Manual for Soil Analysis-Monitoring and Assessing Soil Bioremediation Phần 2 doc

1.4.2 Type of Sample There are three basic approaches to taking samples from the ground forthe purpose of investigating soil and ground conditions.. Type 2 A composite of small increment

Sampling locations should be determined with an appropriate degree ofaccuracy Because it may be necessary to vary the actual location away fromthe predetermined location because of the presence of obstructions, it may

be preferable to do the accurate surveying of sampling locations once thesampling exercise is completed or as it progresses Surface levels can bedetermined at the same time

When investigating abandoned industrial, waste disposal, or other tentially contaminated sites, the horizontal and vertical location of sam-pling points or probing points should be recorded The location of samplingpoints should be marked before sampling begins using poles/markers withcolor sprays Color sprays should not be used if soil air has to be sampled

po-Preparation of the Sampling Site

Depending on the objective of the investigation, a sampling pattern ischosen at the design stage and is then applied in the field Within therange of patterns are some very complex ones developed with the help ofcomputer-aided statistics Preparation for sampling with the use of suchpatterns, e.g., location of desired sampling points on the ground, can bevery time-consuming, especially when samples are to be obtained by bor-ing/drilling techniques or from trial pits Preparation of the site includes,for example, removal of superficial deposits (e.g., uncontrolled deposition

of urban wastes), establishment of safety measures, installation of surement devices (if field tests are carried out together with sampling), aswell as exactly locating the sampling points In many cases, preparation

mea-of the site takes longer than the actual sampling procedures Both duringand on completion of sampling all necessary measures must be taken toavoid hazards to the health and safety of anyone entering the site, and tothe environment

Barriers to Sampling

It may not be possible to sample at a planned location due to a variety

of reasons (e.g., trees, large rocks, buildings, buried foundations or publicutility services, difficulties of access) and contingency plans for dealing withsuch situations should be made in advance The action to take will depend

on the circumstances The investigator may ignore the unavailable point

or follow predetermined rules for choosing a nearby substitute location(e.g., alternative position within 10% of grid spacing or paired samplingalong grid lines on either side the obstruction) Ad hoc decisions made inthe field can lead to bias An attempt should be made when mapping outthe site to identify such obstructions in advance of actual field work In allcases when a sampling point has to be relocated, this fact, and the reasonsfor relocation, should be clearly indicated in the report

Preliminary investigations as described in Sect 1.3.2 should provide asmuch detail as possible about conditions expected to exist on the site andshould therefore guide the design and execution of the sampling program.However, such investigations cannot totally prevent the danger of misin-terpretation of the results of borings, and the selection of sampling pointsshould take this into account.

Depth of Sampling

No general recommendation can be given on the depths at which samplesshould be taken or on the final depths to which trial pits or boring/drillingshould extend This depends on the objectives and might be subject tochange during a running program Investigation of soil for chemical char-acteristics can be divided into two general types:

1 The investigation of agricultural and similar near-natural sites, whereinformation is required mostly on the topsoil or plowed horizon or arablezone but often over an extended area

2 The investigation of sites which are known or suspected to be nated, where information is required from deeper layers, sometimes to

contami-a depth of severcontami-al tens of meters, the extent of the contami-arecontami-a usucontami-ally beingrather small compared to agricultural sites

A mixture of both cases is realized in so-called “soil-monitoring sites,”which represent larger areas of homogeneous soil development and in mostcases are established to monitor environmental effects to the completeprofile over a long-term scale A precise description should be made ofall soil horizons or layers encountered during the sampling exercise andincluded in the report

If a profile is to be sampled, care should be taken that every horizon/layer

of interest is sampled and that different horizons/layers are not mixed Ingeneral, contaminated sites should be sampled horizon by horizon unlessstated otherwise by the client Care should be taken in a site investigation

to ensure that pathways for migration of contamination are not created,particularly where impermeable strata may be penetrated

When trial pits are used it may be appropriate to sample from morethan one site A depth-related sampling program is based on a number

of conventions, depending on the project It is not as representative withregard to the soil as a horizon-related sampling program can be Themode of sampling from each depth should be carefully specified; e.g., themaximum depth range (usually not more than 0.1 m) and how horizontalvariations are to be dealt with

The total depth reached, the thickness of the horizons/layers penetrated,and the depth from which the samples are obtained should be recorded All

data should be recorded in meters below surface The soil depth should bemeasured from the ground surface with the thickness of the humus litterlayer recorded separately.

