ASTM D6634-01(2006)
(Guide)Standard Guide for the Selection of Purging and Sampling Devices for Groundwater Monitoring Wells
Standard Guide for the Selection of Purging and Sampling Devices for Groundwater Monitoring Wells
SIGNIFICANCE AND USE
Appropriate purging and sampling equipment must be used to ensure that samples collected from monitoring wells represent the groundwater chemistry of the desired water bearing zone.
This guide is intended to be a common reference for purging and sampling devices. It can be applied to groundwater quality sampling from monitoring wells used for groundwater contamination evaluation, water supply characterization, and research.
This guide includes a number of general guidance statements that are not directly related to the operating principles or characteristics of the equipment. These statements are given to assist the user in understanding the application of the equipment, which could ultimately affect the selection process.
SCOPE
1.1 This guide describes the characteristics and operating principles of purging and sampling devices available for use in groundwater 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 groundwater 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 groundwater 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.
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Designation: D6634 − 01 (Reapproved2006)
Standard Guide for
the Selection of Purging and Sampling Devices for
Groundwater Monitoring Wells
This standard is issued under the fixed designation D6634; 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
1.1 This guide describes the characteristics and operating 2.1 ASTM Standards:
principles of purging and sampling devices available for use in D5088 Practice for Decontamination of Field Equipment
groundwater monitoring wells and provides criteria for select- Used at Waste Sites
ing appropriate devices for specific applications. The selected D6452 Guide for Purging Methods for Wells Used for
device(s) should be capable of purging the well and providing Ground-Water Quality Investigations
valid representative samples of groundwater and any included
dissolved constituents. The scope does not include procedures 3. Summary of Guide
for purging or collecting samples from monitoring wells,
3.1 The primary objective of groundwater sampling pro-
samplingdevicesfornon-aqueousphaseliquids,diffusion-type
grams is to collect representative samples of groundwater.
sampling devices or sampling from devices other than moni-
Depending on the purging and sampling protocol, this may
toring wells.
require that the well is purged of all stagnant water, or until
pre-determined purging criteria are met. Therefore, device(s)
1.2 This guide reviews many of the most commonly used
selected for use in groundwater sampling programs must be
devices for purging and sampling groundwater monitoring
capable of purging the well as needed and/or delivering to the
wells. The practitioner must make every effort to ensure that
surface, a sample representative of in-situ groundwater condi-
the purging and sampling methods used, whether or not they
tions. A number of factors can influence whether or not a
are addressed in this guide, are adequate to satisfy the
particularsampleorsetofsamplesisrepresentative,andoneof
monitoring objectives at each site.
the significant elements of sample collection protocols is the
1.3 This guide offers an organized collection of information
sampling mechanism (1, 2, 3).
oraseriesofoptionsanddoesnotrecommendaspecificcourse
of action. This document cannot replace education or experi- 3.2 In selecting a purging and/or sampling device for use in
a groundwater monitoring well, a number of factors must be
ence and should be used in conjunction with professional
judgement. Not all aspects of this guide may be applicable in considered.Among these are1) outside diameter of the device;
2) materials from which the device and associated equipment
all circumstances. This ASTM standard is not intended to
representorreplacethestandardofcarebywhichtheadequacy are made; 3) overall impact of the device on groundwater
sample integrity with respect to the analytes of interest; 4)
of a given professional service must be judged, nor should this
document be applied without consideration of the many unique ability to control the discharge rate of the device; 5 ) depth to
water; 6) ease of operation and servicing; 7) reliability and
aspects of a project. The word “Standard” in the title of this
durability of the device; 8) portability of the device and
document means only that the document has been approved
required accessory equipment, if applicable; 9) other opera-
through the ASTM consensus process.
tional limitations of the device; and 10) initial and operating
1.4 This standard does not purport to address all of the
cost of the device and accessory equipment. Based on these
safety problems, if any, associated with its use. It is the
considerations,eachofthedevicesavailableforpurgingand/or
responsibility of the user of this standard to establish appro-
sampling groundwater from monitoring wells has its own
priate safety and health practices and determine the applica-
unique set of advantages and limitations.
bility of regulatory limitations prior to use.
1 2
This guide is under the jurisdiction ofASTM CommitteeD18 on Soil and Rock For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and is the direct responsibility of Subcommittee D18.21 on Groundwater and contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Vadose Zone Investigations. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved July 1, 2006. Published July 2006. Originally approved the ASTM website.
in 2001. Last previous edition approved in 2001 as D6634 – 01. DOI: 10.1520/ The boldface numbers in parentheses refer to a list of references at the end of
D6634-01R06. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6634 − 01 (2006)
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 groundwater 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
purgingandsamplingdevices.Itcanbeappliedtogroundwater
chain) may be a source of bias or error. Materials used should
quality sampling from monitoring wells used for groundwater
not sorb analytes from samples, desorb previously-sorbed
contamination evaluation, water supply characterization, and
analytes into samples, leach matrix components of the material
research.
