ASTM D4696-18

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D4696 − 18
Standard Guide for
Pore-Liquid Sampling from the Vadose Zone
This standard is issued under the fixed designation D4696; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* unique aspects. The word “Standard” in the title of this
document means only that the document has been approved
1.1 This guide covers the equipment and procedures used
through the ASTM consensus process.
for sampling pore-liquid from the vadose zone (unsaturated
zone). The guide is limited to in situ techniques and does not 1.7 This international standard was developed in accor-
include soil core collection and extraction methods for obtain- dance with internationally recognized principles on standard-
ing samples. ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.2 The term “pore-liquid” is applicable for liquids from
mendations issued by the World Trade Organization Technical
aqueous pore-liquid to oil. However, the samplers described in
Barriers to Trade (TBT) Committee.
this guide were designed, and are used to sample aqueous
pore-liquids only. The abilities of these samplers to collect
2. Referenced Documents
other pore-liquids may be quite different than those described.
2.1 ASTM Standards:
1.3 Some of the samplers described in this guide are not
D653Terminology Relating to Soil, Rock, and Contained
currently commercially available. These samplers are pre-
Fluids
sented because they may have been available in the past, and
D3740Practice for Minimum Requirements for Agencies
may be encountered at sites with established vadose zone
Engaged in Testing and/or Inspection of Soil and Rock as
monitoring programs. In addition, some of these designs are
Used in Engineering Design and Construction
particularly suited to specific situations. If needed, these
samplers could be fabricated.
3. Terminology
1.4 The values stated in SI units are to be regarded as
3.1 Definitions—
standard. No other units of measurement are included in this
3.1.1 Forcommondefinitionsoftermsinthisstandard,refer
standard.
to Terminology D653.
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.2 Definitions of Terms Specific to This Standard:
responsibility of the user of this standard to establish appro- 3.2.1 air entry value, n—in vadose zone,theappliedsuction
priate safety, health, and environmental practices and deter- at which water menisci of the porous segment of a suction
mine the applicability of regulatory limitations prior to use. sampler break down, and air enters.
1.6 This guide offers an organized collection of information
3.2.2 bubbling pressure, n—in vadose zone, the applied air
or a series of options and does not recommend a specific
pressure at which water menisci of the porous segment of a
course of action. This document cannot replace education or
suction sampler break down, and air exits.
experienceandshouldbeusedinconjunctionwithprofessional
3.2.3 cascading water, n—in groundwater, perched ground-
judgment. Not all aspects of this guide may be applicable in all
water that enters a well casing via cracks or uncovered
circumstances. This ASTM standard is not intended to repre-
perforations, trickling, or pouring down the inside of the
sent or replace the standard of care by which the adequacy of
casing.
a given professional service must be judged, nor should this
3.2.4 hydrophobicity, n—in vadose zone, the property that
document be applied without consideration of a project’s many
defines a material as being water repellent. Water exhibits an
obtuse contact angle with hydrophobic materials.
ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
and is the direct responsibility of Subcommittee D18.21 on Groundwater and
Vadose Zone Investigations.
Current edition approved Nov. 15, 2018. Published November 2018. Originally For referenced ASTM standards, visit the ASTM website, www.astm.org, or
approved in 1992. Last previous edition approved in 2008 as D4696–92(2008), contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
which was withdrawn January 2017 and reinstated in November 2018. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D4696-18. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4696 − 18
3.2.5 matricpotential,n—invadosezone,theenergyneeded aeration.”These alternate names are inadequate as they do not
toextractwaterfromasoilagainstthecapillaryandadsorptive take into account locally saturated regions, such as perched
forces of the soil matrix. groundwater.
3.2.6 pore-liquid, n—in vadose zone,liquidthatoccupiesan
4. Summary of Guide
open space between solid soil particles. Within this guide,
pore-liquid is limited to aqueous pore-liquid; that includes 4.1 Poresinthevadosezonecanbesaturatedorunsaturated.
Somesamplersaredesignedtoextractliquidsfromunsaturated
water and its solutes.
pores; others are designed to obtain samples from saturated
3.2.7 pore-liquid tension—see soil-water pressure.
pores (for example, perched groundwater) or saturated mac-
3.2.8 soil-water pressure, n—in vadose zone, the pressure
ropores (for example, fissures, cracks, and burrows). This
on the water in a soil-water system, as measured by a
guide addresses these categories. The sampler types discussed
piezometer for a saturated soil, or by a tensiometer for an
are:
unsaturated soil.
4.1.1 Suction samplers (unsaturated sampling), (see Section
7),
3.2.9 tensiometer, n—in vadose zone, a device for measur-
4.1.2 Free drainage samplers (saturated sampling), (see
ing soil-water matric potential (or tension or suction) of water
Section 8),
in soil in situ; a porous, permeable ceramic cup connected
4.1.3 Perched groundwater samplers (saturated sampling),
through a water filled tube to a pressure measuring device.
(see Section 9), and
3.2.10 tremie, n—in groundwater, the method whereby
4.1.4 Experimental absorption samplers (unsaturated
materialsareemplacedinthebottomofaboreholewithasmall
sampling), (see Section 10).
diameter pipe.