Mountain regions or hilly areas with pronounced slopes require specialconsideration For slopes of 10◦and greater, vertical drilling lengths should

be extended according to the cosine rule in order to maintain constantslope-parallel thicknesses of soil layers The extension factor is 1/cos ofslope Without correction, for example, the error will be 2% at a slope of11.5◦

Timing of Investigation

In some circumstances, it may be necessary to restrict sampling to specificperiods of the year For example, if the characteristic or substance to bedetermined is likely to be affected by seasonal factors or human activities(weather, soil conditioning/fertilization, use of plant protecting agents), thisshould be taken into account in the design of the sampling program This isparticularly important where monitoring continues for several months oryears or is repeated periodically, and therefore requires similar conditionsevery time sampling is carried out

Sample Quantity

At least 1,000 g of fine soil should be obtained for chemical analysis Thisfigure applies both to single samples and composite samples, in the lattercase after sufficient homogenization Samples obtained to serve as referencematerial or to be stored in a soil specimen bank should be of larger size,usually larger than 2,000 g

Where the sampling of soil involves the separation of oversized material(i.e., mineral grains, sand, pebbles, and all other materials) due to verycoarse-grained or heterogeneous soil conditions, the material removedshall be weighed or estimated and recorded and described to enable theanalytical results to be given with reference to the composition of theoriginal sample These procedures should be carried out in accordancewith ISO 11464 (1994)

Details on the amount of sample materials needed for determination

of specific physical soil parameters are given in the respective methods(Chap 2) In particular, the determination of the particle size distributionmay need a very large mass of soil material The actual mass required willusually depend on the largest grain size to be determined (see ISO 112771998) The quantity of soil sample needed for biological or ecotoxicologicalinvestigations is highly dependent on the aim of the investigation and therelated soil organisms

Single Samples vs Composite Samples

Composite samples are usually required in cases where the average centration of a substance in a defined horizon/layer is to be determined.Single samples are required in cases in which the distribution of a sub-stance over a defined area and/or depth is sought In most guidelines onsampling for agricultural or similar investigations, it is recommended thatcomposite samples be collected by taking a number of increments (accord-ing to ISO 10381-4 (2003) at least 25 increments should be obtained) andcombining them to form a composite sample When preparing compositesamples regard should be paid to analytical requirements For example,composite samples should never be used if volatile compounds are to bedetermined

1.4.2

Type of Sample

There are three basic approaches to taking samples from the ground forthe purpose of investigating soil and ground conditions A sample may be:Type 1 Material collected from a single point (disturbed or undisturbed

sample)

Type 2 A composite of small incremental point samples taken close

to-gether [disturbed sample; perhaps not suitable for certain tests,e.g., the determination of volatile organic compounds; (VOCs)].Type 3 A composite of small incremental point samples taken over an area

(such as a field; disturbed sample)

Samples taken to identify the distribution and concentration of lar elements or compounds will normally be samples of type 1 or perhapstype 2 within the area being examined Such samples would be appropriatefor geological or contamination investigations and any other investigationinvolving disturbed samples Samples taken to assess the overall quality ornature of the ground in an area would be type 3 Such samples would betaken for agricultural purposes

particu-Disturbed samples may be taken by any of the three basic methods sincethese samples do not require the maintenance of the original ground struc-ture Undisturbed samples will always require type 1 sampling because theoriginal ground structure needs to be retained in the sample Undisturbedsamples can be taken using a coring tool or cylinder or with a samplingframe Whichever of these sampling devices is used, the mode of operation

is the same The sampling device is pushed into the ground to be pled and then subsequently removed complete with the sample so that theground is collected in its original physical form

sam-Type 1 samples can be readily collected using hand augers and othersimilar sampling techniques Any of the following tools (as well as others)may be used as appropriate:

• Cutting cylinders of different size, cutting frame

• Special hand augers [gauge auger (shallow-profile sampler), bucket auger

to bring down borings for cutting cylinder application];

