ASTM D4448-01(2019)

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

• Status: Published
• Publication Date: 31-Jan-2019
• ICS: 13.060.10 - Water of natural resources
• Technical Committee: D34 - Waste Management
• Drafting Committee: D34.01.02 - Sampling Techniques

Relations

• Replaces: ASTM D4448-01(2013) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Feb-2019
• 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 D6517-18(2023) - Standard Guide for Field Preservation of Ground Water Samples
• 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 D5792-10(2023) - Standard Practice for Generation of Environmental Data Related to Waste Management Activities: Development of Data Quality Objectives
• Effective Date: 01-Nov-2023
• Refers: ASTM D5088-20 - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 01-May-2020
• Refers: ASTM D6089-19 - Standard Guide for Documenting a Groundwater Sampling Event
• Effective Date: 01-Aug-2019
• Refers: ASTM D6452-18 - Standard Guide for Purging Methods for Wells Used for Ground Water Quality Investigations
• Effective Date: 01-Dec-2018
• Refers: ASTM D6517-18 - Standard Guide for Field Preservation of Ground Water Samples
• Effective Date: 01-Dec-2018
• Refers: ASTM D5792-10(2015) - Standard Practice for Generation of Environmental Data Related to Waste Management Activities: Development of Data Quality Objectives
• Effective Date: 01-Sep-2015
• Refers: ASTM D5088-15a - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 01-Aug-2015
• Refers: ASTM D6089-15 - Standard Guide for Documenting a Groundwater Sampling Event
• Effective Date: 01-Mar-2015
• Refers: ASTM D5088-15 - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 15-Jan-2015
• Refers: ASTM D6452-99(2012)e1 - Standard Guide for Purging Methods for Wells Used for Groundwater Quality Investigations
• Effective Date: 01-Jul-2012
• Refers: ASTM D5903-96(2012) - Standard Guide for Planning and Preparing for a Groundwater Sampling Event
• Effective Date: 01-Jul-2012

Overview

ASTM D4448-01(2019), Standard Guide for Sampling Ground-Water Monitoring Wells, is established by ASTM International to assist environmental professionals in the collection of representative groundwater samples. This guide addresses the appropriate selection of sampling equipment, field procedures, and sample preservation techniques to ensure that sample integrity is maintained and that data quality objectives (DQOs) are met. With groundwater quality being a nationally significant concern, this standard supports efforts to monitor, detect contamination, and evaluate the effectiveness of hazardous material management practices.

Key Topics

• Sampling Equipment and Materials: The guide reviews commonly used devices, such as bailers, bladder pumps, and low-flow samplers, outlining the importance of using materials compatible with sample constituents to avoid contamination.
• Sampling Methods: Advantageous and disadvantageous aspects of various sampling techniques, including well purging methods (full, minimal, or no purge), low-flow sampling, and passive collection, are discussed to aid in method selection based on site-specific hydrogeology.
• Sample Preservation and Handling: Recommendations for in-field preservation address techniques to prevent chemical or biological alterations before laboratory analysis, ensuring sample accuracy.
• Contamination Control: The guide emphasizes decontamination procedures for field equipment to prevent cross-contamination between wells and samples, as well as the importance of personal and environmental safety.
• Indicator Parameters: Parameters such as pH, temperature, specific conductance, dissolved oxygen, redox potential, and turbidity are highlighted for field monitoring and evaluating sample stability and representativeness.
• Data Quality Objectives (DQOs): Strategies for ensuring sample quality meet project objectives and regulatory requirements are outlined, stressing the necessity of well-defined sampling plans.

Applications

The practical applications of ASTM D4448-01(2019) are broad and crucial for environmental management and regulatory compliance:

• Contamination Assessment: Groundwater monitoring wells, following this standard, help delineate contamination plumes and determine the extent of pollutant migration.
• Facility Integrity Evaluation: The guide aids in assessing the performance and containment of hazardous waste management facilities.
• Environmental Site Characterization: Provides protocols for collecting high-quality groundwater data needed in site investigation and remediation projects.
• Regulatory Compliance: Ensures sampling practices align with local, national, and international environmental protection guidelines and reporting requirements.
• Long-Term Monitoring: Supports facilities and agencies in ongoing groundwater quality surveillance programs aimed at protecting public health and the environment.

