1、Designation: D6634/D6634M 14Standard Guide forSelection of Purging and Sampling Devices for GroundwaterMonitoring Wells1This standard is issued under the fixed designation D6634/D6634M; the number immediately following the designation indicates theyear of original adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This guide describes the characteristics and operatingprinciples of purging and sampling devices avail
3、able for use ingroundwater monitoring wells and provides criteria for select-ing appropriate devices for specific applications. The selecteddevice(s) should be capable of purging the well and providingvalid representative samples of groundwater and includeddissolved constituents. The scope does not
4、include proceduresfor purging or collecting samples from monitoring wells,sampling devices for non-aqueous phase liquids, diffusion-typesampling devices or sampling from devices other than moni-toring wells.1.2 This guide reviews many of the most commonly useddevices for purging and sampling groundw
5、ater monitoringwells. The practitioner should ensure that the purging andsampling methods used, whether or not they are addressed inthis guide, are adequate to satisfy the monitoring objectives ateach site.1.3 This guide offers an organized collection of informationor a series of options and does no
6、t recommend a specific courseof action. This guide cannot replace education or experienceand should be used in conjunction with professional judgment.Not all aspects of this guide may be applicable in all circum-stances. This ASTM guide is not intended to represent orreplace the standard of care by
7、which the adequacy of a givenprofessional service must be judged, nor should this documentbe applied without consideration of the many unique aspects ofa project. The word “Standard” in the title of this documentmeans only that the document has been approved through theASTM consensus process.1.4 The
8、 values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the sta
9、ndard. Dimensions provided are typical.1.5 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory l
10、imitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD5088 Practice for Dec
11、ontamination of Field EquipmentUsed at Waste SitesD6452 Guide for Purging Methods for Wells Used forGroundwater Quality Investigations3. Terminology3.1 Definitions: For definitions of general terms used withinthis guide, refer to Terminology D653.4. Summary of Guide4.1 The primary objective of groun
12、dwater sampling pro-grams is to obtain samples that are representative of existinggroundwater conditions retaining the physical and chemicalproperties of the groundwater in a specific water-bearing zone.3Depending on the purging and sampling protocol, this mayrequire that the well is purged of stagn
13、ant water, or until1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.21 on Groundwater andVadose Zone Investigations.Current edition approved Feb. 1, 2014. Published February 2014. Originallyapproved in 2001. Last previous
14、 edition approved in 2006 as D6634 01 (2006).DOI: 10.1520/D6634_D6634M-14.2For 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 standards Document Summary page onthe
15、ASTM website.3For example, the plasticizers in flexible PVC can contaminate samples withphthalate esters. The use of silicone rubber tubing, which contains no plasticizers,can obviate this problem; however, the potential for sample bias due to sorption/desorption exists with both materials (1). Thes
16、e pumps can be used with theintermediate vessel system described above, so that the sample contacts only theintake tubing and vessel avoiding contact with the pump mechanism tubing.Alternatively, using silicone rubber tubing at the pump head only can minimize thisproblem (2, 3).*A Summary of Changes
17、 section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1pre-determined purging criteria are met. Therefore, device(s)selected for use in groundwater sampling programs must becapable of purging the w
18、ell as needed or delivering to thesurface, or both, a sample representative of in-situ groundwaterconditions. A number of factors can influence whether or not aparticular sample or set of samples is representative, and one ofthe significant elements of sample collection protocols is thesampling mech
19、anism (4, 5, 6).44.2 In selecting a purging or sampling device, or both, foruse in a groundwater monitoring well, a number of factorsmust be considered.Among these are 1) outside diameter of thedevice; 2) materials from which the device and associatedequipment are made; 3) overall impact of the devi
20、ce ongroundwater sample integrity with respect to the analytes ofinterest; 4) ability to regulate the discharge rate of the device;5) depth to water; 6) ease of operation and servicing; 7)reliability and durability of the device; 8) portability of thedevice and any needed accessory equipment, if app
21、licable; 9)other operational limitations of the device; and 10) initial andoperating cost of the device and accessory equipment. Basedon these considerations, each of the devices available forpurging or sampling groundwater, or both, from monitoringwells has its own unique set of advantages and limi
22、tations.NOTE 1The quality of the result produced by this guide is dependenton the competence of the personnel performing it, and the suitability of theequipment and facilities used. Agencies that meet the criteria of PracticeD3740 are generally considered capable of competent and objectivetesting/sa
23、mpling/inspection/etc. Users of this guide are cautioned thatcompliance with Practice D3740 does not in itself ensure reliable results.Reliable results depend on many factors; Practice D3740 provides a meansof evaluating some of those factors.5. Significance and Use5.1 Appropriate purging and sampli
24、ng equipment must beused to make sure that samples collected from monitoringwells represent the groundwater chemistry of the desired waterbearing zone.5.2 This guide is intended to be a common reference forpurging and sampling devices. It can be applied to groundwaterquality sampling from monitoring
25、 wells used for groundwatercontamination evaluation, water supply characterization, andresearch.5.3 This guide includes a number of general guidancestatements that are not directly related to the operating prin-ciples or characteristics of the equipment. These statements aregiven to assist the user
26、in understanding the application of theequipment, which could ultimately affect the selection process.6. Apparatus6.1 The apparatus described in this guide is commonlyavailable from commercial suppliers.7. Criteria for Selection of Purging and SamplingDevices7.1 When selecting purging or sampling de
27、vice(s), or both,a number of criteria must be evaluated as discussed below.Based on these criteria, each device has a unique set ofadvantages and limitations that define suitability to site-specificapplications.7.2 Outside Diameter of the DeviceIf the well(s) to bepurged and sampled is (are) already
28、 in place, the initialconsideration in selecting a device is whether or not the well(s)will accommodate the device. It is important to consider thatthe wells may not be plumb, may have constrictions in thecasing (that is, at joints), or may contain other obstructions thatmake the effective inside di
29、ameter of the well smaller than theinside diameter of the casing. Alternately, if the monitoringwells are not in place, it may be more prudent to first select adevice that meets the requirements of the sampling programand then select the size of the casing to be used in the wells.The smaller the ins
30、ide diameter of the well, the more limitedthe selection of devices becomes. The majority of groundwatermonitoring wells installed at various types of sites are small-diameter wells, or wells with inside diameters of 100 mm 4in. or less. All of the devices described herein will fit into a100 mm 4 in.
