The general position is that it is up to the Contractor to satisfy itself as to the condition of the Site and it is therefore the responsibility of the Contractor to investigate the site and take the risk of unforeseen problems with the Site's condition.
There may, however, be circumstances where it will cost more money for the Board to pay the Contractor to take the "risk" on the condition of the Site than for the Board to take that risk itself. An example might be if the Site is not "greenfield" (perhaps because the Board currently occupy facilities on the Site). In these circumstances it may be impractical to expect the Contractor to make investigations beneath buildings that are currently in use to discover all the potential problems. It may be better value for the Board to take the risk for potential difficulties (such as environmental contamination) and bear any related costs.
The standard contract contains an optional provision which enables the Board to retain this risk allowing the Contractor to claim recovery of the cost of any work required and the costs of any subsequent delay as a result of the discovery of unforeseen ground conditions. The Board can also consider the risk of asbestos on a case by case basis and decide whether it is better value for the Board to retain the risk.
See also the comments on "Delay Events" at paragraph 21.