribution of COC(s) from a source area and the
E3382 − 23
adjacent areas required to implement the corrective action. A 3.2.4 high nondetect, n—a nondetect concentration with a
site could be an entire water body or a defined portion of a highly elevated detection limit; for example, a concentration
water body. (Guide E3240) that resides in the upper decile of the analyte’s distribution (that
is, a detection limit above the 90th percentile of the data set).
3.1.18 sheen, n—a silvery, rainbow, or dark rainbow film on
3.2.5 representative background concentrations,
the water surface. (Guide E3300)
n—chemical concentrations that are inclusive of naturally
3.1.19 sheen blossom, n—the emergence of NAPL trans-
occurring sources and anthropogenic sources similar to those
ported by a gas bubble at the water surface followed by
present at a sediment site but not related to current or historical
spreading of NAPL into a sheen at the air-water interface.
site releases or activities.
(Guide E3300)
3.2.6 representative background data set, n—a background
3.1.20 tolerable error rate, n—the specified maximum ac-
data set obtained by evaluating candidate background data
ceptable error rate set by the decision maker. (Guide E3242)
using the steps described in Guide E3242.
3.1.21 true outlier, n—measurements that are very large or 3.2.6.1 Discussion—The evaluation determines if there are
small relative to the rest of the data and are a result of any data points in the candidate background data set that are
transcription errors, data coding errors, or measurement system not representative of sediment site background conditions.
problems, or it is not representative of the investigated data These data points are then removed from the candidate
population as confirmed by other lines of evidence. background data set (using technically justifiable rationale) to
(Guide E3242) obtain a representative background data set, which is then used
to calculate representative background concentrations for the
3.1.22 upper tolerance limit (UTL), n—the value below
sediment site using methodologies described in Guide E3242.
which a specified percentage of observed values falls, with a
specified confidence level. (Guide E3242)
4. Significance and Use
3.1.23 urban runoff, n—a non-point source of contaminants
4.1 Intended Use:
to the water body.
4.1.1 This guide may be used by various parties involved in
3.1.23.1 Discussion—Typically, this is stormwater from city
sediment corrective action programs, including regulatory
streets and adjacent properties that carries contaminants into
agencies, project sponsors, environmental consultants,
receiving waters directly, or indirectly via sewer systems.
toxicologists, risk assessors, site remediation professionals,
(Guide E3344)
environmental contractors, and other stakeholders.
3.2 Definitions of Terms Specific to This Standard:
4.2 Updates to CSM:
4.2.1 The CSM should be updated as needed and refined to
3.2.1 background (aka “reference”), adj—a term applied to
substances, conditions, or locations that are similar to those describe the physical properties, chemical composition and
occurrence, biological features, and environmental conditions
found at a sediment site but not influenced by current or
historical releases or activities from the sediment site; these are of the sediment corrective action project (Guide E1689).
usually a combination of naturally occurring (consistently
4.3 Reference Material:
present in the environment but not influenced by human
4.3.1 This guide should be used in conjunction with other
activity) and anthropogenic (influenced by human activity but
ASTM guides listed in 2.1 (especially Guides E3163, E3164,
not related to specific current or historical releases or activities
E3240, E3242, and E3344), as well as the material in the
at the sediment site) components.
References section (including (1)).
3.2.2 candidate background data set, n—a raw (that is,
4.4 Flexible Site-Specific Implementation:
unprocessed) background data set obtained either by the
4.4.1 This guide provides a systematic but flexible frame-
collection of data from a background reference area(s), or by
work to accommodate variations in approaches by regulatory
the extraction of background data from the sediment site data
agencies and by the user based on project objectives, site
set, or a combination of both.
complexity, unique site features, regulatory requirements,
3.2.2.1 Discussion—The candidate background data set
newly developed guidance, newly published scientific
must first be evaluated using the steps described in Guide
research, changes in regulatory criteria, advances in scientific
E3242 and Section 6 to obtain a representative background
knowledge and technical capability, and unforeseen circum-
data set, which can then be used to calculate representative
stances.
background concentrations for the sediment site.
4.5 Regulatory Frameworks:
3.2.3 contaminant of concern (COC), n—substances identi-
4.5.1 This guide is intended to be applicable to a broad
fied as posing a risk based on a tiered risk assessment and that
range of local, state, tribal, federal, or international
may warrant corrective action.
jurisdictions, each with its own unique regulatory framework.
