There will indeed be an environmental statement to address the impact that will arise from the 18 changes that require additional powers in the Bill—for example, a new location for the replacement village hall for Burton Green. An environmental statement will accompany those additional provisions, and some changes that do not require additional provisions will also have their own environmental statement, which will allow those particularly important environmental considerations to be discussed.
The additional provision includes powers to build sidings for Crossrail at Old Oak Common which may in future enable a link to be built between Crossrail and the west coast main line. That is not in itself part of HS2, but doing the work after HS2 is built would incur significant expense and disruption.