Archaeological evaluation trenching and how it is priced
Trial trenching quotes vary because the brief varies. Understanding what the curator specifies, and which parts of a contractor's price are fixed, is how a developer keeps control of the figure.
Archaeological trial trenching cost is driven by the brief, not by the contractor. The council's archaeological adviser, usually a county archaeologist or a shared historic environment service, sets the sample to be examined and the standards it must meet, and everything in a contractor's quotation follows from that. Two tenders for the same field can differ by a factor of three simply because one has read the brief as 20 trenches and the other as 30.
So the first move on any site with archaeological potential is to get the brief in writing before asking anyone to price the work.
What the county archaeologist specifies and why
A pre-determination evaluation is asked for where the desk study has identified potential that the council cannot weigh without knowing what is actually in the ground. The national historic environment policy in the NPPF (August 2026 edition) expects an applicant to describe the significance of any heritage asset affected, including archaeological interest, and field evaluation is how that is done where the desk study leaves the question open.
The brief will normally set out the sample to be examined, expressed as a proportion of the developable area, the trench dimensions, the standards to be followed, and what happens if something is found. Trenched samples in England are commonly specified in low single figures as a percentage of the site area, but that is a convention rather than a rule, and a site next to a known Roman road may be asked to do more. Read the brief rather than assume.
An Archaeological Desk-Based Assessment should always come first. It costs a fraction of fieldwork, and on a good number of sites it persuades the curator that evaluation is unnecessary or can be reduced to a watching brief during groundworks.
Pricing by trench, by day or by area
Contractors price the same job in different shapes, and comparing tenders means converting them to a common basis.
| Pricing basis | Typical use | What to watch |
|---|---|---|
| Per trench | Fixed trench count and dimensions in the brief | Whether reinstatement and spoil handling are inside the rate |
| Per team day | Open-ended briefs, urban sites, unpredictable ground | The assumed team size and the number of days allowed for |
| Per hectare | Geophysical survey | Whether processing and reporting are separate |
| Fixed lump sum | Post-excavation assessment and reporting | What triggers an uplift |
The variable cost sits in the field phase. The fixed costs sit around it: mobilisation, welfare, plant hire and standing time, fencing, insurance, and the archive. On a small site the fixed element can be a large share of the total, which is why splitting a site into two separate evaluation visits is usually a false economy.
Ask for the quotation broken down by those headings and ask what the day rate assumes about the team. A two-person team on a heavy clay site in February is not the same offer as a four-person team in June.
Geophysical survey as a lower cost first step
Magnetometer survey covers ground quickly and at far lower cost than trenching, and on the right geology it produces a plan of ditches, pits and industrial features that lets the trenches be aimed rather than scattered. That targeting is where the saving comes from. A curator will often accept a reduced trench count where geophysics has already characterised the site.
It does not work everywhere. Response depends on the contrast between features and the natural subsoil, so some geologies give a weak or confused picture, and made ground, modern services, fencing and reinforced concrete all interfere. Alluvium can mask everything beneath it. A contractor who says the geology is unpromising before taking your money is giving you good advice.
Treat geophysics as a way of designing the evaluation, not as a substitute for it. Very few curators will accept survey results alone where the decision turns on whether remains survive.
Machine and operator against hand excavation
Trenches are opened by a tracked excavator with a toothless grading bucket, under continuous archaeological supervision, removing topsoil and subsoil in level spits down to the first archaeological horizon or the natural geology. After that the work is by hand.
The machine is not usually the expensive part. Standing time is. An excavator and operator sitting idle while a team hand-excavates a feature it has just exposed burns money quietly, which is why experienced contractors phase the machining across trenches rather than opening everything at once. Spoil handling matters too: a site with no room for stockpiles means muck away and return, and that is a haulage cost nobody put in the first estimate.
Urban sites change the arithmetic completely. Services, deep made ground, shoring and confined space working can put a single city centre trench above the cost of a dozen in a green field.
