ASTM D7758-17

Standard Practice for Passive Soil Gas Sampling in the Vadose Zone for Source Identification, Spatial Variability Assessment, Monitoring, and Vapor Intrusion Evaluations

SIGNIFICANCE AND USE
5.1 Passive soil gas samplers are a minimally invasive, easy-to-use technique in the field for identifying VOCs and SVOCs in the vadose zone. Similar to active soil gas and other field screening techniques, the simplicity and low cost of passive samplers enables them to be applied in large numbers, facilitating detailed mapping of contamination across a site, for the purpose of identifying source areas and release locations, focusing subsequent soil and groundwater sampling locations, focusing remediation plans, identifying vapor intrusion pathways, tracking groundwater plumes, and monitoring remediation progress. Data generated from passive soil gas sampling are semi-quantitative and are dependent on numerous factors both within and outside the control of the sampling personnel. Key variables are identified and briefly discussed in the following sections.
Note 1: Additional non-mandatory information on these factors or variables are covered in the applicable standards referenced in Section 2, and the footnotes and Bibliography presented herewith.  
5.2 Application—The techniques described in this practice are suitable for sampling soil gas with sorbent samplers in a wide variety of geological settings for subsequent analysis for VOCs and SVOCs. The techniques also may prove useful for species other than VOCs and SVOCs, such as elemental mercury, with specialized sorbent media and analysis.  
5.2.1 Source Identification and Spatial Variability Assessment—Passive soil gas sampling can be an effective method to identify contaminant source areas in the vadose zone and delineate the extent of contamination. By collecting samples in a grid with fewer data gaps, the method allows for an increase in data density and, therefore, provides a high-resolution depiction of the nature and extent of contamination across the survey area. By comparing the results, as qualitative or quantitative, from one location to another, the relative distribution and spatial variability of t...
SCOPE
1.1 Purpose—This practice covers standardized techniques for passively collecting soil gas samples from the vadose zone and is to be used in conjunction with Guide D5314.  
1.2 Objectives—Objectives guiding the development of this practice are: (1) to synthesize and put in writing good commercial and customary practice for conducting passive soil gas sampling, (2) to ensure that the process for collecting and analyzing passive soil gas samples is practical and reasonable, and (3) to provide standard guidance for passive soil gas sampling performed in support of source identification, spatial variability/extent determinations, site assessment, site monitoring, and vapor intrusion investigations.  
1.3 This practice does not address requirements of any federal, state, or local regulations or guidance or both with respect to soil gas sampling. Users are cautioned that federal, state, and local guidance may impose specific requirements that differ from those of this practice.  
1.4 Units—The values stated in SI units are to be regarded as 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 practice offers a set of instructions for performing one or more specific operations. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this practice may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique asp...

General Information

• Status: Published
• Publication Date: 31-May-2017
• ICS: 93.020 - Earthworks. Excavations. Foundation construction. Underground works
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.21 - Groundwater and Vadose Zone Investigations

Relations

• Replaces: ASTM D7758-11(2016) - Standard Practice for Passive Soil Gas Sampling in the Vadose Zone for Source Identification, Spatial Variability Assessment, Monitoring, and Vapor Intrusion Evaluations
• Effective Date: 01-Jun-2017
• Refers: ASTM D5792-10(2023) - Standard Practice for Generation of Environmental Data Related to Waste Management Activities: Development of Data Quality Objectives
• Effective Date: 01-Nov-2023
• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Sep-2020
• Refers: ASTM D5088-20 - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 01-May-2020
• Refers: ASTM D1356-20 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Mar-2020
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D2216-19 - Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• Effective Date: 01-Mar-2019
• Refers: ASTM D2487-17e1 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2487-17 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D6196-15 - Standard Practice for Choosing Sorbents, Sampling Parameters and Thermal Desorption Analytical Conditions for Monitoring Volatile Organic Chemicals in Air
• Effective Date: 01-Nov-2015
• Refers: ASTM D1356-15a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Oct-2015
• Refers: ASTM D5792-10(2015) - Standard Practice for Generation of Environmental Data Related to Waste Management Activities: Development of Data Quality Objectives
• Effective Date: 01-Sep-2015
• Refers: ASTM D5088-15a - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 01-Aug-2015
• Refers: ASTM D1356-15 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Jul-2015

Overview

ASTM D7758-17: Standard Practice for Passive Soil Gas Sampling in the Vadose Zone establishes standardized procedures for the passive collection of soil gas samples to identify sources of volatile and semi-volatile organic compounds (VOCs and SVOCs), assess spatial variability, monitor contaminants, and evaluate vapor intrusion. Developed by ASTM International, this standard is designed for use in a broad range of environmental investigations, supporting site assessments, source identification, and long-term remediation monitoring.

Passive soil gas sampling is recognized for being minimally invasive and cost-effective, allowing large numbers of samples to be collected efficiently across extensive survey areas. The technique, which involves deploying sorbent samplers into the unsaturated vadose zone, provides high-density data useful for delineating the extent and distribution of subsurface contamination.

Key Topics

Passive Soil Gas Sampling Methodology

• Passive Sampling Technology: Utilizes sorbent materials to capture VOCs and SVOCs from the vadose zone atmosphere over a specified exposure period.
• Deployment: Samplers are typically installed in shallow subsurface locations, either in open soils or beneath impervious surfaces like concrete or asphalt, to collect time-integrated samples.
• Ease of Use: The method does not require active pumping equipment, making field deployment simpler and less disruptive.

