ASTM D7929-20

Standard Guide for Selection of Passive Techniques for Sampling Groundwater Monitoring Wells

SIGNIFICANCE AND USE
4.1 General—Passive groundwater sampling has increased use since the polyethylene diffusion bag sampler was first introduced (5). As defined above, different types of passive samplers are now available with different functions and usages. The Interstate Technology Regulatory Council (ITRC) has provided several technical and regulatory documents on the use of passive groundwater sampling methods (1, 5-7). Collectively, these documents have provided information and references on the technical basis for their use, comparison of sampling results with more traditional sampling methods, descriptions of their proper use, limitations, and a survey of their acceptance and use by responding state regulators. However, the ITRC documents are older and do not include more recent assessments and publications. This Standard seeks to provide newer information on current practice and implementation of passive groundwater sampling techniques.  
4.1.1 Because of the large number of passive samplers that have been developed over the years for various types of environmental sampling, it is beyond the scope of this standard to discuss separately each of the methods that could or can be used to sample groundwater. Extensive literature reviews on diffusion- and accumulation-passive samplers can be found in the scientific literature (that is, 3, 8-14). These reviews provide information on a wide variety of passive sampling devices for use in air, soil vapor, and water. A review paper on the use of diffusion and accumulation-type passive samplers specifically for sampling volatile organic compounds (VOCs) in groundwater (15) includes information on other passive samplers that are not included in the ITRC documents (1, 7) and discusses their use with respect to measuring mass flux.  
4.2 Use—Passive samplers are deployed at a pre-determined depth, or depths, within a well for a minimum or pre-determined period of time. They should remain submerged at the target depth for their entire deploy...
SCOPE
1.1 This standard provides guidance and information on passive sampling techniques for collecting groundwater from monitoring wells. Passive groundwater samplers are able to acquire a sample from the screen interval in a well, without the active transport associated with a pump or purge technique (1).2 Passive groundwater sampling is a type of no-purge groundwater sampling method where the samplers are left in the well for a predetermined period of time prior to collecting the sample.  
1.2 Methods for sampling monitoring wells include low-flow purging and sampling methods, traditional well-volume purging and sampling methods, post-purge grab sampling methods (for example, using a bailer), passive no-purge sampling methods, and active no-purge sampling methods such as using a bailer to collect a sample without purging the well. This guide focuses on passive no-purge sampling methodologies for collecting groundwater samples. These methodologies include the use of diffusion samplers, accumulation samplers, and passive-grab samplers. This guide provides information on the use, advantages, disadvantages, and limitations of each of these passive sampling technologies.  
1.3 ASTM Standard D653 provides standard terminology relevant to soil, rock, and fluids contained in them. ASTM Standard D4448 provides a standard guide to sampling groundwater wells, and ASTM Standards D5903 and D6089 provide guides for planning and documenting a sampling event. Groundwater samples may require preservation (Guide D6517), filtration (Guide D6564/D6564M), and measures to pack and ship samples (Guide D6911). Standard D7069 provides guidance on the quality control and quality assurance of sampling events. ASTM Standard D5092/D5092M provides standard practice for the design and installation of groundwater monitoring wells, ASTM Standard D5521/D5521M provides a standard guide for developing groundwater monitoring wells in granular aquifers, and D...

General Information

• Status: Published
• Publication Date: 14-Feb-2020
• ICS: 13.060.10 - Water of natural resources
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.21 - Groundwater and Vadose Zone Investigations

Relations

• Replaces: ASTM D7929-14 - Standard Guide for Selection of Passive Techniques for Sampling Groundwater Monitoring Wells
• Effective Date: 15-Feb-2020
• Refers: ASTM D7069-24 - Standard Guide for Field Quality Assurance in a Groundwater Sampling Event
• Effective Date: 15-Mar-2024
• Refers: ASTM D6564/D6564M-17(2024) - Standard Guide for Field Filtration of Groundwater Samples
• Effective Date: 01-Feb-2024
• Refers: ASTM D6517-18(2023) - Standard Guide for Field Preservation of Ground Water Samples
• Effective Date: 01-Nov-2023
• Refers: ASTM D6452-18(2023) - Standard Guide for Purging Methods for Wells Used for Ground Water Quality Investigations
• Effective Date: 01-Nov-2023
• Refers: ASTM D6089-19(2023) - Standard Guide for Documenting a Groundwater Sampling Event
• 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 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 D6089-19 - Standard Guide for Documenting a Groundwater Sampling Event
• Effective Date: 01-Aug-2019
• Refers: ASTM D4448-01(2019) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Feb-2019
• Refers: ASTM D6517-18 - Standard Guide for Field Preservation of Ground Water Samples
• Effective Date: 01-Dec-2018
• Refers: ASTM D6452-18 - Standard Guide for Purging Methods for Wells Used for Ground Water Quality Investigations
• Effective Date: 01-Dec-2018
• Refers: ASTM D5521/D5521M-18 - Standard Guide for Development of Groundwater Monitoring Wells in Granular Aquifers
• Effective Date: 01-Jun-2018
• Refers: ASTM D6564/D6564M-17 - Standard Guide for Field Filtration of Groundwater Samples
• Effective Date: 15-Dec-2017
• Refers: ASTM D5092/D5092M-16 - Standard Practice for Design and Installation of Groundwater Monitoring Wells
• Effective Date: 15-Nov-2016

Overview

ASTM D7929-20: Standard Guide for Selection of Passive Techniques for Sampling Groundwater Monitoring Wells provides comprehensive guidance on the selection and use of passive sampling methods for groundwater monitoring wells. Developed by ASTM International, this standard addresses the increasing adoption of passive groundwater sampling technologies, offering an up-to-date overview of current practices, limitations, and advantages. It targets environmental professionals, hydrogeologists, and regulators responsible for groundwater quality monitoring, focusing on techniques that do not require active purging or pumping to obtain groundwater samples.

Key Topics

• Passive Groundwater Sampling: Passive samplers are placed at a specific depth within a monitoring well and left in place for a predetermined period. Unlike active methods (such as pumping and purging), passive methods collect groundwater samples without disturbing the aquifer or requiring the removal of well water prior to sampling.
• Types of Passive Samplers:
  • Diffusion Samplers: Rely on analyte diffusion through a membrane, reaching equilibrium with groundwater concentrations.
  • Accumulation Samplers: Use a sorbent medium within a membrane to accumulate analytes over time, suitable for integrative or equilibrium sampling.
  • Passive-Grab Samplers: Designed to collect whole water samples after an equilibration period, minimizing disturbance to the water column.
• Considerations for Use:
  • Well Construction: Properly designed, installed, and developed wells are essential for accurate sampling.
  • Sample Volume and Analyte Suitability: Each sampler type has limitations in sample volume and analyte specificity.
  • Deployment and Equilibration Time: Adequate deployment ensures samples are representative and minimizes turbidity increase.
• Advantages and Limitations:
  • Advantages: Lower cost per sample, minimal operator training, reduced logistical requirements, and elimination of purge water handling.
  • Limitations: Possible sample volume constraints, analyte specificity, and potential need for well maintenance.

Applications

• Regulatory Groundwater Monitoring: Passive sampling is increasingly accepted by regulators as a reliable alternative to conventional purged sampling methods. It is useful where data quality objectives can be met with no-purge techniques.
• Environmental Site Assessment: Especially effective for long-term monitoring, site characterization, and vertical contaminant profiling. Passive samplers allow for discrete interval sampling, revealing contaminant stratification within wells.
• Difficult Site Conditions: Well suited for locations where active sampling is logistically challenging, such as low-yield formations, remote sites, or areas sensitive to equipment disturbance.
• Contaminant Fate and Transport Studies: Enable assessment of temporal and spatial contaminant distributions, supporting environmental decision-making and remediation planning.

Related Standards

• ASTM D653 – Terminology Relating to Soil, Rock, and Contained Fluids
• ASTM D4448 – Guide for Sampling Groundwater Monitoring Wells
• ASTM D5903 and D6089 – Guides for Planning and Documenting Groundwater Sampling Events
• ASTM D6517, D6564/D6564M, D6911 – Guides for Sample Preservation, Filtration, and Packaging
• ASTM D7069 – Guide for Field Quality Assurance in Groundwater Sampling
• ASTM D5092/D5092M, D5521/D5521M – Practices for Well Design, Installation, and Development
• ASTM D6452 – Guide for Well Purging Methods

Practical Value

Adopting ASTM D7929-20 helps organizations modernize their groundwater monitoring practices, improve efficiency, and lower costs while maintaining data quality. This standard facilitates the selection of appropriate passive sampling technologies tailored to specific site requirements and regulatory frameworks. By leveraging passive groundwater sampling, professionals can enhance sampling representativeness, minimize environmental impact, and comply with the latest industry guidelines for groundwater quality monitoring.