3.2.3.1 Discussion—Typically, all PCOCs identified for a As such, this guide does not provide a detailed discussion of
sediment site are evaluated in the risk assessment process. the requirements or guidance associated with any of these
PCOCs that have sediment concentrations greater than risk- regulatory frameworks, nor is it intended to supplant applicable
based thresholds identified in the risk assessment process are regulations and guidance. The user of this guide will need to be
defined as COCs. Thus, the COCs identified for a sediment site aware of the regulatory requirements and guidance in the
are a subset of the PCOCs identified for that site. jurisdiction where the work is being performed.
E3382 − 23
4.6 Systematic Project Planning and Scoping Process: 4.7.9 In this guide, “sediment” (3.1.16) is defined as a
matrix being found at the bottom of a water body. Upland soils
4.6.1 When applying this guide, the user should undertake a
of sedimentary origin are excluded from consideration as
systematic project planning and scoping process to collect
sediment in this guide.
information to assist in making site-specific, user-defined
4.7.10 In this guide, only COC concentrations are consid-
decisions for a particular project, including assembling an
ered. Residual background radioactivity is out of scope for this
experienced team of project professionals. These practitioners
guide.
should have the appropriate expertise to scope, plan, and
execute a sediment data acquisition and analysis program. This
4.8 Structure and Components of This Guide: The user of
team may include, but is not limited to, project sponsors,
this guide should review the overall structure and components
environmental consultants, toxicologists, site remediation
of this guide before proceeding with use, including:
professionals, analytical chemists, geochemists, and statisti-
• Section 1 Scope
cians.
• Section 2 Referenced Documents
• Section 3 Terminology
4.7 Other Considerations:
• Section 4 Significance and Use
• Section 5 Overview of Representative Background Concentrations
4.7.1 This guide does not provide a detailed description of
• Section 6 Framework for Developing Representative Background
all topics of a program to derive representative sediment
Concentrations for Sediment Sites
background concentrations. It is meant to be used in conjunc-
• Section 7 Conceptual Site Model Considerations When Developing
Representative Background Concentrations for
tion with other guides (such as Guides E3163, E3164, E3240,
Sediment Sites
E3242, and E3344) to do so.
• Section 8 Keywords
• References
4.7.2 Sediment sampling and laboratory analyses are not
covered in detail in this guide. Guides E3163 and E3164
5. Overview of Representative Background
contain extensive information concerning sediment sampling
Concentrations
and laboratory analysis methodologies.
4.7.3 Data quality objectives are not covered in this guide.
5.1 Importance of Representative Background Concentra-
Data quality objectives are described in (2).
tions:
4.7.4 The selection of a background reference area(s) is not 5.1.1 It has been recognized for more than three decades
covered in detail in this guide but is extensively described in
that establishing a reliable representation of background is of
Guide E3344. key importance at contaminated sediment sites (1, 5, 6). This
4.7.5 Background study design considerations are not cov- guide has been prepared to provide an overarching framework
for the development of representative background concentra-
ered in detail in this guide, but are extensively described in
other references, including Guide E3164 and (3). tions at such sites. Technically defensible, representative back-
ground concentrations are critical in establishing an appropri-
4.7.6 The use of data evaluation methodologies to obtain
ate remedial response and providing realistic cleanup levels.
representative background data sets from candidate back-
ground data sets is not covered in detail in this guide but is
5.2 Representative Background Concentrations—
discussed in more depth in Guide E3242.
Anthropogenic and Natural Contributions:
4.7.6.1 Identification and removal of high nondetect values
5.2.1 Anthropogenic background is defined in 3.1.1 and
from candidate background data sets are discussed in detail in
natural background is defined in 3.1.10.
Guide E3242.
5.2.2 For certain constituents, such as metals, the represen-
4.7.6.2 Identification and removal of outliers from candidate tative background concentrations contain contributions from
background data sets are discussed in detail in Practice E178,
both naturally occurring and anthropogenic background
as well as Guide E3242. sources. For others, such as synthetic chemicals, the represen-
tative background concentrations contain contributions from
4.7.6.3 Geochemical methodologies used in evaluating can-
only anthropogenic background sources.
didate background data sets to obtain representative back-
5.2.3 This guide recognizes ongoing background chemical
ground data sets are discussed in detail in Guide E3242; their
inputs to a sediment site (that are not from current or historical
applications during reference-area selection are discussed in
site releases or activities) from point sources (such as dis-
Guide E3344.
charges from municipal and industrial outfalls) and from
4.7.6.4 Chemical forensics methodologies used in evaluat-
non-point and diffuse watershed-wide sources (such as sedi-
ing candidate background data sets to obtain representative
ment transported from off-site, urban runoff, and atmospheric
background data sets are discussed in detail in Guide E3242;
deposition).
their applications during reference-area selection are discussed
in Guide E3344.