4.2 Most samplers designed for sampling liquid from un-
3.3 Terminology from D653:
saturated pores may also be used to sample from saturated
3.3.1 The following terms are found in D653 and are
pores. This is useful in areas where the water table fluctuates,
presented here as a convenience to users. so that both saturated and unsaturated conditions occur at
differenttimes.However,samplersdesignedforsamplingfrom
3.3.1.1 cation exchange capacity, CEC, n—in soils,isapH
saturated pores cannot be used in unsaturated conditions. This
dependent measure ofthenegativeelectricalchargepresent on
is because the liquid in unsaturated pores is held at less than
thesurfacesofsoilminerals,particularlyclayminerals,andon
atmospheric pressures. According to Richards Outflow Prin-
soilorganicmaterials,especiallyhumiccompounds,capableof
ciple that states that pore-liquid will not generally flow into an
dynamically adsorbing positively charged ions (cations) and
air-filled cavity (at atmospheric pressure) in unsaturated soil.
polar compounds.
3.3.1.1.1 Discussion—The units for CEC are typically in
4.3 The discussion of each sampler is divided into specific
milliequivalents per 100 grams of oven-dry soil (meq/100 g).
topics that include:
The SI units for CEC are centimoles of charge per kilogram of
4.3.1 Operating principles,
oven-dry soil (cmolc/kg).
4.3.2 Description,
3.3.1.2 exchange capacity—the capacity to exchange ions 4.3.3 Installation,
4.3.4 Operation, and
as measured by the quantity of exchangeable ions in a soil or
4.3.5 Limitations.
rock.
3.3.1.2.1 Discussion—Exchange capacity is only significant
5. Significance and Use
in materials having high specific surface area, such as clay
minerals.
5.1 Sampling from the vadose zone may be an important
3.3.1.3 hydraulic gradient, i [D], n—in hydraulics, the component of some groundwater monitoring strategies. It can
changeintotalhead(headloss,∆h)perunitdistance(L)inthe provide information regarding contaminant transport and at-
direction of fluid flow, in which i = ∆h/L. tenuation in the vadose zone.This information can be used for
mitigatingpotentialproblemspriortodegradationofaground-
3.3.1.3.1 Discussion—In most cases, the application of hy-
water resource (1).
draulic gradient applies to flowing water in a saturated test
specimen or aquifer consisting of soil or rock, or both. The
5.2 The choice of appropriate sampling devices for a par-
literature typically does not use ∆h/L to indicate head loss;
ticular location is dependent on various criteria. Specific
however,thereisaneedtoemphasizethatheadlossisachange
guidelines for designing vadose zone monitoring programs
(delta), ∆, in total head.
have been discussed by Morrison (1), Wilson (2), Wilson (3),
3.3.1.4 vadose zone, n—in geohydrology/hydrogeology, the
Everett (4), Wilson (5), Everett, et al (6), Wilson (7), Everett,
hydrogeological region extending from the soil surface to the
et al (8), Everett, et al (9), Robbins, et al (10), Merry and
top of the water (groundwater) table.
Palmer (11), U.S. EPA (12), Ball (13), and Wilson (14).In
general, it is prudent to combine various unsaturated and free
3.3.1.4.1 Discussion—The capillary fringe is included in
this zone. Overall movement of water is vertical in the vadose
zone.Therecanbemorethanonevadosezoneinspecialcases,
suchaswhenthereisperchedgroundwater.Thevadosezoneis
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
commonly referred to as the “unsaturated zone” or “zone of this standard.
D4696 − 18
drainage samplers into a program, so that the different flow The range of operating depths is the major criterion by which
regimes may be monitored. suctionsamplersaredifferentiated.Accordingly,thecategories
of suction samplers are as follows:
5.3 This guide does not attempt to present details of
7.1.1 Vacuum Lysimeters—These samplers are theoretically
installation and use of the equipment discussed. However, an
operational at depths less than about 7.5 m. The practical
effort has been made to present those references in which the
operational depth is 6 m under ideal conditions.
specific techniques may be found.
7.1.2 Pressure-Vacuum Lysimeters—These samplers are op-
NOTE 1—The quality of the result produced by this standard is
erational at depths less than about 15 m.
dependent on the competence of the personnel performing it and the
7.1.3 High Pressure-Vacuum Lysimeters—(also known as
suitability of the equipment and facility used. Agencies that meet the
pressure-vacuum lysimeters with transfer vessels) These sam-
criteria of Practice D3740 are generally considered capable of competent
plers are normally operational down to about 46 m, although
and objective testing/sampling/observation/ and the like. Users of this
standardarecautionedthatcompliancewithPracticeD3740doesnotitself
installations as deep as 91 m have been reported (15).
guaranteereliableresults.Reliableresultsdependonmanyfactors;D3740
7.1.4 Suction Lysimeters with Low Bubbling Pressures
provides a means of evaluating some of those factors.
(Samplers With PTFE Porous Sections)—These samplers are
available in numerous designs that can be used to maximum
6. Criteria for Selecting Pore-Liquid Samplers
depths varying from about 7.5 to 46 m.
6.1 Decisions on the types of samplers to use in a monitor-
ing program should be based on consideration of a variety of NOTE 2—The samplers of 7.1.1, 7.1.2, 7.1.3, and 7.1.4 are referred to
collectively as suction lysimeters. Within this standard, lysimeter is
criteria that include the following:
defined as a device used to collect percolating water for analyses (16).
6.1.1 Needed sampling depths,
7.1.5 Filter Tip Samplers—These samplers theoretically
6.1.2 Needed sample volumes,
have no maximum sampling depth.
