ASTM D6452-99
(Guide)Standard Guide for Purging Methods for Wells Used for Ground-Water Quality Investigations
Standard Guide for Purging Methods for Wells Used for Ground-Water Quality Investigations
SCOPE
1.1 This guide covers methods for purging wells used for gound-water 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 well-head.
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 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 document 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.
1.4 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 determine the applicability of regulatory limitations prior to use.
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Designation:D6452–99
Standard Guide for
Purging Methods for Wells Used for Ground-Water Quality
Investigations
This standard is issued under the fixed designation D 6452; 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 Water Monitoring Wells in Aquifers
D 5521 Guide for Development of Ground-Water Monitor-
1.1 This guide covers methods for purging wells used for
ing Wells in Granular Aquifers
ground-water quality investigations and monitoring programs.
D 5730 Guide for Site Characterization for Environmental
These methods could be used for other types of programs but
Purposes with Emphasis on Soil, Rock, the Vadose Zone,
are not addressed in this guide.
and Ground Water
1.2 This guide applies only to wells sampled at the well-
D 6089 Guide to Documenting a Ground-Water Sampling
head.
Event
1.3 This guide offers an organized collection of information
or a series of options and does not recommend a specific
3. Terminology
course of action. This document cannot replace education or
3.1 Definitions of Terms Specific to This Standard:
experience and should be used in conjunction with professional
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.
3.1.5 grab sampling device—a bailer or similar device that
1.4 This standard does not purport to address all of the
removes an aliquot of water from the well with each insertion
safety concerns, if any, associated with its use. It is the
and removal from the well.
responsibility of the user of this standard to establish appro-
3.1.6 indicator parameters (purging)—those physical or
priate safety and health practices and to determine the
chemical properties, or both, used as a correlative measure to
applicability of regulatory limitations prior to use.
determine when water to be sampled reflects ambient ground-
2. Referenced Documents water chemistry.
3.1.7 low yield well—a well that does not produce sufficient
2.1 ASTM Standards:
water such that the objectives of purging and sampling cannot
D 653 Terminology Relating to Soil, Rock, and Contained
be achieved without first removing all water from the well.
Fluids
3.1.8 packer (purging)—an expandable device used to
D 4448 Guide for Sampling Groundwater Monitoring
physically isolate one or more zones in a well.
Wells
3.1.9 purge volume—the quantity of water removed from
D 4750 Guide for Determining Subsurface Liquid Levels in
the well to accomplish the objectives of purging.
a Borehole or Monitoring Well (Observation Well)
3.1.10 purging—the practice of removing stagnant (stand-
D 5088 Guide for Decontamination of Field Equipment
ing) water from a well prior to sampling.
Used at Non-Radioactive Waste Sites
3.1.11 purging rate—the rate at which water is removed
D 5092 Practice for Design and Installation of Ground-
from a well or sampling point during purging.
3.1.12 recovery rate (purging)—the rate at which the water
level in a well returns to equilibrium with the hydraulic
This guide is under the jurisdiction of ASTM Committee D-18 on Soil and
conditions of the formation after the removal of water.
Rock and is the direct responsibility of Subcommittee D18.21 on GroundWater and
Vadose Zone Investigations.
Current edition approved July 10, 1999. Published October 1999.
Annual Book of ASTM Standards, Vol 04.08.
3 4
Annual Book of ASTM Standards, Vol 11.04. 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.
D6452–99
3.1.13 stabilization—a decrease in the change between 5.3 Well Design (Practice D 5092)—The design of the well
measured values to a specified range or percentage of the must be considered to select an appropriate purging method.
measured value over a selected number of consecutive read- Refer to Section 7 for how specific well design details affect
ings. the selection of purging methods.
