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Mike is correct in that the shafts are lined with cast iron tubbing which generally extends to a depth below the sand bed. At a number of collieries valves were inserted into the tubbing at various levels in order to extract water for the colliery's own use. The more recent shaft sinkings generally involved freezing the strata and lining the shafts with concrete. As I understand it it is not just the water levels in the shafts that are the problem, it is the minewater levels in the surrounding strata. The inland boundary of the minewater in the former Durham Coalfield is generally taken as being the Butterknowle fault that is located in the Bishop Auckland area. The levels of the minewater in part of the inland area are controlled by six pumping stations. However there is still a large volume of water that drains into the workings of the former coastal colllieries. The flows to the coast have been intentially increased by ceasing pumping at three other inland pumping stations causing the minewater to overflow into the 'coastal pond' undeerneath the magnesian limestone aquifer. The idea being to pump out the minewater at the coast, treat it and then discharge to sea in order to provide a greater dilution. This was done in order to protect the River Wear from which supplies raw water to provide supplies for approximately one-third of the population of the City of Snderland The current activity is to try and lower the minewater levels in the Blackhall and Horden area. Shortly it is planned to lower the levels in the Seaham area where the minewater is again a threat to the aquifer. In the longer term similar action will have to be taken in the area of the workings of the former Wearmouth Colliery. Separate from all this the workings of the former Silksworth Colliery, which closed in November 1971, were not connected to any adjacent colliery. These workings were extensive and it is currently not known what the minewater levels are in that area. More information on the Coal Authority's short, medium and long term strategy in regard to the minewater problems can be found on the Minewater Update page of their website. Alan.