1、Designation: D4448 01 (Reapproved 2013)Standard Guide forSampling Ground-Water Monitoring Wells1This standard is issued under the fixed designation D4448; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、 number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers sampling equipment and proceduresand “in the field” preservation, and it does not include welllocation, depth, well
3、development, design and construction,screening, or analytical procedures that also have a significantbearing on sampling results.This guide is intended to assist aknowledgeable professional in the selection of equipment forobtaining representative samples from ground-water monitor-ing wells that are
4、 compatible with the formations beingsampled, the site hydrogeology, and the end use of the data.1.2 This guide is only intended to provide a review of manyof the most commonly used methods for collecting ground-water quality samples from monitoring wells and is notintended to serve as a ground-wate
5、r monitoring plan for anyspecific application. Because of the large and ever increasingnumber of options available, no single guide can be viewed ascomprehensive. The practitioner must make every effort toensure that the methods used, whether or not they are ad-dressed in this guide, are adequate to
6、 satisfy the monitoringobjectives at each site.1.3 The values stated in SI units are to be regarded asstandard. The values given in parentheses are provided forinformation only.1.4 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsi
7、bility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4750 Test Method for Determining Subsurface LiquidLevels in a Borehole or Monitoring Well (Obs
8、ervationWell) (Withdrawn 2010)3D5088 Practice for Decontamination of Field EquipmentUsed at Waste SitesD5792 Practice for Generation of Environmental Data Re-lated to Waste Management Activities: Development ofData Quality ObjectivesD5903 Guide for Planning and Preparing for a GroundwaterSampling Ev
9、entD6089 Guide for Documenting a Ground-Water SamplingEventD6452 Guide for Purging Methods for Wells Used forGroundwater Quality InvestigationsD6517 Guide for Field Preservation of GroundwaterSamples2.2 EPA Standards:EPA Method 9020AEPA Method 90223. Terminology3.1 Definitions:3.1.1 low-flow samplin
10、ga ground water sampling tech-nique where the purge and sampling rates do not result insignificant changes in formation seepage velocity.3.1.2 minimal purge samplingthe collection of groundwater that is representative of the formation by purging onlythe volume of water contained by the sampling equi
11、pment (thatis, tubing, pump bladder).3.1.2.1 DiscussionThis sampling method should be con-sidered in situations where very low yield is a considerationand results from this sampling method should be scrutinized toconfirm that they meet data quality objectives (DQOs) and thework plan objectives.3.1.3
12、 passive samplingthe collection of ground-waterquality data so as to induce no hydraulic stress on the aquifer.3.1.4 water quality indicator parametersrefer to fieldmonitoring parameters that include but are not limited to pH,specific conductance, dissolved oxygen, oxidation-reductionpotential, temp
13、erature, and turbidity that are used to monitorthe completeness of purging.1This guide is under the jurisdiction of ASTM Committee D34 on WasteManagement and is the direct responsibility of Subcommittee D34.01.02 onSampling Techniques.Current edition approved April 1, 2013. Published April 2013. Ori
14、ginallyapproved in 1985. Last previous edition approved in 2007 as D444801 (2007).DOI: 10.1520/D4448-01R13.2For 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 stand
15、ards 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 States14. Summary of Guide4.1 The equipment and procedures used
16、 for sampling amonitoring well depend on many factors. These include, butare not limited to: the design and construction of the well, rateof ground-water flow, and the chemical species of interest.Sampling procedures may be different if analyses for traceorganics, volatiles, oxidizable species, or t
17、race metals areneeded. This guide considers all of these factors by discussingequipment and procedure options at each stage of the samplingsequence. For ease of organization, the sampling process canbe divided into three steps: well purging, sample withdrawal,and field preparation of samples. Certai