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: D7929 − 20
Standard Guide for
Selection of Passive Techniques for Sampling Groundwater
Monitoring Wells
This standard is issued under the fixed designation D7929; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* standardguidefordevelopinggroundwatermonitoringwellsin
granular aquifers, and D6452 provides a standard guide for
1.1 This standard provides guidance and information on
purging methods used in groundwater quality investigations.
passive sampling techniques for collecting groundwater from
Consult ASTM Standard D6724/D6724M for a guide on the
monitoring wells. Passive groundwater samplers are able to
installation of direct-push groundwater monitoring wells and
acquireasamplefromthescreenintervalinawell,withoutthe
ASTMStandardD6725/D6725Mforaguideontheinstallation
active transport associated with a pump or purge technique
2 of direct-push groundwater monitoring wells with pre-pack
(1). Passive groundwater sampling is a type of no-purge
screens.
groundwater sampling method where the samplers are left in
the well for a predetermined period of time prior to collecting
1.4 The values stated in SI Units are to be regarded as the
the sample.
standard. Values in inches (such as with well diameters) are
given in parentheses, and are provided for information. Use of
1.2 Methods for sampling monitoring wells include low-
unitsotherthanSIshallnotberegardedasnonconformingwith
flow purging and sampling methods, traditional well-volume
this standard.
purging and sampling methods, post-purge grab sampling
methods (for example, using a bailer), passive no-purge sam-
1.5 Thisguideprovidesinformationonpassivegroundwater
pling methods, and active no-purge sampling methods such as
samplingingeneralandalsoprovidesaseriesofconsiderations
usingabailertocollectasamplewithoutpurgingthewell.This
when selecting a passive groundwater sampling method.
guidefocusesonpassiveno-purgesamplingmethodologiesfor
However, it does not recommend a specific course of action,
collecting groundwater samples. These methodologies include
and not all aspects of this guide may be applicable in all field
the use of diffusion samplers, accumulation samplers, and
situations. This document cannot replace education or experi-
passive-grab samplers. This guide provides information on the
ence and should be used in conjunction with professional
use,advantages,disadvantages,andlimitationsofeachofthese
judgment. ThisASTM standard is not intended to represent or
passive sampling technologies.
replace the standard of care by which the adequacy of a given
professional service must be judged, nor should this document
1.3 ASTM Standard D653 provides standard terminology
be applied without consideration of a project’s many unique
relevant to soil, rock, and fluids contained in them. ASTM
aspects. The word “standard” in the title of this document
StandardD4448providesastandardguidetosamplingground-
means only that the document has been approved through the
water wells, and ASTM Standards D5903 and D6089 provide
ASTM consensus process.
guides for planning and documenting a sampling event.
Groundwater samples may require preservation (Guide
1.6 This standard does not purport to address all of the
D6517), filtration (Guide D6564/D6564M), and measures to
safety concerns, if any, associated with its use. It is the
pack and ship samples (Guide D6911). Standard D7069
responsibility of the user of this standard to establish appro-
provides guidance on the quality control and quality assurance
priate safety, health, and environmental practices and deter-
ofsamplingevents.ASTMStandardD5092/D5092Mprovides
mine the applicability of regulatory limitations prior to use.
standardpracticeforthedesignandinstallationofgroundwater
1.7 This international standard was developed in accor-
monitoring wells,ASTM Standard D5521/D5521M provides a
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland Development of International Standards, Guides and Recom-
Rock and is the direct responsibility of Subcommittee D18.21 on Groundwater and
mendations issued by the World Trade Organization Technical
Vadose Zone Investigations.
Barriers to Trade (TBT) Committee.
Current edition approved Feb. 15, 2020. Published March 2020. Originally
approved in 2014. Last previous edition approved in 2014 as D7929-14. DOI:
10.1520/D7929-20.
2. Referenced Documents
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. 2.1 ASTM Standards:
*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
D7929 − 20
D653Terminology Relating to Soil, Rock, and Contained equilibrium, and these are described based on the device’s
Fluids physical basis of operation as defined below.
D3740Practice for Minimum Requirements for Agencies 3.2.2 equilibrium samplers, n—in groundwater, passive
Engaged in Testing and/or Inspection of Soil and Rock as samplers that have an exposure time that is sufficiently long to
Used in Engineering Design and Construction permit the establishment of thermodynamic equilibrium be-
D4750Test Method for Determining Subsurface Liquid tween the sampled medium and receiving phase (3).
Levels in a Borehole or Monitoring Well (Observation
3.2.3 integrative or kinetic samplers, n—passive samplers
Well) (Withdrawn 2010)
that work in the linear uptake phase (of a standard uptake
D4448GuideforSamplingGround-WaterMonitoringWells
curve) where the rate of desorption of analytes from the
D5092/D5092MPractice for Design and Installation of
receivingphasetothesampledmediumisnegligible(2 and 3).
Groundwater Monitoring Wells
3.2.3.1 Discussion—Thesesamplersprovideatotalmassfor
D5521/D5521MGuide for Development of Groundwater
the time they are deployed, which can be converted to
Monitoring Wells in Granular Aquifers
concentration values in some cases.
D5903Guide for Planning and Preparing for a Groundwater
3.2.4 no-purge groundwater sampling, n—in groundwater,
Sampling Event
sampling methods that differ from active purging-and-
D6089Guide for Documenting a Groundwater Sampling
sampling methods for sampling groundwater (as described in
Event
Guide D6452) in that there is no requirement to remove water
D6452Guide for Purging Methods for Wells Used for
from the well prior to sampling.
Ground Water Quality Investigations
3.2.4.1 Discussion—No-purgemethodscancollectasample
D6517 Guide for Field Preservation of Ground Water
using an active method (such as pumping, suction, bailing) or
Samples
a passive method without purging the well.
D6564/D6564MGuide for Field Filtration of Groundwater
Samples 3.2.5 passive groundwater sampling, n—in groundwater,a
D6724/D6724M Guide for Installation of Direct Push
type of no-purge groundwater sampling method where the
Groundwater Monitoring Wells samplers are deployed in the well at one or more target depths
D6725/D6725MPractice for Direct Push Installation of
withinthewellscreenoropenboreholeandarethenleftinthe
Prepacked Screen Monitoring Wells in Unconsolidated well for a period of time prior to collecting the sample (rather
Aquifers
than collecting a sample immediately).
D6911Guide for Packaging and Shipping Environmental 3.2.5.1 Discussion—These sampling methods do not use
Samples for Laboratory Analysis
pumping, suction, or bailing to collect the sample and thus do
D7069Guide for Field QualityAssurance in a Groundwater not induce stress on the aquifer (Guide D4448).
Sampling Event
3.2.6 passive-groundwater samplers, n—in groundwater,
devices deployed in a well for the purpose of passive ground-
3. Terminology
water sampling.
3.1 Forcommondefinitionofcommontechnicaltermsused
3.2.6.1 Discussion—These devices provide a sample from a
in this standard, refer to Terminology D653. specific location within the well screen or borehole. Spatial
integration, which is likely, is a result of natural ambient flow
3.2 Definitions of Terms Specific to This Standard:
andmixingofthesampledmediumwithinthemonitoringwell
3.2.1 passive environmental sampling, n—in groundwater,
(4).Thesesamplerscanbeclassifiedbythemechanismusedto
is a group of sampling techniques based on the free flow of
collect the sample and include: diffusion samplers (5 and 6),
analyte molecules from the sampled medium to a receiving
accumulation samplers (1, 7), and passive-grab samplers.
phase in a sampling device as a result of a difference between
3.2.7 diffusion samplers, n—in groundwater, usually con-
thechemicalpotentialsoftheanalytesinthetwomedia(2 and
3). tain deionized (DI) or distilled water inside a membrane and
rely on diffusion of analytes through the membrane to reach
3.2.1.1 Discussion—These passive sampling devices are
equilibrium with concentrations in the well.
usually based on diffusion through a diffusion barrier or
3.2.7.1 Discussion—Thesesamplersareanequilibriumtype
permeation through a membrane into a sorptive membrane or
of passive sampler (as defined in 3.2.2.1). The length of the
medium (2 and 3). Uptake of analytes follows a standard
equilibration period depends primarily upon the types of
uptake curve where uptake initially is linear, followed by a
analytes,themembranematerial,therateofexchangeofwater
period of time where uptake is no longer linear (that is,
in the well, and temperature of the well water.
becomes curvilinear), and finally equilibration is reached.
3.2.8 accumulation samplers, n—in groundwater, typically
Analytes are retained in a suitable medium within the passive
consist of a liquid or solid sorbent medium, contained in a
sampler,knownasareferenceorreceivingphase,whichcanbe
permeable membrane or in direct contact with the water
a solvent, chemical reagent, or a porous adsorbent (2 and 3).
sample, and rely on diffusion and sorption to accumulate
There are two main accumulation regimes, kinetic and
analytes in the sampler.
3.2.8.1 Discussion—Although, these samplers can be used
as either an integrative or equilibrium sampler, adsorptive
The last approved version of this historical standard is referenced on
www.astm.org. samplers are prone to saturation effects and other reactions
D7929 − 20
which make them less suitable for equilibrium sampling (8). are not included in the ITRC documents (1, 7) and discusses
When these samplers are used in the integrative (or kinetic) their use with respect to measuring mass flux.
mode, the sampling time must be within the linear portion of
4.2 Use—Passivesamplersaredeployedatapre-determined
the uptake curve.
depth, or depths, within a well for a minimum or pre-
determined period of time. They should remain submerged at
3.2.9 passive-grab samplers, n—in groundwater, grab sam-
plers that collect a whole water sample and require an the target depth for their entire deployment period. All of the
equilibration period prior to sample collection. Passive-grab passive technologies described in this document rely on the
samplers should not disturb the water column during sample sampling device being exposed to the groundwater during
