A programme of archaeological observation, investigation and recording was undertaken during groundworks associated with the expansion of Eydon sewerage treatment works, Northamptonshire, by Network Archaeology In November 2014. The works fell under 'permitted development' and, as such, were not subject to any planning conditions or controls. Thames Water, however, as part of its best practice policy, decided to consider the potential impact of its planned work upon the historic environment and, following consultation with Network Archaeology, a programme of archaeological observation and recording during groundworks was agreed. The planned focus of archaeological observation was topsoil stripping of the working area and excavation of the humus tank. Deturfing and partial topsoil stripping of the working area, however, took place prior to archaeological attendance. A walkover survey was, therefore undertaken over the stripped surface, and two spadesized holes were handexcavated to investigate the underlying soil stratigraphy. A fulltime presence was maintained during mechanical excavation of the pit for the humus tank. The works identified no archaeological finds, features or deposits.