3.1.13.1 Discussion—The interval between readings is cho- 5.4 Well Development (Guide D 5521)—Well development
sen for either a given time period or volume of water removed. is part of the well construction or maintenance process and not
3.1.14 stagnant water—the water contained in a well be- part of a purging and sampling event. Information on well
tween sampling events that may have interacted with materials development can be found in Guide D 5521.
or the headspace in the well, or both, and thus may be different
NOTE 3—Improper or inadequate well development can affect the
from ambient ground water conditions.
suitability of the well for use in the sampling program.
3.1.15 target analyte (purging)—a chemical constituent or
5.5 Hydraulics of the Well—Selection of a purging method
physical characteristic to be analyzed for the purpose of
should include an assessment of well-specific hydraulic con-
fulfilling program objectives.
ditions, which are directly related to formation transmissivity
3.1.16 well volume—the quantity of water contained in the
and well design, construction, development, and maintenance.
casing and the screen for a screened well, or in the open
Well and formation hydraulics (the 3-dimensional distribution
borehole and casing in an unscreened well. For an unscreened
of head) influence the rate at which water flows through or
well,thisvolumemayalsobereferredtoasaboreholevolume.
enters the well intake under laminar flow conditions. Purging
3.1.16.1 Discussion—Regulations or guidance documents
strategies are commonly categorized as being suitable for
may contain other definitions of well volume and should be
high-yield wells or low-yield wells.
consulted.
5.6 Purge Water Management—Manage purge water in
accordancewiththesite-specificwastemanagementprovisions
4. Significance and Use
ofthesamplingandanalysisplan.Itmaybepreferabletoselect
4.1 Wells used in ground-water quality investigations or
a purging method to minimize the purge volume, especially
monitoring programs are generally purged prior to sampling
when purge water must be containerized. (See Note 1.)
(Note 1). Purging is done to minimize the bias associated with
5.7 Physical Condition of the Wells—The physical condi-
stagnant water in the well, which generally does not accurately
tion of a well may affect the purging method by limiting the
reflect ambient ground-water chemistry (Note 2).
choice of equipment. For example, physical aberrations of the
NOTE 1—Some sampling methods, such as passive sampling, do not
sampling point such as a cracked casing or siltation could
require the practice of purging prior to sample collection (1,2).
preclude the use of certain purging devices.
NOTE 2—This guide does not address the practice of post-sample
5.8 Subsurface Geochemistry—Knowledge of the subsur-
purging(purgingagainaftersamplingiscompleted),whichisintendedfor
face geochemistry can be useful in selecting a purge method
purposes other than the minimization of bias associated with stagnant
that will best achieve the goal of removing stagnant water. It
water in the well.
canalsobeusefulindistinguishingbetweenambientformation
4.2 There are various methods for purging. Each purging
water and stagnant water during the purging process. Chemical
method may have a different volume of influence within the
and biological interaction between formation water and the
aquiferorscreenedinterval.Therefore,asamplecollectedafter
solid-phase materials in the aquifer, bacteria, or the well
purging by any one method is not necessarily equivalent to
materials can modify the chemistry of water standing in the
samples collected after purging by the other methods. The
well or in the vicinity of the well. Dissolved gases can be
selection of the appropriate method will be dependent on a
transported into or out of the screened or open interval and
number of factors, which should be defined during the devel-
added to or removed from the ground water across the free
opment of the sampling and analysis plan.This guide describes
surface of the water in the well.
the methods available and defines the circumstances under
5.9 Hydrogeologic Setting—Optimizing purging rates re-
which each method may be appropriate.
quires consideration of the hydrogeologic characteristics that
control the direction and rate of water movement and the
5. Criteria and Considerations for Selecting an
transport of dissolved and colloidal material. Constituents or
Appropriate Purging Method
concentrations of constituents not characteristic of the forma-
5.1 RegulationsorOtherGuidance—DetermineifanyState
tionwaterchemistryatthewellintakemaybetransportedfrom
or Federal regulations or guidance exist pertaining to purging
distant areas to the well by induced flow or reversal of flow
monitoring wells. Purging may be addressed as part of a
direction when purging rates are higher than optimal or when
broader regulation or guidance document on field investiga-
purging times are longer than optimal.
tions or ground-water monitoring.
