The Association for Environmental Archaeology (AEA)

AEA Working Papers - Evaluations

Environmental archaeology and archaeological evaluations.  Recommendations concerning the environmental archaeology component of archaeological evaluations in England - Working Papers of the Association for Environmental Archaeology - Number 2

Report of the Association for Environmental Archaeology Working Party on Sampling and Recovery, September 1995

About this document
1 - Introduction
2 - Range of materials to be considered in evaluations
3 - The Specification
4 - Site visits
5 - Sampling
6 - Number of samples required
7 - Sample storage and processing
8 - Archaeological information
9 - The report
10 - Retention of material
11 - Cost of environmental component
12 - References (includes references within the Appendix)
Appendix 1 - Sample types
Appendix 2 - Sample storage
Appendix 3 - Sample processing
Appendix 3.1 - CS and BS samples (usually processed on site)
Appendix 3.2 - GBA samples (processed in the laboratory)
Suppliers of tubs and labels

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About this document

This document is intended for use by all archaeologists undertaking archaeological evaluations as part of the planning process and curators preparing specifications for evaluations; much of it will be of general use to all those undertaking archaeological excavations. 

Archaeological evaluations are defined as small-scale field interventions designed to establish the nature and potential of archaeological deposits prior to development, as part of the planning process. The aim of the environmental archaeology component of an archaeological evaluation is to determine the potential importance of soils and sediments, and of biological remains, to the archaeological, historical and ecological interpretation of a site. 

Environmental archaeology is recognised as often contributing a significant or predominant component of archaeological projects. It may provide an appreciation of the site in its past environmental setting, or an understanding of diet, living conditions, butchery practices, agricultural regimes, public health, craft working, and a variety of other issues. Such aspects of the past will rarely be more than sketchily revealed by the field record and the study of cultural artefacts. 

The field examination of deposits and the collection of an appropriate quantity and range of samples during archaeological evaluation should be designed to allow the pedological or sedimentological characteristics and biological components of the deposits and the soils of the locality to be investigated, and their potential to provide information about the past to be determined. This document provides guidelines concerning each stage of the process from planning through to reporting and archive deposition. 

Although largely written in the context of British archaeology, much of this document may be applicable internationally. 

This document has been prepared and edited largely by Keith Dobney, Annie Milles, Harry Kenward and Allan Hall, Environmental Archaeology Unit, University of York, with plentiful comments from the members of the AEA Work Group on Sampling and Recovery and members of the Managing Committee of the AEA.

Association for Environmental Archaeology Sampling and Recovery Work Group: Keith Dobney, Anton Ervynck, Allan Hall, Andrew Jones, Harry Kenward, Annie Milles, Jackie Mulville, Bas Payne and Ken Whittaker 

The printed version of this document was prepared for publication on behalf of the Association for Environmental Archaeology by Allan Hall, Environmental Archaeology Unit, University of York and printed at the Printing Unit, University of York (September 1995). The internet version of this document was prepared by Mark Beech (May 2000). 

This document should be cited as follows: Association for Environmental Archaeology (1995). Environmental archaeology and archaeological evaluations. Recommendations concerning the environmental archaeology component of archaeological evaluations in England. Working Papers of the Association for Environmental Archaeology 2, 8 pp. York: Association for Environmental Archaeology.

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1 - Introduction

1.1. Archaeological evaluations may be carried out as part of the planning process within the framework of Planning Policy Guidance Note 16, 1990 (and its equivalents in Scotland and Wales), Development Plan Policy, and the Coastal Protection Act 1949, or as a result of other management plans. The Institute of Field Archaeologists' Standard and Guidance for Archaeological Field Evaluations (in preparation) and the Association of County Archaeological Officers' Model Briefs and Specifications for Archaeological Assessments and Field Evaluations (1993) also offer relevant guidance. 

1.2. Archaeological evaluations may be commissioned by a number of organisations, such as local planning authorities, national advisory bodies, government agencies, private landowners, and developers or their agents. 

1.3. Environmental archaeology is an integral part of a proper archaeological investigation. Although it is not the remit of this document to provide a justification for undertaking environmental archaeology, it may be stated briefly that it contributes data concerning a multitude of topics, for example land use, the agricultural base of a settlement, resource exploitation, crafts and industries, living conditions (including aspects of health and diet), storage problems, and local environment, trade networks and social status. 

