An evaluation by trial trenching is sometimes requested as a condition of planning consent, or more frequently since the advent of NPPF, on advice from the planning authority prior to the application being submitted or determined. The condition or advice is based on the likelihood that the site holds archaeological potential. The applications vary but could for instance concern a small or large scale development that involves any below ground impacts such as housing developments, industrial developments or landscaping.

Company director Chris Clay watching a trench being opened

Several factors play a part for allocating the trenches within the development area. Some may be based on geophysical survey results that target certain anomalies of archaeological potential, whilst others may be strategically placed within the area to try and determine the extent of any potential archaeology. How much of the site that will be sampled is usually down to the local authorities and their policies, but tends to vary between 2% and 5% of a development area GPS survey equipment allows us to target our trenches at agreed locations to centimetre accuracy.

The majority of trenches are excavated by a mechanical excavator fitted with a smooth ditching bucket. However, to everyone’s dread, there are those cases where hand dug trenches are the only way forward! In either case, it is up to the supervising archaeologist to decide on the appropriate depth. Either this will be on the first significant archaeological horizon or when the natural geology has been reached.

Once open, the trench is ready to be investigated and recorded. If there are any archaeological features, these will be excavated by hand. Any finds will be retained, bagged and labelled and soil samples may be taken to identify the feature’s function or to give information about the past surrounding landscape and environment. Plans, section drawings, descriptions of deposits and further photographs will also be taken.

When all the trenches have been recorded, they are backfilled and the post-excavation work can begin in the office. Finds are washed and marked and submitted to the relevant specialists for detailed analysis.

After all the data has been compiled and a report has been written and sent off to the client and the local planning authority, a decision will be made by the county or city archaeologist for that area, whether any further work is required. If the results show the potential for significant archaeology, or features of archaeological importance, the evaluation may be followed by an open area excavation, where a large part of the development area is stripped down to the archaeological horizon. If the evaluation shows some more limited archaeological presence that requires further investigation, but none that warrants an excavation, the evaluation may be followed by an archaeological watching brief. This work will be carried out during the actual development groundworks.