The excavation tool store contains many things, including a very large number of buckets, both black and orange. It seems that local DIY stores must have had their entire stock bought up by the excavation!
When the sediment samples are brought up to the sieving area, they are laid out to dry, then transferred to buckets to be soaked in water with some washing powder (a very effective way of breaking down the clay lumps). After soaking overnight, the samples can be sieved and the residues bagged up for later sorting and identification.
The massed ranks of buckets spread out across the field stand as testament to the large quantity of material that is being excavated – several tonnes will have been processed on site by the end of the dig.