Given the amount of GO construction projects I can't recall a similar situation. I guess with the proximity to the Credit River it's logical. Will read the study Paul posted. I wonder if a similar situation will arise for the proposed Silver Grade Separation, somewhere between the Credit River and the Mount Pleasant GO station.
I can't see how the original Treaty in itself would create constraints... except that it falls into the same category as others where the Crown commited to pay $X per year in 1808 dollars in exchange for land, and the absolute dollars remain closer to their 1808 values.
The Assessment reports, however, appear to suggest that there are heritage considerations to this exact parcel of land that need further exploration. The proximity to the Credit, which was clearly a transportation corridor from pre-contact Indigenous days, might imply that this land has a past life that needs to be explored before we pave it over. There is also the issue of an adjoining cemetery.
I'm not that knowledgeable about how the depth of archaeology assessment of this EA might compare to other ML EA's. But certainly, ML is doing the right thing by stopping and collecting input, as opposed to pushing ahead.