6.1.3 Soil characteristics,
7.1.6 Experimental Suction Samplers—The samplers have
6.1.4 Chemistry and biology of the liquids to be sampled,
limited field applications at the present time. They include
6.1.5 Moisture flow regimes,
cellulose-acetate hollow-fiber samplers, membrane filter
6.1.6 Durability of the samplers,
samplers, and vacuum plate samplers. They are generally
6.1.7 Reliability of the samplers,
limited to depths less than about 7.5 m.
6.1.8 Climate,
6.1.9 Installation requirements of the samplers,
7.2 Operating Principles:
6.1.10 Operational requirements of the samplers,
7.2.1 General:
6.1.11 Commercial availability, and
7.2.1.1 Suction lysimeters consist of a hollow, porous sec-
6.1.12 Costs.
tion attached to a sample vessel or a body tube. Samples are
6.2 Some of these criteria are discussed in this guide. obtained by applying suction to the sampler and collecting
pore-liquidinthebodytube.Samplesareretrievedbyavariety
However, the ability to balance many of these factors against
one another can only be obtained through field experience. of methods.
7.2.1.2 Unsaturated portions of the vadose zone consist of
7. Suction Samplers
interconnecting soil particles, interconnecting air spaces, and
7.1 Table 1 presents the various types of suction samplers. interconnecting liquid films. Liquid films in the soil provide
TABLE 1 Suction Sampler Summary
A
Porous Section Maximum Pore Air Entry Operational Suction Maximum Operation
Sampler Type
Size (µm)
Material Value (cbar) Range (cbar) Depth (m)
A
Vacuum lysimeters Ceramic 1.2 to 3.0 (1) >100 <60 to 80 <7.5
A
PTFE 15 to 30 (2) 10 to 21 <10 to 21 <7.5
B
Stainless steel NA 49 to 5 49 to 5 <7.5
A
Pressure-vacuum lysimeters Ceramic 1.2 to 3.0 (1) >100 <60 to 80 <15
A
15 to 30 (2)
PTFE 10 to 21 <10 to 21 <15
A
High pressure-vacuum lysimeters Ceramic 1.2 to 3.0 (1) >100 <60 to 80 <91
A
15 to 30 (2)
PTFE 10 to 21 <10 to 21 <91
B B B
Filter tip samplers Polyethylene NA NA NA None
2to3(1) >100 <60 to 80
Ceramic <7.5
B B B
NA NA NA
Stainless steel none
Cellulose-acetate hollow-fiber samplers Cellulose <2.8 >100 <60 to 80 <7.5
Acetate
Non cellulosic
Polymer <2.8 >100 <60 to 80 <7.5
Membrane filter samplers Cellulose <2.8 >100 <60 to 80 <7.5
Acetate
B B
PTFE 2to5 NA NA <7.5
B B B
Vacuum plate samplers Alundum NA NA NA <7.5
Ceramic 1.2 to 3.0 >100 60 to 80 <7.5
B B
Fritted glass 4 to 5.5 NA NA <7.5
B
Stainless steel NA 49 to 5 49 to 5 <7.5
A
Pore size determined by bubbling pressure (1) or mercury intrusion (2).
B
NA = Not available.
D4696 − 18
hydraulic contact between the saturated porous section of the crease. Also, the soil hydraulic conductivity decreases expo-
samplerandthesoil(seeFig.1).Whensuctiongreaterthanthe nentially. These result in lower flow rates into the sampler.At
soil pore-liquid tension is applied to the sampler, a pressure pore-liquid tensions above about 60 (for coarse grained soils)
potential gradient towards the sampler is created. If the to 80 cbar (for fine grained soils), the flow rates are effectively
meniscuses of the liquid in the porous segment are able to zero and samples cannot be collected.
withstand the applied suction (depending on the maximum
7.2.2 Suction Lysimeters:
pore sizes and hydrophobicity/hydrophilicity), liquid moves
7.2.2.1 Vacuum lysimeters directly transfer samples to the
into the sampler. The ability of the meniscuses to withstand a
surfaceviaasuctionline.Becausethemaximumsuctionliftof
suction decreases with increasing pore size and also with
water is about 7.5 m, these samplers cannot be operated below
increasing hydrophobicity of the porous segment (see 7.6). If
this depth. In reality, suction lifts of 6 m should be considered
the maximum pore sizes are too large and hydrophobicity too
a practical maximum depth.
great, the meniscuses are not able to withstand the applied
7.2.2.2 Samples may be retrieved using the same technique
suction.As a result, they break down, hydraulic contact is lost,
as for vacuum lysimeters or, for deeper applications, the
and only air enters the sampler. As described in 7.6, ceramic
sample is retrieved by pressurizing the sampler with one line;
porous segments are hydrophilic and the maximum pore sizes
this pushes the sample up to the surface in a second line.
are small enough to allow meniscuses to withstand the entire
7.2.2.3 High pressure-vacuum lysimeters operate in the
range of sampling suctions. Presently available polytetrafluo-
same manner as pressure-vacuum lysimeters. However, they
roethylene (PTFE) porous segments are hydrophobic, the
include an inbuilt check transfer vessel or a chamber between
maximum pore sizes are larger, and only a very limited range
thesamplerandthesurface.Thispreventssamplelossthrough
of sampling suction can be applied before meniscuses break
the porous section during pressurization, and prevents the
down and sampling ends (see 7.6.1.3). Therefore, samplers
potential cup damage due to overpressurization.