Post-excavation assessment and reporting
Fieldwork is not the end of the price. Finds have to be washed, marked, quantified and assessed by specialists, environmental samples processed, and a report written to a standard the curator will accept and the Historic Environment Record will take.
Specialist input is priced per assemblage rather than per day, so a site producing a large pottery group, animal bone, or waterlogged environmental material carries a bigger post-excavation bill than the trench count suggested. Archive deposition with the receiving museum is a separate cost and some museums now charge a per-box fee. Get the deposition policy of the relevant museum before the fieldwork starts.
An Archaeological Field Evaluation report is expected by councils to come from a suitably qualified author, and professional review is strongly advised. Field evaluation is not a document you can produce from a desk.
Where a positive result escalates to full excavation
The uncomfortable part of budgeting evaluation is that the evaluation itself is the inexpensive stage. A trench that finds nothing closes the question. A trench that finds a well preserved settlement opens a much larger one.
The usual escalation runs: preservation in situ by redesign where that is achievable, then strip map and sample across the affected footprint, then open area excavation of the parts that cannot be avoided, then a watching brief on the remainder. Each of those is an order of magnitude apart. A scheduled monument is a different regime again, requiring scheduled monument consent under the Ancient Monuments and Archaeological Areas Act 1979 rather than anything the planning system can resolve.
Build a contingency on the basis of the desk study's risk rating rather than a round percentage, and hold it until the evaluation report is signed off. The same discipline applies to the ground investigation budget, and the thinking behind a contaminated land investigation programme transfers directly.
Controlling cost through a written scheme of investigation
The written scheme of investigation is the contract between what the curator wants and what the contractor will do. A loose one is an invitation to variations.
- Get the brief from the curator in writing before tendering, and send the same brief to every contractor.
- Have the winning contractor draft the scheme and submit it for approval before mobilising, not afterwards.
- Fix the trench count, dimensions and locations in the scheme, with a named process for moving a trench that hits a service.
- State who pays for standing time, spoil removal, reinstatement and topsoil separation.
- Set out the reporting timetable and the archive destination, with the museum's acceptance confirmed.
- Include a stop point: if defined thresholds are met, work pauses and the curator, client and contractor meet before anything further is committed.
That last item is the one that saves money. Without it, a contractor with an open brief keeps digging because the scheme told them to.
Costs for specialist work of this kind sit outside PlanScope's published pricing, which covers report drafting at £50 per report or £150 per month for unlimited reports. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval, and for specialist technical reports, qualified professional input may be required. This is general guidance rather than legal advice, so confirm the archaeological requirement with your local planning authority before committing to a programme.
Frequently asked questions
Who decides whether trial trenching is needed?
The local planning authority decides, on the advice of its archaeological adviser, usually a county archaeologist or a shared historic environment service. That adviser issues a brief setting out the sample and the standards. The trigger is normally a desk-based assessment showing potential the council cannot weigh without physical evidence from the ground itself.
Can geophysical survey replace trenching altogether?
Rarely. Survey characterises a site and lets trenches be targeted, which often reduces the number required, but very few curators accept it alone where the decision turns on whether archaeological remains survive and in what condition. Its usefulness also depends heavily on geology, made ground and nearby services, so it fails on some sites.
What makes one trenching quote so much higher than another?
Usually a different reading of the brief, a different assumed team size, or different assumptions about spoil, reinstatement and standing time. Convert every tender to the same basis before comparing. Ask each contractor to state the trench count, trench dimensions, team composition, number of field days and what is excluded from the price.
Is post-excavation work included in the fieldwork price?
Not always, and it is a real cost. Finds washing, specialist assessment, environmental sample processing, reporting and archive deposition are often quoted separately or against assumed quantities. A site producing a large assemblage can carry a post-excavation bill out of proportion to the trench count, so check what quantities the price assumes.
What happens if the evaluation finds significant remains?
The response is usually redesign to preserve remains in place where that works, then strip map and sample, then open area excavation of what cannot be avoided, then a watching brief. Each step is considerably more expensive than the last. Where the remains are a scheduled monument, separate consent under the 1979 Act is needed.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.