ASTM D6452-99(2005)
(Guide)Standard Guide for Purging Methods for Wells Used for Groundwater Quality Investigations
Standard Guide for Purging Methods for Wells Used for Groundwater Quality Investigations
SIGNIFICANCE AND USE
Wells used in ground-water quality investigations or monitoring programs are generally purged prior to sampling (Note 1). Purging is done to minimize the bias associated with stagnant water in the well, which generally does not accurately reflect ambient ground-water chemistry (Note 2).
Note 1—Some sampling methods, such as passive sampling, do not require the practice of purging prior to sample collection (1,2).3
Note 2—This guide does not address the practice of post-sample purging (purging again after sampling is completed), which is intended for purposes other than the minimization of bias associated with stagnant water in the well.
There are various methods for purging. Each purging method may have a different volume of influence within the aquifer or screened interval. Therefore, a sample collected after purging by any one method is not necessarily equivalent to samples collected after purging by the other methods. The selection of the appropriate method will be dependent on a number of factors, which should be defined during the development of the sampling and analysis plan. This guide describes the methods available and defines the circumstances under which each method may be appropriate.
SCOPE
Wells used in groundwater quality investigations or monitoring programs are generally purged prior to sampling (Note 1). Purging is done to minimize the bias associated with stagnant water in the well, which generally does not accurately reflect ambient groundwater chemistry (Note 2).
Note 1—Some sampling methods, such as passive sampling, do not require the practice of purging prior to sample collection (1,2).
Note 2—This guide does not address the practice of post-sample purging (purging again after sampling is completed), which is intended for purposes other than the minimization of bias associated with stagnant water in the well.
There are various methods for purging. Each purging method may have a different volume of influence within the aquifer or screened interval. Therefore, a sample collected after purging by any one method is not necessarily equivalent to samples collected after purging by the other methods. The selection of the appropriate method will be dependent on a number of factors, which should be defined during the development of the sampling and analysis plan. This guide describes the methods available and defines the circumstances under which each method may be appropriate.
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Designation: D6452 − 99(Reapproved 2005)
Standard Guide for
Purging Methods for Wells Used for Groundwater Quality
Investigations
This standard is issued under the fixed designation D6452; 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 D5088 Practice for Decontamination of Field Equipment
Used at Waste Sites
1.1 This guide covers methods for purging wells used for
D5092 Practice for Design and Installation of Ground Water
groundwater quality investigations and monitoring programs.
Monitoring Wells
These methods could be used for other types of programs but
D5521 GuideforDevelopmentofGround-WaterMonitoring
are not addressed in this guide.
Wells in Granular Aquifers
1.2 This guide applies only to wells sampled at the well-
D6089 Guide for Documenting a Ground-Water Sampling
head.
Event
1.3 This guide offers an organized collection of information
3. Terminology
or a series of options and does not recommend a specific
course of action. This document cannot replace education or
3.1 Definitions of Terms Specific to This Standard:
experienceandshouldbeusedinconjunctionwithprofessional
3.1.1 casing volume—the quantity of water contained in the
judgment. Not all aspects of this guide may be applicable in all
casing above the screen or open borehole.
circumstances. This ASTM standard is not intended to repre-
3.1.2 fixed volume purging—removing a specified number
sent or replace the standard of care by which the adequacy of
of well volumes to achieve purging.
a given professional service must be judged, nor should this
3.1.3 flow-through cell (purging)—a vessel that allows
documente be applied without consideration of a project’s
purge water to pass over sensors for continuous measurement
many unique aspects. The word “Standard” in the title of this
of indicator parameters.
guide means only that the document has been approved
3.1.4 flushing—see purging .
through the ASTM consensus process.
1.4 This standard does not purport to address all of the
3.1.5 grab sampling device—a bailer or similar device that
safety concerns, if any, associated with its use. It is the
removes an aliquot of water from the well with each insertion
responsibility of the user of this standard to establish appro-
and removal from the well.
priate safety and health practices and to determine the
3.1.6 indicator parameters (purging)—those physical or
applicability of regulatory limitations prior to use.
chemical properties, or both, used as a correlative measure to
determine when water to be sampled reflects ambient ground-
2. Referenced Documents
water chemistry.
2.1 ASTM Standards:
3.1.7 low yield well—a well that does not produce sufficient
D4750 Test Method for Determining Subsurface Liquid
water such that the objectives of purging and sampling cannot
Levels in a Borehole or Monitoring Well (Observation
be achieved without first removing all water from the well.
Well) (Withdrawn 2010)
3.1.8 packer (purging)—an expandable device used to
physically isolate one or more zones in a well.
1 3.1.9 purge volume—the quantity of water removed from
This guide is under the jurisdiction ofASTM CommitteeD18 on Soil and Rock
and is the direct responsibility of Subcommittee D18.21 on Groundwater and
the well to accomplish the objectives of purging.