made with PTFE porous segments may be used only for
7.2.2.4 Suction lysimeters with low bubbling pressures are
sampling soils with low pore-liquid tensions (12, 17).
available in each of the three previous designs. The only
7.2.1.3 The ability of a sampler to withstand applied suc-
difference between these samplers and the three previous
tions can be directly measured by its bubbling pressure. The
designs is that these porous sections are made with PTFE.The
bubbling pressure is measured by saturating the porous
low bubbling pressure (and hence large pore size or
segment, immersing it in water, and pressurizing the inside of
hydrophobicity, or both) of PTFE constrains these samplers to
the porous segment with air. The pressure at which air starts
soils that are nearly saturated (see 7.2.1.2 and 7.6.1.3).
bubbling through the porous segment into the surrounding
7.2.3 Filter Tip Samplers—Samples are collected from a
water is the bubbling pressure. The magnitude of the bubbling
filter tip sampler by lowering an evacuated sample vial down
pressureisequaltothemagnitudeofthemaximumsuctionthat
an access tube to a permanently emplaced porous tip. The vial
can be applied to the sampler before air entry occurs (air entry
is connected to the porous tip and sample flows through the
value). Because the bubbling pressure is a direct measure of
poroussectionandintothevial.Oncefull,thevialisretrieved.
how a sampler will perform, it is more useful than measure-
ment of pore size distributions. 7.2.4 Experimental Suction Samplers—Experimental suc-
tion samplers generally operate on the same principle as
7.2.1.4 As soil pore-liquid tensions increase (low pore-
vacuum lysimeters with different combinations of porous
liquid contents), pressure gradients towards the sampler de-
materials to enhance hydraulic contact. The samplers are
generally fragile and difficult to install. As with vacuum
lysimeters, they are generally limited to depths of less than
about 7.5 m.
7.3 Description:
7.3.1 Vacuum Lysimeters:
7.3.1.1 Vacuumlysimetersgenerallyconsistofaporouscup
mountedontheendofatube,similartoatensiometer.Thecup
isattachedtothetubewithadhesives (18 )orwith“V”shaped
flush threading sealed with an “O” ring. A stopper is inserted
into the upper end of the body tube and fastened in the same
manner as the porous cup or, in the case of rubber stoppers,
inserted tightly (12). To recover samples, a suction line is
inserted through the stopper to the base of the sampler. The
suction line extends to the surface and connects to a sample
bottleandsuctionsourceinseries.Bodytubesupto1.8mlong
have been reported (15) (see Fig. 2).
This reference is manufacturer’s literature, and it has not been subjected to
FIG. 1 Porous Section/Soil Interactions technical review.
D4696 − 18
Designs are available that do not use a stopper but rather an
“O” ring sealed, flush threaded top plug (25 ). Tubing lines to
the surface are attached to the top plug with threaded tubing
fittings of appropriate materials. Body tubes are commonly
available with 2.2 and 4.8 cm diameters and in a variety of
lengths(seeFig.3).Thesampleranditscomponentshavebeen
made out of the same materials used for vacuum lysimeters.
7.3.2.2 These samplers can retrieve samples from depths
below 7.5 m because pressure is used for retrieval. However,
during pressurization some of the sample is forced back out of
the cup.At depths over about 15 m, the volume of sample lost
in this fashion may be significant. In addition, at depths over
about15m,pressuresneededtobringthesampletothesurface
may be high enough to damage the cup or to reduce its
hydraulic contact with the soil (27, 28). Rapid pressurization
causes similar problems. Morrison and Tsai (29) developed a
tube lysimeter with the porous section located midway up the
body tube instead of at the bottom (see Fig. 4). This design
mitigatestheproblemofsamplebeingforcedbackthroughthe
cup. However, it does not prevent problems with porous
segment damage due to overpressurization or rapid pressuriza-
tion. The sleeve lysimeter (that is no longer available) was a
modification to this design for use with a monitoring well (1)
(see Fig. 5). Another modification is the casing lysimeter that
consists of several tube lysimeters threaded into one unit (see
Fig.6).Thisarrangementallowsprecisespacingbetweenunits
(30).
7.3.2.3 Nightingale,etal (31)describedadesignthatallows
incoming samples to flow into a portion of the sampler not in
FIG. 2 Vacuum Lysimeter
7.3.1.2 Harris and Hansen (19) described a vacuum lysime-
terwitha6mmby65mm ceramic porous cup designed for
intensive sampling in small areas.
7.3.1.3 Avarietyofmaterialshavebeenusedfortheporous
segment including nylon mesh (20), fritted glass (21), sintered
glass (22),Alundum(manufacturername),stainlesssteel (23 ),
and ceramics (1.2 to 3.0 µm max pore size) (18 ).The sampler
body tube has been made with PVC, ABS, acrylic, stainless
4 4
steel (24) and PTFE (18 , 25 ). Ceramic porous segments are
attached with epoxy adhesives or with flush threading. The
stopper is typically made of rubber (12), neoprene, or PTFE.
The outlet lines are commonly PTFE, rubber, polyethylene,
polypropylene, vinyl, nylon, and historically, copper. Fittings
and valves are available in brass or stainless steel.