31、 inside diameter well, most can be installed ina 50 mm 2 in. inside diameter well, and several can be usedin wells of 19 mm 0.75 in. inside diameter or less.7.3 Materials and ManufactureThe choice of materialsused in the construction of purging and sampling devicesshould be based upon knowledge of t
32、he geochemical environ-ment and how the materials may interact with the sample viaphysical, chemical, or biological processes. Materials used inthe manufacture of purging and sampling devices and associ-ated tubing, hoses, pipes and support lines (for example, rope,cable or chain) may be a source of
33、 bias or error. Materials usedshould not sorb analytes from samples, desorb previously-sorbed analytes into samples, leach matrix components of thematerial that could affect analyte concentrations or causeartifacts, or be physically or chemically degraded due to waterchemistry. Materials commonly us
34、ed in the manufacture ofsampling devices include rigid polyvinyl chloride (Type IPVC), stainless steel, polytetrafluorethylene (PTFE),5polyeth-ylene (PE), polypropylene (PP), flexible polyvinyl chloride(Type II PVC), fluoroelastomers5polyvinylidene fluoride(PVDF), and Buna-N, ethylene-propylene dien
35、e monomer(EPDM) and silicone rubbers. Studies are available whichindicate the relative sorption/desorption rates of thesematerials, their potential for alteration of the sample chemistry,and their ranking of desirability for use in sampling devices (4,7, 8, 9, 1, 10). Extrusions and molded parts mad
36、e of polymericmaterials may contain surface traces of organic extrusion aidsor mold release compounds. Also, some formulations ofpolymeric materials may contain fillers or processing additivesthat can leach from the material and alter sample quality.Traces of cutting oils, solvents or surface coatin
37、gs may bepresent on metallic materials. These should be removed and,once removed, should not affect sample chemistry. It isgenerally preferable to use materials produced without the use4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.5PTFE is also commonl
38、y known by the trade name Teflon, which includesother fluoropolymer formulations. Teflon is a registered trademark of E. I. DuPontDe Nemours electropolishing or other surface passiva-tion processes can improve corrosion resistance. Corrosion andresidues from unfinished metallic materials could affec
39、t samplequality.7.4 Impact on Sample IntegrityWhile it is not particularlyimportant to preserve the chemical integrity of water purgedfrom a monitoring well, the device(s) chosen for purging andsampling should be evaluated to make sure that they minimizephysical or chemical alteration of the water i
40、n the well and thesubsequent sample by their methods of delivering water to thesurface. Because the subsurface environment is under differenttemperature, pressure, gas content, and redox potential condi-tions than those at the surface, precautions must be taken sothat these conditions are preserved
41、as much as possible assample water is transported to the surface. Devices thatintroduce air or non-inert gas into a sample or that cause asample to undergo significant temperature or pressure changesfrom the sampling depth to the surface are less desirable fromthe standpoint of preserving the chemic
42、al quality of the sample(5, 11). For example, systems that allow air to contact thesample could cause oxidation of the samples, which can havea significant impact on both organic and inorganic chemicalconstituents (5, 11, 12). In general, the rate at which a samplingdevice is operated could affect s
43、ample quality, with higher rateshaving greater effect. Turbulence and depressurization couldresult in significant changes in dissolved oxygen, carbondioxide, dissolved metals and volatile organic compounds(VOCs) in a sample (4, 5). Inserting a device into the watercolumn, withdrawing the device, and
44、 the rate at which water isremoved from a well can often affect sample turbidity (13, 14).This can impact concentrations of some analytes or interferewith some analytical determinations (15).7.5 Water Removal Rate and Flow Rate ControlConsideration should be given to appropriate water removalrates w
45、hen selecting purging and sampling devices. Forexample, samples collected for analysis of some sensitiveparameters (that is, VOCs and trace metals) should be taken atlow flow rates. Sampling rates should be high enough to fillsample containers efficiently but low enough to minimizesample alteration.
46、 Additionally, the use of low flow ratepurging techniques may require adjusting the pumping rate toaccount for the hydraulic performance of the well. Therefore, itis generally desirable to have the ability to control the flow rateof a purging or sampling device. Throttling down the deviceusing a val
47、ve in the discharge line reduces the flow rate, butcreates a pressure drop across the valve, and does not neces-sarily reduce the speed of the device in the well. Anothermethod of reducing flow rate is to divert a portion of thedischarge stream.7.6 Depth to Water and Lift CapabilityThe greater thede
48、pth to water, the more pumping head the device mustovercome to deliver water to the surface. Thus, the pumpinglift capability of the device determines whether or not thedevice is suitable for individual applications. In addition, thegreater the depth to water, the more time-consuming thepurging and
49、sampling operation becomes. Generally, the selec-tion of available purging and sampling devices is more limitedwith increased depth to water.7.7 Operation and ServicingEase of operation and servic-ing are important but frequently overlooked considerations inthe selection of purging and sampling devices. A commonsource of poor precision in sampling results is sampling deviceoperating problems (16). This could be due to any one ofseveral factors either: 1) the device and accessory equipmentare too complicated to operate efficiently under field condi-tions; 2) the operato