Related Standards

Several referenced and companion standards enhance the scope and utility of ASTM D4448-01(2019):

• ASTM D4750: Test Method for Determining Subsurface Liquid Levels in a Borehole or Monitoring Well.
• ASTM D5088: Practice for Decontamination of Field Equipment Used at Waste Sites.
• ASTM D5792: Practice for Generation of Environmental Data Related to Waste Management Activities: Development of Data Quality Objectives.
• ASTM D5903: Guide for Planning and Preparing for a Groundwater Sampling Event.
• ASTM D6089: Guide for Documenting a Groundwater Sampling Event.
• ASTM D6452: Guide for Purging Methods for Wells Used for Ground Water Quality Investigations.
• ASTM D6517: Guide for Field Preservation of Ground Water Samples.
• EPA Methods 9020A and 9022: U.S. EPA-approved groundwater monitoring and analytical procedures.

Practical Value

By adopting ASTM D4448-01(2019), professionals ensure the validity and reliability of groundwater data, essential for accurate contamination assessments, risk management, and environmental compliance. The guide addresses the growing demand for transparent, high-quality environmental sampling, supporting sustainable management of water resources and safeguarding public health. Adherence to internationally recognized groundwater sampling protocols enhances data comparability, decision-making, and regulatory acceptance across diverse projects.

