SPIA Survey (AKA DAPAS)
The SPIA Survey: Systematic, Partial and Intensive Artefact Survey
Since 2017, the DIF initiative has focused on a combined approach to embedding metal detecting and fieldwalking into professional practice and has participated in many archaeological digs over these years.
The SPIA Survey, previously known as the DAPAS Approach, was developed in response to the need for a consistent and systematic approach to utilising detectorists on archaeological sites, stemming from a series of issues observed in the field.
Repeated issues of concern include the following: ranging poles used to define transects are set too far apart; metal poles are used in closely quartered areas that require intensive surveys; small finds needing to be retrieved before being geolocated; a lack of a clear discard policy; spoil is placed on tarpaulins with metal eyelets; and detectorists wearing steel-capped safety footwear.
- A non-intrusive approach involving surveying areas divided into grids and transects.
- As part of mitigation efforts, detecting in test pits, trenches, and the generated spoil.
- For example, the DIF conducted a ‘partial’ site survey on the HS2 project that included chemical analysis and magnetic susceptibility, with transects set at 20-meter intervals. The purpose of this survey was to investigate areas designated as ‘blank’—zones where other methods had not detected evidence of human habitation. This approach can potentially uncover evidence from challenging periods, such as the early medieval era.
- Conversely, for a War of the Roses project where Oxford Archaeology had already identified an area of interest through magnetometry, an ‘intensive’ survey was required. This involved conducting surveys at 2-meter transect intervals over the archaeological site, while the hinterland was ‘partially’ surveyed at 10-meter intervals.
In large-scale surveys, it is challenging for detectorists to maintain a straight line while implementing the ‘head down’ policy. This policy involves searching for all-material surface finds while ensuring the detector’s head is close to and parallel with the ground. The difficulty lies in staying aligned with the transect flags and navigating accurately across extensive areas. The SPIAS Partial approach utilises 1.5m yellow fibreglass poles and an alternating-coloured flag system, set at close intervals. The Intensive approach employs a series of ropes cut to predetermined lengths, with nylon hard eye splices, along with fibreglass stakes. This facilitates quick setup from a designated GPS location. With ropes of 20m and either 2m or 1.5m, a grid up to 200 square metres can be easily established and moved across the survey area.
Rather than flagging targets for others to retrieve, DIF Practitioner Detectorists are best positioned to retrieve topsoil finds when a target is discovered. They utilise their knowledge and expertise with a metal detector to determine the approximate size, depth, and position of a target, ensuring that the artefact is not damaged during retrieval.
The artefact is then bagged, staked, and tagged. The necessary information for labelling is written on both the bag and the tag, which are affixed to the plastic stake with a cable tie. This arrangement permits the small finds expert to retrieve the find, even if the GPS coordinates have not yet been documented, as the essential transferable information remains on the staked tag.
As part of a thorough mitigation policy, detecting trench positions and each archaeological layer within the trench requires an intensive approach. This ensures that all potential finds are discovered before engaging mechanical excavators and mattocks.
An essential team member for conducting a successful SPIA Survey is the mechanical excavator driver, whose expertise is crucial to the mitigation strategy. Spoil, often heaped alongside trenches, presents a significant challenge for detectorists. Our instruments struggle to penetrate the loosely compacted material, making the search comparable to finding a needle in a haystack when considering the mathematical relationship of ‘surface area to volume x detector penetration’.
The conventional ‘bucket and sieving’ method, which focuses on identifying where deposits have been retained from trench layers, is utilised in the SPIA Survey, albeit on a much larger scale. This system is designed to favour the detectorist in finding both metal and non-metal artefacts.
Further information on the SPIA Survey will be included in the Resource Hub.
