ASTM D4448-01(2013)
(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 problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D4448 − 01 (Reapproved 2013)
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 Well) (Withdrawn 2010)
D5088 Practice for Decontamination of Field Equipment
1.1 This guide covers sampling equipment and procedures
Used at Waste Sites
and “in the field” preservation, and it does not include well
D5792 Practice for Generation of Environmental Data Re-
location, depth, well development, design and construction,
lated to Waste Management Activities: Development of
screening, or analytical procedures that also have a significant
Data Quality Objectives
bearing on sampling results.This guide is intended to assist a
D5903 Guide for Planning and Preparing for a Groundwater
knowledgeable professional in the selection of equipment for
Sampling Event
obtaining representative samples from ground-water monitor-
D6089 Guide for Documenting a Groundwater Sampling
ing wells that are compatible with the formations being
Event
sampled, the site hydrogeology, and the end use of the data.
D6452 Guide for Purging Methods for Wells Used for
1.2 This guide is only intended to provide a review of many
Groundwater Quality Investigations
of the most commonly used methods for collecting ground-
D6517 Guide for Field Preservation of Groundwater
water quality samples from monitoring wells and is not
Samples
intended to serve as a ground-water monitoring plan for any
2.2 EPA Standards:
specific application. Because of the large and ever increasing
EPA Method 9020A
number of options available, no single guide can be viewed as
EPA Method 9022
comprehensive. The practitioner must make every effort to
ensure that the methods used, whether or not they are ad-
3. Terminology
dressed in this guide, are adequate to satisfy the monitoring
3.1 Definitions:
objectives at each site.
3.1.1 low-flow sampling—a ground water sampling tech-
1.3 The values stated in SI units are to be regarded as
nique where the purge and sampling rates do not result in
standard. The values given in parentheses are provided for
significant changes in formation seepage velocity.
information only.
3.1.2 minimal purge sampling—the collection of ground
1.4 This standard does not purport to address all of the
water that is representative of the formation by purging only
safety problems, if any, associated with its use. It is the
thevolumeofwatercontainedbythesamplingequipment(that
responsibility of the user of this standard to establish appro-
is, tubing, pump bladder).
priate safety and health practices and determine the applica-
3.1.2.1 Discussion—This sampling method should be con-
bility of regulatory limitations prior to use.
sidered in situations where very low yield is a consideration
and results from this sampling method should be scrutinized to
2. Referenced Documents
confirm that they meet data quality objectives (DQOs) and the
2.1 ASTM Standards:
work plan objectives.
D4750 Test Method for Determining Subsurface Liquid
3.1.3 passive sampling—the collection of ground-water
Levels in a Borehole or Monitoring Well (Observation
quality data so as to induce no hydraulic stress on the aquifer.
3.1.4 water quality indicator parameters—refer to field
This guide is under the jurisdiction of ASTM Committee D34 on Waste
monitoring parameters that include but are not limited to pH,
Management and is the direct responsibility of Subcommittee D34.01.02 on
specific conductance, dissolved oxygen, oxidation-reduction
Sampling Techniques.
potential, temperature, and turbidity that are used to monitor
Current edition approved April 1, 2013. Published April 2013. Originally
approved in 1985. Last previous edition approved in 2007 as D4448–01 (2007). the completeness of purging.
DOI: 10.1520/D4448-01R13.
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 The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4448 − 01 (2013)
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
completely inert material, does not subject the sample to
pressurechange,doesnotexposethesampletotheatmosphere,
6.1 Water that stands within a monitoring well for a long
or any other gaseous atmosphere before conveying it to the
period of time may become unrepresentative of formation
sample container or flow cell for on-site analysis. Since these
water because chemical or biochemical change mayalterwater
ideals are not always obtainable, compromises must be made
quality or because the formation water quality may change
by the knowledgeable individual designing the sampling pro-
over time (see Guide D6452). Even if it is unchanged from the
gram.Theseconcernsshouldbedocumentedinthedataquality
time it entered the well, the stagnant water may not be
objectives (DQOs) of the sampling plan (see Practice D5792)
representative of formation water at the time of sampling.
(4).
There are two approaches to purging that reflect two differing
viewpoints: to purge a large volume of ground water and to
4.6 The degree and type of effort and care that goes into a
purge a minimum of, or no ground water before collecting a
sampling program is always dependent on the chemicals of
sample. The approach most often applied is to purge a
sufficientvolumeofstandingwaterfromthecasing,alongwith
The boldface numbers in parentheses refer to a list of references at the end of
this guide. sufficient formation water to ensure that the water being
D4448 − 01 (2013)
withdrawn at the time of sampling is representative of the ground-water flow through the screen provides a more consis-
formation water.Typically, three to five well volumes are used. tent sample. This sampling method also produces less turbid
Analternativemethodthatisgainingacceptanceistominimize samples that may eliminate the need for filtration when
purging and to conduct purging at a low flow rate or to collecting metals. This method is commonly referred to as
eliminate purging entirely. low-flow sampling.
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 gasses,
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) wel
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