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 [e-mail]. 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 notes or purge logs generated during
type of pump is dependent on site-specific conditions and
previous sampling or development of the well, as well as
DQOs. The bladder pump design is most commonly used in
construction logs, should be reviewed to assist in the selection
this sampling method; however, the depth limitation of this
of the most appropriate sampling method.
pump may necessitate the use of a gas-driven piston pump in
6.3 The most often applied purging method has an objective some instances.
to remove a predetermined volume of stagnant water from the
6.7 A variation on the above purging approaches is to
casing prior to sampling. The volume of stagnant water can
monitor one or more indicator parameters until stabilization of
either be defined as the volume of water contained within the
the selected parameter(s) has been achieved. Stabilization is
casing and screen, or to include the well screen and any gravel
considered achieved when measurements are within a pre-
pack if natural flow through these is deemed insufficient to
defined range. This range has been suggested to be approxi-
keep them flushed out. Research with a tracer in a full-scale
mately 10 % over two successive measurements made 3 min
model 2-in. polyvinyl chloride (PVC) well (6) indicates that
apart by the U.S. EPA (4). More recent documents (9) have
pumping five to ten times the volume of the well via an inlet
suggestedranges 60.2 °Cfortemperature, 60.1standardunits
near the free water surface is sufficient to remove all the
for pH, 63 % for specific conductance, 610 % for DO, and
stagnant water in the casing. This approach (with three to five
610 mV for redox potential. A disadvantage of the stabiliza-
casing volumes purged) was suggested by the U.S. EPA (7).
tion approach is that there is no assurance in all situations that
6.4 In deep or large-diameter wells having a volume of the stabilized parameters represent formation water. These
water so large as to make removal of all the water impractical, criteria should therefore be set on a site-by-site basis since if
it may be feasible to lower a pump or pump inlet to some point set too stringent, large volumes of contaminated purge water
wellbelowthewatersurface,purgeonlythevolumebelowthat may be generated without ensuring that the samples are any
point, then withdraw the sample from a deeper level. Research more representative. In a low yielding formation, this could
indicates this approach should avoid most contamination resultinthewellbeingemptiedbeforetheparametersstabilize.
associated with stagnant water (6, 8). Sealing the casing above Also, if significant drawdown has occurred, water from some
the purge point with a packer may make this approach more distance away may be pulled into the screen causing a steady
dependable by preventing migration of stagnant water from parameter reading but not a representative reading. If these
D4448 − 01 (2019)
criteria are properly selected, the volume of investigative must be collected within the screened interval with little or no
derived waste water may be reduced. mixing of the water column within the casing. Examples of
these techniques include minimal purge sampling which uses a
6.8 The indicator parameters that may be monitored include
dedicatedsamplingpumpcapableofpumpingratesoflessthan
pH, temperature, specific conductance, turbidity, redox
0.1 L/min, discrete depth sampling using a bailer that allows
potential, and DO.Acombination of a pump and field meter(s)
ground water entry at a controlled depth (for example, differ-
or sondes equipped with a flow-through cell is ideal for this
ential pressure bailer (14)), or diffusion sampling. These
purpose since it allows the monitoring of one or more of these
sampling techniques are discussed in 8.1.10.
parameters on a continuous basis without exposure to the
atmosphere.Atypicalflow-throughcellapplicationisshownin
7. Materials and Manufacture
Fig. 1. The pump used in this technique may be any pump
7.1 The choice of materials used in the construction of
capable of producing a steady flow, such as a peristaltic or
sampling devices should be based upon knowledge of what
bladder pump. If a submersible pump is used, the hydraulic
compounds may be present in the sampling environment and
pressuredevelopedintheflow-throughcellmaybesufficientto
how the sample materials may interact via leaching,
force the probes out of their position. This problem may be
adsorption, or catalysis. A second concern is that corrosion or
eliminated by installing a tee connector in the discharge line to
degradation may compromise the structural integrity of the
allow only a portion of the flow to enter the flow-through cell.
sampling device. In some situations, PVC or other plastic may
Another concern with the low-flow sampling method is sorp-
