Largely they followed the rules as existed at the time, consider that before the late 60's most states had no rules on dumping chemicals into the environment - and the EPA didnt even exist before 1972 - the regulatory scheme as it exists now was developed largely between 72 and 92.
They really shouldn't have skipped the rules, a common source of solvent plumes in groundwater is drycleaners. When did they start using halogenated solvents, in the 1930s?
At this point it should be obvious that those starting out an industry, or those disrupting it so much as to make it in their image, have all the incentive in the world to break rules in small to medium ways consistently and pay for it later (if at all) from a position of dominance. Not only can they afford it later, but enough elites usually get in on the deal to make money on the way up help shield it from any major blowback.
Just look at Uber for a recent example. I'd bet you could pick any decade of the last 150 years and it wouldn't be that hard to find obvious, well known examples.
While I mostly agree, I was mainly trying to distinguish ignoring regulations and fraud and generally being horrible from murder, kidnapping, treason, etc which some people's minds might have gone to otherwise.
That said, I don't doubt some companies fitting my initial criteria also dabbled in these more extreme crimes occassionally to get what they wanted. I'd like to think it's much less common though.
Post war I think. I saw an old educational movie from the 30/40s. 'How a dry cleaners works' they were using ether or some such for dry cleaning. Film went over how the fire alarm/suppression system worked.
I think the issue with halogenated solvents wasn't really understood at first. Businesses would just dump the stuff in the drain or on the ground. I remember a news report in Santa Cruz country, some business was getting harassed because they were supposedly illegally dumping perch. Turned out there was dry cleaners there in the 1950's and they were dumping perch in the septic system. 50 years later it was seeping into the San Lorinzo river.
I agree they shouldn't have skipped the rules. But, at the time, I guess they kind of knew they were onto something (semiconductors) and the decided to cut a few corners?
Note that this was before "semiconductor plants" as a thing existed: Moore invented a lot of the technology underlying semi plants at Fairchild.