Case Study 11: Applying Lean Processes to the Excavation of Flint Scatters on Major Infrastructure Projects
Kristina Pill (Costain), Caroline Raynor (Costain), Sean Taylor (Cornwall Archaeological Unit)
This case study describes the implementation of construction-based Lean processes and innovation to support and expedite the excavation and processing of large flint scatters, specifically a Mesolithic-Neolithic scatter discovered during the construction programme for the A30 Chiverton to Carland Cross dualling scheme in Cornwall (Figs 11.1–11.2).
The scheme was delivered by Costain Jacobs Partnership (CJP) on behalf of National Highways with archaeological fieldwork by Cornwall Archaeological Unit (CAU). The scheme spans 8.7 miles of new road in an area of high archaeological potential, where the topography follows the prehistoric and historic route along the central ridge of Cornwall, which is noted for the presence of 68 Bronze Age barrows, including the Carvinack Barrow which was excavated in the 1950s (Dudley 1964).
During the project CAU excavated two of the known barrows and identified an additional four.
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The fieldwork was undertaken as part of wider archaeological mitigation during the delivery of the A30 Chiverton to Carland Cross dualling scheme, in line with the requirements set out during the Development Consent Order (DCO).
Two flint scatters were identified during the evaluation phase, which took place between 2017 and 2021. The smaller scatter at Rosemerryn Lane had been previously identified and recorded in the Historic Environment Record (HER 32064/32065) although it comprised only four flints. The second, larger scatter, at Ventonteague, was identified during the evaluation phase and yielded about 500 flints from one 50x1.6 metre trench.
CAU had previously fieldwalked and test-pitted similar lithic scatters as part of a research project at North Cliffs in 2016 (Jones et al 2018).
Preliminary analysis indicated that the Ventonteague site had a high concentration of Mesolithic and transitional Mesolithic-Neolithic flints. Bronze Age lithics associated with a nearby barrow were also identified.
Excavation in surrounding areas confirmed the high potential, with sites including Neolithic pits, Bronze Age barrows and a possible stone circle setting. These were centred around a natural promontory and spring which had been canalised in the post-medieval period.
As the work was being undertaken within the context of a major infrastructure project, it was important to balance the commitments made at DCO, as set out in the Overarching Written Scheme of Investigation (OWSI) and the Regional Research Framework for the South West, with the programme and needs of the construction team. Costain worked with the project leads at CAU to apply process mapping, Lean and construction innovation to support the excavation strategy, flint collection and post-excavation processing.
The aim of the collaborative process was to share learning from other major infrastructure projects, as well as reducing the need for extensive hand excavation. This had the benefits of mitigating musculoskeletal and manual handling risk and expediting the programme of works.
Fieldwork strategy at Ventonteague
The initial approach involved mechanically deturfing the site before excavating 68 targeted test pits on a grid arrangement across the area. The work was carried out with the aid of local volunteers who were supported and monitored by the archaeological fieldwork team for safety, training and quality control purposes.
Simultaneously, around 3000m² of the wider area was subject to systematic fieldwalking which resulted in the hand collection of 1005 flints in addition to the 490 retrieved from the test pits. GPS data associated with the hand collection was used to make a heat map of the area and build a greater understanding of the distribution of the assemblage (which included nine arrowheads, 212 blades or bladelets and 31 scrapers).
The plotted distribution showed two distinct concentrations of lithics and led to subsequent expansion of the area under investigation. This in turn led to the discovery of a previously unidentified barrow and a further 7044 hand-collected flints.
The scale and extent of the flint scatter (spread over 0.65ha) was not immediately apparent due to the geology (highly fractured slate affected by periglacial frost heave intermixed with clays which have weathered out from the slate formation) and levels of agricultural disturbance.
The excavations were in their twelfth week before discussions were initiated around the growing complexity and challenge. With a tight programme for delivery of the archaeological works it was imperative that a solution was found to manage the estimated 50,000 flints thought to be present on site.