5.3 Determination of Representative Background Concen-
4.7.7 The use of statistical methods to calculate BTVs from
trations:
representative background data sets and to compare such data
5.3.1 For sediment sites, the goal is to derive representative
sets to the site data sets are discussed in detail in Guide E3242.
background concentrations, which are equivalent to anthropo-
4.7.8 Geospatial analysis considerations are not thoroughly genic background for man-made chemicals and the combina-
discussed in this guidance but are discussed in more depth tion of naturally occurring and anthropogenic backgrounds for
relative to environmental evaluations in (4), which focuses on naturally occurring chemicals (such as metals). Technically
quality assurance concerns relative to geospatial analyses. defensible representative sediment background concentrations
E3382 − 23
are typically derived using data collected from a site’s back- sediments may initially meet all chemical concentration-based
ground reference area(s), which is an area(s) similar to the remedial objectives (such as cleanup levels) upon corrective
sediment site but not affected by current or historical site action completion, but they will eventually return to represen-
releases or activities. Representative sediment background tative background concentrations at some time after
concentrations can also be extracted from the sediment site completion, and the cleanup levels will again be exceeded.
data set. Derivation of these representative sediment back-
5.5.1.1 Due to inappropriate cleanup levels based (in part)
ground concentrations is performed using appropriate statisti-
on the selection of unrepresentative background
cal and geochemical evaluation methods (refer to Section 6). concentrations, perceived failure of the corrective action has
5.3.2 At many sediment sites, multiple sources may contrib-
been observed at numerous sediment sites throughout the
ute to the nature and extent of contamination. The largest United States, under both federal and state jurisdiction (8). The
contributor of contamination at sediment sites is typically
framework outlined in this guide is intended to avoid costly
current or historical site releases or activities. However, con- perceived remedy failures due to recontamination (that is,
tamination can also result from natural and ongoing anthropo-
equilibration to representative background sediment concen-
genic sources not related to current or historical site releases or trations) by highlighting approaches to obtain technically
activities.
defensible, representative background concentrations.
5.3.3 Off-site contamination not associated with current or
5.5.2 Attempting to implement corrective actions to achieve
historical sediment site releases or activities is considered a
concentrations less than representative background is not
component of representative background concentrations and
sustainable over the long term and can require considerable
will continue to be a source of contamination to the sediment
expenditures that serve no environmental or public health
site unless all transport pathways onto the sediment site are
purpose. The framework described in this guide, as well as
eliminated. Technically defensible representative background
components of this framework described in more detail in
concentrations account for any background chemical input
Guides E3163, E3164, E3240, E3242, and E3344, is intended
(both natural and anthropogenic) that is expected to continue
to help promote a scientifically sound approach for establishing
migrating onto the sediment site after the completion of
representative background concentrations, leading to correc-
corrective actions.
tive action decisions that avoid costly perceived corrective
5.3.4 An important principle for management of contami-
action failures at sediment sites. Once derived, these represen-
nated sediment sites is control of background sources of
tative background concentrations should ideally remain fixed
contamination, to the greatest extent practicable, prior to
for the duration of the remedial investigation and remedial
initiating corrective actions. However, it is rarely practicable to
response processes. This will help to ensure long-term remedy
control all background sources before corrective action initia-
success, a goal shared by all stakeholders.
tion.
5.5.3 Long-term remedy success depends on the degree of
site understanding. This guide highlights CSM elements
5.4 Use of Representative Background Concentrations:
(which are not discussed in Guides E3163, E3164, E3242, and
5.4.1 Once established, representative background concen-
E3344) whose consideration is necessary to achieve a more
trations may be applied as cleanup levels at sites where these
complete understanding of the historical and current inputs to
derived concentrations are greater than risk-based cleanup
the sediment site for derivation of representative background
levels, thereby setting the scope and scale of the sediment site
values.
corrective actions. “The reasons for this approach include
cost-effectiveness, technical practicability, and the potential for
5.6 Status of Regulations, Standards, and Guidance:
recontamination of remediated areas by surrounding areas with
5.6.1 Local, tribal, and individual state regulatory agencies
elevated background concentrations” (7). This approach (de-
may have background guidance documents for different matri-
veloped by USEPA) highlights the importance of deriving
ces such as soil, groundwater, or sediments. However, a
representative background concentrations that are technically
comprehensive review of these background documents is out
defensible.