1.4. This paper is concerned primarily with archaeological evaluation in the sense of trial excavations, most of which are small-scale and carried out as part of the planning process. It is not concerned with desktop studies, sometimes referred to as evaluations or assessments, nor with assessments in the sense of the first stage of post-excavation work, often carried out under English Heritage's (1991a) 'MAP2' scheme. There is an urgent need to standardise terminology, since there is at present confusingly inconsistent use of the terms 'evaluation' and 'assessment', in particular. 

1.5. It is also important to avoid confusion between 'environmental assessment', in the sense of prediction of ecological and visual impact, and environmental archaeology 'assessment', correctly called evaluation in the present context; this document is concerned with the latter. 

1.6. The initial aim of the environmental archaeology component of an archaeological evaluation is to assess the importance of the deposits and soils associated with the site, i.e. their potential use for archaeological and ecological reconstruction. The interpretative value of the contexts should be established by an estimation of the range, preservational quality and concentration of different kinds of biological remains, and of the potential for appropriate sedimentological and pedological (including micro-morphological) study. As a result, information will be provided which will identify the need for, and facilitate the more accurate planning of, any future 'environmental' work on the same site or, indeed, in the area or region. 

1.7. The environmental archaeology component of an evaluation will thus: 

1. Characterise (a) the nature of soils and sediments and (b) the assemblages of biological material from different periods, areas and context types, with emphasis on those contexts which are: 

  • believed not to be contaminated or of mixed origin
  • thought or known to contain well preserved biological remains
  • likely to be closely datable
  • interpretatively important at the context or site level
  • archaeologically or historically significant (English Heritage's Exploring Our Past (1991b) provides particularly useful guidance in this respect).
2. Identify the range of soils and sediments, and the range, quality, method of preservation and concentration of preserved plant and animal remains by field inspection and by analysing samples. 

3. Assess the archaeological (and historical) relevance and importance of the biological material and sediments. 

4. Determine whether the study of the soils of the site and its environs will contribute to understanding of the soil-based resources associated with the site. 

5. Recommend any suitable further work required on the material recovered by the trial excavation, whether or not further excavation might take place. 

6. Make further, detailed, recommend-ations about sampling and recovery of biological material from the site in the event of further excavation. 

7. Make recommendations concerning the protection and long-term conservation of the deposits if appropriate. 

It is obvious that, wherever practicable, the involvement of environmental archaeologists in any archaeological evaluation is essential at as early a stage as possible within the project.

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2 - Range of materials to be considered in evaluations

2.1. Present and former soil horizons, and the matrix and micro- and macroscopic inorganic inclusions of any deposit, may yield important, archaeologically relevant, information about depositional history and the history of the environment, resources, and exploitation of the locality. 

2.2. Deposits-the mineral and organic matrices of which may themselves be of considerable value in environmental archaeology-may contain: 

  • microfossils (phytoliths, pollen, diatoms, and fungal and fern spores)
  • plant macrofossils (e.g. seeds, leaves, mosses-these may, variously, be waterlogged, charred or mineralised), large timbers and small roundwood
  • the eggs of internal parasites
  • arthropods, particularly insects, ostracods, cladocerans and mites
  • terrestrial, freshwater and marine molluscs
  • vertebrates, particularly large and small mammals, birds and fish
as well as some other, minor, groups (such as annelid worms, larger crustaceans, and bryozoa); a range of biologically-derived residues, including humates, lipids, DNA and starches may also be present. 

2.3. In Britain, at least, good preservation may result from: 

  • inherent robustness of the biological material (as in the case of bone and marine molluscs in many deposits)
  • anoxic waterlogging 
  • charring
  • mineralisation
  • desiccation (e.g. in daub-and in thatch in standing buildings)
  • the effects of decay-inhibiting chemicals, e.g. copper corrosion products.
2.4.  Favourable burial conditions for certain kinds of material may be detrimental to other types. Thus, for example, a moderately acidic burial environment will favour organic material such as plant and insect remains at the expense of calcified tissue such as bone and shell, whilst free-draining alkaline conditions will favour calcified material, particularly mollusc shell, but lead to the destruction of most delicate organic remains. 

