The 'empty lake' is part of the drainage system and part of the water works. This is where all the drains meet up to run over under the tracks to the water works. Look at the Durham County website, go to Maps and onto the GIS mapping system. You can look at maps and go back in time to see the wells, drains and water works all over Shildon.
"One of the old boys (ex Shildon ) recons theres a huge lake under the the old sidings, accessed from first quarry. No one else has ever heard of it though ?"
Please- Miss- Me Me me - I know what it is just ask me nicely and I'll tell ya!