of scope for this guidance. As stated in 4.5.1, the users of this
5.4.2 Additionally, representative background concentra-
guide need to be aware of the regulatory requirements and
tions can assist in determining sediment site boundaries,
guidance applicable in the jurisdiction where the work is being
understanding risks at a site due to background concentrations,
performed.
establishing and optimizing realistic long-term monitoring
5.6.2 In the United States, the Interstate Technology and
plans, and assessing the performance of corrective actions
Regulatory Council (ITRC) has published guidance on deter-
(Guide E3242).
mining representative soil background concentrations at upland
sites (9). However, ITRC has not published guidance specifi-
5.5 Corrective Action Sustainability:
cally targeting background at sediment sites.
5.5.1 In the absence of technically defensible representative
background concentrations, risk-based cleanup levels may be 5.6.3 At the federal level in the United States, the U.S.
used inappropriately at sediment sites where representative Environmental Protection Agency (USEPA) discusses back-
background concentrations would actually be greater than the ground in a number of documents (1, 3, 5, 10, 11, 12, 13, 14,
risk-based cleanup levels. Similarly, if the representative back- 15, 16, 17, 18), but technical guidance specific to background
ground concentrations have been erroneously calculated, inap- at sediment sites (as opposed to soil and groundwater at upland
propriately low cleanup goals could be used in the corrective sites, which are the topic for these referenced USEPA docu-
action evaluation process. Under both circumstances, surface ments) has not been issued by USEPA. However, technical
E3382 − 23
guidance for background at sediment sites has been issued by developed using site-specific information, with the concept
the U.S. Department of Navy (19). being that screening criteria can be made less stringent by the
5.6.4 Internationally, guidance documents regarding the incorporation of site-specific information. Application of this
derivation of representative background concentrations have tiered screening process leads to identification of a COC list
also been published (20, 21, 22, 23, 24); these are examples of
(that is, any PCOC whose concentration in the sediment at the
international guidance and not a comprehensive list, which is sediment site exceeds the risk-based criteria) for the sediment
out of scope for this guidance. Again, this guidance is focused
site.
on soil and groundwater at upland sites; no sediment-specific
6.2.1.2 Only a subset of the elements required for a prelimi-
background guidance has been published (other than Guides
nary sediment site CSM (that is, the contaminant sources and
E3242 and E3344).
associated PCOCs) are needed for the development of repre-
5.6.5 Practitioners should be aware of background guidance
sentative background concentrations for the sediment site.
documents that are applicable to the jurisdiction in which the
6.3 Selection of Background Reference Areas for Determi-
sediment site is located. Even if the background guidance is not
nation of Representative Sediment Background Concentrations
specifically for sediments, but is for soil or groundwater at
(refer to Guide E3344):
upland sites, regulators may attempt to utilize concepts and
6.3.1 Once the preliminary CSM has been developed for the
methodologies from their upland guidance at sediment sites
under their jurisdiction. sediment site, a suitable background reference area(s) can be
identified for sampling. Considerations and methodologies for
5.6.6 Application of background guidance for soil and
groundwater at upland sites may not be appropriate at sediment identifying an appropriate background reference area(s) are
described in detail in Guide E3344.
sites. Sediment sites have many different characteristics that
are not present at upland sites (Guide E3248), including
6.3.2 In general, determination of representative back-
physical characteristics, geochemical characteristics, biologi-
ground concentrations requires additional sampling away from
cal characteristics, and different contaminant emplacement and
the area(s) where current or historical site releases or activities
transport.
have contaminated the sediment site. This process typically
5.6.7 This guide and its associated guides (Guides E3163,
involves identifying a suitable background reference area(s),
E3164, E3240, E3242, and E3344) have been developed (in
which should have physical, chemical, geological, biological,
part) to fill a gap due to the absence of existing guidance from
and anthropogenic characteristics as similar as possible to the
various regulatory agencies for the derivation of representative
sediment site being investigated but should not have been
background concentrations for contaminated sediment sites.
affected by current or historical sediment site activities or
releases. This background reference area(s) should include
6. Framework for Developing Representative
ongoing and uncontrolled sources similar to those (or the same,
Background Concentrations for Sediment Sites
if an unimpacted area of the sediment site is being used as the
background reference area[s]) that will continue to contribute
6.1 Framework Overview:
contaminant concentrations to the sediment site (Guide E3344)
6.1.1 Fig. 1 presents the overall framework to calculate
(7, 19).
representative background concentrations at a sediment site.