collection, should be able to collect a sample at the target deployment and the continuous flushing of the open or
depth(s) in the well, and should be able to isolate the sample screenedintervalofthewellbyambientgroundwaterflow((4),
inside the sampler prior to removing it from the well. (5-7), 16) to produce water quality conditions in the well bore
that effectively mimic those conditions in the aquifer adjacent
3.2.10 equilibration period, n—in groundwater, the sug-
to the screen or open interval. For samplers that require the
gested deployment period for passive-grab samplers, diffusion
establishment of equilibrium, it is important that the equilibra-
samplers, and accumulation samplers when they are used as
tion period be long enough to allow the well to recover from
equilibrium samplers.
any disturbance caused by placing the sampler in the well and
3.2.10.1 Discussion—The appropriate deployment period
to prevent, or reduce, losses of analytes from the water sample
depends upon one or more of the following factors: the time
by sampler materials due to sorption. For kinetic accumulation
needed for environmental disturbances caused by sampler
samplers (used as kinetic samplers), it is important that the
deployment to dissipate and ambient conditions in the well to
deployment time is long enough that quantitative uptake can
return, the time needed for equalization of analyte concentra-
occur but not so long that uptake is no longer in the linear
tionswithsurroundingconcentrationsinthewellwater,andthe
portion of the uptake curve (that is, has become curvilinear).
time needed to reduce losses due to sorption of the analytes by
4.2.1 As with all types of groundwater sampling methods,
the sampler materials to negligible levels.
the appropriate use of passive methods assumes that the well
3.2.11 deployment time, n—in groundwater, Deployment
has been properly located (laterally and vertically), designed,
time is the period required for an accumulation sampler to
constructed, and was adequately developed (as described in
achieve quantitative levels of uptake of the target analytes
Guide D5521/D5521M) and maintained (as described in Prac-
when being used as an integrative (or kinetic) sampler.
tices D5092/D5092M and D6725/D6725M, or Guide D6724/
D6724M). These measures are necessary so that the well is in
4. Significance and Use
hydraulic communication with the aquifer.
4.2.2 Each type of passive sampler has its own attributes
4.1 General—Passive groundwater sampling has increased
and limitations, and thus data-quality objectives (DQOs) for
use since the polyethylene diffusion bag sampler was first
the site should be reviewed prior to selecting a device. For
introduced (5). As defined above, different types of passive
wells in low-permeability formations, diffusive flux may be-
samplersarenowavailablewithdifferentfunctionsandusages.
come more important than advective flow in maintaining
The Interstate Technology Regulatory Council (ITRC) has
aquifer-quality water in the well.
providedseveraltechnicalandregulatorydocumentsontheuse
of passive groundwater sampling methods (1, 5-7). 4.3 Advantages—Whilepassivemethodsarenotexpectedto
Collectively, these documents have provided information and
replace conventional pumped sampling in all situations, they
references on the technical basis for their use, comparison of oftenofferafasteralternative“tool”forsamplinggroundwater
sampling results with more traditional sampling methods,
monitoring wells because purging is eliminated from the
descriptions of their proper use, limitations, and a survey of pre-sampling procedure. Other advantages include that these
their acceptance and use by responding state regulators.
samplerscanbeusedinmostwellsandtypicallyhavenodepth
However, the ITRC documents are older and do not include limitation.Thesesamplersareeitherdisposableordedicatedto
morerecentassessmentsandpublications.ThisStandardseeks
a well. This eliminates or reduces the need for decontamina-
to provide newer information on current practice and imple- tion. Passive samplers typically reduce the logistics associated
mentation of passive groundwater sampling techniques.
with sampling and are especially useful at sites where it is
difficult to bring larger equipment (such as pumps and com-
4.1.1 Because of the large number of passive samplers that
have been developed over the years for various types of pressors) to the well location.
4.3.1 Passive groundwater sampling techniques typically
environmentalsampling,itisbeyondthescopeofthisstandard
to discuss separately each of the methods that could or can be provide a lower “per-sample” cost than conventional pumped
sampling methods (17-26). This is primarily because the labor
used to sample groundwater. Extensive literature reviews on
diffusion- and accumulation-passive samplers can be found in associatedwithcollectingasampleissubstantiallyreducedand
wastehandlinganddisposalissubstantiallyreduced.Eliminat-
thescientificliterature(thatis, 3, 8-14).Thesereviewsprovide
information on a wide variety of passive sampling devices for ing handling and disposal of purge water is an environmental
benefit and advantage.
use in air, soil vapor, and water.Areview paper on the use of
diffusion and accumulation-type passive samplers specifically 4.3.2 If there is interest in identifying contaminant stratifi-
for sampling volatile organic compounds (VOCs) in ground- cationwithinthewell,multiplepassivesamplerscanbeusedto
water (15) includes information on other passive samplers that characterize vertical contaminant distribution with depth.
D7929 − 20
Baffles or packers can be used to segregate the sampling zones 5. Considerations for Passive Groundwater Sampling
and often provide better characterization of each zone. Profil-
5.1 Planning a Passive Sampling Event—As with all sam-
ing contamination with depth in a well can be informative
pling activities, it is essential that all parties involved in
when trying to decide where to place a single passive sampler
planningtheuseofanysamplingmethodidentifyandagreeon
within the well screen for long-term monitoring; placing a
the sampling and data-quality objectives, data-evaluation
sampler at the mid-point of the screen may not yield a sample
criteria, end use of the data, target analytes, and hydrogeologic
with the highest contaminant concentrations or one that agrees
concerns before the sampling method is selected. The appro-
best with previous low-flow concentrations (for example, 26).
priateness of any method is determined by the data-quality
objectives (DQOs) for the sampling event and overall site
4.4 Disadvantages—As with any groundwater sampling
monitoringprogram,andbytheabilityofthesamplingmethod
method, rapid or rigorous deployment of the sampler(s) can
to meet them accurately and reliably. Considerations when
increase turbidity in the well. For passive groundwater
selecting a passive sampling method can include sampler
samplers, this can be reduced or eliminated if the equilibration
design,abilityofthesamplertocollectthetargetcontaminants,
time is long enough to allow the return of the natural ambient
well construction (including well diameter, screen and filter
turbidity in the well. In many cases, passive samplers are
pack length, and proper slot size for the screen and filter pack
deployed at the end of a sampling event and left in the well
design as described in Practice D5092/D5092M), vertical and
until the next scheduled sampling event; this practice provides
horizontal flow patterns within the well, and contaminant
more than enough time for equilibration to occur. Some
stratification.Additional guidance on the selection of a passive
methods require dedicated equipment purchase which may
sampling method can be found in Table X2.1.
increase the cost for the initial sampling event in order to
obtain the overall cost advantage.
5.2 Analytes of Interest—When deciding whether to use
passive sampling or which passive sampling method to use,
4.5 Limitations—There are three primary limitations with
consideration should be given to the contaminants of concern
passive samplers: analyte capability, sample volume, and
(COCs) for the site and other analytes or parameters that may
physical size with respect to well diameter. For the diffusion
be used to evaluate the geochemical processes of interest.
and accumulation samplers, the membrane and or sorbent,
Some passive samplers collect only specific analytes, whereas
respectively,determinetheanalytecapabilityofthesampler.In
other devices can be used for a broader suite of analyte types.
contrast, passive-grab samplers collect whole water samples
5.2.1 Some samplers collect a limited volume of sample,
and can be used for any analyte, subject to sample volume and
and this may limit the use of these samplers. The sample
physical size limitations.
volume that can be collected will be determined by the type of
4.5.1 Analyte capability is often unique to individual pas-
passive sampler, the diameter of the well, and the length of the
sive samplers. In the case of diffusion-based passive samplers,
desired sampling interval in the well. A larger total sample
the user should verify that the membrane is suitable for the
volume can be obtained by increasing the number of samplers
analytes to be tested. ITRC (5-7) describes the analyte capa-
usedwithinthesamplinginterval(atthesamedepthorinseries
bility of diffusion-bases passive samplers. Two or more indi-
with depth) or, in some cases, by increasing the size of the
vidualtypesofpassivesamplerscanbeusedsimultaneouslyto
sampling device (that is, using a longer or wider diameter
sample for a broader spectrum of analyte types.
sampler). However, when samplers are deployed in series with
4.5.2 Passive-grab and passive-diffusion samplers collect a
depth, concentrations in the samplers will reflect any stratifi-
finite sample volume. Total sampler volume may limit the
cation that exists in the sampling zone. Also, as mentioned
number and type of analytes that can be practically collected.
previously,consultingwiththeanalyticallaboratorymaymake
Additional samplers or larger volume samplers may be avail-
it possible to reduce the minimum volume of sample. (See
able and can be used to meet the volume requirements. Also,
Table X1.1 for suggested minimum volumes.)
because laboratories typically use only a small portion of the
5.2.2 More specific information on the capabilities of par-
sample collected, it may be possible to provide the laboratory
ticular sampling devices can be found in 6.1, 6.2, and 6.3, and
with a smaller sample volume. Table X1.1 provides suggested
in Table X2.1. For devices that are available commercially,
minimum volumes for several analyte classes. The laboratory
current information can also be obtained by contacting the
shouldbeconsultedtoconfirmadequatesamplevolumeduring
sampler manufacturer(s) or supplier(s).
the method selection process.
