1、Designation: D 4696 92 (Reapproved 2000)Standard Guide forPore-Liquid Sampling from the Vadose Zone1This standard is issued under the fixed designation D 4696; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. 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 discusses equipment and procedures used forsampling pore-liquid from the vadose zone (unsaturated zone).The guide is
3、limited to in-situ techniques and does not includesoil core collection and extraction methods for obtainingsamples.1.2 The term “pore-liquid” is applicable to any liquid fromaqueous pore-liquid to oil. However, all of the samplersdescribed in this guide were designed, and are used to sampleaqueous p
4、ore-liquids only. The abilities of these samplers tocollect other pore-liquids may be quite different than thosedescribed.1.3 Some of the samplers described in this guide are notcurrently commercially available. These samplers are pre-sented because they may have been available in the past, andmay b
5、e encountered at sites with established vadose zonemonitoring programs. In addition, some of these designs areparticularly suited to specific situations. If needed, thesesamplers could be fabricated.1.4 The values stated in SI units are to be regarded as thestandard.1.5 This standard does not purpor
6、t 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 limitations prior to use.1.6 This guide offers an organized collection of
7、 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 professionaljudgment. Not all aspects of this guide may be applicable in allcircumstances. This ASTM standard is not intend
8、ed to repre-sent or replace the standard of care by which the adequacy ofa given professional service must be judged, nor should thisdocument be applied without consideration of a projects manyunique aspects. The word “Standard” in the title of thisdocument means only that the document has been appr
9、ovedthrough the ASTM consensus process.2. Referenced Documents2.1 ASTM Standards:D 653 Terminology Relating to Soil, Rock, and ContainedFluids23. Terminology3.1 Definitions:3.1.1 Where reasonable, precise terms and names have beenused within this guide. However, certain terms and names withvarying d
10、efinitions are ubiquitous within the literature andindustry of vadose zone monitoring. For purposes of recogni-tion, these terms and names have been included in the guidewith their most common usage. In these instances, the commondefinitions have been included in Appendix X1. Examples ofsuch terms a
11、re soil, lysimeter, vacuum and pore-liquid tension.3.2 Definitions of Terms Specific to This Standard:3.2.1 Appendix X1 is a compilation of those terms used inthis guide. More comprehensive compilations, that were usedas sources for Appendix X1, are (in decreasing order of theirusage):3.2.1.1 Termin
12、ology D 653,3.2.1.2 Compilation of ASTM Terminology,33.2.1.3 Glossary of Soil Science Terms, Soil Science Societyof America,4and,3.2.1.4 Websters New Collegiate Dictionary,54. Summary of Guide4.1 Pores in the vadose zone can be saturated or unsaturated.Some samplers are designed to extract liquids f
13、rom unsaturatedpores; others are designed to obtain samples from saturatedpores (for example, perched ground water) or saturatedmacropores (for example, fissures, cracks, and burrows). Thisguide addresses these categories. The sampler types discussedare:4.1.1 Suction samplers (unsaturated sampling),
14、 (see Section7),4.1.2 Free drainage samplers (saturated sampling), (seeSection 8),4.1.3 Perched ground water samplers (saturated sampling),(see Section 9), and4.1.4 Experimental absorption samplers (unsaturated sam-pling), (see Section 10).1This guide is under the jurisdiction of ASTM Committee D18
15、on Soil and Rockand is the direct responsibility of Subcommittee D18.21 on Ground Water VadoseZone Investigations.Current edition approved April 15, 1992. Published June 1992.2Annual Book of ASTM Standards, Vol 04.08.3Compilation of ASTM Terminology, Sixth edition, ASTM, 1916 Race Street,Philadelphi
16、a, PA 19103, 1986.4Glossary of Soil Science Terms, Soil Science Society of America, 1987.5Websters New Collegiate Dictionary, Fifth edition, 1977.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.4.2 Most samplers designed for sampling liquid from un-saturated p
17、ores may also be used to sample from saturatedpores. This is useful in areas where the water table fluctuates,so that both saturated and unsaturated conditions occur atdifferent times. However, samplers designed for sampling fromsaturated pores cannot be used in unsaturated conditions. Thisis becaus
18、e the liquid in unsaturated pores is held at less thanatmospheric pressures (see Richards outflow principle,inAppendix X1).4.3 The discussion of each sampler is divided into specifictopics that include:4.3.1 Operating principles,4.3.2 Description,4.3.3 Installation,4.3.4 Operation, and4.3.5 Limitati
