Michael Heaton Heritage Consultants provide professional and technical support in the planning and management of works affecting archaeological sites and historic buildings
specialising in Heritage Statements and the archaeological analysis -'building palaeopathology' - of historic buildings.
Archaeologists use the term 'evaluation' to refer to what everyone else in the Development and Construction industries know as 'site investigation'. The principles and practices are virtually the same, the only difference being that archaeologists normally stop digging when they encounter parent material bedrock. The guidelines of BS5930 and the Code of Practice of the AGS apply equally well to archaeological site investigation and geotechnic/geoenvironmental site investigation, and the same range of intrusive (excavation, augering) and non-intrusive (geophysics) techniques are employed.
Evaluation forms most of the workload of most archaeological companies and practices and most of the archaeological work required by planning authorities. Over 75% of evaluations reveal no significant archaeological deposits.
Most clients and their advisors think of an archaeological evaluation simply as a procedural hurdle in the planning system. In many cases it is, but it also the only way that the archaeological liabilities of a development project can be realistically estimated. We recommend that, irrespective of whether the planning authority requests a pre-determination evaluation, clients should commission such works before finalising project budgets and preferable before site purchase. Archaeological costs are a development cost and they should be factored into all site acquisition costs.
The most commonly employed technique - and the one that invariably has to be employed at some point, if only to corroborate the results of geophysics - is sample excavation. This is effected by manual excavation of test pits or mechanical excavation of test trenches, the choice of technique being determined by the nature of the anticipated archaeological deposits, the size of the site, plant access etc. It is a destructive technique, and for that reason should aim to investigate (destroy) the minimum volume of archaeological deposits necessary. The most commonly made mistake is not excavating deep enough, normally made by inexperienced or overly cautious technicians: if you are being asked to pay for a second and unprogrammed phase of evaluation on the same site, you are probably paying for incompetence.
Because sample excavation is destructive - not least because it introduces oxygen into biologically inactive deposits, thereby re-igniting the touchpaper of biological degradation - evaluation of environmentally rich deposits (such as estuarine of deep alluvial deposits) should commence with the specialised geophysical techniques and borehole surveys being pioneered by David Jordan and Terra Nova Limited, with who we frequently work in partnership.
Evaluation is defined by the Standards and Guidelines of the Institute of Field Archaeologists, which provides a detailed specification for the reports, and the Association of
Local Government Archaeological Officers (formerly ACAO):
"...a limited programme of ...fieldwork which determines the presence or absence of archaeological features, structures, deposits, artefacts or ecofacts within a specified area or site...... If such archaeological remains are present, field evaluation defines their character, extent, quality and preservation (sic) and enables an assessment of their worth in a local, regional, national or international context, as appropriate."(IFA, 1999)
"...a programme of ...fieldwork designed to supplement and improve existing information to a level of confidence at which planning recommendations can be made."(ALGAO, 1993)
The latter is arguably the more verifiable.
The term is also applied to the intrusive investigation of Historic Buildings, where opening-up and other forms of destructive investigation/testing are employed to augment analytical measured surveys. (ALGAO, 1997)
Project management Flow Diagram
Sequence of post-excavation operations
The Spa at Bath
Decimus Burton's 19th C Swimming Pool