Data Quality and Limitations

• Semi-Quantitative Results: Data generated are generally reported as mass per sampler and provide relative, rather than absolute, concentration measurements.
• Site Variability: Results are influenced by a range of factors, including soil type, moisture content, sampler design, and exposure duration.
• Quality Control: Emphasizes the use of duplicates, field and trip blanks, and proper equipment decontamination to ensure defensible data.

Survey Design Considerations

• Sampler Spacing: Grid-based or biased sampling patterns can be used, with spacing tailored to site-specific conditions and investigation objectives.
• Depth of Sampling: Typically ranges from 15 cm to 1.0 m, with the potential for deeper installations as required by project goals and site conditions.
• Exposure Period: Determined by factors such as compound volatility, soil permeability, and anticipated contaminant concentrations.

Applications

Passive soil gas sampling by ASTM D7758-17 is used in a variety of environmental applications, including:

• Site Assessment: Rapidly screens large areas to identify contaminant sources and direct further investigation.
• Source Identification: Provides high-resolution mapping of VOC and SVOC distribution, facilitating pinpointing of release locations.
• Vapor Intrusion Evaluation: Helps identify vapor migration pathways into buildings, supporting risk assessments under standards such as ASTM E2600.
• Monitoring Remediation: Offers a practical approach to track changes in subsurface conditions and verify remediation effectiveness.
• Spatial Variability Assessment: Collects data at numerous locations to thoroughly delineate contaminant plumes and inform conceptual site models.

Related Standards

ASTM D7758-17 references and complements a range of related standards and regulatory methods:

• ASTM D5314 - Guide for Soil Gas Monitoring in the Vadose Zone
• ASTM D653, D2487 - Terminology and soil classification relevant to sampling
• ASTM D5088 - Equipment decontamination at waste sites
• ASTM D6311, D5792 - Quality objectives and sampling design
• ASTM D6196, D4597 - Sorbent and diffusive sampling methods for environmental air monitoring
• EPA Methods 8260C, 8270C, TO-17 - Analytical methods for VOC and SVOC quantification
• ASTM E2600 - Guide for vapor encroachment screening

Keywords: passive soil gas sampling, ASTM D7758-17, vadose zone, VOCs, SVOCs, environmental site assessment, vapor intrusion, contamination mapping, remediation monitoring, soil gas monitoring, sorbent samplers, spatial variability, ASTM standards.

Implementing ASTM D7758-17 ensures reliable, consistent results in soil gas surveys for source identification, risk evaluation, and long-term site management.

