Generic brief for an archaeological evaluation (trial trenching)

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Last updated: 18 August 2021

1. Summary

This is a generic brief for use on small to medium scale archaeological evaluations required as a condition of, or prior to the determination of, a planning application. Evaluations are requested where there is good reason to believe there may be important remains but insufficient information to determine the actual archaeological impact of a proposed development. An evaluation entails the excavation of trial trenches by a suitably qualified archaeologist to identify the presence, extent and character of any archaeological deposits that may be affected.

This brief sets out the standard requirements for the archaeological contractor who will undertake this work. It can be used to obtain quotes from archaeological contractors (they will also need details of the development) and will inform the preparation of a project design (Written Scheme of Investigation), which must be agreed by the Council Archaeology Service before commencing fieldwork.

Evaluations will normally include 1) The production of the Written Scheme of Investigation; 2) Excavation of trial trenches by machine acting under archaeological supervision; 3) Sampling and recording of archaeological features revealed; 4) The production of a final report including specialist post fieldwork analyses.

For advice on commissioning archaeological work please see 'Advice on commissioning archaeological work in Buckinghamshire'.


2. Scope of this brief

a. This brief will be appropriate for small scale developments such as small/medium sized residential developments, industrial or agricultural units.
b. It may not be appropriate to use this brief if :

  • The site is larger than 0.1 hectare (urban) or 1 hectare (rural)
  • The development requires an Environmental Assessment
  • The works affects a Scheduled Monument or Listed Building or the setting of either
  • The site is suited to a range of other archaeological survey techniques (e.g. geophysical survey, fieldwalking)

In such instances please contact the Council Archaeology Service for further advice.


3. Definition

"The definition of archaeological field evaluation is a limited programme of non-intrusive and/or intrusive fieldwork which determines the presence or absence of archaeological features, structures, deposits, artefacts or ecofacts within a specified area or site on land … or underwater. If such archaeological remains are present Field Evaluation defines their character, extent, quality and preservation, and enables an assessment of their worth in a local, regional, national or international context as appropriate." (CIfA, 2014)


4. Requirement for an evaluation

Paragraph 194 of the National Planning Policy Framework (2021) states that where a site has potential to include heritage assets with archaeological interest, local planning authorities should require developers to submit an appropriate desk-based assessment and, where necessary, field evaluation. Field evaluation can involve a wide range of survey and investigative techniques, including for example fieldwalking and geophysical survey – however, this brief only covers situations where trial trenching is considered the most appropriate approach.


5. Project objectives

Trial trenching should aim to gather sufficient information to generate a reliable predictive model of the extent, character, date, state of preservation and depth of burial of important archaeological remains within the area of study.

The project design (Written Scheme of Investigation) should identify the specific objectives with reference to the advice set out by the Council Archaeology Service to the Local Planning Authority and following the consultation of the County Historic Environment Record and/or any desk-based assessment by the contracting unit.

Copies of the Council Archaeology Service advice letters are now routinely posted on council websites.


6. Project design - 'written scheme of investigation'

Trial trenching should be undertaken in accordance with the Standard and Guidance for archaeological field evaluations" published by the Chartered Institute for Archaeologists (CIfA, 2014). Each project must be governed by a project design which has been agreed in writing by the Council Archaeology Service. The project design should be based on a thorough study of all relevant background information (especially assessment and evaluation reports, historic maps and data held or referenced in the HER). It should conform to the guidelines set out in paragraph 3.2.17 of the CIfA guidelines and should in particular specify: 

  • an archaeological background, utilising an up to date Historic Environment Record search
  • the project's objectives
  • the location of trial trenches and any constraints (to be shown on a plan). The extent and positioning of trial trenches required will depend upon the project objectives, nature of the archaeological interest, nature and location of groundworks and constraints. On some sites it will be possible to target specific archaeological issues, such as the potential for medieval occupation along a street frontage. Simplistic mechanistic application of percentage samples is not encouraged without consideration of the site specifics. Trenching samples should therefore be ‘as appropriate’. In addition a contingency for additional trenching should normally be allowed for, typically 20% on top of the basic trench length or 50m, whichever is the greatest
  • procedures for project management (to follow the principles set out in Management of Research Projects in the Historic Environment (MoRPHE) (Historic England, 2015))
  • the expertise of the project team. The project manager should ideally be a named Member of the Chartered Institute for Archaeologists (MCIfA) who is adequately qualified to manage the required archaeological work in line with the guidance set out in the CIfA code of conduct or can demonstrate an equivalent level of competence. The composition and experience of the project team should be described. Specialists should be identified where required (e.g. for finds and environmental work). CVs should be supplied outlining the relevant qualifications and experience of key personnel - where relevant this should include specific reference to knowledge of particular periods and local/ regional traditions. Note: Specialists should be able to demonstrate a relevant qualification and track record of at least 3 years continuous relevant work (or equivalent) and appropriate publication. In appropriate circumstances, less experienced staff may conduct work under the supervision of well-established and widely recognised specialists
  • reporting and archiving arrangements.
  • an outline of the proposed timetable and staff resources - this must be non-binding and presented "for information only"


