Site Event/Activity record ECH7200 - Origins, extent and implications of the so-called St Werburgh Street Dip,

For several years, a noticeable dip has been forming in the road surface extending under the properties on both sides of the street, including the Cathedral’s grounds. This dip appears to have been growing more severe in recent years. It has caused serious subsidence of the columns under the arcade that fronts the properties on the south-western side of the street and the distortion and fracturing of the iron railings bounding the Cathedral’s land on the north-eastern side of the street. The purpose of this paper is to collate what is presently known of the cause, history and extent of the dip. The information comes from a variety of sources. Conclusion of the paperis that the "dip" is a man-made feature and, on the currently known evidence, it is of late medieval date. The feature appears to lie in what was then open ground within the abbey precinct and avoids known buildings. The most likely purpose for such a hole dug deep into the rock is that it was a quarry providing stone for building work at the adjacent abbey. The overall dimensions of the quarry is not yet determined. Its depth exceeded 10m, the depth to which the bore hole rig was able to reach. Medieval and early post-medieval urban populations produced huge quantities of organic rich rubbish. This included organic material such as food waste, sweepings from floors and byres, cloth, leather and wooden artefacts of all kinds and sewage as well as environmental material such as plants, insects and parasites. As Chester is built on a well-drained sandstone hill, in most archaeological deposits this organic material tends to have completely decomposed. However, in exceptional environmental conditions such as pits and ditches the organic material compresses to form a such dense carbon-rich deposit that holds moisture and excludes oxygen that decomposition ceases. This has the potential to become an extremely rich and valuable archaeological deposit containing large quantities of artefacts and environmental material. It appears that the St Werburgh Street quarry contains such a deposit