6.3.2.1 In addition, the background reference area(s) should
This guide (refer to Section 7) provides a detailed discussion of
have a similar land use to the subject site (for example, if the
the first step in the process. The other steps in the process are
subject site is in an industrial area, the background reference
described in detail in other guides. However, brief descriptions
area(s) should be in an industrial area). As described in Guide
of all the other steps in this framework are provided in this
E3344, the background reference area(s) should be as similar
section, along with references to other guides where more a
to the site as possible, but it is recognized that there will always
detailed discussion of each step is offered (if applicable).
be differences between the two. USEPA notes that for soils,
6.2 Sediment Site Preliminary CSM Development and Iden-
“the ideal background reference area would have the same
tification of Elements Needed to Develop Representative Back-
distribution of concentrations of the chemicals of concern as
ground Concentrations (refer to Guide E3240):
those which would be expected on the site, if the site had never
6.2.1 As a first step in this framework (Fig. 1), a thorough
been impacted” (3).
understanding of the sediment site is necessary. This can be
6.3.3 If a suitable off-site background reference area(s)
accomplished by developing a preliminary CSM for the
cannot be identified, nonimpacted site data may be extracted to
sediment site (Guide E3240), which includes the initial iden-
obtain a candidate background data set (Guide E3242) (7, 9).
tification of contaminant sources (and PCOCs associated with
6.3.3.1 All samples of suitable quality and usability col-
them), exposure pathways, and receptors. Refer to Section 7
lected within the background reference area(s) are included as
for a detailed discussion of the elements of the CSM needed to
part of the candidate background reference area data set.
develop representative background concentrations.
6.2.1.1 As part of this CSM, the sediment site PCOCs must 6.3.4 Typical components of a background reference area
be identified. Guide E3240 describes the process of performing sampling design include media type (that is, bulk sediment
a tiered evaluation to first screen sediment site PCOC concen- samples); the number and type of samples; sampling depth;
trations against generic sediment criteria developed using sampling methodology; and laboratory/chemical analyses (in-
conservative exposure and toxicity assumptions. The sediment cluding quality assurance, quality control, and data validation
site data are then further screened against sediment criteria requirements). Design components of sampling procedures,
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FIG. 1 Framework to Determine Representative Sediment Background Concentrations
including determination of the number of samples based on (that is, background reference subareas with varying degrees of
statistical methodologies, are described in (19, 25, 26, 27). anthropogenic influences in different parts of the background
6.3.5 Selection of an off-site background reference area(s) reference area[s]). Under such situations, the part of the
analogous to the sediment site is complicated by the fact that targeted background reference area(s) (or subareas) that is most
sediment background often represents mixtures of naturally analogous to the sediment site must be selected as the
occurring and anthropogenic influences. In some cases, these background reference area(s). Any other choice would result in
mixtures yield geographically distinct background populations nonrepresentative candidate background data sets.
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6.4 Sediment Sampling and Laboratory Analysis of Repre- many instances, existing sediment site data sets include
sentative Background Reference Area Samples (refer to Guides samples that are free of site influences. Particularly, within a
E3163 and E3164) and Use of Data Extraction of Sediment larger sediment site data set, there likely will be samples not
Site Data Sets (refer to Guide E3242) to Obtain Candidate affected by current or historical sediment site activities or
Background Data Sets: releases. These samples will be reflective of representative
background conditions. This approach not only maximizes the
6.4.1 Once an appropriate off-site background reference
utility of existing data, but also avoids the often-complex task
area(s) is identified for the sediment site, existing sample data
of selecting a separate background reference area(s) that
(if available) should be acquired for the background reference
adequately represents the sediment site.
area(s) and evaluated for data quality and useability. Existing
6.4.5.1 Further details of the process used for extracting
data from a previous study may be suitable for inclusion in the
representative background sample data from the sediment site
candidate background data set or to inform the study design for
data set are presented in Guide E3242 and (9).
new background reference area sediment sample collection.