7. Fieldwork methodology

a. Surveying

Accurate and precise surveying is essential. Trenches should be set out using GNSS or TST survey equipment. Trench locations should be tied in to the Ordnance Survey (OS) National Grid and Ordnance Datum (OD) (Newlyn).
Coordinates relative to both the OS and OD should be obtained for all sampling locations, small finds and any other relevant deposits or features.

b. Machine stripping

Trial trenches are normally a minimum of c 1.8m wide, although wider trenches or "boxes" are sometimes more appropriate. Machinery may be used to remove topsoil and overburden to reveal the archaeological deposits. Such excavation should be undertaken in level spits using an appropriate machine using a toothless bucket and working under archaeological supervision. Archaeological deposits should not be removed by machine except where such a procedure has been sanctioned by the Council Archaeology Service. Particular care should be taken when controlling machining in situations where vertical stratigraphy is to be expected or where it is considered that significant archaeological deposits may be vulnerable to damage - in such circumstances machining should be controlled by experienced senior staff. Potentially significant deposits should not be removed by machine before their character is reasonably understood.

c. Cleaning and Recording in plan-form

Each trench should be cleaned by hand sufficiently to allow the identification and planning of archaeological features and scanned with a metal-detector. Spoil heaps should also be scanned. Experienced metal-detectorists should be used but only on the understanding that they work to the direction of the archaeological contractor and that the ownership of all finds remains with the landowner. Where archaeological features appear to be absent sufficient work should be done to demonstrate this. Each trench should be planned at an appropriate scale (normally 1:20 where complex deposits are present or 1:50 or 1:100 in areas of lesser complexity). Spot levels should be taken as appropriate.

d. Sampling

Sufficient features should be sampled by hand excavation to achieve the project objectives. For discrete features such as pits and postholes this will normally involve half-sectioning a representative sample. Linear features should be sectioned. Individual complex features such as kilns or burials should be cleaned and recorded but, subject to the agreement of the Council Archaeology Service, it will normally be preferable to leave them in-situ (if necessary with specific protection against disturbance during backfilling). If deeply stratified deposits are encountered it may be appropriate to excavate sample boxes and/or examine the stratigraphy revealed in the section of excavated cut features.

e. Context recording

i. Each context should be recorded on pro-forma records which should include the following minimum details: character; contextual relationships; detailed description (dimensions and shape; soil components, colour, texture and consistency); associated finds; interpretation and phasing as well as cross-references to the drawn, photographic and finds registers. Normally each context should be recorded on an individual record. Sections should be drawn through all significant cut features and levelled to ordnance datum. Trench sides should also be drawn in section where they contain significant information.

ii. Both a digital and a black and white film photographic record should be maintained including photos of all significant features and overall photos of each area or trench. Selected colour transparencies should also be taken.

f. Artefact and Ecofact collection and recording

i. All stratified finds should be collected by context or, where appropriate, surveyed to provide co-ordinates relative to both the OS and OD. Unstratified finds should only be collected where they contribute significantly to the project objectives or are of particular intrinsic interest. Provision should be made for on-site conservation advice for the lifting and treatment of fragile objects. Finds of "treasure" must be reported to the Coroner in accordance with the Treasure Act procedures.

ii. Collection policies for structural remains and industrial residues have been set out by the Society of Museum Archaeologists (SMA, 1993). The presence of such materials within a context should always be recorded and, where they are considered to be of importance, the evaluation strategy should aim to quantify their occurrence, even where comprehensive retention is not considered appropriate.