7.3.2 Pressure-Vacuum Lysimeters:
7.3.2.1 ThesesamplersweredevelopedbyParizekandLane
(26) for sampling deep moving pollutants in the vadose zone.
The porous segment is usually a porous cup at the bottom of a
body tube. The porous cup is attached with epoxy adhesives
(18 ) or with “V” shaped flush threading sealed with an “O”
ring (25 ). Two lines are forced through a two-hole stopper
sealed into the upper end of the body tube. The discharge line
extends to the base of the sampler and the pressure-vacuum
line terminates a short distance below the stopper. At the
surface, the discharge line connects to a sample bottle and the
pressure-vacuum line connects to a pressure-vacuum pump. FIG. 3 Pressure-Vacuum Lysimeter
D4696 − 18
FIG. 4 Tube Pressure-Vacuum Lysimeter
FIG. 6 Casing Lysimeter
FIG. 5 Sleeve Lysimeter
contact with the basal, porous ceramic cup (see Fig. 7). The FIG. 7 Modified Pressure-Vacuum Lysimeter
ceramiccupiswedgedintothebodytubewithoutadhesivesor
threading. The sampler was used to sample the vadose zone,
the capillary fringe, and the fluctuating water table in a used with cup diameters ranging from 7.6 to 12.7 cm (see Fig.
recharge area. Knighton and Streblow (32) reported a sampler 8).Thesedesignsalsoallowpressurizationforsampleretrieval
withtheporouscupuponthetopofachamber.Thisdesignwas without significant liquid loss. However, because the porous
D4696 − 18
FIG. 9 High Pressure-Vacuum Lysimeter
in each of the three categories described in 7.3.1, 7.3.2, and
7.3.3. The only difference between this group of samplers and
thepreviousthreesamplersisthatPTFEisusedfortheporous
FIG. 8 Knighton and Streblow-Type Vacuum Lysimeter sections of this group of samplers (25 ). The porous PTFE is
attached with “V” shaped flush threading sealed with an “O”
ring.
cupsareopentotherestofthesamplers,potentialdamagedue 7.3.5 Filter Tip Samplers:
to overpressurization or rapid pressurization is still a problem. 7.3.5.1 Filter tip samplers consist of two components: a
7.3.3 High Pressure-Vacuum Lysimeters (Lysimeters with a permanently installed filter tip, and a retrievable glass sample
Transfer Vessel)—High pressure-vacuum lysimeters overcome vial. The filter tip includes a pointed end to help with
the problems of fluid loss and overpressurization through the installation,aporoussection,anozzle,andaseptum.Thetipis
use of an attached chamber or a connected transfer vessel (see threaded onto extension pipes that extend to the surface. The
Fig. 9). The porous segment is usually a porous cup at the sample vial includes a second septum.When in use, the vial is
bottom of the body tube. The cup is attached with epoxy
seated in an adaptor that includes a disposable hypodermic
adhesives (18 )orwith“V”shapedflushthreadingsealedwith needle to penetrate both the septa, allowing sample to flow
an “O” ring (25 ). In the attached chamber design, the body
from the porous segment into the vial (see Fig. 10). Extension
tube is separated into two chambers connected by a one-way pipes vary from 2.5 to 5.1 cm inside diameter. Vial volumes
checkvalve.Apressure-vacuumlineandadischargelineenter range from 35 to 500 mL (32 ).
through a two-hole plug at the top of the body tube. The 7.3.5.2 The body of the filter tip is made of thermoplastic,
pressure-vacuumlineterminatesbelowtheplug.Thedischarge stainless steel, or brass. The attached porous section is avail-
line extends to the bottom of the upper chamber. The transfer ableinhighdensitypolyethylene,sinteredceramic,orsintered
vesseldesignissimilar.However,thevesselandbodytubeare stainless steel. The septum is made of natural rubber, nitrile
integralcomponentsjoinedbyacommondoublethreaded,“O” rubber, or fluororubber (32 ).
ringsealedplugcontainingacheckvalve.Bodytubediameters 7.3.6 Experimental Suction Samplers:
range from 2.7 to 8.9 cm outside diameter. Total sampler 7.3.6.1 Cellulose-acetate, hollow-fiber samplers were de-
lengthscommonlyrangefrom15.2to182.9cm.Athreadedtop scribed by Jackson, et al (33) and Wilson (3). A sampler
plug allows attachment of casing to the lysimeter. This facili- consists of a bundle of these flexible, hollow fibers (<2.8 µm
tates accurate placement and provides long-term protection for max pore size) pinched shut at one end and attached to a
thetubinglines.Thesamplersandtheircomponentshavebeen suction line at the other end. The suction line leads to the
made out of the same materials as vacuum lysimeters. surfaceandattachestoasamplebottleandsourceofsuctionin
7.3.4 Suction Lysimeters with Low Bubbling Pressures the same manner as a vacuum lysimeter (see Fig. 11). The
(Samplers with PTFE Porous Sections)—Designsareavailable fibers, that are analogous to the porous sections of vacuum
D4696 − 18
FIG. 10 Filter Tip Sampler
FIG. 11 Cellulose-Acetate Hollow-Fiber Sampler
lysimeters,haveoutsidediametersofupto250µm (33).Levin
and Jackson (34) described similar fibers made from a noncel- 7.3.6.3 A vacuum plate sampler consists of a flat porous
lulosicpolymersolution(maxporesize<2.8µm).Thosefibers disk fitted with a nonporous backing attached to a suction line
have dense inner layers surrounded by open celled, spongy that leads to the surface (see Fig. 13). Plates are available in
layers with diameters ranging from 50 to 250 µm. diameters ranging from 4.3 to 25.4 cm and custom designs are
7.3.6.2 Membrane filter samplers were described by Morri- easily arranged (1, 18 ). Plates are available in alundum,
son (1), Everett and Wilson (6), U.S. EPA (12) and Stevenson porous stainless steel (23 ), ceramic (1.2 to 3.0 µm max pore
(35).Asamplerconsistsofamembranefilterofpolycarbonate, size)orfrittedglass(4to5.5µmmaxporesize) (38 , 6, 39, 40,
cellulose acetate (<2.8 µm max pore size), cellulose nitrate or 41, 42, 43, 44). The nonpermeable backing can be a fiberglass
PTFE(2to5µmmaxporesize);mountedina“swinnex”type resin, glass, plastic, or butyl rubber.