It was very clear that amendments would need to be made to the Site-Specific Written Scheme of Investigation (SSWSI) and a proactive and early approach would need to be made to stakeholders. The Planning Archaeologist for Cornwall Council and Historic England’s Inspector of Ancient Monuments and Senior Science Advisor were approached for consultation and advice and helped to shape the strategy, taking into consideration the needs of the small archaeological team and the construction programme.
An interim report on the most recent findings was produced by CAU and provided to give context and background to the proposed WSI amendments. This document contained clear statements and data on the distribution of the artefact scatter and the fact that the majority of flints, aside from those within sealed/discrete features, were not in situ and had originated from further upslope.
Using this data, the team proposed a gridded (1m x 1m), sequenced mechanical excavation using a 0.9t mechanical excavator with bladed bucket. This ensured 100% retrieval of flints at a rapid rate, while also safely and efficiently exposing buried features and sealed deposits which could be excavated by hand. Quick and efficient access to these sealed features and in situ deposits was of paramount importance as it was here that the specific nature and extent of human activity at the site would be best understood.
This approach was agreed on the basis that a stringent methodology was applied to the management of samples, including labelling regime, storage and rapid processing at a bespoke sieving area to provide iterative data back to the fieldwork team throughout later hand excavation. It was also agreed that the stakeholder team would be regularly informed of progress and able to monitor the success of the proposed methodology through shared digital data and site visits.
In total the scatter area was split into 452 1m x 1m grid squares. Of these 236m² were subject to machine excavation with a further 214m² undertaken by hand (68m² in the first phase and 146m² in the second phase). The bulk excavation of the flint scatter at Ventonteague yielded over 30,000 litres of sample material to be transported, stored and processed.
Application of Lean to streamline the archaeological process: site management and finds processing
Costain previously deployed Lean processes to the management of archaeological works on HS2 to support the excavation of a large post-medieval cemetery at Euston (Bicknell et al 2019). There was a clear opportunity to build on this learning and adapt the process to suit the management of complex large-scale Mesolithic sites in Cornwall.
A workshop was set up to allow the team to carry out a mapping activity. This involved defining each activity or stage of the archaeological process and breaking it down into clear steps with ‘zones’ for each activity. Defined steps in the process included excavation, labelling of samples, storage of samples prior to transportation, transportation to the processing area, and processing in a bespoke facility.
Measurement of inputs, outputs and flow rate were addressed by calculating the number of personnel and projected productivity of the archaeological fieldwork team during each step of the process. This allowed the construction team to define the volumetric output and area of each activity zone and put measures in place to prevent backlogs or stoppages due to lack of space or running out of core equipment such as sample buckets and labels.
Team members were given clear instructions and made accountable for the labelling, stacking and placement of sample tubs to ensure no data loss. Labels were completed in triplicate and boxes were colour-coded according to area. A regular transportation schedule was defined to ensure a constant flow of excavated samples arriving at the sieving and processing area. By understanding flow rates and productivity it was possible to deliver a safe and streamlined process which supported an environment of continuous improvement.
The team was proactively encouraged to report on issues and help define areas for improvement as part of the Lean process. An example of this was the redesign of the wash stations and mesh, which were improved with the addition of rubberised edging to eliminate the risk of cuts and abrasions.
The site was divided into seven clear work zones: (z1) the excavation area, (z2) sample collection point (at excavation area), (z3) sample tub storage (at finds processing area), (z4) sample washing/sorting, (z4&5) sample drying facility, (z6) finds processing and (z7) store where boxed lithics were placed ready for post-excavation assessment.
At the main site compound a segregated area was created to house a bespoke flint-processing area (z3–z7). This small facility was constructed using the same Lean principles to enable the onsite washing and sorting of heavy residue and flint processing (Figs 11.3–11.4). Based on staff availability and storage capacity in z2 and z3, the facility comprised two washing stations (large water tanks with interchangeable mesh of different grades to ensure capture of debitage), two heavy residue sorting stations and a drying room.