5.3 Site Considerations—In general, passive groundwater
4.5.3 Regarding physical sizes of the sampler(s), the diam-
samplers can be used in a wide variety of hydrogeologic
eter of the sampler or combination of samplers must be able to
settings. Site considerations can include: accessibility of the
fit in the well or multi-level sampler.
wells, well diameter, screen length, saturated thickness, the
hydraulic connection between the well and aquifer, and the
NOTE 1—The quality of the result produced by this standard is
dependent on the competence of the personnel performing it, and the hydraulic gradient that generates flow. Passive samplers are
suitability of the equipment and facilities used. Agencies that meet the
particularly well suited for conditions where active sampling
criteria of Practice D3740 are generally considered capable of competent
methods can be problematic. These conditions can include
andobjectivetesting.Usersofthisstandardarecautionedthatcompliance
low-yield formations where excessive drawdown is unavoid-
with Practice D3740 does not in itself assure reliable results. Reliable
able even at low flow rates, locations where purge methods
results depend on many factors; Practice D3740 provides a means of
evaluating some of those factors. result in large volumes of purge water that must be disposed,
D7929 − 20
locations that are difficult to access with a vehicle, or where needs, and site conditions for each proposed application. A
low-turbidity samples are needed but cannot be obtained using fundamental concern of regulators is that the sampling method
other sampling methods such as with a bailer or a pump. used at a site, or at a particular well, provides results that meet
5.3.1 However, there can be situations that preclude the use the DQOs for the project.
of any sampling method, including standard purged methods. 5.5.1 Method Selection—There are different passive sam-
Both passive and active sampling methods may inadvertently plingsystemsandthesetechnologiesvaryinthedegreeoffield
collect non-aqueous phase liquid (NAPL). For example, this validation. Methods that have strong field validation and
can occur when a sampler or pump passes through a NAPL provide good reproducibility among different users, field
zone during deployment or when droplets are drawn down or conditions, and time frames are best suited for long-term
entrained while pumping the well. In these cases, collection of monitoring strategies. Two or more passive sampling tech-
water samples from wells containing NAPLmay overestimate niques may be deployed simultaneously and provide samples
dissolved-phase concentrations and may complicate data inter- for a broader range of analytes and thereby meet the site
pretation. Therefore, the practical effect of this bias on the DQOs. For a broad range of analyte concentrations, it may be
sampling objectives and project DQOs should be evaluated, necessary to deploy two or more samplers of the same type in
and continued collection of the water sample may not be a well.
5.5.2 New Sites—In cases where new wells or a new site is
warranted.
under consideration, selection of a sampling method does not
5.4 Acceptability of Passive Groundwater Sampling
rely on historical data continuity and thus method selection
Methods—Numerous studies have shown that passive-
would rely on an evaluation of the data quality needs for the
groundwater sampling methods collect representative concen-
site. Improved site-characterization methods can yield better
trations of groundwater constituents of concern and are appro-
designed wells (often with shorter screens) and thereby im-
priate alternatives to purged sampling methods. Studies
prove this decision process. Data from passive sampling
illustratingrepresentativenessandcomparabilitytopurgesam-
methods that use multi-level samplers may provide more
pling approaches are listed for each type of sampling device in
specific and detailed high-resolution information in terms of
6.1, 6.2, and 6.3.
aquifer stratigraphy, contaminant fate and transport, and site
5.4.1 Questionsaboutthe“needtopurge”havebeenlargely
management.
answered over the course of the last few decades (16, 27, 28).
5.5.3 Older Sites—There should be no impediment to
In properly designed, developed, and maintained monitoring
switching to a passive method as long as the DQOs of the site
wells,hydrauliccommunicationexistsbetweentheaquiferand
can be met by the particular sampling method chosen. A
well. With adequate hydraulic gradient, aquifer water flows
number of field and laboratory studies (listed in 6.1, 6.2, and
intoandoutofthescreenedoropensectionsofawell.Passive
6.3) have been conducted to determine the comparability of
sampling devices set in such screened or open zones will
passive methods with conventional sampling methods. These
collect aquifer water that is in dynamic equilibrium with the
studies reveal that in most situations, passive methods provide
aquifer without purging. As with pumping, the hydraulics
samples that have analyte concentrations that are not signifi-
within the well, well bore, and the formation will determine
cantly different (on a statistical basis) from those collected
what the sample represents. The same factors are at play with
using other conventional sampling methods such as low-flow
the different available passive sampling methods.
purgingandsampling.Whenconsideringachangeinsampling
5.4.2 There are conditions where a passive sample does not
methods,thequestionariseshowtheresultsoftheexistingand
collect a sample from the entire screened zone of a well. This
new methods will compare. When converting to a passive
may be due to, for example, vertical flow in the well,
samplingmethod,aside-by-sidecomparisontestwiththesite’s
contaminant stratification, poor hydraulic communication, or a
current method or comparison with historical data may be
low hydraulic conductivity in the formation (creating a long
desirable to understand data differences between sampling
residencetimeinthewell).However,theseconditionscanalso
methods. Further discussion on how to conduct this type of
be problematic for purged sampling methods (29, 30). These
test, how to analyze the data, and how to interpret the data are
conditions do not necessarily make passive sampling an
given in Appendix X3.
unacceptable alternative, rather, passive sampling may simply
represent the adjacent aquifer differently than a pumped
6. Types of Passive Groundwater Sampling Devices
sampling method. Recommendations on how to deal with
The three types of passive groundwater sampling devices—
differences between analyte concentrations when comparing
that is, passive-grab samplers, diffusion samplers, and accu-
passivevs.activesamplingmethodsaregiveninAppendixX3.
mulation samplers—vary greatly in how they function and
5.4.3 In instances where there is poor hydraulic communi-
each type has its own specific deployment-time requirements.
cation between the aquifer and the well, rehabilitation of the
This section describes these three general types of passive
well or redevelopment often improves the communication
samplers and the supporting validation references.
between the aquifer and well. This can be necessary for both
6.1 Passive-grab Samplersareusedtocollectawholewater
pumped and passive methods.
sample from a discrete depth or interval within the well or
5.5 Implementing Passive Sampling Methods—There are borehole after a recommended deployment period in the well.
inherent advantages and limitations in every groundwater Residencetimeallowsthewelltorecoverfromthedisturbance
sampling method. These differences should be examined caused by inserting the sampler in the well and thus allows the
within the context of the particular project objectives, data water in the screened interval to return to the ambient flow
D7929 − 20
conditions that existed between the well and the formation. 6.1.3 Limitations—The primary limitations with these sam-
This reduces the possibility of collecting a sample with an plers are their size and the sample volume collected.Typically,
artificially elevated turbidity and thus obtaining falsely el- these samplers do not fit in wells less than 5 cm (2 in.) in
evated concentrations of particle-borne contaminants. Deploy- diameter. In instances where a larger sampler volume is
ment residence time also allows the sampler materials to needed, a larger sampler may be available or, it may be
equilibrate with analyte concentrations in the surrounding well possible to place several samplers at the same depth in larger
water prior to sample collection, and thereby prevents, or diameter wells or in series with depth in smaller diameter
reduces,analytelossesduetosorptionbythesamplermaterials wells.
(31-35). Sample collection does not occur until the device is 6.1.4 Additional Information—There are several field and
triggeredoractuated.Passive-grabsamplersshouldnotdisturb laboratorystudiesthathaveevaluatedtheperformanceofthese
the water column during sample collection, should be able to types of groundwater samplers include peer-reviewed reports,
collect a sample at the target depth(s), and should be able to papers (22-25, 35, 36) and other reports (17, 37).Also, several
isolate the sample inside the sampler prior to moving the of these reports (17, 24, 25) include cost analyses that
sampler within the well. These criteria distinguish “passive- demonstrate the cost savings that can be achieved using these
grab samplers” from other grab samplers that are used as types of passive samplers when compared with conventional
no-purge samplers, such as various types of bailers including pumped sampling methods.
point-source bailers and collapsible bailers (for example,
6.2 Diffusion Samplers rely on diffusion of analytes of
sleeve-type samplers). The ITRC Diffusion/Passive Sampler
interest through a membrane into distilled or deionized (DI)
Team (1, 7) previously categorized grab samplers used in
water contained inside the sampler. Polymeric materials com-
passive sampling as “equilibrated-grab samplers.” However,
monly used for the membranes include low-density polyethyl-
not all of “equilibrated-grab samplers” meet the more restric-
ene (LDPE), regenerated cellulose (or dialysis membrane),
tive definition for “passive-grab samplers” given in this stan-
nylon, and polymethylsulfone. While typically a minimum of
dard.
two weeks is recommended for equilibration (1, 5-7), a longer
6.1.1 Advantages—The primary advantage of passive-grab
period may be needed for some analytes such as explosives
samplers is that typically they can be used to collect samples
(18-20). Diffusion samplers provide a time-weighted average
for a wide range of organic and inorganic analytes. This is
concentration that is weighted most heavily towards concen-
because sample collection is not limited by the sampler
trations in the well over the last few days the sampler is in the
membrane or the collection media inside the device. These