The mode(s) of preservation will, of course, affect fundamentally the potential of environmental archaeology to contribute to the interpretation of any given site.

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3 - The Specification

3.1. The specification inviting tenders for the archaeological work should include a clear and detailed definition of the environmental archaeology component. It is hoped that this document will provide guidance for those drawing up such specifications. 

3.2. The 'environmental' component must be planned, costed for, and executed as an integral part of the evaluation process; it should not be left until the field stage before decisions are made. (The English Heritage document Management of Archaeological Projects, 'MAP2', provides exemplary guidance concerning the management of projects, much of it relevant to evaluations.) 

It is therefore desirable to involve appropriately qualified environmental archaeologists at the beginning of the evaluation project (i.e. at the specification design, planning, and tendering stages), and these environmental archaeologists will need to have access to an appropriate range of facilities and to other specialists. One 'generalist' environmental archaeologist may have the knowledge and breadth of experience to carry out this stage, but it is emphasised that a range of specialists (e.g. a pedologist/sedimentologist, botanist, entomologist, malacologist and osteologist) will usually need to be involved in the execution of the evaluation proper and should ideally be involved at the planning stage, too. Co-ordination of work by a range of specialists may be undertaken by one of them or by someone employed as part of the excavation team to undertake 'environmental liaison'. 

3.3. The specification should include a statement which will ensure that the level of skill of the environmental archaeologist is appropriate for the planned project. Guidelines such as the following 'The contractor will be required to demonstrate by providing CVs that the staff appointed to direct, supervise and work on the project have relevant experience of working both on complex urban sites and the complex archives which they produce' (used by York City Council Planning Department) should be seen as including the environmental archaeology component.

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4 - Site visits

4.1. It is highly desirable that at least one of the environmental archaeologists responsible for producing the report should-whenever possible-visit the site at an early stage of the excavation, and on other occasions when a visit is deemed appropriate. It is particularly important that, if a soil scientist or sedimentologist is involved in the evaluation, he or she should have adequate opportunities (including funding) to carry out work on and around the site as necessary.

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5 - Sampling

5.1. Sampling may be carried out by members of the excavation team or by specialists as appropriate. When samples are to be collected by site staff or an on-site environmental co-ordinator the exact sampling strategy must be decided with the appropriate specialists in advance (see §3.2). Since sites differ greatly in the kinds of soils/sediments and biological remain likely to be encountered, it is important that a specialist is involved at an early stage in the decision-making process, and that a mechanism for seeking further advice (as necessary) during excavation is established. 

5.2. The environmental samples should reflect the complexity of the site and its spatial and chronological extent. Care should be taken when selecting contexts for evaluation that they are archaeologically relevant, that they can be placed within a useful chronological framework, and that they are believed not to be contaminated or of mixed origin (unless this is a specific question to be addressed by bio or geoarchaeological analysis). 

5.3. In order to ensure that representative material is collected for evaluation of the full range of biological remains, it will generally be necessary to take a range of different types of sample in consultation with the relevant specialists. Examples of the kinds of samples that may be collected are detailed in Appendix 1

5.4. Various terminologies are used for kinds of samples; that used here appears to be a reasonable compromise when a wide range of remains is being recovered (rather than, for example, just bones or just charred plant remains). 

5.5. It is accepted that, in some exceptional circumstances, limitations in the availability of water, drainage, and storage on or near the excavation, or of vehicular access to it, will have implications for the kind of sampling and on-site processing strategy that can be employed. Such difficulties should be discussed with the environmental archaeologists at an early stage so that a solution (or at least a compromise!) can be reached. 

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6 - Number of samples required

6.1. It is prudent to collect more samples than the number specified for processing, in order to allow a degree of selection on both archaeological and bioarchaeological grounds before analysis in the laboratory. 

6.2. A financial contingency should be allowed, so that if the deposits on the site differ markedly from what was expected, further advice from the environmental specialist may be sought, and the scale of sampling and subsequent laboratory work increased.

