Complex sentence: Treorchy Comprehensive school was built on the old site of the Tylecoch colliery, with its western athletics track being named the "Red Ash", after it being the remnants of the mine shaft.
Split into simpler sentences: Treorchy Comprehensive school was built on the old site of the Tylecoch colliery. Its western athletics track was named the "Red Ash", being the remnants of the mine shaft.