ASTM D6452-99(2012)e1
(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
4.1 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).4Note 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.
4.2 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
1.1 This guide covers methods for purging wells used for groundwater quality investigations and monitoring programs. These methods could be used for other types of programs but are not addressed in this guide.
1.2 This guide applies only to wells sampled at the wellhead.
1.3 This standard describes seven methods (A-G) for the selection of purging methods. Method A—Fixed Volume Purging, Method B—Purging Based on Stabilization of Indicator Parameters, Method C—Purging Based on Stabilization of Target Analytes, Method D—Purging Based on Fixed Volume Combined with Indicator Parameter Stabilization, Method E—Low Flow/Low Volume (Minimal Drawdown) Purging, Method F—Well Evacuation Purging, and Method G—Use of Packers in Purging.
1.4 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 judgment. 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 documente be applied without consideration of a project's many unique aspects. The word “Standard” in the title of this guide means only that the document has been approved through the ASTM consensus process.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use.
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Designation: D6452 − 99 (Reapproved 2012)
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.
ε NOTE—Editorial changes were made throughout in July 2012.
1. Scope 2. Referenced Documents
1.1 This guide covers methods for purging wells used for
2.1 ASTM Standards:
groundwater quality investigations and monitoring programs.
D653 Terminology Relating to Soil, Rock, and Contained
These methods could be used for other types of programs but
Fluids
are not addressed in this guide.
D4750 Test Method for Determining Subsurface Liquid
Levels in a Borehole or Monitoring Well (Observation
1.2 This guide applies only to wells sampled at the well-
Well) (Withdrawn 2010)
head.
D5088 Practice for Decontamination of Field Equipment
1.3 This standard describes seven methods (A-G) for the
Used at Waste Sites
selection of purging methods. Method A—Fixed Volume
D5092 Practice for Design and Installation of Ground Water
Purging, Method B—Purging Based on Stabilization of Indi-
Monitoring Wells
cator Parameters, Method C—Purging Based on Stabilization
D5521 GuideforDevelopmentofGround-WaterMonitoring
of Target Analytes, Method D—Purging Based on Fixed
Wells in Granular Aquifers
Volume Combined with Indicator Parameter Stabilization,
D6089 Guide for Documenting a Ground-Water Sampling
Method E—Low Flow/Low Volume (Minimal Drawdown)
Event
Purging, Method F—Well Evacuation Purging, and Method
G—Use of Packers in Purging.
3. Terminology
1.4 This guide offers an organized collection of information
3.1 Definitions:
or a series of options and does not recommend a specific
3.1.1 For definitions of common technical terms in this
course of action. This document cannot replace education or
standard, refer to Terminology D653.
experience and should be used in conjunction with professional
3.1.2 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-
sent or replace the standard of care by which the adequacy of
3.1.3 fixed volume purging—removing a specified number
a given professional service must be judged, nor should this
of well volumes to achieve purging.
documente be applied without consideration of a project’s
3.1.4 flow-through cell (purging)—a vessel that allows
many unique aspects. The word “Standard” in the title of this
purge water to pass over sensors for continuous measurement
guide means only that the document has been approved
of indicator parameters.
through the ASTM consensus process.
1.5 This standard does not purport to address all of the
3.1.5 flushing—see purging.
safety concerns, if any, associated with its use. It is the
3.1.6 grab sampling device—a bailer or similar device that
responsibility of the user of this standard to establish appro-
removes an aliquot of water from the well with each insertion
priate safety and health practices and to determine the
and removal from the well.
applicability 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, 2012. Published November 2012. Originally the ASTM website.
approved in 1999. Last previous edition approved in 2005 as D6452–99(2005). The last approved version of this historical standard is referenced on
DOI: 10.1520/D6452-99R12E01. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D6452 − 99 (2012)
3.1.7 indicator parameters (purging)—those physical or purging by any one method is not necessarily equivalent to
chemical properties, or both, used as a correlative measure to samples collected after purging by the other methods. The
determine when water to be sampled reflects ambient ground- selection of the appropriate method will be dependent on a
water chemistry. number of factors, which should be defined during the devel-
opment of the sampling and analysis plan.This guide describes
3.1.8 low yield well—a well that does not produce sufficient
the methods available and defines the circumstances under
water such that the objectives of purging and sampling cannot
which each method may be appropriate.
be achieved without first removing all water from the well.
3.1.9 packer (purging)—an expandable device used to
5. Criteria and Considerations for Selecting an
physically isolate one or more zones in a well.
Appropriate Purging Method
3.1.10 purge volume—the quantity of water removed from
5.1 Regulations or Other Guidance—Determine if any State
the well to accomplish the objectives of purging.
or Federal regulations or guidance exist pertaining to purging
3.1.11 purging—the practice of removing stagnant (stand-
monitoring wells. Purging may be addressed as part of a
ing) water from a well prior to sampling.
broader regulation or guidance document on field investiga-
3.1.12 purging rate—the rate at which water is removed tions or groundwater monitoring.
from a well or sampling point during purging.
5.2 Historical Data—Review of historical data can provide
3.1.13 recovery rate (purging)—the rate at which the water
the user with information about the chemical and physical
level in a well returns to equilibrium with the hydraulic behavior of the groundwater at the sampling point during
conditions of the formation after the removal of water.
purging and details regarding past purging practices.