be sufficient. In others, an all TFE-fluorocarbon apparatus may
tionontothetubing.Studieshaveindicatedthatatflowratesof
be necessary. The potential presence of nonaqueous phase
0.1 L/min (0.026 gal/min), low-density polyethylene (LDPE)
liquid(NAPL)shouldalsobeaconsiderationsinceitspresence
andplasticizedpolypropylenetubingsarepronetosorptionand
would expose the sampling equipment to high concentrations
TFE-fluorocarbon should be used. This is especially a concern
of potential solvents. No one material is ideal in that each
if tubing lengths of 15 m (50 ft) or longer are used (10).
material will, to some degree, absorb or leach chemicals or
6.9 GibbandSchuller (11)havedescribedatime-drawdown
may degrade on exposure to a chemical.
approach using knowledge of the well hydraulics to predict the
7.2 The advantages and disadvantages of these materials for
percentage of stagnant water entering a pump inlet near the top
sampling equipment are summarized in Table 1.
of the screen at any time after flushing begins. Samples are
collectedwhenthepercentageisacceptablylow.Asbefore,the 7.3 PVC:
advantage is that well volume has no direct effect on the
duration of pumping. A current knowledge of the well’s
hydraulic characteristics is necessary to employ this approach.
Downward migration of stagnant water due to effects other
than drawdown (for example, density differences) is not
accounted for in this approach.
6.10 An alternative to purging a well before sampling is to
collect a water sample within the screened zone without
purging. These techniques are based on studies that under
certain conditions, natural ground-water flow is laminar and
horizontal with little or no mixing within the well screen (12,
13).Toproperlyusethesesamplingtechniques,awatersample
FIG. 1 Flow-Through Cell FIG. 2 Single Check Valve Bailer
D4448 − 01 (2019)
resin is heated to its melting point. Relative to PVC and
stainless steel, TFE-fluorocarbon is less sorptive of cations
(27).
7.4.2 Extruded TFE-fluorocarbon tubing may contain sur-
face traces of an organic solvent extrusion aid. This can be
removed easily by the fabricator and, once removed by
flushing, should not affect the sample. TFE-fluorocarbon fluo-
rinated ethylene propylene (FEP) and TFE-fluorocarbon per-
fluoroalkoxy (PFA) resins do not require this extrusion aid and
may be suitable for sample tubing as well. Unsintered thread-
sealant tape of TFE-fluorocarbon is available in an “oxygen
service” grade and contains no extrusion aid and lubricant.
7.5 Glass and Stainless Steel:
7.5.1 Glass and stainless steel are two other materials
generally considered inert in aqueous environments. Glass is
generally not used, however, because of difficulties in handling
and fabrication. Stainless steel is strong and easily machined to
fabricate equipment. It is, however, not totally immune to
corrosion that could release metallic contaminants (see Table
1). Stainless steel contains various alloying metals, some of
these (that is, nickel) may catalyze reactions. The alloyed
constituents of some stainless steels can be solubilized by the
pittingactionofnonoxidizinganionssuchaschloride,fluoride,
and in some instances sulfate, over a range of pH conditions.
Aluminum, titanium, polyethylene, and other corrosion-
resistant materials have been proposed by some as acceptable
materials, depending on ground-water quality and the constitu-
ents of interest.
FIG. 3 Double Check Valve Bailer
7.5.2 Where temporarily installed sampling equipment is
used, the sampling device that is chosen should be able to be
7.3.1 If adhesives are avoided, PVC is acceptable in many
cleaned of trace organics, and must be cleaned between each
cases, although their use may still lead to some problems if
monitoring well use to avoid cross-contamination of wells and
trace organics are of concern or NAPL is present (24).At
samples. Decontamination of equipment PVC and stainless
present, interactions occurring between PVC and ground water
steel constructed sampling equipment exposed to organic
are not well understood. Tin, in the form of an organotin
stabilizer added to PVC, may enter samples taken from PVC chemicals, pesticides, or nitroaromatic compounds generally
(25). can be successfully accomplished using a hot detergent solu-
7.3.2 The structural integrity concerns with PVC increase
tion followed by a hot water rinse. Equipment constructed of
with the concentration of PVC solvents in ground water. As
LDPE and TFE-fluorocarbon should also be hot air dried or
such, NAPLs that are PVC solvents are a primary concern.
oven dried at approximately 105 °C to remove residual pesti-
Potential NAPLs that are of a concern for PVC and other
cides and organic contaminants, respectively (28, 29).A
commonly used plastics are listed in Table 2. Degradation of
common method to verify that the device is “clean” and
these materials is primarily by solvation, which is the penetra-
acceptable is to analyze a sample (equipment blank) that has
