GEA completed a desk study and ground investigation within these three basement vaults, located behind the Strand in the City of Westminster. The site is located within a Grade II* listed building in the Adelphi Conservation Area and lies within the Lundenwic and Thorney Island Special Archaeological Priority Area. The unused vaults have been transformed into a luxury spa with several swimming pools. Given the archaeological importance of this site, GEA worked closely with Archaeology Collective.

The investigation involved over 30 hand-dig trial pits, supported by archaeologists and UXO specialists undertaking a watching brief. Three cable percussion boreholes were also drilled as part of the works to a maximum depth of 20 m, using a low headroom dismantlable cable percussion rig with fume extraction equipment.

The site investigation encountered a significant thickness of made ground / Alluvium to depths of 5 m, overlying Kempton Park Gravel, which thickens in a southerly direction across the site and is in turn underlain by London Clay. Two of the boreholes were drilled through wooden posts, sat on limestone boulders, thought to be associated with a former wharf / jetty.

The foundation pits exposed foundations and structures thought to be associated with a former palatial home dating back to the 15 th Century.

Excavation of a number of swimming pools within the vaults, which comprise the lower ground floor of the existing building, together with other structural alterations, including a new lift shaft, resulted in concerns regarding soil movements. GEA therefore completed a ground movement analysis and building damage assessment to investigate the possible effects of the structural work on a number of surrounding archeologically significant buildings.