filter holder (35, 36, 37 ). The filter rests on a glass fiber 7.3.7 Comments:
prefilter. The prefilter rests on a glass fiber “wick” that in turn 7.3.7.1 Whensomeceramiccupsaregluedtotheinnerwall
sits on a glass fiber collector. The collector is in contact with of the body tube in a suction lysimeter, an inner lip is formed
the soil and extends the sampling area of the small diameter (45).As the discharge line is pushed through the stopper at the
filter (see Fig. 12 and 7.5.1.6). A suction line leads from the topofthesampler,itmaycatchonthislipandtheoperatormay
filter holder to the surface. At the surface, the suction line is conclude that the line has reached the bottom of the ceramic
attached to a sample bottle and suction source in a manner cup (see Fig. 14). As a result, an 80 mL error can occur in
similar to vacuum lysimeters. sampling rate determinations.This 80 mLof fluid accumulates
D4696 − 18
FIG. 12 Membrane Filter Sampler; (a) Preparation of Filter Sam-
pler; and (b) Installation of Filter Sampler
FIG. 14 Location of Potential Dead Volume in Suction Lysimeter
(18 ) suggested that the line can be kept from catching by
cutting its tip at an angle. In all-PTFE suction lysimeters, the
discharge line is a rigid PTFE tube extending to the bottom of
the cup. This results in a zero accumulation of fluid. Older
samplers with PTFE porous segments and PVC body tubes
have a discharge line that does not extend fully to the bottom.
This problem has been corrected in newer PTFE and PVC
samplers (25 ). This results in a 34 mL accumulation of fluid
(12).Filtertipsamplersdevelopan8mLaccumulationoffluid.
Haldorsen, et al (46) suggested collecting and discarding an
initial sample to purge this accumulated fluid.
7.3.7.2 Because samplers are often handled roughly during
installation, durability and ruggedness are important. It has
been shown that PTFE has a higher impact strength than
ceramics which need to be installed with care (25 ). It has also
beenfoundthatPTFEthreadsandceramicthreads(whenused)
are susceptible to leakage, and should be securely sealed with
pipe threading tape (45). TFE-fluorocarbon (PTFE) tape is not
recommended in square threaded joints since the tape is
designed for tapered “V” threaded compression joints.
7.3.7.3 As described above, porous sections can be made
from various materials. These materials have physical and
chemicallimitationsthatshouldbeconsideredwhendesigning
FIG. 13 Vacuum Plate Sampler Installation
a monitoring program. Physical limitations are described in
7.6.1. Chemical limitations are described in 7.6.2.
in the cup, is not removed during sampling, and will cause 7.4 Installation Methods:
cross contamination between sampling events. Soil moisture 7.4.1 Pre-Installation:
D4696 − 18
7.4.1.1 As demonstrated by Neary andTomassini (47), new 7.4.1.5 Stevenson (35) recommended treating cellulose-
samplers may be contaminated with dust during manufactur- acetatehollow-fiberswithsilvernitrateandsodiumchlorideto
prevent biofilm growths. Morrison (1) suggested rinsing mem-
ing. In order to reduce chemical interferences from substances
on the porous sections, U.S. EPA (12) recommended prepara- brane filters with distilled water.
tion of ceramic units prior to installation following procedures
7.4.1.6 The porous section and fittings of individual sam-
originallydevelopedbyWolff (48),modifiedbyWood (49)and
plers may have defects that could cause air entry during
recommended by Neary and Tomassini (47). The process
sampling.Therefore, prior to taking samplers to the field, each
involves passing hydrochloric acid (HCl) (for example, 8N)
unit should be checked for its bubbling pressure, pressure
through the porous sections. This is followed by flushing with
tested and vacuum tested for leaks. Procedures for these tests
distilled water until the specific conductance of the outflowing are given in U.S. EPA (12) and Timco (25 ). Washers or “O”
water is within 2% of the inflowing water. Debyle, et al (50)
rings are used to seal the plugs at the tops of body tubes.