Vadose Zone Investigations.
3.1.10 purging—the practice of removing stagnant (stand-
Current edition approved Jan. 1, 2005. Published February 2005. Originally
approved in 1999. Last previous edition approved in 1999 as D6452–99. DOI: ing) water from a well prior to sampling.
10.1520/D6452-99R05.
3.1.11 purging rate—the rate at which water is removed
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
from a well or sampling point during purging.
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
3.1.12 recovery rate (purging)—the rate at which the water
the ASTM website.
level in a well returns to equilibrium with the hydraulic
The last approved version of this historical standard is referenced on
www.astm.org. conditions of the formation after the removal of water.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6452 − 99 (2005)
3.1.13 stabilization—adecreaseinthechangebetweenmea- 5.3 Well Design (Practice D5092)—The design of the well
sured values to a specified range or percentage of the measured must be considered to select an appropriate purging method.
value over a selected number of consecutive readings. Refer to Section 7 for how specific well design details affect
3.1.13.1 Discussion—The interval between readings is cho- the selection of purging methods.
sen for either a given time period or volume of water removed.
5.4 Well Development (Guide D5521)—Well development
3.1.14 stagnant water—the water contained in a well be-
is part of the well construction or maintenance process and not
tween sampling events that may have interacted with materials
part of a purging and sampling event. Information on well
or the headspace in the well, or both, and thus may be different
development can be found in Guide D5521.
from ambient groundwater conditions.
NOTE 3—Improper or inadequate well development can affect the
3.1.15 target analyte (purging)—a chemical constituent or
suitability of the well for use in the sampling program.
physical characteristic to be analyzed for the purpose of
5.5 Hydraulics of the Well—Selection of a purging method
fulfilling program objectives.
should include an assessment of well-specific hydraulic con-
3.1.16 well volume—the quantity of water contained in the
ditions, which are directly related to formation transmissivity
casing and the screen for a screened well, or in the open
and well design, construction, development, and maintenance.
borehole and casing in an unscreened well. For an unscreened
Well and formation hydraulics (the 3-dimensional distribution
well,thisvolumemayalsobereferredtoasaboreholevolume.
of head) influence the rate at which water flows through or
3.1.16.1 Discussion—Regulations or guidance documents
enters the well intake under laminar flow conditions. Purging
may contain other definitions of well volume and should be
strategies are commonly categorized as being suitable for
consulted.
high-yield wells or low-yield wells.
4. Significance and Use
5.6 Purge Water Management—Manage purge water in
accordancewiththesite-specificwastemanagementprovisions
4.1 Wells used in groundwater quality investigations or
ofthesamplingandanalysisplan.Itmaybepreferabletoselect
monitoring programs are generally purged prior to sampling
a purging method to minimize the purge volume, especially
(Note 1). Purging is done to minimize the bias associated with
when purge water must be containerized. (See Note 1.)
stagnant water in the well, which generally does not accurately
reflect ambient groundwater chemistry (Note 2).
5.7 Physical Condition of the Wells—Thephysicalcondition
of a well may affect the purging method by limiting the choice
NOTE 1—Some sampling methods, such as passive sampling, do not
require the practice of purging prior to sample collection (1,2).
of equipment. For example, physical aberrations of the sam-
NOTE 2—This guide does not address the practice of post-sample
pling point such as a cracked casing or siltation could preclude
purging(purgingagainaftersamplingiscompleted),whichisintendedfor
the use of certain purging devices.
purposes other than the minimization of bias associated with stagnant
water in the well.
5.8 Subsurface Geochemistry—Knowledge of the subsur-
4.2 There are various methods for purging. Each purging
face geochemistry can be useful in selecting a purge method
method may have a different volume of influence within the that will best achieve the goal of removing stagnant water. It
aquiferorscreenedinterval.Therefore,asamplecollectedafter
canalsobeusefulindistinguishingbetweenambientformation
purging by any one method is not necessarily equivalent to water and stagnant water during the purging process. Chemical
samples collected after purging by the other methods. The
and biological interaction between formation water and the
selection of the appropriate method will be dependent on a solid-phase materials in the aquifer, bacteria, or the well
number of factors, which should be defined during the devel- materials can modify the chemistry of water standing in the
opment of the sampling and analysis plan.This guide describes well or in the vicinity of the well. Dissolved gases can be
the methods available and defines the circumstances under transported into or out of the screened or open interval and
which each method may be appropriate. added to or removed from the groundwater across the free
surface of the water in the well.
