1、Designation: D6452 99 (Reapproved 2012)1Standard Guide forPurging Methods for Wells Used for Groundwater QualityInvestigations1This standard is issued under the fixed designation D6452; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEEditorial changes were made throughout in July 2012.1. Scope1.1 This guide covers methods for purging wells us
3、ed forgroundwater quality investigations and monitoring programs.These methods could be used for other types of programs butare not addressed in this guide.1.2 This guide applies only to wells sampled at the well-head.1.3 This standard describes seven methods (A-G) for theselection of purging method
4、s. Method AFixed VolumePurging, Method BPurging Based on Stabilization of Indi-cator Parameters, Method CPurging Based on Stabilizationof Target Analytes, Method DPurging Based on FixedVolume Combined with Indicator Parameter Stabilization,Method ELow Flow/Low Volume (Minimal Drawdown)Purging, Metho
5、d FWell Evacuation Purging, and MethodGUse of Packers in Purging.1.4 This guide offers an organized collection of informationor a series of options and does not recommend a specificcourse of action. This document cannot replace education orexperience and should be used in conjunction with profession
6、aljudgment. Not all aspects of this guide may be applicable in allcircumstances. This ASTM standard is not intended to repre-sent or replace the standard of care by which the adequacy ofa given professional service must be judged, nor should thisdocumente be applied without consideration of a projec
7、tsmany unique aspects. The word “Standard” in the title of thisguide means only that the document has been approvedthrough the ASTM consensus process.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this
8、standard to establish appro-priate safety and health practices and to determine theapplicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD4750 Test Method for Determining Subsurface LiquidLevels in
9、a Borehole or Monitoring Well (ObservationWell) (Withdrawn 2010)3D5088 Practice for Decontamination of Field EquipmentUsed at Waste SitesD5092 Practice for Design and Installation of Ground WaterMonitoring WellsD5521 Guide for Development of Ground-Water MonitoringWells in Granular AquifersD6089 Gui
10、de for Documenting a Ground-Water SamplingEvent3. Terminology3.1 Definitions:3.1.1 For definitions of common technical terms in thisstandard, refer to Terminology D653.3.1.2 casing volumethe quantity of water contained in thecasing above the screen or open borehole.3.1.3 fixed volume purgingremoving
11、 a specified numberof well volumes to achieve purging.3.1.4 flow-through cell (purging)a vessel that allowspurge water to pass over sensors for continuous measurementof indicator parameters.3.1.5 flushingsee purging.3.1.6 grab sampling devicea bailer or similar device thatremoves an aliquot of water
12、 from the well with each insertionand removal from the well.1This guide is under the jurisdiction of ASTM CommitteeD18 on Soil and Rockand is the direct responsibility of Subcommittee D18.21 on Groundwater andVadose Zone Investigations.Current edition approved July 1, 2012. Published November 2012.
13、Originallyapproved in 1999. Last previous edition approved in 2005 as D645299(2005).DOI: 10.1520/D6452-99R12E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the
14、standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.7 indicator parameters (purging)those physical
15、orchemical properties, or both, used as a correlative measure todetermine when water to be sampled reflects ambient ground-water chemistry.3.1.8 low yield wella well that does not produce sufficientwater such that the objectives of purging and sampling cannotbe achieved without first removing all wa
16、ter from the well.3.1.9 packer (purging)an expandable device used tophysically isolate one or more zones in a well.3.1.10 purge volumethe quantity of water removed fromthe well to accomplish the objectives of purging.3.1.11 purgingthe practice of removing stagnant (stand-ing) water from a well prior
17、 to sampling.3.1.12 purging ratethe rate at which water is removedfrom a well or sampling point during purging.3.1.13 recovery rate (purging)the rate at which the waterlevel in a well returns to equilibrium with the hydraulicconditions of the formation after the removal of water.3.1.14 stabilization
18、a decrease in the change between mea-sured values to a specified range or percentage of the measuredvalue over a selected number of consecutive readings.3.1.14.1 DiscussionThe interval between readings is cho-sen for either a given time period or volume of water removed.3.1.15 stagnant waterthe wate