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:D7758 −17
Standard Practice for
Passive Soil Gas Sampling in the Vadose Zone for Source
Identification, Spatial Variability Assessment, Monitoring,
and Vapor Intrusion Evaluations
This standard is issued under the fixed designation D7758; 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* nor should this document be applied without consideration of
a project’s many unique aspects. The word “Standard” in the
1.1 Purpose—This practice covers standardized techniques
title means only that the document has been approved through
for passively collecting soil gas samples from the vadose zone
the ASTM consensus process.
and is to be used in conjunction with Guide D5314.
1.7 This international standard was developed in accor-
1.2 Objectives—Objectives guiding the development of this
dance with internationally recognized principles on standard-
practice are: (1) to synthesize and put in writing good com-
ization established in the Decision on Principles for the
mercial and customary practice for conducting passive soil gas
Development of International Standards, Guides and Recom-
sampling, (2) to ensure that the process for collecting and
mendations issued by the World Trade Organization Technical
analyzing passive soil gas samples is practical and reasonable,
Barriers to Trade (TBT) Committee.
and (3) to provide standard guidance for passive soil gas
sampling performed in support of source identification, spatial
2. Referenced Documents
variability/extent determinations, site assessment, site
2.1 ASTM Standards:
monitoring, and vapor intrusion investigations.
D653 Terminology Relating to Soil, Rock, and Contained
1.3 This practice does not address requirements of any
Fluids
federal, state, or local regulations or guidance or both with
D1356 Terminology Relating to Sampling and Analysis of
respect to soil gas sampling. Users are cautioned that federal,
Atmospheres
state, and local guidance may impose specific requirements
D2216 Test Methods for Laboratory Determination of Water
that differ from those of this practice.
(Moisture) Content of Soil and Rock by Mass
1.4 Units—The values stated in SI units are to be regarded
D2487 Practice for Classification of Soils for Engineering
as standard. No other units of measurement are included in this
Purposes (Unified Soil Classification System)
standard.
D3740 Practice for Minimum Requirements for Agencies
Engaged in Testing and/or Inspection of Soil and Rock as
1.5 This standard does not purport to address all of the
Used in Engineering Design and Construction
safety concerns, if any, associated with its use. It is the
D4597 Practice for Sampling Workplace Atmospheres to
responsibility of the user of this standard to establish appro-
Collect Gases or Vapors with Solid Sorbent Diffusive
priate safety, health, and environmental practices and deter-
Samplers
mine the applicability of regulatory limitations prior to use.
D5088 Practice for Decontamination of Field Equipment
1.6 This practice offers a set of instructions for performing
Used at Waste Sites
one or more specific operations. This document cannot replace
D5314 Guide for Soil Gas Monitoring in the Vadose Zone
education or experience and should be used in conjunction
(Withdrawn 2015)
with professional judgment. Not all aspects of this practice may
D5792 Practice for Generation of Environmental Data Re-
be applicable in all circumstances. This ASTM standard is not
lated to Waste Management Activities: Development of
intended to represent or replace the standard of care by which
Data Quality Objectives
the adequacy of a given professional service must be judged,
1 2
This practice is under the jurisdiction of ASTM Committee D18 on Soil and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Rock and is the direct responsibility of Subcommittee D18.21 on Groundwater and contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Vadose Zone Investigations. Standards volume information, refer to the standard’s Document Summary page on
CurrenteditionapprovedJune1,2017.PublishedJuly2017.Originallyapproved the ASTM website.
in 2011. Last previous edition approved in 2016 as D7758–11(2016). DOI: The last approved version of this historical standard is referenced on
10.1520/D7758-17. www.astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7758−17
D6196 Practice for Choosing Sorbents, Sampling Param- 3.2.10 preparation blank, n—quality control check to define
eters and Thermal Desorption Analytical Conditions for theefficiencyofconditioningabatchofsorbentsamplersatthe
Monitoring Volatile Organic Chemicals in Air laboratory for sample collection (also referred to as manufac-
D6311 Guide for Generation of Environmental Data Related turing blanks).
to Waste ManagementActivities: Selection and Optimiza-
3.2.11 sampling rate, n—the ratio of mass of a given
tion of Sampling Design
compound collected by a diffusive sampler per unit time of
E2600 Guide for Vapor Encroachment Screening on Prop-
exposure to the concentration of that compound in the atmo-
erty Involved in Real Estate Transactions
sphere being sampled.The sampling rate is sometimes referred
2.2 U.S. EPA Methods to as the uptake rate.
Method 8260C Volatile Organic Compounds by Gas
3.2.12 soil gas, n—vadose zone atmosphere; soil gas is the
Chromatography/Mass Spectrometry (GC/MS)
air existing in void spaces in the soil between the groundwater
Method 8270C Semivolatile Organic Compounds by Gas
table and the ground surface.
Chromatography/Mass Spectrometry
3.2.13 soil moisture, n—water contained in the pore spaces
Method TO-17 Determination of Volatile Organic Com-
in the vadose zone.
pounds in Ambient Air Using Active Sampling Onto
3.2.14 sorbent, n—a solid or liquid medium in or upon
Sorbent Tubes
which materials are collected by adsorption, absorption, or
chemisorption.
3. Terminology
3.2.15 sorbent sampling, v—the collection of chemicals
3.1 Definitions:
fromanairoremissionsamplebyallowingtheairoremissions
3.1.1 Forcommondefinitionsoftermsinthisstandard,refer
to contact a sorbent.
to Terminology D653 and D1356.
3.2.16 source, n—area(s) at a site where releases have
3.2 Definitions of Terms Specific to This Standard:
occurredthatareemanatingvaporsfromeitherthevadosezone
3.2.1 absorption, n—the penetration of one substance into
or groundwater.
the inner structure of another.
3.2.16.1 Discussion—There may be multiple sources at a
3.2.2 adsorption, n—adherence of the atoms, ions, or mol-
siteandtheareaoverwhichanyonesourceisdefinedissubject
ecules of a gas or liquid to the surface of another substance
to interpretation from multiple data sets.
(chemisorption).
3.2.17 spatial variability, n—relationship of organic com-
3.2.3 ambient air, n—any unconfined portion of the atmo-
pound mass from one location to many others at a site as a
sphere; open air.
function of distance.
3.2.4 blank sample, n—clean sample or a sample of matrix
3.2.18 starvation effect, n—when the analyte uptake rate of
processed to measure artifacts in the measurement process.