18、n sampling protocolseliminate the first step.4.2 The sampling must be well planned and all samplecontainers must be prepared prior to going to the field. Theseprocedures should be incorporated in the approved work planthat should accompany the sampling crew so that they mayrefer to it for guidance o
19、n sampling procedures and analytes tobe sampled (see Guide D5903).4.3 Monitoring wells must be either purged to removestagnant water in the well casing or steps must be taken toensure that only water meeting the DQOs and the work planobjectives is withdrawn during sampling (see Practice D5792).When
20、well purging is performed, it is accomplished by eitherremoving a predetermined number of well volumes or by theremoval of ground water until stable water quality parametershave been obtained. Ideally this purging is performed withminimal well drawdown and minimal mixing of the formationwater with t
21、he stagnant water above the screened interval in thecasing. Passive sampling and the minimal purge methods donot attempt to purge the water present in the monitoring wellprior to sampling (1).4The minimal purge method attempts topurge only the sampling equipment. Each of these methods isdiscussed in
22、 greater detail in Section 6.4.4 The types of chemical species that are to be sampled aswell as the reporting limits are prime factors for selectingsampling devices (2, 3). The sampling device and all materialsand devices the water contacts must be constructed of materialsthat will not introduce con
23、taminants or alter the analytes ofconcern in any way. Material compatibility is further discussedin Section 8.4.5 The method of sample collection can vary with theparameters of interest. The ideal sampling scheme employs acompletely inert material, does not subject the sample topressure change, does
24、 not expose the sample to the atmosphere,or any other gaseous atmosphere before conveying it to thesample container or flow cell for on-site analysis. Since theseideals are not always obtainable, compromises must be madeby the knowledgeable individual designing the sampling pro-gram. These concerns
25、should be documented in the data qualityobjectives (DQOs) of the sampling plan (see Practice D5792)(4).4.6 The degree and type of effort and care that goes into asampling program is always dependent on the chemicals ofconcern and their reporting levels as documented in theprojects DQOs. As the repor
26、ting level of the chemical speciesof analytical interest decreases, the precautions necessary forsampling generally increase. Therefore, the sampling objectivemust clearly be defined ahead of time in the DQOs. Thespecific precautions to be taken in preparing to sample for traceorganics are different
27、 from those to be taken in sampling fortrace metals.Adraft U.S. EPAguidance document (5) concern-ing monitoring well sampling, including considerations fortrace organics, is available to provide additional guidance.4.7 Care must be taken not to contaminate samples ormonitoring wells. All samples, sa
28、mpling devices, and contain-ers must be protected from possible sources of contaminationwhen not in use. Water level measurements should be madeaccording to Test Method D4750 before placing, purging, orsampling equipment in the well. Redox potential, turbidity, pH,specific conductance, DO (dissolved
29、 oxygen), and temperaturemeasurements should all be performed on the sample in thefield, if possible, since these parameters change too rapidly tobe conducted by a fixed laboratory under most circumstances.Field meter(s) or sondes equipped with flow-through cells areavailable that are capable of con
30、tinuously monitoring theseparameters during purging if they are being used as waterquality indicator parameters. These devices prevent the mixingof oxygen with the sample and provide a means of determiningwhen the parameters have stabilized. Certain measurementsthat are used as indicators of biologi
31、cal activity, such as ferrousiron, nitrite, and sulfite, may also be conducted in the fieldsince they rapidly oxidize.All temperature measurements mustbe done prior to any significant atmospheric exposure.5. Significance and Use5.1 The quality of ground water has become an issue ofnational concern.
