Per this source, it was marshland before it was the Vet. Of course, back in the old days, people used to dump stuff all the time in any open space so I suppose the possibility exists that someone may have been dumping bad stuff there.
http://explorepahistory.com/hmarker.php?markerId=1-A-313
I think I have an unread copy of that book by Rich Westcott. I'll have to look further into this!