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7 - Sample storage and processing

It is recommended that sediment samples are stored so as to minimise damage to biological remains or changes to sediments. Some guide-lines are offered in Appendix 2

Within the (usually short) timescale of most evaluations, processing needs to be undertaken rapidly and efficiently to ensure that both biological material and artefacts can be passed to the appropriate specialists in reasonable time for them to examine and report on them within the project deadlines. Appendix 3 offers some specific recommendations concerning the processing of samples on site and in the laboratory. With regard to samples for pedological/sediment-ological analysis, these may need to be subjected to appropriate laboratory analyses for interpretation as part of the evaluation exercise. In this case, no preliminary processing is required before the material is passed to the specialist. 

Coarse- and/or bulk-sieving (Appendix 3.1) may have to be carried out off site in an appropriately equipped laboratory because of the difficulties of providing adequate storage, water supply and drainage facilities on many evaluation sites. Appropriate costing and facilities should be arranged for the storage, transport and processing of such samples. In particular, suitable provision should be made for the disposal of fine sediment resulting from the sieving process.

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8 - Archaeological information

The environmental archaeology team under-taking the evaluation will require relevant archaeological information to be imparted to them before and during excavation and in more detail after excavation, before selection and analysis is carried out; the minimum requirements set out in Management of Archaeological Projects Section 6.10 provide a useful basis here.

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9 - The report

The report should be written in such a way that a non-specialist can appreciate the potential value of work on the sediments and plant and animal remains from the site. It should: 

  • include an adequate description of the methodology used
  • include a sample-by-sample description of the material including the size of the processed sample or subsample; soil/sediment description in standard terminology (e.g. Spence and Westman 1994); the archaeological context; the presence of non-biological materials (such as artefacts and stones) in samples; a clear statement of the presence/absence of each group of biological remains, its mode of preservation, and an estimate of its abundance; an appropriate measure of the taxonomic range of each biological group; if appropriate, a summary table showing which classes of biological material were identified from each context, and their interpretative value (this level of detail is important if the evaluation report is (a) to be read in isolation from the main archaeological report and (b) if no further work is carried out on the material in question)
  • include an estimation of the potential for archaeological and palaeoenvironmental information to be obtained from the deposits at the context, site, and higher synthesis levels
  • address any questions raised in the original specification
  • make recommendations for future work on the site or on selected material from it
  • include recommendations concerning the role of environmental archaeology in any future excavation, and its aims and objectives (and might include specifications concerning methodology)
  • be lodged where it is accessible (certainly with the Sites and Monuments Record); it may be necessary to delay deposition until the planning process is complete, but it is recommended that curators specify a maximum of a six month delay in such cases.

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10 - Retention of material

Recommendations should also be given regarding which samples and processed material should be retained, and for what reason, where they should be stored, and where paper and electronic records are or will be archived. Since, for many sites, the analyses and observations made during the evaluation may be all the work that is ever undertaken for the deposits concerned, it is important that adequate arrangements are made for the long-term storage and archiving of relevant materials.

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11 - Cost of environmental component

The scale and cost of the environmental archaeology component of archaeological evaluation might typically be of the order of 10-20% of the cost of the entire evaluation, but it may be substantially higher (perhaps 50% or more) on certain types of site.

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12 - References (includes references within the Appendix)

Association of County Archaeological Officers (1993). Model Briefs and Specifications for Archaeological Assessments and Field Evaluations. 

Dainton, M. (1992). A quick, semi-quantitative method for recording nematode gut parasite eggs from archaeological deposits. Circaea 9, 58-63. 

Dobney, K., Hall, A., Kenward, H., and Milles, A. (1992). A working classification of sample types for environmental archaeology. Circaea 9, 24-6. 

English Heritage (1991a). Management of Archaeological Projects. London: Historic Buildings and Monuments Commission for England. (MAP2). 

English Heritage (1991b). Exploring Our Past. London: Historic Buildings and Monuments Commission for England. 

IFA (in preparation). Standard and Guidance for archaeological field evaluations. IFA Manuals. 

Kenward, H. K., Hall, A. R. and Jones, A. K. G. (1980). A tested set of techniques for the extraction of plant and animal macrofossils from waterlogged archaeological deposits. Science and Archaeology 22, 3-15. 

