ASTM D4448-85a(1992)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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Designation: D 4448 – 85a (Reapproved 1992)
Standard Guide for
Sampling Groundwater Monitoring Wells
This standard is issued under the fixed designation D 4448; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2.3 The types of species that are to be monitored as well as
the concentration levels are prime factors for selecting sam-
1.1 This guide covers procedures for obtaining valid, rep-
pling devices (1,2). The sampling device and all materials and
resentative samples from groundwater monitoring wells. The
devices the water contacts must be constructed of materials that
scope is limited to sampling and “in the field” preservation and
will not introduce contaminants or alter the analyte chemically
does not include well location, depth, well development,
in any way.
design and construction, screening, or analytical procedures.
2.4 The method of sample withdrawal can vary with the
1.2 This guide is only intended to provide a review of many
parameters of interest. The ideal sampling scheme would
of the most commonly used methods for sampling groundwater
employ a completely inert material, would not subject the
quality monitoring wells and is not intended to serve as a
sample to negative pressure and only moderate positive pres-
groundwater monitoring plan for any specific application.
sure, would not expose the sample to the atmosphere, or
Because of the large and ever increasing number of options
preferably, any other gaseous atmosphere before conveying it
available, no single guide can be viewed as comprehensive.
to the sample container or flow cell for on-site analysis.
The practitioner must make every effort to ensure that the
2.5 The degree and type of effort and care that goes into a
methods used, whether or not they are addressed in this guide,
sampling program is always dependent on the chemical species
are adequate to satisfy the monitoring objectives at each site.
of interest and the concentration levels of interest. As the
1.3 This standard does not purport to address all of the
concentration level of the chemical species of analytical
safety problems, if any, associated with its use. It is the
interest decreases, the work and precautions necessary for
responsibility of the user of this standard to establish appro-
sampling are increased. Therefore, the sampling objective must
priate safety and health practices and determine the applica-
clearly be defined ahead of time. For example, to prepare
bility of regulatory limitations prior to use.
equipment for sampling for mg/L (ppm) levels of Total Organic
2. Summary of Guide
Carbon (TOC) in water is about an order of magnitude easier
than preparing to sample for μg/L (ppb) levels of a trace
2.1 The equipment and procedures used for sampling a
organic like benzene. The specific precautions to be taken in
monitoring well depend on many factors. These include, but
preparing to sample for trace organics are different from those
are not limited to, the design and construction of the well, rate
to be taken in sampling for trace metals. No final Environmen-
of groundwater flow, and the chemical species of interest.
tal Protection Agency (EPA) protocol is available for sampling
Sampling procedures will be different if analyzing for trace
of trace organics. A short guidance manual (3) and an EPA
organics, volatiles, oxidizable species, or trace metals is
document (4) concerning monitoring well sampling, including
needed. This guide considers all of these factors by discussing
considerations for trace organics, are available.
equipment and procedure options at each stage of the sampling
2.6 Care must be taken not to cross contaminate samples or
sequence. For ease of organization, the sampling process can
monitoring wells with sampling or pumping devices or mate-
be divided into three steps: well flushing, sample withdrawal,
rials. All samples, sampling devices, and containers must be
and field preparation of samples.
protected from the environment when not in use. Water level
2.2 Monitoring wells must be flushed prior to sampling so
measurements should be made before the well is flushed.
that the groundwater is sampled, not the stagnant water in the
Oxidation-reduction potential, pH, dissolved oxygen, and tem-
well casing. If the well casing can be emptied, this may be done
perature measurements and filtration should all be performed
although it may be necessary to avoid oxygen contact with the
on the sample in the field, if possible. All but temperature
groundwater. If the well cannot be emptied, procedures must be
measurement must be done prior to any significant atmospheric
established to demonstrate that the sample represents ground-
exposure, if possible.
water. Monitoring an indicative parameter such as pH during
2.7 The sampling procedures must be well planned and all
flushing is desirable if such a parameter can be identified.
sample containers must be prepared and labeled prior to going
to the field.
