ASTM D6634-01
(Guide)Standard Guide for the Selection of Purging and Sampling Devices for Ground-Water Monitoring Wells
Standard Guide for the Selection of Purging and Sampling Devices for Ground-Water Monitoring Wells
SCOPE
1.1 This guide describes the characteristics and operating principles of purging and sampling devices available for use in ground-water monitoring wells and provides criteria for selecting appropriate devices for specific applications. The selected device(s) should be capable of purging the well and providing valid representative samples of ground water and any included dissolved constituents. The scope does not include procedures for purging or collecting samples from monitoring wells, sampling devices for non-aqueous phase liquids, diffusion-type sampling devices or sampling from devices other than monitoring wells.
1.2 This guide reviews many of the most commonly used devices for purging and sampling ground-water monitoring wells. The practitioner must make every effort to ensure that the purging and sampling methods used, whether or not they are addressed in this guide, are adequate to satisfy the monitoring objectives at each site.
1.3 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgement. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of the many unique aspects of a project. The word "Standard" in the title of this document means only that the document has been approved through the ASTM consensus process.
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
Relations
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:D6634–01
Standard Guide for
the Selection of Purging and Sampling Devices for Ground-
Water Monitoring Wells
This standard is issued under the fixed designation D 6634; 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 D 653 Terminology Relating to Soil, Rock, and Contained
Fluids
1.1 This guide describes the characteristics and operating
D 4448 Guide for Sampling Ground Water Monitoring
principles of purging and sampling devices available for use in
Wells
ground-water monitoring wells and provides criteria for select-
D 5088 Practice for Decontamination of Field Equipment
ing appropriate devices for specific applications. The selected
Used at Non-Radioactive Waste Sites
device(s) should be capable of purging the well and providing
D 5092 Practice for Design and Installation of Ground-
valid representative samples of ground water and any included
Water Monitoring Wells in Aquifers
dissolved constituents. The scope does not include procedures
D 5903 Guide for Planning and Preparing for a Ground-
for purging or collecting samples from monitoring wells,
Water Sampling Event
samplingdevicesfornon-aqueousphaseliquids,diffusion-type
D 6089 Guide for Documenting a Ground-Water Sampling
sampling devices or sampling from devices other than moni-
Event
toring wells.
D 6452 Guide for Purging Methods for Wells Used for
1.2 This guide reviews many of the most commonly used
Ground-Water Quality Investigations
devices for purging and sampling ground-water monitoring
wells. The practitioner must make every effort to ensure that
3. Summary of Guide
the purging and sampling methods used, whether or not they
3.1 The primary objective of ground-water sampling pro-
are addressed in this guide, are adequate to satisfy the
grams is to collect representative samples of ground water.
monitoring objectives at each site.
Depending on the purging and sampling protocol, this may
1.3 This guide offers an organized collection of information
require that the well is purged of all stagnant water, or until
oraseriesofoptionsanddoesnotrecommendaspecificcourse
pre-determined purging criteria are met. Therefore, device(s)
of action. This document cannot replace education or experi-
selected for use in ground-water sampling programs must be
ence and should be used in conjunction with professional
capable of purging the well as needed and/or delivering to the
judgement. Not all aspects of this guide may be applicable in
surface, a sample representative of in-situ ground-water con-
all circumstances. This ASTM standard is not intended to
ditions. A number of factors can influence whether or not a
representorreplacethestandardofcarebywhichtheadequacy
particularsampleorsetofsamplesisrepresentative,andoneof
of a given professional service must be judged, nor should this
the significant elements of sample collection protocols is the
document be applied without consideration of the many unique
sampling mechanism (1, 2, 3).
aspects of a project. The word “Standard” in the title of this
3.2 In selecting a purging and/or sampling device for use in
document means only that the document has been approved
a ground-water monitoring well, a number of factors must be
through the ASTM consensus process.
considered.Among these are1) outside diameter of the device;
1.4 This standard does not purport to address all of the
2) materials from which the device and associated equipment
safety problems, if any, associated with its use. It is the
are made; 3) overall impact of the device on ground-water
responsibility of the user of this standard to establish appro-
sample integrity with respect to the analytes of interest; 4)
priate safety and health practices and determine the applica-
ability to control the discharge rate of the device; 5) depth to
bility of regulatory limitations prior to use.
water; 6) ease of operation and servicing; 7) reliability and
2. Referenced Documents durability of the device; 8) portability of the device and
required accessory equipment, if applicable; 9) other opera-
2.1 ASTM Standards:
tional limitations of the device; and 10) initial and operating
cost of the device and accessory equipment. Based on these
This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rock
and is the direct responsibility of Subcommittee D18.21 on Ground Water and
Vadose Zone Monitoring. Annual Book of ASTM Standards, Vol 04.08.