Kenward, H. K., Engleman, C., Robertson, A. and Large, F. (1986). Rapid scanning of urban archaeological deposits for insect remains. Circaea 3 (for 1985), 163-72. 

Spence, C. and Westman, A. (eds.) (1994). Archaeological site manual. (3rd ed.) London: Museum of London.

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Appendices:

This section amplifies some of the general comments made in the body of this document and offers details on matters of sampling and processing which may be of value to curators, field archaeologists and environmental archaeologists. It is stressed that it is very difficult to reach a consensus  with  regard  to, for example, sample sizes, and individual specialists may make recommendations which do not precisely follow those outlined here-the vagaries of site and deposit types make this inevitable.

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Appendix 1 - Sample types

This scheme follows the widely adopted classification of Dobney et al. (1992), with some modifications. The use of 10 litre plastic tubs is strongly recommended for sieved and unprocessed samples since these are much more easily handled, both on site and in the laboratory, than polyethylene bags (which are prone to splitting and are more difficult both to label adequately and to store with a view to easy access). 

  • Coarse-Sieving sample (CS) (also known as Site-Riddled sample, designated SR): 40 litre (4 x 10 litre buckets) samples; wet (or rarely, for some unconsolidated deposits, dry) sieved using 8 mm meshes, mainly to recover larger vertebrates. This technique is also useful for artefact recovery and is usually undertaken on site. (Some workers prefer a smaller mesh aperture, e.g. 4 mm.)
  • Bulk-Sieving sample (BS): (Bulk-sieving is also sometimes referred to as 'flotation', but the more general term is preferable, since flotation in the strict sense may not be involved in the extraction process). This process is carried out in various ways, ranging from simple sieving to flotation using a rapid water flow ('washover'). Samples of at least 35 litres per context are preferred for most sites and 500 micron meshes are usually employed (see Appendix 3.1). Bulk-sieving may be undertaken on site but in some circumstances may be carried out in the laboratory.
  • General Biological Analysis sample (GBA): sediment samples, each preferably filling a 10 litre plastic tub; a subsample (typically 1 kg or 0.5 litres) sieved using 300 micron mesh, primarily to collect plant remains, land and freshwater molluscs and insects (the last normally separated by paraffin flotation); at least 1 kg to be kept as raw sediment to be used for special extraction procedures (e.g. for pollen, parasite eggs) if necessary. Under certain circumstances, close sequences of GBA samples may be taken to represent a stratigraphic column. GBA samples are intended for analysis in the laboratory.

  •  
  • Closely sampled vertical sequences of small samples (typically a few grammes) may be collected (usually by the specialists concerned) for specific investigations, e.g. of pollen and other microfossils.

  •  
  • Block samples representing undisturbed sediment/soil profiles for laboratory analysis (including particle size analysis and thin sectioning; again, these will probably be taken by the appropriate specialists).
  • 'Spot' samples can be collected where, for example, particularly dense concentrations of biological material or unusual sediments are found.

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Appendix 2 - Sample storage

Samples of sediment for biological analysis should (ideally) be 

  • stored in strong, stackable, re-usable 10 litre plastic tubs, preferably black and with handles (polyethylene bags have proved to be very troublesome, especially for long-term storage; naturally, many small samples in polyethylene bags can safely and conveniently be stored together in plastic tubs!)
  • labelled clearly internally and externally with non-degradable (e.g. 'Tyvek') labels and waterproof marker (permanent adhesive labels can be used on the outside of the tubs)
  • given simple designators to specify site, context and sample numbers. It is important that context and sample numbers are provided as a cross-check in case of errors.
Sediment samples should not be subject to crushing and specialists should be consulted at an early stage as to whether drying is to be allowed or is specifically required. 

Hand-collected bone should be washed and dried and kept at all times completely separate from material recovered from CS and BS samples. All bone should be stored dry in plastic 'zip-type' bags within sturdy cardboard boxes. Individual bones should not be routinely marked, it being sufficient to place non-degradable labels within plastic bags duplicating the information written on the outside. It is also useful if the contents of each box (i.e. a list of the contexts represented) are clearly detailed on the outside. 