apassivesorbentsamplerisgreaterthanthereplenishmentrate
3.2.4.1 Discussion—Blank samples are named according to
of the analyte around the sampler, which results in a low bias
their type and use (for example, method blank, trip blank, field
measurement.
blank, and preparation or manufacturing blank).
3.2.19 trip blank, n—clean, unused sampling media that is
3.2.5 desorption, n—the process of freeing from a sorbed
carried to the sampling site and transported to the laboratory
state.
for analysis without having been exposed to field sampling
3.2.6 duplicate samples, n—two samples taken from and
procedures.
representative of the same population that are carried through
3.2.20 vapor intrusion, n—migration of a volatile chemi-
all steps of the sampling and analytical procedures in an
cal(s)fromsubsurfacesoilorwaterintoanoverlyingornearby
identical manner.
building.
3.2.7 field blank, n—clean sampling media that is carried to
3.3 Acronyms:
the sampling site, exposed to ambient air during field sampling
3.3.1 BLS—Below land surface (also know as below ground
procedures, and transported to the laboratory for analysis (also
surface (bgs))
referred to as an ambient air control sample).
3.3.2 QA/QC—Quality assurance and quality control
3.2.8 method blank, n—quality control check to measure
laboratory contamination during sample analysis. 3.3.3 PSG—Passive soil gas
3.2.9 moisture content, n—the moisture present in a
3.3.4 SVOC—Semivolatile organic compound
material, as determined by definite prescribed methods, ex-
3.3.5 VOC—Volatile organic compound
pressed as a percentage of the mass of the sample on either of
the following bases: (1) original mass ; (2) moisture-free (oven
4. Summary of Practice
dried) mass (see Test Method D2216).
4.1 This practice describes the passive collection and sub-
sequent analysis of soil gas samples, using sorbent samplers to
trapVOCs and SVOCs in soil vapor by placing samplers in the
Available from United States Environmental Protection Agency (EPA), Ariel
subsurface for a period of time at multiple locations across a
Rios Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20004, http://
www.epa.gov. site. Placement of the sampler can be in open soils (that is, not
D7758−17
covered by a surface such as asphalt or concrete), or advanced 5.2.2 Monitoring—Passive soil gas samplers are used to
through slab surfaces (for example, parking lots, streets, monitor changes in site conditions (for example, new releases
sidewalks, building slabs, and basement floors) to allow for on-site, an increase in contaminant concentrations in ground-
subslab soil gas sampling. This practice provides standard water from onsite or off-site sources, and effectiveness of
guidance for passive soil gas (PSG) sampling and analysis remedial system performance) as reflected by the changes in
performedinsupportof,butnotlimitedto,siteassessment,site soil gas results at fixed locations over time. An initial set of
monitoring, and vapor intrusion investigations. While several dataiscollectedtoestablishabaselineandsubsequentdatasets
different types and combinations of sorbent materials can be are collected for comparison. The sampling and analytical
used to trap VOCs and SVOCs in soil gas, this practice is procedures should remain as near to constant as possible so
intended to achieve representative and reproducible samples of significant changes in soil gas results can be attributed to those
known quality. The design of PSG surveys (for example, changes in subsurface contaminant levels at the site that will
sampler design, sample spacing, the sampler exposure period, then warrant further investigation to identify the cause.
and analytical methods) is within the scope of this practice. 5.2.3 Vapor Intrusion Evaluation—Passive soil gas sam-
These guidelines are not intended to restrict the sampler design pling can be used to identify vapor migration and intrusion
or its application in regards to spacing, sampler distribution, or pathways (see Practice E2600), with the data providing a line
time of exposure; however, these guidelines are meant to
of evidence on the presence or absence of the compounds in
provide a general idea of common practice at the time this soil vapor, the nature and extent in relation to potential
standard was prepared.
receptors, and whether a vapor pathway is complete. Sorbent
samplers can be placed beneath the slab or in close proximity
5. Significance and Use
to buildings to collect time-integrated samples targeting VOCs
5.1 Passive soil gas samplers are a minimally invasive, and SVOCs at concentrations often lower than can be achieved
easy-to-use technique in the field for identifying VOCs and with active soil gas sampling methods.
SVOCs in the vadose zone. Similar to active soil gas and other
5.3 Limitations—Passive soil gas data are reported in mass
field screening techniques, the simplicity and low cost of
of individual compounds or compound groups identified per
passive samplers enables them to be applied in large numbers,
sample location, with the reporting units generally in nano-
facilitatingdetailedmappingofcontaminationacrossasite,for
grams (ng) or micrograms (µg) per sampler and not a concen-
the purpose of identifying source areas and release locations,
tration (see 6.8). Ideally, the data produced using this method
focusing subsequent soil and groundwater sampling locations,
willberepresentativeoftime-weightedsoilgasconcentrations,
focusing remediation plans, identifying vapor intrusion
present in the vicinity of the PSG sampler and sorbed on the
pathways, tracking groundwater plumes, and monitoring reme-
sampler during the exposure period; however, non-uniformity
diation progress. Data generated from passive soil gas sam-
of sampler design, starvation effects during sample collection,
pling are semi-quantitative and are dependent on numerous
or an insufficient amount of sorbent that results in saturation of
factors both within and outside the control of the sampling
the sorbent surface area, or combinations thereof, will affect
personnel. Key variables are identified and briefly discussed in
the relationship between sorbed mass and soil gas concentra-
the following sections.
tionspresent.Thedegreetowhichthesedataarerepresentative
NOTE 1—Additional non-mandatory information on these factors or
of any larger areas or different times depends on numerous
variables are covered in the applicable standards referenced in Section 2,
site-specific factors. In general, information obtained from a
and the footnotes and Bibliography presented herewith.
passive soil gas sampling program alone is not sufficient to
5.2 Application—The techniques described in this practice
support a quantitative determination of soil gas concentrations.
are suitable for sampling soil gas with sorbent samplers in a
5.4 Sampler Design—Passive soil gas is an effective
wide variety of geological settings for subsequent analysis for
investigatory/monitoring tool if the appropriate quality con-