well.Thedegreeofthisweightingdependsontheequilibration
devicesdonotexcludecolloidalparticles,andthuscanbeused
rates for the analytes of interest for the membrane being used
to collect samples for analyses of total and dissolved concen-
(thatis,thetypeandthickness),thewatertemperature,andrate
trationsofanalytes.Samplescollectedwiththesesamplerscan
of recharge (flow rate) in the well.
be used to measure pH, oxidation-reduction potential (ORP),
6.2.1 Advantages—Diffusion samplers are functionally
electrical conductivity, and dissolved gases. These samplers
simple and can be quickly deployed and retrieved. Waste
can be used for quarterly, semi-annual, or annual sampling
disposal is limited to a small amount of unused water from
events with single mobilizations for sample collection. After
spent disposable samplers. Diffusion samplers are typically
collecting each sample, a new sampler or sample bottle is
disposable so little or no decontamination is required. Most of
replaced in the well in preparation for the next event, avoiding
these samplers can be used for quarterly, semi-annual, or
asecondtriptothefield.Foronetypeofpassive-grabsampler,
annual sampling events. Depending upon the membrane used
the samples are sealed in a sample bottle in the well. In some
inthesampler,itmaybepossibletocollectsamplesthatcanbe
instances the sample bottle can remain sealed until the sample
used to measure pH, ORP, electrical conductivity, or dissolved
is analyzed; this prevents loss of VOCs during transfer in the
gases. Some diffusion samplers can be used to collect samples
field or in the laboratory ((36)).
for a variety of organic and inorganic analytes, and some
6.1.2 Disadvantages—For passive-grab samplers, inadver- membranes provide unique advantages. As an example, the
tentlyagitatingoraeratingthewellordislodgingparticlesfrom LDPEmembraneusedinsomesamplerswillpreventalkalinity
the inside of the well casing or well bore during sampler exchange of the aquifer water with the (DI) water in the
deployment can alter some analyte concentrations including sampler (38). This can be an advantage when collecting VOC
metals subject to oxidation/precipitation reactions, and samplesfromalkalineaquiferswhereadditionofthesampleto
particle-borneorcolloid-bornecontaminants.Thelengthofthe the acid preservative in the vial (or vice versa) results in
equilibrationperiodshouldbesufficienttoprovidetimeforthe effervescence and subsequent loss of VOCs. Several of these
well to recover from any disturbance caused by inserting the samplers are available commercially and generally are rela-
sampling device in the well.The extent of recovery in the well tively inexpensive to purchase. Samplers that are not commer-
depends upon the flow rate in and out of the screened interval cially available (and thus have to be constructed) may still be
and the condition of the well. In instances where entraining cost effective (17-25).
extraneousparticlesisaproblem,thiscanbemitigatedinsome 6.2.2 Disadvantages—These samplers exclude all particles
cases by redeveloping the well. biggerthantheporesizeofthemembraneandthustheycannot
D7929 − 20
be used to collect samples for analytes that are particle-borne Thus, the recommended exposure time can range from a time
or colloid-borne such as total metals or hydrophobic organic scale of minutes or hours to months, depending on whether
analytes (for example, polycyclic aromatic hydrocarbons they are being used as a kinetic (integrative) or equilibrium
(PAHs) and polychlorinated biphenyls PCBs). Another disad- sampler. Typically, the exposure time for kinetic (accumula-
vantage is that some of these samplers are not commercially tion) samplers ranges from minutes to several hours and the
available and therefore have to be constructed by the user in a exposure time of equilibrium (accumulation) samplers ranges
clean environment. from days to months. Sampler design ranges from complex (in
terms of assembly and adsorbent housing) to relatively simple
6.2.3 Limitations—The primary limitations associated with
designs that require minimal handling.
using diffusion samplers are that: 1) their use is limited to only
thoseanalytesthatwilldiffusethroughthemembrane(depend- 6.3.2 As a group, these samplers can detect a wide range of
ing upon the type of membrane), 2) their use is limited to volatile and semi-volatile organic compounds. Examples in-
analytesinthedissolvedform, 3)thesamplevolumeislimited clude fuel-related and chlorinated compounds, PAHs, organo-
to the size of the sampler, 4) depending upon the size of the chlorine pesticides, dioxins and furans, PCBs, and pharmaceu-
sampler, deployment may be limited to 5-cm (2-in.) diameter tical compounds. Other samplers have been developed for
or larger wells, and 5) depending upon the sampler membrane, sampling for inorganic compounds including some metals.
the maximum deployment time may be limited. In instances
6.3.3 While other passive groundwater samplers provide a
where a larger volume is needed, longer samplers often can be
watersamplethatisanalyzed,itisthesorbentmaterialinthese
custom made. Smaller-diameter samplers can also be custom
samplers that is analyzed. Particulate sorbents may be ex-
made. While most samplers can be deployed after a sampling
tractedwithwater(orsomeotheraqueoussolution),anorganic
event and left until the next sampling event, some membranes,
solvent,orthermallydesorbed.Samplerscontaininganorganic
such as the regenerated-cellulose membrane, may undergo
solvent do not require further extraction but may require
biodegradation if left in some wells for more than two weeks
additional cleanup prior to analyses.
(7, 38). In those instances, two trips to the field are typically
6.3.4 Typically, the results of these analyses are given in a
required (one to deploy the sampler and one to collect it).
total mass for each of the analytes for the exposure time.
However, even with two trips to the field, these samplers may
However, there is an extensive body of research on passive,
still provide cost savings over traditional sampling methods
sorbent-based methods which can allow one to estimate
(17-21).Samplersthatareleftinthewellforalongtime(such
concentrations in water by measuring sampler uptake rates.
as between quarterly sampling events) should be examined to
Thetotalmassmeasured(perexposuretime)andthemeasured
determine that biofouling has not occurred.
uptake rate of the analytes by the sampler can be used to
6.2.4 Additional Information—Besides those reports and
calculate analyte concentrations present in the well water.
papers already cited, there are several other peer-reviewed
Monitoring well-specific data may be needed to calibrate the
reports and journal papers (8, 9, 22-25, 28, 36, 39-45) that
measured uptake rate of the samplers. This data can include
provideadditionalinformationonpassive-diffusiongroundwa-
water pressure (that is, sampler depth in water column), water
ter samplers.
temperature, groundwater velocity, and the performance of
reference compounds incorporated in the sampler.
6.3 Accumulation Samplers rely on diffusion through a
6.3.5 Advantages vary with sampler design.These samplers
membrane and then sorption by sorbent media within the
can be designed to target a specific class, type, or species of
sampler that accumulates the analytes of interest within the
analytes. Common advantages associated with using these
sampler (1, 7). The sorbent is typically a sorbent powder but
samplers result from not having to handle and transport vials
can be a liquid. These samplers include nonporous, semi-
and bottles (especially glass) containing aqueous samples,
permeable, or permeable membrane devices that allow either
reduced shipping weight, easier handling in the field, and in
direct diffusion of the analytes in the groundwater through the
somecasesnothavingtorefrigeratethesamplesduringstorage
membrane, or there can be direct partitioning into the mem-
or shipping.
brane or partitioning to the vapor phase with subsequent
6.3.6 Disadvantages vary considerably depending upon the
diffusion through the membrane. The analytes accumulate in
sampler design, sample handling procedures, extraction
solid or liquid sorbent material housed within the sampler.The
methods, and the analytical methods used. Depth below the
membranescontrolthetype,uptakerateandsizeoftheanalyte
water table may limit sampler placement, if the water entry
molecules that reach the adsorbent (for example, hydrophilic
pressureofthesamplermembraneisovercomeorifthesealing
compounds), while protecting the integrity of the sample.
of the membrane to the housing is breached due to pressure.
Alternatively, the sorbent can be directly exposed to the water
Also, some regulators may object to using calculated concen-
column and utilize materials such as those used in solid-phase
tration values.
extraction (SPE) materials (46). Stationary phases can include
extraction cartridges and disks. 6.3.6.1 Those samplers that contain an organic solvent as
the sorbent medium may require special handling because of
6.3.1 These samplers are placed at the desired depth in the
concerns with flammability, and regulatory agency approval
well and left for an exposure period that allows the sorbent to
should be obtained prior to placing them in a groundwater
accumulate a detectable level of the target analytes. Exposure
environment.
periods are a function of the sampler design and target analyte
capability, estimated contaminant concentrations, temperature 6.3.7 Limitations are a function of the sampler design and
ofthewellwater,andtherateofexchangeofwaterinthewell. handling. Typically accumulation samplers are limited to
D7929 − 20
certain types of analytes. For metals, depending upon the demonstration that used an accumulation sampler at two
DQOs, it may be important to know whether a particular Department of Defense sites and presents data on the associ-
sampler provides total or dissolved concentrations of these ated cost savings that can occur when this sampling method is
analytes. Kinetic (accumulation) samplers rely on a brief used (when compared with conventional low-flow sampling).
exposure (so that uptake of the analytes remains in the linear
portionoftheuptakecurve),andthus,theycannotbeleftinthe
7. Selecting a Passive Sampling Method
well between sampling events. In contrast, the exposure time
7.1 Table X2.1 provides a matrix table that can aid the user
for equilibrium (accumulation) samplers is much longer and
when selecting a passive sampling method.
some of these samplers can be left in the well between
sampling events, depending upon the sampler design and well
8. Keywords
conditions.
6.3.8 Additional Information—Several sources (1, 7, 15) 8.1 accumulation sampler; diffusion sampler; equilibrated-
provide more specific information on the use of accumulation grab sampler; equilibrium sampler; groundwater sampling
...