5.2 Historical Data—Review of historical data can provide
6. Equipment Used for Purging
the user with information about the chemical and physical
6.1 A variety of devices are appropriate for purging wells.
behavior of the ground water at the sampling point during
Consideration of the factors in Section 5 may also be useful in
purging and details regarding past purging practices.
selecting purging devices.
6.2 All of the purging methods described herein require
water level measurements (see Guide D 4750). For some of the
The boldface numbers given in parentheses refer to a list of references at the
end of the text. purging methods, measurement of indicator parameters is also
D6452–99
required. When pumping devices are used for purging, it is 7.2.3.2 May result in a lower total purge volume.
preferable to use a flow through cell for optimal measurement 7.2.3.3 Provides well-specific chemical data to determine
of indicator parameters. when the well has been adequately purged.
7.2.4 Limitations.
7. Purging Methods
7.2.4.1 Requires the use and calibration of field parameter
7.1 Fixed Volume Purging:
measurement instrumentation.
7.1.1 Method Description—This method involves the re-
7.2.4.2 Requires knowledge of the instrumentation to be
movalofaspecifiednumberofwellvolumespriortosampling.
used.
The well volume is calculated in the field and multiplied by the
7.2.4.3 Accurate measurement of indicator parameters may
specifiednumbertoberemoved.Theminimumnumberofwell
be difficult to accomplish when using a grab sampler for
volumes to be removed should be prescribed in the sampling
purging.
and analysis plan and is often selected based on regulatory
7.3 Purging Based on Stabilization of Target Analytes:
guidance or requirements.
7.3.1 Method Description—This method uses concentra-
7.1.2 Applicability—Fixed well volume purging is best
tions of selected target analytes or their chemical analogs,
applied to wells that will yield multiple well volumes during
instead of indicator parameters, to determine when a well is
purging without fully dewatering.
sufficientlypurged.Dataareproducedbysequentialanalysisof
7.1.3 Advantages:
the purge water during well purging. Analyte concentrations
7.1.3.1 Can use a variety of pumps or grab sampling
are determined at the site using a mobile field laboratory unit
devices.
or smaller portable analytical equipment (Note 4). Depending
7.1.3.2 Does not require chemical measurements for deter-
on equipment capability, analyses may be run on continuous-
mining when purging is complete.
flow samples or sample aliquots. The frequency of measure-
7.1.4 Limitations:
ment should be based on purging rate.The acceptable variation
7.1.4.1 May increase the cost associated with management
oftargetanalytevaluestodefinestabilizationandtheminimum
of purge water.
number of consecutive stable readings within the prescribed
7.1.4.2 Not practical for use in low yield wells.
variation for each target analyte should be defined in the
7.1.4.3 Sometimes the number of well volumes is expressed
sampling and analysis plan (3,5).
as a range (for example, 3 to 5 volumes) making actual purge
NOTE 4—Examples of such equipment include field gas chromato-
volume open to interpretation and potentially variable between
graphs (for organic compounds), field ion chromatographs (for anions),
sampling events.
field spectrophotometers (for a large variety of chemical constituents and
7.1.4.4 There are no well-specific indicator parameter or
species), and ion-specific electrodes, colorimetric reagent kits, and titra-
target analyte data to determine when the well has been
tion reagent kits.
adequately purged.
7.3.2 Applicability—This method can be used for wells
7.1.4.5 The determination of an appropriate purging device,
where sufficient yield can be sustained to measure target
intake location, and rate of water removal are prerequisite to
analyte concentrations.
the effective use of this method.
7.3.3 Advantages:
7.2 PurgingBasedonStabilizationofIndicatorParameters:
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 plan. The most commonly
purged.
measured parameters include (but are not limited to) pH,
7.3.4 Limitations:
specific conductance, turbidity, temperature, dissolved oxygen,
7.3.4.1 Requires the use and calibration of target analyte
and oxidation-reduction potential. The parameters should be
measurement in
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