tion of the material by the solvent that ultimately causes
been soaked in or passed through the sampling device, or both,
softening and swelling that can lead to failure. Even in lower
to check for the background levels that may result from the
concentrations, however, PVC solvents may deteriorate PVC.
sampling materials or from field conditions. Thus, all sam-
Methylenechloride,whichisaveryeffectivePVCsolvent,will
plings for trace materials should be accompanied by samples
soften PVC at one-tenth its solubility limit while
that represent the sampling equipment blank, in addition to
trichloroethylene, which is a less effective solvent, will begin
other blanks (field blank and trip blank). Decontamination
to soften PVC at six-tenths its solubility limit (16).
procedures are further discussed in Practice D5088.
7.4 TFE-Fluorocarbon Resins:
7.6 Additional samples are often collected in the field and
7.4.1 TFE-fluorocarbon resins are highly inert and have
spiked (spiked field samples) in order to verify that the sample
sufficientmechanicalstrengthtopermitfabricationofsampling
handling procedures are valid. The American Chemical Soci-
devices. Molded parts are exposed to high temperature during
ety’s committee on environmental improvement has published
fabrication that destroys any organic contaminants. The evo-
guidelines for data acquisition and data evaluation, which
lution of fluorinated compounds can occur during fabrication,
will cease rapidly, and does not occur afterwards unless the should be useful in such environmental evaluations (30).
D4448 − 01 (2019)
TABLE 1 Material Considerations In Selection Of Sampling Equipment (15)
Material Considerations
Polytetrafluoroethylene • Virgin PTFE readily sorbs some organic solutes (16)
• Ideal material in corrosive environments where inorganic compounds are of interest
• Useful where pure product (organic compound) or high concentrations of PVC solvents exist
• Potential structural problems because of its low tensile and compressive strengths, low wear resistance, and the
extreme flexibility of the casing string as compared to other engineering plastics (17-19)
• Potential problems with obtaining a seal between the casing and the annular sealant because of PTFEs low co-
efficient of friction and antistick properties as compared to other plastics (19)
• Maximum string length of 2-in. (~5-cm) diameter schedule PTFE casing should not exceed about 375 ft (~115 m)
(20)
• Expensive
Polyvinylchloride • Leaching of compounds of tin or antimony, which are contained in original heat stabilizers during polymer
formulation, could occur after long exposure
• When used in conjunction with glued joints, leaching of volatile organic compounds from PVC primer and glues,
such as THF (tetrahydrofuran), MEK (methylethylketone), MIBK (methylisobutylketone) and cyclohexanone could
leach into ground water. Therefore, threaded joints below the water table, sealed with O-rings or Teflon tape, are
preferred
• Cannot be used where pure product or high concentrations of a PVC solvent exist
• There is conflicting data regarding the resistance of PVC to deterioration in the presence of gasoline (21)
• Maximum string length of 2-in. (~5-cm) diameter threaded PVC casing should not exceed 2000 ft (~610 m) (20)
• PVC can warp and melt if neat cement (cement and water) is used as an annular or surface seal because of
heat of hydration (22, 17)
• PVC can volatilize CFCs into the atmosphere within the unsaturated zone, which can be a potential problem for
studies of gas and moisture transport through the unsaturated zone
• Easy to cut, assemble, and place in the borehole
• Inexpensive
Stainless steel • Generally has high corrosion resistance, which differs with type
• Corrosion can occur under acidic and oxidizing conditions
• Corrosion products are mostly iron compounds, with some trace elements
• Primarily two common types:
(1) Type 304 Stainless Steel: Iron alloyed with the following elements (percentages): Chromium (18-20 %),
Nickel (8-11 %), Manganese (2 %), Silicon (0.75 %), Carbon (0.08 %), Phosphorus (0.04 %), Sulfur (0.03 %)
(2) SS 316: Iron alloyed with the following elements (in percentages): Chromium (16-18 %), Nickel (11-14 %),
Manganese (2 %), Molybdenum (2-3 %), Silicon (0.75 %), Carbon (0.08 %), Phosphorus (0.04 %), Sulfur (0.03 %)
• Corrosion resistance is good for Type 304 stainless steel under aerobic conditions. Type 316 stainless steel has
improved corrosion resistance over Type 304 under reducing conditions (23)
• Expensive
Galvanized steel • Less corrosion resistance than stainless steel and more resistance to corrosion than carbon steel (see Carbon
steel entry)
• Oxide coating could dissolve under chemically reduced conditions and release zinc and cadmium, and raise pH
• Weathered or corroded surfaces present active adsorption sites for organic and inorganic constituents
• Inexpensive