19、r contained in a well be-tween sampling events that may have interacted with materialsor the headspace in the well, or both, and thus may be differentfrom ambient groundwater conditions.3.1.16 target analyte (purging)a chemical constituent orphysical characteristic to be analyzed for the purpose off
20、ulfilling program objectives.3.1.17 well volumethe quantity of water contained in thecasing and the screen for a screened well, or in the openborehole and casing in an unscreened well. For an unscreenedwell, this volume may also be referred to as a borehole volume.3.1.17.1 DiscussionRegulations or g
21、uidance documentsmay contain other definitions of well volume and should beconsulted.4. Significance and Use4.1 Wells used in groundwater quality investigations ormonitoring programs are generally purged prior to sampling(Note 1). Purging is done to minimize the bias associated withstagnant water in
22、 the well, which generally does not accuratelyreflect ambient groundwater chemistry (Note 2).NOTE 1Some sampling methods, such as passive sampling, do notrequire the practice of purging prior to sample collection (1,2).4NOTE 2This guide does not address the practice of post-samplepurging (purging ag
23、ain after sampling is completed), which is intended forpurposes other than the minimization of bias associated with stagnantwater in the well.4.2 There are various methods for purging. Each purgingmethod may have a different volume of influence within theaquifer or screened interval. Therefore, a sa
24、mple collected afterpurging by any one method is not necessarily equivalent tosamples collected after purging by the other methods. Theselection of the appropriate method will be dependent on anumber of factors, which should be defined during the devel-opment of the sampling and analysis plan. This
25、guide describesthe methods available and defines the circumstances underwhich each method may be appropriate.5. Criteria and Considerations for Selecting anAppropriate Purging Method5.1 Regulations or Other GuidanceDetermine if any Stateor Federal regulations or guidance exist pertaining to purgingm
26、onitoring wells. Purging may be addressed as part of abroader regulation or guidance document on field investiga-tions or groundwater monitoring.5.2 Historical DataReview of historical data can providethe user with information about the chemical and physicalbehavior of the groundwater at the samplin
27、g point duringpurging and details regarding past purging practices.5.3 Well Design (Practice D5092)The design of the wellmust be considered to select an appropriate purging method.Refer to Section 7 for how specific well design details affectthe selection of purging methods.5.4 Well Development (Gui
28、de D5521)Well developmentis part of the well construction or maintenance process and notpart of a purging and sampling event. Information on welldevelopment can be found in Guide D5521.NOTE 3Improper or inadequate well development can affect thesuitability of the well for use in the sampling program
29、.5.5 Hydraulics of the WellSelection of a purging methodshould include an assessment of well-specific hydraulicconditions, which are directly related to formation transmis-sivity and well design, construction, development, and main-tenance. Well and formation hydraulics (the 3-dimensionaldistributio
30、n of head) influence the rate at which water flowsthrough or enters the well intake under laminar flow condi-tions. Purging strategies are commonly categorized as beingsuitable for high-yield wells or low-yield wells.5.6 Purge Water ManagementManage purge water inaccordance with the site-specific wa
31、ste management provisionsof the sampling and analysis plan. It may be preferable to selecta purging method to minimize the purge volume, especiallywhen purge water must be containerized. (See Note 1.)5.7 Physical Condition of the WellsThe physical conditionof a well may affect the purging method by
32、limiting the choiceof equipment. For example, physical aberrations of the sam-pling point such as a cracked casing or siltation could precludethe use of certain purging devices.5.8 Subsurface GeochemistryKnowledge of the subsur-face geochemistry can be useful in selecting a purge methodthat will bes
33、t achieve the goal of removing stagnant water. Itcan also be useful in distinguishing between ambient formationwater and stagnant water during the purging process. Chemicaland biological interaction between formation water and thesolid-phase materials in the aquifer, bacteria, or the wellmaterials c
34、an modify the chemistry of water standing in the4The boldface numbers given in parentheses refer to a list of references at theend of the text.D6452 99 (2012)12well or in the vicinity of the well. Dissolved gases can betransported into or out of the screened or open interval andadded to or removed f
