I am not required to and don't want to post a job opening notice. I'd rather just name the rising star and turn over the reins to her. So, assuming the new position is not open for competitive appointment, the question is: how do I announce this decision gracefully and then handle the anticipated backlash from the passed over professional?

Though your mind is made up, I would at least give the more senior construction employer a chance. Meet with them both and explain the new position. Make sure that both are willing to fill the role and then ask them to submit to you in writing why they should be considered. Prepare each of them for an " interview" and ask them to specifically lay out the plans and guidelines that they will set for this new encounter. Confer with any manager and then award the position to the one who you feel 1qualifies the most. You will have done your part as a good construction employer without damaging the morale of the dept or the other employee.