ASTM D4448-01(2019)
(Guide)Standard Guide for Sampling Ground-Water Monitoring Wells
Standard Guide for Sampling Ground-Water Monitoring Wells
SIGNIFICANCE AND USE
5.1 The quality of ground water has become an issue of national concern. Ground-water monitoring wells are one of the more important tools for evaluating the quality of ground water, delineating contamination plumes, and establishing the integrity of hazardous material management facilities.
5.2 The goal in sampling ground-water monitoring wells is to obtain samples that meet the DQOs. This guide discusses the advantages and disadvantages of various well sampling methods, equipment, and sample preservation techniques. It reviews the variables that need to be considered in developing a valid sampling plan.
SCOPE
1.1 This guide covers sampling equipment and procedures and “in the field” preservation, and it does not include well location, depth, well development, design and construction, screening, or analytical procedures that also have a significant bearing on sampling results. This guide is intended to assist a knowledgeable professional in the selection of equipment for obtaining representative samples from ground-water monitoring wells that are compatible with the formations being sampled, the site hydrogeology, and the end use of the data.
1.2 This guide is only intended to provide a review of many of the most commonly used methods for collecting ground-water quality samples from monitoring wells and is not intended to serve as a ground-water monitoring plan for any specific application. Because of the large and ever increasing number of options available, no single guide can be viewed as comprehensive. The practitioner must make every effort to ensure that the methods used, whether or not they are addressed in this guide, are adequate to satisfy the monitoring objectives at each site.
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 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.
General Information
Relations
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: D4448 − 01 (Reapproved 2019)
Standard Guide for
Sampling Ground-Water Monitoring Wells
This standard is issued under the fixed designation D4448; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This guide covers sampling equipment and procedures
D4750 Test Method for Determining Subsurface Liquid
and “in the field” preservation, and it does not include well
Levels in a Borehole or Monitoring Well (Observation
location, depth, well development, design and construction,
Well) (Withdrawn 2010)
screening, or analytical procedures that also have a significant
D5088 Practice for Decontamination of Field Equipment
bearing on sampling results. This guide is intended to assist a
Used at Waste Sites
knowledgeable professional in the selection of equipment for
D5792 Practice for Generation of Environmental Data Re-
obtaining representative samples from ground-water monitor-
lated to Waste Management Activities: Development of
ing wells that are compatible with the formations being
Data Quality Objectives
sampled, the site hydrogeology, and the end use of the data.
D5903 Guide for Planning and Preparing for a Groundwater
1.2 This guide is only intended to provide a review of many
Sampling Event
of the most commonly used methods for collecting ground-
D6089 Guide for Documenting a Groundwater Sampling
water quality samples from monitoring wells and is not
Event
intended to serve as a ground-water monitoring plan for any
D6452 Guide for Purging Methods for Wells Used for
specific application. Because of the large and ever increasing Ground Water Quality Investigations
number of options available, no single guide can be viewed as D6517 Guide for Field Preservation of Ground Water
comprehensive. The practitioner must make every effort to Samples
ensure that the methods used, whether or not they are ad-
2.2 EPA Standards:
dressed in this guide, are adequate to satisfy the monitoring
EPA Method 9020A
objectives at each site.
EPA Method 9022
1.3 The values stated in SI units are to be regarded as
3. Terminology
standard. The values given in parentheses are provided for
information only. 3.1 Definitions:
3.1.1 low-flow sampling—a ground-water sampling tech-
1.4 This standard does not purport to address all of the
nique where the purge and sampling rates do not result in
safety concerns, if any, associated with its use. It is the
significant changes in formation seepage velocity.
responsibility of the user of this standard to establish appro-
3.1.2 minimal purge sampling—the collection of ground
priate safety, health, and environmental practices and deter-
water that is representative of the formation by purging only
mine the applicability of regulatory limitations prior to use.
thevolumeofwatercontainedbythesamplingequipment(that
1.5 This international standard was developed in accor-
is, tubing, pump bladder).
dance with internationally recognized principles on standard-
3.1.2.1 Discussion—This sampling method should be con-
ization established in the Decision on Principles for the
sidered in situations where very low yield is a consideration
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
This guide is under the jurisdiction of ASTM Committee D34 on Waste the ASTM website.
Management and is the direct responsibility of Subcommittee D34.01.02 on The last approved version of this historical standard is referenced on
Sampling Techniques. www.astm.org.