found (in agreement with 49 and 51) that flushing with HCl However,theaccessesforpressure-vacuumanddischargelines
strips cations off of the ceramic. This results in an initial
passingthroughtheseplugsarenotsealed.Theseaccessesmay
adsorption of cations from pore-liquid onto the ceramic sur- leak, and should also be sealed. In the past, lubricants have
face. This continues until the cation exchange capacity (CEC)
been used when cutting threads into body tubes, porous
of the ceramic has been satisfied. The effect is not reduced by segmentsandfittings.Inaddition,lubricantshavebeenusedin
distilled water flushing after the acid flushing. Therefore, they various pressure-vacuum pumps. The user should contact the
suggestedthatthesampleralsobeflushed,priortoinstallation, manufacturer to determine if these lubricants are still used. If
present, these lubricants should be removed.
with a solution similar in composition to the expected soil
solution.Alternately,thefirstsampleafterinstallationcouldbe
7.4.1.7 After cleaning and testing, samplers should be
discarded(see7.5.2.1).Bottcher,etal (52)attributedincreased
bagged to prevent contamination during transport to the field.
adsorptionofPO totheacidleachingprocess.Therefore,they
Compatibilityofbagmaterialandanalyticalparametersshould
recommended a thorough flushing with a PO solution of
be considered. Upon arrival at the installation location, and
approximately the same concentration as that found in the soil immediately prior to installation, the porous section should be
solution, rather than the acid leaching procedure, when sam-
placedindistilledwaterforabout30mintosaturatetheporous
pling for PO . Peters and Healy (53) used H SO rather than section (1). Timco (25 ) indicated that applying a suction of
4 2 4
HCl.
about 50 cbar to a submerged PTFE sampler for about an hour
would saturate the sampler porous section. Finally, immedi-
7.4.1.2 Hydrochloric acid may corrode valves within PVC
ately prior to installation, the sampler and associated lines
and ceramic high pressure-vacuum lysimeters. Therefore, the
should be assembled and checked for defects (for example,
poroussegmentflushingforthesedesignsshouldbeperformed
crimped lines).
priortoattachmentifpracticable.Themaximumsuctionwhich
can be applied is one atmosphere, therefore the flushing 7.4.2 Suction Lysimeter and Filter Tip Sampler Installation:
processwillbeslowifsuctionisusedtodrawHClthroughthe
7.4.2.1 Suction lysimeter installation procedures have been
4 4
poroussegment.Theflushingcanbeperformedmorerapidlyif
described by U.S. EPA (12), Soilmoisture (18 ), Timco (25 ),
the porous segment is filled with HCl and pressurized to force
Linden (54), and Rhoades and Oster (55). Filter tip sampler
the acid out of the porous segment since more than one installation procedures were described by Torstensson and
atmosphereofpressurecanbeapplied.Thisprocedurecanonly
Petsonk (32).
be used if the cups are not attached. Care should be taken to
7.4.2.2 The goals of installation are to make sure that
prevent overpressurization that might damage the porous
hydraulic contact between the porous segment and the sur-
section.
rounding soil, and to minimize leakage of liquid along the
7.4.1.3 Corning Laboratories (38 ) recommended washing
outside of the sampler. U.S. EPA (12) recommended a silica
fritted glass with hot HCl followed by a distilled water rinse.
flour/bentonite clay method to achieve these goals for suction
Cleaning procedures for Alundum have not been reported,
lysimeters.Asilicaflourlayer(installedasaslurry,see7.4.2.6)
although an acid and water rinse procedure similar to that for
placed around the porous segment increases hydraulic contact
ceramic would appear to be appropriate (1). Timco (25 )
with the surrounding soil. Screened native backfill is placed
described cleaning procedures for PTFE.The method includes
abovethesilicaflour,andabentoniteplugabovethebodytube
passing 0.5 Lof distilled water through the material.An I.P.A.
prevents liquid leakage down the installation hole and along
bath followed by another in hydrogen peroxide or rinsing with
the body tube (see Fig. 15 and Fig. 16). Klute (56) indicated
HCl followed by a distilled water rinse.
thatascreenednativesoilslurrycouldbeusedinplaceofsilica
flour for shallow installations.
7.4.1.4 The use of HCl to wash/flush porous segments of
lysimeters, that are to be used in sanitary landfills, may cause
7.4.2.3 Samplers may be installed in the sidewall of an
water quality interpretation problems. Sanitary landfills are excavationor,fordeeperapplications,inaboreholepreferably
notoriousgeneratorsofmethanegas.Reactionofmethanewith
advanced with a hollow stem auger (12). U.S. EPA (12)
free chloride ion may result in the generation of di- and suggested that suction lysimeters should be installed at an
trichloromethane (also known as methylene chloride and
angle of 30 to 45° from vertical whenever practicable. This
chloroform).Becauseofthesmallliquidvolumesinlysimeters makes sure that an intact column of soil is retained above the
and the sensitivity of EPA methods (including 601), false porous cup.Accordingly, pore liquid samples will reflect flow
positives for one or both of these constituents may occur. through pore sequences that have not been disturbed by
D4696 − 18
FIG. 15 Pressure-Vacuum Lysimeter Installation in the Sidewall
of a Trench
sampler installation.This angular placement also improves the
sampler’s ability to collect macropore flow. When installed in
thesidewallofatrench,theangledemplacementissimple(see
Fig. 15). However, when installed in a borehole, angular
emplacement entails angled drilling. Where soils permit, filter
tip samplers can be installed by pushing the filter tip into the
FIG. 16 Pressure-Vacuum Lysimeter Installation in a Borehole
ground by applying a static load to the extention pipe (32).
