What Lurks Below?

On my way to work this morning I took this photo of the Royal Observatory on the crag and tail of Blackford Hill and of Blackford quarry, where work ceased in the 1950's.
The central part of the quarry was used for landfill and in 2002 this was covered with topsoil, turfed and planted with the trees seen here.
However within 2 years there were concerns regarding the high content of ammonia in the leachate which was draining to the Braid Burn at the foot of the slope and measures had to be taken to capture and dispose of this safely.