iii. Contractors should, where relevant, follow the guidelines for handling Post-Roman Ceramics produced by the Medieval Pottery Research Group (Slowikowski, Nenk & Pearce, 2001). This specifies that all ceramic finds must be collected, washed, marked, bagged, boxed and assessed with regard to the project aims and objectives. Where a sampling procedure is employed this should be undertaken in consultation with a ceramic specialist.

iv. Contractors should refer to Environmental Archaeology: A guide to the theory and practice of methods from sampling and recovery to post excavation (English Heritage, 2011) as a guide to best practice in this field.

v. Waterlogged wood should be treated accordance with English Heritage guidelines (English Heritage, 2010) and left in-situ where this is practical and its long-term preservation is achievable.

vi. A contingency for scientific dates should be allowed if pre-Iron Age remains are potentially present.

vii. In the event of discovery of any human remains the archaeological contractor should inform the client, the Council Archaeology Service, and the Ministry of Justice via the submission of an application form for the ‘Archaeological/Accidental/Site Investigation Licence regarding the disturbance of human remains’. The Human remains should be left in-situ, covered and protected. Where a licence for their excavation is issued by the Ministry of Justice, the requirements of that licence must be followed. The only exception is where excavations are being undertaken in a churchyard under a faculty issued by the Chancellor of Oxford Diocese (in such cases the faculty requirements should be followed). In certain situations special arrangements may be required for the recovery of samples for DNA analysis. Human remains should be treated in accordance with CIfA guidelines (CIfA, 2004) and the advice set out in Guidance for best practice for treatment of human remains excavated from Christian burial grounds in England (English Heritage, 2005).

viii. An initial assessment of the site's palaeo-environmental potential should be made by the project manager in consultation with the Council Archaeology Service. Where a site may have significant potential it may be necessary to obtain specialist advice and undertake sampling in accordance with a programme agreed with Historic England's Adviser in Archaeological Science. A contingency should be allowed for this.

g. Metal Detecting

i. Whenever private individuals or subcontractors are engaged to undertake metal detecting as part of an archaeological fieldwork project they should be asked to sign a formal agreement in which the right to claim Treasure is waived. Please refer to the 2nd revision of the Treasure Act Code of Practice (2008, paragraph 81). A suggested clause is:-

ii. “In the process of working on the archaeological/ excavation at [location of site] between the dates of [insert dates], [name of person contributing to the project] has been working under the direction or permission of [name of archaeological organisation or responsible individual archaeologist] and hereby waives all rights to rewards for objects discovered that could be otherwise payable under the Treasure Act 1996.”

iii. Contracts should ensure that investigations are covered by a written agreement with the owner & occupier regarding rewards which may be payable.

h. Outreach

Wherever possible, attempts should be made to seek opportunities to disseminate the results of the evaluation to the wider public. This could be in the form of open days, social media or press releases.


8. Post-excavation methodology

a. A report will be required for every field evaluation and should always contain the following elements:

  • A non-technical summary
  • The objectives of the project
  • The circumstances and date at which it was undertaken
  • The identity of the organisation and individuals carrying out the work (in particular the names of the project director, site supervisor and any specialists)
  • A summary written account of the evaluation strategy and the results of the project with appropriate supporting illustrations
  • A site location plan at 1:2500 or 1:10000 as appropriate
  • A gazetteer, referenced summary, and location plan (at 1:2500 or 1:10 000) of all previously known and newly discovered sites within or adjacent to the evaluation site.
  • A 1:2500 or 1:10,000 scale plan indicating areas surveyed by each method; present land use; geology and topography
  • A summary of physical and health and safety constraints
  • A conclusion, including a confidence rating
  • An index to and the proposed location of the archive, including an accession number
  • References

b) Reports on evaluations which identified significant archaeological remains should also include:

  • Detailed description and plans (at appropriate scales) of any surveys or trial trenches which provided significant archaeological information
  • Finds quantification and assessment
  • Environmental archaeology assessment
  • A summary of the extent, depth and state of preservation of archaeological deposits across the site. For large urban sites, a "deposit model" (Ove Arup, 1991) will usually be necessary
  • Where more than one technique has been used, the report should integrate the results of the trenching with the previous survey work

c. In addition:

  • All plans should be clearly related to the national grid
  • All levels should be quoted relative to ordnance datum
  • If a report includes assessments of archaeological importance or recommendations for further work these will be noted but will not be binding on the Council Archaeological Service

d. Submission of the report

i. One hard copy of the final report should be supplied to the County Historic Environment Record along with a digital copy in PDF format (to allow reports to be made available on the web). A copy of any specialist papers relating to the project should also be supplied to the Council Archaeology Service.

ii. One copy of the report should also be supplied to the local planning authority, if appropriate.

iii. Reports submitted in support of planning applications are automatically considered to be public documents and will be made available for public consultation through the Historic Environment Record. Other reports will also be treated as a public document unless specifically identified as being confidential. Where a report is so identified then confidentiality should apply for an agreed period not normally exceeding 12 months from its submission to the CAS.
ii. The photographic record should be maintained including photos of all significant features and overall photos of each watching brief area.


9. Publication

a. For all projects, a summary report (including illustrations where appropriate) should be sent to the editors of South Midlands Archaeology and Records of Buckinghamshire not later than three months after the end of the calendar year in which the work is undertaken. In this case publication of above and below ground archaeology should be integrated.

b. For projects which have produced results of significant county, regional or national importance, an illustrated final report which meets the guidelines set out in MAP2 Appendix 7 and is suitable for publication in an approved archaeological journal (normally Records of Buckinghamshire) should be provided to the Council Archaeology Service within one year of the completion of fieldwork (unless a longer time period has been agreed in the updated project design). The overall content of the report should be agreed with the Council Archaeology Service. The report should be clearly referenced in all respects to all work on the site, evaluation, excavation, watching briefs, building recording, background research including aerial photography etc, in order that a coherent picture may be presented. It should place the site in its local archaeological, historical and topographical context and include a clear location map. Each plan included should clearly relate to some other included plan of an appropriate scale and should normally include national grid references.

c. One bound copy of the final publication and a digital copy, in pdf format, must be supplied to the County Historic Environment Record. A further offprint should accompany the archive. A copy of any specialist papers relating to the site should also be supplied to the Council Archaeology Service.

d. One bound off-print of the final publication should be supplied by the applicant to the district council (if appropriate) in support of the fulfilment of the archaeological condition.

e. A publication grant should be provided to the publishers of the report in accordance with their requirements.



Once the final report has been accepted by the Council Archaeology Service, it is highly recommended that contractors complete an OASIS fieldwork summary form and submit it to the Archaeology Data Service.

Visit the Oasis website to access the form and guidance for its completion.


11. Archiving

The archaeological contractor should endeavour to ensure that the site archive (including any artefacts recovered) are deposited in an acceptable condition with a museum which is registered with the Museums, Libraries and Archives Council and approved for the storage of archaeological archives. The digital archive should be deposited with an accredited digital repository.

The preferred repository for the physical archive in Buckinghamshire is the County Museum, who should be contacted for an accession number at the earliest opportunity. The procedures and requirements which must be followed for the deposit of archaeological archives with Buckinghamshire County Museum are documented in the Museum's Procedures for Notifying and Transferring Archaeological Archives (BCM, 2013), available from the Curator (address below). A storage grant should be provided to the museum in accordance with their requirements.

The preferred repository for the digital archive in Buckinghamshire is the Archaeology Data Service. The guidelines for depositing with the ADS can be found on their website.

The archaeological contractor should agree Transfer of Ownership with the legal landowner at the earliest opportunity. In the event of the legal owner(s) resolving to retain all or part of the site archive, it is necessary that the archaeological contractor make them aware that they shall be responsible for the future preservation and maintenance of any material element of that archive. The part of the site archive in question shall be transferred to the legal owner only after the following stages have been completed and:

  • all necessary processing, research, analysis and investigation
  • a full inventory of all elements of the archive to be returned to the landowner, complete with photographs
  • all necessary stabilising, conservation and packing necessary to prepare the archive for preservation and in a usable, accessible form
  • the provision of a final approved report for submission to the HER and/or publication
  • the owner has demonstrated that all necessary provision is made for the long-term preservation of the archive in a satisfactory environment, and that it is accessible for future research


12. Monitoring

a. Monitoring is carried out by the Council Archaeology Service, normally acting on behalf of the local planning authority, to ensure that projects are being carried out in accordance with the brief and approved project design, to enable the need for modifications to the project to be independently considered and validated and to control and validate the use of available contingencies.