Carbon steel • Corrosion products can occur (for example, iron and manganese oxides, metal sulfides, and dissolved metal spe-
cies)
• Sorption of organic compounds onto metal corrosion products is possible
• Weathered surfaces present active adsorption sites for organic and inorganic constituents
• Inexpensive
8. Sampling Equipment widely used. These devices can be constructed in various
shapes and sizes from a variety of materials. They do not
8.1 The choice of sampling technique must be based on an
subject the sample to pressure extremes.
understanding of the hydrogeology of the site under investiga-
8.1.1.2 A schematic of a single check valve unit is illus-
tion and the end use of the data. Since each technique has its
trated in Fig. 2. The bailer may be threaded in the middle so
advantages and disadvantages, no one technique can be chosen
that additional lengths of blank casing may be added to
as the best overall technique. Since different techniques will
increase the sampling volume. TFE-fluorocarbon, stainless
likely yield different results, it is best to be consistent through-
steel, and PVC are the most common materials used for
out an investigation to facilitate the comparison of data values
construction (33).
over time.There is a fairly large choice of equipment presently
available for ground-water sampling. The sampling devices 8.1.1.3 In operation, the single check valve bailer is gently
can be categorized into the following nine basic types as lowered into the well to a depth just below the water surface,
described in the following sections: waterentersthechamberthroughthebottom,andtheweightof
8.1.1 Down-Hole Collection Devices: the water column closes the check valve upon bailer retrieval.
8.1.1.1 Bailers, messenger bailers, or thief (31, 32) are The specific gravity of the ball should be about 1.4 to 2.0 so
examples of down-hole collection devices. They are not thattheballalmostsitsonthecheckvalveseatduringchamber
practical for removal of large volumes of water, but are filling. Upon bailer withdrawal, the ball will immediately seat
relatively inexpensive permitting their dedicated use and are without sample loss through the check valve.
D4448 − 01 (2019)
TABLE 2 Chemical Compatibility Table for Selected NAPL (26)
Chemical PTFE (Teflon) PP (Polypropylene) PVC (Type I) PVC (Type II) 304 Stainless 316 Stainless Carbon Steel
Benzene R X U U G G G
Carbon Tetrachloride R U X U E E G
Dichlorobenzene R R U U . . . G . . .
Dichloroethane (DCA) R X U U G G G
Dichloroethylene (DCE) R R U U G G . . .
Diesel Fuel R R R . . . E E G
Ethyl Benzene R U U U S G U
Gasoline R X R . . . G G G
Hydraulic Oil (petro.) R X R . . . R R . . .
Hydraulic Oil (synthetic) R X R . . . R R . . .
Jet Fuels R X R R G G G
Kerosene R R R R G G G
Motor Oil R X R R G G G
Napthalene R R U U E E G
Tetrachloroethylene (PCE) R U U U E E G
Toluene R R U U E E E
Trichloroethylene (TEC) R R U U G G G
Xylenes R R U U G G G
For Metals
E < 2 mills Penetration/Year
G < 20 mills Penetration/Year
S < 50 mills Penetration/Year
U > 50 mills Penetration/Year
(1 mill = 0.001 in.)
R = Resistant (No corrosion rate reported)
For All Non-Metals
R = Resistant
U = Unsatisfactory
X = Conflicting Data, at least one reference reported unsatisfactory
8.1.1.4 A double check valve bailer allows point source tube. This type of bailer minimizes the exposure of the sample
sampling at a specific depth (34, 35). The double check valve to air especially if fitted with internal 40-mL vials for direct
bailer is also effective at collecting dense, non-aqueous phase sample bottle filling.
liquid (DNAPL) from the bottom of a monitoring well. An 8.1.1.7 Special care must be taken to minimize exposing the
example is shown in Fig. 3. In this double check valve design, sample to the atmosphere during the transfer of the sample
water flows through the sample chamber as the unit is lowered. from the bailer to the sample bottle. There are several ap-
A venturi tapered inlet and outlet ensures that water passes proachestoovercomethisissue.Bottom-emptyingbailersused
through the unit with limited restriction. When a depth where for sampling of VOCs, for example, should have an insertable
the sample is to be collected is reached, the unit is retrieved. sample cock or draft valve cock (often referred to as a bottom
Because the difference between each ball and check valve seat or bailer emptying device) in or near the bottom of the sampler
is maintained by a pin that blocks vertical movement of the allowing withdrawal of a sample from the bailer with minimal
check ball, both check valves close simultaneously upon atmosphere exposure.
retrieval.Adrainage pin is placed into the bottom of the bailer 8.1.1.8 Suspension lines for bailers and other samplers
to drain the sample directly into a collection vessel to reduce should be kept off the ground and free of other contaminating
the possibility of air oxidation. materials that could be carried into the well. A plastic sheet