• Protective cap, hydraulic or handpowered supporting ring

Special bags should be used for storage and transport of “sample rings”(actually sample cylinders of limited height) to prevent disturbance anddrying out Where undisturbed samples are required, special equipment(see above) will be necessary in order to collect the sample while maintain-ing the original ground structure

Type 2 samples will be appropriate when using machines for excavatingground to obtain samples In these circumstances the samples should beformed by taking portions from locations within the bucket of excavatedmaterial (e.g., nine-point sample, according to Fig 1.4)

Type 3 samples can be collected using hand or powered augers, but careneeds to be taken to ensure the auger repetitively collects the same amount

of sample

Disturbed samples are suitable for most purposes except for some cal measurements, profiles, and microbiological examinations when undis-turbed samples may be required Undisturbed samples should be collectedwhere it is intended to determine the presence and concentration of VOCs,since disturbance will result in loss of these compounds to the atmosphere.Choices of sampling method include the use of machinery or manualmethods The sampling may be carried out near the ground surface, atsome depth below ground level, or from locations deep below the groundsurface Methods of achieving the desired depth for sampling are either byexcavating (e.g., trial pits), driving probes, or drilling (e.g., boreholes).Sampling during borehole creation allows the required integrity for thechemical, physical, and biological investigation of selected soil horizons.Gas and water sampling may also be undertaken for specific purposes re-lating to the need to acquire information rapidly, for example monitoring

physi-a borehole for methphysi-ane physi-and cphysi-arbon dioxide or VOCs on occphysi-asions when therapid identification of chemical constituents in groundwater is required It

is recommended that monitoring groundwater horizons over time for drogeological and chemical parameters, as well as ground composition, beundertaken from cased wells or standpipes installed in boreholes The re-quirements of the sampling strategy should identify the nature of boreholeconstruction so that the appropriate monitoring design can be specified

hy-1.4.3

Undisturbed Samples

If undisturbed samples are required for soil sampling, these can easily

be taken, for example, using a Kubiena box, a coring tool, or cylinder Ineach case the sampling device is pushed into the soil and subsequentlyremoved with the sample so that the soil is collected in its original physicalform Beside these simple techniques, many others exist, some of which aredescribed later

Hand-Operated Auger Techniques

There are many designs of hand auger samplers available The designshave been developed over many years to deal with different soil typesand conditions Ease of use depends upon the nature of the ground to besampled In general, handaugers are easier to use in a sandy soil than inother soils, particularly where obstructions such as stones are encountered

In sandy soils, hand augers can be used to sample to a depth of about

5 m Hand augers are usually used for sampling homogeneous soils, e.g.,agricultural soils When using hand augers, care should be taken to ensurethat the soil is not contaminated by material dropping into the sample from

higher up the bore either during augering or during withdrawal of thesamples Lining the borehole carefully with a plastic tube can prevent thiscross contamination.

Preferred forms of hand augers to be used for collection of soil samplesare those which take a core sample Other types of auger may be used tofacilitate drilling to the requisite depth for sampling providing it is possible

to clean the bore to prevent cross contamination

Sampling by hand augers allows observation of the ground profile andthe collection of samples at preselected depths Particular care should

be taken to obtain representative samples if localized contamination ispenetrated When a hand auger is to be used to take samples for testingsoil for agricultural purposes, and the samples are to be composited, it

is essential that the auger should be capable of consistently collecting thesame sample volume Such sampling of the near-surface soil is normallydone at approx 150−250 mm depth

Power-Operated Auger Techniques

It is possible to obtain augers powered by small motors to reduce the laborrequired to carry out the sampling The need to avoid cross contaminationwithin the bore applies equally to augering with power-operated augers

as with hand augers Powered augers mounted on rough-terrain vehiclesare available for repetitive sampling for agricultural purposes Care should

be exercised when using fuel-driven motors to avoid contamination of thesample by the fuel, the motor lubricant, and the exhaust fumes Augerspowered by electric motors that minimize the risk of such contaminationare available

