Sediment filled bedrock depressions in the Carboniferous Limestone were revealed during construction of a supermarket in Chepstow. They were interpreted as swallets.
An initial site investigation did not reveal the features, which were less than 10 m across and about 8 m deep. They were not suspected at the desk study stage since the site was on a valleyside location and did not lie on an obvious abandoned drainage route.
The features were investigated in less than one week and the investigation and redesign of foundations did not incur any delay to the contract.