VOCs and SVOCs. The techniques also may prove useful for
trols are included in the technology design, which includes
species other than VOCs and SVOCs, such as elemental
uniformity in the construction of the sampler. At a minimum,
mercury, with specialized sorbent media and analysis.
controls should be in place to ensure that (1) the appropriate
5.2.1 Source Identification and Spatial Variability
sorbents with hydrophobic properties are used to target the
Assessment—Passive soil gas sampling can be an effective
methodtoidentifycontaminantsourceareasinthevadosezone compoundsofconcern(seePracticeD6196),(2)materialsused
to house the sorbents are chemically-inert, non-reactive or
and delineate the extent of contamination. By collecting
samples in a grid with fewer data gaps, the method allows for corrosive, and will not off-gas compounds or act as competing
sorbents (see Guide D5314, paragraph 6.5.3), and (3) the
an increase in data density and, therefore, provides a high-
resolution depiction of the nature and extent of contamination sorbents are housed in suitable containers that protect the
sorbents, allow diffusion of the soil gas to the sorbents, and
across the survey area. By comparing the results, as qualitative
or quantitative, from one location to another, the relative facilitate installation of the sampler to the desired sampling
depth.
distribution and spatial variability of the contaminants in the
subsurface can be determined, thereby improving the concep- 5.4.1 Sampler Conditioning—Before being sent to the field
tual site model. Areas of the site reporting non-detects can be for deployment, the PSG sampler should be conditioned to
removed from further investigation, while subsequent sam- remove any potential contamination present on or in the
pling and remediation can be focused in areas determined from sorbent and sampler materials or both encountered during
the PSG survey to be impacted. sampler construction or storage prior to use. The conditioning
D7758−17
process should be one that does not damage the sorptive 5.6.2 Site-specific information (investigation area size,
capability of the sorbent. Following conditioning, the sampler groundwater depth, soil type and moisture content, purpose of
the investigation, etc.) should be considered along with these
is then capped/resealed and stored in a container that provides
adequate protection against ambient sources of contamination guidelines in determining the grid spacing used. The selection
of grid cell size (a direct function of the sampler spacing
before and after sample collection in the field, including during
deployed in a grid pattern) is strongly dependent upon the
transport. Preparation blanks from each batch of conditioned
relationship between both project confidence level and budget
samplers should be analyzed to verify that the sorbents were
requirements. The tendency exists for investigators with con-
effectively conditioned and do not retain measurable masses of
strained budgets to use overly large grid cell spacing. This
target compounds above reporting limits. Furthermore, when
action of “undersampling” normally results in inadequate,
trip blanks, which are included with all shipments to and from
over-interpreted data with unsupported conclusions. Care shall
the field, report non-detects for the targeted compounds, these
be taken to avoid this problem (Guide D5314). In designing an
QCsamplesprovideadditionalevidencethatthesamplerswere
effective soil gas survey to develop a rational conceptual site
conditioned to have no measurable mass of target compounds
model, the survey objective balanced by budget should deter-
and that the measurements on field samples originate from the
mine the sample spacing.
site itself.
5.7 Sampling Depth—Consideration of project objectives
5.5 Sampler Exposure Periods—Guidelines for PSG expo-
should be taken into account when determining deployment
sure periods for source identification, spatial variability
depth.Itisideal,whenpossible,todeploysamplersatthesame
assessment, and vapor intrusion evaluation should consider the
depth to ensure data consistency. PSG samplers are generally
project objectives, target compounds, required detection limits
installed from a depth of 15-cm to 1.0-m BLS; however, holes
or anticipated soil gas concentrations or both, design of the
may be advanced to greater depths when appropriate, and
passive sampler, matrix heterogeneity, soil types (total
samplers can also be suspended beneath surface flux chambers
porosity), soil moisture level (water filled porosity), and depth
or in permanent vapor ports.
to expected contaminants. Sites having coarse-grained dry
5.8 Soil Types—In general, sandy soils tend to be more
soils, high concentrations, shallow groundwater or soil con-
porous and permeable and, thus, require shorter exposure
tamination or both, and volatile compounds typically require
times. Conversely, soils with high clay contents tend to be less
shorter exposure periods. Sites with finegrained, clays or moist
porous and permeable and typically have lower flux rates (see
soils or both, deep contaminant sources, low concentrations, or
Practice D2487). Soil types vary in vapor permeability due to
SVOCs, or combinations thereof, typically require longer
the differences in the number and interconnectivity of air-filled
exposure periods. Exposure periods typically range from days
pores. The more air-filled, interconnected the pores are, the
to weeks but can be as brief as one hour when high concen-
greaterthepotentialfluxofcontaminantsthroughthesoiltothe
trations of target compounds are expected in the soil vapor.
sampler. Starvation effects resulting in low bias are more likely
5.6 Sampler Spacing—Grid designs can consist of regularly
to occur in low permeability soils where the flux through the
spaced sampler locations, random or irregular spaced, and as
soil matrix is limited.
transects or varying spatial intervals (see Guide D6311).
5.9 Effects of Soil Moisture—Because diffusion of vapors
Biased spacing in which smaller sample spacing is used in
from subsurface sources to passive samplers relies on inter-
areas with known or suspected targets (that is, source areas)
connected and air-filled pores within the soil column, soil
and large spacing in areas not believed to be impacted are also
moisture can have a significant effect on the flux of contami-
used.Forlargeareainvestigations,astagedorphasedsampling
nants and, therefore, the mass of the contaminant available for
program can be used. The investigation begins with a widely
adsorption by the sampling device. The use of hydrophobic
spaced regular grid design. The initial soil gas results are
sorbents minimizes the effect on sampler sensitivity, but does
reviewed and subsequent sampling is conducted at locations
not change the impact of soil moisture on contaminant soil gas
where the target compounds were observed. The subsequent
concentrations. As a
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7758 − 11 (Reapproved 2016) D7758 − 17
