When I heard that, I meant to raise it eventually.
To make what seems to me to be an obvious observation, we should be trying to minimize to the extent we can, in a way that is compatible with the other objectives we have to achieve, the amount of bedrock we have to blast and remove. If there's anything that can be done elsewhere rather than there, then it should be moved there.
I offer the fact that at number 1 Wellington, we have a series of underused committee rooms in what used to be a railway tunnel. If, for example, there were a desire to display some of the artifacts associated with Parliament's history to interested visitors, it would be reasonable to use that space once the Senate has returned to the Centre Block rather than try to create space in what is now solid bedrock, both because that would be very expensive and also because it would be more intrusive.
If you're blasting further out, you've got to come further out, and you take up more of the Hill, and that blasting really is intrusive. When we were sitting through the House of Commons and committee meetings, I think we'd all agree when the blasting was under way it was genuinely intrusive.