1、Designation: D 6452 99 (Reapproved 2005)Standard Guide forPurging Methods for Wells Used for Ground-Water QualityInvestigations1This standard is issued under the fixed designation D 6452; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers methods for purging wells used forground-water quality investigations and monitori
3、ng 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 guide offers an organized collection of informationor a series of options and does not recommend a specificcourse of action. T
4、his document cannot replace education orexperience and should be used in conjunction with professionaljudgment. 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 profes
5、sional service must be judged, nor should thisdocumente be applied without consideration of a projectsmany unique aspects. The word “Standard” in the title of thisguide means only that the document has been approvedthrough the ASTM consensus process.1.4 This standard does not purport to address all
6、of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this 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:2D 4750 Guide for Dete
7、rmining Subsurface Liquid Levels ina Borehole or Monitoring Well (Observation Well)D 5088 Guide for Decontamination of Field EquipmentUsed at Non-Radioactive Waste SitesD 5092 Practice for Design and Installation of Ground-Water Monitoring Wells in AquifersD 5521 Guide for Development of Ground-Wate
8、r Monitor-ing Wells in Granular AquifersD 6089 Guide to Documenting a Ground-Water SamplingEvent3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 casing volumethe quantity of water contained in thecasing above the screen or open borehole.3.1.2 fixed volume purgingremoving a spec
9、ified numberof well volumes to achieve purging.3.1.3 flow-through cell (purging)a vessel that allowspurge water to pass over sensors for continuous measurementof indicator parameters.3.1.4 flushingsee purging.3.1.5 grab sampling devicea bailer or similar device thatremoves an aliquot of water from t
10、he well with each insertionand removal from the well.3.1.6 indicator parameters (purging)those physical orchemical properties, or both, used as a correlative measure todetermine when water to be sampled reflects ambient ground-water chemistry.3.1.7 low yield wella well that does not produce sufficie
11、ntwater such that the objectives of purging and sampling cannotbe achieved without first removing all water from the well.3.1.8 packer (purging)an expandable device used tophysically isolate one or more zones in a well.3.1.9 purge volumethe quantity of water removed fromthe well to accomplish the ob
12、jectives of purging.3.1.10 purgingthe practice of removing stagnant (stand-ing) water from a well prior to sampling.3.1.11 purging ratethe rate at which water is removedfrom a well or sampling point during purging.3.1.12 recovery rate (purging)the rate at which the waterlevel in a well returns to eq
13、uilibrium with the hydraulicconditions of the formation after the removal of water.3.1.13 stabilizationa decrease in the change betweenmeasured values to a specified range or percentage of themeasured value over a selected number of consecutive read-ings.1This guide is under the jurisdiction ofASTM
14、Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.21 on Ground Water andVadose Zone Investigations.Current edition approved Jan. 1, 2005. Published February 2005. Originallyapproved in 1999. Last previous edition approved in 1999 as D 645299.2For referenced ASTM stan
15、dards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
16、PA 19428-2959, United States.3.1.13.1 DiscussionThe interval between readings is cho-sen for either a given time period or volume of water removed.3.1.14 stagnant waterthe water contained in a well be-tween sampling events that may have interacted with materialsor the headspace in the well, or both,
17、 and thus may be differentfrom ambient ground water conditions.3.1.15 target analyte (purging)a chemical constituent orphysical characteristic to be analyzed for the purpose offulfilling program objectives.3.1.16 well volumethe quantity of water contained in thecasing and the screen for a screened w
18、ell, or in the openborehole and casing in an unscreened well. For an unscreenedwell, this volume may also be referred to as a borehole volume.3.1.16.1 DiscussionRegulations or guidance documentsmay contain other definitions of well volume and should beconsulted.4. Significance and Use4.1 Wells used
19、in ground-water quality investigations ormonitoring programs are generally purged prior to sampling(Note 1). Purging is done to minimize the bias associated withstagnant water in the well, which generally does not accuratelyreflect ambient ground-water chemistry (Note 2).NOTE 1Some sampling methods,
20、 such as passive sampling, do notrequire the practice of purging prior to sample collection (1,2).3NOTE 2This guide does not address the practice of post-samplepurging (purging again after sampling is completed), which is intended forpurposes other than the minimization of bias associated with stagn
21、antwater 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 sample collected afterpurging by any one method is not necessarily equivalent tosamples collected after purging by the othe
22、r 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 guide describesthe methods available and defines the circumstances underwhich each method may be appropriate.5. Criteria
23、and Considerations for Selecting anAppropriate Purging Method5.1 Regulations or Other GuidanceDetermine if any Stateor Federal regulations or guidance exist pertaining to purgingmonitoring wells. Purging may be addressed as part of abroader regulation or guidance document on field investiga-tions or
24、 ground-water monitoring.5.2 Historical DataReview of historical data can providethe user with information about the chemical and physicalbehavior of the ground water at the sampling point duringpurging and details regarding past purging practices.5.3 Well Design (Practice D 5092)The design of the w