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: D7929 − 14 D7929 − 20
Standard Guide for
Selection of Passive Techniques for Sampling Groundwater
Monitoring Wells
This standard is issued under the fixed designation D7929; 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 This standard provides guidance and information on passive sampling techniques for collecting groundwater from
monitoring wells. Passive groundwater samplers are able to acquire a sample at a discrete depth or from the screen interval in a
well, without the active transport associated with a pump or purge technique (1). Passive groundwater sampling is a type of
no-purge groundwater sampling method where the samplers are left in the well for a predetermined period of time prior to
collecting the sample.
1.2 Methods for sampling monitoring wells include low-flow purging and sampling methods, traditional well-volume purging
and sampling methods, post-purge grab sampling methods (for example, using a bailer), passive no-purge sampling methods, and
active no-purge sampling methods such as using a bailer to collect a sample without purging the well. This guide focuses on passive
no-purge sampling methodologies for collecting groundwater samples. These methodologies include the use of diffusion samplers,
accumulation samplers, and passive-grab samplers. This guide provides information on the use, advantages, disadvantages, and
limitations of each of these passive sampling technologies.
1.3 ASTM Standard D653 provides standard terminology relevant to soil, rock, and fluids contained in them. ASTM Standard
D4448 provides a standard guide to sampling groundwater wells, and ASTM Standards D5903 and D6089 provide guides for
planning and documenting a sampling event. Groundwater samples may require preservation (Guide D6517), filtration (Guide
D6564D6564/D6564M), and measures to pack and ship samples (Guide D6911). Standard D7069 provides guidance on the quality
control and quality assurance of sampling events. ASTM Standard D5092D5092/D5092M provides standard practice for the design
and installation of groundwater monitoring wells, ASTM Standard D5521D5521/D5521M provides a standard guide for
developing groundwater monitoring wells in granular aquifers, and D6452 provides a standard guide for purging methods used in
groundwater quality investigations. Consult ASTM Standard D6724D6724/D6724M for a guide on the installation of direct-push
groundwater monitoring wells and ASTM Standard D6725D6725/D6725M for a guide on the installation of direct-push
groundwater monitoring wells with pre-pack screens.
1.4 The values stated in SI Units are to be regarded as the standard. Values in inches (such as with well diameters) are given
in parentheses, and are provided for information. Use of units other than SI shall not be regarded as nonconforming with this
standard.
1.5 This guide provides information on passive groundwater sampling in general and also provides a series of considerations
when selecting a passive groundwater sampling method. However, it does not recommend a specific course of action, and not all
aspects of this guide may be applicable in all field situations. This document cannot replace education or experience and should
be used in conjunction with professional judgment. 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 of this document means only that the document has been
approved through the ASTM consensus process.
1.6 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.
This test method 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 Aug. 15, 2014Feb. 15, 2020. Published October 2014March 2020. Originally approved in 2014. Last previous edition approved in 2014 as
D7929 - 14. DOI: 10.1520/D7929-14.10.1520/D7929-20.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
*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
D7929 − 20
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
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4750 Test Method for Determining Subsurface Liquid Levels in a Borehole or Monitoring Well (Observation Well)
(Withdrawn 2010)
D4448 Guide for Sampling Ground-Water Monitoring Wells
D5092D5092/D5092M Practice for Design and Installation of Groundwater Monitoring Wells
D5521D5521/D5521M Guide for Development of Groundwater Monitoring Wells in Granular Aquifers
D5903 Guide for Planning and Preparing for a Groundwater Sampling Event
D6089 Guide for Documenting a Groundwater Sampling Event
D6452 Guide for Purging Methods for Wells Used for Ground Water Quality Investigations
D6517 Guide for Field Preservation of Ground Water Samples
D6564D6564/D6564M Guide for Field Filtration of Groundwater Samples
D6724D6724/D6724M Guide for Installation of Direct Push Groundwater Monitoring Wells
D6725D6725/D6725M Practice for Direct Push Installation of Prepacked Screen Monitoring Wells in Unconsolidated Aquifers
D6911 Guide for Packaging and Shipping Environmental Samples for Laboratory Analysis
D7069 Guide for Field Quality Assurance in a Groundwater Sampling Event
3. Terminology
3.1 For common definition of terms about soil and rock and the fluids contained in them, common technical terms used in this
standard, refer to Terminology in D653.
3.2 ExplanationDefinitions of Terms Specific to thisThis Standard:
3.2.1 passive environmental sampling, n—in groundwater, is a group of sampling technologies that were first developed to
sample air, were subsequently adapted to sample soil vapor, and now are being used to sample water. In the scientific literature,
passive sampling in air, soil, and water has been defined as any sampling technique techniques based on the free flow of analyte
molecules from the sampled medium to a receiving phase in a sampling device as a result of a difference between the chemical
potentials of the analytes in the two media (2 and 3). These passive sampling devices are usually based on diffusion through a
diffusion barrier or permeation through a membrane (2 and 3). Uptake of analytes follows a standard uptake curve where uptake
initially is linear, followed by a period of time where uptake is no longer linear (that is, becomes curvilinear), and finally
equilibration is reached. Analytes are retained in a suitable medium within the passive sampler, known as a reference or receiving
phase, which can be a solvent, chemical reagent, or a porous adsorbent (2 and 3). There are two main accumulation regimes, kinetic
and equilibrium, and these are described based on the device’s physical basis of operation as defined below.
3.2.1.1 equilibrium samplers, n—passive samplers that have an exposure time that is sufficiently long to permit establishment
of thermodynamic equilibrium between the sampled medium and receiving phase (3).
3.2.1.1 Discussion—
These passive sampling devices are usually based on diffusion through a diffusion barrier or permeation through a membrane into
a sorptive membrane or medium (2 and 3). Uptake of analytes follows a standard uptake curve where uptake initially is linear,
followed by a period of time where uptake is no longer linear (that is, becomes curvilinear), and finally equilibration is reached.
Analytes are retained in a suitable medium within the passive sampler, known as a reference or receiving phase, which can be a
solvent, chemical reagent, or a porous adsorbent (2 and 3). There are two main accumulation regimes, kinetic and equilibrium,
and these are described based on the device’s physical basis of operation as defined below.
3.2.1.2 integrative or kinetic samplers, n—passive samplers that work in the linear uptake phase (of a standard uptake curve)
where the rate of desorption of analytes from the receiving phase to the sampled medium is negligible (2 and 3). These samplers
provide a total mass for the time they are deployed, which can be converted to concentration values in some cases.
3.2.2 equilibrium samplers, n—in groundwater, passive samplers that have an exposure time that is sufficiently long to permit
the establishment of thermodynamic equilibrium between the sampled medium and receiving phase (3).
The last approved version of this historical standard is referenced on www.astm.org.
D7929 − 20
3.2.3 integrative or kinetic samplers, n—passive samplers that work in the linear uptake phase (of a standard uptake curve)
where the rate of desorption of analytes from the receiving phase to the sampled medium is negligible (2 and 3).
3.2.3.1 Discussion—
These samplers provide a total mass for the time they are deployed, which can be converted to concentration values in some cases.
3.2.4 no-purge groundwater sampling, n—in groundwater, sampling methods that differ from active purging-and-sampling
methods for sampling groundwater (as described in Guide D6452) in that there is no requirement to remove water from the well
prior to sampling.
3.2.4.1 Discussion—
No-purge methods can collect a sample using an active method (such as pumping, suction, bailing) or a passive method without
purging the well.
3.2.5 passive groundwater sampling, n—most in groundwater,groundwater sampling methods currently involve purging the well
prior to sample collection although, samples can be collected without purging the well as long as the data-quality objectives of the
investigation are met. Additional information on active sampling methods that involve purging the well can be found in Guides
a type of no-purge groundwater sampling method where the samplers are deployed in the well at one or more target depths within
the well screen or open bore hole and are then left in the well for a period of time D4448 andprior to D6452.collecting the sample
(rather than collecting a sample immediately).
3.2.5.1 Discussion—
These sampling methods do not use pumping, suction, or bailing to collect the sample and thus do not induce stress on the aquifer
(Guide D4448).
3.2.2.1 no-purge groundwater sampling, n—sampling methods that differ from active purging-and-sampling methods for
sampling groundwater (as described in Guide D6452) in that there is no requirement to remove water from the well prior to
sampling. Thus, without purging the well, no-purge methods can collect a sample using an active method (such as pumping,
suction, bailing) or a passive method.
3.2.2.2 passive groundwater sampling, n—a type of no-purge groundwater sampling method where the samplers are deployed
in the well at one or more target depths within the well screen or open bore hole and are then left in the well for a predetermined
period of time prior to collecting the sample (rather than collecting a sample immediately). These sampling methods do not use
pumping, suction, or bailing to collect the sample and thus do not induce stress on the aquifer (Guide D4448).
3.2.6 passive-groundwater samplers, n—in groundwater, devices deployed in a well for the purpose of passive groundwater
sampling.
3.2.6.1 Discussion—
These devices provide a sample from a specific location within the well screen or borehole. Spatial integration, which is likely,
is a result of natural ambient flow and mixing of the sampled medium within the monitoring well (4). These samplers can be
classified by the mechanism used to collect the sample and include: diffusion samplers (5 and 6), accumulation samplers (1, 7),
and passive-grab samplers.
3.2.7 diffusion samplers, n—in groundwater, usually contain deionized (DI) or distilled water inside a membrane and rely on
diffusion of analytes through the membrane to reach equilibrium with concentrations in the well.
3.2.7.1 Discussion—
These samplers are an equilibrium type of passive sampler (as defined in 3.2.2.1). The length of the equilibration period depends
primarily upon the types of analytes, the membrane material, the rate of exchange of water in the well, and temperature of the well
water.
3.2.8 accumulation samplers, n—in groundwater, typically consist of a liquid or solid sorbent medium, contained in a
permeable membrane or in direct contact with the water sample, and rely on diffusion and sorption to accumulate analytes in the
sampler.
3.2.8.1 Discussion—
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Although, these samplers can be used as either an integrative or equilibrium sampler, adsorptive samplers are prone to saturation
effects and other reactions which make them less suitable for equilibrium sampling (8). When these samplers are used in the
integrative (or kinetic) mode, the sampling time must be within the linear portion of the uptake curve.
3.2.9 passive-grab samplers, n—in groundwater, grab samplers that collect a whole water sample and require an equilibration
period prior to sample collection. Passive-grab samplers should not disturb the water column during sample collection, should be
able to collect a sample at the target depth(s) in the well, and should be able to isolate the sample inside the sampler prior to
removing it from the well.
3.2.10 passive-groundwater samplers,equilibration period, n—are deployedin groundwater, in the well for a set period of time
prior to sample collection; this is either an equilibration time or a deployment time that is based upon linear uptake of the analytes
by the sampler. All of these devices provide a sample from a specific location within the well screen or borehole. Spatial
integration, if any, is a result of natural ambient flow of the sampled medium. These samplers can be classified by the mechanism
used to collect the sample and include: diffusion samplers (the suggested deployment period for passive-grab samplers, diffusion
samplers, and 4 and 5), accumulation samplers (when1, 6), and passive-grab they are used as equilibrium samplers.
3.2.10.1 Discussion—
The appropriate deployment period depends upon one or more of the following factors: the time needed for environmental
disturbances caused by sampler deployment to dissipate and ambient conditions in the well to return, the time needed for
equalization of analyte concentrations with surrounding concentrations in the well water, and the time needed to reduce losses due
to sorption of the analytes by the sampler materials to negligible levels.
3.2.3.1 diffusion samplers, n—usually contain deionized (DI) or distilled water inside a membrane and rely on diffusion of
