RE:1.291 million It is likely due to one of the following reasons, more likely the first
1. Two institutions agreed to exchange a large block of shares at a convened or at the closing price of the day through a broker who arranged the deal between a seller and a buyer;
2. A market maker had to sell a large number of long options or had to buy too many put options, disrupting the market neutral position, now skewed to short. In order to balance the position back to neutral, ie, make money only between the bid and the ask, regardless of where the stock is heading, the market maker needs to buy a large volume of stock to compensate the short position. I don't think this is the case because Aecon has a very large bid-ask spread on its options, enough to deter the smartest..