7.4.2.4 When suction lysimeters are installed in a borehole
advanced by a drill rig, the hole is usually advanced 15 to 20 the flour pack and elimination of pack contamination by soils
cm below the desired location of the porous section. Morrison whichsloughdowntheborehole.U.S.EPA (12)recommended
and Szecsody (30) found that the radius of sampling influence filling the borehole to about 30 cm above the suction lysimeter
ispotentiallyincreasediftheboreholediameterisonlyslightly body with the silica. In addition, it was recommended that the
larger than that of the sampler and if silica flour pack is used. powderedbentoniteplugplacedontopofthesilicabeabout15
U.S. EPA (12) recommended that the hole have a diameter of cm thick.The bentonite is also sometimes installed as a slurry,
5 cm larger than the sampler. Timco (25 ) recommended that being allowed to hydrate before emplacement. Mixing the
the hole have a diameter of 8 cm greater than that of the bentonite with fine sand ata1to9 ratio, respectively, reduces
sampler to facilitate installation of the silica flour. the potential for shrinking and swelling inherent with pure
7.4.2.5 Suction lysimeters are preferably lowered into place bentonite (1). The excavated soil should be backfilled above
attached to risers. These protect the lines and allow exact the bentonite in the order in which it was withdrawn.An effort
placement at the desired depth. Centralizers are often used to tocompactthesoiltoitsoriginalbulkdensityshouldbemade.
center the sampler in the hole. Suction lysimeters float in the When more than one suction lysimeter is installed in one
silica flour that is installed as a slurry. Therefore, the samplers borehole, these procedures are repeated at the various desired
should be installed full of distilled water or held in place by sampling depths (see Fig. 17). Care should be taken with these
rigid risers. installationstomakesurethatlinesfromlowersamplersdonot
7.4.2.6 The silica flour slurry (for example 200 to 75 µm interfere with the hydraulic contact of shallower samplers.
mesh opening, silica to distilled water ratio of 0.45 kg to 150 Designs are available to avert these problems (25 ).
mL) is usually installed using the tremie method (side dis- 7.4.2.7 U.S. EPA (12) recommended removal of the water
charge). Alternately, Brose, et al (57) described a method for within the sampler and silica slurry after installation. Litaor
freezingthesilicaslurryaroundthesamplerpriortoplacement. (58) recommended installation of samplers a year before
The sampler and frozen pack are then lowered to the sampling samplingistobegin,inordertoallowthemtoequilibratewith
location in the borehole. They cited advantages of this tech- thesurroundingsoil.Thelinesatthesurfaceshouldbelabeled,
nique as including ensurance of proper sampler placement in clamped and housed in locked containers such as valve boxes
D4696 − 18
(59) installed these samplers within a length of perforated,
protective PVC tubing filled with soil slurry.
7.4.3.3 Membranefiltersamplersareplacedinaholedugto
thetopoftheselectedsamplingdepth.First,sheetsoftheglass
fiber “collectors” are placed at the bottom of the hole. These
develop the necessary hydraulic contact between the sampler
and the soil. In addition, the “collectors” extend the area of
samplingastheycoveralargerareathanthefilterholderalone.
Second, two or three smaller glass fiber “wick” discs that fit
withinthefilterholderareplacedonthe“collectors.”Third,the
filterholderfittedwithaglassfiberprefilterandthemembrane
filter is placed on top of the “wick” disks. The suction line
leads to the surface. Finally, the hole is backfilled (1, 9).
7.4.3.4 Vacuum plate lysimeters are normally installed on
the ceiling of a cavity cut into the side of a trench. In order to
obtain the necessary contact between the porous plate and the
soil, pneumatic bladders, inner tubes, or similar devices are
placed beneath the sampler and are used to force it against the
cavity ceiling (1). The cavity ceiling is not a smooth surface.
Therefore, a layer of silica flour between the plate and the soil
is sometimes used to enhance hydraulic contact.
7.4.4 Maintenance:
7.4.4.1 Themajorcausesofsamplerfailurearelinedamage
and leaks (caused by freezing, installation, rodents, and alike),
connection leaks, and clogging of the porous material. Freeze
damage to the lines can be minimized if the lines are emptied
of sample prior to applying a vacuum. Care needs to be taken
that the tubing line closure devices are freeze proof.
7.4.4.2 The possibility of line and connection leaks is
minimized by rigorously sealing and pressure testing connec-
tions and lines before installation. A common precaution to
assistinrepairingsurfacedamagetolinesistostoreexcessline
below the surface (within the riser pipe when used) when
FIG. 17 Multiple Pressure-Vacuum Lysimeter Installations in a
backfilling the borehole. In the event of severed lines, an
Borehole
excavation to this buried length allows restoration of an
operationalsystem (1).Linesshouldbeclampedshutwhennot
inusetopreventforeignobjectsorinsectsfromenteringthem.
Thelinesshouldbeprotectedfromweather,sunlightexposure,
or casing (1). Methods for cutting and splicing tubing may be
and vandalism with a locked housing. The use of riser pipe
found in Timco (25 ). The user should be careful when using
around the sampler lines prevents punctures by backfill mate-
clamps and tubing provided by different manufacturers, inap-
rials and prevents rodents from damaging the lines.
propriate clamps may damage tubing. Clamps should be
7.4.4.3 Whenshallowsamplersareused,thegroundsurface
restricted to permanently flexible tubing otherwise stopcocks
above the sampler should be maintained in a fairly represen-
should be used.
...