6.4.5.2 Even when data from an off-site background refer-
However, the inclusion of existing data in the candidate
ence area(s) are available, an extracted site-specific back-
background data set must be assessed on a case-by-case basis
ground data set provides an additional line of evidence for
(9).
determining site-specific representative background concentra-
6.4.1.1 Inclusion of existing data in the candidate back-
tions. Therefore, background extraction analysis of an existing
ground data is inappropriate if different analytical test methods
sediment site data set is always recommended.
were used to generate the existing candidate background data
set and the sediment site data set. Background data sets
6.5 Data Visualization (refer to Guide E3242):
generated by different analytical laboratories should also be
6.5.1 Candidate background data sets obtained from a
subjected to a careful assessment of laboratory standard
background references area(s) or from data extraction of the
operating procedures to ensure comparability of results. Addi-
sediment site data set (or from a combination of both) should
tional statistical comparison of results generated from the
first be evaluated by visualizing the data. This is accomplished
different laboratories are also recommended. The objective is
using various graphical techniques that are presented in Guide
to have comparable background data sets even if derived from
E3242.
different laboratories.
6.5.1.1 Dot plots, box plots, percentile plots, and histograms
6.4.2 Preferably, sample collection and analysis methods at can all be used to identify potential outlying data points.
the background reference area(s) will be as similar as possible 6.5.1.2 For metals data, scatter plots and ratio plots can be
to those used during sediment site data collection. When used in geochemical evaluations to identify whether these
collecting data from a site’s background reference area(s) to potential outlying data points are true outliers (that is, due to
compare to sediment site data, it is critical for background data metals contamination of the sediment) or a false outlier (that is,
to be collected in the same manner as the sediment site under due to the inherent variation in the data).
investigation and to use the same analytical test methodology
6.6 Evaluation of Candidate Background Data Sets to
that was used to determine compliance with cleanup levels
Obtain Representative Background Data Sets (refer to Guide
(ideally, using the same laboratory that analyzed the samples
E3242):
from the sediment site). This allows a direct comparison
6.6.1 Candidate background data sets for the sediment site
between chemical concentrations in background reference
are generated using data extracted from the sediment site data
samples relative to sediment site samples—a crucial step in the
set or by sampling a representative background reference
development of representative background concentrations.
area(s) (refer to 6.4), or a combination of both.
6.4.3 New sediment samples from the off-site background
6.6.2 Candidate background data sets are then evaluated
reference area(s) should be collected and sent to the laboratory
using the methodologies outlined in this section (that is,
for analysis of PCOCs and other parameters (such as total
handling nondetect results, treatment of outliers, geochemical
organic carbon and grain size distribution). Upon validation,
evaluation of metals, and forensic evaluation of organic con-
the laboratory results and suitable existing data would consti-
taminants) and discussed in detail in Guide E3242. If techni-
tute the candidate background reference area data set. Detailed
cally justifiable, some data points may be excluded from the
sediment sampling and analysis guidance is provided in Guides
candidate background data set.
E3163 and E3164; guidance on various sampling designs is
6.6.3 Site and background data sets often include samples
provided in (3).
with nondetect results. Nondetects occur in environmental data
6.4.4 Regulatory agency agreement on the scope and scale
sets because laboratory methods used to measure contaminants
of the sampling effort to determine representative background
are limited in their sensitivity.
concentrations is important and should be captured in a site’s
6.6.3.1 The appropriate treatment of nondetects depends on
Data Quality Objectives. In the United States, the use of the
several factors, including the proportion of nondetects in the
USEPA’s Data Quality Assessment approach (2) is recom-
data set, the distribution of detection limits within the data set,
mended if no superseding regulatory guidance is available.
and whether the statistical distribution of the data set as a
whole can be reliably determined.
6.4.5 If the identification of the off-site representative back-
ground reference area(s) or subareas proves to be impossible, 6.6.3.2 In addition to providing data for use in procedures
determination of representative background concentrations such as two-sample hypothesis tests and geochemical
may be performed using the existing sediment site data. In evaluations, representative background data sets are commonly
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used to calculate BTVs that are intended to represent a truncated (omitting known and disputed outliers) data sets to
reasonable upper threshold of the background distribution. evaluate the effect of maintaining or eliminating the disputed
Nondetect results that reside in the upper decile of an analyte’s outliers (7, 25).
data distribution (that is, nondetect results above the 90th (3) It is critical that outliers that are real values (that is, not
percentile of the candidate background data set) should be errors) and that accurately represent conditions at the back-
removed from the candidate background data set because their ground reference area(s) are be retained in the data set used to
inclusion may bias BTVs toward higher, unrepresentative determine representative sediment background concentrations.
values. Removing high nondetects also ensures that estimates This ensures a technically defensible derivation of representa-
of the mean and variance of the candidate background data set tive background concentrations.
more closely represent background conditions. 6.6.4.4 A more detailed discussion of statistical outlier
6.6.3.3 Simple examples of how to handle nondetect values evaluation when determining representative sediment back-
when evaluating candidate backg
...