Current edition approved Feb. 1, 2019. Published February 2019. Originally AvailablefromUnitedStatesEnvironmentalProtectionAgency(EPA),William
approved in 1985. Last previous edition approved in 2013 as D4448 – 01 (2013). Jefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460,
DOI: 10.1520/D4448-01R19. http://www.epa.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4448 − 01 (2019)
and results from this sampling method should be scrutinized to completely inert material, does not subject the sample to
confirm that they meet data quality objectives (DQOs) and the pressurechange,doesnotexposethesampletotheatmosphere,
work plan objectives. or any other gaseous atmosphere before conveying it to the
sample container or flow cell for on-site analysis. Since these
3.1.3 passive sampling—the collection of ground-water
ideals are not always obtainable, compromises must be made
quality data so as to induce no hydraulic stress on the aquifer.
by the knowledgeable individual designing the sampling pro-
3.1.4 water quality indicator parameters—refer to field
gram.Theseconcernsshouldbedocumentedinthedataquality
monitoring parameters that include but are not limited to pH,
objectives (DQOs) of the sampling plan (see Practice D5792)
specific conductance, dissolved oxygen, oxidation-reduction
(4).
potential, temperature, and turbidity that are used to monitor
4.6 The degree and type of effort and care that goes into a
the completeness of purging.
sampling program is always dependent on the chemicals of
4. Summary of Guide
concern and their reporting levels as documented in the
project’s DQOs.As the reporting level of the chemical species
4.1 The equipment and procedures used for sampling a
of analytical interest decreases, the precautions necessary for
monitoring well depend on many factors. These include, but
sampling generally increase. Therefore, the sampling objective
are not limited to: the design and construction of the well, rate
must clearly be defined ahead of time in the DQOs. The
of ground-water flow, and the chemical species of interest.
specificprecautionstobetakeninpreparingtosamplefortrace
Sampling procedures may be different if analyses for trace
organics are different from those to be taken in sampling for
organics, volatiles, oxidizable species, or trace metals are
tracemetals.AdraftU.S.EPAguidancedocument (5)concern-
needed. This guide considers all of these factors by discussing
ing monitoring well sampling, including considerations for
equipment and procedure options at each stage of the sampling
trace organics, is available to provide additional guidance.
sequence. For ease of organization, the sampling process can
be divided into three steps: well purging, sample withdrawal,
4.7 Care must be taken not to contaminate samples or
and field preparation of samples. Certain sampling protocols
monitoring wells.All samples, sampling devices, and contain-
eliminate the first step.
ers must be protected from possible sources of contamination
when not in use. Water level measurements should be made
4.2 The sampling must be well planned and all sample
according to Test Method D4750 before placing, purging, or
containers must be prepared prior to going to the field. These
samplingequipmentinthewell.Redoxpotential,turbidity,pH,
procedures should be incorporated in the approved work plan
specific conductance, DO (dissolved oxygen), and temperature
that should accompany the sampling crew so that they may
measurements should all be performed on the sample in the
refer to it for guidance on sampling procedures and analytes to
field, if possible, since these parameters change too rapidly to
be sampled (see Guide D5903).
be conducted by a fixed laboratory under most circumstances.
4.3 Monitoring wells must be either purged to remove
Field meter(s) or sondes equipped with flow-through cells are
stagnant water in the well casing or steps must be taken to
available that are capable of continuously monitoring these
ensure that only water meeting the DQOs and the work plan
parameters during purging if they are being used as water
objectives is withdrawn during sampling (see Practice D5792).
quality indicator parameters.These devices prevent the mixing
When well purging is performed, it is accomplished by either
of oxygen with the sample and provide a means of determining
removing a predetermined number of well volumes or by the
when the parameters have stabilized. Certain measurements
removal of ground water until stable water quality parameters
thatareusedasindicatorsofbiologicalactivity,suchasferrous
have been obtained. Ideally, this purging is performed with
iron, nitrite, and sulfite, may also be conducted in the field
minimal well drawdown and minimal mixing of the formation
since they rapidly oxidize.All temperature measurements must
waterwiththestagnantwaterabovethescreenedintervalinthe
be done prior to any significant atmospheric exposure.
casing. Passive sampling and the minimal purge methods do
not attempt to purge the water present in the monitoring well
5. Significance and Use
prior to sampling (1). The minimal purge method attempts to
5.1 The quality of ground water has become an issue of
purge only the sampling equipment. Each of these methods is
national concern. Ground-water monitoring wells are one of
discussed in greater detail in Section 6.
