Project Co shall implement the plan submitted in accordance with Section 4.6(a)(iii) upon receipt of a NO COMMENT notification from Contracting Authority, in accordance with Schedule 10 - Review Procedure.
This language is familiar to me. It describes a process where Project Co submits a plan to do some work at certain cost on certain time frame. Contracting Authority then may send comments back on the plan, ask for additions or changes, etc. And then Project Co sends a revised plan, and around and around it goes until Project Co submits a plan and receives a notice back that says "NO COMMENT", which is essentially Contracting Authority's method of accepting the agreement, at which point Project Co is obligated to carry out the plan. The very minor legal purpose of this language is to establish that if Project Co submits a plan and receives comment, they can still back out of the plan at that point, but once they get a "NO COMMENT", then they are on the hook.
When an offer is made in contract law, there are only two possible responses: acceptance or refusal.
A reply to the offer that includes modification of the terms is an implicit refusal of the offer, and is itself a new offer.
When the Project Company (PC) provides a plan to the Contracting Authority (CA) it is making an offer of terms. The CA then responds with commentary that involves modification of the terms of the agreement (an implicit refusal) or with "NO COMMENT" (by definition, an acceptance of the offer, thereby forming the agreement necessary for a contract).
In short, this is simply the way in which acceptance of the offer has been defined, in order to avoid ambiguous responses or neutral responses from being construed as a form of acceptance.
This ensures the liability for any activity is clear - either the PC has received notification of acceptance from the CA and can begin work knowing there is an agreed plan, or they should not begin any work knowing that any offered plan may change.