As part of their work to identify a preferred solution for stabilising the mines, Parsons Brinckerhoff were instructed to undertake a series of geophysical ground investigations, borehole investigations and physical inspection of mine workings to assess the extent of the affected area and the condition of the mines themselves.
The geophysical investigations started in March 2001, comprising both a ground penetrating radar survey and a gravity survey. The key aim of the geophysical investigation was to confirm parts of the mine boundaries and to provide information on the nature of the mines in terms of collapse, open mines, backfilled areas and stowed areas. The techniques were operated from the ground surface and so avoided the need to enter the mine or physically penetrate its roof.
Borehole investigations were also undertaken during the summer of 2001 to correlate the result of the geophysical investigations. They were also conducted to study the nature of the saturated zone (the geological area below the ground surface entirely filled with water) and the rock structure, as well as for groundwater monitoring, given the sensitivity of the area due to the mines being located on a major aquifer and in a groundwater Source Protection Zone.