Light Cable Percussion Boring

Light cable percussion boring general uses a mobile rig with winch of 1−2 tcapacity driven by a diesel engine and a tripod derrick of about 6 m height.With many types the derrick folds down so that the rig can be towed by

a small vehicle (frequently four-wheel drive) The light cable percussiontechnique is commonly used for geotechnical purposes, and boreholesover 20 m deep can be created This technique can be of particular use ininvestigating deep sites such as refuse tips and other unstable ground Theground is penetrated using different tools, depending on the strata A claycutter is used for cohesive soils and a shell (or bailer) for cohesionlesssoils Chisels may be used to penetrate very hard ground and obstructions.The borehole formed by these tools is supported by a steel casing that isadvanced as the borehole proceeds

Depending upon the nature of the ground, the tool may form the borehole

in advance of the steel casing being pushed down the hole, e.g., in clay

strata This often results in material from the side of the borehole beingdislodged as the casing is pushed down the borehole, and can result incross-contamination If the borehole is being formed in sands or gravels,particularly in the saturated zone, the steel casing may be pushed into place

to support the borehole sides before the material is removed with the shell.This can disturb the ground and make sampling difficult

In some strata it may be necessary to add water to the borehole toprovide lubrication In this situation tap water may be used, if available,and care should be taken with respect to the effects on both soil andwater samples The addition of water should be recorded on the boreholelog and, if appropriate, on the sample details The clay cutter and theshell bring up disturbed material from the borehole which is generallysufficiently representative to permit recording of the strata, but care has

to be taken to avoid misinterpretation due to ground being pushed downwithin the borehole – for example, when the casing is moved The casingavoids most of the problems of cross contamination, but the boreholeshould be cleaned out each time the supporting casing is driven furtherinto the borehole, before taking a sample Samples may be collected fromboth the clay cutter and the shell The resultant sample size, although largerthan obtained by hand-augering techniques, is still restricted Undisturbedsamples may be collected in cohesive strata and in weak rock (e.g., chalk)

by driving a hollow tube (100 mm open-tube sampler) into the ground andwithdrawing the resultant core for examination and analysis Use of suchundisturbed sampling equipment may be preferred in order to minimizecross-contamination of samples collected for testing purposes

Water samples may be obtained as drilling proceeds and, because thecasing of the borehole seals the borehole from the surrounding ground asthe borehole advances, it is possible to sample water horizons at differentdepths with minimal risk of cross contamination However water samplesthat are truly representative of the ground water necessitate the installation

of an appropriately designed monitoring well The borehole atmospherecan be monitored for gas concentrations as the borehole proceeds, or gassamples may be taken so that the profile of the ground gas composition can

be determined

Rotary Drilling

Powered rotary cutting tools use a shaft fitted with a cutter head that

is driven into the ground as it rotates The system requires some form

of lubrication (air, water, or drilling mud) to keep the cutting head cooland remove the soil and other material that has been cut through Thelubricant lifts the debris from the cutting head up the borehole formedand ejects the material at ground level This results in the potential for

cross contamination due to contact with the ground forming the sides ofthe hole This technique is particularly useful for digging a hole quickly

in order to form a deep observation well or for obtaining samples using

a technique appropriate at greater depths only The uncontrolled ejection

of material that can occur with this technique (for instance where air orwater is used for lubrication) can lead to extensive surface contaminationwhen drilling through contaminated ground This may be hazardous, both

to the investigation team and the environment

There are two basic types of rotary drilling, (1) open hole (or full hole)drilling in which the drill cuts all the material within the diameter of theborehole, and (2) core drilling where an annular bit fixed to the bottom

of the outer rotating tube of the core barrel assembly cuts a core that isrecovered within the inner most tube of the core barrel assembly and isbrought to the surface for examination and testing Rotary drilling requireswell-maintained equipment operated by a specialist driller with adequatetraining and considerable experience

Driven Auger

The driven auger is powered by machine, so that great force can be exerteddownwards The cutter head consists of one or more 360◦spirals, usuallywith a shallow pitch to prevent ground falling off when withdrawn fromthe borehole The method of forming the borehole is to advance the cutterhead approx 1 m into the ground, withdraw the head from the hole and spinoff the spoil This process is repeated until the required depth is reached.This method is not very satisfactory for sampling, because of the potentialfor cross contamination, nor is it suitable for strata logging The methoddoes enable the formation of a large diameter hole (up to 25 cm) into theground relatively quickly Lubrication of the auger is not required, but somedispersal of contaminated material may occur as the spoil is spun from thecutter head