8.1.1.5 A top-filling bailer is a closed-bottom tubular may be spread out on the ground around the monitoring well
device, opened on top and provided with a loop or other fixture for this purpose. Disposable TFE-fluorocarbon, PVC,
to attach to the drop line. The top-filling bailer is gently polyethylene, and polypropylene bailers are available which
lowered below the water surface in the well and water pours offer time savings and all but eliminates the potential for cross
into the bailer from the top. Although this variation on the contamination during sampling.
bailer design results in greater agitation of the sample, it may 8.1.1.9 Sample oxidation is a concern with single check
be used to collect a sample of light, non-aqueous phase liquid valve and top filling bailers. Sample oxidation might occur
(LNAPL) by lowering it just below the surface of the LNAPL duringtheextendedtimeittakestobailasampleifwaterlevels
and allowing the bailer to skim the LNAPLfrom the surface of are a great depth below the ground surface or if there is a delay
the water column. in the transfer of the sample from the bailer to the sample
8.1.1.6 The differential pressure bailer is a sealed canister bottles. Using point source bailers, however, minimizes the
body with two small-diameter tubes of different heights built oxidation problem.
into its removable top (14).The bailer is usually constructed of 8.1.1.10 Another approach for obtaining point source
stainless steel to provide sufficient weight to allow it to sink samples employs a weighted messenger or pneumatic change
relatively quickly to the desired sampling depth. Once the to “trip” plugs at either end of an open tube (for example, tube
bailer’s downward progress is stopped, differences in hydro- water sampler or thief sampler) to close the chamber (36).
static pressure between the two tubes allows the bailer to fill Foerst, Kemmerer, and Bacon samplers are of this variety (32,
through the lower tube as air is displaced through the upper 33, 35). A number of thief or messenger devices are available
D4448 − 01 (2019)
in various materials and shapes. Differential pressure bailers through an inlet, usually located on the bottom of the pump.
(14) also provide a point source sample but do not require Compressed gas, either from a compressor or air cylinder, is
manual tripping. injected into a bladder within the pump cavity, forcing the
8.1.2 Bladder Pumps: check valve on the inlet to close and the sample up through a
8.1.2.1 Bladder pumps consist of a flexible membrane second check valve at the top of the pump and into a discharge
enclosed by a rigid housing. Water enters the pump cavity line (Fig. 4). Water is prevented from re-entering the bladder
FIG. 4 Squeeze-Type Bladder Pump
D4448 − 01 (2019)
by the top check valve. The bladder is then depressurized, other types of tubing can be used particularly for the sections
allowingthepumptorefill.Theprocessisrepeatedtocyclethe extending into the well or from the pump to the receiving
water to the surface. Samples taken from depths of 122 m container. The National Council of the Paper Industry for Air
(400 ft) have been reported. and Stream Improvement (41) recommends using medical
grade silicone tubing for VOC sampling purposes, as the
8.1.2.2 A variety of design modifications and materials are
standard grade uses an organic vulcanizing agent which has
available (37, 38) however, TFE-fluorocarbon bladders, either
been shown to leach into samples. Various manufacturers offer
PVC, TFE-fluorocarbon resin, or stainless steel bodies and
tubinglinedwithTFE-fluorocarbonorViton forusewiththeir
fittings are most common. An automated controller system is
pumps.PlasticizedpolypropylenetubingsandLDPEshouldbe
used to control the time between pressurization cycles and
avoidedifflowrateslessthan0.1L/min(0.025g/min)areused
regulate pressure.
(10). The extraction rate with this method can range from 0.04
8.1.2.3 Bladder pumps have a distinct advantage over gas
to 30 L/min (0.01 to 8 gal/min) (42).
displacement pumps in that there is no contact with the driving
8.1.3.5 There is disagreement on the applicability of peri-
gas.Disadvantagesincludethelargegasvolumesrequired,and
staltic pumps for the collection of groundwater samples.
difficulty in decontaminating the pump. This pump design is
Research by Tai, et al. (43) has shown that peristaltic pumps
most applicable to dedicated well installations and where low
provide adequate recovery of VOCs. The U.S. EPA (4) does
pump rate or flow rate (less than 0.5 L/min) is required. The
not recommend their use because of studies that suggest that
flow rate from a bladder pump is dependent on the dimensions
VOCs may be lost during sampling (44).
of the bladder pump, controller settings, gas pressure, and total
8.1.3.6 A direct method of collecting a sample by suction
dynamic head.
consists of lowering one end of a length of plastic tubing into
8.1.3 Suction Lift Pumps:
