Reuse of Mines for Geothermal Water

Scotland is embarking on reusing mines in the Lanarkshire area with a major £31m project - the mines are coal and historically are the classic situations that the Victorians were masters of - pumping stations and sound engineering concepts.  Except of course, the realisation that the vast volumes of water in Coal and associated Mines are full of heavy minerals.  The remit Scottish companies and Academia are using for this project is renewable heat energy to be transferred to housing and urban heating projects.  However having followed a few conversations on this site there looks to be a huge range of interesting and pivotal views on the risks of Sulphides, Cadnium, Arsenic, Mercury,  it would be good to hear what people have to say, noting that in the aims of decarbonising, are we running close to the edge of our capabilities with regards to keeping water clean? Bearing in mind that changes in Water pressure unlike Fracking have a greater risk of breaching potable water let alone subsidence