3.1.14 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
3.1.14.1 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
3.1.15 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
3.1.16 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
3.1.17 well volume—the quantity of water contained in the
conditions, which are directly related to formation transmis-
casing and the screen for a screened well, or in the open
sivity and well design, construction, development, and main-
borehole and casing in an unscreened well. For an unscreened
tenance. Well and formation hydraulics (the 3-dimensional
well,thisvolumemayalsobereferredtoasaboreholevolume.
distribution of head) influence the rate at which water flows
3.1.17.1 Discussion—Regulations or guidance documents
through or enters the well intake under laminar flow condi-
may contain other definitions of well volume and should be
tions. Purging strategies are commonly categorized as being
consulted.
suitable for high-yield wells or low-yield wells.
5.6 Purge Water Management—Manage purge water in
4. Significance and Use
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
5.7 Physical Condition of the Wells—Thephysicalcondition
reflect ambient groundwater chemistry (Note 2).
of a well may affect the purging method by limiting the choice
NOTE 1—Some sampling methods, such as passive sampling, do not
of equipment. For example, physical aberrations of the sam-
require the practice of purging prior to sample collection (1,2).
pling point such as a cracked casing or siltation could preclude
NOTE 2—This guide does not address the practice of post-sample
the use of certain purging devices.
purging(purgingagainaftersamplingiscompleted),whichisintendedfor
purposes other than the minimization of bias associated with stagnant
5.8 Subsurface Geochemistry—Knowledge of the subsur-
water in the well.
face geochemistry can be useful in selecting a purge method
4.2 There are various methods for purging. Each purging
that will best achieve the goal of removing stagnant water. It
method may have a different volume of influence within the
canalsobeusefulindistinguishingbetweenambientformation
aquiferorscreenedinterval.Therefore,asamplecollectedafter
water and stagnant water during the purging process. Chemical
and biological interaction between formation water and the
solid-phase materials in the aquifer, bacteria, or the well
The boldface numbers given in parentheses refer to a list of references at the
end of the text. materials can modify the chemistry of water standing in the
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D6452 − 99 (2012)
well or in the vicinity of the well. Dissolved gases can be 7.2.1 Method Description—In this method, field measure-
transported into or out of the screened or open interval and ments of selected parameters are taken to indicate when the
added to or removed from the groundwater across the free well is sufficiently purged. The indicator parameters to be
surface of the water in the well. measured and frequency of measurements should be specified
in the sampling and analysis plan. The most commonly
5.9 Hydrogeologic Setting—Optimizing purging rates re-
measured parameters include (but are not limited to) pH,
quires consideration of the hydrogeologic characteristics that
specific conductance, turbidity, temperature, dissolved oxygen,
control the direction and rate of water movement and the
and oxidation-reduction potential. The parameters should be
transport of dissolved and colloidal material. Constituents or
selected based on knowledge of water chemistry and analytes
concentrations of constituents not characteristic of the forma-
of interest, or regulatory requirements, or both. The frequency
tionwaterchemistryatthewellintakemaybetransportedfrom
of measurement should be based on purging rate. The accept-
distant areas to the well by induced flow or reversal of flow
able variation of parameter values to define stabilization and
direction when purging rates are higher than optimal or when
the minimum number of consecutive stable readings within the
purging times are longer than optimal.
prescribed variation for each indicator parameter should be
6. Equipment Used for Purging
defined in the sampling and analysis plan (3,4). Once stabili-
zation has been reached, purging is complete regardless of the
6.1 A variety of devices are appropriate for purging wells.
volume of water removed.
Consideration of the factors in Section 5 may also be useful in
7.2.2 Applicability—This method can be used in all wells
selecting purging devices.
wheresufficientyieldcanbesustainedtoreliablymeasurefield
6.2 All of the purging methods described herein require
indicator parameter concentrations.
water level measurements. For some of the purging methods,
7.2.3 Advantages:
measurement of indicator parameters is also required. When
7.2.3.1 Can be performed using a variety of grab sampling
pumping devices are used for purging, it is preferable to use a
and pumping devices.
flow through cell for optimal measurement of indicator param-
7.2.3.2 May result in a lower total purge volume.
eters.
7.2.3.3 Provides well-specific chemical data to determine
7. Purging Methods when the well has been adequately purged.
7.2.4 Limitations.
7.1 Method A—Fixed Volume Purging:
7.2.4.1 Requires the use and calibration of field parameter
7.1.1 Method Description—This method involves the re-
measurement instrumentation.
movalofaspecifiednumberofwellvolumespriortosampling.
7.2.4.2 Requires knowledge of the instrumentation to be
The well volume is calculated in the field and multiplied by the
used.
specifiednumbertoberemoved.Theminimumnumberofwell
7.2.4.3 Accurate measurement of indicator parameters may
volumes to be removed should be prescribed in the sampling
be difficult to accomplish when using a grab sampler for
and analysis plan and is often selected based on regulatory
purging.
guidance or requirements.
7.1.2 Applicability—Fixed well volume purging is best
7.3 Method C—Purging Based on Stabilization of Target
applied to wells that will yield multiple well volumes during
Analytes:
purging without fully dewatering.
7.3.1 Method Description—This method uses concentra-
7.1.3 Advantages:
tions of selected target analytes or their chemical analogs,
7.1.3.1 Can use a variety of pumps or grab sampling
instead of indicator parameters, to determine when a well is
devices.
sufficientlypurged.Dataareproducedbysequentialanalysisof
7.1.3.2 Does not require chemical measurements for deter-
the purge water during well purging. Analyte concentrations
mining when purging is complete.
are determined at the site using a mobile field laboratory unit
7.1.4 Limitations:
or smaller portable analytical equipment (Note 4). Depending
7.1.4.1 May increase the cost associated with management
on equipment capability, analyses may be run on continuous-
of purge water.
flow samples or sample aliquots. The frequency of measure-
7.1.4.2 Not practical for use in low yield wells.
ment should be based on purging rate.The acceptable variation
7.1.4.3 Sometimes the number of well volumes is ex
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