Archaeological methodology
Introduction
The next major consideration in project design is the selection of field techniques and the anticipated method of on-site working. The following is a summary of matters to be borne in mind when undertaking a project. Some of these are relevant only to one form of historic environment work whereas others may apply to a number of different types of historic environment project.
Background
Those undertaking historic environment projects have an obligation to carry out that project to a professional standard. This standard ensures that sufficient information is provided by the project for planning purposes and that reporting and archiving meet the requirements of the receiving HER and museum. Guidance on standards of historic environment work has been issued by various bodies including Historic England, ADS and the CIfA.
Site location
All historic environment fieldwork must be subject to adequate horizontal and vertical survey control. The location of the grid will be established, relative to the OS national grid. In most instances it will be expected that control points and trenches will be surveyed using an EDM or GPS (Global Positioning System). The GPS equipment which is use should be accurate to the sub-centimetre level (differential GPS). The vertical survey control will be tied to the Ordnance Datum. The accuracy must be of a level to allow the work to be repeated by a third party.
Consideration of techniques
When preparing a project design, and/or specification, account must be taken of the local geology, topography and land-use as it affects the feasibility of the various techniques. Consideration should be given to additional aerial survey, lidar, field-walking, earthwork survey, geophysical survey and the observation of geotechnical test-pits (if appropriate), as well as the undertaking of archaeological test-pits, as possible field evaluation techniques.
Earthwork survey
Earthwork surveys may form part of a pre-determination evaluation or a post-determination mitigation strategy. They should not normally be carried out at a scale less than 1:500 and using an agreed methodology appropriate to the site’s location and size.
Fieldwalking
Fieldwalking is essentially a technique used for prospection during the field evaluation of a rural site. Such a reconnaissance survey can be carried out on transects spaced 10 to 20m apart. Surface material can also be collected to give a more detailed indication of likely buried remains at a finer scale. Both levels of fieldwalking should only be carried out in conditions of suitable ground visibility which would normally be after the land has been ploughed, harrowed and left to weather for an appropriate length of time.
Geophysical survey
Archaeological geophysical survey should be undertaken in accordance with current guidance (EAC Guidelines).
Environmental evidence
Environmental evidence is a necessary and potentially important element of the archaeological record. During a field evaluation an accurate assessment of the preservation of environmental evidence, including animal bone, shell, waterlogged and charred organic remains, and the condition of any buried soils and sediments should be made. This assessment should be sufficiently comprehensive to allow an evaluation of its potential archaeological relevance and to enable the construction of a structured sampling strategy and post-excavation programme, should the evaluation go to the full excavation stage. When undertaking this work advice must be sought from an appropriate environmental consultant or from Historic England Regional Science Advisor. Environmental sampling should be undertaken according to current Historic England guidance.
Trial excavation
Excavation is a potentially destructive evaluation technique and, where possible attempts must be made to maximise data retrieval from non-destructive techniques before undertaking excavation. However, should trial excavation be required the specification should include a detailed reasoning for the application of the technique.
Whether excavation is being undertaken as part of a pre-determination evaluation or as part of a mitigation strategy the following factors should be borne in mind:
- all machine work should be supervised by an experienced archaeologist
- machining should stop at the first archaeological horizon
- the use of an appropriate machine with a wide, toothless ditching blade, when archaeological features are revealed these will be cleaned by hand
- a representative sample (as agreed with the planning archaeologist) of every archaeological feature must be excavated by hand (although the depth of surviving deposits must be determined, it is not expected that every trench will be excavated to natural)
- adequate recovery of finds and an appropriate sampling programme to provide environmental evidence from all archaeological deposits should be ensured. A site visit by the nominated environmental specialist may be required
- where appropriate, a level of science advice either from the Historic England Regional Science Advisor or an appropriate specialist should be sought
- if human remains are encountered these would normally be left in-situ
- It is expected that an acceptable recording system will be used for all on-site and post fieldwork procedures. The recording procedure must take into account the long-term archival requirements of archaeological records. Due attention must be given to the drawn and photographic record. Both artefacts and ecofacts must be handled according to the requirements of the document Conditions for the acceptance of archaeological archives (produced by The Collection, Lincoln and reproduced here). Prior to fieldwork commencing discussions should take place with The Collection, or any other receiving museum regarding archive deposition. At this time an accession number will be issued and should be used throughout the project.
- All faces of the trench which require examination should be cleaned using hand tools. All investigation of archaeological deposits will be by hand. Cleaning, examination and recording should take place in both plan and section.
- The objective of any excavation within a field evaluation programme should be to define remains rather than totally remove them. Excavation should normally be limited to the minimum necessary to characterise the value or potential of the remains.
- As well as the excavation or sampling of archaeological features it may be necessary to examine naturally deposited material. Such layers may contain environmental material.
- When the decision has been made that archaeologically significant remains warrant preservation in situ, suitable arrangements must be made to prevent their deterioration. The area to be preserved should be clearly defined, fenced off and a suitable preservation strategy produced.
Test pitting
A further prospection technique is that of test pitting. Test pitting is not to be used instead of trial excavation, which is the preferred method of evaluation; however it may be used in exceptional circumstances. This will consist of the excavation of trial pits (normally 1.5 by 1.5m) on a regular pattern such as for example, a 50m grid. Full details must be agreed in detail with the planning archaeologist. The general standards and methods of work should conform to those for trial excavation as outlined above.
Building recording
In undertaking building recording reference should be made to CIfA and Historic England’s guidance for advice on the appropriate techniques to be used. It should be remembered that each project is unique and often a mixture of levels may be required. As a minimum each report must contain some level of written account, drawings and photographs.
Use of specialists
For the smooth running of an archaeological project it is essential that close liaison takes place between the archaeological contractors and their specialists. This would be of particular value when specialist advice might be needed, for example, if a fragile find requires lifting or environmental samples are to be taken.