Buckinghamshire Council Archaeology Service (BCAS) generic brief for an archaeological geophysical survey (magnetometer and resistivity)
|Last updated:||18 August 2021|
This is a generic brief for use on archaeological geophysical surveys required as part of a planning application or part an environmental impact assessment, or similar document. Geophysical surveys 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. A geophysical survey entails the non-intrusive collection of data relating to physical properties of subsurface soils and deposits to enable a suitably qualified archaeologist to identify the presence, extent and character of significant archaeological deposits that may be buried below ground.
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 would normally be agreed by the Council Archaeology Service before commencing fieldwork.
Geophysical surveys will normally include 1) The production of the Written Scheme of Investigation; 2) Geophysical survey; 3) The production of a final report including greyscale plots of the raw data, plots of the processed data, and interpretive analysis of the results identifying potential archaeological features. 4) The production and supply of the digital data as specified in 8 c ii.
For advice on commissioning archaeological work please see ‘Advice on commissioning archaeological work in Buckinghamshire’ (Annexed to this brief).
2. Scope of this brief
a. This brief will be appropriate for all residential developments, industrial or agricultural units where general magnetometer and or resistance surveys are required.
b. It may not be appropriate to use this brief if :
- The works affects a Scheduled Monument or Listed Building or the setting of either
- Geophysical survey techniques other than magnetometer or earth resistance are used (Ground penetrating radar)
- The site to be surveyed requires a higher density of data collection
In such instances please contact the Council Archaeology Service for further advice.
"Archaeological geophysical survey uses non-intrusive and non-destructive techniques to determine the presence or absence of anomalies likely to be caused by archaeological features, structures or deposits, as far as reasonably possible, within a specified area or site on land, in the intertidal zone or underwater. Geophysical survey determines the presence of anomalies of archaeological potential through measurement of one or more physical properties of the subsurface." (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. It is normal practice for the results of a geophysical survey to be 'ground truthed' through targeted archaeological trail trenching.
5. Project objectives
a. The geophysical survey should aim to generate a plan to help delineate areas archaeological remains within the area of study to help advise planning applications and potential future archaeological works. It should also aim to characterise the nature of belowground anomalies/archaeological features. 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. (NB: copies of the Council Archaeology Service advice letters are now routinely posted on council websites).
6. Project design – written scheme of investigation
a. Geophysical surveys should be undertaken in accordance with the Standard and Guidance for archaeological geophysical survey published by the Chartered Institute for Archaeologists (CIFA, 2014), Geophysical Survey in Archaeological Field Evaluation (HE 2015), and EAC Guidelines for the use of geophysics in archaeology (EAC 2016).
b. Each project would normally 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 3.2.13 of the CIFA guidelines and should in particular specify:
- The project's objectives
- Reason for the project and commissioning body
- The location of the area(s) to be surveyed and any constraints (to be shown on a plan)
- Geology and topography
- Survey methodology
- Reporting and archiving arrangements
- Procedures for project management (to follow the principles set out in Management of Research Projects in the Historic Environment (MoRPHE) (English Heritage, 2015))
- The expertise of the project team. The project manager should 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. In appropriate circumstances, less experienced staff may conduct work under the supervision of more experienced colleagues
- An outline of the proposed timetable and staff resources - this must be non-binding and presented "for information only"
7. Fieldwork methodology
Accurate and precise surveying is essential and therefore preference is for a cart-based system with automatic RTK GPS logging, although, data collection using handheld gradiometers is also acceptable for magnetometer surveys.
As a minimum it is expected that:
- All survey techniques will follow the guidance set out by the CIFA, Historic England, and the European Archaeology Council (EAC)
- For handheld magnetometer surveys the standard survey resolution shall be no coarser than 1m x 0.25m (traverse lines 1m apart with data collected every 0.25m). For a cart-based system a higher resolution will be expected
- The maximum survey resolution for earth resistance surveys shall be no greater than 1m x 0.5m (traverse lines 1m apart, data collected every 0.5m)
- Instruments will be set up carefully to collect highest quality raw data to minimise the need for any post-survey processing
- The location of survey grids will be plotted using a GPS system accurate to within ±0.01m relative to the Ordnance Survey National Grid
8. Post-excavation methodology
a. A report will be required for every geophysical survey and should always contain the following elements:
- A non-technical summary of the results
- 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)
- Methodology and techniques
- A summary written account of the strategy and the results of the project with appropriate supporting illustrations
- A site location plan at an appropriate scale
- A 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 plan at an appropriate scale indicating areas surveyed by each method
- Description of present land use; geology and topography
- A summary of physical and health and safety constraints
- A conclusion, including a confidence of the results
- The proposed location of the archive
b. In addition:
- All plans should be clearly related to the Ordnance Survey national grid
- If a report includes assessments of archaeological importance or recommendations or further work these will be noted but will not be binding on the Council Archaeology Service
c. Submission of the report and data
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. The HER will be supplied with copies of all grayscale plots of the processed data, preferably ArcGIS georeferenced, and interpretation layers as ArcGIS shapefiles for inclusion into the HER.
iii. One copy of the report should also be supplied to the local planning authority, if appropriate.
iv. 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 Council Archaeology Service.
a. 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. A publication grant should be provided to the publishers in accordance with their requirements.
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.
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.
The form and guidance for its completion can be found on the OASIS website.
The archaeological contractor should endeavour to ensure that the site archive (including digital data) 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 preferred archive for Buckinghamshire is the County Museum. 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.
a. Site monitoring visits are not envisaged for geophysical surveys, however, larger surveys should provide the Council Archaeology Service with updated rectified plots of significant discoveries during the survey.
b. 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.
c. 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.
d. 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 our archaeological enforcement policy.
13. Health and safety and other constraints
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.
Buckinghamshire County Museum, 2013. Procedures for Notifying and Transferring Archaeological Archives.
CIFA, 2014. Standard and Guidance for archaeological Geophysical Survey.
EAC, 2016, Guidelines for the use of geophysics in archaeology
Historic England, 2015, Geophysical Survey in Archaeological Field Evaluation, Historic England
Historic England, 2015, Management of Archaeological Projects.
Historic England, 2015. Management of Research Projects in the Historic Environment. The MoRPHE Project Manager’s Guide.
MHC&LG, 2019. National Planning Policy Framework.
Buckinghamshire Council Archaeology Service
Planning and Environment
Walton Street Offices
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
Buckinghamshire Archaeology Society (Records of Buckinghamshire)
Mr Bob Zeepvat, Archaeological Editor
c/o ASC Ltd
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 & Archaeology
1 Saxon Gate East
Historic England Regional Science Adviser (London and the South East Region)
Jane Corcoran, Science Advisor
Cannon Bridge House
25 Dowgate Hill