ADC
If the work is necessary to bring the airport 'up to scratch' so to speak, then the cost of the work should have been factored into the purchase price.
However, if the work is necessary for future expansion of services, I would consider the cost an investment in the future.
Either way, in my opinion, the cost of the work should be absorbed by BB and recovered in the same way that all other airports recover their costs, not simply burdening passengers alone.