Standard Practice for
Passive Soil Gas Sampling in the Vadose Zone for Source
Identification, Spatial Variability Assessment, Monitoring,
and Vapor Intrusion Evaluations
This standard is issued under the fixed designation D7758; 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 Scope*
1.1 Purpose—This practice covers standardized techniques for passively collecting soil gas samples from the vadose zone and
is to be used in conjunction with Guide D5314.
1.2 Objectives—Objectives guiding the development of this practice are: (1) to synthesize and put in writing good commercial
and customary practice for conducting passive soil gas sampling, (2) to ensure that the process for collecting and analyzing passive
soil gas samples is practical and reasonable, and (3) to provide standard guidance for passive soil gas sampling performed in
support of source identification, spatial variability/extent determinations, site assessment, site monitoring, and vapor intrusion
investigations.
1.3 This practice does not address requirements of any federal, state, or local regulations or guidance or both with respect to
soil gas sampling. Users are cautioned that federal, state, and local guidance may impose specific requirements that differ from
those of this practice.
1.4 Units—The values stated in SI units are to be regarded as 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This practice offers a set of instructions for performing one or more specific operations. This document cannot replace
education or experience and should be used in conjunction with professional judgment. Not all aspects of this practice may be
applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the
adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project’s
many unique aspects. The word “Standard” in the title means only that the document has been approved through the ASTM
consensus process.
1.7 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.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D2487 Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
This practice is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.21 on Groundwater and Vadose
Zone Investigations.
Current edition approved Oct. 1, 2016June 1, 2017. Published October 2016July 2017. Originally approved in 2011. Last previous edition approved in 20112016 as
D7758D7758–11(2016).–11. DOI: 10.1520/D7758-11R16.10.1520/D7758-17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7758 − 17
D4597 Practice for Sampling Workplace Atmospheres to Collect Gases or Vapors with Solid Sorbent Diffusive Samplers
D5088 Practice for Decontamination of Field Equipment Used at Waste Sites
D5314 Guide for Soil Gas Monitoring in the Vadose Zone (Withdrawn 2015)
D5792 Practice for Generation of Environmental Data Related to Waste Management Activities: Development of Data Quality
Objectives
D6196 Practice for Choosing Sorbents, Sampling Parameters and Thermal Desorption Analytical Conditions for Monitoring
Volatile Organic Chemicals in Air
D6311 Guide for Generation of Environmental Data Related to Waste Management Activities: Selection and Optimization of
Sampling Design
E2600 Guide for Vapor Encroachment Screening on Property Involved in Real Estate Transactions
2.2 U.S. EPA Methods
Method 8260C Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS)
Method 8270C Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry
Method TO-17 Determination of Volatile Organic Compounds in Ambient Air Using Active Sampling Onto Sorbent Tubes
3. Terminology
3.1 Definitions:
3.1.1 For common definitions of terms in this standard, refer to Terminology D653 and D1356.
3.2 Definitions of Terms Specific to This Standard:
3.1.1 This section provides definitions and descriptions of terms used in or related to this practice. A list of acronyms and a list
of symbols are also included. The terms are an integral part of this practice and are critical to an understanding of the practice and
its use. Also see Terminology D653 and D1356.
3.2.1 absorption, n—the penetration of one substance into the inner structure of another.
3.1.3 active sampling, v—means of collecting a gas-phase substance that uses a mechanical device such as a pump or
vacuum-assisted critical orifice to draw air into or through a sampling device.
3.2.2 adsorption, n—adherence of the atoms, ions, or molecules of a gas or liquid to the surface of another substance
(chemisorption).
3.2.3 ambient air, n—any unconfined portion of the atmosphere; open air.
3.1.6 background level, n—concentration of a substance that is typically found in ambient air (for example, as a result of
industrial or automobile emissions), indoor air (for example, from building materials or indoor activities), or the natural geology
of an area.
3.2.4 blank sample, n—clean sample or a sample of matrix processed to measure artifacts in the measurement process.
The last approved version of this historical standard is referenced on www.astm.org.
Available from United States Environmental Protection Agency (EPA), Ariel Rios Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20004, http://www.epa.gov.
3.2.4.1 Discussion—
Blank samples are named according to their type and use (for example, method blank, trip blank, field blank, and preparation or
manufacturing blank).
3.1.8 contaminant, n—substances not normally found in an environment at the observed concentration.
3.2.5 desorption, n—the process of freeing from a sorbed state.
3.2.6 duplicate samples, n—two samples taken from and representative of the same population that are carried through all steps
of the sampling and analytical procedures in an identical manner.
3.2.7 field blank, n—clean sampling media that is carried to the sampling site, exposed to ambient air during field sampling
procedures, and transported to the laboratory for analysis (also referred to as an ambient air control sample).
3.1.12 groundwater, n—part of the subsurface water that is in the saturated zone.
3.2.8 method blank, n—quality control check to measure laboratory contamination during sample analysis.
3.2.9 moisture content, n—the moisture present in a material, as determined by definite prescribed methods, expressed as a
percentage of the mass of the sample on either of the following bases: (1) original mass ; (2) moisture-free (oven dried) mass (see
Test Method D2216).
3.1.15 passive sampling, v—means of collecting a gas-phase substance that uses sorbent materials in a sampling device exposed
for a finite duration in the medium being sampled.
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3.2.10 preparation blank, n—quality control check to define the efficiency of conditioning a batch of sorbent samplers at the
laboratory for sample collection (also referred to as manufacturing blanks).
3.1.17 porosity, n—volume fraction of rock or soil not occupied by solid material but usually occupied by liquids, vapor, or air,
or combinations thereof.
3.1.17.1 Discussion—