25、ellmust 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 (Guide D 5521)Well developmentis part of the well construction or maintenance process and notpart of a purging and samplin
26、g event. Information on welldevelopment can be found in Guide D 5521.NOTE 3Improper or inadequate well development can affect thesuitability of the well for use in the sampling program.5.5 Hydraulics of the WellSelection of a purging methodshould include an assessment of well-specific hydraulic con-
27、ditions, which are directly related to formation transmissivityand well design, construction, development, and maintenance.Well and formation hydraulics (the 3-dimensional distributionof head) influence the rate at which water flows through orenters the well intake under laminar flow conditions. Pur
28、gingstrategies are commonly categorized as being suitable forhigh-yield wells or low-yield wells.5.6 Purge Water ManagementManage purge water inaccordance with the site-specific waste management provisionsof the sampling and analysis plan. It may be preferable to selecta purging method to minimize t
29、he purge volume, especiallywhen purge water must be containerized. (See Note 1.)5.7 Physical Condition of the WellsThe physical condi-tion of a well may affect the purging method by limiting thechoice of equipment. For example, physical aberrations of thesampling point such as a cracked casing or si
30、ltation couldpreclude the use of certain purging devices.5.8 Subsurface GeochemistryKnowledge of the subsur-face geochemistry can be useful in selecting a purge methodthat will best achieve the goal of removing stagnant water. Itcan also be useful in distinguishing between ambient formationwater and
31、 stagnant water during the purging process. Chemicaland biological interaction between formation water and thesolid-phase materials in the aquifer, bacteria, or the wellmaterials can modify the chemistry of water standing in thewell or in the vicinity of the well. Dissolved gases can betransported i
32、nto or out of the screened or open interval andadded to or removed from the ground water 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
33、 and thetransport of dissolved and colloidal material. Constituents orconcentrations 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 tha
34、n optimal or whenpurging times are longer than optimal.6. Equipment Used 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 m
35、easurements (see Guide D 4750). For some of thepurging methods, measurement of indicator parameters is alsorequired. When pumping devices are used for purging, it ispreferable to use a flow through cell for optimal measurementof indicator parameters.3The boldface numbers given in parentheses refer t
36、o a list of references at theend of the text.D 6452 99 (2005)27. Purging Methods7.1 Fixed Volume Purging:7.1.1 Method DescriptionThis method involves the re-moval of a specified number of well volumes prior to sampling.The well volume is calculated in the field and multiplied by thespecified number
37、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 ApplicabilityFixed well volume purging is bestapplied to wells that will yield multiple well volumes duringpurg
38、ing 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 complete.7.1.4 Limitations:7.1.4.1 May increase the cost associated with managementof purge water.7.1.4.2 Not pract
39、ical 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 potentially variable betweensampling events.7.1.4.4 There are no well-specific indicator parameter ortarget analyte d
40、ata 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 effective use of this method.7.2 Purging Based on Stabilization of Indicator Parameters:7.2.1 Method DescriptionIn thi
41、s 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 should be specifiedin the sampling and analysis plan. The most commonlymeasured parameters include (but are not limited
42、 to) pH,specific conductance, turbidity, temperature, dissolved oxygen,and oxidation-reduction potential. The parameters should beselected based on knowledge of water chemistry and analytesof interest, or regulatory requirements, or both. The frequencyof measurement should be based on purging rate.
43、The accept-able variation of parameter values to define stabilization andthe minimum number of consecutive stable readings within theprescribed variation for each indicator parameter should bedefined in the sampling and analysis plan (3,4). Once stabili-zation has been reached, purging is complete r
44、egardless 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 concentrations.7.2.3 Advantages:7.2.3.1 Can be performed using a variety of grab samplingand pumping devices.7.2.3.2 May
45、 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 calibration of field parametermeasurement instrumentation.7.2.4.2 Requires knowledge of the instrumentation to beused
46、.7.2.4.3 Accurate measurement of indicator parameters maybe difficult to accomplish when using a grab sampler forpurging.7.3 Purging Based on Stabilization of Target Analytes:7.3.1 Method DescriptionThis method uses concentra-tions of selected target analytes or their chemical analogs,instead of ind
47、icator 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 equip
48、ment capability, analyses may be run on continuous-flow samples or sample aliquots. The frequency of measure-ment should be based on purging rate. The acceptable variationof target analyte values to define stabilization and the minimumnumber of consecutive stable readings within the prescribedvariat
49、ion for each target analyte should be defined in thesampling and analysis plan (3,5).NOTE 4Examples of such equipment include field gas chromato-graphs (for organic compounds), field ion chromatographs (for anions),field spectrophotometers (for a large variety of chemical constituents andspecies), and ion-specific electrodes, colorimetric reagent kits, and titra-tion reagent kits.7.3.2 ApplicabilityThis method can be used for wellswhere sufficient yield can be sustained to measure targetanalyte concentrations.7.3.3 Advantages:7.3.3.1 Can use a var
