1、Designation: D 4448 01 (Reapproved 2007)Standard Guide forSampling Ground-Water Monitoring Wells1This standard is issued under the fixed designation D 4448; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、 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 sampling equipment and proceduresand “in the field” preservation, and it does not include welllocation, depth, we
3、ll 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
4、are 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-w
5、ater 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
6、 to 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 therespo
7、nsibility 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:2D 4750 Test Method for Determining Subsurface LiquidLevels in a Borehole or Monitoring Well
8、(ObservationWell)D 5088 Practices for Decontamination of Field EquipmentUsed at Waste SitesD 5792 Practice for Generation of Environmental DataRelated to Waste Management Activities: Development ofData Quality ObjectivesD 5903 Guide for Planning and Preparing for a Groundwa-ter Sampling EventD 6089
9、Guide for Documenting a Ground-Water SamplingEventD 6452 Guide for Purging Methods for Wells Used forGround-Water Quality InvestigationsD 6517 Guide for Field Preservation of Ground-WaterSamples2.2 EPA Standards:EPA Method 9020AEPA Method 90223. Terminology3.1 Definitions:3.1.1 low-flow samplinga gr
10、ound 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 equipment
11、 (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 pass
12、ive 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, temperatu
13、re, and turbidity that are used to monitorthe completeness of purging.4. Summary of Guide4.1 The equipment and procedures used 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 chemic
14、al species of interest.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 Oct. 15, 2007. Published October 2007. Originallyapproved in 1985. Last previous edition app
15、roved in 2001 as D 444801.2For 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 ASTM website.1Copyright ASTM International, 100
16、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Sampling procedures may be different if analyses for traceorganics, volatiles, oxidizable species, or trace metals areneeded. This guide considers all of these factors by discussingequipment and procedure options at each
17、 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. Certain sampling protocolseliminate the first step.4.2 The sampling must be well planned and all samplecontainers must be p
18、repared 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 on sampling procedures and analytes tobe sampled (see Guide D 5903).4.3 Monitoring wells must be either purged to remo
19、vestagnant 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 D 5792).When well purging is performed, it is accomplished by eitherremoving a predetermined number of well volumes or by therem
20、oval 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 the stagnant water above the screened interval in thecasing. Passive sampling and the minimal purge methods donot at
21、tempt to purge the water present in the monitoring wellprior to sampling (1).3The minimal purge method attempts topurge only the sampling equipment. Each of these methods isdiscussed in greater detail in Section 6.4.4 The types of chemical species that are to be sampled aswell as the reporting limit
22、s 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 contaminants or alter the analytes ofconcern in any way. Material compatibility is further discussedin Section 8.4.5 T
23、he 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 not expose the sample to the atmosphere,or any other gaseous atmosphere before conveying it to thesample container
24、 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 should be documented in the data qualityobjectives (DQOs) of the sampling plan (see Practice D 5792)(4).4.6 The deg
25、ree 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 reporting level of the chemical speciesof analytical interest decreases, the precautions necessary forsampling generall
26、y 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 from those to be taken in sampling fortrace metals.Adraft U.S. EPAguidance document (5) concern-ing monitoring we
27、ll 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, sampling devices, and contain-ers must be protected from possible sources of contaminationwhen not in use. Water lev
28、el measurements should be madeaccording to Test Method D 4750 before placing, purging, orsampling equipment in the well. Redox potential, turbidity, pH,specific conductance, DO (dissolved oxygen), and temperaturemeasurements should all be performed on the sample in thefield, if possible, since these
29、 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 continuously monitoring theseparameters during purging if they are being used as waterquality indicator parameters.
30、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 biological activity, such as ferrousiron, nitrite, and sulfite, may also be conducted in the fieldsince they rapidly oxi
31、dize.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. Ground-water monitoring wells are one ofthe more important tools for evaluating the quality of groundwater, delin
32、eating 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 the DQOs. This guide discusses theadvantages and disadvantages of various well sampling meth-ods, equipment, and
33、 sample preservation techniques. It reviewsthe variables that need to be considered in developing a validsampling plan.6. Well Purging6.1 Water that stands within a monitoring well for a longperiod of time may become unrepresentative of formationwater because chemical or biochemical change may alter
34、 waterquality or because the formation water quality may changeover time (see Guide D 6452). Even if it is unchanged from thetime it entered the well, the stagnant water may not berepresentative of formation water at the time of sampling.There are two approaches to purging that reflect two differing
35、viewpoints: 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 standing water from the casing, along withsufficient formation water to ensure that the water beingwithdrawn a
36、t the time of sampling is representative of theformation water. Typically, three to 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 ra
37、te that mini-mizes drawdown while satisfying time constraints should be3The boldface numbers in parentheses refer to a list of references at the end ofthis guide.D 4448 01 (2007)2used. Excessive drawdown distorts the natural flow patternsaround the well. Two potential negative effects are the intro-
38、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 analytical data that reflects the absorption of contaminantsto physical particles rather than soluble concent
39、rations 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 theanalytes of interest through the oxidation of dissolved metalsand possible loss of volatile organic compou
40、nds (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. Ifavailable, the field notes or purge logs generated duringprevious sampling or development of the well as well
41、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 volume of stagnant water from thecasing prior to sampling. The volume of stagnant water caneither be defined as
42、 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. Research with a tracer in a full scalemodel 2-in. polyvinyl chloride (PVC) well (6) indicates thatpumping 5 to 10
43、 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 suggested by the U.S. EPA (7).6.4 In deep or large diameter wells having a volume ofwater so large as to make
44、 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 sample from a deeper level. Researchindicates this approach should avoid most contaminationassociated with stagnan
45、t 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 the top of the screenedzone, or stagnant water from above the packer may flow intothe purged zone through the
46、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/min(approximately 0.25 gal/min) provides more reproducibleVOCs and metals analytical results than purging at
47、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-tent sample. This sampling method also produces less turbidsamples that may eliminate the need for filtratio
48、n 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 equal to thepumping rate.Amonitoring well with a very low yield may notbe applicable to this technique since it m
49、ay 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 signal indicating submersion.When the well is purged, if the water level falls below thewater-level indicator pro