19、ons.5. Significance and Use5.1 Sampling from the vadose zone may be an importantcomponent of some ground water monitoring strategies. It canprovide information regarding contaminant transport and at-tenuation in the vadose zone. This information can be used formitigating potential problems prior to
20、degradation of a groundwater resource (1).65.2 The choice of appropriate sampling devices for a par-ticular location is dependent on various criteria. Specificguidelines for designing vadose zone monitoring programshave been discussed by Morrison (1), Wilson (2), Wilson (3),Everett (4), Wilson (5),
21、Everett et al (6), Wilson (7), Everett etal (8), Everett et al (9), Robbins et al (10), Merry and Palmer(11), U.S. EPA (12), Ball (13), and Wilson (14). In general, itis prudent to combine various unsaturated and free drainagesamplers into a program, so that the different flow regimes maybe monitore
22、d.5.3 This guide does not attempt to present details ofinstallation and use of the equipment discussed. However, aneffort has been made to present those references in which thespecific techniques may be found.6. Criteria for Selecting Pore-Liquid Samplers6.1 Decisions on the types of samplers to use
23、 in a monitor-ing program should be based on consideration of a variety ofcriteria that include the following:6.1.1 Required sampling depths,6.1.2 Required sample volumes,6.1.3 Soil characteristics,6.1.4 Chemistry and biology of the liquids to be sampled,6.1.5 Moisture flow regimes,6.1.6 Required du
24、rability of the samplers,6.1.7 Required reliability of the samplers,6.1.8 Climate,6.1.9 Installation requirements of the samplers,6.1.10 Operational requirements of the samplers,6.1.11 Commercial availability, and6.1.12 Costs.6.2 Some of these criteria are discussed in this guide.However, the abilit
25、y to balance many of these factors againstone another can only be obtained through field experience.7. Suction Samplers7.1 Table 1 presents the various types of suction samplers.The range of operating depths is the major criterion by whichsuction samplers are differentiated. Accordingly, the categor
26、iesof suction samplers are as follows:7.1.1 Vacuum LysimetersThese samplers are theoreticallyoperational at depths less than about 7.5 m. The practicaloperational depth is 6 m under ideal conditions.7.1.2 Pressure-Vacuum LysimetersThese samplers are op-erational at depths less than about 15 m.7.1.3
27、High Pressure-Vacuum Lysimeters (Also known aspressure-vacuum lysimeters with transfer vessels.) These sam-plers are normally operational down to about 46 m, although6The boldface numbers in parentheses refer to the list of references at the end ofthis standard.TABLE 1 Suction Sampler SummarySampler
28、 TypePorous SectionMaterialMaximumAPoreSize (m)Air EntryValue (cbar)Operational SuctionRange (cbar)Maximum OperationDepth (m)Vacuum lysimeters Ceramic 1.2 to 3.0 (1)A100 10010 to 2110010 to 21100NABNAB100 100 100NAB100 60 to 80 7.5Fritted glass 4 to 5.5 NABNAB7.5Stainless steel NAB49 to 5 49 to 5 7.
29、5APore size determined by bubbling pressure (1) or mercury intrusion (2).BNA = Not available.D 46962installations as deep as 91 m have been reported (15).7.1.4 Suction Lysimeters With Low Bubbling Pressures(Samplers With PTFE Porous Sections)These samplers areavailable in numerous designs that can b
30、e used to maximumdepths varying from about 7.5 to 46 m.NOTE 1The samplers of 7.1.1, 7.1.2, 7.1.3, and 7.1.4 are referred tocollectively as suction lysimeters. Within this standard, lysimeter isdefined as a device used to collect percolating water for analyses (16).7.1.5 Filter Tip SamplersThese samp
31、lers theoreticallyhave no maximum sampling depth.7.1.6 Experimental Suction Samplers The samplers havelimited field applications at the present time. They includecellulose-acetate hollow-fiber samplers, membrane filter sam-plers, and vacuum plate samplers. They are generally limited todepths less th
32、an about 7.5 m.7.2 Operating Principles:7.2.1 General:7.2.1.1 Suction lysimeters consist of a hollow, porous sec-tion attached to a sample vessel or a body tube. Samples areobtained by applying suction to the sampler and collectingpore-liquid in the body tube. Samples are retrieved by a varietyof me
33、thods.7.2.1.2 Unsaturated portions of the vadose zone consist ofinterconnecting soil particles, interconnecting air spaces, andinterconnecting liquid films. Liquid films in the soil providehydraulic contact between the saturated porous section of thesampler and the soil (see Fig. 1). When suction gr
34、eater than thesoil pore-liquid tension is applied to the sampler, a pressurepotential gradient towards the sampler is created. If themeniscuses of the liquid in the porous segment are able towithstand the applied suction (depending on the maximumpore sizes and hydrophobicity/hydrophilicity), liquid