Continuous Flight Auger

A similar system is the continuous flight auger, which consists of a uous helix welded to the center shaft Downward force is again provided bythe machine and continuous rotation lifts the ground to the surface fromthe base of the hole This technique is only of use in site investigations informing a hole rapidly to give depth in the ground and cannot be used forsampling or strata logging Lubrication of the auger is not required

contin-Hollow Stem Auger

Hollow stem augers are a form of continuous flight auger in which thecontinuous helix is attached to a hollow central shaft The drill head is

formed of two pieces, a circular outer head and an inner pilot or center bitthat is fixed on a plug on the hollow shaft that can be withdrawn throughthe center of the auger up to the surface This ability to withdraw the centerbit and plug whilst leaving the auger in place is the principal advantage ofthe hollow stem auger Withdrawing the plug provides an open cored holeinto which samplers, undisturbed samplers, instruments, borehole casing,and numerous other items can be inserted to the depth achieved.

Removal of any such equipment and replacing the center plug and bitenables the continuation of the borehole The technique provides a fullycased hole and can avoid some of the potential cross-contamination prob-lems of percussion boring Ground samples are collected by open drivesamplers or core barrels inserted down the hollow stem The method hasbeen successful on some landfill sites and can be used for the installation

of groundwater monitoring wells and gas standpipes Some versions of thehollow stem auger allow continuous access to the bottom of the boreholeand will permit percussion drilling or driven sampling through the center,while the hollow stem auger is actually forming the hole The technique willallow collection of samples, particularly undisturbed samples, in addition

to other down-hole testing, and also enables strata logs to be produced.Lubrication of the auger is not required

Percussive window sampling involves driving cylindrical steel tubes intothe ground using a high frequency percussive hammer Usually, the hammer

is driven by a hydraulic power pack, but electric and pneumatic hammersare also available to suit particular site conditions Sample tubes are 1 or 2 mlong and have a broad slot or window cut down one side The soil materialpasses into the sample tube, through a cutting shoe at the end, as it is driveninto the ground Drill rods are used to drive the sample tubes to greaterdepths On reaching the required depth for sampling, the sample tube andany drill rods are withdrawn using a mechanical jack After removal fromthe probe hole, the soil material can then be inspected and the strata loggedand sampled from the window

Soil samples may also be obtained using split tubes or split spoon plers These are effectively tubes linearly split in half but held together bysecuring rings during sampling Such devices are often used in conjunc-tion with driven bar probes, and they allow ready retrieval of the core Soilsamples may also be obtained using a tube combined with an inert liner

sam-to enable ease of removal of the core from the sampler The system can beused to collect samples at different depths, to rapidly penetrate to the depth

at which the sample is to be taken, or to provide a continuous core.Sample tubes of various diameters are available (35−80 mm) and se-lected according to the ground conditions Tubes are normally selected in

a sequence of reducing diameters to penetrate to depth The depth thatcan be achieved depends on the soil type and particularly on the presence

(or absence) of obstructions Depths of 10−12 m can be achieved wherethe probe hole remains open without support Piezometers and ground gasmonitoring pipes can be installed in the resultant probe holes where theground is sufficiently stable Systems are available to allow a probe head,with a sampling device, to be inserted into the previously formed hole to thedesired sampling depth The probe head is then unscrewed and withdrawn

up the inside of the shaft, and the exposed sampling device is pushed intothe ground to collect the sample The sampling head is then withdrawn andremoved for analysis This system also enables undisturbed samples to becollected

Driven Probes

Driven probes may be used to make continuous geophysical measurements,for example, resistance to penetration, or may be fitted with instrumentsfor gathering other data Care should be taken to avoid cross contaminationfrom the sides of the probe hole and from the base of the probe hole Thissystem can be used to either monitor ground water parameters (such pH,electrical conductivity, temperature, etc.) using monitors in the probe, or toaccess groundwater so that a representative sample can be taken without theneed for purging as associated with conventional monitoring wells Groundgases can be similarly accessed and sampled Driven probes have the usualdisadvantage of difficulty in penetrating ground with obstructions, andcannot be used for logging the ground strata unless continuous soil samplesare taken Driven probes are, however, considerably faster than traditionalboreholing techniques