The washing, sorting and drying areas were given a linear configuration to reduce manual handling and risk of slips, trips, falls and cross contamination of samples. This ensured a ‘flow’ through the process from start to finish.
Staff were also issued with ergonomic tooling including brush kits to reduce fatigue and musculoskeletal issues during the washing process. The area was not enclosed but had a roof to permit all-weather working. Attenuation tanks and silt traps were incorporated into the design to ensure compliance with water management and environmental requirements. A radio was also provided as this has previously been found to deliver a high level of wellbeing benefit to the teams when carrying out static processing activities.
The defined work zones around the excavation helped to shape a more streamlined, safe and efficient working environment and the combination of machine and hand excavation provided comprehensive retrieval of the lithics.
The linear process drove efficiency at the flint washing stations and provided a positive opportunity for team members to gain a good understanding of the initial stages of post-excavation processing. This was further enhanced by the presence of the CAU flint specialist who was on hand to expedite sorting of lithics and to provide immediate advice and expertise.
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The results of the fieldwork at Ventonteague are yet to be fully collated but the site ultimately yielded over 80,000 lithics (see Fig 11.5).
The practical application of Lean, and collaboration between the construction and archaeological teams, has yielded clear benefits. The programme of work was delivered much more efficiently, reducing the anticipated programme by more than six weeks, and increasing productivity by a factor of three compared with the initial projected time for excavation by hand. The use of small 0.9t excavators eliminated a substantial manual handling and occupational health risk for the archaeological team, permitting fewer staff to deliver more targeted work.
There were no reported accidents or incidents during the discharging of the excavation phase.
The enhanced finds processing area resulted in no lost samples and zero data loss and enhanced onsite learning as the site team were rotated through activities to gain experience of all aspects of the process including working alongside the CAU lithics specialist.
The overall process of mapping and defining the archaeological process was strategically valuable to both the engineering and archaeological teams as it provided them with a common language and understanding of activity types, helped to define the scope of works, and ensured clear agreement around key metrics associated with measuring a successful delivery.
Cornwall Council: Phil Copleston; Historic England: Phil McMahon and Jim Williams; National Highways: Nick Simmonds-Screech; Costain-Jacobs Delivery Partnership: John Green, Phil Grosvenor, John Lee, Jamie Lewis, Mike Moore, Michelle Parsons, Ali Thomas and the A30 construction team.
Working on behalf of CAU: Graham Britton, James Burley, Ben Clayden, Max Dampier, Chelsea Fulman, Johnnie Gallagher, Jay Gossip, James Graham Carmelo Grasso, Phoebe Holmes, Trevor Jose Steve Joyce, Conner Kenway, Dave King, Ben Lang, Anna Lawson-Jones, Arthur Lazarus, Leah Marshall , Charlotte Mathews, Chris Michel, Richard Mikulski , Laura Miucci, Des O'Donoghue, Ian Rose, Carolyn Royall, Paul Redish, Sara Rogers, Cathryn Shean, Joel Smith, Andy Sturdy, Ryan Smith, Alex Taylor and Gemma Witchals.
Our capable local community volunteer archaeologists: Callum Booker, David Carlisle, David Clifton, Val Dawson, Frances Deacon, Esther Dunstan, Steve Hartgroves, Linda Hitchcox, Madelaine Hart, Tracie Haslam, Jo May, Tamara Moluch, Eileen Partington, Julie Pinkney, Angela Praed, Jo Pye, Roger Smith, Marilyn Thompson, Patricia Tremain.
Bicknell, J, Foster, F and Raynor, C, 2019 Preserving the Past. The Ergonomist (Chartered Institute for Ergonomics and Human Factors)
Dudley, D, 1964 ‘The Excavation of the Carvinack Barrow, Tregavethan, near Truro’. Journal of the Royal Institute of Cornwall 4(4), 414-51
Jones, A M, Jones, A L, Quinnell, H and Tyacke, A, 2018 ‘The North Cliffs Project’. Mesolithic Miscellany 26, 23-48