There was a real nice fellow--believe his last name was Smith--who worked at the Denver Koppers facility. I believe he was the manager or asst. manager. I don't know whether or not he is still around--that's been some years back. He was with the company for a long time and knew a lot of the railroad history of both the plant in Denver and the long-gone tie plant in Salida.
An interesting side note: the Koppers plant in Denver (near 60th and Broadway) sits alongside some of the old Denver, South Park & Pacific RR trackage locations. Within the plant grounds, there used to be (at least when I was there in the mid-1990's) a couple of 3-rail switches and some remnant 3-rail trackage.
Tie treating is a pretty interesting operation--I got to watch some of the process. And, yes, they do get creosote delivered in railroad tank cars.