Porosity is the void volume of soil or rock or both divided by the total volume of soil or rock or both.
3.2.11 sampling rate, n—the ratio of mass of a given compound collected by a diffusive sampler per unit time of exposure to
the concentration of that compound in the atmosphere being sampled. The sampling rate is sometimes referred to as the uptake
rate.
3.1.19 saturated zone, n—zone in which all of the voids in the rock or soil are filled with water at a pressure that is greater than
atmospheric.
3.1.19.1 Discussion—
The water table is the top of the saturated zone in an unconfined aquifer.
3.2.12 soil gas, n—vadose zone atmosphere; soil gas is the air existing in void spaces in the soil between the groundwater table
and the ground surface.
3.2.13 soil moisture, n—water contained in the pore spaces in the vadose zone.
3.2.14 sorbent, n—a solid or liquid medium in or upon which materials are collected by adsorption, absorption, or
chemisorption.
3.2.15 sorbent sampling, v—the collection of chemicals from an air or emission sample by allowing the air or emissions to
contact a sorbent.
3.1.24 sorption, n—a process by which one material (the sorbent) takes up and retains another material (the sorbate) by the
processes of adsorption or absorption.
3.2.16 source, n—area(s) at a site where releases have occurred that are emanating vapors from either the vadose zone or
groundwater.
3.2.16.1 Discussion—
There may be multiple sources at a site and the area over which any one source is defined is subject to interpretation from multiple
data sets.
3.2.17 spatial variability, n—relationship of organic compound mass from one location to many others at a site as a function
of distance.
3.2.18 starvation effect, n—when the analyte uptake rate of a passive sorbent sampler is greater than the replenishment rate of
the analyte around the sampler, which results in a low bias measurement.
3.2.19 trip blank, n—clean, unused sampling media that is carried to the sampling site and transported to the laboratory for
analysis without having been exposed to field sampling procedures.
3.1.29 vadose zone, n—hydrogeological region extending from the soil surface to the top of the principal water table.
3.1.29.1 Discussion—
Perched groundwater may exist within this zone.
3.2.20 vapor intrusion, n—migration of a volatile chemical(s) from subsurface soil or water into an overlying or nearby
building.
3.1.31 water table, n—top of the saturated zone in an unconfined aquifer.
3.3 Acronyms:
3.3.1 BLS—Below land surface (also know as below ground surface (bgs))
3.2.2 COC—Compound of concern
3.2.3 EPA—Environmental Protection Agency
3.2.4 ID—Identification
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3.2.5 MDL—Method detection limit
3.3.2 QA/QC—Quality assurance and quality control
3.3.3 PSG—Passive soil gas
3.3.4 SVOC—Semivolatile organic compound
3.2.9 TD-GC/MS—Thermal desorption-gas chromato-
graphy/mass spectrometry
3.2.10 U.S.—United States
3.3.5 VOC—Volatile organic compound
3.3 Symbols:
3.3.1 cm—centimeter
3.3.2 m—meter
3.3.3 mm—millimeter
3.3.4 min—minute
-9
3.3.5 ng—mass in nanograms or 10 g
3.3.6 s—seconds
-6
3.3.7 μg—mass in micrograms or 10 g
4. Summary of Practice
4.1 This practice describes the passive collection and subsequent analysis of soil gas samples, using sorbent samplers to trap
VOCs and SVOCs in soil vapor by placing samplers in the subsurface for a period of time at multiple locations across a site.
Placement of the sampler can be in open soils (i.e., (that is, not covered by a surface such as asphalt or concrete), or advanced
through slab surfaces (e.g., (for example, parking lots, streets, sidewalks, building slabs, and basement floors) to allow for subslab
soil gas sampling. This practice provides standard guidance for passive soil gas (PSG) sampling and analysis performed in support
of, but not limited to, site assessment, site monitoring, and vapor intrusion investigations. While several different types and
combinations of sorbent materials can be used to trap VOCs and SVOCs in soil gas, this practice is intended to achieve
representative and reproducible samples of known quality. The design of PSG surveys (for example, sampler design, sample
spacing, the sampler exposure period, and analytical methods) is within the scope of this practice. These guidelines are not intended
to restrict the sampler design or its application in regards to spacing, sampler distribution, or time of exposure; however, these
guidelines are meant to provide a general idea of common practice at the time this standard was prepared.
5. Significance and Use
5.1 Passive soil gas samplers are a minimally invasive, easy-to-use technique in the field for identifying VOCs and SVOCs in
the vadose zone. Similar to active soil gas and other field screening techniques, the simplicity and low cost of passive samplers
enables them to be applied in large numbers, facilitating detailed mapping of contamination across a site, for the purpose of
identifying source areas and release locations, focusing subsequent soil and groundwater sampling locations, focusing remediation
plans, identifying vapor intrusion pathways, tracking groundwater plumes, and monitoring remediation progress. Data generated
from passive soil gas sampling are semi-quantitative and are dependent on numerous factors both within and outside the control
of the sampling personnel. Key variables are identified and briefly discussed in the following sections.
NOTE 1—Additional non-mandatory information on these factors or variables are covered in the applicable standards referenced in Section 2, and the
footnotes and Bibliography presented herewith.
5.2 Application—The techniques described in this practice are suitable for sampling soil gas with sorbent samplers in a wide
variety of geological settings for subsequent analysis for VOCs and SVOCs. The techniques also may prove useful for species
other than VOCs and SVOCs, such as elemental mercury, with specialized sorbent media and analysis.
5.2.1 Source Identification and Spatial Variability Assessment—Passive soil gas sampling can be an effective method to identify
contaminant source areas in the vadose zone and delineate the extent of contamination. By collecting samples in a grid with fewer
data gaps, the method allows for an increase in data density and, therefore, provides a high-resolution depiction of the nature and
extent of contamination across the survey area. By comparing the results, as qualitative or quantitative, from one location to
another, the relative distribution and spatial variability of the contaminants in the subsurface can be determined, thereby improving
the conceptual site model. Areas of the site reporting non-detects can be removed from further investigation, while subsequent
sampling and remediation can be focused in areas determined from the PSG survey to be impacted.
5.2.2 Monitoring—Passive soil gas samplers are used to monitor changes in site conditions (e.g., (for example, new releases