Samples thought to contain remains which will decay quickly should be stored under appropriate environmental conditions of low temperature (ideally no more than 4 deg. C) and darkness if analysis is not to take place within a few weeks of excavation.

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Appendix 3 - Sample processing  

Appendix 3.1 - CS and BS samples (usually processed on site)

Coarse-sieved (CS) samples should be sieved to 8 mm using a sieving frame and hoses. Bulk-sieved (BS) samples are sieved using a bulk-sieving tank (sensu Kenward et al. 1980). The mesh size used for the residue is usually 500 microns (in some cases 1 mm) whilst the mesh for collecting the 'washover' or 'flot' may be between 250 and 500 microns (consultation with the specialist concerned is important here). It is important that all material from samples should be labelled and bagged separately from hand-collected material from the same contexts; as implied above, under no circumstances should the two groups of material be amalgamated. 

During wet sieving using a bulk-sieving tank, it is important that 

  • lumps of material should not be forced through the mesh
  • all sieved residues and flots/washovers should be clean of fine sediment
  • the flots/washovers and residues from sieving should be dried thoroughly before storage, unless there is an agreed reason for leaving them wet (see below). There may be consequent implications for packaging and storage if material is kept wet
  • adequate provision is made for drying and refloating of samples with a high clay content from which charred plant remains are being sought.
Typically, sorting of the residue from bulk-sieving small mammal and fish bones, molluscs and artefacts is carried out after drying; however, since plant and invertebrate remains preserved by waterlogging may be damaged by drying, it is imperative that consultation with appropriate specialists is made beforehand. The 'flot' or 'washover' will usually be examined for charred plant material, though for some deposits it may be a source of uncharred plant and invertebrate remains, too, and this fraction of the samples, again, should not be dried without checking with the specialists concerned. Artefacts recovered by this technique should be returned promptly to the excavator or finds staff (a record should be made of the kinds of materials returned). 

Processing and sorting times may vary enormously depending on the nature of the deposit, particularly its clay content, and on how rich it is in biological remains: intelligent estimates must be made (preferably by those expecting to undertake the work) on the basis of the likely nature of the deposits. 

With regard to sorting, the 8 mm residue from coarse-sieving should be sorted in its entirety, and it is not normally necessary to retain the sorted residue. It is rarely practicable to sort more than a small proportion of the material from each bulk-sieved sample for an evaluation-for some classes of material it may be enough for an evaluation simply to 'scan' residues rather than to sort them. It is important that an adequate record is made of the methodology used (e.g. the percentage of the residue 'scanned'). 

Appendix 3.2 -  GBA samples (processed in the laboratory)

For plant macrofossils, snails, insects and other macro-invertebrates a subsample (typically 1 kg or 0.5 litres) should be processed following methods described by Kenward et al. (1980) and modified by Kenward et al. (1986). 

Microfossil subsamples can be taken from GBA samples for the evaluation of pollen, cladocerans and ostracods (although some of the larger fossils will be found in other samples), diatoms, and eggs of intestinal parasitic worms (e.g. using the 'squash' method described by Dainton 1992). Separate sampling for certain remains may be desirable, however-for example from old ground surfaces where a GBA sample would not provide an appropriate pollen sequence or undisturbed sediment for micromorphological study. Such samples will need to be processed separately (and probably by the specialist) if evaluation is required. The high cost of such work should be recognised.

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Suppliers of tubs and labels:  

Thurgar Bolle, Telford Way, Kettering, Northamptonshire NN16 8UY (01536 410111):

Suppliers of 10 l. plastic tubs (manufacturer's code: PO200); minimum order is 600; price per 100 at time of writing: £95.25+VAT (i.e. approximately £1 each). 
 

IML Ltd., 6 Thorncliffe Distribution Centre, Brookdale Road, Thorncliffe Park Estate, Chapeltown, Sheffield S30 4PH (0114 246 5771):

Suppliers of 'Tyvek' white woven plastic labels (prices on request); these can be supplied pre-printed with site names/codes and so forth, and with washered or punched holes. They are effectively indestructible and can be almost indelibly marked with waterproof, spirit-based black markers.

© AEA 2007