I don't think that this kind of particulate would matter that much (although I don't know what kind of chemical additives are in the concrete), but about as the particulate I think that the concerns about silt are overblown in general.
I hate going onto the record about specific projects or recommendations for many of the same reason that I don't think the government should be doing it. I don't know enough about what is going on unless I have spent not a little time on the land in question, and even then, without a personal, long-term stake in the land and its health, my perceptions would be skewed.
What I prefer is to make an issue is how such decisions are made, the motives of the "decision-makers" and their sponsors, and how that combination affects outcomes (about which I am certain you agree).