on-site, an increase in contaminant concentrations in groundwater from onsite or off-site sources, and effectiveness of remedial
system performance) as reflected by the changes in soil gas results at fixed locations over time. An initial set of data is collected
to establish a baseline and subsequent data sets are collected for comparison. The sampling and analytical procedures should
D7758 − 17
remain as near to constant as possible so significant changes in soil gas results can be attributed to those changes in subsurface
contaminant levels at the site that will then warrant further investigation to identify the cause.
5.2.3 Vapor Intrusion Evaluation—Passive soil gas sampling can be used to identify vapor migration and intrusion pathways
(see Practice E2600), with the data providing a line of evidence on the presence or absence of the compounds in soil vapor, the
nature and extent in relation to potential receptors, and whether a vapor pathway is complete. Sorbent samplers can be placed
beneath the slab or in close proximity to buildings to collect time-integrated samples targeting VOCs and SVOCs at concentrations
often lower than can be achieved with active soil gas sampling methods.
5.3 Limitations—Passive soil gas data are reported in mass of individual compounds or compound groups identified per sample
location, with the reporting units generally in nanograms (ng) or micrograms (μg) per sampler and not a concentration (see 6.8).
Ideally, the data produced using this method will be representative of time-weighted soil gas concentrations, present in the vicinity
of the PSG sampler and sorbed on the sampler during the exposure period; however, non-uniformity of sampler design, starvation
effects during sample collection, or an insufficient amount of sorbent that results in saturation of the sorbent surface area, or
combinations thereof, will affect the relationship between sorbed mass and soil gas concentrations present. The degree to which
these data are representative of any larger areas or different times depends on numerous site-specific factors. In general,
information obtained from a passive soil gas sampling program alone is not sufficient to support a quantitative determination of
soil gas concentrations.
5.4 Sampler Design—Passive soil gas is an effective investigatory/monitoring tool if the appropriate quality controls are
included in the technology design, which includes uniformity in the construction of the sampler. At a minimum, controls should
be in place to ensure that (1) the appropriate sorbents with hydrophobic properties are used to target the compounds of concern
(see Practice D6196), (2) materials used to house the sorbents are chemically-inert, non-reactive or corrosive, and will not off-gas
compounds or act as competing sorbents (see Guide D5314, paragraph 6.5.3), and (3) the sorbents are housed in suitable containers
that protect the sorbents, allow diffusion of the soil gas to the sorbents, and facilitate installation of the sampler to the desired
sampling depth.
5.4.1 Sampler Conditioning—Before being sent to the field for deployment, the PSG sampler should be conditioned to remove
any potential contamination present on or in the sorbent and sampler materials or both encountered during sampler construction
or storage prior to use. The conditioning process should be one that does not damage the sorptive capability of the sorbent.
Following conditioning, the sampler is then capped/resealed and stored in a container that provides adequate protection against
ambient sources of contamination before and after sample collection in the field, including during transport. Preparation blanks
from each batch of conditioned samplers should be analyzed to verify that the sorbents were effectively conditioned and do not
retain measurable masses of target compounds above reporting limits. Furthermore, when trip blanks, which are included with all
shipments to and from the field, report non-detects for the targeted compounds, these QC samples provide additional evidence that
the samplers were conditioned to have no measurable mass of target compounds and that the measurements on field samples
originate from the site itself.
5.5 Sampler Exposure Periods—Guidelines for PSG exposure periods for source identification, spatial variability assessment,
and vapor intrusion evaluation should consider the project objectives, target compounds, required detection limits or anticipated
soil gas concentrations or both, design of the passive sampler, matrix heterogeneity, soil types (total porosity), soil moisture level
(water filled porosity), and depth to expected contaminants. Sites having coarse-grained dry soils, high concentrations, shallow
groundwater or soil contamination or both, and volatile compounds typically require shorter exposure periods. Sites with
finegrained, clays or moist soils or both, deep contaminant sources, low concentrations, or SVOCs, or combinations thereof,
typically require longer exposure periods. Exposure periods typically range from days to weeks but can be as brief as one hour
when high concentrations of target compounds are expected in the soil vapor.
5.6 Sampler Spacing—Grid designs can consist of regularly spaced sampler locations, random or irregular spaced, and as
transects or varying spatial intervals (see Guide D6311). Biased spacing in which smaller sample spacing is used in areas with
known or suspected targets (that is, source areas) and large spacing in areas not believed to be impacted are also used. For large
area investigations, a staged or phased sampling program can be used. The investigation begins with a widely spaced regular grid
design. The initial soil gas results are reviewed and subsequent sampling is conducted at locations where the target compounds
were observed. The subsequent survey design consists of more closely spaced samples to resolve the feature of interest in greater
detail. Multiple phases of soil gas sampling can be combined to provide one comprehensive image of the soil gas results. Staged
or phased investigations require multiple deployments adding costs to the overall investigations. However, areas of the site that
have nondetectable values in the soil gas may be removed from further investigation.
5.6.1 There is no prescribed or set sampler spacing appropriate for all sites, as sample spacing and survey design are based on
project objectives and each site is unique. General recommendations for sampler spacing range from 3 to 30 m, with 7.5- to 15-m
spacing when site knowledge is lacking. Infill sampling is recommended in areas having wider sample spacing initially.
5.6.2 Site-specific information (investigation area size, groundwater depth, soil type and moisture content, purpose of the
investigation, etc.) should be considered along with these guidelines in determining the grid spacing used. The selection of grid
cell size (a direct function of the sampler spacing deployed in a grid pattern) is strongly dependent upon the relationship be
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