Is this a proper use of the dash?
Should "as well as" be removed?
The contamination of the aquifer, the cessation of the water supply, the loss of animal and plant life, as well as the disruption of farming–these things would harm the people of the U.S.
That source also says "Use a dash at the beginning and end of a series separated by commas" which I guess is the rule I'm trying to apply to the original sentence, though I still can't tell if it is correct in the manner I first posted.
In more formal writing, say for a university assignment, I'd use proper dashes, but given the relative difficulty of producing them in this editor, I generally use one or two hyphens instead.
There are various styles of orthography. You've quoted Columbia University's style guide, but you'll find that not all publishing houses and universities recommend the same style.
There are em-dashes, en-dashes, and hyphens.
Your example is a good time to use an em-dash.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.