Archaeological Field Evaluation
An archaeological field evaluation is the next step after a desk-based assessment has identified that significant archaeological remains may survive on a development site. It involves physical investigation of the ground to determine what is actually present, how significant the remains are, and what mitigation will be needed before or during construction. Field evaluation is a common planning requirement across England and is typically secured through a pre-commencement condition.
Typical Cost
£300 – £5,000+
Turnaround
1 – 6 weeks
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What is a Archaeological Field Evaluation?
An archaeological field evaluation is a programme of intrusive or non-intrusive investigation designed to establish the presence, extent, date, character, and significance of archaeological remains on a development site. The most common form is trial trenching, where machine-excavated trenches are opened across the site and any archaeological features exposed are recorded by professional archaeologists. Non-intrusive methods such as geophysical survey and fieldwalking may also form part of the evaluation. The results inform decisions about what further mitigation is needed, ranging from full excavation to a watching brief during construction.
When is a Archaeological Field Evaluation required?
A field evaluation is required when a desk-based assessment or the local authority's archaeological advisor identifies that the site has moderate to high potential for containing significant archaeological remains that cannot be adequately assessed from desk-based sources alone. It is most commonly required for greenfield sites, large brownfield redevelopments, sites in Archaeological Priority Areas, and locations where previous finds suggest important below-ground remains. The requirement is usually imposed as a planning condition, though some authorities request evaluation before determining the application.
What does a Archaeological Field Evaluation include?
A field evaluation report includes the project background and archaeological context, a description of the methodology used including trench locations and survey techniques, a detailed account of all archaeological features and deposits encountered, specialist analysis of finds such as pottery, metalwork, and environmental samples, an interpretation of the date and significance of the remains, an assessment of the impact of the proposed development on the archaeology, and recommendations for further mitigation. The report is accompanied by plans, sections, and photographs documenting the findings.
How much does a Archaeological Field Evaluation cost?
Costs vary considerably depending on the size of the site and the evaluation method used. A geophysical survey for a small to medium site typically costs between £1,500 and £4,000. Trial trenching on a residential plot might cost £3,000 to £8,000 for a few trenches. Larger sites requiring extensive trenching across several hectares can cost £15,000 to £50,000 or more. Costs include machine hire, archaeological staff, finds processing, specialist analysis, and report production.
Who can prepare a Archaeological Field Evaluation?
Archaeological field evaluations must be carried out by a professional archaeological contractor or consultancy. The work should be undertaken by archaeologists who are members of the Chartered Institute for Archaeologists (CIfA) and who operate to CIfA's Standard and Guidance for Archaeological Field Evaluation. The local authority's archaeological advisor will normally need to approve a Written Scheme of Investigation (WSI) before fieldwork can commence.
How long does a Archaeological Field Evaluation take?
The timescale depends on the size of the site and the scope of fieldwork required. Geophysical survey of a small site can be completed in a few days. Trial trenching on a residential plot typically takes 1 to 2 weeks on site, with the report following 4 to 8 weeks later. Larger evaluations involving extensive trenching and specialist analysis can take several months from fieldwork to final report. Factor in time for the local authority to approve the Written Scheme of Investigation before work begins.
Frequently Asked Questions
What is trial trenching?
Trial trenching involves excavating narrow trenches, typically 1.8 metres wide, across the development site using a mechanical excavator under archaeological supervision. The topsoil and subsoil are removed to expose the surface of any archaeological features, which are then investigated by hand. The standard sample is usually 3 to 5 percent of the site area, though this varies depending on the archaeological potential and the advice of the local authority.
What is a geophysical survey?
A geophysical survey uses instruments such as magnetometers or resistivity meters to detect buried features without breaking the ground. It can identify ditches, pits, walls, kilns, and other features by measuring variations in the magnetic or electrical properties of the soil. It is a useful first step before trial trenching, though it does not work well on all soil types and cannot determine the date or significance of features without subsequent excavation.
What happens if significant remains are found?
If the evaluation reveals remains of significant archaeological interest, the local authority's archaeological advisor will recommend appropriate mitigation. This could range from redesigning the development to avoid the most sensitive areas, through to a programme of full archaeological excavation and recording before construction begins. Only remains of national importance equivalent to Scheduled Monuments are likely to prevent development entirely.
What is a Written Scheme of Investigation?
A Written Scheme of Investigation (WSI) is a project design document that sets out the objectives, methodology, and standards for the archaeological fieldwork. It must be submitted to and approved by the local authority's archaeological advisor before work begins. The WSI covers trench locations, recording methods, finds processing, environmental sampling strategy, reporting requirements, and archive deposition arrangements.
Can I carry out construction while the evaluation is ongoing?
No. The field evaluation must be completed and the results assessed before any construction work begins on the affected area. Starting construction before the evaluation is finished would breach the planning condition and could result in enforcement action. In some cases, phased evaluations can be agreed to allow construction on parts of the site that have been cleared.
How deep do archaeological trenches go?
Trenches are excavated to the depth at which archaeological features are first encountered or to the surface of natural geological deposits if no archaeology is present. On most sites in England, this is typically between 0.3 and 1.2 metres below ground level. Deeper excavation may be needed in areas with thick alluvial or colluvial deposits, particularly in river valleys and floodplains.
Who pays for the archaeological field evaluation?
The developer is responsible for all costs associated with the archaeological field evaluation. This is an established principle in the planning system, set out in paragraph 205 of the NPPF, which states that developers are expected to record and advance understanding of the significance of heritage assets. There are no grants or public funding available for developer-led archaeological work.
What is the difference between evaluation and excavation?
Evaluation is a sampling exercise designed to establish what archaeological remains are present on a site. Excavation is a more intensive programme of investigation that aims to fully record and understand the remains before they are removed by construction. Evaluation comes first and informs whether excavation is needed. Excavation is only required where significant remains are confirmed and cannot be preserved in situ.
Do I need to reinstate the ground after trenching?
Yes. After the evaluation is complete, trenches are backfilled with the excavated material and the ground surface reinstated. On agricultural land, the topsoil and subsoil must be replaced in the correct order to maintain soil quality. On brownfield sites, compaction and reinstatement may need to meet engineering standards, particularly if the trenches are in areas where buildings or roads are planned.
Can archaeological evaluation be done in winter?
Fieldwork can be carried out at any time of year, though wet winter conditions can make trenching more difficult and slow progress. Waterlogged trenches may need pumping, and heavy rain can damage exposed archaeological features. Geophysical survey works best on moist but not saturated ground. Where possible, scheduling fieldwork for spring or summer is preferable, though delays are not always avoidable given planning timescales.