analytes through the membrane to reach equilibrium with concentrations in the well. These samplers are an equilibrium type of
passive sampler (as defined in 3.2.3). The length of the equilibration period depends primarily upon the types of analytes, the
membrane material, the rate of exchange of water in the well, and temperature of the well water.
3.2.3.2 accumulation samplers, n—typically consist of a membrane that houses a sorbent medium, either liquid or particulate,
and rely on diffusion and sorption to accumulate analytes in the sampler. Although, these samplers can be used as either an
integrative or equilibrium sampler, adsorptive samplers are prone to saturation effects and other reactions which make them less
suitable for equilibrium sampling (7). When these samplers are used in the integrative (or kinetic) mode, the sampling time must
be within the linear portion of the uptake curve.
3.2.3.3 passive-grab samplers, n—are grab samplers that collect a whole water sample and require an equilibration period prior
to sample collection. Passive-grab samplers should not disturb the water column during sample collection, should be able to collect
a sample at the target depth(s) in the well, and should be able to isolate the sample inside the sampler prior to removing it from
the well.
3.2.3.4 equilibration period, n—the suggested deployment period for all passive-grab and diffusion samplers and accumulation
samplers when they are used as equilibrium samplers. The appropriate deployment period depends upon one or more of the
following factors: the time needed for environmental disturbances caused by sampler deployment to dissipate and ambient
conditions in the well to return, the time needed for equalization of analyte concentrations with surrounding concentrations in the
well water, and the time needed to reduce losses due to sorption of the analytes by the sampler materials to negligible levels.
3.2.3.5 deployment time, n—a term used for an accumulation sampler that is being used as an integrative (or kinetic) sampler
and is a function of the time needed for the sampler to achieve quantitative levels of uptake of the target analytes. For accurate
quantitative measurements, the deployment time must be within the linear portion of the uptake curve of the sampler for the
analytes of interest.
3.2.11 deployment time, n—in groundwater, Deployment time is the period required for an accumulation sampler to achieve
quantitative levels of uptake of the target analytes when being used as an integrative (or kinetic) sampler.
4. Significance and Use
4.1 General—In the past ten (plus) years, the Passive groundwater sampling has increased use since the polyethylene diffusion
bag sampler was first introduced (5). As defined above, different types of passive samplers are now available with different
functions and usages. The Interstate Technology Regulatory Council (ITRC) has provided several technical and regulatory
documents on the use of passive groundwater sampling methods (1, 4-5-67). Collectively, these documents have provided
information and references on the technical basis for their use, comparison of sampling results with more traditional sampling
methods, descriptions of their proper use, limitations, and a survey of their acceptance and use by responding state regulators.
However, the ITRC documents are older and do not include more recent assessments and publications. This Standard seeks to
provide newer information on current practice and implementation of passive groundwater sampling techniques.
4.1.1 Because of the large number of passive samplers that have been developed over the past fifteen years for various types
of environmental sampling, it is beyond the scope of this standard to discuss separately each of the methods that could or can be
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used to sample groundwater. Extensive literature reviews on diffusion- and accumulation-passive samplers can be found in the
scientific literature (that is, 3, 7-8-1314). These reviews provide information on a wide variety of passive sampling devices for use
in air, soil vapor, and water. A review paper on the use of diffusion and accumulation-type passive samplers specifically for
sampling volatile organic compounds (VOCs) in groundwater (1415) includes information on other passive samplers that are not
included in the ITRC documents (1, 67) and discusses their use with respect to measuring mass flux.
4.2 Use—Passive samplers are deployed at a pre-determined depth, or depths, within a well for a minimum or pre-determined
period of time andtime. They should remain submerged at the target depth for their entire deployment time.period. All of the
passive technologies described in this document rely on the sampling device being exposed to the groundwater during deployment
and the continuous flushing of the open or screened interval of the well by ambient groundwater flow (((154), (5-7),16) to produce
water quality conditions in the well bore that effectively mimic those conditions in the aquifer adjacent to the screen or open
interval. For samplers that require the establishment of equilibrium, it is important that the equilibration period be long enough
to allow the well to recover from any disturbance caused by placing the sampler in the well and to prevent, or reduce, losses of
analytes from the water sample by sampler materials due to sorption. For kinetic accumulation samplers (used as kinetic samplers),
it is important that the deployment time is long enough that quantitative uptake can occur but not so long that uptake is no longer
in the linear portion of the uptake curve (that is, has become curvilinear).
4.2.1 As with all types of groundwater sampling methods, the appropriate use of passive methods assumes that the well has been
properly located (laterally and vertically), designed, constructed, and was adequately developed (as described in Guide
D5521D5521/D5521M) and maintained (as described in Practices D5092D5092/D5092M and D6725D6725/D6725M, or Guide
D6724D6724/D6724M). These measures are necessary so that the well is in hydraulic communication with the aquifer.
4.2.2 Each type of passive sampler has its own attributes and limitations, and thus data-quality objectives (DQOs) for the site
should be reviewed prior to selecting a device. For wells in low-permeability formations, diffusive flux may become more
important than advective flow in maintaining aquifer-quality water in the well.
4.3 Advantages—While passive methods are not expected to replace conventional pumped sampling in all situations, they often
offer an easier-to-use (requiring only minimal operator training), a faster alternative “tool” for sampling groundwater monitoring
wells when their use meets DQOs and regulatory requirements.because purging is eliminated from the pre-sampling procedure.
Other advantages include that these samplers can be used in most wells and typically have no depth limitation. These samplers
are either disposable or dedicated to a well, and this well. This eliminates or reduces the need for decontamination. Passive
samplers typically reduce the logistics associated with sampling and are especially useful at sites where it is difficult to bring larger
equipment (such as pumps and compressors) ontoto the site.well location.
4.3.1 Passive groundwater sampling techniques typically provide a much lower “per-sample” cost than conventional pumped
sampling methods (16-17-2526). This is primarily because the labor associated with collecting a sample is substantially
reduced.reduced and waste handling and disposal is substantially reduced. Eliminating handling and disposal of purge water is an
environmental benefit and advantage.
4.3.2 If there is interest in identifying contaminant stratification within the well, multiple passive samplers can be used to
characterize vertical contaminant distribution with depth. Baffles or packers can be used to segregate the sampling zones and often
provide better characterization of each zone. (In cases where turbidity is a concern, it is important to deploy the sampling devices
as gently as possible.) Profiling contamination with depth in a well can be especially useful informative when trying to decide
where to place a single passive sampler within the well screen; screen for long-term monitoring; placing a sampler at the mid-point
of the screen may not yield a sample with the highest contaminant concentrations or one that agrees best with previous low-flow
concentrations (for example, 2526).
4.4 Disadvantages—As with any groundwater sampling method, rapid or rigorous deployment of the sampler(s) (or pumps in
the case of active sampling methods) can increase turbidity in the well. For passive groundwater samplers, this can be reduced or
eliminated if the equilibration time is long enough to allow the return of the natural ambient turbidity in the well. In many cases,
passive samplers are deployed at the end of a sampling event and left in the well until the next scheduled sampling event; this
practice provides more than enough time for equilibration to occur. Some methods require dedicated equipment purchase which
may increase the cost for the initial sampling event in order to obtain the overall cost advantage.
4.4.1 It is also possible that some wells where only passive sampling methods are used may require more frequent maintenance
than wells that are routinely pumped. However in other instances, sampling methods that utilize pumping can bring fines into the
well and the well may need more maintenance than if a passive method is used.
4.5 Limitations—There are three primary limitations with passive samplers: analyte capability, sample volume, and physical size
(that is, with respect to well diameter).diameter. For the diffusion and accumulation samplers, the membrane and sorbent (for
accumulation samplers) or sorbent, respectively, determine the specificity analyte capability of the sampler. Although, two or more
individual types of samplers can be used simultaneously to sample for a broader spectrum of analyte types. In contrast,
passive-grab samplers collect whole water samples and can be used for most analytes.any analyte, subject to sample volume and
physical size limitations.
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4.5.1 Analyte capability is often unique to individual passive samplers. In the case of diffusion-based passive samplers, the user
should verify that the membrane is suitable for the analytes to be tested. ITRC (5-7) describes the analyte capability of
diffusion-bases passive samplers. Two or more individual types of passive samplers can be used simultaneously to sample for a
broader spectrum of analyte types.
4.5.2 With respect to volume limitations, the passive-grab Passive-grab and passive-diffusion samplers collect a finite sample
volume. This volume may not be sufficient when there are several types of analytes to be analyzed or when several water-quality
measurements (such as dissolved oxygen (DO), pH, etc.) need to be conducted (that is, surface measurements versus in-situ
measurements). Total sampler volume may limit the number and type of analytes that can be practically collected. Additional
samplers or larger volume samplers may be available and can be used to meet the volume requirements. Alternatively,Also,
because laboratories typically use only a small portion of the sample collected, it may be possible to provide the laboratory with
a smaller sample volume. Table X1.1 provides suggested minimum volumes for several analyte classes. However prior to
sampling, the total volume of sample needed to run all of the chemical analyses should be confirmed (for each sampling point)
with the laboratory.The laboratory should be consulted to confirm adequate sample volume during the method selection process.
4.5.3 Finally, the Regarding physical sizes of the sampler(s), the diameter of the sampler or combination of samplers must be
able to fit in the well or multi-level sampler.
NOTE 1—The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the
equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing. Users
of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors;
Practice D3740 provides a means of evaluating some of those factors.
5. Considerations for Passive Groundwater Sampling
5.1 Planning a Passive Sampling Event—As with all sampling activities, it is essential that all parties involved in planning the
use of any sampling method identify and agree on the sampling and data-quality objectives, data-evaluation criteria, end use of
the data, target analytes, and hydrogeologic concerns before the sampling method is selected. The appropriateness of any method
is determined by the data-quality objectives (DQOs) for the sampling event and overall site monitoring program, and by the ability
of the sampling method to meet them accurately and reliably. Considerations when selecting a passive sampling method can
include sampler design, ability of the sampler to collect the target contaminants, well construction (including well diameter, screen
and filter pack length, and proper slot size for the screen and filter pack design as described in Practice D5092D5092/D5092M),
vertical and horizontal flow patterns within the well, and contaminant stratification. Additional guidance on the selection of a
passive sampling method can be found in Table X2.1.
5.2 Analytes of Interest—When deciding whether to use passive sampling or which passive sampling method to use,
consideration should be given to the contaminants of concern (COCs) for the site and other analytes or parameters that may be
used to evaluate the geochemical processes of interest. Some passive samplers collect only specific analytes, whereas other devices
can be used for a broader suite of analyte types.
5.2.1 Some samplers collect a limited volume of sample, and this may limit the use of these samplers. The sample volume that
can be collected will be determined by the type of passive sampler, the diameter of the well, and the length of the desired sampling