This guide is under the jurisdiction of ASTM Committee D34 on Waste
Management and is the direct responsibility of Subcommittee D34.01.02 on
Sampling Techniques. The boldface numbers in parentheses refer to a list of references at the end of
Current edition approved Aug. 23 and Oct. 25, 1985. Published May 1986. this guide.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 4448
3. Significance and Use no longer change. The advantage of this method is that
pumping can be done from any location within the casing and
3.1 The quality of groundwater has become an issue of
the volume of stored water present has no direct bearing on the
national concern. Groundwater monitoring wells are one of the
volume of water that must be pumped. Obviously, in a low
more important tools for evaluating the quality of groundwater,
yielding well, the well may be emptied before the parameters
delineating contamination plumes, and establishing the integ-
stabilize. A disadvantage of this approach is that there is no
rity of hazardous material management facilities.
assurance in all situations that the stabilized parameters repre-
3.2 The goal in sampling groundwater monitoring wells is
sent formation water. If significant drawdown has occurred,
to obtain samples that are truly representative of the aquifer or
water from some distance away may be pulled into the screen
groundwater in question. This guide discusses the advantages
causing a steady parameter reading but not a representative
and disadvantages of various well flushing, sample withdrawal,
reading. Also, a suitable indicator parameter and means of
and sample preservation techniques. It reviews the parameters
continuously measuring it in the field must be available.
that need to be considered in developing a valid sampling plan.
4.6 Gibb (4,8) has described a time-drawdown approach
using a knowledge of the well hydraulics to predict the
4. Well Flushing (Purging)
percentage of stored water entering a pump inlet near the top of
4.1 Water that stands within a monitoring well for a long
the screen at any time after flushing begins. Samples are taken
period of time may become unrepresentative of formation
when the percentage is acceptably low. As before, the advan-
water because chemical or biochemical change may cause
tage is that well volume has no direct effect in the duration of
water quality alterations and even if it is unchanged from the
pumping. A current knowledge of the well’s hydraulic charac-
time it entered the well, the stored water may not be represen-
teristics is necessary to employ this approach. Downward
tative of formation water at the time of sampling, or both.
migration of stored water due to effects other than drawdown
Because the representativeness of stored water is questionable,
(for example density differences) is not accounted for in this
it should be excluded from samples collected from a monitor-
approach.
ing well.
4.7 In any flushing approach, a withdrawal rate that mini-
4.2 The surest way of accomplishing this objective is to
mizes drawdown while satisfying time constraints should be
remove all stored water from the casing prior to sampling.
used. Excessive drawdown distorts the natural flow patterns
Research with a tracer in a full scale model 2 in. PVC well (5)
around a well and can cause contaminants that were not present
indicates that pumping 5 to 10 times the volume of the well via
originally to be drawn into the well.
an inlet near the free water surface is sufficient to remove all
5. Materials and Manufacture
the stored water in the casing. The volume of the well may be
calculated to include the well screen and any gravel pack if
5.1 The choice of materials used in the construction of
natural flow through these is deemed insufficient to keep them
sampling devices should be based upon a knowledge of what
flushed out.
compounds may be present in the sampling environment and
4.3 In deep or large diameter wells having a volume of
how the sample materials may interact via leaching, adsorp-
water so large as to make removal of all the water impractical,
tion, or catalysis. In some situations, PVC or some other plastic
it may be feasible to lower a pump or pump inlet to some point
may be sufficient. In others, an all glass apparatus may be
well below the water surface, purge only the volume below that
necessary.
point then withdraw the sample from a deeper level. Research
5.2 Most analytical protocols suggest that the devices used
indicates this approach should avoid most contamination
in sampling and storing samples for trace organics analysis
associated with stored water (5, 6,7). Sealing the casing above
(μg/L levels) must be constructed of glass or TFE–fluorocarbon
the purge point with a packer may make this approach more
resin, or both. One suggestion advanced by the EPA is that the
dependable by preventing migration of stored water from
monitoring well be constructed so that only TFE–fluorocarbon
above. But the packer must be above the top of the screened
tubing be used in that portion of the sampling well that extends
zone, or stagnant water from above the packer will flow into
from a few feet above the water table to the bottom of the
the purged zone through the well’s gravel/sand pack.