5. Criteria and Considerations for Selecting an
5.9 Hydrogeologic Setting—Optimizing purging rates re-
Appropriate Purging Method
quires consideration of the hydrogeologic characteristics that
5.1 Regulations or Other Guidance—Determine if any State
control the direction and rate of water movement and the
or Federal regulations or guidance exist pertaining to purging
transport of dissolved and colloidal material. Constituents or
monitoring wells. Purging may be addressed as part of a
concentrations of constituents not characteristic of the forma-
broader regulation or guidance document on field investiga-
tionwaterchemistryatthewellintakemaybetransportedfrom
tions or groundwater monitoring.
distant areas to the well by induced flow or reversal of flow
5.2 Historical Data—Review of historical data can provide direction when purging rates are higher than optimal or when
the user with information about the chemical and physical purging times are longer than optimal.
behavior of the groundwater at the sampling point during
purging and details regarding past purging practices.
6. Equipment Used for Purging
6.1 A variety of devices are appropriate for purging wells.
Consideration of the factors in Section 5 may also be useful in
The boldface numbers given in parentheses refer to a list of references at the
end of the text. selecting purging devices.
D6452 − 99 (2005)
6.2 All of the purging methods described herein require 7.2.2 Applicability—This method can be used in all wells
water level measurements (see Guide D4750). For some of the wheresufficientyieldcanbesustainedtoreliablymeasurefield
purging methods, measurement of indicator parameters is also indicator parameter concentrations.
required. When pumping devices are used for purging, it is 7.2.3 Advantages:
preferable to use a flow through cell for optimal measurement 7.2.3.1 Can be performed using a variety of grab sampling
of indicator parameters. and pumping devices.
7.2.3.2 May result in a lower total purge volume.
7. Purging Methods 7.2.3.3 Provides well-specific chemical data to determine
when the well has been adequately purged.
7.1 Fixed Volume Purging:
7.2.4 Limitations.
7.1.1 Method Description—This method involves the re-
7.2.4.1 Requires the use and calibration of field parameter
movalofaspecifiednumberofwellvolumespriortosampling.
measurement instrumentation.
The well volume is calculated in the field and multiplied by the
7.2.4.2 Requires knowledge of the instrumentation to be
specifiednumbertoberemoved.Theminimumnumberofwell
used.
volumes to be removed should be prescribed in the sampling
7.2.4.3 Accurate measurement of indicator parameters may
and analysis plan and is often selected based on regulatory
be difficult to accomplish when using a grab sampler for
guidance or requirements.
purging.
7.1.2 Applicability—Fixed well volume purging is best
7.3 Purging Based on Stabilization of Target Analytes:
applied to wells that will yield multiple well volumes during
7.3.1 Method Description—This method uses concentra-
purging without fully dewatering.
tions of selected target analytes or their chemical analogs,
7.1.3 Advantages:
instead of indicator parameters, to determine when a well is
7.1.3.1 Can use a variety of pumps or grab sampling
sufficientlypurged.Dataareproducedbysequentialanalysisof
devices.
the purge water during well purging. Analyte concentrations
7.1.3.2 Does not require chemical measurements for deter-
are determined at the site using a mobile field laboratory unit
mining when purging is complete.
or smaller portable analytical equipment (Note 4). Depending
7.1.4 Limitations:
on equipment capability, analyses may be run on continuous-
7.1.4.1 May increase the cost associated with management
flow samples or sample aliquots. The frequency of measure-
of purge water.
ment should be based on purging rate.The acceptable variation
7.1.4.2 Not practical for use in low yield wells.
oftargetanalytevaluestodefinestabilizationandtheminimum
7.1.4.3 Sometimes the number of well volumes is expressed
number of consecutive stable readings within the prescribed
as a range (for example, 3 to 5 volumes) making actual purge
variation for each target analyte should be defined in the
volume open to interpretation and potentially variable between
sampling and analysis plan (3,5).
sampling events.
NOTE 4—Examples of such equipment include field gas chromato-
7.1.4.4 There are no well-specific indicator parameter or
graphs (for organic compounds), field ion chromatographs (for anions),
target analyte data to determine when the well has been
field spectrophotometers (for a large variety of chemical constituents and
adequately purged.
species), and ion-specific electrodes, colorimetric reagent kits, and titra-
tion reagent kits.
7.1.4.5 The determination of an appropriate purging device,
intake location, and rate of water removal are prerequisite to
7.3.2 Applicability—This method can be used for wells
the effective use of this method.
where sufficient yield can be sustained to measure target
analyte concentrations.
7.2 Purging Based on Stabilization of Indicator Param-
7.3.3 Advantages:
eters:
7.3.3.1 Can use a variety of grab sampling and pumping
7.2.1 Method Description—In this method, field measure-
devices.
ments of selected parameters are taken to indicate when the
7.3.3.2 May result in a lower total purge volume.
well is sufficiently purged. The indicator parameters to be
7.3.3.3 Provides well-specific and analyte-specific chemical
measured and frequency of measurements should be specified
data to determine precisely when the well has been adequately
in the sampling and analysis pla
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