b. A programme of monitoring should be agreed with the Council Archaeology Service prior to the commencement of fieldwork. The archaeological contractor should keep the Council Archaeology Service regularly informed of the project's progress and facilitate the monitoring of the project at each stage, including post-excavation. In particular, there should be no substantial modification of the approved brief and project design without the prior consent of the Council Archaeology Service and no fieldwork should be carried out without the service's knowledge and approval.

c. Monitoring visits will normally be documented by the Council Archaeology Service and the archaeological contractor will be informed of any perceived deficiencies. The Council Archaeology Service has a charging policy in place for site monitoring visits.

d. The Council Archaeology Service should be informed at the earliest opportunity of any unexpected discoveries, especially where there may be a need to vary the project design. The archaeological contractor should carry out such reasonable contingency works as requested by the Council Archaeology Service within the resources defined in the project design.

e. In the event that the Council Archaeology Service considers that the approved project design is not being complied with without reasonable justification then action will be taken in accordance with Buckinghamshire Council's archaeological enforcement policy.


13. Health and safety

a. Health and Safety must take priority over archaeological requirements. It is essential that all projects are carried out in accordance with safe working practices and under a defined Health and Safety Policy. Risk Assessments must be carried out for every field project. If the risk assessment indicates it is necessary, the requirements of the brief can be varied in the interests of health and safety.

b. It is the responsibility of the archaeological contractor and their client to ensure that other constraints (e.g. SSSI’s or protected trees) are identified and properly safeguarded.

c. Approval for proposed changes to the project design must be obtained from the Council Archaeology Service.


14. Bibliography

Buckinghamshire County Museum, 2013. Procedures for Notifying and Transferring Archaeological Archives.
CIfA, 2014. Standard and Guidance for archaeological field evaluation.

Historic England, 2015. Good Practice Advice in Planning Note 2: Managing Significance in Decision-Taking in the Historic Environment

Historic England, 2015. Management of Research Projects in the Historic Environment. The MoRPHE Project Manager’s Guide.

Historic England 2018 The Role of the Human Osteologist in an Archaeological Fieldwork Project

English Heritage, 2010. Waterlogged wood. Guidelines on the Recording, Sampling, Conservation and Curation of Waterlogged Wood (third edition).

English Heritage, 2011. Environmental Archaeology: A guide to the theory and practice of methods from sampling and recovery to post excavation (second edition)

MHC&LG, 2019. National Planning Policy Framework.

Slowikowski, A, Nenk, B, & Pearce, J 2001. Minimum Standards for the Processing, Recording, Analysis and Publication of Post Roman Ceramics, Medieval Pottery Research Group, Occasional Paper No2
SMA, 2018. Guidance on the Rationalisation of Museum Archaeology Collections


15. Contacts

Buckinghamshire Council Archaeology Service

Planning and Environment
Walton Street Offices
HP20 1UA

Phil Markham BA MA MCIfA, Senior Archaeological Officer
Telephone: 01296 382 705

Lucy Lawrence BA ACIfA, Archaeological Officer
Telephone: 01296 674 592

Julia Wise BA MCIfA, HER Officer
Telephone: 01296 382 072

Paul Clements BA HER Assistant
Telephone: 01296 382 624

Please note that the HER operates an appointment system and there is a charge for commercial enquiries.

Buckinghamshire County Museum Trust

Brett Thorn, Keeper of Archaeology
Museum Resource Centre
Tring Road
HP22 5PN

Tel: 01296 624 519. Email:

Buckinghamshire Archaeology Society (Records of Buckinghamshire)

Mr Bob Zeepvat, Archaeological Editor
c/o ASC Ltd
Letchworth House
Chesney Wold
Bleak Hall
Milton Keynes

Tel: 01908 608 989. Fax: 01908 605700.

Council For British Archaeology South Midlands Group (South Midlands Archaeology)

Mr Nick Crank, Editor 
c/o Milton Keynes Council
Conservation and Archaeology
Civic Offices
1 Saxon Gate East
Milton Keynes

Tel: 01908 254 259 Email:

Historic England Regional Science Adviser (London and the South East Region)

Jane Corcoran, Science Advisor
Historic England
4th Floor
Cannon Bridge House
25 Dowgate Hill

Tel: 0207 973 3700. Email:


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