It looks like Onondaga Lake was a dumping ground for remnants and castoffs of Syracuse China pottery shards also. When I did a search of Solvay Process, I discovered there is a plant in a neighboring town to where I currently live. I rarely go to that town so I don't know about slag piles there.
Yeah, the article mentions that there is an unknown number in the U.S.A. because they weren't kept track of. In my home county I can think of one for sure. But for all I know, there are more.
Immediately thought of Doctor Who when I saw the pic. The curtain kind of reminds me of the villain Cassandra. And the lady's face kind of reminds me of The Silence villains.