Current edition approved Feb. 10, 2001. Published March 2001. Annual Book of ASTM Standards, Vol 04.09.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6634
considerations,eachofthedevicesavailableforpurgingand/or into a 4 in. (100 mm) inside diameter well, most can be
sampling ground water from monitoring wells has its own installed in a 2 in. (50 mm) inside diameter well, and several
unique set of advantages and limitations. can be used in wells of 0.75 in. (19 mm) inside diameter or
less.
4. Significance and Use
6.3 Materials and Manufacture—The choice of materials
used in the construction of purging and sampling devices
4.1 Appropriate purging and sampling equipment must be
should be based upon knowledge of the geochemical environ-
used to ensure that samples collected from monitoring wells
ment and how the materials may interact with the sample via
represent the ground-water chemistry of the desired water
physical, chemical, or biological processes. Materials used in
bearing zone.
the manufacture of purging and sampling devices and associ-
4.2 This guide is intended to be a common reference for
ated tubing, hoses, pipes and support lines (e.g., rope, cable or
purging and sampling devices. It can be applied to ground-
chain) may be a source of bias or error. Materials used should
waterqualitysamplingfrommonitoringwellsusedforground-
not sorb analytes from samples, desorb previously-sorbed
water contamination evaluation, water supply characterization,
and research. analytes into samples, leach matrix components of the material
that could affect analyte concentrations or cause artifacts, or be
4.3 This guide includes a number of general guidance
physically or chemically degraded due to water chemistry.
statements that are not directly related to the operating prin-
Materials commonly used in the manufacture of sampling
ciples or characteristics of the equipment.These statements are
devices include rigid polyvinyl chloride (Type I PVC), stain-
given to assist the user in understanding the application of the
less steel, polytetrafluorethylene (PTFE) , polyethylene (PE),
equipment, which could ultimately affect the selection process.
polypropylene (PP), flexible polyvinyl chloride (Type II PVC),
5. Objectives of Well Purging and Sampling
fluoroelastomers polyvinylidene fluoride (PVDF), and
Buna-N, ethylene-propylene diene monomer (EPDM) and
5.1 The primary objective of ground-water sampling pro-
silicone rubbers. Studies are available which indicate the
grams is to obtain samples that are representative of existing
relative sorption/desorption rates of these materials, their
ground-water conditions retaining the physical and chemical
potential for alteration of the sample chemistry, and their
properties of the ground water in a specific water-bearing
ranking of desirability for use in sampling devices (1, 4, 7, 8,
zone.
9, 10). Extrusions and molded parts made of polymeric
6. Criteria for Selection of Purging and Sampling materials may contain surface traces of organic extrusion aids
Devices or mold release compounds. Also, some formulations of
polymeric materials may contain fillers or processing additives
6.1 When selecting purging and/or sampling device(s), a
that can leach from the material and alter sample quality.
numberofcriteriamustbeevaluatedasdiscussedbelow.Based
Traces of cutting oils, solvents or surface coatings may be
on these criteria, each device has a unique set of advantages
present on metallic materials. These should be removed and,
and limitations that define suitability to site-specific applica-
once removed, should not affect sample chemistry. It is
tions.
generally preferable to use materials produced without the use
6.2 Outside Diameter of the Device— If the well(s) to be
of these processing or surface coatings. Metallic materials are
purged and sampled is (are) already in place, the initial
subject to corrosion; electropolishing or other surface passiva-
consideration in selecting a device is whether or not the well(s)
tion processes can improve corrosion resistance. Corrosion and
will accommodate the device. It is important to consider that
residuesfromunfinishedmetallicmaterialscouldaffectsample
the wells may not be plumb, may have constrictions in the
quality.
casing (i.e. at joints), or may contain other obstructions that
6.4 Impact on Sample Integrity—While it is not particularly
make the effective inside diameter of the well smaller than the
important to preserve the chemical integrity of water purged
inside diameter of the casing. Alternately, if the monitoring
from a monitoring well, the device(s) chosen for purging and
wells are not in place, it may be more prudent to first select a
sampling should be evaluated to ensure that they minimize
device that meets the requirements of the sampling program
physical or chemical alteration of the water in the well and the
and then select the size of the casing to be used in the wells.