the well or piezometer. The opposite end of the tubing is
8.1.3.1 Three types of suction lift pumps are the direct line,
connected to a two-way stopper bottle and a hand-held or
centrifugal, and peristaltic. A major disadvantage of any
mechanical vacuum pump is attached to a second tubing
suction pump is that it is limited in its ability to raise water by
leaving the bottle. A check valve is attached between the two
the head available from atmospheric pressure. The theoretical
lines to maintain a constant vacuum control.Asample can then
suction limit is about 10.4 m (34 ft), but most suction pumps
be drawn directly into the collection vessel without contacting
are capable of maintaining a water lift of only 7.6 m (25 ft)
the pump mechanism (45, 46).
(39).
8.1.3.7 A centrifugal pump can be attached to a length of
8.1.3.2 Many suction pumps draw water through a volute in
plastic tubing that is lowered into the well. A foot valve is
which impellers, pistons, or other devices operate to induce a
usually attached to the end of the well tubing to assist in
vacuum. Such pumps are probably unacceptable for most
priming the tube. The maximum lift is about 4.6 m (15 ft) for
sampling purposes because they are usually constructed of
such an arrangement (45-47).
non-inert materials such as brass or mild steel and may expose
8.1.3.8 Suction pump approaches offer a simple sample
samples to lubricants. They often induce very low pressures
retrieval method for shallow monitoring wells. The direct line
aroundrotatingvanesorothersuchpartssuchthatdegassingor
method is portable though considerable oxidation and mixing
potentially cavitation may occur. They can mix air with the
may occur during collection. A centrifugal pump will agitate
sample via small leaks in the casing, and they are difficult to
thesampletoanevengreaterdegreealthoughpumpingratesof
adequatelycleanbetweenuses.Suchpumpsmaybeacceptable
19 to 151 L/min (5 to 40 gal/min) can be attained.Aperistaltic
for purging of wells, but should not generally be used for
pump provides a lower sampling rate with less agitation than
sampling.
the other two pumps, as discussed in 8.1.3.4.
8.1.3.3 An exception to the above statements is a peristaltic
8.1.3.9 All three systems can be specially designed so that
pump (also known as a rotary peristaltic pump). A peristaltic
the water sample contacts only the TFE-fluorocarbon or
pump is a self-priming, low-volume suction pump that consists
silicone tubing prior to sample bottle entry. Dedicated tubing is
of a rotor with rollers (40). Flexible tubing is inserted around
recommended for each well or piezometer sampled. Each of
the pump rotor and squeezed by rollers as they rotate. One end
these methods that relies on suction can change solution
of the tubing is placed into the well (a weighted end may be
chemistry by causing degassing which may result in loss of
used) while the other is connected directly to a receiving
volatile compounds and dissolved gases, and this should be a
vessel. As the rotor moves, reduced pressure is created in the
consideration in their application (42).
well tubing and an increased pressure on the tube leaving the
8.1.4 Electric Submersible Pumps:
rotor head. Pumping rates may be controlled by varying the
8.1.4.1 A submersible pump consists of a sealed electric
speed of the rotor or by changing the size of the pump head,
motor that powers a piston, impeller, or helical single thread
which contains the pump rotor.
worm.Waterisbroughttothesurfacethroughadischargetube.
8.1.3.4 The peristaltic pump moves the liquid totally within
Similar pumps are commonly used in the water well industry
the sample tube. No part of the pump contacts the liquid. The
and many designs exist (17).
sample may be degassed (cavitation is unlikely), but the
8.1.4.2 Submersible pumps provide relatively high dis-
problems due to contact with the pump mechanism are
charge rates for water withdrawal at depths beyond suction lift
eliminated.Peristalticpumpsdorequireafairlyflexiblesection
of tubing within the pump head itself. A section of silicone
VitonisatrademarkofE.I.duPontdeNemours&Co.,Wilmington,DE19898
tubing is commonly used within the peristaltic pump head, but and has been found suitable for this purpose.
D4448 − 01 (2019)
capabilities.Abattery-operatedunit3.6cm(1.4in.)indiameter solubility constant changes resulting from stripping, oxidation,
and with a 4.5-L/min (1.2-gal/min) flow rate at 33.5 m (110 ft) and pressure changes.
8.1.6 Gas Displacement Pumps:
has been developed (48). Another submersible pump has an
outer diameter of 11.4 cm (4.5 in.) and can pump water from 8.1.6.1 Gas displacement or gas drive pumps are distin-
guished from gas-lift pumps by the method of sample trans-
91 m (300 ft). Pumping rates vary up to 53.0 L/min
port. Gas displacement pumps force a discrete column of water
(14 gal⁄min) depending upon the depth of the total dynamic
to the surface via mechanical lift without extensive mixing o
...