35、rom the groundwater across the freesurface of the water in the well.5.9 Hydrogeologic SettingOptimizing purging rates re-quires consideration of the hydrogeologic characteristics thatcontrol the direction and rate of water movement and thetransport of dissolved and colloidal material. Constituents o
36、rconcentrations of constituents not characteristic of the forma-tion water chemistry at the well intake may be transported fromdistant areas to the well by induced flow or reversal of flowdirection when purging rates are higher than optimal or whenpurging times are longer than optimal.6. Equipment U
37、sed for Purging6.1 A variety of devices are appropriate for purging wells.Consideration of the factors in Section 5 may also be useful inselecting purging devices.6.2 All of the purging methods described herein requirewater level measurements. For some of the purging methods,measurement of indicator
38、 parameters is also required. Whenpumping devices are used for purging, it is preferable to use aflow through cell for optimal measurement of indicator param-eters.7. Purging Methods7.1 Method AFixed Volume Purging:7.1.1 Method DescriptionThis method involves the re-moval of a specified number of we
39、ll volumes prior to sampling.The well volume is calculated in the field and multiplied by thespecified number to be removed. The minimum number of wellvolumes to be removed should be prescribed in the samplingand analysis plan and is often selected based on regulatoryguidance or requirements.7.1.2 A
40、pplicabilityFixed well volume purging is bestapplied to wells that will yield multiple well volumes duringpurging without fully dewatering.7.1.3 Advantages:7.1.3.1 Can use a variety of pumps or grab samplingdevices.7.1.3.2 Does not require chemical measurements for deter-mining when purging is compl
41、ete.7.1.4 Limitations:7.1.4.1 May increase the cost associated with managementof purge water.7.1.4.2 Not practical for use in low yield wells.7.1.4.3 Sometimes the number of well volumes is expressedas a range (for example, 3 to 5 volumes) making actual purgevolume open to interpretation and potenti
42、ally variable betweensampling events.7.1.4.4 There are no well-specific indicator parameter ortarget analyte data to determine when the well has beenadequately purged.7.1.4.5 The determination of an appropriate purging device,intake location, and rate of water removal are prerequisite tothe effectiv
43、e use of this method.7.2 Method BPurging Based on Stabilization of IndicatorParameters:7.2.1 Method DescriptionIn this method, field measure-ments of selected parameters are taken to indicate when thewell is sufficiently purged. The indicator parameters to bemeasured and frequency of measurements sh
44、ould be specifiedin the sampling and analysis plan. The most commonlymeasured parameters include (but are not limited to) pH,specific conductance, turbidity, temperature, dissolved oxygen,and oxidation-reduction potential. The parameters should beselected based on knowledge of water chemistry and an
45、alytesof interest, or regulatory requirements, or both. The frequencyof measurement should be based on purging rate. The accept-able variation of parameter values to define stabilization andthe minimum number of consecutive stable readings within theprescribed variation for each indicator parameter
46、should bedefined in the sampling and analysis plan (3,4). Once stabili-zation has been reached, purging is complete regardless of thevolume of water removed.7.2.2 ApplicabilityThis method can be used in all wellswhere sufficient yield can be sustained to reliably measure fieldindicator parameter con
47、centrations.7.2.3 Advantages:7.2.3.1 Can be performed using a variety of grab samplingand pumping devices.7.2.3.2 May result in a lower total purge volume.7.2.3.3 Provides well-specific chemical data to determinewhen the well has been adequately purged.7.2.4 Limitations.7.2.4.1 Requires the use and
48、calibration of field parametermeasurement instrumentation.7.2.4.2 Requires knowledge of the instrumentation to beused.7.2.4.3 Accurate measurement of indicator parameters maybe difficult to accomplish when using a grab sampler forpurging.7.3 Method CPurging Based on Stabilization of TargetAnalytes:7
49、.3.1 Method DescriptionThis method uses concentra-tions of selected target analytes or their chemical analogs,instead of indicator parameters, to determine when a well issufficiently purged. Data are produced by sequential analysis ofthe purge water during well purging. Analyte concentrationsare determined at the site using a mobile field laboratory unitor smaller portable analytical equipment (Note 4). Dependingon equipment capability, analyses may be run on continuous-flow samples or sample aliquots. The frequency of measure-ment sh
