A watching brief was undertaken during the laying of an electricity cable through the tunnel of Efford Emplacement. Part of a 19th-century drain survives within the surface of the tunnel. No other archaeological deposits were present within the tunnel or embankment over the ditch, but 19th-centry make-up deposits for a path were present to either side. Foundations of one of the walls of the tunnel were exposed in test pits excavated prior to the main works.