borehole. (3,5) Although this type of well casing is now
4.4 In low yielding wells, the only practical way to remove
commercially available, PVC well casings are currently the
all standing water may be to empty the casing. Since it is not
most popular. If adhesives are avoided, PVC well casings are
always possible to remove all water, it may be advisable to let
acceptable in many cases although their use may still lead to
the well recover (refill) and empty it again at least once. If
some problems if trace organics are of concern. At present, the
introduction of oxygen into the aquifer may be of concern, it
type of background presented by PVC and interactions occur-
would be best not to uncover the screen when performing the
ring between PVC and groundwater are not well understood.
above procedures. The main disadvantage of methods designed Tin, in the form of an organotin stabilizer added to PVC, may
to remove all the stored water is that large volumes may need
enter samples taken from PVC casing. (9)
to be pumped in certain instances. The main advantage is that 5.3 Since the most significant problem encountered in trace
the potential for contamination of samples with stored water is
organics sampling, results from the use of PVC adhesives in
minimized. monitoring well construction, threaded joints might avoid the
4.5 Another approach to well flushing is to monitor one or problem (3,5). Milligram per litre (parts per million) levels of
more indicator parameters such as pH, temperature, or conduc- compounds such as tetrahydrofuran, methyl-ethyl-ketone, and
tivity and consider the well to be flushed when the indicator(s) toluene are found to leach into groundwater samples from
D 4448
monitoring well casings sealed with PVC solvent cement. 5.9 Additional samples are often taken in the field and
Pollutant phthalate esters (8,10) are often found in water spiked (spiked-field samples) in order to verify that the sample
samples at ppb levels; the EPA has found them on occasion at handling procedures are valid. The American Chemical Soci-
ppm levels in their samples. The ubiquitous presence of these ety’s committee on environmental improvement has published
phthalate esters is unexplained, except to say that they may be guidelines for data acquisition and data evaluation which
leached from plastic pipes, sampling devices, and containers. should be useful in such environmental evaluations (10,12).
5.4 TFE–fluorocarbon resins are highly inert and have
6. Sampling Equipment
sufficient mechanical strength to permit fabrication of sampling
6.1 There is a fairly large choice of equipment presently
devices and well casings. Molded parts are exposed to high
available for groundwater sampling from single screened wells
temperature during fabrication which destroys any organic
and well clusters. The sampling devices can be categorized into
contaminants. The evolution of fluorinated compounds can
the following eight basic types.
occur during fabrication, will cease rapidly, and does not occur
6.1.1 Down-Hole Collection Devices:
afterwards unless the resin is heated to its melting point.
6.1.1.1 Bailers, messenger bailers, or thief samplers (13,14)
5.5 Extruded tubing of TFE-fluorocarbon for sampling may
are examples of down-hole devices that probably provide valid
contain surface traces of an organic solvent extrusion aid. This
samples once the well has been flushed. They are not practical
can be removed easily by the fabricator and, once removed by
for removal of large volumes of water. These devices can be
flushing, should not affect the sample. TFE-fluorocarbon FEP
constructed in various shapes and sizes from a variety of
and TFE-fluorocarbon PFA resins do not require this extrusion
materials. They do not subject the sample to pressure extremes.
aid and may be suitable for sample tubing as well. Unsintered
6.1.1.2 Bailers do expose part of the sample to the atmo-
thread-sealant tape of TFE-fluorocarbon is available in an
sphere during withdrawal. Bailers used for sampling of volatile
“oxygen service” grade and contains no extrusion aid and
organic compounds should have a sample cock or draft valve in
lubricant.
or near the bottom of the sampler allowing withdrawal of a
5.6 Lou
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