the more important tools for evaluating the quality of ground
4.4 The types of chemical species that are to be sampled, as
water, delineating contamination plumes, and establishing the
well as the reporting limits, are prime factors for selecting
integrity of hazardous material management facilities.
sampling devices (2, 3). The sampling device and all materials
5.2 The goal in sampling ground-water monitoring wells is
anddevicesthewatercontactsmustbeconstructedofmaterials
toobtainsamplesthatmeettheDQOs.Thisguidediscussesthe
that will not introduce contaminants or alter the analytes of
advantages and disadvantages of various well sampling
concern in any way. Material compatibility is further discussed
methods, equipment, and sample preservation techniques. It
in Section 8.
reviews the variables that need to be considered in developing
4.5 The method of sample collection can vary with the a valid sampling plan.
parameters of interest. The ideal sampling scheme employs a
6. Well Purging
6.1 Water that stands within a monitoring well for a long
The boldface numbers in parentheses refer to a list of references at the end of
this guide. period of time may become unrepresentative of formation
D4448 − 01 (2019)
waterbecausechemicalorbiochemicalchangemayalter water above. But the packer must be above the top of the screened
quality or because the formation water quality may change zone, or stagnant water from above the packer may flow into
over time (see Guide D6452). Even if it is unchanged from the the purged zone through the well’s gravel/sand pack.
time it entered the well, the stagnant water may not be
6.5 An alternate method is based on research by Barcelona,
representative of formation water at the time of sampling.
Wehrmann, and Varlien (1) and Puls and Powell (2). Their
There are two approaches to purging that reflect two differing
research suggests that purging at rates less than 1 L/min
viewpoints: to purge a large volume of ground water and to
(approximately 0.25 gal/min) provides more reproducible
purge a minimum of, or no ground water before collecting a
VOCs and metals analytical results than purging at high rates.
sample. The approach most often applied is to purge a
This method is based on the premise that at very low pumping
sufficientvolumeofstandingwaterfromthecasing,alongwith
rates, there is little mixing of the water column and laminar
sufficient formation water to ensure that the water being
ground-water flow through the screen provides a more consis-
withdrawn at the time of sampling is representative of the
tent sample. This sampling method also produces less turbid
formation water.Typically, three to five well volumes are used.
samples that may eliminate the need for filtration when
Analternativemethodthatisgainingacceptanceistominimize
collecting metals. This method is commonly referred to as
purging and to conduct purging at a low flow rate or to
low-flow sampling.
eliminate purging entirely.
6.6 The low-flow sampling approach is most applicable to
6.2 In any purging approach, a withdrawal rate that mini-
wells capable of sustaining a yield approximately equal to the
mizes drawdown while satisfying time constraints should be
pumpingrate.Amonitoringwellwithaverylowyieldmaynot
used. Excessive drawdown distorts the natural flow patterns
be applicable to this technique, since it may be difficult to
around the well. Two potential negative effects are the intro-
reduce the pumping rate sufficiently to prevent mixing of the
duction of ground water that is not representative of water
water column in the well casing in such a well.The water level
quality immediately around the monitoring well and artificially
in the well being sampled should be continuously monitored
high velocities entering the well resulting in elevated turbidity
using an electronic water-level indicator during low-flow
and analytical data that reflects the absorption of contaminants
sampling. Such a water-level indicator could be set below the
to physical particles rather than soluble concentrations in
water surface after sufficient water has been withdrawn to fill
ground water. It may also result in cascading water from the
the pump, tubing, and flow cell. The water-level indicator
top of the screen that can result in changes in dissolved gases,
wouldthenproduceacontinuoussignalindicatingsubmersion.
redox state, and ultimately affect the concentration of the
When the well is purged, if the water level falls below the
analytes of interest through the oxidation of dissolved metals
water-level indicator probe, the signal indicates that the water
andpossiblelossofvolatileorganiccompounds(VOCs).There
level has fallen below the maximum allowable drawdown and
may also be a lingering effect on the dissolved gas levels and
the pumping rate should be decreased. Pumping is started at
redox state from air being introduced and trapped in the
approximately 100 mL/min discharge rate and gradually ad-
sandpack. In no instance shall a well be purged dry. If
justed to match the well’s recharge rate. The selection of the
available, the field
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