Excavations (Trial Pits)

This is a widely used technique for collecting samples for site investigationsrelated to contamination The advantages of the method are the applicability

over a wide range of ground conditions, the opportunity for close visualexamination of the strata, and the speed with which the work can becarried out Trial pits can be dug where the ground will stand temporarilyunsupported and permit the observation of the in-situ condition of theground both vertically and laterally Where there is water present in theexcavation, problems are presented due to instability of the sides and thedifficulty of obtaining representative samples of the ground (finer materialtends to wash out with the water as the sample is collected) In this situationthe trial pit may be dewatered by pumping, providing there is a safe andsuitable means of disposal of the water – or an alternative technique ofsampling should be used In deeper trial pits formed by machines, samples

of the ground can be collected by careful use of the machine bucket, therebyavoiding any need to enter the pit In carrying out excavations, whatevertechnique is used to form a trial pit, the excavated material should beplaced on the adjacent ground (this should be protected as necessary fromcontamination) in a way that ensures it will not fall back into the excavationcausing cross contamination

The surface soil layer should be kept separate so that it can be replaced

on the surface after the trial pit is backfilled It may be necessary to separateother material as it is excavated so that any deep lying contamination isreplaced at the same depth when back filling and not mixed with othermaterial or replaced near the surface For environmental reasons and due

to legislation, it may be necessary to dispose of excavated material off-siteand to complete the backfilling of the trial pit and restoration of the siteusing clean imported material

Entry of the excavation by personnel should be avoided where possiblesince the unsupported sides of a trial pit may readily collapse If it isessential that an excavation is to be entered for sampling purposes, e.g.,the collection of undisturbed samples, then shoring should be used andreference should be made to the guidance given in ISO 10381-3 (2001) Inunstable ground the trial pit may collapse and extra care should be takenwhen observing the excavation and collecting samples If necessary, thesides should be supported or made to slope to improve stability For allground conditions, if the depth of excavation is greater than 1−1.2 m andthe excavation is to be entered by personnel, the sides should be adequatelyshored to prevent collapse

Manual

Shovel, pick, and fork may be used to excavate trial pits down to about

2 m and, if only a small number of such excavations are required, this may

be the easiest technique for collecting soil samples The trial pit shouldhave a plan area of approx 1× 1 m to enable easy collection of samples

and recording of the soil profile Hand excavation is necessary particularly

in urban areas if services (water, gas, electricity, etc.) are known to exist

in the vicinity, and particularly if their location is uncertain Once thebase of the excavation is below the depth at which any services may exist,then the excavation or boreholing may be continued using the appropriatemachinery

1.4.4

Cross-Contamination

Whatever method is used, it is important that nothing connected with thesampling system itself contaminates the sample This includes avoidingcontamination by contact with the sampling equipment or containers andalso avoiding the loss of contaminants from the sample by adsorption orvolatilization The sampling equipment should be kept clean so that parts

of a previous sample are not transmitted to a subsequent sample causingcross contamination For agricultural purposes, even with repetitive sam-pling across a field to form a composite sample, the sampling device should

at least be brushed clean between each location For geological and tamination investigations, all sampling equipment should be thoroughlycleaned between each sample Contamination of samples due to lubrica-tion used to ease sample collection, or contamination due to equipmentlubricants, oils, greases, or fuels should be avoided Where it is necessary

con-to use lubrication, e.g., water, con-to ease forming a borehole con-to enable samplecollection, only lubrication that will not conflict with nor confound theanalysis of the samples (in the sense of matrix effects or contribution to thecontamination) should be used

A hand trowel of stainless steel should be used to place samples intosample containers The quality of the stainless steel should, however, first

be verified to ensure that cross contamination of the samples will not occur

or interfere with the quality of the analytical data The most commonlyused methods of drilling, excavating, and sampling of the ground producedisturbed samples If undisturbed samples are required, special samplingequipment is required and extra care should be taken in collection

of soils contaminated with volatile constituents The causes of variationsare numerous and may include:

• Changes of certain constituents due to the activities of living organisms

in the soil

• Oxidation of certain compounds by atmospheric oxygen

• Changes in the chemical nature of certain substances due to changes oftemperature, pressure, and hygroscopicity (e.g., loss to the vapor phase);

• Modification of pH, conductivity, carbon dioxide content, etc., by theabsorption of carbon dioxide from the air

• Irreversible adsorption on the surface of containers by metals in solution

or in a colloidal state, or by certain organic compounds

to analyze the sample with a minimum of delay Any of the proceduresshould be mentioned in the sampling report if applied during sampling

Preservation

The addition of chemical preservatives or stabilizing agents is not a mon practice for soil sampling This is because a single soil sample is usuallyused for a large number of different determinations, and moreover has toundergo preparation (drying, milling, etc.) during which unwanted andunquantifiable reactions of the preservatives may occur If, in special cases,

com-it is necessary to preserve samples a method that does not introduce acceptable contamination should be chosen Generally, stability of samplescan be considered in three classes:

un-1 Samples in which the contaminant(s) is/are stable

2 Samples in which the contaminant(s) is/are unstable but stability can beachieved by a preservation method

3 Samples in which the contaminant(s) is/are unstable and cannot bereadily stabilized

For those contaminants that are unstable, loss or change (chemical orbiological) of the contaminant should be minimized by either preservingthe contaminant (e.g., freezing or adding a stabilizing agent) or by arrang-ing for analysis to be undertaken immediately or soon after sampling Theuse of liquid nitrogen for immediate deep freezing of soil samples in vaporphase is effective, and containers made of stainless steel (not chromium ornickel plated) are recommended Some contaminants are not easily stabi-lized in a manner compatible with subsequent analysis Volatile solventsfall into this category and some of them may begin to volatilize as soon asthe soil is exposed by sampling A special sampling procedure is needed

to minimize such loss In spite of numerous investigations carried out insearch of methods that will enable soil samples to be stored without modifi-cation of their composition, it is impossible to give absolute rules that coverall cases and all situations and that do not have exceptions In every case,the method of storage must be compatible with the analytical techniques

to be used and should be discussed with the analytical laboratory

Use of Appropriate Containers

The choice and the preparation of containers can be of major importance.The most frequently encountered problems are:

• Adsorption onto the walls of the containers

• Improper cleaning resulting in contamination of the container prior tosampling

• Contamination of the sample by the material of which the container ismade

• Reaction between constituents of the sample and the container

The purpose of the container is to protect the sample from losses due toadsorption or volatilization, or from contamination by foreign substances.Other factors to be considered in selection of the sample container used tocollect and store the sample include:

• Resistance to temperature extremes

Cleaning of the sample container is a very important part of any pling/analysis program Two basic situations can be distinguished: (1) clean-ing of new containers to remove dust and packing material; (2) cleaning ofused containers prior to re-use The type of cleaners used depends on thekind of container material and on the material to be analyzed The selection

sam-of acids or other cleaning agents should ensure that no contamination sam-ofthe containers results with regard to the constituents to be analyzed and,moreover, that there is no harm to the environment or human health.Containers already used for investigations of contaminated sites shouldnot be used again because cleaning containers of soils containing unknownsubstances may cause risks to health The determination of organic con-stituents may require drying or cooling procedures under carefully con-trolled conditions to avoid microbial contamination Sterilization is re-quired whenever biological or microbiological determinations are to becarried out

1.5

Pretreatment

1.5.1

Chemical Analysis

Inorganic Parameters and Soil Characteristics

Soil samples are dried in the air or in an oven at temperature not exceeding

40◦C, or are freeze-dried If necessary, the soil sample is crushed while stilldamp and friable and again after drying The soil is sieved and the fractionsmaller than 2 mm is divided into portions mechanically or by hand, to

enable representative subsampling for analysis If small subsamples (< 2 g)

are required for analysis, the size of the particles of the fraction smallerthan 2 mm is further decreased

• A drying temperature of 40◦C in an oven is preferable to air drying

at room temperature because the increased speed of the drying limitschanges due to microbial activity

• It should be noted that every type of pretreatment will have an influence

on several soil properties

• The sieve aperture size of 2 mm is generally used However, before thepretreatment is started, check should be made to see if any of the ana-lytical methods to be applied require other sieve sizes

• Storing soil samples, including samples that are air dried, refrigerated

or stored in the absence of light, for a long time may have an influence

on a number of soil parameters, especially solubilities of both inorganicand organic fractions.

