Schwyll Aquifer Wikipedia
Schwyll Aquifer (pronounced 'Shwill') was historically known as 'the Great Spring of Glamorgan'.
Until recently, Welsh Water used the resurgence at the Schwyll Spring near Ewenny as the main source of water for the Bridgend area. It now functions as a backup supply and as such has a number of associated source protection zones policed by the Environment Agency. The outflow of the spring is far larger than any other freshwater spring in Wales and greater than that from Wookey Hole or Cheddar Gorge risings.
The aquifer consists of an underground waterway in the Carboniferous Limestone of South Wales. Due to the delay between local heavy rain and discoloration of the water at the spring, it is believed that the water originates from as far as 20 miles away. This would locate the main source in the limestone of the southern edge of the Brecon Beacons. The lack of an accessible cavern at the rising hinders exploration of the cave system. The only known point of access so far is at the pumping shaft of the extraction plant at Schwyll. The system was explored by cave divers in 1998 to a distance of 440 metres from the shaft. At 400 metres, a large cavern was discovered containing some bones which were identified as a species of horse. The bones were submitted for dating.