Well, IMHO, this is a less than ideal situation, but isn’t a huge, imminent threat or disaster, and is quite possibly legal (I don’t know anything about that jurisdiction). Remember, the concrete that is being used properly to build things is also pretty much just dumped into holes in the ground, so has the same environmental impact (the washout water is slightly bigger concern, but again not a disaster). There are a lot worse environmental violations going on every day, believe me…
So, I’m a pretty strong environmentalist, but I’d say this isn’t worth losing your job over. If you do drop a dime, just do so anonymously. In general, as long as they have jurisdiction, the Province is probably going to be less swayed by whatever pull the company has.