• Special measures should usually be taken for samples from contaminatedsoils It is important to avoid contact with the skin, and special measuresshould be taken when drying such samples (ventilation, air removal,etc.) Samples may be hazardous because of the presence of chemicalcontaminants, fungal spores, or pathogens such as leptospirosis, andappropriate safety precautions should be taken

• According to the international standard, it is generally assumed that atleast 500 g of fresh soil shall be available

• Keeping an archive sample is optional and should be clearly stated in theoverall description of the investigation program

• They may be labile or reactive at ambient or elevated temperatures

• They may be biodegradable or UV degradable

• They may have considerably different solubilities in water

• They require different analytical procedures

Because of these differences a general pretreatment procedure cannot beproposed The goal of a pretreatment procedure is to prepare a test sample

in which the concentration of the contaminant is equal to the concentration

in the original soil, provided, however, that this procedure does not alter thechemical species to be analyzed If the sample contains only small particlesand the contaminant is homogeneously distributed it is, for instance, notnecessary to grind the sample According to the international standard thesize 2 mm is used to distinguish between small and large soil particles Careshould be taken to ensure consistency among the following aspects:

• Soil diversity

• The aim and accuracy of the analysis

• The nature of the chemical species to be analyzed

Important to pretreatment is the particle size distribution of the sample

in relation to the mass of sample taken for analysis For the analysis of

organic contaminants, the mass taken in most cases is about 20 g Withsuch a sample mass, and provided that the contaminant is homogeneouslydistributed and the particles in the sample are smaller than about 2 mm,further grinding of the sample is not necessary If the sample contains largeparticles or if the contaminant is heterogeneously distributed (for instance,tar particles), it is not possible to take a representative test sample of about

20 g without grinding the sample To improve the homogeneity, samplesare grinded to a size smaller than 1 mm Prior to analysis very often noinformation about the distribution of the contaminant in the soil is known.Some analytical procedures start with a field-moist sample Drying of thesample will give lower extraction results, But because the sample is not dry,grinding is not possible In a situation in which accurate results are needed,the best available pretreatment procedure should be used If it is necessary

to establish whether the concentration is above a certain limit, and it isalready known that the soil is heavily polluted, the simplest pretreatmentprocedure will perhaps meet the needs despite drawbacks In that case,however, the result may have to be presented as not representative of thewhole sample

Three methods for the pretreatment of soil samples in the laboratoryprior to the determination of organic contaminants are applied in routineanalysis:

1 A method for pretreatment if VOCs are to be measured Core test ples are taken from the sample and extracted according to the specificanalytical procedure If composite samples are required, extracts of indi-vidual samples are mixed It is usually not possible to obtain compositesamples without severe losses of volatiles

sam-2 A method for pretreatment of moderately volatile to non-volatile organiccompounds where the result of analysis must be accurate and repro-ducible The sample contains particles larger than 2 mm and/or the con-taminant is heterogeneously distributed: Samples are chemically dried

at a low temperature (−196◦C, liquid nitrogen) The freeze-dried ples are ground with a cross beater mill with a sieve of 1 mm (cryogeniccrushing) After grinding suitable test portions are processed according

sam-to the specific analytical procedures Composite samples can be prepared

by mixing of the ground samples If the extraction procedure prescribes

a field-moist sample, drying and grinding is not possible If the originalsamples only contain a small fraction of particles greater than 2 mm andthe distribution of contaminants is likely to be homogeneous, grindingmay be omitted In these two cases suitable test portions are directlytaken after mixing of the sample To distinguish more volatile from lessvolatile organic compounds, boiling points are used instead of vaporpressure at ambient temperature For some specific components in the