32、Ground-water monitoring wells are one ofthe more important tools for evaluating the quality of groundwater, delineating contamination plumes, and establishing theintegrity of hazardous material management facilities.5.2 The goal in sampling ground-water monitoring wells isto obtain samples that meet
33、 the DQOs. This guide discusses theadvantages and disadvantages of various well samplingmethods, equipment, and sample preservation techniques. Itreviews the variables that need to be considered in developinga valid sampling plan.6. Well Purging6.1 Water that stands within a monitoring well for a lo
34、ngperiod of time may become unrepresentative of formationwater because chemical or biochemical change may alter waterquality or because the formation water quality may changeover time (see Guide D6452). Even if it is unchanged from thetime it entered the well, the stagnant water may not berepresenta
35、tive of formation water at the time of sampling.There are two approaches to purging that reflect two differingviewpoints: to purge a large volume of ground water and topurge a minimum of, or no ground water before collecting asample. The approach most often applied is to purge asufficient volume of
36、standing water from the casing, along withsufficient formation water to ensure that the water being4The boldface numbers in parentheses refer to a list of references at the end ofthis guide.D4448 01 (2013)2withdrawn at the time of sampling is representative of theformation water. Typically, three to
37、 five well volumes are used.An alternative method that is gaining acceptance is to minimizepurging and to conduct purging at a low flow rate or toeliminate purging entirely.6.2 In any purging approach, a withdrawal rate that mini-mizes drawdown while satisfying time constraints should beused. Excess
38、ive drawdown distorts the natural flow patternsaround the well. Two potential negative effects are the intro-duction of ground water that is not representative of waterquality immediately around the monitoring well and artificiallyhigh velocities entering the well resulting in elevated turbidityand
39、analytical data that reflects the absorption of contaminantsto physical particles rather than soluble concentrations inground water. It may also result in cascading water from thetop of the screen that can result in changes in dissolved gasses,redox state, and ultimately affect the concentration of
40、theanalytes of interest through the oxidation of dissolved metalsand possible loss of volatile organic compounds (VOCs). Theremay also be a lingering effect on the dissolved gas levels andredox state from air being introduced and trapped in thesandpack. In no instance shall a well be purged dry. Ifa
41、vailable, the field notes or purge logs generated duringprevious sampling or development of the well as well asconstruction logs should be reviewed to assist in the selectionof the most appropriate sampling method.6.3 The most often applied purging method has an objectiveto remove a predetermined vo
42、lume of stagnant water from thecasing prior to sampling. The volume of stagnant water caneither be defined as the volume of water contained within thecasing and screen, or to include the well screen and any gravelpack if natural flow through these is deemed insufficient tokeep them flushed out. Rese
43、arch with a tracer in a full scalemodel 2-in. polyvinyl chloride (PVC) well (6) indicates thatpumping 5 to 10 times the volume of the well via an inlet nearthe free water surface is sufficient to remove all the stagnantwater in the casing. This approach (with three to five casingvolumes purged) was
44、suggested by the U.S. EPA (7).6.4 In deep or large diameter wells having a volume ofwater so large as to make removal of all the water impractical,it may be feasible to lower a pump or pump inlet to some pointwell below the water surface, purge only the volume below thatpoint then withdraw the sampl
45、e from a deeper level. Researchindicates this approach should avoid most contaminationassociated with stagnant water (6, 8). Sealing the casing abovethe purge point with a packer may make this approach moredependable by preventing migration of stagnant water fromabove. But the packer must be above t
46、he top of the screenedzone, or stagnant water from above the packer may flow intothe purged zone through the wells gravel/sand pack.6.5 An alternate method is based on research by Barcelona,Wehrmann, and Varlien (1) and Puls and Powell (2). Theirresearch suggests that purging at rates less than 1 L/
47、min(approximately 0.25 gal/min) provides more reproducibleVOCs and metals analytical results than purging at high rates.This method is based on the premise that at very low pumpingrates, there is little mixing of the water column and laminarground-water flow through the screen provides a more consis
48、-tent sample. This sampling method also produces less turbidsamples that may eliminate the need for filtration whencollecting metals. This method is commonly referred to aslow-flow sampling.6.6 The low-flow sampling approach is most applicable towells capable of sustaining a yield approximately equa
49、l to thepumping rate.Amonitoring well with a very low yield may notbe applicable to this technique since it may be difficult toreduce the pumping rate sufficiently to prevent mixing of thewater column in the well casing in such a well. The water levelin the well being sampled should be continuously monitoredusing an electronic water-level indicator during low-flowsampling. Such a water-level indicator could be set below thewater surface after sufficient water has been withdrawn to fillthe pump, tubing, and flow cell. The water-level indicatorwould then produce a continuous sig