35、movesinto the sampler. The ability of the meniscuses to withstand asuction decreases with increasing pore size and also withincreasing hydrophobicity of the porous segment (see 7.6). Ifthe maximum pore sizes are too large and hydrophobicity toogreat, the meniscuses are not able to withstand the appl
36、iedsuction. As a result, they break down, hydraulic contact is lost,and only air enters the sampler. As described in 7.6, ceramicporous segments are hydrophilic and the maximum pore sizesare small enough to allow meniscuses to withstand the entirerange of sampling suctions. Presently available polyt
37、etrafluo-roethylene (PTFE) porous segments are hydrophobic, themaximum pore sizes are larger, and only a very limited rangeof sampling suction can be applied before meniscuses breakdown and sampling ends (see 7.6.1.3). Therefore, samplersmade with PTFE porous segments may be used only forsampling so
38、ils with low pore-liquid tensions (12, 17).7.2.1.3 The ability of a sampler to withstand applied suc-tions can be directly measured by its bubbling pressure. Thebubbling pressure is measured by saturating the porous seg-ment, immersing it in water, and pressurizing the inside of theporous segment wi
39、th air. The pressure at which air startsbubbling through the porous segment into the surroundingwater is the bubbling pressure. The magnitude of the bubblingpressure is equal to the magnitude of the maximum suction thatcan be applied to the sampler before air entry occurs (air entryvalue). Because t
40、he bubbling pressure is a direct measure ofhow a sampler will perform, it is more useful than measure-ment of pore size distributions.7.2.1.4 As soil pore-liquid tensions increase (low pore-liquid contents), pressure gradients towards the sampler de-crease. Also, the soil hydraulic conductivity decr
41、eases expo-nentially. These result in lower flow rates into the sampler. Atpore-liquid tensions above about 60 (for coarse grained soils)to 80 cbar (for fine grained soils), the flow rates are effectivelyzero and samples cannot be collected.7.2.2 Suction Lysimeters:7.2.2.1 Vacuum lysimeters directly
42、 transfer samples to thesurface via a suction line. Because the maximum suction lift ofwater is about 7.5 m, these samplers cannot be operated belowthis depth. In reality, suction lifts of 6 m should be considereda practical maximum depth.7.2.2.2 Samples may be retrieved using the same techniqueas f
43、or vacuum lysimeters or, for deeper applications, thesample is retrieved by pressurizing the sampler with one line;this pushes the sample up to the surface in a second line.7.2.2.3 High pressure-vacuum lysimeters operate in thesame manner as pressure-vacuum lysimeters. However, theyinclude an inbuil
44、t check transfer vessel or a chamber betweenthe sampler and the surface. This prevents sample loss throughthe porous section during pressurization, and prevents possiblecup damage due to overpressurization.7.2.2.4 Suction lysimeters with low bubbling pressures areavailable in each of the three previ
45、ous designs. The onlydifference between these samplers and the three previousdesigns is that these porous sections are made with PTFE. Thelow bubbling pressure (and hence large pore size or hydropho-bicity, or both) of PTFE constrains these samplers to soils thatare nearly saturated (see 7.2.1.2 and
46、 7.6.1.3).7.2.3 Filter Tip SamplersSamples are collected from afilter tip sampler by lowering an evacuated sample vial downan access tube to a permanently emplaced porous tip. The vialis connected to the porous tip and sample flows through theporous section and into the vial. Once full, the vial is
47、retrieved.FIG. 1 Porous Section/Soil InteractionsD 469637.2.4 Experimental Suction Samplers Experimental suc-tion samplers generally operate on the same principle asvacuum lysimeters with different combinations of porousmaterials to enhance hydraulic contact. The samplers aregenerally fragile and di
48、fficult to install. As with vacuumlysimeters, they are generally limited to depths of less thanabout 7.5 m.7.3 Description:7.3.1 Vacuum Lysimeters:7.3.1.1 Vacuum lysimeters generally consist of a porous cupmounted on the end of a tube, similar to a tensiometer. The cupis attached to the tube with ad
49、hesives (187) or with “V” shapedflush threading sealed with an “O” ring. A stopper is insertedinto the upper end of the body tube and fastened in the samemanner as the porous cup or, in the case of rubber stoppers,inserted tightly (12). To recover samples, a suction line isinserted through the stopper to the base of the sampler. Thesuction line extends to the surface and connects to a samplebottle and suction source in series. Body tubes up to 1.8 m longhave been reported (15) (see Fig. 2).7.3.1.2 Harris and Hansen (19) described a vacuum lysim-eter witha6mmby65mmceramic poro
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