subsequent sample by their methods of delivering water to the
The smaller the inside diameter of the well, the more limited
surface. Because the subsurface environment is under different
the selection of devices becomes. The majority of ground-
temperature, pressure, gas content, and redox potential condi-
water monitoring wells installed at various types of sites are
tions than those at the surface, precautions must be taken to
small-diameter wells, or wells with inside diameters of 4 in.
ensure that these conditions are preserved as much as possible
(100 mm) or less. All of the devices described herein will fit
as sample water is transported to the surface. Devices that
introduce air or non-inert gas into a sample or that cause a
sample to undergo significant temperature or pressure changes
For example, the plasticizers in flexible PVC can contaminate samples with
phthalate esters. The use of silicone rubber tubing, which contains no plasticizers,
can obviate this problem; however, the potential for sample bias due to sorption/
desorption exists with both materials (9). These pumps can be used with the
intermediate vessel system described above, so that the sample contacts only the PTFE is also commonly known by the trade name Teflont, which includes
intake tubing and vessel, avoiding contact with the pump mechanism tubing. other fluoropolymer formulations. Teflon is a registered trademark of E. I. DuPont
Alternatively, using silicone rubber tubing at the pump head only can minimize this De Nemours & Company. Fluoroelastomers (FPM, FKM) are commonly known by
problem (20, 23). the trade name Vitont, a registered trademark of DuPont.
D6634
from the sampling depth to the surface are less desirable from field repairs, requiring servicing by the manufacturer or a
the standpoint of preserving the chemical quality of the sample qualified service facility.
(2, 11). For example, systems that allow air to contact the
6.8 Reliability and Durability—Reliability and durability
sample could cause oxidation of the samples, which can have
are two additional factors related to maintenance that warrant
a significant impact on both organic and inorganic chemical
attention. Devices used in some monitoring programs must be
constituents(2,11,12).Ingeneral,therateatwhichasampling
capable of operating for extended periods of time in subsurface
deviceisoperatedcouldaffectsamplequality,withhigherrates
environmentscontainingavarietyofchemicalconstituentsthat
having greater effect. Turbulence and depressurization could may cause corrosion of metallic parts or degradation of plastic
result in significant changes in dissolved oxygen, carbon materials (8). This is especially true where devices are dedi-
dioxide, dissolved metals and volatile organic compounds cated to wells and thus are continually exposed to potentially
(VOCs) in a sample (1, 2). Inserting a device into the water aggressive chemical environments.
column, withdrawing the device, and the rate at which water is
6.9 Portability vs. Dedication—In practice, purging and
removed from a well can all affect sample turbidity (5, 6).This
sampling devices are employed in one of two modes: portable
can impact concentrations of some analytes or interfere with
(used in multiple wells) or dedicated (installed for use in a
some analytical determinations (13).
single well). Dedicating sampling equipment eliminates the
need to decontaminate this equipment after each use, and can
6.5 Water Removal Rate and Flow Rate Control—
eliminate the potential for cross-contamination of wells and
Consideration should be given to appropriate water removal
samplesandpossiblecontaminationfromhandlingorimproper
rates when selecting purging and sampling devices. For ex-
storage of portable equipment. Dedicated equipment can also
ample, samples collected for analysis of some sensitive param-
be more cost effective to use in routine monitoring programs
eters (i.e. VOCs and trace metals) should be taken at low flow
due to reduced field labor and the elimination of the cost of
rates. Sampling rates should be high enough to fill sample
decontamination and analytical blanks. Portable equipment
containers efficiently but low enough to minimize sample
must be cleaned between use in each monitoring well or
alteration. Additionally, the use of low flow rate purging
discarded after use to avoid cross-contamination of wells and
techniques may require adjusting the pumping rate to account
samples. In addition, the components must withstand the
for the hydraulic performance of the well. Therefore, it is
necessary cleaning processes. Some devices, by virtue of their
generally desirable to have the ability to control the flow rate
design,maybedifficulttodisassembletoclean.Itmaybemore
of a purging or sampling device. Throttling down the device
practical to clean these devices by circulating cleaning solu-
using a valve in the discharge line reduces the flow rate, but
tions and rinses through the device and any associated tubing,
creates a pressure drop across the valve, and
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.