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.
Materials commonly used in the manufacture of sampling
statements that are not directly related to the operating prin-
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),
polypropylene (PP), flexible polyvinyl chloride (Type II PVC),
equipment, which could ultimately affect the selection process.
fluoroelastomers polyvinylidene fluoride (PVDF), and
Buna-N, ethylene-propylene diene monomer (EPDM) and
5. Objectives of Well Purging and Sampling
silicone rubbers. Studies are available which indicate the
5.1 The primary objective of groundwater sampling pro-
relative sorption/desorption rates of these materials, their
grams is to obtain samples that are representative of existing
potential for alteration of the sample chemistry, and their
groundwater conditions retaining the physical and chemical
ranking of desirability for use in sampling devices (1, 4, 7, 8,
propertiesofthegroundwaterinaspecificwater-bearingzone.
9, 10). Extrusions and molded parts made of polymeric
materials may contain surface traces of organic extrusion aids
6. Criteria for Selection of Purging and Sampling
or mold release compounds. Also, some formulations of
Devices
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
of these processing or surface coatings. Metallic materials are
6.2 Outside Diameter of the Device— If the well(s) to be
purged and sampled is (are) already in place, the initial subject to corrosion; electropolishing or other surface passiva-
tionprocessescanimprovecorrosionresistance.Corrosionand
consideration in selecting a device is whether or not the well(s)
residuesfromunfinishedmetallicmaterialscouldaffectsample
will accommodate the device. It is important to consider that
quality.
the wells may not be plumb, may have constrictions in the
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 groundwater
temperature, pressure, gas content, and redox potential condi-
monitoring wells installed at various types of sites are small-
tions than those at the surface, precautions must be taken to
diameter wells, or wells with inside diameters of 4 in. (100
ensure that these conditions are preserved as much as possible
mm) or less. All of the devices described herein will fit into a
as sample water is transported to the surface. Devices that
4 in. (100 mm) inside diameter well, most can be installed in
introduce air or non-inert gas into a sample or that cause a
a 2 in. (50 mm) inside diameter well, and several can be used
sample to undergo significant temperature or pressure changes
in wells of 0.75 in. (19 mm) inside diameter or less.
from the sampling depth to the surface are less desirable from
the standpoint of preserving the chemical quality of the sample
(2, 11). For example, systems that allow air to contact the
For example, the plasticizers in flexible PVC can contaminate samples with sample could cause oxidation of the samples, which can have
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 Teflon®, 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 Viton®, a registered trademark of DuPont.
D6634 − 01 (2006)
a significant impact on both organic and inorganic chemical attention. Devices used in some monitoring programs must be
constituents (2, 11, 12).Ingeneral,therateatwhichasampling capableofoperatingforextendedperiodsoftimeinsubsurface
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
6.5 Water Removal Rate and Flow Rate Control—
need to decontaminate this equipment after each use, and can
Consideration should be given to appropriate water removal
eliminate the potential for cross-contamination of wells and
rates when selecting purging and sampling devices. For ex-
samplesandpossiblecontaminationfromhandlingorimproper
ample, samples collected for analysis of some sensitive param-
storage of portable equipment. Dedicated equipment can also
eters (i.e. VOCs and trace metals) should be taken at low flow
be more cost effective to use in routine monitoring programs
rates. Sampling rates should be high enough to fill sample
due to reduced field labor and the elimination of the cost of
containers efficiently but low enough to minimize sample
decontamination and analytical blanks. Portable equipment
alteration. Additionally, the use of low flow rate purging
must be cleaned between use in each monitoring well or
techniques may require adjusting the pumping rate to account
discarded after use to avoid cross-contamination of wells and
for the hydraulic performance of the well. Therefore, it is
samples. In addition, the components must withstand the
generally desirable to have the ability to control the flow rate
necessary cleaning processes. Some devices, by virtue of their
of a purging or sampling device. Throttling down the device
design,maybedifficulttodisassembletoclean.Itmaybemore
using a valve in the discharge line reduces the flow rate, but
practical to clean these devices by circulating cleaning solu-
creates a pressure drop across the valve, and does not neces-
tions and rinses through the device and any associated tubing,
sarily reduce the speed of the device in the well. Another
hose or pipe in accordance with Practices D5088, or to replace
method of reducing flow rate is to divert a portion of the
the associated tub
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