interval in the well. A larger total sample volume can be obtained by increasing the number of samplers used within the sampling
interval (at the same depth or in series with depth) or, in some cases, by increasing the size of the sampling device (that is, using
a longer or wider diameter sampler). However, when samplers are deployed in series with depth, concentrations in the samplers
will reflect any stratification that exists in the sampling zone. Also, as mentioned previously, consulting with the analytical
laboratory may make it possible to reduce the minimum volume of sample. (See Table X1.1 for suggested minimum volumes.)
5.2.2 More specific information on the capabilities of particular sampling devices can be found in 6.1.46.1, 6.2.46.2, and
6.3.86.3, and in Table X2.1. For devices that are available commercially, current information can also be obtained by contacting
the sampler vendor(s).manufacturer(s) or supplier(s).
5.3 Site Considerations—In general, passive groundwater samplers can be used in a wide variety of hydrogeologic settings. Site
considerations can include: accessibility of the wells, well diameter, screen length, saturated thickness, the hydraulic connection
between the well and aquifer, and the hydraulic gradient that generates flow. Passive samplers are particularly well suited for
conditions where active sampling methods can be problematic. These conditions can include low-yield formations where excessive
drawdown is unavoidable even at low flow rates, locations that where purge methods result in large volumes of purge water that
must be disposed, locations that are difficult to access with a vehicle, or where low-turbidity samples are needed but cannot be
obtained using other sampling methods such as with a bailer or a pump.
5.3.1 However, there can be situations that preclude the use of any sampling method, including standard purged methods. Both
passive and active sampling methods may inadvertently collect non-aqueous phase liquid (NAPL). For example, this can occur
when a sampler or pump passes through a NAPL zone during deployment or when droplets are drawn down or entrained while
pumping the well. In these cases, collection of water samples from wells containing NAPL may overestimate the risk to human
health dissolved-phase concentrations and may complicate data interpretation. Therefore, the practical effect of this bias on the
sampling objectives and project DQOs should be evaluated, and continued collection of the water sample may not be warranted.
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5.4 Acceptability of Passive Groundwater Sampling Methods—Numerous studies have shown that passive-groundwater
sampling methods can be valid and viable collect representative concentrations of groundwater constituents of concern and are
appropriate alternatives to purged sampling methods. (These studies Studies illustrating representativeness and comparability to
purge sampling approaches are listed for each type of sampling device in 6.1.46.1, 6.2.46.2, and 6.3.86.3.) As a whole, passive
groundwater sampling methods continue to gain acceptance among the regulatory, scientific, and user communities. Much of the
acceptance of these methods can be attributed to the publication of guidance documents and free internet training provided by the
ITRC Diffusion/Passive-Sampler Team.
5.4.1 Questions about the “need to purge” have been largely answered over the course of the last few decades (1516, 2627,
2728). In properly designed, developed, and maintained monitoring wells, adequate hydraulic communication exists between the
aquifer and well. With adequate hydraulic gradient, aquifer water flows into and out of the screened or open sections of a well.
Passive sampling devices set in such screened or open zones will collect aquifer water that is in dynamic equilibrium with the
aquifer without purging. The As with pumping, the hydraulics within the well, well bore, and the formation will determine what
the sample actually represents. It is not in the scope of this guide to describe how an aquifer is to be represented; that is for the
user to determine.represents. The same factors are at play with the different available passive sampling methods.
5.4.2 There are conditions where a passive sample does not collect a sample from the entire screened zone of a well. This may
be due to, for example, vertical flow in the well, contaminant stratification, poor hydraulic communication, or a low hydraulic
conductivity in the formation (creating a long residence time in the well). However, these conditions can also be problematic for
purged sampling methods (2829, 2930). These conditions do not necessarily make passive sampling an unacceptable alternative
becausealternative, rather, passive sampling can may simply represent the adjacent aquifer differently than a pumped sampling
method. In contrast, pumped sampling methods collect a flow-weighted average sample that is more heavily weighted by the more
transmissive portions of the adjacent aquifer(s). Recommendations on how to deal with differences between analyte concentrations
when comparing passive vs. active sampling methods are given in Appendix X3.
5.4.3 In instances where there is poor hydraulic communication between the aquifer and the well, rehabilitation of the well or
redevelopment often improves the communication between the aquifer and well. This can be necessary for both pumped and
passive methods.
5.5 Implementing Passive Sampling Methods—Technical concerns, regulatory concerns, or both should be addressed when
selecting a sampling method or changing one, as there There are inherent advantages and limitations in every groundwater
sampling method. These differences should be examined within the context of the particular project objectives, data needs, and site
conditions for each proposed application. A fundamental concern of regulators is that the sampling method used at a site, or at a
particular well, provides results that meet the DQOs for the project.
5.5.1 Method Selection—There are many different passive sampling systems,systems and these technologies vary with respect
to in the degree of field validation they have received. Methods that can validation. Methods that have strong field validation and
provide good reproducibility among different users, field conditions, and time frames are best suited for long-term monitoring
strategies. Two or more passive sampling techniques may be deployed simultaneously and provide samples for a broader range of
analytes and thereby meet the site DQOs. Also for well water with For a broad range of analyte concentrations, it may be necessary
to deploy two or more samplers of the same type in a well.
5.5.2 New Sites—In cases where new wells or a new site is under consideration, selection of a sampling method does not rely
on historical data continuity,continuity and thus method selection would rely on a rigorous an evaluation of the data quality needs
for the site. Improved site-characterization methods can yield better designed wells (often with shorter screens) and thereby
improve this decision process. Data from passive sampling methods that use multi-level samplers may provide more specific and
detailed high-resolution information in terms of aquifer stratigraphy, contaminant fate and transport, and site management.
5.5.3 Older Sites—There should be no impediment to switching to a passive method as long as the DQOs of the site are well
understood and can be met by the particular sampling method chosen. A number of field and laboratory studies (listed in 6.1.46.1,
6.2.46.2, and 6.3.86.3) have been conducted to determine the comparability of passive methods with conventional sampling
methods. These studies reveal that in most situations, passive methods provide samples that have analyte concentrations that are
not significantly different (on a statistical basis) from those collected using other conventional sampling methods such as low-flow
purging and sampling. When considering a change in sampling methods, the question arises how the results of the existing and
new methods will compare. When converting to a passive sampling method, a side-by-side comparison test with the site’s current
method or comparison with historical data may be desirable to understand data differences between sampling methods. Further
discussion on how to conduct this type of test, how to analyze the data, and how to interpret the data are given in Appendix X3.
5.5.3.1 When considering a change in sampling methods, the question arises how the results of the existing and new methods
will compare. When converting to a passive sampling method, a side-by-side comparison test with the site’s current method or
comparison with historical data may be necessary to understand data differences between sampling methods or may be required
by a regulator. Further discussion on how to conduct this type of test, how to analyze the data, and how to best interpret the data
are given in Appendix X3.
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6. Types of Passive Groundwater Sampling Devices
The three types of passive groundwater sampling devices (that devices—that is, passive-grab samplers, diffusion samplers, and
accumulation samplers) vary samplers—vary greatly in how they function and each type has its own specific deployment-time
requirements. This section describes these three general types of passive samplers and the supporting validation references.
6.1 Passive-grab Samplers are used to collect a whole water sample from a discrete depth or interval within the well or borehole
after a predeterminedrecommended deployment period in the well. This residence Residence time allows the well to recover from
the disturbance caused by inserting the sampler in the well and thus allows the water in the screened interval to return to the
ambient flow conditions that existed between the well and the formation. This reduces the possibility of collecting a sample with
an artificially elevated turbidity and thus obtaining falsely elevated concentrations of particle-borne contaminants. ThisDeployment
residence time also allows time for the sampler materials to effectively equilibrate with analyte concentrations in the surrounding
well water prior to sample collection, and thereby prevents, or reduces, analyte losses due to sorption by the sampler materials
(30-31-3435). Sample collection does not occur until the device is triggered or actuated. Passive-grab samplers should not disturb
the water column during sample collection, should be able to collect a sample at the target depth(s), and should be able to isolate
the sample inside the sampler prior to removing it from the moving the sampler within the well. These criteria distinguish
“passive-grab samplers” from other grab samplers that are used as no-purge samplers, such as various types of bailers including
point-source bailers and collapsible bailers (for example, sleeve-type samplers). The ITRC Diffusion/Passive Sampler Team (1, 67)
previously categorized grab samplers used in passive sampling as “equilibrated-grab samplers.” However, not all of “equilibrated-
grab samplers” meet the more restrictive definition for passive-grab“passive-grab samplers” given in this standard.
6.1.1 Advantages—The primary advantage of passive-grab samplers is that typically they can be used to collect samples for a
wide range of organic and inorganic analytes. This is because sample collection is not limited by the sampler membrane or the
collection media inside the device. These devices do not exclude colloidal particles, and thus can be used to collect samples for
analyses of total and dissolved concentrations of analytes. Samples collected with these samplers can be used to measure pH,
oxidation-reduction potential (ORP), electrical conductivity, and dissolved gases. Also, these These samplers can be used for
quarterly, semi-annual, or annual sampling events. After collecting aevents with single mobilizations for sample collection. After
collecting each sample, a new sampler or sample bottle is placedreplaced in the well thereby eliminating having to make in
preparation for the next event, avoiding a second trip to the field. For one passive-grab sampler (that is commercially available),
type of passive-grab sampler, the samples are sealed in a sample bottle in the well. In some instances the sample bottle can remain
sealed until the sample is analyzed; this prevents loss of VOCs during transfer in the field or in the laboratory.laboratory ((36)).
6.1.2 Disadvantages—For passive-grab samplers, inadvertently agitating or aerating the well or dislodging particles from the
inside of the well casing or well bore during sampler deployment can alter some analyte concentrations including dissolved gases,
metals subject to oxidation/precipitation reactions, and particle-borne or colloid-borne contaminants. However, entraining particles
that are not part of the total mobile load moving through the aquifer under ambient conditions can also occur with pumped
sampling methods. Therefore, the The length of the equilibration period should be sufficient to provide time for the well to recover
from any disturbance caused by inserting the sampling device in the well. The extent of recovery in the well depends upon the
flow rate in and out of the screened interval and the condition of the well. In instances where entraining extraneous particles is
a problem, this can be mitigated in some cases by redeveloping the well.
6.1.3 Limitations—The primary limitations with these samplers are their size and the sample volume collected. Typically, these
samplers do not fit in wells less than 5 cm (2 in.) in diameter. In instances where a larger sampler volume is needed, a larger sampler
may be available or, it may be possible to place several samplers at the same depth in larger diameter wells or in series with depth
in smaller diameter wells. However, placing multiple samplers in series with depth extends the length of sampling interval, and
this longer sampler could also dislodge particles from the wall of the well, which could become entrained in the sample.
6.1.4 Additional Information—
...